Application of Active NPC Converter on Generator Side for MW Direct-driven Wind Turbine

3L-NPC topology is usually used in MW wind turbine (WT) systems with full-scale converter configuration. However, due to its drawback of unequal device loss distribution, the converter rated power, and thus the WT unit capacity is limited. Moreover, in cased of device failure in generator converter, in order to protect the WT system, the converter has to shut down to disconnect the WT. This paper presents the application of active NPC (ANPC) converter on generator side. Loss-balancing schemes are discussed, and thermal performance of NPC and ANPC generator converters are compared. Also, the control scheme of generator converter under single device failure condition is proposed to maintain the WT in service and continue to provide real power, which brings benefits in the reliable and economic aspects to the WT system. Simulation results are provided to validate the proposed control methods.