Hierarchically-Coordinated Voltage/VAR Control of Distribution Networks Using PV Inverters

Photovoltaic (PV) inverters can provide fast and flexible reactive power support for voltage regulation and power loss reduction in distribution networks. Conventionally, central and local voltage/VAR control (VVC) strategies are separately determined, lacking a cross-hierarchy coordination. This paper proposes a novel hierarchically-coordinated VVC (HC-VVC) method where central hierarchy dispatches the inverter reactive power output to minimize network power loss and local hierarchy responds to real-time voltage deviation through a linear droop controller. The proposed method simultaneously optimizes inverter reactive power output setpoints for the central dispatch and droop functions for the local control so that the two control hierarchies are optimally coordinated under stochastic PV power generation and load variations. The coordination model is solved by a scenario-based stochastic optimization approach with probabilistic uncertainty modeling where real-time variations of the uncertainties are fully addressed. Simulation results show that, compared with existing methods, the proposed HC-VVC method is overall superior in minimizing power loss and voltage deviation.