Motorola M68HC08 - Manual (Page 25)

BLDC Motor Control
Brushless DC Motor Control Theory
DRM028 — Rev 0 Designer Reference Manual
MOTOROLA BLDC Motor Control 25
back-EMF and commutation events is very important. In this condition,
the motor behaves as a dc motor and runs at the best working point.
Thus, simplicity of control and good performance make this motor a
natural choice for low-cost and high-efficiency applications.
Figure 3-3 shows a number of waveforms:
• Magnetic flux linkage
• Phase back-EMF voltage
• Phase-to-phase back-EMF voltage
Magnetic flux linkage can be measured. However, in this case it was
calculated by integrating the phase back-EMF voltage (which was
measured on the non-fed motor terminals of the BLDC motor). As can
be seen, the shape of the back-EMF is approximately trapezoidal and
the amplitude is a function of the actual speed. During speed reversal,
the amplitude changes its sign and the phase sequence changes.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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