A Constant Frequency Based Torque Ripple Free Three level NPC Brushless Motor Drive

The Brushless DC motor with trapezoidal back EMF enables them to be smaller, lighter, and more robust in design. Multilevel inverter-based drives have become crucial for medium and high-power applications of Brushless DC motor drives. However, a Brushless DC(BLDC) motor suffers from the severe drawback of commutation torque ripples, mainly due to the inductive nature of the stator. Nevertheless, with a three-level inverter to a BLDC motor, a significant torque ripple reduction can be observed compared to a conventional two-level BLDC drive. In addition, the good dynamic performance of hysteresis controllers makes them reliable for the current control. However, the major demerit is that it gives a variable switching frequency and asymmetrical switching pulses, which could amplify the torque ripples. An interleaving constant switching frequency-based current controller is proposed in this work, which divides the error into multiple bands. The error is compared to an interleaving carrier frequency-based comparator to produce the switching signal for the given reference torque. The proposed controller remarkably improves the performance of the BLOC drive in the low-speed region, and a significant reduction in torque ripple is obtained. The proposed method is implemented on the MATLAB Simulink platform, and the effectiveness is validated by the results presented.