Study On The Protect And Control Strategy Of EV Battery Swap Stations Connecting To Medium Voltage Distribution Network

With the rise of the electric vehicle industry, a large number of large-scale battery swap stations (BSS) are also constructed and access to the medium voltage distribution network. BSS generally is constituted by power electronic devices of IGBT type. BSS can operate in two states of charge and discharge by PWM technology. When in charging state BSS is just equivalent to the general load, and it does not take any impact on the distribution network, but when in discharge state, BSS may make the distribution network from conventional single power-supply into multiple power-supplies. So when faulty occurs, BSS can take an impact on the protection, even miss disoperation.This paper studied the method of simulation modeling for BSS. Construct the circuit topology of the charge-discharge motor. Introduce the mathematical model of charge and discharge motor’s AC/DC link, DC/DC link, power battery, filter links. The control strategies in charging and discharging of BSS are studied.Then study the impacts on the medium voltage after BSS access to distribution network. Particularly study the FTU and recloser-fuse of distribution automation equipment. We analysis the current changes after BSS access to system in two cases: For BSS near the point of fault in the access, low transition resistance and far from the point of fault, high transition resistance. And we study the changes after reactive power injected into the system by BSS. We found in transition resistance near the BSS, with reactive power injected to the system, where will make it easier for recloser-fuse disoperation.An output current control strategy of BSS is proposed to militate the impacts when distribution network occurs fault plant. The strategy can reduce the inverter current based on the severity of the voltage drop, in order to solve the disoperation problem and go through the small interference, so there is no need to fully remove BSS from the system.The simulation model uses a typical 10kV radiant distribution network in PSCAD/ EMTDC. The impact of the battery swap station on fault characteristics is simulated, and the results show the effectiveness of the strategy proposed by this paper.