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Motorola M68HC08 User Manual

Page 145

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User Guide

Tuning for Customer Motor

DRM028 — Rev 0

Designer Reference Manual

MOTOROLA

User Guide

145

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.

(EQ 6-7.)

(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 [

µs]:

/* 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

Advance_angle

30 Deg

ZC-Cmt angle

=

COEF_HLFCMT

1

2

-

Advance_angle

60

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Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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