Improved Direct Torque Control for Open-Winding PMSM System Considering Zero-Sequence Current Suppression With Low Switching Frequency

This article proposes an improved direct torque control strategy for open-winding permanent magnet synchronous motor (OW-PMSM) with common dc bus for zero-sequence current (ZSC) suppression. The proposed strategy builds a novel voltage vectors (VVs) look-up table, which keeps the simple control structure of the conventional DTC (C-DTC) and effectively suppresses the ZSC. In each control period, two VVs are selected. One is selected based on torque and flux control mode in the C-DTC strategy with two switching phases conducting for the whole control period; the other is selected to produce a suitable zero-sequence voltage based on the ZSC control with an additional third switching phase conducting for a short period of time. Since the duty cycle generation controller only adjusts the conducting time of one switching phase and the duration time of VV for the torque and flux control is not affected, the proposed strategy has low switching frequency and wide modulation range. Experimental results validate that the proposed strategy has a favorable control performance.