Dynamic interactions between distribution network voltage regulators for large and distributed PV plants

This paper summarizes the initial investigation of dynamic interactions of voltage regulating equipment when allowed to act together with one or more large voltage-controlled solar photovoltaic (PV) generation plants. The study results are based on an existing large PV plant and distribution circuit in the service area of a major electric utility. The existing feeder does not have any voltage regulating equipment and the PV plant is not allowed to control voltage, hence injects real power only. However, in light of the growing interest in allowing PV plants to control voltage, several scenarios are considered by allowing PV plants to control the voltage at the Point of Common Coupling (PCC) along with the traditional voltage regulators. Further case studies are performed by distributing the large PV plant into six PV plants of equal power rating connected at different feeder locations. This configuration has been investigated to determine possible differences in interactions of voltage regulators between a large plant and distributed plants. The voltage regulating equipment considered are On-Load Tap-Changing Transformers (OLTC), Switched Capacitor Banks (SCB) and also PV plant inverters capable of controlling the voltage at the PCC. The 12.6 MW (peak a.c.) PV plant and its controls, the regulating equipment, and the distribution network are modeled using a Real Time Digital Simulator (RTDS). Initial study suggests that allowing PV plants to actively participate in the voltage control process requires a coordinated control to minimize the number of operations of traditional voltage regulators.