Nonlinear Adaptive Direct Power Controllers of DFIG-Based Wind Farms for Enhancing FRT Capabilities

Abstract

In this paper, a nonlinear adaptive direct power control scheme is proposed for doubly fed induction generator (DFIG)-based wind farms to enhance fault ride through (FRT) capabilities. Both rotor- and grid-side converters (i.e., RSCs and GSCs) are controlled through the proposed direct power control scheme where RSCs are controlled to ensure the desired DC-link voltage and GSCs are controlled for injecting desired reactive power during grid faults. Hence, the proposed adaptive direct power controller (ADPC) appropriately injects the reactive power for ensuring FRT operations. The proposed scheme is employed by transforming the dynamics of RSCs, GSCs, and DC-link voltage as active and reactive power. The parameters of filters in both RSCs and GSCs along the DC-link capacitor are considered as completely unknown while adaptation laws are used to estimate these parameters. The parameter adaptation laws and switching control signals for ADPCs are determined in such a way that the overall stability of wind farms is preserved. The stability of the DFIG-based wind farm with the proposed ADPC is analyzed through the Lyapunov stability theory and simulations are performed on a single 9 MW wind farm to validate its effectiveness. Simulation results demonstrate that the proposed scheme ensures the FRT operation of wind farms in a better way as compared to the direct power control-based sliding mode controller (DPC-SMC).