Coordinated charging strategies for electric bus fast charging stations

Plug-in electric bus (PEB) is regarded as a promising mode of public transport in the future. This paper proposes two real-time coordinated charging strategies to improve the charging costs of electric bus fast charging station (EBFCS) by responding to the Time-of-Use (TOU) electricity prices. At first, a mixed integer linear programming (MILP) based optimal charging strategy is formulated by considering the constraints of PEB charging needs, continuous charging and distribution transformer capacity. To reduce the computation time, a suboptimal strategy is presented with a two-stage model. At the first stage, an ideal charging load profile is optimized without consideration of continuous charging; at the second stage, the continuous charging loads are scheduled to follow the ideal profile through heuristic method. In case studies, charging costs and load profiles under the distribution transformer are respectively simulated under optimal charging strategy, suboptimal charging strategy and uncoordinated charging scenarios. Simulation results demonstrate that the proposed two strategies reduce both the charging costs and the peak load effectively. Comparison between two strategies indicates that the suboptimal charging strategy improves computation efficiency dramatically with only a little charging cost increment.