Comparison between Modifications of SFOC and DPC in Control of Grid-Connected Doubly Fed Induction Generator under Unbalanced Voltage Dip

This paper presents both the previously and newly modified Stator Flux Oriented Control (SFOC) and Direct Power Control (DPC) 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 newly proposed SFOC-based scheme, which emphasizes on improvement of generator's torque performance, PI controllers with anti-windup, Notch filters and the Sequence Component Controller (SCC) 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 DPC-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.