Device Loading of a Modular Multilevel Converter in Wind Power

Modular multilevel converter (MMC) is a recently emerged multilevel topology for high-voltage high-power applications. However, in wind power applications, to the best of the authors knowledge, the performance of the MMC has not been extensively investigated. In this paper, the application of the MMC to wind energy systems is studied. The converters used to connect the wind turbine to the grid, which have rated active powers of 2MW and 10MW, are proposed and investigated. The electrical losses and thermal loading of the power devices in the proposed converter solutions are analyzed based on the gird conditions/requirements for wind power. The efficiency of the MMC under different P/Q boundaries defined by grid codes is investigated and compared with two-level (2L) and three-level (3L) neutral point clamped converters. It is concluded that it is possible to use the MMC in wind power applications, and the losses are evenly distributed between the submodules of the MMC. However, inside a submodule, the losses of the power devices are not equal, which may lead to the de-rating of the converter.