A modular direct-drive permanent magnet wind generator system eliminating the grid-side transformer

This paper has presented a modular converter for multi-coil direct-drive permanent magnet wind generator system. The converter modules are connected in series to achieve medium voltage output, thus eliminating the grid-side step-up transformer. The generator coils with 90 degree phase shift are rectified through power factor correction (PFC) circuit and connected in parallel to get unit power factor and stable dc-link power. The generator armature inductance is used as the AC-side PFC boost inductor, reducing the system size and cost. The required value of the inductor is derived based on the current ripple and zero-crossing distortion. The H-bridge inverters are cascaded to achieve multilevel voltage output and the vector control scheme is adopted to regulate the converter active and reactive power transferred to the grid. Simulation results with a 1.5MW wind system and experimental results with a scaled 3kW system validate the proposed topology and control method.