Flux-weakening operation of open-end winding drive integrating a cost-effective high-power charger

In this study, a three-phase drive with a six-leg voltage source inverter and an open-end winding interior permanent magnet synchronous machine designed for traction of an electric vehicle is studied in a flux-weakening operation. The topology allows the functionality of a high-power charger to be obtained, without adding any other supplementary power devices. On the other hand, since there are three independent currents, the control structure has to handle not only the two dq-current components but also a zero-sequence current. If neglected, in comparison with a wye-coupled three-phase drive, this zero-sequence component can cause a higher maximum peak value of the phase currents, additional stator Joule losses, torque ripple, inverter voltage saturation and insulated gate bipolar transistor (IGBT) oversizing. The proposed control strategy consists in adapting a conventional method used for wye-connected machines particularly in flux-weakening operation. This strategy allows the closed-loop control of the zero-sequence current to be maintained in the whole speed range and therefore inverter saturation is avoided. Simulations and experimental results are presented and analysed.