Open-End Winding Multilevel Unidirectional Six-Phase Rectifier With Reduced Switch Count

In this paper, a new unidirectional multilevel six-phase power rectifier topology, which may be applied to wind energy conversions systems (WECS), is proposed and investigated. Such topology is composed by two three-level neutral-point-clamped (NPC) converters connected to the open-end windings (OEW) of a six-phase permanent magnet synchronous generator (PMSG), a non-controlled three-phase converter and three isolated DC-links. The use of a non-controlled converter with diodes makes the system non-reversible. It aims to reduce the controlled switch count, the system complexity and the costs. The system model, operating principles, a space vector pulse width modulation (SV-PWM) strategy and a control system to ensure the elimination of the zero-crossover distortion caused by the use of the diodes are presented. The SV-PWM technique, implementated by means of equivalent level-shifted PWM (LS-PWM), generates multilevel voltage waveforms with reduced harmonic distortion. Due to the high number of levels generated, the system is suitable for high power applications with voltage and current ratings restrictions. A study concerning harmonic distortion, semiconductor losses and the common-mode voltage (CMV) investigation is carried out. The performance of the system is compared with a standard configuration. The feasibilty of the system is demonstrated by simulation and experimental results.