Commutation strategy of high-speed maglev brushless dc motors based on the line-to-line back-EMF without position sensor

This paper presents a position sensorless control strategy based on depth low-pass filter of the line-to-line back-EMF, and analyzes the cause of the high-speed motor inaccurate commutation and the relationship between the phase current and the resistance and the DC voltage drop of the device considering the large electromagnetic interference of high-power high-speed maglev brushless DC motor. An exact phase current expression in the accurate commutation case is presented then. For inaccurate commutation of high-speed magnetic levitation motor caused by high speed bandwidth, an optimal commutation signal compensation strategy based on hysteresis transition between '90-α' and '150-α' is described. The strategy determines the optimal width of the hysteresis complying with the principle of minimum current ripple before and after transition. The motor runs to a maximum of 32 000r/min smoothly through experiments. The Experimental results show that the method achieves smooth transition between the two kinds of motor commutation strategy, and compensates for the commutation error effectively.