Impact Assessment and Mitigation of Electric Vehicle Smart Charging Harmonics

Abstract

Smart charging of electric vehicles (EVs) offers significant opportunities for grid operators and EV users, including deferring costly network reinforcements and reducing charging costs. However, reduced charging rates inherently introduce higher harmonic content, posing a serious risk to distribution transformers in heavily loaded networks and elevating total harmonic distortion (THD) levels in mildly loaded ones. This paper leverages harmonic profiles from eight EV models to quantify the impact of large-scale EV charging on both heavily and mildly loaded distribution systems. For heavily loaded networks, a Monte Carlo-based framework is developed to evaluate transformer aging under various charging current scenarios, and a rule-based harmonics-averse EV charging management strategy is proposed for peak demands. For mildly loaded networks, a harmonics-aware smart charging scheme is introduced to ensure THD remains within regulatory limits. The underlying optimization problem is solved using particle swarm optimization, augmented with a Water Filling algorithm to address discontinuities in infeasible charging rates (e.g., 0–1.38 kW). Numerical results demonstrate that by strategically adjusting charging rates, THD compliance can be achieved without costly network upgrades.