Voltage, var and watt optimization for a distribution system with high PV penetration: A probabilistic study

Abstract

High penetration of rooftop photovoltaic (PV) panels in the distribution grid can affect the node voltages, and under light loading conditions, may even result in reverse power flow and localized overvoltage instances. While voltage control at the distribution grid level has been traditionally addressed using voltage and var control (VVC) techniques, with the introduction of PV resource as well as active demand, the problem needs to be reformulated as voltage, var and watt optimization (VVWO). A mixed-integer nonlinear multi-objective optimization solution has been proposed in this paper for the control of active and reactive power resources in an unbalanced distribution grid with high PV penetration. The goal of the proposed methodology is to simultaneously minimize line losses, active power curtailment of PVs, demand curtailment, and operation instances of voltage regulating transformers and shunt capacitors. Due to the stochastic nature of load and solar irradiance, at each PV penetration level the problem is solved probabilistically by using random samples for network loading levels and cloud coverage in the sky. A case study is presented using a modified version of the IEEE 123-bus test distribution feeder. Simulation results indicate that if voltages and reactive powers are optimally controlled, high PV penetration levels can be achieved at the distribution grid without any complications. It is also observed that allowing PVs to exchange reactive power with the grid can significantly affect the operation of voltage regulators and shunt capacitors.