Coordination of transformer on-load tap changer and PV smart inverters for voltage control of distribution feeders

The increasing penetration of photovoltaic (PV) generation in distribution systems has entailed dramatic deterioration of distribution system voltage quality due to power injection by PV systems. This paper presents a coordinating control strategy of on-load tap changer (OLTC) of the main transformer in a substation and PV smart inverters to maintain good service voltage quality for the distribution network with high penetration of PV systems. The voltage level at the end-point of each distribution feeder and the power generation by each PV system are collected via a renewable management system. The hourly tap position of OLTC is then derived based on the daily profiles of feeder voltage variation and the injected power generated by all PV systems along the feeder. The PV smart inverters execute an autonomous control of reactive power compensation so that the voltage at the point of common coupling (PCC) can be fixed at the specified voltage level. A main transformer, which serves six feeders with high PV penetration in Taiwan Power Company (Taipower), was selected for this case study. With the proposed coordinating control of OLTC and PV smart inverters, the impact of service voltage quality due to the high penetration of PV systems in the distribution system can be effectively mitigated.