Multi-Objective Volt/Var Control of Virtual Power Plant for Mitigating Voltage Unbalance

Increasing photovoltaic (PV) installation and power generation cause heavy unbalanced bus voltages in three-phase distribution networks, impairing power quality for three-phase loads. Meanwhile, a virtual power plant (VPP) can aggregate PVs and control their smart inverters to provide Volt/Var control (VVC) functionality. This paper firstly proposes a new voltage unbalance approximation index (VUAI) which is compatible with an efficient branch flow model for three-phase distribution networks. Then, this paper develops a multi-objective VVC method of VPP minimizing the VUAI and network power loss simultaneously under uncertainties of PV power generation and loads. Utilizing second-order conic relaxation and a multi-objective programming method, the proposed VVC optimization problem is efficiently solved to obtain the Pareto front. Numerical simulations on the IEEE 123-bus system with highly penetrated PVs validate the effectiveness of the VUAI and the high performance of the proposed VVC method in mitigating voltage unbalance in three-phase distribution networks.