Parabola‐trapezoid and staircase current supply methods for PMBLM with full inverter utility and reduced torque ripple

Abstract

The permanent magnet brushless motors (PMBLM) are utilised extensively in many high-performance applications where smoothness of output torque is necessary. When driven with conventional square-wave current, the PMBLM is hard to make full use of inverter capacity because of short current supply time. Besides, it is hard to produce smooth output torque because the phase inductances slow down the desired step response of the phase current seriously. Although the sinusoidal-wave current changes continuously, there exists a fixed-frequency torque ripple for trapezoid back-electromotive force motor. To solve the problems, two novel current supply methods, called as staircase waveform and parabola-trapezoid waveform, are proposed in this study. With the same phase current magnitude as square waveform, the staircase waveform can output two times torque with low-resolution position sensors. The parabola-trapezoid supply method can further improve the smoothness of doubled output torque by unique parabolic rising and falling edge waveform design, while a high-resolution position sensor is needed. Simulation and experimental tests of four different current supply methods are given to corroborate the effectiveness of the proposed method in inverter utility and torque ripple reduction.