Coordinated Charging of Spatially Distributed Electric Vehicles for Mitigating Voltage Rise and Voltage Unbalance in Modern Distribution Networks

Abstract

This paper proposes a decentralised control strategy using droop-based control to vary the charging rates of electric vehicles (EVs) in real-time in response to nodal voltages, voltage unbalance and the state-of-charge (SOC). This strategy developed aims to mitigate excessive voltage rise caused by rooftop solar photovoltaic (PV) systems and voltage unbalance caused by unbalanced loads in a low-voltage (LV) distribution network. This will also smooth the voltage profile through peak reduction and valley filling by EV charging during times of low load, high generation and performing vehicle-to-grid operations during times of high load, low generation. Reference voltages are calculated and used to coordinate the control of the EV chargers by assigning each a target voltage based on their location and local conditions without the use for any common communication channel or a centralised controller. The local voltage, phase unbalance and current EV SOC are used to determine a suitable charging rate for the vehicle. A modified IEEE 13 node test feeder inclusive of an LV network based on a semi-rural Australian town was used to assess the impacts of PV and EV charging in the network and validate the proposed strategy as a means to reduce voltage rise and voltage unbalance in the network. Simulations were performed using OpenDSS and MATLAB in four scenarios, with and without charging control, to verify the effectiveness of the proposed strategy.