A Simple Duty Cycle Control Strategy to Reduce Torque Ripples and Improve Low Speed Performance of a Three Level Inverter Fed DTC IPMSM Drive
This paper presents a novel duty cycle based direct torque control (DDTC) strategy for a three level neutral point clamped inverter fed interior permanent magnet synchronous motor. DDTC methods proposed in the literature for three level inverter fed DTC (3L DTC) are complicated, parameter dependent, and pay little attention to inverter inherent switching constraints. In this paper, a simple yet robust duty ratio calculation method, which respects the inverter switching constraints, is proposed. Additionally, a novel switching strategy is adopted to minimize the effects of flux drooping phenomena seen in 3L DTC drives during low speed operations. The proposed 3L DTC method is efficient in reducing both torque and flux ripples while operating at low switching frequencies. Therefore, it is suitable for medium high power ac drives. Experimental results on a scaled down test rig and comparative analysis are provided to validate the effectiveness of the proposed strategy.
IEEE Transactions on Industrial Electronics