Unbalanced fault analysis of doubly fed induction generator drive system for wind turbine applications

This paper presents detailed analysis of the doubly fed induction generator (DFIG), converters and step-up transformer under normal and fault conditions for wind turbine applications. 2.5 MW DFIG is modeled through finite element analysis in Ansoft-Maxwell, and the simulation is coupled to Ansoft-Simplorer and Matlab-Simulink for the drive circuit and controller implementation. Single phase to ground short circuit which has the highest probability to occur in the grid is tested through coupled simulators. The effect of short circuit stator current on the rotor currents are analyzed for rotor side converter protection. The FFT analysis of the stator and rotor fluxes in simulation during fault conditions are carried to be able to develop advanced control techniques in eliminating the harmonics and protecting the overall drive system. Experimental 7.5 HP DFIG test system has been developed to verify the simulation results. The FFT analysis of stator fluxes under fault condition from experimental results agrees well with the simulation results.