Analysis of Power Loss and Reliability on Hybrid Modular Multilevel Converter With Redundancy Configuration for Offshore Wind Turbines

With the rise of power capability and voltage class in offshore wind turbines, modular multilevel converters (MMCs) have become a promising candidate for offshore wind energy conversion systems. The hybrid MMC consisting of full-bridge submodules (SMs) and half-bridge SMs is able to handle dc faults but lower in efficiency and reliability, which need to be improved for offshore wind turbines. Active redundancy configurations are suitable for medium-voltage MMC to increase reliability at the expense of efficiency. This paper presents quantified analysis of power loss and reliability on MMC with different active redundancy configurations, taking 10 MW, 10 kV for example. Firstly, considering active redundancy, the numerical approach to power loss is derived based on the operation modes of hybrid MMC as a rectifier, and the impact of hybrid redundant SMs in full wind speed range is analyzed. Then, the reliability model of MMC considering redundancy configuration is established and the impact is assessed. Finally, analysis of power loss and reliability on hybrid MMC with different redundant SMs is obtained based on engineering parameters, and effectiveness of the proposed assessment method is verified through Matlab.