Motorola M68HC08 User Manual

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Sensorless BLDC Motor Control

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M68HC08

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MC68HC908MR32

Designer Reference Manual

DRM028/D Rev. 0, 03/2003

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MC68HC908MR32

Designer Reference Manual — Rev 0

by: Libor Prokop Motorola Czech System Laboratories Roznov pod Radhostem, Czech Republic

DRM028 — Rev 0 Designer Reference Manual

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Revision history

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To provide the most up-to-date information, the revision of our documents on the World Wide Web will be the most current. Your printed copy may be an earlier revision. To verify you have the latest information available, refer to:

http://www.motorola.com/semiconductors

The following revision history table summarizes changes contained in this document. For your convenience, the page number designators have been linked to the appropriate location.

Revision history

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Date

February,

2003

Revision

Level

1 Initial release N/A

Description

Page

Number(s)

Designer Reference Manual DRM028 — Rev 0

4 MOTOROLA

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Designer Reference Manual — Sensorless BLDC Motor Control

List of Sections

Section 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Section 2. System Description. . . . . . . . . . . . . . . . . . . . . 15

Section 3. BLDC Motor Control . . . . . . . . . . . . . . . . . . . .23

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Section 4. Hardware Design. . . . . . . . . . . . . . . . . . . . . . .57

Section 5. Software Design . . . . . . . . . . . . . . . . . . . . . . . 75

Section 6. User Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Appendix A. References. . . . . . . . . . . . . . . . . . . . . . . . .161

Appendix B. Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . .163

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List of Sections

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Designer Reference Manual DRM028 — Rev 0

6 MOTOROLA

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Designer Reference Manual — Sensorless BLDC Motor Control

Section 1. Introduction

1.1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

1.2 Application Functionality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

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1.3 Benefits of the Solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Section 2. System Description

2.1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

2.2 System Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

2.3 System Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Section 3. BLDC Motor Control

3.1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

3.2 Brushless DC Motor Control Theory. . . . . . . . . . . . . . . . . . . . .23

3.3 Used Control Technique. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.4 Application Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Section 4. Hardware Design

4.1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

4.2 System Configuration and Documentation . . . . . . . . . . . . . . . . 57

4.3 All HW Sets Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

4.4 High-Voltage Hardware Set Components. . . . . . . . . . . . . . . . .66

4.5 Low-Voltage Evaluation Motor Hardware Set Components . . .70

4.6 Low-Voltage Hardware Set Components . . . . . . . . . . . . . . . . .72

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Table of Contents

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Section 5. Software Design

5.1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

5.2 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

5.3 Data Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

5.4 Main Software Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

5.5 State Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89

5.6 Implementation Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

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Section 6. User Guide

6.1 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109

6.2 Application Suitability Guide . . . . . . . . . . . . . . . . . . . . . . . . . .109

6.3 Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112

6.4 Application Hardware and Software Configuration . . . . . . . . .113

6.5 Tuning for Customer Motor. . . . . . . . . . . . . . . . . . . . . . . . . . .126

Appendix A. References

Appendix B. Glossary

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Designer Reference Manual — Sensorless BLDC Motor Control

List of Figures

Figure Title Page

2-1 System Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

3-1 BLDC Motor Cross Section. . . . . . . . . . . . . . . . . . . . . . . . . . . .24

3-2 3-Phase Voltage System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3-3 BLDC Motor Back EMF and Magnetic Flux . . . . . . . . . . . . . . .26

3-4 Classical System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

3-5 Power Stage — Motor Topology. . . . . . . . . . . . . . . . . . . . . . . .28

3-6 Phase Voltage Waveform. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3-7 Mutual Inductance Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3-8 Detail of Mutual Inductance Effect . . . . . . . . . . . . . . . . . . . . . . 33

3-9 Mutual Capacitance Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3-10 Distributed Back-EMF by Unbalanced

Capacity Coupling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3-11 Balanced Capacity Coupling. . . . . . . . . . . . . . . . . . . . . . . . . . .36

3-12 Back-EMF Sensing Circuit Diagram . . . . . . . . . . . . . . . . . . . . . 37

3-13 The Zero Crossing Detection . . . . . . . . . . . . . . . . . . . . . . . . . .38

3-14 Commutation Control Stages . . . . . . . . . . . . . . . . . . . . . . . . . .39

3-15 Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

3-16 BLDC Commutation with Back-EMF

Zero Crossing Sensing Flowchart. . . . . . . . . . . . . . . . . . . . . . . 42

3-17 BLDC Commutation Time with Zero Crossing Sensing . . . . . .43

3-18 Vectors of Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

3-19 Back-EMF at Start Up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

3-20 Calculation of the Commutation Times During the Starting

(Back-EMF Acquisition) State. . . . . . . . . . . . . . . . . . . . . . . . . .49

4-1 High-Voltage Hardware System Configuration . . . . . . . . . . . . .59

4-2 Low-Voltage Evaluation Motor Hardware

System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4-3 Low-Voltage Hardware System Configuration . . . . . . . . . . . . .63

4-4 MC68HC908MR32 Control Board . . . . . . . . . . . . . . . . . . . . . . 65

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List of Figures

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4-5 3-Phase AC High Voltage Power Stage . . . . . . . . . . . . . . . . . . 67

4-6 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

5-1 Main Data Flow — Part1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

5-2 Main Data Flow — Part 2: Alignment, Starting,

5-3 Closed Loop Control System . . . . . . . . . . . . . . . . . . . . . . . . . . 81

5-4 Main Software Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

5-5 Main Software Flowchart — Main Software Loop. . . . . . . . . . .86

5-6 Software Flowchart — Interrupts . . . . . . . . . . . . . . . . . . . . . . . 89

5-7 Application State Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . 90

5-8 Stand-by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

5-9 Align State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

5-10 Back-EMF Acquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

5-11 Running State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

5-12 STOP State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

5-13 Fault State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

6-1 High-Voltage Hardware System Configuration . . . . . . . . . . . .114

6-2 Low-Voltage Evaluation Motor Hardware

6-3 Low-Voltage Hardware System Configuration . . . . . . . . . . . .116

6-4 Controller Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

6-5 Execute Make Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

6-6 PC Master Software Control Window . . . . . . . . . . . . . . . . . . . 124

6-7 Follow-up for Software Customizing to Customer Motor . . . . 128

6-8 Follow-up for Advanced Software Customizing . . . . . . . . . . .129

6-9 Follow-up for Software Customizing Trouble Shouting. . . . . .129

6-10 PC Master Software Parameters Tuning Control Window . . .130 6-11 PC Master Software Parameters Tuning Control Window . . .131 6-12 PC Master Software Current Parameters Tuning Window . . . 141

6-13 PC Master Software Start Parameters Tuning Window . . . . .149

6-14 PC Master Software Speed Parameters Tuning Window. . . .154

Running Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80

System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

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List of Tables

Table Title Page

2-1 Software Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

2-2 High Voltage Hardware Set Specifications. . . . . . . . . . . . . . . . 20

2-3 Low Voltage Evaluation Hardware Set Specifications . . . . . . .21

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2-4 Low Voltage Hardware Set Specifications . . . . . . . . . . . . . . . .22

3-1 PC Master Software Communication Commands . . . . . . . . . . 51

3-2 PC Master Software API Variables. . . . . . . . . . . . . . . . . . . . . .52

4-1 Electrical Characteristics of Control Board . . . . . . . . . . . . . . . . 66

4-2 Electrical Characteristics of Power Stage. . . . . . . . . . . . . . . . .68

4-3 Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

4-4 Electrical Characteristics of the EVM Motor Board. . . . . . . . . .71

4-5 Characteristics of the BLDC motor . . . . . . . . . . . . . . . . . . . . . . 71

4-6 Electrical Chatacteristics of the 3-Ph BLDC

Low Voltage Power Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

5-1 Software Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

6-1 Required Software Configuration

for Dedicated Hardware Platform . . . . . . . . . . . . . . . . . . . . . .118

6-2 Start-up Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146

6-3 PWM Frequency Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . .157

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List of Tables

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Designer Reference Manual DRM028 — Rev 0

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Designer Reference Manual — Sensorless BLDC Motor Control

Section 1. Introduction

1.1 Contents

1.2 Application Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.3 Benefits of the Solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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1.2 Application Functionality

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This Reference Design describes the design of a low-cost sensorless 3-phase brushless dc (BLDC) motor control with back-EMF (electromotive force) zero-crossing sensing. It is based on Motorola’s MC68HC908MR32 microcontroller which is dedicated for motor control applications. The system is designed as a motor drive system for medium power three phase BLDC motors and is targeted for applications in automotive, industrial and appliance fields (e.g. compressors, air conditioning units, pumps or simple industrial drives). The reference design incorporates both hardware and software parts of the system including hardware schematics.

1.3 Benefits of the Solution

The design of very low cost variable speed BLDC motor control drives has become a prime focus point for the appliance designers and semiconductor suppliers.

Today more and more variable speed drives are put in appliance or automotive products to increase the whole system efficiency and the product performance. Using of the control systems based on semiconductor components and MCUs is mandatory to satisfy requirements for high efficiency, performance and cost of the system.

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Once using the semiconductor components, it is opened to replace classical universal and DC-motors with maintenance-free electrically commutated BLDC motors. This brings many advantages of BLDC motors when the system costs could be maintained equivalent.

The advantages of BLDC motor versus universal and DC-motors are:

• high efficiency

• reliability (no brushes)

• low noise

• easy to drive features

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To control the BLDC motor, the rotor position must be known at certain angles in order to align the applied voltage with the back-EMF, which is induced in the stator winding due to the movement of the permanent magnets on the rotor.

Although some BLDC drives uses sensors for position sensing, there is a trend to use sensorless control. The position is then evaluated from voltage or current going to the motor. One of the sensorless technique is sensorless BLDC control with back-EMF (electromotive force) zero-crossing sensing.

The advantages of this control are:

• Save cost of the position sensors & wiring

• Can be used where there is impossibility or expansive to make additional connections between position sensors and the control unit

• Low cost system (medium demand for control MCU power)

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Section 2. System Description

2.1 Contents

2.2 System Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

2.3 System Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

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2.2 System Concept

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The application block diagram is shown in Figure 2-1. The sensorless rotor position technique detects the zero crossing points of back-EMF induced in the motor windings. The phase back-EMF zero crossing points are sensed while one of the three phase windings is not powered. The information obtained is processed in order to commutate the energized phase pair and control the phase voltage, using pulse width modulation.

The back-EMF zero crossing detection enables position recognition. The resistor network is used to step down sensed voltages to a 0–3.3 V level. Zero crossing detection is synchronized with the middle of center aligned PWM signals by the software, in order to filter high voltage spikes produced by switching the IGBTs (MOSFETs). The software selects by MUX command the phase comparator output that corresponds to the current commutation step. The multiplexer (MUX) circuit selects this signal, which is then transferred to the MCU input.

The voltage drop resistor is used to measure the dc-bus current which is chopped by the pulse-width modulator (PWM). The signal obtained is rectified and amplified (0–3.3 V with 1.65 V offset). The internal MCU analog-to-digital (A/D) converter and zero crossing detection are synchronized with the PWM signal. This synchronization avoids spikes when the IGBTs (or MOSFETs) are switched and simplifies the electric circuit.

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System Description

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MUX Command

Commutation Control

Three-Phase

Inverter

PWM

Generator

Dead Time

with

PWM

Duty Cycle

HC08MR32

3-ph

BLDC

Motor

DC Bus Current &

DC Bus Voltage

Sensing

Power line

DC-Bus Voltage/ Current Temperature

ADC

PC Master

START

STOP

SPEED

SCI

Required Speed

Required Alignment Current

3 BEMF Voltage

Zero Crossing

Comparators

MUX

Digital Inputs

Zero Crossing

Zero Crossing Period, Position Recognition

1/T

Actual Current

3 phase BLDC

Power Stage

BEMF Zero Crossing signal

Digital Outputs

Zero Crossing Time moment

Commutation Period

Actual Speed

Speed PI

Regulator

Current PI Regulator (for Alignment)

Figure 2-1System Concept

During the rotor alignment state, the dc-bus current is controlled by the current PI regulator. In the other states (motor running), the phase voltage (PWM duty cycle) is controlled by the speed PI regulator.

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The A/D converter is also used to sense the dc-bus voltage and the drive temperature. The dc-bus voltage is stepped down to a 3.3-V signal level by a resistor network.

The six IGBTs (copack with built-in fly back diode), or MOSFETs, and gate drivers create a compact power stage. The drivers provide the level shifting that is required to drive the high side switch. The PWM technique is used to control motor phase voltage.

2.3 System Specification

System Description

System Specification

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The concept of the application is that of a speed-closed loop drive using back-EMF zero crossing technique for position detection. It serves as an example of a sensorless BLDC motor control system using Motorola’s MC68HC908MR32 MCU. It also illustrates the usage of dedicated motor control on-chip peripherals.

The system for BLDC motor control consists of hardware and software. The application uses universal modular motion control development hardware boards, which are provided by Motorola for customer development support. For a description of these hardware boards refer to Appendix A. References 3.,4.,5.,6.,7., and the World Wide Web at:

http://www.motorola.com

There are three board and motor hardware sets for the application:

1. High-Voltage Hardware Set — For variable line voltage 115–230 Vac and medium power (phase current < 2.93 A)

2. Low-Voltage Evaluation Motor Hardware Set — For automotive voltage (12 V) and very low power (phase current < 4 A)

3. Low-Voltage Hardware Set — For automotive voltage (12 V or possibly 42 V) and medium power (phase current < 50 A)

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System Description

2.3.1 Software Specification

The application software is practically the same for all three hardware platforms. The only modification needed is to include one of three constants that customize the hardware and motor parameter settings.

