A UPFC with reduced DC bus capacitance for LV distribution networks with high PV penetrations

A low voltage (LV) distribution level unified power flow controller (UPFC) is shown capable of regulating the positive sequence voltage with a network while simultaneously correcting phase unbalance voltages that can be produced by high levels of distributed photovoltaic (PV) generation. Instantaneous reactive power theory shows that DC-bus capacitor power will fluctuate at twice mains frequency during any unbalanced operation. Instantaneous power balance can be maintained by allowing the input converter to draw a small negative sequence current. This allows a hundred-fold reduction in the value of the DC bus capacitance allowing long life ceramic or polypropylene capacitors to replace electrolytic capacitors in this application.