Enhancement of LVRT Capability of DFIG Wind Turbine by Using Advanced Control Strategy

In this paper, doubly fed induction generator (DFIG) based wind turbine (WT) low voltage ride through (LVRT) capability is enhanced by using advanced control strategy for the rotor side converter (RSC) and grid side converter (GSC) to meet grid code requirements. The conventional crowbar with constant resistance method is used to protect and improve the LVRT. However, its response varies accordingly to the voltage dip level. In addition conventional method may be over or under estimate fault in certain condition which results in damage to the converters and DFIG. The proposed advanced control strategy introduces the instantaneous DC link current of the RSC as compensating term on GSC control scheme to smooth the DC link voltage fluctuations during the grid at the point of common coupling (PCC). By using pitch control, the wind energy is captured as rotor inertia during faults which significantly reduce the oscillations in the stator and rotor currents and the DC bus voltage during fault, the remaining energy is available to the grid after fault clearance and also it ensures smooth release of the excessive inertia energy into the grid. A time domain model for the 1.5 MW DFIG test system with the decoupled dq controller is implemented using MATLAB/SIMULINK and its effectiveness has been demonstrated through various simulation cases. The proposed control strategy results compared with conventional crowbar method shows not only the enhancement of LVRT capability of DFIG, but also helps maintaining continuous active and reactive power control during the grid fault.