The software (written in C language) specifications are listed in

Table 2-1. A useful feature of the software is serial communication with

PC master software protocol via RS232. The PC master software is PC computer software which allows reading and setting of all the system variables, and can also run html script pages to control the application from the PC. Another feature of the BLDC control software, is on-line

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Table 2-1. Software Specifications

3-phase trapezoidal BLDC motor control star or delta!

connected

Control Algorithm

Target Processor MC68HC908MR32

Language C-language with some arithmetical functions in assembler

Compiler Metrowerks ANSI-C/cC++ Compiler for HC08

Application

Control

MCU Oscillator

Frequency

MCU Bus

Frequency

Minimal BLDC

Motor

Commutation

Period

(Without PC

Master

Software

Communication)

Sensorless, with back-EMF zero crossing commutation

control

Speed closed loop control

Motoring mode

Manual interface (start/stop switch, speed potentiometer

control, LED indication)

PC master software (remote) interface (via RS232 using PC

computer)

4 MHz (with default software setting)

8 MHz (with default software setting)

333 µs (with default software setting and COEF_HLFCMT =

0.450)

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Table 2-1. Software Specifications

Minimal BLDC

Motor

Commutation

Period (with PC

Master Software

Control)

Targeted

Hardware

Software

Configuration

and Parameters

Setting

2.3.2 Hardware and Drive Specifications

The other system specifications are determined by hardware boards and motor characteristics. The boards and their connections are shown in

Section 4. Hardware Design. and Section 6. User Guide, 6.4.1 Hardware Configuration. The hardware set specifications are

discussed in the following subsections.

System Description

System Specification

520 µs (with default software setting and COEF_HLFCMT =

0.450)

Software is prepared to run on three optional board and

motor hardware sets:

• High-voltage hardware set at variable line voltage 115–230 Vac

(software customizing file const_cust_hv.h)

• Low-voltage evaluation motor hardware set (software customizing file const_cust_evmm.h)

• Low-voltage hardware set (software customizing file const_cust_lv.h)

Configuration to one of the three required hardware sets is

provided by inclusion of dedicated software customizing files. The software pack contains the files const_cust_hv.h, const_cust_lv.h, and const_cust_evm.h with predefined parameter settings for running on one of the optional board and motor hardware sets. The required hardware must be selected in code_fun.c file by one of these files #include.

Where software is configuration for different customer

motors, the software configuration for any motor is provided in the dedicated customizing file, according to the hardware board used.

PWM frequency 15.626 kHz with default software setting,

possibly changeable in const.h file

2.3.2.1 High-Voltage Hardware Set Specification

This hardware set is dedicated for medium power (phase current <

2.93 A) and main voltage. The specifications for a high-voltage hardware

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System Description

and motor set are listed in Table 2-2. The hardware operates on both 230 Vac and 115 Vac mains.

Table 2-2. High Voltage Hardware Set Specifications

Input voltage: 230 Vac or 115 Vac

Hardware Boards

Characteristics

Motor -Brake Set Manufactured EM Brno, Czech Republic

nc...

Maximum dc-bus voltage: 407 V

Maximal output current: 2.93A

EM Brno SM40V

Motor type:

Pole-Number: 6

3 phase, star connected

BLDC motor,

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Motor Characteristics

Brake Characteristics

Maximum dc-bus voltage: 380 V

Drive Characteristics

Speed range: 2500 rpm (at 310 V)

Maximum electrical

power:

Phase voltage: 3*220 V

Phase current: 0.55 A

Brake Type:

Nominal Voltage: 3 x 27 V

Nominal Current: 2.6 A

Pole-Number: 6

Nominal Speed: 1500 rpm

Speed range:

Optoisolation: Required

Protection:

150 W

SG40N 3-Phase BLDC Motor

< 2500 rpm (determined by motor

used)

Over-current,

over-voltage, and under-voltage fault protection

Load Characteristic Type: Varying

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System Description

System Specification

2.3.2.2 Low-Voltage Evaluation Hardware Set Specification

This hardware set is dedicated for 12 V voltage and very low power (phase current < 4 A). The specifications for a low-voltage evaluation hardware and motor set are listed in Table 2-3. It is targeted first of all to software evaluation with small motors.

Table 2-3. Low Voltage Evaluation Hardware Set Specifications

Input voltage: 12 Vdc

nc...

Hardware Boards

Characteristics

Maximum dc-bus voltage: 16.0 V

Maximal output current: 4.0 A

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Motor Characteristics

Drive Characteristics

Load Characteristic Type: Varying

2.3.2.3 Low-Voltage Hardware Set Specification

Motor type:

Speed range: < 5000 rpm (at 60 V)

Maximal line voltage: 60 V

Phase current: 2 A

Output torque: 0.140 Nm (at 2 A)

Speed range: < 1400 rpm

Input voltage: 12 Vdc

Maximum dc-bus voltage: 15.8 V

Protection:

4 poles, three phase, star

connected, BLDC motor

Over-current,

over-voltage, and under-voltage fault protection

This hardware set is dedicated for medium power (phase current < 50 A) and automotive voltage. The specifications for a low-voltage hardware and motor set are listed in Table 2-4. The hardware power stage board is dedicated for 12 V, but can be simply configured to a 42 V supply (described in documentation for the ECLOVACBLDC board). The supplied motor is targeted for 12 V.

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System Description

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Table 2-4. Low Voltage Hardware Set Specifications

Input voltage: 12 Vdc or 42 V

Hardware Boards

Characteristics

Motor -Brake Set Manufactured EM Brno, Czech Republic

Maximum dc-bus voltage: 16.0 V or 55.0 V

Maximal output current: 50.0 A

EM Brno SM40N

Motor type:

Pole-Number: 6

3 phase, star connected

BLDC motor,

nc...

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Motor Characteristics

Brake Characteristics

Drive Characteristics

Maximum dc-bus voltage: 15.8 V

Speed range: 3000 rpm (at 12 V)

Maximum electrical

power:

Phase voltage: 3*6.5 V

Phase current: 17 A

Brake Type:

Nominal Voltage: 3 x 27 V

Nominal Current: 2.6 A

Pole-Number: 6

Nominal Speed: 1500 rpm

Speed range: < 2500 rpm

Input voltage: 12 Vdc

Protection:

150 W

SG40N 3-Phase BLDC Motor

Over-current,

over-voltage, and under-voltage fault protection

Load Characteristic Type: Varying

Designer Reference Manual DRM028 — Rev 0

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Designer Reference Manual — Sensorless BLDC Motor Control

Section 3. BLDC Motor Control

3.1 Contents

3.2 Brushless DC Motor Control Theory. . . . . . . . . . . . . . . . . . . . .23

3.3 Used Control Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

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3.4 Application Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

3.2 Brushless DC Motor Control Theory

3.2.1 BLDC Motor Targeted by This Application

The brushless dc motor (BLDC motor) is also referred to as an electronically commutated motor. There are no brushes on the rotor, and commutation is performed electronically at certain rotor positions. The stator magnetic circuit is usually made from magnetic steel sheets. Stator phase windings are inserted in the slots (distributed winding) as shown in Figure 3-1, or it can be wound as one coil on the magnetic pole. Magnetization of the permanent magnets and their displacement on the rotor are chosen in such a way that the back-EMF (the voltage induced into the stator winding due to rotor movement) shape is trapezoidal. This allows a rectangular shaped 3-phase voltage system (see Figure 3-2) to be used to create a rotational field with low torque ripples.

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STATOR

STATOR WINDING (IN SLOTS)

SHAFT

ROTOR

AIR GAP

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PERMANENT MAGNETS

Figure 3-1. BLDC Motor Cross Section

The motor can have more than just one pole-pair per phase. This defines the ratio between the electrical revolution and the mechanical revolution. The BLDC motor shown has three pole-pairs per phase, which represent three electrical revolutions per one mechanical revolution.

Voltage

VOLTAGE

Phase A

PHASE A

Phase B

PHASE B

Phase C

PHASE C

30° 90° 150° 210° 270° 330°

120°

ELECTRICAL

electrical

ANGLE

angle

Figure 3-2. 3-Phase Voltage System

The easy to create rectangular shape of applied voltage ensures the simplicity of control and drive. But, the rotor position must be known at certain angles in order to align the applied voltage with the back-EMF (voltage induced due to movement of the PM). The alignment between

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back-EMF and commutation events is very important. In this condition, the motor behaves as a dc motor and runs at the best working point. Thus, simplicity of control and good performance make this motor a natural choice for low-cost and high-efficiency applications.

Figure 3-3 shows a number of waveforms:

• Magnetic flux linkage

• Phase back-EMF voltage

• Phase-to-phase back-EMF voltage

Magnetic flux linkage can be measured. However, in this case it was

nc...

calculated by integrating the phase back-EMF voltage (which was measured on the non-fed motor terminals of the BLDC motor). As can be seen, the shape of the back-EMF is approximately trapezoidal and the amplitude is a function of the actual speed. During speed reversal, the amplitude changes its sign and the phase sequence changes.

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Brushless DC Motor Control Theory

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BLDC Motor Control

Phase Magnetic

Flux Linkage

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Ps i_ A

Ps i_ B

Ps i_ C

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PH. A

Phase Back EMF

Atop Btop Ctop

Cbot Abot Bbot

Phase-Phase

Back EMF

Figure 3-3. BLDC Motor Back EMF and Magnetic Flux

The filled areas in the tops of the phase back-EMF voltage waveforms

PH. A

A–B

PH. B

PH. C

PH. B

PH. C

“NATURAL” COMMUTATION POINT

“Natural” commutation point

ACTING POWER SWITCH IN THE POWER STAGE

B–C

C–A

SPEED REVERSAL

Speed reversal

Ui_A

Ui_B

Ui_C

Ui_A B

Ui_B C

Ui_CA

indicate the intervals where the particular phase power stage commutations occur. The power switches are cyclically commutated through the six steps; therefore, this technique is sometimes called six step commutation control. The crossing points of the phase back-EMF voltages represent the natural commutation points. In normal operation the commutation is performed here. Some control techniques advance the commutation by a defined angle in order to control the drive above the pulse-width modulator (PWM) voltage control.

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BLDC Motor Control

Brushless DC Motor Control Theory

3.2.2 3-Phase BLDC Power Stage

The voltage for 3-phase BLDC motor is provided by a 3-phase power stage controlled by digital signals. Its topology is the one as for the AC induction motor (refer to Figure 3-5). The power stage is usually controlled by a dedicated microcontroller with on-chip PWM module.

3.2.3 Why Sensorless Control?

As explained in the previous section, rotor position must be known in order to drive a brushless dc motor. If any sensors are used to detect rotor position, sensed information must be transferred to a control unit

nc...

(see Figure 3-4). Therefore, additional connections to the motor are necessary. This may not be acceptable for some applications (see 1.3

Benefits of the Solution).

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AC LINE VOLTAGE

SPEED

SETTING

–

CONTROL SIGNALS

3.2.4 Power Stage — Motor System Model

In order to explain and simulate the idea of back-EMF sensing techniques a simplified mathematical model based on the basic circuit topology has been created. See Figure 3-5.

POWER STAGE

CONTROL UNIT

MOTOR DRIVE

POSITION FEEDBACK

Figure 3-4. Classical System

POSITION SENSORS

LOAD

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backEMF a

Ra Rc

Figure 3-5. Power Stage — Motor Topology

The second goal of the model is to find how the motor characteristics

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depend on the switching angle. The switching angle is the angular difference between a real switching event and an ideal one (at the point where the phase-to-phase back-EMF crosses zero).

B u

backEMF b

backEMF c

Frees

The motor-drive model consists of a normal 3-phase power stage plus a brushless dc motor. Power for the system is provided by a voltage source (U

). Six semiconductor switches (S

A/B/C t/b

), controlled elsewhere, allow the rectangular voltage waveforms (see Figure 3-2) to be applied.

The semiconductor switches and diodes are simulated as ideal devices. The natural voltage level of the whole model is put at one half of the dc-bus voltage. This simplifies the mathematical expressions.

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3.2.4.1 Stator Winding Equations

The BLDC motor is usually very symmetrical. All phase resistances, phase and mutual inductances, flux-linkages can be thought of as equal to, or as a function of the position θ with a 120° displacement.

The electrical BLDC motor model then consists of a set of the following stator voltage equations (EQ 3-1.).

BLDC Motor Control

Brushless DC Motor Control Theory

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The task of this section is to explain the background of the back-EMF sensing and to demonstrate how the zero crossing events can be detected. Parasitic effects that negatively influence the back-EMF detection are discussed and their nature analyzed.

3.2.4.2 Indirect Back EMF Sensing

Let us assume a usual situation, where the BLDC motor is driven in six-step commutation mode using PWM technique, where both top and bottom switches in the diagonal are controlled using the same signal (so called “hard switching PWM” technique). The motor phases A and B are powered, and phase C is free, having no current. So the phase C can be used to sense the back-EMF voltage. This is described by the following conditions:

---± u 2

d–id==,

SAbSBt, PWM←

iSb–i==i

backEMF aubackEMF bubackEMF c

++ 0=

−

---u

0=i

d0=,

(EQ 3-1.)

(EQ 3-2.)

The branch voltage u

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---u

xa=

can be calculated using the above conditions,

∑

backEMF x

LacLbc–()

---- uVC–+–= td

(EQ 3-3.)

BLDC Motor Control

After evaluation the expression of the branch voltage uVc is as follows:

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---u

backEMF c

–()

---L

acLbc

(EQ 3-4.)

----–= td

The same expressions can also be found for phase A and B:

---u

backEMF a

---u

backEMF b

–()

---L

baLca

–()

---L

cbLab

----–= td

(EQ 3-5.)

(EQ 3-6.)

The first member in the equation (EQ 3-6.) demonstrates the possibility to indirectly sense the back-EMF between the free (not powered) phase terminal and the zero point, defined at half of the dc-bus voltage (see Figure 3-5.). Simple comparison of these two levels can provide the required zero crossing detection.

As shown in Figure 3-5, the branch voltage of phase B can be sensed between the power stage output B and the zero voltage level. Thus, back-EMF voltage is obtained and the zero crossing can be recognized.

When Lcb = Lab, this general expressions can also be found:

---u

backEMFx

where x A B C,,==

(EQ 3-7.)

There are two necessary conditions which must be met:

• Top and bottom switches (in diagonal) have to be driven with the same PWM signal

• No current goes through the non-fed phase that is used to sense the back-EMF

Figure 3-6 shows branch and motor phase winding voltages during a

0–360° electrical interval. Shaded rectangles designate the validity of the equation (EQ 3-7.). In other words, the back-EMF voltage can be sensed during designated intervals.

