A reverse current tracking based LVRT strategy for doubly fed induction generator (DFIG)

Abstract

This paper proposed an improved control strategy for doubly fed induction generator (DFIG) to enhance its low voltage ride-through (LVRT) capability. Under serious grid faults, the rotor side induced electromotive force (EMF) would exceed the maximum output voltage of the rotor side converter (RSC), leading to over-currents and runaway of DFIG and RSC. To address this issue, a LVRT control strategy based on reverse current tracking is proposed. According to the restriction that the vector sum of the stator and rotor current equals to the excitation current corresponding to the stator flux, the rotor current is controlled to proportionally track the stator current in the opposite direction. Thus, the rotor current is limited in a certain range with restricted RSC output voltage. In comparison to the demagnetization control or the flux linkage tracking control, the proposed strategy no longer relies on the estimation of flux linkage or its sequence component separation, so it is simple to implement. Based on Matlab/Simulink, a typical 1.5 MW DFIG is simulated with the proposed strategy. The results demonstrated that fault currents can be effectively suppressed with little torque oscillation under serious grid faults.