Fault Analysis And Protection Research On DC Fast Charging Station Of Electric Vehicle

Charging station is the supporting facility of electric vehicles, its construction and development level is of great importance for the scale and industrialization of electric vehicles. Different from other distributed charging devices, electric vehicle charging station (EVCS) is more limited to users’ need and other factors in planning and operation, which leads that high power fast charging mode is more suitable for this kind of centralized charging place. Compared with the EVCS with AC power supply, DC fast chargign station has the advantage of less power conversion level and better acess of DC type distributed generators such as photovoltaic and battery storage, has become the hot spot recently. Related research is still in the initial stage, and the lack of effective protection solution is one of the main barriers to the wild application of DC fast EVCS. In this thesis, we focus on the fault protection of DC fast EVCS and gradually do research on the fault propagation characteristics, fault feature analysis and protection method in order to support the protection design and implement of DC fast charging stations.Firstly, this paper introduces the DC fast charging station power system, analyzes and models the construction of different components. Based on the key equipment of the system, analysis the topological structure and control strategy of key converter equipment with reasonable topology of the three-phase PWM voltage source converter (VSC) and half bridge DC converter. Considering current related technology standard, a complete system model of EVCS is built in the MATLAB for simulation verification.Afterwards, focused on the AC/DC grid-connected converter, which acts as the interface of AC gird and DC system, this thesis analyzes the AC and DC fault response in each time-period. With the blocking self-protection of VSC, the transient process after faults could be divided into several periods, thereby the specific theoretical derivation and corresponding simulation are proposed. Then it discusses the interactive effect of AC and DC parts in the charging station and concludes the fault propagation characteristic.Besides, in order to put forward the protection strategy of DC charging system, this paper continues the fault circuit analysis. Before the circuit calculation, common DC fault type and fault feathers of DC converter in battery charger are introduced to differentiate the fault circuits and quantity variation curves. According to the numerous fault scene simulation, pick up characteristic parameter that fit for protection requirements.Finally, this research put forward the protection method and configuration scheme for DC charging station. To grace time for action and break the DC fault current more easily, capacitor current limiter could be used in suitable protection requirement. On another Forthis thesis proposed a centralized current differential protection method on the reference of the existing protection approaches.This method mainly solve the difficulty in protection rapidity and selectivity through a centralized protection control center and high-speed communication system. The protection logical estimation process are described in detail, and the simulation results show that the method is effective and feasible. Based on this, the paper discusses the configuration of DC charging station system in three level of device, line and system. The proposed protection method has theoretical and practical significance for protection design and implementation of DC charging station.