Motorola M68HC08 manual Bldc Motor Control Brushless DC Motor Control Theory

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

BLDC Motor Control

Brushless DC Motor Control Theory

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 3-3shows 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.

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	BLDC Motor Control	25
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