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0 30 60 90 120 150 180 210 240 270 300 330 360 390

BLDC Motor Control

Brushless DC Motor Control Theory

uVA

uSa

- Back-EMF can be sensed

Figure 3-6. Phase Voltage Waveform

nc...

However simple this solution looks, in reality it is more difficult, because the sensed “branch” voltage also contains some ripples.

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3.2.4.3 Effect of Mutual Inductance

As shown in previous equations (EQ 3-4.) through (EQ 3-6.), the mutual inductances play an important role here. The difference of the mutual inductances between the coils which carry the phase current, and the coil used for back-EMF sensing, causes the PWM pulses to be superimposed onto the detected back-EMF voltage. In fact, it is produced by the high rate of change of phase current, transferred to the free phase through the coupling of the mutual inductance.

Figure 3-7 shows the real measured “branch” voltage. The red curves

highlight the effect of the difference in the mutual inductances. This difference is not constant.

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0 V

Figure 3-7. Mutual Inductance Effect

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Due to the construction of the BLDC motor, both mutual inductances vary. They are equal at the position that corresponds to the back-EMF zero crossing detection.

The branch waveform detail is shown in Figure 3-8. Channel 1 in

Figure 3-8 shows the disturbed “branch” voltage. The superimposed

ripples clearly match the width of the PWM pulses, and thus prove the conclusions from the theoretical analysis.

The effect of the mutual inductance corresponds well in observations carried out on the five different BLDC motors. These observations were made during the development of the sensorless technique.

NOTE: The BLDC motor with stator windings distributed in the slots has

technically higher mutual inductances than other types. Therefore, this effect is more significant. On the other hand the BLDC motor with windings wounded on separate poles, shows minor presence of the effect of mutual inductance.

CAUTION: However noticeable this effect, it does not degrade the back-EMF zero

crossing detection because it is cancelled at the zero crossing point. Simple additional filtering helps to reduce ripples further.

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Brushless DC Motor Control Theory

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Figure 3-8. Detail of Mutual Inductance Effect

3.2.4.4 Effect of Mutual Phase Capacitance

The negative effect of mutual inductance is not the only one to disturb the back-EMF sensing. So far, the mutual capacitance of the motor phase windings was neglected in the motor model, since it affects neither the phase currents nor the generated torque. Usually the mutual capacitance is very small. Its influence is only significant during PWM switching, when the system experiences very high du/dt.

The effect of the mutual capacitance can be studied using the model shown in Figure 3-9.

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BLDC Motor Control

Figure 3-9. Mutual Capacitance Model

nc...

Let us focus on the situation when the motor phase A is switched from negative dc-bus rail to positive, and the phase B is switched from positive to negative. This is described by these conditions (EQ 3-8.):

Cab

Cba

Cac

Ccb

VC Cap

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SAbSBt, PWM←

–

---u

→=u

---u

CaciCcbiC

The voltage that disturbs the back-EMF sensing, utilizing the free (not powered) motor phase C, can be calculated based the equation:

VC Cap

++()u

---u

CcbuCac

The final expression for disturbing voltage can be found as follows:

VC Cap



---



-------C

--------–

iCtd

∫

---u

+()–

CcbRC

cbCac



---

----------------------



cbCac

–→=,

---u

–()==

CacuCcb

–

⋅

∫

(EQ 3-8.)

(EQ 3-9.)

(EQ 3-10.)

NOTE: (EQ 3-10.) expresses the fact that only the unbalance of the mutual

capacitance (not the capacitance itself) disturbs the back-EMF sensing. When both capacities are equal (they are balanced), the disturbances disappear. This is demonstrated in Figure 3-10 and Figure 3-11.

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Brushless DC Motor Control Theory

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Figure 3-10. Distributed Back-EMF by Unbalanced

Capacity Coupling

Channel 1 in Figure 3-11 shows the disturbed “branch” voltage, while the other phase (channel 2) is not affected because it faces balanced mutual capacitance. The unbalance was purposely made by adding a small capacitor on the motor terminals, in order to better demonstrate the effect. After the unbalance was removed the “branch” voltage is clean, without any spikes.

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NOTE: The configuration of the phase windings end-turns has significant

impact; therefore, it needs to be properly managed to preserve the balance in the mutual capacity. This is important, especially for prototype motors that are usually hand-wound.

CAUTION: Failing to maintain balance in the mutual capacitance can easily

disqualify such a motor from using sensorless techniques based on the back-EMF sensing. Usually, the BLDC motors with windings wound on separate poles show minor presence of the mutual capacitance. Thus, the disturbance is also insignificant.

3.2.5 Back-EMF Sensing Circuit

An example of the possible implementation of the back-EMF sensing circuit is shown in Figure 3-12.

Figure 3-11. Balanced Capacity Coupling

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+DC_BUS PHASE A PHASE B PHASE C

BLDC Motor Control

Brushless DC Motor Control Theory

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560k

2x27k

560k

2x27k 2x27k 2x27k

560k

+ –

MUX

ZERO

CROSSING

DETECTION

SIGNAL

MUX COMMAND

Figure 3-12. Back-EMF Sensing Circuit Diagram

As explained in the theoretical part of this designer reference manual, the phase zero crossing event can be detected at the moment when the branch voltage (of a free phase) crosses the half dc-bus voltage level. The resistor network is used to step down sensed voltages down to a 0–15 V voltage level. The comparators sense the zero voltage difference in the input signal. The multiple resistors reduce the voltage across each resistor component to an acceptable level. A simple RC filter prevents the comparators from being disturbed by high voltage spikes produced by IGBT switching. The multiplexer (MUX) selects the phase comparator output, which corresponds to the current commutation stage. This zero crossing detection signal is transferred to the timer input pin.

The comparator control and zero crossing signals plus the voltage waveforms are shown in Figure 3-13.

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BLDC Motor Control

Phase Selection MUX Command

Phase Comparator Output

(Zero crossing edge)

"Branch" Voltage

(Interval of phase Back-EMF zero crossing detection)

Reference Level

nc...

Commutation Signal

Zero Crossing Signal

90°

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3.3 Used Control Technique

3.3.1 Sensorless Commutation Control

This section concentrates on sensorless BLDC motor commutation with back-EMF zero crossing technique.

In order to start and run the BLDC motor, the control algorithm has to go through the following states:

• Alignment

• Starting (Back-EMF Acquisition)

• Running

Figure 3-14 shows the transitions between the states. First the rotor is

aligned to a known position; then the rotation is started without the position feedback. When the rotor moves, back-EMF is acquired so the

Figure 3-13. The Zero Crossing Detection

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BLDC Motor Control

Used Control Technique

position is known, and can be used to calculate the speed and processing of the commutation in the running state.

START MOTOR

ALIGNMENT

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3.3.1.1 Alignment

ALIGNMENT TIME

EXPIRED?

YES

STARTING

(BACK-EMF ACQUISITION)

MINIMAL CORRECT

COMMUTATIONS DONE?

YES

RUNNING

Figure 3-14. Commutation Control Stages

Before the motor starts, there is a short time (depending on the motor’s

electrical time constant) when the rotor position is stabilized by applying PWM signals to only two motor phases (no commutation). The current controller keeps current within predefined limits. This state is necessary in order to create a high start-up torque. When the preset time-out expires then this state is finished.

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BLDC Motor Control

The current controller subroutine, with PI regulator, is called to control dc-bus current. It sets the correct PWM ratio for the required current. The current PI controller works with constant execution (sampling) period. This period should be a multiple of the PWM period, in order to synchronize the current measurement with PWM:

Current controller period = n/PWM frequency

The BLDC motor rotor position with flux vectors during alignment is shown in Figure 3-15.

nc...

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3.3.1.2 Running

Figure 3-15. Alignment

The commutation process is a series of states which assure:

• The back-EMF zero crossing is successfully captured

• The new commutation time is calculated

• The commutation is performed

The following processes need to be provided:

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• BLDC motor commutation service

• Back-EMF zero crossing moment capture service

• Calculation of commutation time

• Interactions between these commutation processes

From diagrams an overview of how the commutation works can be understood. After commuting the motor phases, there is a time interval (Per_Toff[n]) when the shape of back-EMF must stabilized (after the commutation the fly-back diodes are conducting the decaying phase current; therefore, sensing of the back-EMF is not possible). Then the new commutation time (T2[n]) is preset. The new commutation will be

nc...

performed at this time if the back-EMF zero crossing is not captured. If the back-EMF zero crossing is captured before the preset commutation time expires, then the exact calculation of the commutation time (T2*[n]) is made, based on the captured zero crossing time (T_ZCros[n]). The new commutation is performed at this new time.

BLDC Motor Control

Used Control Technique

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If for any reason the back-EMF feedback is lost within one commutation period, corrective actions are taken in order to return to the regular states.

The flowchart explaining the principle of BLDC commutation control with back-EMF zero crossing sensing is shown in Figure 3-16.

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COMMUTATION DONE

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BEMF ZERO CROSSING

DETECTED BETWEEN PREVIOUS

COMMUTATIONS?

YES

SERVICE OF COMMUTATION:

PRESET COMMUTATION

WAIT FOR PER_TOFF UNTIL PHASE

CURRENT DECAYS TO ZERO

BEMF ZERO CROSSING

MISSED?

BEMF ZERO CROSSING

HAS COMMUTATION

DETECTED?

TIME EXPIRED?

YES

MAKE MOTOR COMMUTATION

CORRECTIVE CALCULATION 1.

SERVICE OF RECEIVED BEMF

ZERO CROSSING:

CORRECTED SETTING

OF COMMUTATION TIME

HAS COMMUTATION

BEMF ZERO CROSSING MISSED

CORRECTIVE CALCULATION 2

CORRECTED SETTING

OF COMMUTATION TIME

TIME EXPIRED?

YES

Figure 3-16. BLDC Commutation with Back-EMF

Zero Crossing Sensing Flowchart

3.3.1.3 Running — Commutation Time Calculation

Commutation time calculation is shown in Figure 3-17.

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Used Control Technique

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T_Cmt[n-2] T2[n-3] T2[n-2] T2[n-1] T2[n]

T_Cmt[n-1] T_Cmt[n]

n-2

ZERO CROSSING

DETECTION SIGNAL

Per_ZCros0[n] =

Per_ZCros[n-1]Per_ZCros[n-2]

n-1

ZERO CROSSING

DETECTION SIGNAL

T_ZCros[n-1]

Per_Toff[n]

ZERO CROSSING

DETECTION SIGNAL

2*Per_ZCrosFlt[n-1]

Per_ZCros[n]

Per_HlfCmt[n]

T_ZCros[n]

T_Cmt**[n+1]

Per_HlfCmt[n]

Figure 3-17. BLDC Commutation Time with Zero Crossing Sensing

The following calculations are made to calculate the commutation time (T2[n]) during the Running state:

• Service of commutation — The commutation time (T2[n]) is predicted:

T2[n] = T_Cmt[n] + 2*Per_ZCrosFlt[n-1] If 2*Per_ZCrosFlt>Per_Cmt_Max then result is limited at Per_Cmt_Max

COMMUTATION IS PRESET

COMMUTATED AT PRESET TIME NO BACK-BMF FEEDBACK WAS RECEIVED CORRECTIVE CALCULATION 1.

T_Cmt*[n+1]

BACK-EMF FEEDBACK RECEIVED AND EVALUATED

COMMUTATED WHEN BACK-EMF ZERO CROSSING IS MISSED CORRECTION CALCULATION 2.

• Service of received back-EMF zero crossing — The commutation time (T2*[n]) is evaluated from the captured back-EMF zero crossing time (T_ZCros[n]):

Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0 Per_ZCrosFlt[n] = (1/2*Per_ZCros[n]+1/2*Per_ZCros0) HlfCmt[n] = 1/2*Per_ZCrosFlt[n]- Advance_angle =

= 1/2*Per_ZCrosFlt[n]- C_CMT_ADVANCE*Per_ZCrosFlt[n]=

Coef_HlfCmt*Per_ZCrosFlt[n]

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Per_Toff[n+1] = Per_ZCrosFlt*Coef_Toff and Per_Dis minimum

Per_ZCros0 <-- Per_ZCros[n] T_ZCros0 <-- T_ZCros[n] T2*[n] = T_ZCros[n] + HlfCmt[n]

The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg which means Coef_HlfCmt = 0.375 at Running state with default s/w setting

Coef_Toff = 0.375 at Running state, Per_Dis = 150 with default s/w setting

• If no back-EMF zero crossing was captured during preset commutation period (T2P[n] then Corrective Calculation 1. is made:

T_ZCros[n] <-- CmtT[n+1] Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0 Per_ZCrosFlt[n] = (1/2*Per_ZCros[n]+1/2*Per_ZCros0) HlfCmt[n] = 1/2*Per_ZCrosFlt[n]-Advance_angle = Coef_HlfCmt*Per_ZCrosFlt[n]

The best commutation was get with Advance_angle: 60Deg*1/8 = 7.5Deg

which means Coef_HlfCmt = 0.375 at Running state! Per_Toff[n+1] = Per_ZCrosFlt*Coef_Toff and Per_Dis minimum Per_ZCros0 <-- Per_ZCros[n] T_ZCros0 <-- T_ZCros[n]

• If back-EMF zero crossing is missed then Corrective Calculation

2. is made:

T_ZCros[n] <-- CmtT[n]+Toff[n] Per_ZCros[n] = T_ZCros[n] - T_ZCros[n-1] = T_ZCros[n] - T_ZCros0 Per_ZCrosFlt[n] = (1/2*T_ZCros[n]+1/2*T_ZCros0) HlfCmt[n] = 1/2*Per_ZCrosFlt[n]-Advance_angle = Coef_HlfCmt*Per_ZCrosFlt[n]

The best commutation was get with Advance_angle:

60Deg*1/8 = 7.5Deg

which means Coef_HlfCmt = 0.375 at Running state! Per_ZCros0 <-- Per_ZCros[n] T_ZCros0 <-- T_ZCros[n]

• Where:

T_Cmt = time of the last commutation T2 = Time of the Timer 2 event (for Timer Setting) T_ZCros = Time of the last zero crossing T_ZCros0 = Time of the previous zero crossing Per_Toff = Period of the zero crossing off Per_ZCros = Period between zero crossings (estimates required

commutation period) Per_ZCros0 = Pervious period between zero crossings Per_ZCrosFlt = Estimated period of commutation filtered

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Per_HlfCmt = Period from zero crossing to commutation (half commutation)

The required commutation timing is provided by setting commutation constants Coef_HlfCmt, COEF_TOFF.

