Low-voltage ride-through capability of DFIG-based WECS improved by nonlinear backstepping controller synthesized in novel power state model

Abstract

This paper addresses the critical challenge of improving the low-voltage ride-through (LVRT) capability of doubly-fed induction generators (DFIGs) in grid-connected wind energy conversion systems (WECS) during grid faults. The main contribution of this work is the development of a novel control strategy: the Nonlinear Backstepping Controller based on a New State Model in Power Terms (NBC_NSMPT). Unlike conventional control approaches, NBC_NSMPT integrates DC-Link voltage dynamics with active and reactive power behavior throughout the conversion chain, aiming to enhance system stability and fault response. The controller's primary objective is to provide reactive power support at the grid connection point (GCP) during faults while ensuring the overall stability of the DFIG-based WECS. To validate the proposed method, Lyapunov-based stability functions are utilized to ensure that system stability criteria are met, with a focus on the negative definiteness of the Lyapunov function (LF) derivatives. The controller's performance is evaluated through simulations under severe three-phase short-circuit faults (3-PSCF) and varying wind speed (VWS) conditions. A comparative analysis with sliding mode control (SMC) and proportional-integral correctors (PIC) using auxiliary devices demonstrates the superior performance of NBC_NSMPT in terms of reactive power injection, voltage sag mitigation, and DC-Link overvoltage control. Specifically, the NBC_NSMPT injects up to 0.49 pu of reactive power, outperforming the SMC (0.26 pu) and PIC (≈ 0.25 pu) with auxiliary devices, while successfully limiting rotor and stator current peaks to 1.65 pu and 1.66 pu, respectively, and maintaining a stable DC-Link voltage at 1.225 kV. These findings underscore the effectiveness of NBC_NSMPT in enhancing the LVRT capacity and overall stability of DFIG-based WECS under challenging grid conditions.