Analysis of the peak grid load reduction using ECO-charging strategy for e-bus fleets in Gothenburg

Charging Management is essential in minimizing the impact on the local electricity grid when e-bus fleets become widespread in a city. With the advent of high-powered ultrafast opportunity chargers, the electricity grid can quickly become overloaded when multiple such chargers are in operation during peak hours. To be able to cope with this heavy electricity load requires either the reinforcement of the grid and the construction of extra grid infrastructure to handle the higher power load; both options are not cost effective. The cost of the electric grid infrastructure to handle fleet charging, including the high-powered ultrafast DC chargers for opportunity charging, the lower powered depot chargers for overnight charging is already a significant investment for the city bus operator in terms of capital, installation, and grid connection costs, while the distribution system operator must invest in more substation transformers and high and medium voltage grid powerlines. This paper investigates the application of the ECO-charging technique to reduce the impact on the grid and the design of a grid-wide Charging Management System that will actively synchronize all the ultrafast chargers so that the peak load in the grid, even when multiple high-powered chargers are operating simultaneously, is significantly reduced. Utilizing active synchronization further reduces the average load by 15%, the peak load by 55%, and the peak difference by 60%. The ECO-charging technique is based on utilizing short-duration pulsed charging followed by cool-down periods instead of charging in one continuous long-duration pulse, and it lowers the energy requirements of the vehicle by reducing the battery heat generation during high c-rate charging; this results in increased battery longevity.