Improved dynamic voltage restorer with reduced capacity of power inverter and energy storage for voltage sag mitigation

As one of the most representative series active compensators, dynamic voltage restorer (DVR) can solve voltage-related power quality uses effectively. The in-phase voltage control and energy-optimised control are the two typical control strategies of DVR. However, the in-phase voltage control results in a large amount of active power exchange between the main grid and the dc link of DVR, and hence high capacity of storage system is needed in the dc link while the energy-optimised strategy requires high injected voltage, resulting in oversizing of the DVR inverter. Thus, in order to avoid the aforementioned drawbacks, this study proposes a modified DVR, which connects an external capacitor in series with the LC filter (LCC) of DVR (LCC-DVR). Based on the operational principles of the LCC-DVR, an updated procedure of reference voltage is proposed to avoid overmodulation of DVR caused by load variations, ensuring the continuous operation capability of the LCC-DVR. The overall control scheme of the LCC-DVR and the comparative analysis among the proposed strategy and traditional strategies are also presented. The effectiveness of the proposed topology and method is clearly validated by the simulation and experimental results.