A UPFC Topology for LV Feeder Voltage Regulation and Current Balance in High PV Penetration Applications

The integration of large scale photovoltaic (PV) generation causes several power quality issues in low voltage (LV) distribution networks. Among them, network voltage profile variation and voltage unbalance are the two severe issues that affect the normal operation of distribution feeders and restrict the further expansion of PV units. The unified power flow controller (UPFC) is generally used in transmission and sub-transmission to provide power balance for series and shunt compensation, however, their use in distribution networks for voltage management is rare. The paper proposes a four leg (4L) UPFC-like topology with a small dc-link capacitor as a regulatory device to mitigate voltage issues in LV distribution networks. Instantaneous power theory (IPT) is applied to analyze the proposed 4L-UPFC for LV distribution networks. Real and instantaneous power balance of the UPFC is achieved by controlling the input positive and negative sequence current of the shunt converter. Detailed analysis and simulation studies are conducted to show the operation of the 4L-UPFC with a small dc-link capacitor within Australian LV distribution networks. The simulation results show that the UPFC can regulate the sequence voltages to maintain the far end load voltages within the allowable voltage boundaries under high PV penetrations. The results also show that the shunt converter can zero sequence compensation at the input side of the LV feeder.