Three-Stage Hierarchically-Coordinated Voltage/Var Control Based on PV Inverters Considering Distribution Network Voltage Stability

Intermittent photovoltaic (PV) power generation brings voltage fluctuation and stability issues to distribution networks. Meanwhile, PV inverters can support voltage/Var control (VVC) to address these issues. Utilizing PV inverters, this paper proposes a three-stage hierarchically-coordinated (TSHC-) VVC method considering network voltage stability. The first stage schedules on-load tap changers one day ahead, the second stage hourly dispatches reactive power outputs of inverters, and the third stage implements real-time local voltage droop control of inverters. To efficiently address mutual impacts between these stages, the first two central-hierarchy stages are coordinated through interval optimization. Meanwhile, the last two stages are hierarchically coordinated by simultaneously optimizing inverter base reactive power outputs and droop control functions under real-time uncertainty. In the previous work, local droop control functions are not fully optimized, and network voltage stability is not fully considered. To overcome such limitations, this paper develops new constraints of individual control gain for each inverter, taking voltage stability into account. The proposed TSHC-VVC method with the optimized control gains is tested and compared with existing methods. Simulation results verify its better performance in reducing network power losses and bus voltage deviations, as well as maintaining network voltage stability.