3.3.1.4 Starting (Back-EMF Acquisition)

The back-EMF sensing technique enables a sensorless detection of the rotor position; however, the drive must be first started without this feedback. This is due to the fact that the amplitude of the induced voltage is proportional to the motor speed. Hence, the back-EMF cannot be

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sensed at a very low speed and a special start-up algorithm must be performed.

BLDC Motor Control

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In order to start the BLDC motor, the adequate torque must be generated. The motor torque is proportional to the multiplication of the stator magnetic flux, the rotor magnetic flux, and the sine of the angle between these magnetic fluxes.

It implies (for BLDC motors) the following:

1. The level of phase current must be high enough.

2. The angle between the stator and rotor magnetic fields must be 90°±30°.

The first condition is satisfied during the alignment state by maintaining dc-bus current at a level sufficient to start the motor. In the starting (back-EMF acquisition) state, the same value of PWM duty cycle is used as the one which has stabilized the dc-bus current during the align state.

The second condition is more difficult to fulfill without any position feedback information. After the alignment state, the stator and the rotor magnetic fields are aligned (0° angle). Therefore, two fast commutations (faster than the rotor can follow) must be applied to create an angular difference in the magnetic fields (see Figure 3-18).

The commutation time is defined by the start commutation period (Per_CmtStart). This allows starting the motor such that minimal speed (defined by state when back-EMF can be sensed) and is achieved

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during several commutations, while producing the required torque. Until the back-EMF feedback is locked, the commutation process (explained in Running) assures that commutations are done in advance, so that successive back-EMF zero crossing events are not missed.

After several successive back-EMF zero crossings:

• Exact commutation time can be calculated

• Commutation process is adjusted

• Control flow continues to the Running state

The BLDC motor is then running with regular feedback and the speed

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controller can be used to control the motor speed by changing the PWM duty cycle value.

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MOTOR IS RUNNING

AT STEADY-STATE CONDITION

WITH REGULAR BACK-EMF FEEDBACK

STATOR MAGNETIC FIELD

BORDER OF

STATOR POLE

ROTOR MOVEMENT

DURING ONE

COMMUTATION

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ZERO CROSSING

EDGE INDICATOR

PHASE WINDING

ROTOR MAGNETIC

FIELD (CREATED BY PM)

DIRECTION OF

PHASE CURRENT

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MOTOR IS STARTING

ALIGNMENT STATE

STARTING (BACK-EMF ACQUISITION)

The back-EMF feedback is tested. When the back-EMF zero crossing is recognized the time of new commutation is evaluated. Until at least two successive back-EMF zero crossings are received the exact commutation time can not be calculated. Therefore, the commutation is done in advance in order to assure that successive back-EMF zero crossing events would not be missed.

The rotor position is stabilized by applying PWM signals to only two motor phases

The two fast (faster then the rotor can move) commutations are applied to create an angular difference of the stator magnetic field and rotor magnetic field.

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RUNNING

After several back-EMF zero crossing events the exact commutation time is calculated. The commutation process is adjusted. Motor is running with regular back-EMF feedback.

Figure 3-18. Vectors of Magnetic Fields

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Figure 3-19 demonstrates the back-EMF during the start up. The

amplitude of the back-EMF varies according to the rotor speed. During the starting (back-EMF acquisition) state the commutation is done in advance. In the running state the commutation is done at the right moments.

PHASE BACK-EMFS

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BOT

PHASE A

TOP

.................

TOP

BOT

TOP

BOT

TOP

BOT

TOP

BOT

PHASE C

BACK-EMF ZERO CROSSINGS

IDEAL COMMUTATION PATTERN WHEN POSITION IS KNOWN

TOP

BOT

REAL COMMUTATION PATTERN WHEN POSITION IS ESTIMATED

TOP

BOT

FIRST SECOND THIRD FOURTH

TOP

BOT

TOP

BOT

PHASE B

BOT

STARTING (BACK-EMF ACQUISITION)

RUNNINGALIGN

Figure 3-19. Back-EMF at Start Up

Figure 3-20 illustrates the sequence of the commutations during the

starting (back-EMF acquisition) state. The commutation times T2[1] and T2[2] are calculated without any influence of back-EMF feedback. The commutation time calculations are explained in the following section.

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T_Cmt[1]

T_ZCros[0]

T_Cmt[2] T_Cmt[3]

T2[1]

n=1

Per_CmtStart

n=2

2*Per_CmtStart

ZERO CROSSING

DETECTION SIGNAL

ZERO CROSSING

DETECTION SIGNAL

ZERO CROSSING

DETECTION SIGNAL

Per_Toff[n]

T2[2] T2[n]

n=3

2*Per_ZCrosFlt[n-1]

Per_HlfCmt[n]

Figure 3-20. Calculation of the Commutation Times During the Starting

(Back-EMF Acquisition) State

3.3.1.5 Starting — Commutation Time Calculation

Even the sub-states of the commutation process in the starting (back-EMF acquisition) state remain the same as in the running state. The required commutation timing depends on application state (starting state, running state). So the commutation time calculation is the same as that described in

Running — Commutation Time Calculation, but the following

computation coefficients are different:

COMMUTATION IS PRESET

Per_HlfCmt[n]

T_ZCros[n]

T2**[n]

COMMUTATED AT PRESENT TIME NO BACK-EMF FEEDBACK WAS RECEIVED CORRECTIVE CALCULATION 1

T2*[n]

COMMUTED WHEN CORRECT BACK-EMF FEEDBACK RECEIVED AND EVALUATED

COMMUTATED WHEN BACK-EMF ZERO CROSSING IS MISSED CORRECTIVE CALCULATION 2.

coefficient Coef_HlfCmt = 0.125 with advanced angle Advance_angle: 60Deg*3/8 = 22.5Deg

at Starting state!

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Coef_Toff = 0.5 at Running state, Per_Dis = 150 with default s/w setting

3.3.2 Speed Control

The speed close loop control is provided by a well known PI regulator. The required speed is calculated from speed input variable, as explained in Process Desired Speed Setting. The actual speed is calculated from the average of two back-EMF zero crossing periods (time intervals), received from the sensorless commutation control block. The speed regulator output is a PWM duty cycle.

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3.4 Application Control

3.4.1 PC Master Software

The speed controller works with the constant execution (sampling) period PER_T3_RUN_US. A detailed explanation is provided in

Processs Speed Control.

The application can be controlled in two basic modes:

• Manual mode

• PC master software mode

In manual mode, it is controlled by an on-board start/stop switch and speed potentiometer. In PC master mode, it is controlled from a computer using PC master software. In both modes, the individual variables can be observed using the PC master software.

PC master software was designed to provide the debugging, diagnostic, and demonstration tools for developing algorithms and applications. It consists of components running on PCs and parts running on the target MCU, connected by an RS232 serial port. A small program is resident in the MCU that communicates with the PC master software to parse commands, return status information, and process control information

from the PC. The PC master software uses Microsoft as a user interface on the PC.

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3.4.1.1 Communication with PC Master Software Specifications

SCI communication protocol with a default of 9.6 Kbaud, is used for communication as described in User’s Manual for PC Master Software, Motorola 2000, found on the World Wide Web at:

http://e-www.motorola.com

PC master software controls and senses the status of the application with:

• PC master software — BLDC demonstration suitcase communication commands

BLDC Motor Control

Application Control

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• PC master software — BLDC demonstration suitcase communication bytes

After reset, the BLDC control MCU software is in manual mode. In order to control the system from PC master software, it is necessary to set PC master software mode, and then to provide the MCU software control from PC master software via application interface variables.

3.4.1.2 PC Master Software, BLDC Control MCU Software API, Communication Commands

Commands defined for the BLDC control MCU software are listed in

Table 3-1. The commands are very simple. If the software executes the

command, it responds with OK byte 00. If it is unable to execute the command, it responds with failed code 55. The commands “Set PC master software mode”, “Set manual mode” can only be executed when the START/STOP switch on the demonstration suitcase is set to STOP and the motor is stopped. Otherwise, a failed response is sent.

Table 3-1. PC Master Software Communication Commands

Comman

Command

Set PC master software mode

1. Microsoft is a registered trademark of Microsoft Corporation in the United States and/or other countries.

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Code

01 None

Data Byte

Demo

Suitcase Action

Setting of PC master software mode

Respon

Byte

00 55

Response Descriptio

Failed

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Table 3-1. PC Master Software Communication Commands

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Command

Set manual

mode

Comman

Code

02 None

Data Byte

Demo

Suitcase Action

Setting of manual

mode

Respon

Byte

00 55

3.4.1.3 PC Master Software, BLDC Control MCU Software API, Communication Variables

The application interface, data variables used for the exchange between the BLDC control MCU software and PC master software, are shown in

Table 3-2. These variables are used for status sensing and control. PC

master software accesses these bytes directly from their physical memory addresses.

Table 3-2. PC Master Software API Variables

Name Type

Speed_Range_Max_RP

Curr_Range_Max_cA S16 O

Sys3 Sys3_Def

Motor_Ctrl Motor_Ctrl_Def I 8flags Motor control variable

Motor_Status

Failure Failure_Def O 8flags Failure variable

Sp_Input U8 I < 0; 255>

Speed_Max_RPM U16 O

Speed_Min_RPM U16 O

Commut_Rev U8 O < 0; 255> Commutations per motor revolution

Curr S8 O

Motor_Status_D

U16 O

O 8flags Motor status variable

Representing

Range

8flags System variable #3

< 0; 65535>

[rpm]

< 0; 65535>

[rpm]

< 0; 65535>

[rpm]

<-Curr_Range_Max_c

Curr_Range_Max_cA)

<-32768;32767>

[A*10^-2]

Description

Speed input variable used for

required

speed calculation

Speed range maximum

Maximal speed limit

Minimal speed limit

dc-bus current

Current range maximum [A*10^-2]

Response Descriptio

Failed

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Type: S8- signed 8 bit, U8- unsigned 8 bit,S16- signed 16bit, U16unsigned 16bit

The system registers Sys3, Motor_Ctrl, Motor_Status, Failure flags are described by definitions of Sys3_Def, Motor_Ctrl_Def,

Motor_Status_Def, Failure_Def:

typedef union { struct { unsigned int HV : 1; /* BIT0 High Voltage board Flag */ unsigned int LV : 1; /* BIT1 Low Voltage board */ unsigned int EVMm : 1; /* BIT2 EVMm board */ unsigned int BIT3 : 1; /* BIT3 RESERVED */ unsigned int PCMode : 1;/* BIT4 PCMaster/manual mode Flag */ unsigned int BIT5 : 1; /* BIT5 RESERVED */ unsigned int BIT6 : 1; /* BIT6 RESERVED */ unsigned int Alignment : 1; /* BIT7 Alignment state Proceeding */ } B; /* |Alignment|***|***|PCMode|***|EVMm|LV||HV| */ char R; } Sys3_Def; /* System register #3 Definition */

typedef union { struct { unsigned int StartCtrl : 1; /* Switch Start set to START Flag */ unsigned int BIT1 : 1; /* BIT1 RESERVED */ unsigned int BIT2 : 1; /* BIT2 RESERVED */ unsigned int BIT3 : 1; /* BIT5 RESERVED */ unsigned int BIT4 : 1; /* BIT4 RESERVED */ unsigned int BIT5 : 1; /* BIT6 RESERVED */ unsigned int BIT6 : 1; /* BIT6 RESERVED */ unsigned int ClearFail : 1; /* BIT7 Clear failure Status */ } B; /* |ClearFail|***|***|***|***|***|***|StartCtrl| */ char R; } Motor_Ctrl_Def; /* PC master software Motor Control Flags Definition */

typedef union { struct {

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unsigned int Switch_Start : 1; /* BIT0 Switch START/STOP

set to START Flag */ unsigned int Running : 1;/* BIT1 Motor is running (Alignment, Start or Running state) */ unsigned int BIT2 : 1; /* BIT2 RESERVED */ unsigned int V120 : 1; /* BIT3 120 V DC-Bus detected

(only for HV DC-Bus) */ unsigned int BIT4 : 1; /* BIT4 RESERVED */ unsigned int BIT5 : 1; /* BIT5 RESERVED */ unsigned int BIT6 : 1; /* BIT6 RESERVED */ unsigned int BIT7 : 1; /* BIT7 RESERVED */ } B; /* |***|***|***|***|V120|***|Running|Switch_Start| */

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char R; } Motor_Status_Def; /* PC master software Motor Status Flags register Definition */

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typedef union { struct { unsigned int OverCurrent : 1; /* BIT0 Over-Current Failure */ unsigned int OverHeating : 1; /* BIT1 Over-Heating */ unsigned int VoltageFailure : 1; /* BIT2 Over-Voltage */ unsigned int BIT3 : 1; /* BIT5 RESERVED */ unsigned int BIT4 : 1; /* BIT4 RESERVED */ unsigned int BIT5 : 1; /* BIT6 RESERVED */ unsigned int BoardIdFail : 1; /* BIT6 pcb Identification

Failure */ unsigned int ErrCmt : 1; /* BIT7 error Commutation */ } B;

/* |ErrCmt|***|***|***|***|VoltageFailure|OverHeating|OverCurrent| */ char R; } Failure_Def; /* Failure Flags register Definition */

Table 3-2 declares if the variable is used as an output or input from the

BLDC control MCU software side. The variable is described and the unit defined.

When PC master software mode is set, the system start and stop is controlled by StartCtrl flag in

Motor_Ctrl variable. When the application

enters the fault state, the variable Failure displays the fault reason. Setting the ClearFail flag in

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Motor_Ctrl will exit the fault state.

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The Sp_Input variable is used for speed control. In PC master software mode, it can be modified from PC master software (otherwise, it is set according to speed potentiometer value).

