Modelling and control of a multi-phase permanent magnet synchronous generator and efficient hybrid 3L-converters for large direct-drive wind turbines

A novel full-size wind power conversion system based on a multiphase permanent magnet synchronous generator (MPPMSG) and hybrid multi-converter system using 3-level neutral-point-clamp converters (3L-NPC) for high-power direct-drive wind turbines is proposed in this study. Higher efficiency, lower harmonics is achieved by replacing the traditional 2-level converter cells with 3-level cells. Circulating current is eliminated by using hybrid connection for multiphase generator design to replace the commonly used parallel converter structure for 3-phase generator design, the issues for neutral-point voltage imbalance is also eliminated. The mathematical model of MPPMSG and variable-speed control strategy are built and verified in PSCAD/EMTDC. A 3.5 kVA MPPMSG prototype machine and a set of hybrid 3L multi-converter systems are built. The experimental results validate the model and the effectiveness of the control strategies.