Power-dependent efficiency model of EV chargers for distribution grid simulations

Abstract

The growing adoption of Electric Vehicles (EVs) and their integration into electrical distribution grids present various challenges. Among others, the efficiency of bidirectional chargers is critical for accurate energy demand forecasting and charging schedule optimisation. This study adapts a mathematical efficiency model, originally developed for photovoltaic inverters, for application to bidirectional EV chargers and incorporates the charging operation into a distribution grid simulation. To account for the power-dependent efficiency of chargers under diverse charging conditions, an approximation based on a step-function is employed. Simulation results indicate that incorporating variable charger efficiency leads to a moderate increase in total EV energy demand (9.4 %) and a minor increase in transformer loading during charging events (0.4 %), while the impact on line loading remains negligible in the considered scenario. The developed variable efficiency model provides a foundation for future research in larger networks with higher EV penetration levels also incorporating functionalities such as Vehicle-to-Grid.