Neutral-Point Potential Balancing of Three-Level Inverters in Direct-Driven Wind Energy Conversion System

With the increase of wind energy conversion system (WECS) capacity, conventional two-level voltage source converters tend to be replaced gradually by multilevel neutral-point (NP)-clamped converters. In this study, the topology of a boost three-level (TL) chopper on the front of a TL diode-clamped inverter is used for direct-driven WECSs. The switch-signal phase delay control (SSPDC) is proposed for NP potential balancing of TL inverter based on the characteristics of boost TL chopper. As the boost chopper is also used for maximum power point tracking, the controller with dual PI regulators is designed for the chopper. Parameters of the two PI regulators are determined according to the state space averaging model of the boost TL chopper using SSPDC. In addition, the proposed NP balancing method is compared with two methods based on redundant vector selection. The validity of the proposed method is verified by analysis and simulation results.