Torque Quality Improvement of an Open-End Winding PMSM

This paper proposes a new closed-loop control strategy which improves the quality of the torque output of an open-end winding (OEW) permanent magnet synchronous motor (PMSM) with common DC bus. Such a configuration provides a path for the zero sequence currents (ZSC) to flow in the windings. The analysis of the system revealed that these currents result in electromagnetic torque oscillation. It has also been established that the zero sequence currents are caused mainly by the third harmonic component of the back electromotive force (EMF). The research and a thorough analysis of the OEW PMSM showed that the existing methods of minimising the torque ripple cannot be applied when the leakage inductance of a machine is small, because the zero sequence component can no longer be considered as one additional degree of freedom that can be managed. Therefore, a new control strategy presented in this paper was proposed. The strategy is validated in simulation.