Modified controls for doubly fed induction generator under unbalanced voltage for torque stability controller

Abstract

This paper presents both the previously and newly modified Stator Flux Oriented Control (SFOC) with Pulse Width Modulation (PWM) and Hysteresis Current Controller (HCC) structures for Doubly Fed Induction Generator (DFIG) in wind turbines to improve responses of active power, reactive power and generator's torque during the grid voltage unbalance. In the proposed SFOC-based scheme, which emphasizes on improvement of generator's torque performance, PI controllers with Fuzzy logic, Notch filters and the Torque Stability Controller (TSC) are utilized. The other control techniques use single or multiple applications of PI controller with anti-windup, hybrid PI-Fuzzy controller with anti-windup and Notch filter to eliminate the second-order harmonic components. The designed system consists of a wound rotor induction generator and power-electronics converters at both rotor and grid sides. The modifications are applied to the rotor side converter (RSC). Simulations in Matlab/Simulink illustrate the enhanced stability of torque, active and reactive powers delivered by DFIG in both the SFOC-based and HCC-based schemes. Moreover, comparisons in simulation results, obtained separately from all the presented control structures, are provided to evaluate the effectiveness of the newly proposed scheme.