Motorola M68HC08 manual Maximal Application Speed, Voltage Closed Loop, Motor Suitability

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

User Guide

6.2.2 Maximal Application Speed

The maximal motor speed is limited by the minimal commutation period:

maximal speed[rpm] =	60(106 )	(EQ 6-1.)
	min.--------------------------------------------------------------------------------------------------------------------------commutation period [us]*COMMUT_REV

COMMUT_REV — commutations per motor revolution, must be set according to rotor poles:

6p	(EQ 6-2.)
COMMUT_REV = ------
2

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 Table 2-1. So for example, the 4 pole (3-phase) motor can be controlled up to the maximal speed of 15,015 rpm.

NOTE: 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.

6.2.3 Voltage Closed Loop

As shown in Application Hardware and Software Configuration, the speed control is based on voltage closed loop control. This should be sufficient for most applications.

6.2.4 Motor Suitability

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.

Designer Reference Manual		DRM028 — Rev 0
110	User Guide	MOTOROLA
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