Unbalance and non-linear stator voltage control of a grid connected DFIG based WECS using NSC

This paper presents a selective harmonic feedback control strategy with nine switch converter (NSC) instead of using separate PGSC and SGSC to improve the controlled operation of a grid connected doubly fed induction generator (DFIG) based wind energy conversion system (WECS) and also provide voltage harmonic compensation under unbalance non-linear load at PCC. The Nine switch converter having two sets of independent three phase output terminals, one set of three phase output terminal of nine switch converter is connected to the injection transformer winding to inject the voltage in series with the stator terminals during unbalance non-linear load and other set of three phase output terminal is connected to the grid through interfacing inductors to regulate the dc-link voltage to its reference value irrespective of direction of rotor power flow. Simulation has been carried out in MATLAB/Simulink environment and the results have been analyzed. Results show that by injecting required series voltage generated from the NSC to maintain the desired stator voltage, the undesirable effects of unbalance and harmonic non-linearity of grid-voltage at PCC upon the DFIG due to unbalance non-linear load can be removed. In addition the proposed NSC also reduces the number of switching devices thereby minimizing the cost of the system.