Lessening zero sequence effects in dynamic voltage restorers

This paper puts forward an analysis of the effects of zero sequence components on power devices in particularly on the dynamic voltage restorer (DVR) and gives simulation results. It is shown that four-wire DVR do better then the traditional three-wire DVR, unbalance voltage and zero sequence components can be lessened by four-wire DVR effectively, because it provides zero sequence current circuit. However, the interaction between DC-side and AC-side in this topology leads to an unbalance in the DC-link capacitor voltages and it causes zero sequence resonance especially when the DVR is under open loop control. But the closed loop control can provide additional damping to mitigate possible harmonic resonance. In this study, the DVR system is simulated by using PSCAD software. Simulation results are presented to verify the theoretical analysis.