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 longduration
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.

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