Study On The Interaction Between Voltage Quality Of Distribution Network And Electric Vehicle Charging

The charging behavior of electric vehicles is random and uncertain in time and space,the voltage quality may be influenced due to large-scale charging loads connecting to distribution network.At the same time,the normal charge of electric vehicles may be influenced by the voltage quality as well.Among the power quality problems,voltage sag may lead to the abnormal operation of electric vehicle charging equipment,but this problem has not yet caused concern.Therefore,the researches on the voltage quality problems caused by electric vehicle charging and the influence of voltage sag on electric vehicle charging have significant meanings of theory and practice.First of all,the models of electric vehicle charging loads are established in this paper.The main factors that influence the charging loads of electric vehicles are summarized,including the number and types of electric vehicles,the characteristics of battery charging and discharging and the charging mode.Based on the travel habit statistics of main types of electric vehicle users,the charging mode and charging time of each type of electric vehicles are studied;then the charging load models of different types of electric vehicles are established.The calculation method of electric vehicle charging load based on Monte Carlo is proposed,and the charging loads of different types of electric vehicles are calculated using this method.Considering the irrationality of the charging load models with assumption of a daily charging and the constant charging load,a calculation method of private car charging load considering the charging high peak effect at the weekend is proposed,and a more accurate charging load curve can be obtained using this method.Secondly,the model of distribution network is established in MATLAB.The influences of different scales of electric vehicles assess to the network on the node voltage deviation,voltage unbalance and transformer load rate are simulated and analyzed.In the process of simulation,different scenes are designed.The different influences of fast charging and slow charging,battery-electric and plug-in electric vehicle charging on the distribution network are considered.The effects of slow charging in three-phase balanced charging and unbalanced charging mode on the three-phase voltage unbalance are considered as well.At the same time,the importance of coordinated charging in improving the quality of voltage is also analyzed.Finally,the influence of voltage sag on different types of electric vehicle chargers is studied.The types of electric vehicle chargers and classification of voltage sags are summarized in detail.The influence mechanism of voltage sags on electric vehicle chargers is analyzed.The simulation models of the single-phase in-car charger,three-phase six-pulse rectifying charger,twelve-pulse rectifying charger and PWM rectifying charger are established respectively in PSCAD.The influence degrees of voltage sag characteristics including magnitude,duration and phase shift on different types of chargers are analyzed through the simulation.Besides,the influences of the transformer types between the bus and charger on the charger tolerance ability to voltage sag are simulated and analyzed,and the influence degree is evaluated as well.The simulation results show that the influence of voltage sags on the chargers is not only related to the strength and types of voltage sags but also related to the working state of the chargers.