Power Control of Direct Drive Wind Turbine with Simplified Conversion Stage & Transformerless Grid Interface

The paper presents an analysis and simulation study of the power extraction capability of a direct drive wind turbine realised using a modular permanent magnet generator connected to the 11 kV grid via a cascaded multilevel voltage source inverter (CMVSI) without an interface transformer. The DC link in each of the CMVSI modules is supplied by a pair of generator coils connected through uncontrolled bridge rectifiers. The DC link voltage is determined by the required real and reactive power output to the grid, which constrains the available speed range of the turbine, limiting the power extraction at low wind speeds