Desired speed [rpm] =

Sp_Input/255*(Speed_Max_RPM-Speed_Min_RPM) + Speed_Min_RPM

So, the required motor commutation period is determined by the

Speed_Max_RPM and Speed_Min_RPM variables. These are chosen

according to which optional board and motor set by the BLDC control MCU software.

The variable Speed_Range_Max_RPM determines scaling of the

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speed variables.

The actual speed of the motor can be calculated from Per_Speed_MAX_Range and zero crossing period Per_ZCrosFlt_T2:

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Actual speed [rpm] =

Speed_Range_Max_RPM

The variable Commut_Rev can be used for calculation of the BLDC motor commutation period:

Commutation Period [s] = 60 / Actual Speed [rpm] / Commut_Rev

The variable Curr_Range_Max_cA determines scaling of the current variables. So, the actual dc-bus current is:

dc-bus current [A] = Curr / 256*Curr_Range_Max_cA / 100

*Per_Speed_MAX_Range/Per_ZCrosFlt_T2

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Designer Reference Manual — Sensorless BLDC Motor Control

Section 4. Hardware Design

4.1 Contents

4.2 System Configuration and Documentation . . . . . . . . . . . . . . . . 57

4.3 All HW Sets Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

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4.3 All HW Sets Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

4.4 High-Voltage Hardware Set Components. . . . . . . . . . . . . . . . .66

4.5 Low-Voltage Evaluation Motor Hardware Set Components . . .70

4.6 Low-Voltage Hardware Set Components . . . . . . . . . . . . . . . . .72

4.2 System Configuration and Documentation

The application is designed to drive the 3-phase BLDC motor. The HW is a modular system composed from board and motor. There are three possible hardware options:

• High-Voltage Hardware Set Configuration

• Low-Voltage Evaluation Motor Hardware Set Configuration

• Low-Voltage Hardware Set Configuration

The following subsection shows the system configurations.

They systems consists of the following modules (see also Figure 4-1,

Figure 4-2, Figure 4-3):

For all hardware options:

• MC68HC908MR32 Control Board

For High-Voltage Hardware Set cofiguration:

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• 3-Phase AC/BLDC High Voltage Power Stage

• Optoisolation Board

• 3-phase BLDC High Voltage Motor with Motor Brake

For Low-Voltage Evaluation Motor Hardware Set configuration:

• EVM Motor Board

• 3-phase Low Voltage EVM BLDC Motor

Low-Voltage Hardware Set configuration:

• 3-Ph AC/BLDC Low Voltage Power Stage

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• 3-phase BLDC Low Voltage Motor with Motor Brake

The supplied controller boards for MC68HC908MR32 (ECCTRMR32) allows two possibilities for software execution:

1. MMDS Evaluation Board (KITMMDSMR32) Using a real-time debugger (supplied with the Metrowerks

Figure 4-1, Figure 4-2 and Figure 4-3 show the configuration with

MMDS evaluation board.

compiler) the evaluation board is connected to the controller board (ECCTRMR32) via an emulator connector. This solution is recommended for software evaluation.

2. Programmed MCU (MC68HC908MR32)

Where a daughter board module, with MC68HC908MR32 processor, is plugged into the controller board (ECCTRMR32) instead of the emulator cable, the processor must be programmed in an external programmer. This solution is recommended for final tests.

The sections 4.3 All HW Sets Components, 4.4 High-Voltage

Hardware Set Components, 4.5 Low-Voltage Evaluation Motor Hardware Set Components and 4.6 Low-Voltage Hardware Set Components will describe the individual boards.

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4.2.1 High-Voltage Hardware Set Configuration

The system configuration for a high-voltage hardware set is shown in

Figure 4-1.

Hardware Design

System Configuration and Documentation

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100 - 240VAC 49 - 61 Hz

+12VDC

GND

40w flat ribbon

U2 U3

J11.1 J11.2

MB1

Not Connected

3ph AC/BLDC High Voltage Power Stage

J13.1 J13.2 J13.3

Black

White

Red

SM40V

Motor-Brake

SG40N

Red

Not Connected

cable

J14 J1

ECMTRHIVBLDC

White

Black

JP1.1 JP1.2

Optoisolation Board

ECOPT

ECOPTHIVACBLDC

40w flat ribbon cable

Figure 4-1. High-Voltage Hardware System Configuration

All the system parts are supplied and documented according to the following references:

• EVM1 — Modular Development System with EM08MR32 Daughter Board:

PC Computer RS232 PC Master

Controller Board

HC908MR32 ECCTR908MR32

EVM1

KITMMDS08MR32

PC Computer RS232 emulator

– Supplied as: KITMMDS08MR32

– Described in: Manual supplied with kit

• U1 — Controller Board for MC68HC908MR32:

– Supplied as: ECCTR908MR32

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• U2 — 3-Phase AC/BLDC High Voltage Power Stage:

– Described in: MC68HC908MR32 Control Board — User’s

Manual (Motorola document order number

MEMCMR32CBUM/D),

see References 3

– Supplied in kit with optoisolation board as:

ECOPTHIVACBLDC

– Described in: 3-Phase AC Brushless DC High Voltage Power

Stage User’s Manual (Motorola document order number MEMC3PBLDCPSUM/D), see References 4.

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• U3 — Optoisolation Board

– Supplied with 3-phase AC/BLDC high voltage power stage as:

ECOPTHIVACBLDC

– Or, supplied alone as: ECOPT–ECOPT optoisolation board

– Described in: Optoisolation Board User’s Manual (Motorola

document order number MEMCOBUM/D), see References 5

NOTE: It is strongly recommended to use opto-isolation (optocouplers and

optoisolation amplifiers) during development time to avoid any damage to the development equipment.

• MB1 — Motor-Brake SM40V + SG40N

– Supplied as: ECMTRHIVBLDC

The individual modules are described in some sections below. More detailed descriptions of the boards can be found in comprehensive User’s Manuals belonging to each board (References 3, 4, 5). These manuals are available on on the World Wide Web at:

http://www.motorola.com

The User’s Manual incorporates the schematic of the board, description of individual function blocks and a bill of materials. An individual board can be ordered from Motorola as a standard product.

Designer Reference Manual DRM028 — Rev 0

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System Configuration and Documentation

4.2.2 Low-Voltage Evaluation Motor Hardware Set Configuration

The system configuration for a low-voltage evaluation motor hardware set is shown in Figure 4-2.

40w flat

ribbon cable

Hardware Design

PC Computer RS232 PC Master

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+12

GND

12VDC

Evaluation Motor Board

Motor

ECMTREVAL

Controller Board

HC908MR32 ECCTR908MR32

EVM1

KITMMDS08MR32

IB23810

PC Computer RS232 emulator

Figure 4-2. Low-Voltage Evaluation Motor Hardware

System Configuration

All the system parts are supplied and documented according to the following references:

• EVM1 — Modular Development System with EM08MR32 Daughter Board:

– Supplied as: KITMMDS08MR32

– Described in: Manual supplied with kit

• U1 — Controller Board for MC68HC908MR32:

– Supplied as: ECCTR908MR32

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• M1 — IB23810 Motor

• U2 — 3-Phase AC/BLDC Low Voltage Power Stage:

– Described in: MC68HC908MR32 Control Board — User’s

Manual (Motorola document order number

MEMCMR32CBUM/D),

see References 3

– Supplied in kit with IB23810 Motor as: ECMTREVAL —

Evaluation Motor Board Kit

– Supplied in kit with IB23810 Motor as: ECMTREVAL —

Evaluation Motor Board Kit

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– Described in: Motorola Embedded Motion Control Evaluation

Motor Board User’s Manual (Motorola document order number

MEMCEVMBUM/D) see References 6

The individual modules are described in some sections below. More detailed descriptions of the boards can be found in comprehensive

4.2.3 Low-Voltage Hardware Set Configuration

User’s Manuals belonging to each board (References 3, 6). These manuals are available on on the World Wide Web at:

http://www.motorola.com

The User’s Manual incorporates the schematic of the board, description of individual function blocks and a bill of materials. An individual board can be ordered from Motorola as a standard product.

The system configuration for low-voltage hardware set is shown in

Figure 4-3.

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+12

GND

12VDC

J19

J20

MB1

3ph AC/BLDC Low Voltage Power Stage

ECLOVACBLDC

J16 J17 J18

Black

White

Red

System Configuration and Documentation

40w flat ribbon cable

J13

Motor-Brake

Hardware Design

PC Computer RS232 PC Master

Controller Board

HC908MR32 ECCTR908MR32

EVM1

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SM40N

Not Connected

SG40N

White

Black

Red

Not Connected

KITMMDS08MR32

ECMTRLOVBLDC

PC Computer RS232 emulator

Figure 4-3. Low-Voltage Hardware System Configuration

All the system parts are supplied and documented according to the following references:

• EVM1 — Modular Development System with EM08MR32 Daughter Board:

– Supplied as: KITMMDS08MR32

– Described in: Manual supplied with kit

• U1 — Controller Board for MC68HC908MR32:

– Supplied as: ECCTR908MR32

– Described in: MC68HC908MR32 Control Board — User’s

Manual (Motorola document order number

MEMCMR32CBUM/D),

see References 3

• U2 — 3-Phase AC/BLDC Low Voltage Power Stage

– Supplied as: ECLOVACBLDC

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• MB1 — Motor-Brake SM40N + SG40N

The individual modules are described in some sections below. More detailed descriptions of the boards can be found in comprehensive User’s Manuals belonging to each board (References 3, 7). These manuals are available on on the World Wide Web at:

– Described in: Motorola Embedded Motion Control 3-Phase

BLDC Low-Voltage Power Stage User’s Manual (Motorola document order number MEMC3PBLDCLVUM/D3), see

References 7

– Supplied as: ECMTRLOVBLDC

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http://www.motorola.com

The User’s Manual incorporates the schematic of the board, description of individual function blocks and a bill of materials. An individual board can be ordered from Motorola as a standard product.

4.3 All HW Sets Components

4.3.1 MC68HC908MR32 Control Board

Motorola’s embedded motion control series MR32 motor control board is designed to provide control signals for 3-phase ac induction, 3-phase brushless dc (BLDC), and 3-phase switched reluctance (SR) motors. In combination with one of the embedded motion control series power stages, and an optoisolation board, it provides a software development platform that allows algorithms to be written and tested without the need to design and build hardware. With software supplied on the CD-ROM, the control board supports a wide variety of algorithms for ac induction, SR, and BLDC motors. User control inputs are accepted from START/STOP, FWD/REV switches, and a SPEED potentiometer located on the control board. Alternately, motor commands can be entered via a PC and transmitted over a serial cable to DB-9 connector. Output connections and power stage feedback signals are grouped together on 40-pin ribbon cable connector. Motor feedback signals can be connected to Hall sensor/encoder connector. Power is supplied

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Hardware Design

All HW Sets Components

through the 40-pin ribbon cable from the optoisolation board or low-voltage power stage.

The control board is designed to run in two configurations. It can be connected to an M68EM08MR32 emulator via an M68CBL08A impedance matched ribbon cable, or it can operate using the daughter board. The M68EM08MR32 emulator board may be used in either an MMDS05/08 or MMEVS05/08 emulation system.

Figure 4-4 shows a block diagram of the board’s circuitry.

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TERMINAL

I/F

dc POWER

12 Vdc

OPTOISOLATED

RS-232 I/F

REGULATED

POWER SUPPLY

OVERCURRENT/

OVERVOLTAGE

INPUTS

FORWARD/REVERSE

SWITCH

START/STOP

SWITCH

EMULATOR/

PROCESSOR

CONNECTOR

PWM LEDs (6)

OPTO/POWER DRIVER I/O CONNECTOR

CURRENT/TEMP

SENSE INPUTS

PWM (6)

OUTPUTS

CONFIG.

MISC. POWER AND

SPEED

POT

JUMPERS

BACK EMF

CONTROL I/O

(2) OPTION

SWITCHES

INPUTS

Figure 4-4. MC68HC908MR32 Control Board

4.3.1.1 Electrical Characteristics of the MC68HC908MR32 Control Board

RESET

SWITCH

TACHOMETER

INPUT

HALL EFFECT

INPUTS (3)

40-PIN RIBBON

CONNECTOR

The electrical characteristics in Table 4-1 apply to operation at 25°C.

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Table 4-1. Electrical Characteristics of Control Board

Characteristic Symbol Min Typ Max Units

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dc power supply voltage

Quiescent current

Min logic 1 input voltage (MR32)

Max logic 0 input voltage (MR32)

Propagation delay (Hall sensor/encoder input)

Analog input range

RS-232 connection speed — — 9600 Baud

PWM sink current

1. When operated and powered separately from other Embedded Motion Control tool set products

(1)

4.4 High-Voltage Hardware Set Components

4.4.1 3-Phase AC/BLDC High Voltage Power Stage

Motorola’s embedded motion control series high-voltage (HV) ac power stage is a 180-watt (one-fourth horsepower), 3-phase power stage that will operate off of dc input voltages from 140 to 230 volts and ac line voltages from 100 to 240 volts. In combination with one of the embedded motion control series control boards and an optoisolation board, it provides a software development platform that allows algorithms to be written and tested without the need to design and build a power stage. It supports a wide variety of algorithms for both ac induction and brushless dc (BLDC) motors.

Vdc

dly

10.8 12 16.5

—80— mA

2.0 — — V

——0.8 V

——500ns

0—5.0 V

——20 mA

Input connections are made via 40-pin ribbon cable connector J14. Power connections to the motor are made on output connector J13. Phase A, phase B, and phase C are labeled PH_A, Ph_B, and Ph_C on the board. Power requirements are met with a single external 140- to

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Hardware Design

High-Voltage Hardware Set Components

230-volt dc power supply or an ac line voltage. Either input is supplied through connector J11. Current measuring circuitry is set up for 2.93 amps full scale. Both bus and phase leg currents are measured. A cycle-by-cycle over-current trip point is set at 2.69 amps.

The high-voltage ac power stage has both a printed circuit board and a power substrate. The printed circuit board contains IGBT gate drive circuits, analog signal conditioning, low-voltage power supplies, power factor control circuitry, and some of the large, passive, power components. All of the power electronics which need to dissipate heat are mounted on the power substrate. This substrate includes the power IGBTs, brake resistors, current sensing resistors, a power factor

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correction MOSFET, and temperature sensing diodes. Figure 4-5 shows a block diagram.

