Coordinated Control Strategy for Electric Vehicle Charging Piles to Prevent Overload of Distribution Transformer

With the development and popularization of electric vehicle (EV), impacts of large-scale of EV charging to the power system have emerged, especially to the distribution systems. Most of the electricity distribution infrastructure was designed before EV is developed, so most of the existing distribution transformers did not consider the load of the EV charging stations. The large-scale un-coordinated charging EVs can cause the overload or damage of the distribution transformers. Therefore this paper developed a real time control system which monitor the load of the distribution transformers in real time. If it is overloaded, the control system then sends a control command to the charging piles to reduce the output power of the charging piles in order to reduce the overload of the distribution transformers. The coordinated control strategy for electric vehicle charging piles is discussed in the paper. The control strategy under various operation conditions are analyzed. Based on the control strategy, the power output of the charging pile is optimized according to the real-time operation data such as the distribution transformer load, the load of each charging pile and the operation status of the charging piles. Finally, the simulation of cases is performed. The results show that the coordinated control strategy is effective in preventing overload of distribution transformers. It is believed that the control system developed can solve the difficulties of building charging station in old districts and in dense urban areas, where the existing distribution transformers have the risk of overloading during peak demand times.