Motorola M68HC08 Reference Manual page 110

User Guide
6.2.2 Maximal Application Speed
NOTE:
6.2.3 Voltage Closed Loop
6.2.4 Motor Suitability
Designer Reference Manual
110
Freescale Semiconductor, Inc.
The maximal motor speed is limited by the minimal commutation period:
maximal speed[rpm] =
COMMUT_REV — commutations per motor revolution, must be set
according to rotor poles:
COMMUT_REV
where: p = rotor poles
The minimal commutation period is determined by execution time of the
software. With default software settings and COEF_HLFCMT = 0.450 it
is 333 s, as shown in
motor can be controlled up to the maximal speed of 15,015 rpm.
Using PC master software in the application increases the minimal
commutation time. This is due to the execution of PC master software
routine. In this case, the minimal execution time is 520 ms. The minimal
commutation period could be decreased using pure assembler code
instead of C coding.
As shown in Application Hardware and Software
speed control is based on voltage closed loop control. This should be
sufficient for most applications.
Back-EMF zero crossing sensing is achievable for most of BLDC motors
with a trapezoidal back-EMF. However, for some BLDC motors the
back-EMF zero crossing sensing can be problematic since it is affected
by unbalanced mutual phase capacitance and inductance. It can
disqualify some motors from using sensorless techniques based on the
back-EMF sensing.
User Guide
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60 10
------------------------------------------------------------------------------------------------------------------------- -
min. commutation period [us]*COMMUT_REV
6p
= ------ -
2
Table 2-1. So for example, the 4 pole (3-phase)
6
(EQ 6-1.)
(EQ 6-2.)
Configuration, the
DRM028 — Rev 0
MOTOROLA