Closed-Loop Direct Power Control of Brushless DC Motor in Field Weakening Region

An innovative control method for reducing the torque ripple of non-sinusoidal brushless DC motors in field weakening region based on direct power control is proposed here. Torque ripple, due to the disproportionate stator current and its non-sinusoidal back-EMF voltage, is one of the known drawbacks of brushless DC motor drives. Upon motor speed acceleration, the waveform of the stator current becomes distorted, which in turn intensifies the torque ripple. This proposed method is able to control the motor speed from zero to values higher than the base speed range. The realization of the proposed method in the stationary reference-frame makes the method implementation simple and robust. In addition to controlling motor speed, by applying a three-phase conducting method instead of the conventional two-phase conducting method and control of instantaneous input power into the rotor in the proposed method, the torque ripple is also reduced, simultaneously. The torque ripple reduction and robustness of the proposed method are compared with the phase advance angle (PAA) method through simulation and experimental. The results indicate the superiority of the proposed method in both the steady- and transient-states. Moreover, the implementation of the proposed method on a prototype BLDC drive is successfully evaluated.