Asymmetrical hybrid unidirectional T-type rectifier for high-speed gen-set applications

The paper deals with a high efficiency boost rectifier for high rotational speed Gen-Set applications. It is tailored around a permanent magnet synchronous generator (PMSG) featuring an open end winding configuration. According to such a configuration the generator stator windings are connected on one side to a three level T-type unidirectional rectifier, and on the other side, to an auxiliary two-level inverter. The multilevel rectifier is operated at the fundamental frequency, while, the two-level inverter is driven by a standard sine PWM technique, in order to suitably shape the currents produced by the electric generator. The entire system is equivalent to a six-level multilevel converter. As the main stream power is handled by the multilevel rectifier operating at low switching frequency, a higher efficiency is achieved compared to a similar multilevel rectifier driven through a PWM technique, even considering extra losses due to the auxiliary inverter. The last can be supplied through an active source or a floating capacitor, and plays a key role in balancing the voltage across the DC Bus capacitors of the T-type rectifier, making unnecessary additional circuits. Suitable control solutions have been implemented considering either an active source, either a floating capacitor. Simulation results confirm the effectiveness of the proposed configuration.