Comparison study of electric vehicles charging stations with AC and DC buses for bidirectional power flow in smart car parks

This paper presents a comparison study of AC bus and DC bus topologies for electric vehicle (EV) battery chargers in smart car parks. The two charger systems are compared from two aspects: the features from the user side and the power quality on the grid side. Considering the system reliability, cost, size and conversion stage, the pros and cons of AC and DC buses systems are introduced and summarized. To compare the electric parameters of the power quality, model predictive control (MPC) algorithm is proposed and applied to operate in grid-to-vehicle (G2V), vehicle-to-grid (V2G), vehicle-for-grid (V4G) modes. An cost function is designed in MPC to track the active and reactive powers references provided by the main grid. The controllers for AC and DC buses to determine the the active and reactive powers relationships among the grid, charging stations and the storage system are designed, respectively. In terms of power ripple, total harmonic distortion (THD) and execute time, comparative simulations of the two topologies are performed under the proposed operations in Matlab/Simulink. The obtained results show that both the two system structures can operate effectively and the commands from the grid and EVs customers can be satisfied. Fast dynamic performance and good steady-state response are achieved in two systems. However, the power ripple, THD, and the execute time obtained from DC bus topology are much lower compared with the AC bus system.