Improved Virtual Inductance Based Control Strategy of DFIG under Weak Grid Condition

Equivalent input admittance model of DFIG wind turbine is built in synchronous reference frame. DFIG electromagnetic transient, PLL dynamics and rotor side controllers including power control and current control are considered in this model. The influence of rotor inductance on stability of DFIG wind turbine connected with weak grid is investigated based on generalized Nyquist criterion (GNC) which proves that the incensement of rotor inductance has a positive impact on system stability. Phase lock loop (PLL) is a critical component in the system, which may propagate the grid voltage perturbations to the control system and has an adverse impact on stability of DFIG wind turbine. Compared with conventional virtual inductance based control strategy, the improved control strategy proposed in this paper take the influence of PLL dynamics into consideration and can improve the system stability efficiently under weak grid condition. The validity of the improved control strategy is verified by theoretical analysis and simulation.