Research on the Unbalanced Neutral Point Voltage in DC Bipolar System Considering EVs Charging

With the rapid development of electric vehicles (EV s), the lack of the charging infrastructure has become the bottleneck of the development of EVs. Aiming at the problem of the low charging efficiency and power capacity of AC network, the DC distribution system has been introduced for a settlement. However, a large amount of EVs charging would inevitably result in the DC neutral point voltage imbalance, especially using bipolar structure. In this paper, the main topology structures and neutral grounding modes of DC distribution network is researched and analyzed. Based on the structural feature of DC bipolar distribution network, the influencing factors of DC neutral point voltage, such as network parameter and load distribution, is studied. Then, aiming at the problems of the voltage unbalance, a new coordinated control method is designed to suppress the voltage fluctuation. Finally, a study case of DC distribution network is simulated and analyzed to verify the proposed method, and the results show that the unbalanced voltage could be depressed effectively.