A LVRT Control Strategy for Grid-side Converter in DFIG Based on Sliding Mode Control

Grid voltage dips will induce power imbalance on both sides of the DC-link capacitor in the doubly fed induction generators (DFIG). Therefore, it will result in the fluctuation of DC-link voltage or over-voltage, which seriously affects security operation of the DFIG. According to the mathematical models of the grid-side converter (GSC) and the DC-link capacitor, a control strategy based on sliding mode control (SMC) for the GSC is proposed in this paper. In order to improve the response ability and to simplify the design of the controllers, single voltage (power) control loop is adopted instead of cascaded current and voltage (power) control loops. According to power flow characteristics of DC-link capacitor and GSC when the voltage dip occurs, an improved control strategy by considering the power fluctuation in the reactor of the GSC is proposed to suppress the fluctuation of the DC-link voltage. Simulation results show that the proposed control strategies not only have good dynamic response, but also can effectively suppress the DC-link voltage fluctuation during voltage dips, which improves the uninterrupted operation ability of the DFIG.