An improved control for simultaneous sag/swell mitigation and reactive power support in a grid-connected wind farm with DVR

Commonly a Dynamic Voltage Restorer (DVR) is installed to protect a wind farm from grid side disturbances, voltage sag/swell, or for riding through low voltage or fault. This work proposes a novel technique to utilize the DVR to compensate the reactive power demand of the fixed speed wind generator apart from mitigating sag/swell in grid voltage. The voltage injected by the DVR is regulated so as to maintain a constant voltage at the generator terminals while the phase of the generator terminal voltage lags the grid voltage by a constant angle. The possibility of better utilization of DVR to compensate reactive power demand of Fixed Speed Wind Generators (FSWG) along with Fault Ride-Through (FRT), Sag/Swell mitigation is explored in this work by implementing 'Phase Angle'(PA) control in DVR. A comprehensive analysis is presented for the 'Phase Angle' control and the boundaries of operation for simultaneous reactive power supply and sag/swell mitigation are illustrated in graphical analysis. The effectiveness of the proposed 'PA' control scheme on simultaneous operation of sag/swell mitigation and reactive power compensation is verified using simulations in PSCAD/EMTDC for a 2 MW induction generator and also using laboratory tests on a 0.75 kW induction machine.