Motorola M68HC08 Commutation Parameters, Commutation time period to discharge coil current ∝s

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

User Guide

6.5.5.1 Commutation Parameters

Commutation time period to discharge coil current [∝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[∝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°.

COEF_HLFCMT = ZC------------------------Cmt angle
60	(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

Designer Reference Manual		DRM028 — Rev 0
144	User Guide	MOTOROLA
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