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Motorola M68HC08 User Manual

Page 110

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User Guide

Designer Reference Manual

DRM028 — Rev 0

110

User Guide

MOTOROLA

6.2.2 Maximal Application Speed

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

(EQ 6-1.)

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

(EQ 6-2.)

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

µs, 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.

maximal speed[rpm]

60 10

6

(

)

min. commutation period [us]*COMMUT_REV

--------------------------------------------------------------------------------------------------------------------------

=

COMMUT_REV

6p

2

-------

=

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Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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