Series Harmonic Voltage Cancellator for Mitigating Effect of Grid Impedance on the Stability of Microgrids

A series harmonic voltage cancellator (SHVC) that can mitigate the effect of grid impedance on the stability of microgrid having a plurality of grid-connected inverters (GCIs) is proposed. The concept is based on using a series harmonic voltage source to counteract the voltage across the grid impedance, so that the equivalent grid impedance observed by the inverters is reduced. As the SHVC handles harmonic power only, its volt-ampere (VA) rating is significantly lower than the power rating of the entire distributed generation (DG) system. It is realized by an inverter with fixed-frequency predictive control and wide bandwidth. A SHVC has been built and evaluated on a system with two GCIs. Experimental results are favourably compared with theoretical predictions.