Motorola M68HC08 manual Start-up Constants and Maximal Commutation Period

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

User Guide

Tuning for Customer Motor

In the real system, the ZC-Cmt angle is a little bit greater than the theoretical calculation. This is due to the response time of the hardware back-EMF zero crossing sensing. Therefore, the default software setting is COEF_HLFCMT = 0.375

Normally, COEF_HLFCMT should only be changed if you need a different commutation angle (time from back-EMF zero crossing to commutation). For example, for motor field weakening.

The relation between COEF_HLFCMT and the commutation can also be defined by Advance_angle, which is the electrical angle shift from ideal commutation.

Advance_angle = 30 Deg – ZC-Cmt angle		(EQ 6-7.)
1	Advance_angle
COEF_HLFCMT = -	– -------------------------
2	60	(EQ 6-8.)

Advance_angle = 15° for COEF_HLFCMT = 0.25

Advance_angle = 7.5° for COEF_HLFCMT = 0.375

Advance_angle = 0° for COEF_HLFCMT = 0.5

The relation between back-EMF zero crossing and the commutation is explained in the section 3.3.1.3 Running — Commutation Time Calculation.

6.5.5.2 Start-up Constants and Maximal Commutation Period

Constants defining start-up need to be changed according to the drive dynamics.

Start Commutation Period [∝s]:

/* MUST_CHANGE_8_EXPER: */ #define PER_CMT_START_US 4000.0

Range: <0,PER_CMT_MAX_US/2>

PER_CMT_START_US is the period used to calculate the first (start) commutation period.

PER_CMT_START_US period must be changed for any motor accommodation. It can be set experimentally. If the motor displays errors during Starting (Back-EMF Acquisition) state, beginning

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	User Guide	145
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