Research On Dynamic Modeling Of Electric Vehicle Charging Stations

The promotion of electric vehicles has relieved the shortage of fossil energy,but also brought challenges to the power grid.Load modeling of electric vehicles is an important kind of technical reservation work to meet the challenges,but nowadays there is little research on the dynamic charging process of EVs.In order to meet the needs of power grid simulation analysis,this paper s tudied the establishment,simplification,equivalence and application of dynamic load model of electric vehicle charging stations.This paper first analyzed the core equipment and charging system structure of the electric vehicle charging stations.Based on practical engineering applications,a EV charger model consisting of voltage source PWM rectifier,phase-shift full bridge ZVS DC-DC converter was constructed.The charging mode of electric vehicle battery was discussed,and the proper charging mode was selected.By simulation results,It proves that the model meets the various operating conditions of the charger.In order to reduce the time required for simulation,at first the average switch model was used to simplify the charger model when the external characteristics are retained and the switching process of the switch device was not concerned.Then the equivalent input impedance was usd to get a further simplified model which neglected the dynamic process of DC-DC converter.In order to meet the needs of dynamic analysis of the charging stations with large capacity incorporated into the grid,a clustering and equivalence method for the charging station was proposed.The detailed model of a charging station and the equivalent model based on two simplified models were built in matlab/simulink paltform,and the accuracy of equivalent model was caculated.The simulation results showed that the external characteristics of the point of common coupling could be well reflected by these two models,and the equivalent model based on average switch model had higher accuracy,while the simplified equivalent model got faster simulation speed,and had an advantage that the equivalent parameters could be conveniently obtained according to the daily load curve of charging station.Finally,using the flexible active / reactive power regulation ability of electric vehicle charging stations,a electric vehicle charging station dynamic voltage regulation strategy based on voltage droop control and reactive power support was put forward,and its simulation model was build up.When the voltage of the distribution network deviated from the normal range,the charger would switch to the control strategy.The simulation results showed that the equivalent dynamic model of the charging station got good accuracy compared to the detailed model under large disturbances.At last the equivalent model of a charging station with dynamic voltage regulation ability was accessed to the IEEE33 node radial distribution network standard system,the simulation results showed that the model had static voltage regulation ability and transient voltage support ability: reactive power support could be provided,charging power could be reduced during the grid voltage drop,and reactive power could be absorbed when the grid voltage exceeded;when serious fault like short circuit occured,the model could generate reactive power to provide support for transient voltage of the system.So the voltage quality and the voltage stability of the system could be improved by the proposed methods.