Improved Control of Grid Connected DFIG Wind Turbine Under LVRT Conditions Using Full and Partial Compensation Methods

For the grid connected doubly fed induction generator (DFIG) based wind turbine, over current flows through the DFIG rotor circuit during grid faults due to stator transient and negative sequence flux. For better control of DFIG, this paper introduces both full and partial series compensation methods that ensures complete safety for the DFIG and also prevents the isolation of DFIG from the grid during grid voltage disturbances. In this method, a cascaded H-bridge 5-level three phase inverter is used which converts the dc voltage from battery energy storage system into three phase ac voltage. The ac voltage is injected in series with the grid through a series injection transformer during grid faults and hence mitigates the effect of voltage sag on the DFIG.