Fast Commutation Instant Shift Correction Method for Sensorless Coreless BLDC Motor Based on Terminal Voltage Information

Due to the phase delay caused by low-pass filter, device retarding, and software retarding, the extracted sensorless motor commutation signal deviation occurs. Unfortunately, the relationship between the phase shift and inactive phase freewheeling has been scarcely referred to through the published papers, and most of the commutation instant shift compensation methods present slow convergence rate. Therefore, a fast commutation instant shift correction method based on analyzing the back-electromotive force (EMF) harmonic information is proposed in this paper. The method is effective both in the steady-speed control and in variable-speed control. Considering that commutation instant shift may induce inactive phase freewheeling and negative torque in motor windings, the freewheeling condition and motor electric operation condition are analyzed as well. Furthermore, to exactly delay the zero-crossing points (ZCPs) of EMF by 30 degrees and compensate the commutation instant shift, the speed detection accuracy and feedback frequency are enhanced by measuring and summing up the 2 x P consecutive half-period of the ZCPs signal. Finally, the validity of the proposed commutation instant shift correction method is verified through experimental results.