| At present,it is a trend for electric vehicles to replace fuel vehicles with environmentally friendly and efficient because environmental pollution problems and resource shortages are becoming more and more obvious.However,as a newly developed grid load,electric vehicles charging will have an impact on the power quality and economy of the distribution network.Therefore,the effects of grid voltage deviation and network loss are studied based on the charging load characteristics and harmonic characteristics of electric vehicles.From the NHTS big datas,based on the multi-factors affecting the charging load,Monte Carlo method is used to randomly charge the private car,bus,taxi and official car in disorderly charging mode and time-of-use tariff mode and the load model is built.It is found that under the disordered charging mode,the charging load curve is basically consistent with the basic load curve,and there will be short-term peak load due to the taxi driving law.Under the time-sharing tariff mode,bus and taxi can realize the mode of power exchange.At this time,the charging load concentrates on the low valley of the basic load,so as to achieve the effect of filling valley.Some charging loads of private cars and buses are transferred to the low valley of the basic load,which reduces the power consumption burden at the peak of the power grid.Based on the topological structure and working principle of charging pile,the equivalent input impedance of DC/DC circuit with complex structure and control is replaced by variable non-linear resistance R_c without affecting the harmonic characteristic analysis.The controlled current source is used for equivalent treatment on the platform of Matlab/Simulink software.The simplified models of uncontrolled rectifier and PWM controlled charging piles are built.The harmonic characteristics of single and multiple charging piles with different topological structures are simulated when they are charged in different proportion and power.The simulation results are compared with the field measurement results of power quality analyzer FLUKE.The comparative results show the availability of the equivalent simplified model of charging piles in this thesis.This thesis summarizes the harmonic characteristics of existing charging stations under various conditions,and provides a theoretical basis for harmonic control research.Considering the characteristics of charging load and harmonic wave,the influence of charging on voltage deviation and loss of distribution network is studied.Taking the distribution network of common residential areas as a model,the voltage deviation of buses with 10%,30%and 50%penetration in Load1 random charging mode and the same charging load in Load1-Load7 are studied,and compared with time-of-use tariff mode.The results show that the problem of voltage deviation under time-of-use tariff mode is alleviated.At the same time,the relationship between the harmonic current of the charging pile and the fluctuation of the charging load and the loss is analyzed.It is concluded that the uncontrolled rectifying charging pile will bring a large harmonic current loss,mainly with low frequency odd harmonics.Mainly in the case of the same amount of charge,the greater the fluctuation of the charging load,the greater the loss of the grid.An on-line power quality measurement instrument based on ARM is developed for charging station load characteristics and harmonic characteristics.The overall framework,implementation functions and hardware and software parts are designed in detail.The charging station is installed and operated,and the results of FLUKE measurement are used to verify the accuracy of online measurement instrument,which collects relevant data for further research.Finally,the correctness of the contents described in this thesis is verified against the background of Fenghua Park first and last bus charging station and Yangshan Road Guanyu charging station. |
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