Closed Loop Speed Control - Motorola M68HC08 Manual

Software Design
6.1.4 Speed Controller
Reference
Speed
(uiOmegaReqRamp)
6.1.5 Commutation & PWM Generation
Designer Reference Manual
48
Freescale Semiconductor, Inc.
The speed closed loop control is characterized by the measurement of
the actual motor speed. 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
required speed.
The speed PI controller generates the corrected output duty cycle in
order to compensate for the error. The general principle of the voltage
control loop is illustrated in
Speed
Error
PI
Controller
Figure 6-2. Closed Loop Speed Control
The commutation process generates the proper commutation pattern on
six gate signals outputs, while the PWM generation process generates
the appropriate PWM signal for the selected gate outputs. The
commutation pattern is selected from commutation table using the
three-bit commutation vector, ucSensorVector. This pattern is then
loaded into the selected outputs of Port B of the microcontroller. The
PWM is generated by the on-chip timer using the output compare (OC)
function, according to the required output duty cycle,
uiDutyCycleOut. The PWM is generated on timer output of the
microcontroller. Then the on-board logic is used for selection of the
PWM to the 3-phase gate driver.
Software Design
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Figure 6-2. Closed Loop Speed
Corrected
Speed
(uiDutyCycleOut)
Controlled
System
Control.
Actual Motor
Speed
(uiOmegaActual)
DRM046 — Rev 0
MOTOROLA