Coordination of Transformer On-Load Tap Changer and PV Smart Inverters for Voltage Control of Distribution Feeders

To enhance the outage quality of a distribution system with a high penetration of photovoltaic (PV) renewable energy, this paper proposes a coordinating control strategy for an on-load tap changer (OLTC) of the main transformer in a distribution substation and PV smart inverters. The voltages at the end points of all distribution feeders that are served by the main transformer and the power generation of each PV system are collected using a SCADA system. The hourly tap position of the OLTC is then derived from the daily profiles of feeder voltage and the injected power that is generated by all PV systems along the feeder. Thereafter, the PV smart inverters perform autonomous control of reactive power compensation so that the voltage at the point of common coupling can be fixed at the specified voltage level. To demonstrate the effectiveness of the proposed voltage-control strategy, a main transformer, which serves six feeders of the Taiwan Power Company(Taipower) with high PV penetration, was considered in a case study. The proposed coordinating control of the OLTC and PV smart inverters dramatically improved the voltage quality of the distribution feeder and enabled the effective mitigation of the impact of large PV integration in the distribution system.