Harmonic impact of multiple electric vehicle chargers on low-voltage distribution networks

How many electric vehicle chargers can a residential street accommodate before power quality becomes problematic? This increasingly urgent question confronts distribution network operators across the United Kingdom as EV adoption accelerates toward the 2035 petrol and diesel vehicle sales ban. The present investigation quantified harmonic distortion impacts from multiple residential EV chargers operating simultaneously on low-voltage distribution networks through field monitoring, laboratory characterization, and network simulation conducted at the Bristol Institute of Power Systems between November 2023 and September 2024. Field measurements captured power quality parameters on four residential distribution feeders serving 72 households with EV charger penetration ranging from 15% to 45%. Laboratory testing characterized harmonic emission profiles of prevalent 7kW and 22kW charger models under varying charging conditions. Network simulation using validated models projected impacts at higher penetration levels and evaluated mitigation strategies including passive filtering and smart charging coordination. Results demonstrated that voltage total harmonic distortion increased from 2.8% baseline to 8.5% at 45% charger penetration during evening peak periods, approaching but not exceeding the 8% limit specified in Engineering Recommendation G5/5. Third and fifth harmonics dominated the distortion spectrum, with individual harmonic voltages remaining within planning limits. Current THD in feeder cables reached 28% at highest penetration levels, while neutral conductor currents increased by 340% due to triplen harmonic accumulation. Simulation analysis identified 55% penetration as the threshold where voltage THD would exceed statutory limits under uncontrolled charging scenarios. Smart charging strategies coordinating charging start times reduced peak harmonic levels by 35-42%, potentially enabling penetration levels up to 70% without network reinforcement. The findings inform distribution network planning for the anticipated EV charging infrastructure expansion across UK residential areas.