Commutation Point Optimization Method for Sensorless BLdc Motor Control Using Vector Phase Difference of Back EMF and Current

Commutation error is a crucial factor that reduces the efficiency of brushless dc (BLdc) motors. This article presents a commutation point optimization method for a sensorless BLdc motor. First, the sources of commutation error under position sensorless control are analyzed, and a conclusion is drawn that the phase difference between the back electromotive force vector and phase current vector equals the total commutation error. Second, a fundamental waveform extractor is used to eliminate the influence of harmonics on the equivalent commutation error. Third, the phase difference of the fundamental waveforms is extracted by a combined phase-locked loop, and the real-time commutation error is obtained consequently. Finally, accurate commutation is achieved by compensating for the phase difference, and experimental results on a reaction flywheel prototype evaluate the presented method.