| More and more attention has been paid to the shortage of global petroleum resources and serious environmental pollution.Owing to its advantages of economy,low noise,energy saving,environmental protection,low energy consumption and easy maintenance,EVs(electric vehicles)have become the inevitable trend of automobile development.With the continuous development of EV technology,the demand for nonlinear charging equipment,such as charging piles and charging stations,has been increasing.Nowadays,a large number of charging equipment have been built in the distribution network.This will undoubtedly produce harmonic pollution problems to the distribution network.The light increase the energy loss of the power grid and reduce the service life of the distribution transformer,Heavy operation causes the equipment and protection misoperation,the distortion of voltage waveform and so on.Therefore,it is of great practical significance to study the harmonic analysis and treatment of a large number of EV charging.The most effective methods of harmonic control are grid side and user side.At the power grid side,the construction of the power network is all started,such as using harmonic isolating device or reducing the distance between the nonlinear equipment and the power supply,these methods will increase the investment cost of the power network construction and make the planning difficult.Filter devices are used to eliminate harmonic components on the user side.However,the capacity and voltage of power electronic devices can not meet the needs of filtering at present.If the use of a large number of devices will undoubtedly increase the cost of consumption.If the charging behavior of EV can be controlled reasonably and the EV can be connected to the power grid in an orderly way,the harmonic current can be reduced without adding compensator.In this paper,the large-scale EV charging is taken as the research object,and the harmonic current and charging behavior are researched.First,establishing a charger simulation model which can realize continuous charging and incorporated into the distribution network model,which provides a model basis for subsequent harmonic analysis.Then,studing the correlation between the state of charge and harmonic current of EV power battery,and the difference of harmonic current in different initial SOC of EV is analyzed by simulation experiment.The conclusion that the harmonic current can be reduced by using this difference is put forward.Finally,inorder to control harmonics without adding extra equipment,the optimization model of EV's orderly charging is established,and the effectiveness of the proposed orderly charging strategy is verified by simulation experiments.The specific research contents of this paper can be summarized as follows:(1)This paper establishes the simulation model of distribution network with electric vehicle.In order to solve the problem of equivalent discrete charging process of the on-board charging model of EV,this paper starts from the charging mode of EV power battery,and uses DC/DC converter to realize the power conversion part of the on-board charger.The constant current and constant voltage charging control strategy of power battery is designed,and the on-board charging model which can simulate the continuous charging process of EV is established.The simulation model of distribution network with EV is built on Matlab/Simulink platform.The main factors influencing the harmonic characteristics of EV are analyzed.(2)This paper analyzes the influence of SOC of EV power battery on harmonic current.Considering that most of the researches on the harmonic generation of EVs have not done much analysis on the initial SOC of EVs,this paper analyzes the principle of harmonic current generation in the electric network.In this paper,the theoretical relationship of the effect of SOC on harmonic current of EV power battery is established.Based on this,the EV charging with single or multiple initial SOC is simulated,and its harmonic characteristics are compared and analyzed.The harmonic generated by multiple EV is partially offset,and the harmonic current generated by the charging process is continuously changed with the SOC of the EV.Based on this conclusion,using the principle of harmonics reduction between multiple EVs,the initial SOC of charged EV can be controlled,and the theoretical basis for enhancing the phenomenon of harmonic reduction is obtained.(3)This paper establishes the optimal model of the ordered charging of EVs.In order to realize harmonic control without increasing the cost of distribution network construction,an orderly charging control strategy for EVs is made.According to the simulation data of a single EV charging,the relationship model of harmonic current and EV power battery SOC is fitted.The multi harmonic source superposition principle is used to establish multi desk electricity.The harmonic current model produced by the EV is used to minimize the maximum harmonic current produced in the whole charging process as the objective function,and establishing a charging combination optimization model for orderly access of EV.Then,PSO(Particle Swarm Optimization)algorithm isused to solve the optimal charging combination which has the least influence on the harmonics of the power grid,and the optimal initial SOC of multiple EVs is obtained.Comparing the results with the case of unordered charging,the effectiveness of the charging combination optimization model is verified by simulation experiments,the conclusion is that the optimization model is more applicable to the large scale EV. |
PDF Full Text Request