ST AN2316 Application note

AN2316

Application Note

Improved ST7LITE05 AC Chopper Driver Solution

Introduction

This application note presents an AC motor or load circuital solution improvement of efficiency over the one discussed in a previously published application note, AN1255.

Above all, this solution does not have limits on where it may be applied, embracing all types of AC asynchronous monophase motor applications (e.g. refrigerators, hydraulic pumps, fans, and lamps).

Due to the increasing electric pollution of the environment, European standards impose restrictions on Electromagnetic Compatibility (EMC). The proliferation of non-linear loads and the consequential increase in harmonics pollution in power distribution lines have induced various technical committees to establish maximum limits on the harmonic content produced by all industrial and domestic devices. Manufacturers of these devices are required to conform to this new standard and develop products which function with new operational characteristics.

The most common method used to vary the AC monophase motor voltage is a TRIACbased phase angle partialization technique. Although this is a simple, low-cost solution that has been used for several years, it is problematic because of the excessive harmonic distortion which reduces the efficiency of the entire system. These systems typically include a complex inverter drive which is quite expensive, and, while they can solve the load’s harmonic content problems, they do not address those same problems in the electric lines.

March 2006 Rev 1 1/24

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Contents AN2316 - Application Note

Contents

1 STEVAL-IHM006V1 Circuit Description . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 EMC Precompliance Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.1 Electrical Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 EM C D ouble-Filter Bill of Mater ials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Safety and Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 STEVAL-IHM006V1 Board Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Environmental Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.3 Mandatory Checks Before Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4 Start-up Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4 ST7FLITE05 Software Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.1 Peripheral Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.2 Firmware Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.3 Development Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5 Library Source Cod e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.1 Software downloa ds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.2 File Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2/24

AN2316 - Application Note List of Figures

List of Figures

Figure 1. Two-Switch Drive Motor Schematic (ST patented). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 2. Basic Working Principal Illustration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 3. System Waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 4. EMC Measure ment Schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5. EM C Double -Filter Stage Schem atic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figu r e 6 . 20kH z Switc h in g F r e quen c y EMC An a lysi s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figu r e 7 . 35kH z Switc h in g F r e quen c y EMC An a lysi s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 8. STEVAL-IHM0 06V1 Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 9. ST7FLITE05 Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 10. Softec STVD7 v3.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 11. ST7 Visual Programm er . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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STEVAL-IHM006V1 Circuit Description AN2316 - Application Note

1 STEVAL-IHM006 V1 Circuit Description

This ST-patented solution uses a working switch mode to solve third harmonic problems. The base circuit can be viewed as a mains vol tage double-chopper without any preliminar y AC/DC conversion type (see

Note: The AC chopper STEVAL-IHM006V 1 provides customers with a demo that regulates the

voltage in AC motors or loads of up to 300W. This allows the user to demonstrate smooth, silent, and efficient regulation with respect to TRIAC solutions.

The double-chopper is a device which energizes the load beginning from any level of the sinusoidal voltage wave and demagne tizes the load with a freewheeling current system, thereby obtaining voltage and current regulation of the load.

Starting from a perfect sinusoidal-shaped mains curve, the regulated current is also sinusoidal for all the power levels that the user desires to transfer to the load. By neglecting the electronic device losses, the circuit incoming power S is equa l to the outgoing power:

Equation 1

Figure 1 on page 6

AC RMS()IAC RMS()

⋅

⋅=

LOAD RMS()

where, V

AC(RMS)

LOAD(RMS)

The I

= Root Mean Squared (RMS) Mains Volt age,

= RMS Input Current,

= RMS Load Voltage, and

= RMS Output Current.

AC(RMS)

and I

LOAD(RMS)

currents are related as follows:

Equation 2

LOAD RMS()

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

AC RMS()

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

LOAD RMS()

The circuit operates as a converter, particularly as an AC/AC converter or transformer. It has no limitation in terms of load impedance since it works with both, inductive and ohmic loads, with notable angles between the current and the vol tag e.

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AN2316 - Application Note STEVAL-IHM006V1 Circuit Description

The circuit is based on the fo llowing parts (see

● IGBT Z1

Figure 1

Together with diodes D1, D2, D5, and D6, it performs current freewheeling (only for inductive load).

● IGBT Z2

Together with diodes D3, D4, D7, and D8, it is the main switch through which the load is energized.

