User Guide
Designer Reference Manual
DRM028 — Rev 0
144
User Guide
MOTOROLA
6.5.5.1 Commutation Parameters
Commutation time period to discharge coil current [
µ
s]
/* MUST_CHANGE_7: */
#define PER_DIS_US 300.0
Range: <0,minimal commutation period*COEF_TOFF>
It is the maximal allowed current decay period, determined by motor
winding and maximal current.
Must be:
PER_DIS_US
< minimal motor commutation period[
µ
s] *
COEF_TOFF
where:
COEF_TOFF
is commutation Toff period coefficient from
const.h file explained in the section
3.3 Used Control Technique
.
NOTE:
If
PER_DIS_US
is too high, it can cause commutation errors at high
speed
Half Commutation (advancing) Coefficient [-]:
/* CAN_CHANGE_9: */
#define COEF_HLFCMT 0.375
Range: <0,1>
COEF_HLFCMT
, multiplied by commutation period, determines the
time from back-EMF zero crossing to motor commutation. So, it sets
the electrical angle from back-EMF zero crossing to motor
commutation step. The software controls BLDC motor with a 6-step
commutation (six commutations per one electrical rotation), which
means 60° between commutations. For ideal commutation with no
advancing (no field weakening), the back-EMF zero crossing should
be just in the middle between commutations, which means that the
electrical angle (ZC-Cmt angle), between back-EMF zero crossing
and commutation, is 30°.
(EQ 6-6.)
ZC-Cmt angle = 15° for COEF_HLFCMT = 0.25
ZC-Cmt angle = 22.5° for COEF_HLFCMT = 0.375
ZC-Cmt angle = 30° for COEF_HLFCMT = 0.5
COEF_HLFCMT
ZC-Cmt angle
60
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Freescale Semiconductor, Inc.
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