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HV POWER

INPUT

SIGNALS

TO/FROM

CONTROL

BOARD

SWITCH MODE

POWER SUPPLY

GATE

DRIVERS

BOARD

ID BLOCK

PFC CONTROL

dc BUS BRAKE

3-PHASE IGBT

POWER MODULE

PHASE CURRENT

PHASE VOLTAGE

BUS CURRENT

BUS VOLTAGE

MONITOR

ZERO CROSS

BACK-EMF SENSE

Figure 4-5. 3-Phase AC High Voltage Power Stage

4.4.1.1 Electrical Characteristics of the 3-Phase AC/BLDC High Voltage Power Stage

The electrical characteristics in Table 4-2 apply to operation at 25°C with a 160-Vdc power supply voltage.

3-PHASE AC

MOTOR

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Table 4-2. Electrical Characteristics of Power Stage

Characteristic Symbol Min Typ Max Units

dc input voltage Vdc 140 160 230 V

ac input voltage Vac 100 208 240 V

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4.4.2 Optoisolation Board

Quiescent current

Min logic 1 input voltage

Max logic 0 input voltage

Input resistance

Analog output range

Bus current sense voltage

Bus voltage sense voltage

Peak output current

Brake resistor dissipation (continuous)

Brake resistor dissipation (15 sec pk)

Total power dissipation

Sense

BK(Pk)

Out

Bus

diss

—70 —mA

2.0 — — V

——0.8 V

—10 kΩ —

0—3.3V

—563 —mV/A

—8.09 —mV/V

——2.8 A

——50 W

——100W

——85 W

Motorola’s embedded motion control series optoisolation board links signals from a controller to a high-voltage power stage. The board isolates the controller, and peripherals that may be attached to the controller, from dangerous voltages that are present on the power stage. The optoisolation board’s galvanic isolation barrier also isolates control signals from high noise in the power stage and provides a noise-robust systems architecture.

Signal translation is virtually one-for-one. Gate drive signals are passed from controller to power stage via high-speed, high dv/dt, digital optocouplers. Analog feedback signals are passed back through HCNR201 high-linearity analog optocouplers. Delay times are typically

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High-Voltage Hardware Set Components

250 ns for digital signals, and 2 µs for analog signals. Grounds are separated by the optocouplers’ galvanic isolation barrier.

Both input and output connections are made via 40-pin ribbon cable connectors. The pin assignments for both connectors are the same. For example, signal PWM_AT appears on pin 1 of the input connector and also on pin 1 of the output connector. In addition to the usual motor control signals, an MC68HC705JJ7CDW serves as a serial link, which allows controller software to identify the power board.

Power requirements for controller side circuitry are met with a single external 12-Vdc power supply. Power for power stage side circuitry is

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supplied from the power stage through the 40-pin output connector.

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4.4.2.1 Electrical Characteristics of the Optoisolation Board

The electrical characteristics in Table 4-3 apply to operation at 25°C, and a 12-Vdc power supply voltage.

Table 4-3. Electrical Characteristics

Characteristic Symbol Min Typ Max Units Notes

Power Supply Voltage Vdc 10 12 30 V

Quiescent Current

Min Logic 1 Input Voltage

Max Logic 0 Input Voltage

Analog Input Range

Input Resistance

Analog Output Range

Digital Delay Time

Out

DDLY

(1)

2.0 — — V HCT logic

— — 0.8 V HCT logic

0—3.3V

—10—kΩ

0—3.3V

—0.25— µs

200

(2)

500

(3)

mA dc/dc converter

Analog Delay Time

1. Power supply powers optoisolation board only.

2. Current consumption of optoisolation board plus DSP EMV board (powered from this power supply)

3. Maximum current handled by dc/dc converters

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Hardware Design

4.4.3 3-phase BLDC High Voltage Motor with Motor Brake

The High Voltage BLDC motor-brake set incorporates a 3-phase High Voltage BLDC motor and attached BLDC motor brake. The BLDCmotor has six poles. The incremental position encoder is coupled to the motor shaft, and position Hall sensors are mounted between motor and brake. They allow sensing of the position if required by the control algorithm. Detailed motor-brake specifications are listed in Table 2-2, Section 2.

4.5 Low-Voltage Evaluation Motor Hardware Set Components

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4.5.1 EVM Motor Board

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Motorola’s embedded motion control series EVM motor board is a 12-volt, 4-amp, surface-mount power stage that is shipped with an MCG IB23810-H1 brushless dc motor. In combination with one of the embedded motion control series control boards, it provides a software development platform that allows algorithms to be written and tested without the need to design and build a power stage. It supports algorithms that use Hall sensors, encoder feedback, and back EMF (electromotive force) signals for sensorless control.

The EVM motor board does not have overcurrent protection that is independent of the control board, so some care in its setup and use is required if a lower impedance motor is used. With the motor that is supplied in the kit, the power output stage will withstand a full-stall condition without the need for overcurrent protection. Current measuring circuitry is set up for 4 amps full scale. In a 25οC ambient operation at up to 6 amps continuous RMS output current is within the board’s thermal limits.

Input connections are made via 40-pin ribbon cable connector J1. Power connections to the motor are made on output connector J2. Phase A, phase B, and phase C are labeled on the board. Power requirements are met with a single external 12-Vdc, 4-amp power supply. Two connectors, labeled J3 and J4, are provided for the 12-volt power supply. J3 and J4 are located on the front edge of the board. Power is supplied to one or the other, but not both.

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Low-Voltage Evaluation Motor Hardware Set Components

4.5.1.1 Electrical Characteristics of the EVM Motor Board

The electrical characteristics in Table 4-4 apply to operation at 25°C and a 12-Vdc power supply voltage.

Table 4-4. Electrical Characteristics of the EVM Motor Board

Characteristic Symbol Min Typ Max Units

Power Supply Voltage Vdc 10 12 16 V

Hardware Design

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Quiescent Current

Min Logic 1 Input Voltage

Max Logic 0 Input Voltage

Input Resistance

Analog Output Range

Bus Current Sense Voltage

Bus Voltage Sense Voltage

Power MOSFET On Resistance

RMS Output Current

Total Power Dissipation

4.5.2 3-phase Low Voltage EVM BLDC Motor

The EVM Motor Board is shipped with an MCG IB23810-H1 brushless dc motor. Motor-brake specifications are listed in Table 2-3, Section 2. Other detailed motor characteristics are in Table 4-5 this section. They apply to operation at 25°C.

Sense

DS(On)

Out

Bus

diss

—50— mA

2.4 — — V

——0.8 V

—10— kΩ

0—3.3V

—412—mV/A

—206—mV/V

—3240MΩ

—— 6 A

—— 5 W

Table 4-5. Characteristics of the BLDC motor

Characteristic Symbol Min Typ Max Units

Terminal Voltage

Speed @ V

Torque Constant

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—— 60 V

— 5000 — RPM

— 0.08 — Nm/A

Hardware Design

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Table 4-5. Characteristics of the BLDC motor

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Voltage Constant

Winding Resistance

Winding Inductance L — 8.6 — mH

Continuous Current

Peak Current

Inertia J

Thermal Resistance — — 3.6 °C/W

4.6 Low-Voltage Hardware Set Components

4.6.1 3-Ph AC/BLDC Low Voltage Power Stage

Motorola’s embedded motion control series low-voltage (LV) brushless DC (BLDC) power stage is designed to run 3-ph. BLDC and PM Synchronous motors. It operates from a nominal 12-volt motor supply, and delivers up to 30 amps of rms motor current from a dc bus that can deliver peak currents up to 46 amps. In combination with one of Motorola’s embedded motion control series control boards, it provides a software development platform that allows algorithms to be written and tested, without the need to design and build a power stage. It supports a wide variety of algorithms for controlling BLDC motors and PM Synchronous motors.

Input connections are made via 40-pin ribbon cable connector J13. Power connections to the motor are made with fast-on connectors J16, J17, and J18. They are located along the back edge of the board, and are labeled Phase A, Phase B, and Phase C. Power requirements are met with a 12-volt power supply that has a 10- to 16-volt tolerance. Fast-on connectors J19 and J20 are used for the power supply. J19 is labeled +12V and is located on the back edge of the board. J20 is labeled 0V and is located along the front edge. Current measuring circuitry is set up for 50 amps full scale. Both bus and phase leg currents are measured. A cycle by cycle overcurrent trip point is set at 46 amps.

— 8.4 — V/kRPM

—2.8 — Ω

—— 2 A

—— 5.9 A

— 0.075 — kgcm

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Hardware Design

Low-Voltage Hardware Set Components

The LV BLDC power stage has both a printed circuit board and a power substrate. The printed circuit board contains MOSFET gate drive circuits, analog signal conditioning, low-voltage power supplies, and some of the large passive power components. This board also has a 68HC705JJ7 microcontroller used for board configuration and identification. All of the power electronics that need to dissipate heat are mounted on the power substrate. This substrate includes the power MOSFETs, brake resistors, current-sensing resistors, bus capacitors, and temperature sensing diodes. Figure 4-5 shows a block diagram.

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POWER

INPUT

SIGNALS

TO/FROM

CONTROL

BOARD

BIAS

POWER

BOARD

ID BLOCK

BRAKE

MOSFET

POWER MODULE

GATE

DRIVERS

PHASE CURRENT

PHASE VOLTAGE

BUS CURRENT

BUS VOLTAGE

MONITOR

ZERO CROSS

BACK-EMF SENSE

Figure 4-6. Block Diagram

4.6.1.1 Electrical Characteristics of the 3-Ph BLDC Low Voltage Power Stage

The electrical characteristics in Table 4-6 apply to operation at 25°C with a 12-Vdc supply voltage.

MOTOR

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Table 4-6. Electrical Chatacteristics of the 3-Ph BLDC

Low Voltage Power Stage

Characteristic Symbol Min Typ Max Units

Motor Supply Voltage Vac 10 12 16 V

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Quiescent current

Min logic 1 input voltage

Max logic 0 input voltage

Analog output range

Bus current sense voltage

Bus voltage sense voltage

Peak output current (300 ms)

Continuous output current

Brake resistor dissipation (continuous)

Brake resistor dissipation (15 sec pk)

Total power dissipation

4.6.2 3-phase BLDC Low Voltage Motor with Motor Brake

The Low Voltage BLDC motor-brake set incorporates a 3-phase Low Voltage BLDC motor EM Brno SM40N and attached BLDC motor brake SG40N. The BLDCmotor has six poles. The incremental position encoder is coupled to the motor shaft, and position Hall sensors are mounted between motor and brake. They allow sensing of the position if required by the control algorithm, which is not required in this sensorless application. Detailed motor-brake specifications are listed in Table 2-4,

Section 2.

Sense

RMS

BK(Pk)

Out

Bus

diss

—175 — mA

2.0 — — V

——0.8 V

0—3.3V

—33 —mV/A

—60 —mV/V

——46 A

——30 A

——50 W

——100W

——85 W

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Designer Reference Manual — Sensorless BLDC Motor Control

Section 5. Software Design

5.1 Contents

5.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

5.3 Data Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

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5.2 Introduction

5.4 Main Software Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

5.5 State Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

5.6 Implementation Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

This section describes the design of the software blocks of the drive. The software will be described in terms of:

• Data Flow

• Main Software Flowchart

• State Diagram

For more information on the control technique used see 3.3 Used

Control Technique.

5.3 Data Flow

The control algorithm obtains values from the user interface and sensors, processes them and generates 3-phase PWM signals for motor control, as can be seen on the data flow analysis shown in Figure 5-1 and Figure 5-2.

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Software Design

5.3.1 Software Variables and Defined Constants

Important system variables are listed in Table 5-1.

Table 5-1. Software Variables

Name Type Representing Range Description

Sys1 Sys1_Def 8flags System variable #1

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Speed_Min_U8 U8

Sp_Input U8 < 0; 255>

Coef_Speed_Inp U8

Speed_Desired U8

PIParamsScl_U8_Spe

Per_Speed_MAX_Ran

Per_ZCrosFlt U16 [UNIT_PERIOD_T2_US] Zero crossing period — filtered

T_ZCros U16 [UNIT_PERIOD_T2_US] Zero crossing time [n]

T_ZCros0

T_Cmt U16 [UNIT_PERIOD_T2_US] Commutation time

Curr S8

Curr_Align S8

< 0;

Speed_Range_Max_RPM)

< 0;

Speed_Range_Max_RPM)

Structure Speed PI regulator parameters

U16 [UNIT_PERIOD_T2_US]

U16(union

)

U16(union

)

[UNIT_PERIOD_T2_US] Timer 2 variable

[UNIT_PERIOD_T2_US] Zero crossing time [n-1]

<-Curr_Range_Max_cA;

Curr_Range_Max_cA)

<-Curr_Range_Max_cA;

Curr_Range_Max_cA)

Minimal speed [system units]

Speed input variable used for required

speed calculation

Coeficient Sp_Inp to Speed_Desired calculation

Desired speed

Minimal commutation period of the speed

range (at Speed_Range_Max_RPM)

dc-bus current

Required current during alignment state

PIParamsScl_S8_Currr Structure Current PI regulator parameters

Volt U8

V_TASC2 U8 Back-EMF zero crossing expecting edge

V_MUX U8

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<-VOLT_RANGE_MAX;

VOLT_RANGE_MAX)

dc-bus voltage

Preset value of back-EMF zero crossing

phase multiplexer

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Software Design

Data Flow

Type: S8- signed 8 bit, U8- unsigned 8 bit, S16- signed 16bit, U16unsigned 16bit, (union)- 16 bits access or 2*8bit access

The system registers Sys1 flags are described by definitions of

Sys3_Def:

typedef union { struct { unsigned int PC_F : 1; /* BIT0 Phase Commutation Flag */ unsigned int Off_F : 1; /* BIT1 Offset timeout flag

- Offset timeout can be measured */ unsigned int ICR_F : 1; /* BIT2 Input Capture

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5.3.2 Process Measurement

was succesfuly Received - Flag */ unsigned int Rmp_F : 1; /* BIT3 Speed Ramp Flag - motor ramping */ unsigned int Stop_F : 1; /* BIT4 Motor is going or is stopped */ unsigned int Strt_F : 1; /* BIT5 Start Phase Flag */ unsigned int Run_F : 1; /* BIT6 Motor Running with back-EMF feedback Flag */ unsigned int FOK_F : 1; /* BIT7 Feedback within the righ time Flag */ } B; /* |FOK_F|Run_F|Strt_F|Stop_F|Rmp_F|ICR_F|Off_F|PC_F| */ char R; } Sys1_Def; /* System register #1 Definition */

Main data flow is displayed in Figure 5-1. The processes are described in the following subsections.

