| Affected by various random factors,the disorderly charging loads of private electric vehicles(EVs)present uncertainty.It will bring adverse impacts such as voltage reduction and line overload for residential distribution networks with high proportion of EVs.On the other hand,photovoltaic(PV)is connected to the distribution network on a large scale with the promotion of the "Rooftop Photovoltaic" project.The peak-valley difference of system load will be further increased by the fluctuation of PV output.In order to analyze the adaptability of the distribution network to EV access,a model for the randomness and uncertainty of EV charging load is founded.In addition,adaptability evaluation indexes of the distribution network carrying a high proportion of EV is constructed.The adaptability of distribution network under various scenarios of disordered charging and ordered charging of EV with different permeability rates is evaluated.Finally,an adaptive improvement method is proposed which takes into account PV absorption and the EV orderly charge-discharge strategy.Firstly,the EV travel energy consumption model taking into account the energy consumption of driving and air conditioning opening has been established.The impact of traffic congestion and external temperature during travel is considered.Typical scene of the outside temperature is constructed based on K-means clustering algorithm,and the opening state of air conditioner will be judged according to temperature distribution.Besides,considering departure time and other travel characteristics,the changes of road congestion level and EV driving speed are reflected based on Markov transfer matrix.The total driving time is discretized through the state transition matrix,and the total energy consumption of this trip is obtained by superposition of consumption in each period.Secondly,considering the influence of EV residual state of charge(SOC)on user’s selection preference,the probability that the user chooses to charge the EV is calculated.Moreover,in order to establish the EV charging load model,the charging piles in residential areas and the charging characteristics of EV batteries are taken into account.To analyze the phenomenon of voltage deviation and line overload caused by EV disordered charging,random characteristic parameters of EV charging are sampled by Monte Carlo method.In order to evaluate the adaptability of the distribution network carrying different permeability of EV,the evaluation indexes of voltage adaptability and load adaptability are proposed based on probability and statistics theory.Finally,example analysis indicate that EV charging load is related to multiple random factors,and its harm to residential distribution networks cannot be ignored.Finally,an EV orderly charge-discharge model is proposed,which also has the function of photovoltaic absorption.By referring to the total load curve of system,the electricity price is divided into three periods based on K-means clustering algorithm.After the dynamic-time electricity price formulated based on EV charging and discharging plan,the EV charging behavior is guided by user’s independent response of price.The response model of orderly charging demand is established by the difference between peak and valley prices.At the same time,based on the electricity price subsidy and battery residual SOC,user’s responsiveness to Vehicle to Grid(V2G)is calculated.EV users are divided into three categories according to different levels of charge-discharge participation.Finally,aiming at improving the load balance of distribution network,the voltage deviation and line overload indicators are used as opportunity constraints.Then,the optimized EV charging and discharging behavior is optimized by the improved particle swarm optimization algorithm.An example shows that the proposed model can effectively improve the adaptability of distribution network.At the same time,it can smooth the load and increase the absorption of PV. |
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