Probabilistic Assessment of Voltage Unbalance Caused by Single-phase Electric Vehicles

The number of electric vehicles (EVs) connected to the distribution system is growing significantly worldwide. Since the majority of EVs are single-phase connected, there is a concern that voltage unbalance levels may increase in areas with high penetration of EVs. This paper uses a realistic UK network model and electric vehicle charging profiles to perform a probabilistic assessment of the impact of electric vehicles on voltage unbalance in distribution systems. To reduce the simulation time, a current-source based model is used, in combination with real charging data. The results show that for EV penetration levels equal to 60 %, voltage unbalance limits are exceeded at some busbars. For higher penetration levels, voltage unbalance does not change significantly. A mitigation strategy is then deployed, employing three single-phase batteries to equalize current flow in the three phases. This solution is most effective in reducing voltage unbalance at the busbar where the batteries are connected, with reduced impact when the electrical distance increases.