Motorola M68HC08 Reference Manual page 145

6.5.5.2 Start-up Constants and Maximal Commutation Period
DRM028 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
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
COEF_HLFCMT
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
Calculation.
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
User Guide
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–
= 30 Deg ZC-Cmt angle
Advance_angle
1
–
- - - - - - - - - - - - - - - - - - - - - - - - -
= -
60
2
3.3.1.3 Running — Commutation Time
User Guide
Tuning for Customer Motor
(EQ 6-7.)
(EQ 6-8.)
Designer Reference Manual
145