AN2499
Application note
ST10 electric motor control library:
PWM driver
Introduction
STMicroelectronics provides a library of electric motor control functions that can be used as
base blocks for motor control applications.
This application note describes the set of API to manage PWM signals to drive a 3-phase
electric motor with the desired voltage with ST10 microcontrollers.
March 2007 Rev 1 1/13
www.st.com
Contents AN2499
Contents
1 Functions set overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 PWM overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 API specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Functions definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.1 PWM_Init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.2 PWM_start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.3 PWM_Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2/13
AN2499 List of tables
List of tables
Table 1. PWM_Init Parameters: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 2. PWM_start Parameters: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 3. PWM_Register Parameters: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 4. Required library resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table 5. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3/13
List of figures AN2499
List of figures
Figure 1. ST10 EMCL structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 2. Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 3. Output waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
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AN2499 Functions set overview
1 Functions set overview
The PWM driver is a set of functions included in ST10 Electric Motor Control Library (EMCL)
(see Figure 1) useful to generate six PWM signals to drive a 3-phase electric motor by
inverter in electric motor control applications. The document explains how to use and
configure ST10 peripherals in order to produce PWM signals with adjustable pulse width at
the beginning of each new PWM period.
Figure 1. ST10 EMCL structure
ST10 EMCL
Flux
Oriented
Contr o
Sinusoidal
l
Control
Observer
Leunberger
SPI
Driver
oEnc der
Driver
Hall sensors
Driver
Current sensing
Driver
pwm.c
pwm
PWM
Driver
.
h
5/13
PWM overview AN2499
2 PWM overview
A power inverter is a d.c. to a.c. converter used to apply the desired voltage across the
motor phases. In particular for a 3-phase electric motor it is used an 3-phase full bridge
inverter with 6 switches, MOSFETs in low-voltage applications (i.e. automotive field). The
components of the inverter are impulsed, following a specific switching pattern, producing
the symmetric waveforms necessary to drive the motor (see Figure 2).
Figure 2. Inverter
U
phase
V
phase
W
phase
T
semiperiod
0
T
switching period
s
V
U
W
Phase U
Phase V
Phase W
T
0
T
T
0
s
To obtain the waveforms of Figure 2, it is used the ST10 PWM and XPWM Modules
channels configuring their pulse width (PW) registers with the values calculated by control
algorithm and updated at every PWM period. The upper and lower switches of the same leg
of inverter are driven with two complementary pulsed signals (see Figure 3) with a so called
dead-time to avoid shortcut.
Figure 3. Output waveforms
PPx
Phase U +
Phase U -
Phase V +
Phase V -
Phase W +
PU
PV
PW
T
0
t
Phase W -
6/13
AN2499 API specification
3 API specification
The following API allows easy access to the set of functions to configure the PWM and
XPWM modules channels in Center Aligned Mode and to change the pulse width of each
signal simultaneously at every PWM period.
The use of these functions eliminates the need to access directly ST10 registers.
Available functions:
1. void PWM_Init(void);
2. void PWM_start(void);
3. void PWM_Register(PWMFUNCTION pwmfunction);
see file pwm.c in the EMSW_PWM Library.
7/13
API specification AN2499
3.1 Functions definition
This section describes the functions used by the implemented control algorithm in order to:
– - configure the PWM and XPWM modules;
– - start the PWM and XPWM timers;
– - and change the pulse width of the output signals.
3.1.1 PWM_Init
Prototype definition:
void PWM_Init(void)
Table 1. PWM_Init Parameters:
Configuration Parameters Description
none
Global Parameters
PU variable to store current PWM U phase value
PV variable to store current PWM V phase value
PW variable to store current PWM W phase value
pwmFunction pointer to the control algorithm function
Function Parameters
none
Description:
The PWM_Init function is used to initialize the Pulse Width Modulation (PWM) Module and
the XPWM Module selecting three channels for each module in Center Aligned Mode with
the default values of semi period (PP) and pulse width (PW) and enables interrupt from
PWM channel 0 at the beginning of each new PWM cycle.
PWM pin ( output )
channel 0 P7.0
channel 1 P7.1
channel 2 P7.2
XPWM
channel 0 P8.0
channel 1 P8.1
channel 2 P8.2
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AN2499 API specification
3.1.2 PWM_start
Prototype definition:
void PWM_start(void)
Table 2. PWM_start Parameters:
Configuration Parameters Description
none
Global Parameters
PU variable to store current PWM U phase value
PV variable to store current PWM V phase value
PW variable to store current PWM W phase value
pwmFunction pointer to the control algorithm function
Function Parameters
none
Description:
The PWM_start function starts the PWM and XPWM timers simultaneously.
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API specification AN2499
3.1.3 PWM_Register
Prototype definition:
void PWM_Register(PWMFUNCTION pwmfunction)
Table 3. PWM_Register Parameters:
Configuration Parameters Description
none
Global Parameters
PU variable to store current PWM U phase value
PV variable to store current PWM V phase value
PW variable to store current PWM W phase value
pwmFunction pointer to the control algorithm function
Function Parameters
none
Description:
The PWM_Register function points to the control algorithm function. It is needed to declare
in the main a user function with the algorithm control and to register it so that the algorithm
can be executed at every occurrence of PWM interrupt.
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AN2499 API specification
3.2 Resource
For the use of the library the needed resources are:
Table 4. Required library resources
3 PWM channels PWM
3 XPWM channels XPWM
1 Bank register (RB10) interrupt
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Revision history AN2499
4 Revision history
Table 5. Document revision history
Date Revision Changes
29-Mar-2007 1 Initial release.
12/13
AN2499
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