● Pulse Transformer T1

It allows the signal derived from the PWM generator to be transferred to the Z1 gate. This component electrically insulates the input from the output’s entry signal and phase inversion.

● PWM generator

This is provided by the ST7Lite05 microcontroller.

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STEVAL-IHM006V1 Circuit Description AN2316 - Application Note

Figure 1. Two-Switch Dri ve Mo t or S che m at i c (S T patented )

+15V

C15

0.1µF

D15

18V

R10

12K 1/4W

D11

STTH108

D13

15V

NTC22

CONTROL

C10

10µF 25V

t°

D12

STTH108

123

+15V

VDD DDD

678

STTH306

470-1/4W

STTH306

STGP7NB60HD

3.3nF

5.6-1/4W

250V10L

STTH306

RV3

STTH306

STGP7NB60HD

STTH306

1N4148

NOT ASSEMBLED

pulse transformer

0.1µF-100V

D16 1N4148

R15

1.2k

0.1µF-100V

294

D10

18V

270K

PHASE

RS-196-375

L1 1mH

D14

STTH108

VIPer12A DIP

C12

0.1µF

BC547

2.2K

470K

C14

C13

1µF-450V

R11 15

10µF 25V

R13 0

BC547

BC557

S 1

Line filter

5 A

STTH306

250V14L

220K 1/2W

C17

C16

MAINS

320VAC

RV2

250V10L

RV1

1µF 250VAC

100nF x 2

phase

100nF x 2

PHASE

STTH306

ASYNCHRONOUS

MOTOR

+5V

OUT

L78L05A/TO92

+15V

NOT ASSEMBLED

47µF-25V

0.1µF

GND

0.1µF

BC557

321

C18

100pF

R14 R

NOT ASSEMBLED

16151413121110

PA1

PA3

PA4

PA0/LTIC

PA2/ATPWM0

VSS

VDD

RESET

SS/AIN0/PB0

1234567

AIN0

C25

100nF

+5V

RESET

+5V

22K

PA7

PA5/ICCDATA

PA6/MCO/ICCCLK

MISO/AIN2/PB2

MOSI/AIN3/PB3

SCK/AIN1/PB1

0.1µF

R12 10K

CLKIN/AIN4/PB4

ST7LITE09

65432

J10

CON6_0

246

13579

JP1

AI12268

RESET

+5V

CON10A

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AN2316 - Application Note STEVAL-IHM006V1 Circuit Description

In order to avoid short-circuiting the mains through switches Z1 and Z2, they must work in a complementary manner. When Z1 is ON, Z2 must be OFF and vice-versa.

For example, if the line vol tage at J1 i s posi tiv e wi th respect to J2, and the PWM signal goes from high-to-low, Z2 switches ON with a delay inserted by its own gate capacitance and by resistor R3 so the load is energized. In the meantime, Z1 swit ches OFF instant aneously.

Note: In this condition, if the current is positive (i.e. it goes into J1 and comes out from J2), it will

flow through D4, Z2, D7, and the load. Conversely, if the current is negative, it will be going out from J1 and closing through the load, D3, Z2, and D8.

As is the case with the current, when the PWM goes from low-to-high, Z2 is turned OFF instantaneously , while Z1 is switched ON with a delay. This enables a freewheeling current to flow through Z1.

Given these relationships, if “δ” is the duty cycle (see is may be expressed as:

Equation 3

t() δ VACt()⋅δV

LOAD

where,

= Load voltage,

LOAD

= Mains voltage, and

= Maximum sinusoida l vo l t age.

MAX

The load current may be expressed as:

Equation 4

LOAD

t()

-- -

IAC⋅ t()

-- -

MAX

where, I

= Load current,

LOAD

= Input current,

= Maximum current value, and

MAX

ϕ = the angle between the current and voltage.

Figure 2 on page 8

MAX

ωt()sin⋅⋅==

ωt ϕ+()sin⋅⋅==

), the load voltage

7/24

STEVAL-IHM006V1 Circuit Description AN2316 - Application Note

The relationships expressed in

Equation 3

and

Equation 4

, and

Figure 2

show that it is

possible to control power fed to the load by changing the PWM signal duty cycle.

Note: The load is assumed to be inductive so the high frequency harmonics are filtered in the

current waveform (see Figure 3 on page 9 for system wavefor m deta ils).

Figure 2. Basic Working Principal Illustration

Bi-directional PWM Chopping

line

Load Current

duty cycle

Duty Cycle Increase

AI12267

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