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Motorola M68HC08 User Manual

Page 144

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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 [

µs]

/* 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[

µs] *

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.

For More Information On This Product,

Go to: www.freescale.com

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