Modified controls for DFIG under unbalanced voltage dip for reduction of current harmonic using PI-F plus Resonant controller

This paper presents modified Stator Flux Oriented Control (SFOC) for Doubly Fed Induction Generator (DFIG) in wind turbines to reduce torque pulsation during unbalanced voltage dips, and current waveform is also improved with the decreasing of harmonics. The proposed schemes utilize multiple PI with Fuzzy plus Resonant controllers (PI-F+R) to obtain commanded rotor currents and also introduce extra commanded values for rotor current; as well, Notch filters and Sequence Components Controller (SCC) are used to eliminate the high order harmonic components. The resonant controller is tuned to twice the network frequency (2ωs) and designed mitigate against the power oscillations and torque pulsations in a DFIG due to network voltage unbalance conditions. The designed system consists of a wound-rotor induction generator and back-to-back power-electronic converters connected to both rotor and grid sides. Wherein, the modification is applies to the control of Rotor Side Converter (RSC). Simulations in Matlab/Simulink illustrate the improvement of current waveform. Comparisons of the simulation results with SFOC using traditional PI traditional and a previously suggested modification of SFOC using PI-F+R for operation under unbalanced voltage dip are provided to evaluate the newly proposed methods.