Optimized design of two and three level full-scale voltage source converters for multi-MW wind power plants at different voltage levels

Direct Drive Wind Generators with full-scale converters are used increasingly due to the high reliability and efficiency. These systems can also be easily adapted to changing grid quality requirements. Volume and power losses of full scale converters become large increasing the rated power and for this reason an increase of power density and efficiency is desired. For this reason, an optimization is proposed in this paper in order to find convenient converter solutions dependent on the turbine power, number of modules, and switching frequency. Analytical, volume and power loss models are derived for the main converter components. Design and scaling laws are shown, which are used to evaluate the convenience of a converter solution. The optimization shows that semiconductors with lower blocking voltages lead to benefits in terms of both, power density and efficiency. A convenient increase of the rated voltage of the converter can be obtained using multilevel converters.