Reactive Power Control of Doubly Fed Induction Generator during Grid Voltage Dips

The increasing wind power penetration brings big challenge for wind turbine to provide Low Voltage Ride-Through (LVRT) capability. Current grid codes require that wind turbine should support the grid voltage by the reactive power control. Doubly Fed Induction Generation (DFIG) system commonly uses rotor crowbar to protect the vulnerable power converter during grid voltage dips. Its unavoidable drawback is that the stator would absorb reactive power from the grid. This paper analyzes the reactive power capacities of grid side converter (GSC) and rotor side converter (RSC). Then a method is proposed to calculate the amount of stator reactive power when the rotor crowbar is active. To avoid this inductive reactive power consumption, two measures are implemented: (i) a proper dc-chopper is designed to reduce the active probability of crowbar; (ii) GSC compensates the reactive current for the stator. The paper presents the principle of choosing the dc-chopper resistor value and the reactive power priority control strategy of GSC. Simulation results validate the feasibility of the proposed design and control strategy. And the compared reactive power performances indicate the importance of the dc-chopper.