An Improved Modulation Strategy With Torque Ripple Suppression Method for OEW-PMSM Drives With Common DC Bus

The open-end winding permanent magnet synchronous machine drive with a common dc bus has a zero sequence loop, which inevitably generates the zero sequence current (ZSC). Due to the existence of the third harmonic flux linkage, ZSC causes zero sequence torque and augments the torque ripple. In this article, an improved modulation strategy with a torque ripple suppression method is presented. First, to reduce the computation burden, a modified alternate sub-hexagonal center pulsewidth modulation (ASHCPWM) strategy is designed. The switching duration time of two inverters can be obtained by the projection of the voltage vector on the abc coordinate frame. Second, a ZSC suppression method based on the time compensation coefficient is adopted for the modified modulation strategy, which can restrain ZSC and reduce torque ripple. Third, to further reduce torque ripple, a $q$ -axis current injection method is employed in the control scheme. Finally, three methods are presented in simulation and experiments for comparison, namely, the deadbeat predictive current control (DPCC) method with conventional ASHCPWM, the DPCC method with sample-averaged zero-sequence current elimination PWM, and the proposed DPCC method with modified ASHCPWM and $q$ -axis current injection. The results test the effectiveness of the proposed method.