Frees

The process provides measurement of analog values using ADC. The measured inputs are: dc-bus current, dc-bus voltage, and speed input. The measurement is provided by the measurement handler. The state diagram is explained in State Diagram.

5.3.3 Start/Stop Switch Reading and Start/Stop Decision

The process reads the start stop switch and provides start condition and clear failure decisions, as explained in Stand-By and Fault State.

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A/D CONVERTERS

TIMER 1

SPEED INPUT, DC-BUS VOLTAGE

AND DC-BUS CURRENT MEASUREMENT

VOLTAGE

PROCESS

CURRENT

PROCESS

FAULT CONTROL

FAULT STOP

Volt_Max_Fault

5.3.4 Process Fault Control Fault Stop

Curr_Max_Fault

Figure 5-1. Main Data Flow — Part1

The process provides fault control and fault stop as described in Fault

State, Stand-By, Align State, 5.5.5 Back-EMF Acquisition State, and Running State.

PC MASTER SOFTWARE

PCM COMMAND

PC Mode

Sp_Input

FFLAG1 FFLAG2

Start Ctrl

START/STOP SWITCH READING

AND START/STOP DECISION

ALIGNMENT, STARTING, RUNNING

Switch_Start Running

Stop_F

PROCESS

CONTROL

START/STOP

SWITCH

The processes alignment, starting, and running control are displayed in

Figure 5-2. The processes are described in the following subsections.

5.3.5 Process Back, EMF Zero Crossing Sensing

Back-EMF zero crossing process provides:

• Back-EMF zero crossing sampling in synchronization with PWM,

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• Evaluates the zero crossing

• Records its time in T_ZCros

Further explanation is provided in Data Flow and Figure 5-6.

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Data Flow

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PIParamsScl_U8_Speed

Per_Speed_MAX_Range

VIRTUAL

TIMER 3

Sp_Input

Coef_Speed_InpSpeed_Min_U8

PROCESS

DESIRED SPEED SETTING

PROCESS

SPEED CONTROL

PROCESS

ALIGNMENT CONTROL

ACTUAL TIME

ICR_F

Speed_Desired

Per_ZCrosFlt

PWM MODULE

ACTUAL TIME

TIMER 2

TIMER2

TIMEOUT,

ZERO CROSSING

V_TASC2

PROCESS BACK-EMF

ZERO CROSSING SENSING

T_ZCros

PROCESS

COMUTATION TIMES

CALCULATION

TIMER 2

BACK-EMF

INPUT

OF COMMUTATION PARAMETERS

*Only when regular

feedback can not be used

FOK_F

PRESET COMMUTATION

AND ZERO CROSSING

PROCESS

SET COMMUTATION AND

ZERO CROSSING SELECTION

T_CMT

CORRECTIVE CALCULATION 1

OF COMMUTATION PARAMTERS

CORRECTIVE CALCULATION 2

(ACCELERATION)

COMMUTATION HAS BEEN

PERFORMED — FLAG

PC_F

PROCESS

V_TASC2V_MUX

TIMER1

Curr

PIParamsScl_S8_Curr

Curr_Align

INIT

T_Cmt

PC_F

BACK-EMF

ZERO CROSSING

MULTIPLEXER

Figure 5-2. Main Data Flow — Part 2: Alignment, Starting,

Running Control

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Data Flow

5.3.6 Process Commutation Time Calculation, Corrective Calculation 1, Corrective Calculation 2

These processes provide calculations of commutation time intervals (periods) (Per_ZCros, Per_ZCrosFlt), from captured time (T_Cmt, T_ZCros, T_ZCros0), and sets Timer 2 with variable T2. These calculations are described in 3.3.1.5 Starting — Commutation Time

Calculation and 3.3.1.3 Running — Commutation Time Calculation.

5.3.7 Process Desired Speed Setting

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The desired speed, held in register Speed_Desired, is calculated from the following formula:

Speed_Desired = Sp_Input*Coef_Speed_Inp/255 + Speed_Min_U8

5.3.8 Processs Speed Control

The general principle of the speed PI control loop is illustrated in

Figure 5-3.

REFERENCE

SPEED

(Speed_Desired)

PWM

SPEED ERROR

CONTROLLER

(256*Per_Speed_MAX_Range/Per_ZCrosFlt_T2)

DUTY CYCLE

(OutReg_U8)

CONTROLLED

SYSTEM

ACTUA L MOTOR

SPEED

Figure 5-3. Closed Loop Control System

The speed closed loop control is characterized by the feedback of the actual motor speed.

The actual motor speed is calculated from zero crossing period:

Actual motor speed = 256*Per_Speed_MAX_Range/Per_ZCrosFlt_T2

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This information is compared with the reference set point and the error signal is generated. The magnitude and polarity of the error signal corresponds to the difference between the actual and desired speeds. Based on the speed error, the PI controller generates the corrected motor voltage in order to compensate for the error. The speed regulator parameters (gain...), internal, and input/output variables are located in the structure PIParamsScl_U8_Speed.

The speed controller works with a constant execution (sampling) period. The period is timed by timer 3, with the constant PER_T3_RUN_US.

PWM duty cycle is set for all six PWM channels according to regulator

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output, OutReg_U8. The maximum duty cycle is at OutReg_U8 = 255. The implementation is described in Implementation Notes — 5.6.3

BLDC Speed Control and Calculation.

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5.3.9 Process Alignment Control

5.3.10 Processes Commutation and Zero Crossing Preset and Set

The process alignment control controls the current, Curr, using the PI regulator during alignment state (see 5.5 State Diagram). The dc-bus current is regulated to required value Curr_Align. The current regulator parameters (gain...), internal, and input/output variables are located in the structure PIParamsScl_S8_Curr.

The current controller works with a constant execution (sampling) period. The period is timed by timer1, with the constant PER_CS_T1_US.

The processes commutation and zero crossing preset and set provides the BLDC commutation and zero crossing selection. Here the BLDC commutation means generation of the six step commutation which creates the voltage system shown in Figure 3-2. The required BLDC motor voltage system and commutation is provided using the MC68HC08MR32 PWM block.

The zero crossing selection means the selection of the required zero crossing phase as described in 3.2.4.2 Indirect Back EMF Sensing and

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3.2.5 Back-EMF Sensing Circuit.The zero crossing selection is

provided by the multiplexer setting.

As shown in Figure 5-2, the commutation and back-EMF zero crossing selection process is split into two actions:

• Preset commutation and zero crossing selection

• The preset means setting the buffered registers and RAM

• Set commutation and zero crossing selection

• The setting means loading the registers with buffered variables

Software Design

Main Software Flowchart

variables for commutation

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The implementation is described in Implementation Notes - 5.6.2

BLDC Commutation and Zero Crossing Selection.

5.4 Main Software Flowchart

The main software flowchart incorporates the main routine entered from the reset and interrupt states. The main routine includes initializing the MCU and the main loop. The flowcharts are shown in Figure 5-4,

Figure 5-5, and Figure 5-6.

MCU Initialization is entered only after system reset. It provides initialization of system registers, ports, and CPU clock. The MCU Initialization is provided in MCUInit() function.

After MCU Initialization the Application Initialization is executed as AppInit() function, which performs the following actions. First the zero

current offset of the dc-bus current measurement path is calibrated. This offset on the ADC input should be 1.65 V at zero current. This is implemented in the hardware design, in order to be able to measure negative and positive current values. The status registers are initialized and PWM generator is started. Also, timer 1 is started at the right moment to be synchronized with the PWM generator. This way the current measurement is executed at the defined moment of the PWM signal.

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RESET

MCU INITIALIZATION:

– SYSTEM REGISTERS INITIALIZATION

– PORTS INITIALIZATION

– PLL — CPU CLOCK INITIALIZATION

– PC MASTER SOFTWARE (PORT)

INITIALIZATION

APPLICATION INITIALIZATION:

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– CURRENT OFFSET CALIBRATION

– SYSTEM REGISTERS INITIALIZATION

– PWM INITIALIZATION

– TIMER 1 CURRENT SENSING TO PWM

SYNCHRONIZATION

– ADC MEASUREMENT INITIALIZATION

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MAIN S/W LOOP:

– SEE FIGURE 5-5

Figure 5-4. Main Software Flowchart

In the Stand-By state function, the start/stop switch is checked using StSWReadStart () function. The DecideStaSto () function is called to

decide if the application should start. The start condition differs if manual or PC master software mode is set. When in manual mode (PCMode =

0), the start condition is the switch in the start position. When PC master software mode (PCMode = 1), the start condition is a start request from PC master software (StartCtrl = 1). In both modes, Stop_F is cleared when the software evaluates the start condition. When Stop_F is cleared, the software checks the over-voltage condition and the application starts.

The system Alignment and Starting (Back-EMF Acquisition) states are provided by Alignment() and Start () functions in the code_start.c file, both are called from main(). The functionality during the start and running state is described in 3.3.1 Sensorless Commutation Control. During the starting (back-EMF acquisition) state, the commutation time

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preset calculations are prepared in the StrtCmtPreset() function, and commutation time set calculations are provided by the StrtCmtSet() function.

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Main Software Flowchart

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FAULT STATE:

– STOP MOTOR

– WAIT UNTIL FAULT CLEAR

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FAILURE

YES

ALIGNMENT STATE:

– TIME ALIGNMENT (TIMER3)

– APPLY VOLTAGE

– CURRENT CONTROL LOOP

– IF STOP OR FAULT CONDITION:

STOP MOTOR

EXIT RUNNING STATE

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YES

Stop_F Flag or Failure

APPLICATION INITIALIZATION:

– CURRENT OFFSET CALIBRATION

– SYSTEM REGISTERS INITIALIZATION

– PWM INITIALIZATION

– TIMER 1 CURRENT SENSING TO PWM

SYNCHRONIZATION

– ADC MEASUREMENT INIT.

STAND-BY STATE:

– CHECK START STOP SWITCH

– IF PC MASTER S/W MODE:

CHECK STARTCTRL

– IF RUN CONDITIONS:

SET STOP_F FLAG

Stop_F Flag

DC-Bus over-voltage

– SET FAILURE.B.VOLTAGEFAILURE

Stop_F Flag or Failure

FLAG

YES

STARTING (ACQUISITION) STATE:

– PWM INCREMENT OF

– STARTINCROUTREGS8

– SET SPEED REGULATOR INTEGRAL

PORTION ACCORDING TO CUR- RENT REGULATOR

– FIRST COMMUTATION STEP

– SECOND COMMUTATION STEP

– ACQUISITION STATE MOTOR

COMMUTATION LOOP

–IF I_CNTR_FOK SUCCESSIVE

CORRECT COMMUTATIONS:

EXIT STARTING (AQ.) STATE

– IF STOP OR FAULT CONDITION:

STOP MOTOR

EXIT RUNNING STATE

Stop_F Flag or Failure

RUNNING:

– SET TIMER PERIOD FOR SPEED

REGULATOR (VIRTUAL TIMER3)

– MOTOR COMMUTATION CONTROL

LOOP

– MOTOR SPEED CONTROL LOOP

– IF STOP OR FAULT CONDITION:

STOP MOTOR

EXIT RUNNING STATE

YES

Figure 5-5. Main Software Flowchart — Main Software Loop

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When the start is successfully completed, the Running () function is called from main(). During the Running state, the commutation time preset calculations are provided by the CmtPreset() function, and commutation time set calculations are provided by the CmtSet() function.

During the Running, Start or Alignment states, the DecideStop () function is called to check drive stop conditions and can set the Stop_F flag. When the stop flag is set the MotorStop () function is called to stop the motor, and running, start, or alignment state is left. The software enters stand-by state.

Software Design

Main Software Flowchart

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Also, the commutation error (Cntr_Err>= MAX_ZC_ERR) and over-current (OverCurrent flag = 1) fault are checked in ERRHndl () and OVCurrent () functions during the Running, Start or Alignment states. If any error is detected, the function MotorStop () function is called. Then the software enters Fault state through the Fault() function. This is only left when the failures are cleared (variable Failure = 0). This decision is provided DecideCleSto () function, called from ErrorStop (). In manual control, the failures are cleared by setting the Start/Stop switch to Stop. In case of PC master software control, the failures are cleared by the ClearFail flag from the software. When the failures are cleared, the software enters Application Initialization.

Besides the main loop, there are three interrupts: timer 1, timer 2, and PWM reload interrupts. They are described in Figure 5-6.

Interrupt Timer 1 is periodically called with period PER_CS_T1. The interrupt function provides dc-bus current measurement and virtual timer 3 service, where timer 1 is providing the timer 3 time base. When over-current is discovered, the OVC_F flag is set. Finally, the ADC is set according to the Nxt_Chnl variable to prepare speed potentiometer or temperature sensing. This interrupt is provided by the TIMACh1_Int() function.

Interrupt Timer 2 sets commutation actions. If commutation is enabled (CmtE_F flag is set), the following actions are done:

• PWM commutation step

• Synchronization of timer 1, for current measurement with PWM

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• Phase commutated flag PC_F is set

• Actual time (from timer counter register) = commutation time is recorded in T_Cmt.

This interrupt is provided by the TIMACh3_Int() function.

Interrupt PWM Reload provides back-EMF zero crossing sensing. The zero crossing input is sampled 2 or 3 times. The back-EMF state value is compared with expecting (rising/falling) edge. If the value corresponds with expecting edge, the zero crossing get flag ICR_F is set, and the actual time (from timer counter register) = zero crossing time is recorded in T_ZCros. This interrupt is provided by PWMMC_Int() function in

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code_isr.c.

