Direct Torque Control Based on Duty Ratio Modulation for Dual Three-Phase Open-End Winding Permanent Magnet Synchronous Motor

In this paper, direct torque control (DTC) is first introduced into the dual three-phase open-end winding permanent magnet synchronous motor (DT-OW-PMSM). Conventional direct torque control based on switching table (ST-DTC) faces challenges, including large torque ripple and significant harmonic currents. To address these problems, a novel direct torque control based on duty ratio modulation (DRM-DTC) is proposed. Firstly, the basic voltage vectors (VVs) with the maximum amplitude in the αβ plane are selected to construct the switching table to maximize speed range, and the duty ratio of the optimal VV is determined based on deadbeat torque control to minimize torque ripple. Secondly, reference harmonic voltages are obtained through different current controllers in various harmonic planes. The static error-free control of third-, fifth-, and seventh-order harmonic currents is achieved by inserting the basic and virtual VVs into the remaining duty ratio. Finally, a PWM signal generation method is proposed to facilitate implementation on digital processors while simultaneously halving and maintaining a constant switching frequency. Experimental results validate the feasibility and effectiveness of the proposed control strategy.