Charging Management Strategy using ECO-charging for Electric Bus Fleets in Cities

Charging Management Strategy is a critical aspect in electric bus fleets to minimize the impact on the local electricity grid and to minimize the financial cost to the bus operators. To realize a fleet of battery electric public transport buses in a city depends on two major stakeholders, namely the city bus operator and the electricity distribution systems operator. The cost of the electric charging infrastructure, including the high powered ultrafast DC chargers for opportunity charging and lower powered depot chargers for overnight charging is a significant investment for the city bus operator in terms of capital, installation, and grid connection costs, while the distribution system operator has to contend with significant power load on the electricity grid when multiple ultrafast chargers are in operation. This paper investigates a Use Case of an electric bus fleet plying a route, and the optimal selection of chargers, charging duration, and battery State of Charge that will minimize the impact on the local grid and minimize the total cost of ownership. A Simple Optimization algorithm was utilized for this purpose. Results show that the objectives are mutually exclusive, and there need to be a tradeoff to achieve the optimal balance between grid impact and total cost of ownership. Results also show that grid impact and the total cost of ownership are both minimized when opting for low c-rate charging instead of high c-rate charging or when charging only for short durations. Finally, an ECO-charging technique based on utilizing short-duration pulsed charging followed by cool-down periods instead of charging in one continuous long-duration pulse was investigated to determine its efficacy in lowering the energy requirements of the bus by reducing the battery heat generation due to high c-rate charging. The optimum charging-to-cooldown ratio and the optimum charging pulse was found using brute force method to determine the lowest cooling energy consumption for a variety of charging rates. Results show that up to 5% reduction in grid impact can be achieved due to implementation of ECO-charging technique