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State Diagram

INTERRUPT

PWM RELOAD

BEMF ZERO CROSSING SENSING ISR:

SENSE ZERO CROSSING INPUT:

– TAKE 3 ZC INPUT SAMPLES

– BEMF STATE = S1&S2 | S2&S3

BEMF state

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V_TASC = ris. edge

SET ZERO CROSSING GET:

YES

– SET ICR_F - ZERO CROS. GET

– T_ZCROS = TIMER2 TIME

RTI

V_TASC = fal. edge

YES

CURRENT MEASUREMENT ISR:

– START ADC DC-BUS CURRENT CHANNEL

– SERVE VIRTUAL TIMER3

– CURR = VALUE FROM ADC

–IF CURR > CURR_MAX_FAULT:

– SET NEXT ADC CHANNEL NXT_CHNL

COMMUTATION ISR:

– IF CMTE_F (COMMUTATION ENABLED):

– ZERO CROSSING SELECTION

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Figure 5-6. Software Flowchart — Interrupts

INTERRUPT

TIMER 1 (TIM A CH1)

SET OVC_F (OVERCUR.) FLAG

RTI

INTERRUPT

TIMER 2 (TIM A CH3)

DO MOTOR COMMUTATION STEP TIMER 1 CURRENT SENSING TO

PWM SYNCHRONIZATION SET PC_F (PHASE COMMUTATED) T_CMT = TIMER 2 ACTUAL TIME

RTI

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5.5 State Diagram

The motor control application can be in one of the eight states shown in

Figure 5-7. Each of these states is described in the subsections

following the figure.

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RESET

INITIALIZE

MCU

INITIALIZE

APPLICATION

RUN CONDITION

(START SWITCH IS ON

AND PCMode = 0

OR PCMode AND StartCtrl

AND SWITCH IS ON)

STAND-BY STATE

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(Stop_F = 0)

PWM DISABLED

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(START SWITCH SET OFF

ALIGN STATE

PWM ENABLED

ALIGN TIMEOUT EXPIRED

BACK-EMF ACQUISITION STATE

COMMUTATION + PWM ENABLED

COMMUTATION IS LOCKED WITH BACK-EMF FEEDBACK

COMMUTATION + PWM ENABLED

RUNNING STATE

MOTOR STOP IS REQUIRED

(Stop_F = 1)

OVER CURRENT

IRRECOVERABLE

COMMUTATION

STOP STATE

PWM DISABLED

OR PCMode AND CLEAR FAIL)

ERROR

OVER VOLTAGE

CLEAR FAILURE

(FAILURE = 0)

FAULT STATE

PWM

DISABLED

DONE

Figure 5-7. Application State Transitions

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5.5.1 Initialize MCU

This state is entered after the MCU is reset, and performs the following actions:

• MCU ports are configured for the application

• Some application (system) variables are initialized

• MCU clock PLL is locked

• Hardware boards used are identified, and parameters initialized

• PC master communication software is initialized with SCI port

• ADC is initialized

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and the state is exited.

Software Design

State Diagram

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5.5.2 Initialize Application

This state is used as an application reset, called following a return from fault or stop states.

In this state the following actions are done:

• Current measurement path calibrated and checked for error

• Some application (system) variables initialized

• Some MCU peripherals are configured (timer, OC function, PWM)

• PWM outputs for motor control are turned OFF

• Timer 1 (Tim A Ch1) is synchronized with the PWM cycle

• Speed input, dc-bus voltage and temperature measurement is

• Ready LED is turned ON

and the state is exited.

initialized

5.5.3 Stand-By

State diagram for this software is shown in Figure 5-8.

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Current measurement and current calibration when PWM is OFF

Before testing of the start switch, dc-bus current is measured when PWM is OFF. This way the dc-bus current measurement path is calibrated. The calibrated value Offset0_Curr is used for the final current calculation.

This offset on the ADC input should ideally be 1.65 V at 0 dc-bus current.

If the sensed value exceeds the limit (Offset_Max_Curr) when PWM is OFF, this indicates some hardware error, and the control flow enters into the fault state:

Start condition test

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The start condition is tested. If in manual mode (PCMode = 0), the start condition is a movement in the switch from stop to start. In PC master software mode (PCMode = 1), the start condition in switch start position and StartCtrl = 1. If start condition valid then Strt_F is set, Stop_F is cleared, and the next state entered.

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ENTER

Software Design

State Diagram

CURRENT MEASUREMENT

CURRENT CALIBRATION

nc...

START CONDITION

(START SWITCH CHANGED

START AND PC MODE AND START CTRL)

FROM STOP TO START OR

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AND

WHEN PWM IS OFF

DONE

START CONDITION TEST

SPEED INPUT

AND

DC-BUS VOLTAGE

MEASUREMENTS

DONE

EXIT

CURRENT IS HIGHER THAN LIMIT

OVER VOLTAGE

UNDER VOLTAGE

ERROR IN HARDWARE

FAULT STATE

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Figure 5-8. Stand-by State

Speed input and dc-bus voltage measurements

The dc-bus voltage is measured after the start switch is turned ON. This prevents the measurement being disturbed by the power turn ON. Where that dc-bus voltage is not within the limits, the control flow enters into the fault state.

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5.5.4 Align State

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In the align state the rotor position is stabilized by applying PWM signals to only two motor phases (no commutation). When preset time-out expires, then this state is finished. See Figure 5-9.

ENTER

RUN CONDITION (STOP_F = 0)

CURRENT MEASUREMENT IS DONE

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CURRENT CONTROLLER

ALIGN TIME-OUT

SCHEDULER

ALIGN TIME-OUT EXPIRED

EXIT

TIMER1 (TIM A CH1) INTERRUPT

CURRENT MEASUREMENT

ISR

CURRENT MEASUREMENT IS DONE (CMD_F = 1)

DONE

(CMD_F = 1)

(CMD_F = 0)

IRRECOVERABLE OVER-CURRENT

FAULT

STATE

OVER-CURRENT

DETECTION

Figure 5-9. Align State

Scheduler

The scheduler handles the state transitions in the align state. The dc-bus current measurement is done in OC interrupt service routine, in order to keep synchronization with PWM cycle. After measurement is made, the scheduler allows calculation by the current controller and

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the over-current detection. The CMD_F (current measurement done) flag indicates that the new value of dc-bus current is ready to be processed by the current controller.

The time-out (software timer 3) of this state is defined in the software by the constants: PER_T_ALIGN and PER_BASE_T3_ALIGN.

Current Controller

The current controller subroutine is called every PER_CS_T1_US µs (128 µs with default software setting) after a new value of the dc-bus current has been obtained (CMD_F=1). It sets all six PVALx register pairs to get the right PWM ratio for the required current.

Software Design

State Diagram

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Timer 1 Interrupt

Once the synchronization of OC function with the PWM cycle has been achieved, it must be maintained because the current measurement is initiated here.

Over-Current Detection

The dc-bus current is periodically sensed and the over-current condition is evaluated. After a defined number successive over-current events I_CNTR_OVC, the control flow enters into the fault state.

5.5.5 Back-EMF Acquisition State

The back-EMF acquisition state provides the functionality described in

3.3.1.4 Starting (Back-EMF Acquisition) and 3.3.1.5 Starting — Commutation Time Calculation. Figure 5-10 shows the state

transitions for the state.

First Commutation

After the align state time out expires, voltage is applied to another phase pair. The first commutation is made and the PWM duty cycle is constant. This value has been defined by the current controller during the Aalign state.

The calculation of the commutation time is explained in 3.3.1.5

Starting — Commutation Time Calculation.

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Second Commutation

The commutation time (T2) is calculated from the previous commutation time and the start commutation period (Per_CmtStart). This time is set to timer 2. Then, the new PWM multiplexer logic data is readied for when the commutation interrupt performs the next commutation.

The calculation of the commutation time is explained in 3.3.1.5

Starting — Commutation Time Calculation.

Measurements Handler

As explained in Scheduler and Over-Current Detection, the dc-bus

nc...

current is scanned and over-current condition is evaluated. Where there is an over-current, the control enters the fault state (see Fault

State). The voltage and the speed commands are scanned too. When

this state is finished, the values of dc-bus current, dc-bus voltage, and speed command are updated.

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State Diagram

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CURRENT MEASUREMENT

IS DONE

(CMD_F = 1)

MEASUREMENTS

HANDLER

ERROR HANDLER

OVER-CURRENT

TIMER2 (TIM A CH3) INTERRUPT

ENTER

FIRST COMMUTATION

DONE

SECOND COMMUTATION

DONE

ZERO CROSSING EVENT

RECEIVED THE

(ICR_F = 1)

SERVICE OF RECEIVED

BACK-EMF ZERO CROSSING

IRRECOVERABLE COMMUTATION ERROR

PWM DUTY CYCLE IS LEFT AT VALIE FOUND BY THE CURRENT CONTROLLER DURING THE ALIGN STATE

CURRENT MEASUREMENT

DONE

(CMD_F = 1)

SCHEDULER

DONE

FEEDBACK

FAULT STATE

EXIT

COMMUTATIONS ARE LOCKED TO THE BACK-BMF FEEDBACK (START_F = 0)

IS DONE

MEASUREMENTS

HANDLER

DONE

PHASE HAS BEEN

COMMUTATED (PC_F=1)

SERVICE OF COMMUTATION

IRRECOVERABLE OVER-CURRENT

PWM (RELOAD) INTERRUPT (PWM CENTER)

COMMUTATION ISR

PHASE HAS BEEN COMMUTATED

(PC_F=1)

TIMER1 (TIM A CH1) INTERRUPT

CURRENT MEASUREMENT

ISR

CURRENT MEASUREMENT IS DONE (CMD_F = 1)

BEMF ZERO CROSSING

SENSING ISR

DONE

(ICR_F=1)

Figure 5-10. Back-EMF Acquisition

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Service of Commutation

As already explained, the motor phase commutation is performed in the OC interrupt service routine. The phase commutated flag (PC_F=1) indicates this action to the scheduler, which allows the performed commutation to be serviced. Detailed explanation of this state is in Processes Commutation and Zero Crossing Preset and

Set.

Service of Received Back-EMF Zero Crossing

The back-EMF zero crossing is detected by PWM middle function block. Then the appropriate flag (captured received the zero crossing

nc...

event - ICR_F) is set by PWM centre interrupt service routine. This indicates to the scheduler that the zero crossing event must be served.

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The following actions are taken:

1. Commutation parameters are recalculated more precisely based on the received feedback

2. Commutation time is preset to the output compare register of timer 2

For a better understanding of how the commutation process works, see 3.3.1 Sensorless Commutation Control, (see 3.3.1.5 Starting

— Commutation Time Calculation).

BEMF Zero Crossing Sensing Interrupt Service Routine

This ISR is used to evaluate the back-EMF zero crossing. Back-EMF is evaluated here in order to synchronize zero crossing capture with the middle of central-aligned PWM. This technique rejects the noise caused by PWM from the back-EMF signal. When this ISR is initiated, then three samples of the zero crossing input (BEMF_IN) are taken and the state is evaluated. Based on the expected edge (V_TASC2, ELS2A_ELS2B) and the evaluated state of the BEMF_IN pin, the zero crossing event is verified. If it is accepted, then the captured time is stored in variable (T_ZCros) and the PWM ISR is finished. The appropriate flag (captured received the zero crossing event — ICR_F) is set.

Current Measurement Interrupt Service Routine

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The output compare function is used to synchronize initiating the dc-bus current sampling with the PWM cycle, and also for the commutation timing.

Error Handler

If the BLDC motor is controlled properly, commutation events must be locked to the back-EMF zero crossing feedback. When that feedback is lost, commutation time is derived from previous commutation events. If feedback does not recover during a defined number of commutations (constant — C_MaxErr), then the situation is evaluated as irrecoverable commutation error, and the fault state is entered.

Software Design

State Diagram

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5.5.6 Running State

Measurement Handler

The measurement handler assures that the measurement process is done in the right order. The dc-bus voltage, speed command, and temperature are scanned sequentially. After the state has run three times, all the values for dc-bus current, dc-bus voltage, speed input, and temperature are updated. dc-bus current is scanned with a constant time period in the current measurement ISR, but the over-current condition is evaluated in the main software loop. After a defined number (I_OVC_Cnt) of successive over-current events, the control flow enters into the fault state.

The BLDC motor is run with regular feedback. The speed controller is used to control the motor speed by changing the value of PWM duty cycle. Figure 5-11 shows the state transitions.

Measurements Handler

Explained in 5.5.5 Back-EMF Acquisition State.

Service of Commutation

Explained in 5.5.5 Back-EMF Acquisition State.

Service of Received Back-EMF Zero Crossing

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Software Design

Explained in 5.5.5 Back-EMF Acquisition State. The difference is that the commutation parameters are recalculated with different constants (see 3.3.1.3 Running — Commutation Time Calculation)

BEMF Zero Crossing Interrupt Service Routine

Explained in 5.5.5 Back-EMF Acquisition State.

Current Measurement Interrupt Service Routine

Explained in 5.5.5 Back-EMF Acquisition State.

Error Handler

Explained in 5.5.5 Back-EMF Acquisition State.

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Over Current

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Explained in 5.5.5 Back-EMF Acquisition State.

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Motorola M68HC08 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Revision history

List of Sections

Table of Contents

List of Figures

List of Tables

Section 1. Introduction

1.1 Contents

1.2 Application Functionality

1.3 Benefits of the Solution

Section 2. System Description

2.1 Contents

2.2 System Concept

2.3 System Specification

Section 3. BLDC Motor Control

3.1 Contents

3.2 Brushless DC Motor Control Theory

3.3 Used Control Technique

3.4 Application Control

Section 4. Hardware Design

4.1 Contents

4.2 System Configuration and Documentation

4.3 All HW Sets Components

4.4 High-Voltage Hardware Set Components

4.5 Low-Voltage Evaluation Motor Hardware Set Components

4.6 Low-Voltage Hardware Set Components

Section 5. Software Design

5.1 Contents

5.2 Introduction

5.3 Data Flow

5.4 Main Software Flowchart

5.5 State Diagram