A New Nine-Level Active NPC (ANPC) Converter for Grid Connection of Large Wind Turbines for Distributed Generation

Wind power is one of the most promising emerging renewable energy technologies for distributed generation (DG). In this paper, a new nine-level active neutral-point-clamped (9L ANPC) converter is proposed for the grid connection of large wind turbines (WTs) to improve the waveform quality of the converter output voltage and current. Therefore, the bulky passive grid filters can be reduced or even removed. The topology, operating principles, control schemes, and main features, as well as semiconductor device selection of the proposed converter are presented in detail. The floating capacitor voltage control based on redundant switching states and capacitor prioritization is detailed. A comparison between the new topology and other existing 9L topologies is presented to illustrate the characteristics and performance of the new converter. The proposed 9L ANPC converter is studied in the case of the grid connection of a 6-MW WT without using passive grid filters in DG systems. Simulation and experiment results are presented to validate the proposed converter topology and control schemes. The proper operation and the compliance to the harmonic limit standards of the filterless grid-connected WT system are verified by simulation results.