Research On Electric Vehicle Charging Station Micro-grid Providing UPQC Support For Local Distribution Network

ABSTRACT:Electric vehicle (EV) has become the main direction of the development of new energy vehicles in future not only because its clean, environmental protection, energy conversation, but also the effective way to solve the global energy shortage and environmental pollution problems. With the widespread existence of EV, EV charging station is also essential. The EV charging station will occupy a large investment and cost a lot, so making full use of EV charging station has become the direction of research in the world, too. At the same time, the Unified Power Quality Conditioner (UPQC), a device for the multiple control of power quality, has not been widely used for its prohibitive cost and complicated control. This paper presents the building of UPQC structure within the EV (Electric Vehicle) Charging Station, savings cost, realizing the UPQC features while charging EVs.First, we build the UPQC structure with the existing converter and energy saving components of EV charging stations in addition to an additional converter, and suggest a double-layer bi-directional DC/DC structure in order to achieve parallel charging of EV. Second, taking into account the battery performance constraints and user charging needs, with the orderly discharge management of the EV charging station, we can not only avoid the adverse effects of massive charging of EV on the Electricity Grid, but also make the EV a part of the grid control in the form of real-time controllable load or controllable saveable energy. Last but not least, we use DC voltage-stabilized controller to stabilize the voltage of the DC side and calculate the value of Kp and Ki. Then we can stabilize the voltage of the DC side without the energy storage device only by using a small capacitance and adjusting the parameter of the DC voltage control. While ensuring charging, the EV station can be used to compensate effectively the voltage drop, distortion and overvoltage of the regional grid and resolve the problem of inferior power quality caused by nonlinear and unbalanced load of the regional grid, realizing the function of UPQC. Besides, we only discharge EVs when using EV charging stating providing EPS function via V2G at emergencies.The EV charging/discharging and UPQC functions in EV charging station are verified by simulation. Simulation results show that the effectiveness and superiority of the proposed control strategy.