Research On Power Charging And Discharging Scheduling Strategies In Vehicle-To-Grid Systems In The Smart Grid

Along with the increasing demand of electricity,it is necessary that the existing power grid could offer cleaner,more secure,more efficient and more economical electricity.It is inevitable that the existing power grid will be innovated towards smart grid,and research on smart grid becomes a hot issue.Meanwhile,Electric Vehicle(EV)as a traffic tool that uses clean energy should be promoted to be used widely.However,to promote the populization of EVs,the first issue that the power system will come across is how to afford the electricity load brought by a large number of EVs.And people who are hesitating to choose EVs concern about whether EV charging could be in time and convenient,whether the cost of using EV is cheap enough,etc.To facilitate the development of EV industry,the academia proposes to realize the bidirectional flow of electricity and information between EVs and the grid or among EVs by integrating advanced technologies of sensor,measurement,communication,information and control,that is,the Vehicle-to-Grid(V2G)systems in the smart grid.The proposal of V2 G system aims to avoid heavy load of the grid brought by the charging of large scale of EVs,and design low-cost,flexible and convenient charging schemes for EV users.Power charging and discharging management is one of the key technologies existing in the design of V2 G systems.This paper focuses on the power charging and discharging management scheme design.From the perspectives of both the grid and EV users,the optimization objectives in this dissertation are to decrease the peak-to-valley value of electric load of the grid,to reduce the cost of using EVs and to improve the quality of charging.The following parts are discussed in this paper: 1)EV charging scheduling in the parking mode;2)EV charging scheduling in the mobile mode;3)incentive mechanism design for electricity feedback;4)cooperative charging and discharging system design in parking lot.The first issue focuses on the scheduling of EV charging behaviors in the parking mode.To joint optimize the peak-to-valley value of electric load of the grid and the charging cost of EVs,centralized Parking Mode Charging Scheduling(PMCS)scheme is proposed;to joint optimize the revenue of the power utility and satisfication degree of EV users in the power system integrating renewable energy,Stackelberg game model is estabilished between the power utility and EVs,the optimal charging strategies of EVs and discriminatory pricing strategy of the power utility are found in a distributed manner.Numerical results indicate that the peak-to-valley value of the grid is greatly decreased with the proposed PMCS compared to charging of EVs without scheduling.The load of the grid from peak rebound can also be prevented,and cost of EV charging is reduced for EV users.However,the computational complexity of the centralized scheduling scheme is high.Besides,in the power system with renewable energy integrated,since the electricity produced by renewable energy such as solar energy may be uncertain and inconsecutive,discriminatory pricing strategy of the power utility is beneficial to the increase of the power utility revenue and the maximization of the satisfactory degree of EV users.The second part focuses on the charging scheduling problem for EVs in the mobile mode.Compared to the charging problem in the parking mode,charging scheduling problem in the mobile mode is more challenging.Two schemes are designed for EV charging with different levels of emergency.If EV sends charging request when its State Of Charge(SOC)is very low,the Mobile Mode Scheduling(MMS)algorithm is designed to decrease the delay of accessing the charging station.EVs also can reserve charging opportunity when the SOC is relatively high.Traveling plan-aware charging scheduling scheme is adopted to deal with the charging opportunity reservation problem.The scheme considers the detour,schedule of EV users and the amount of electricity demanded as preferences of EV users,and Stable Matching Algorithm(SMA)is proposed to find the stable matching between charging stations and EVs.Simulation results show that with the MMS,the average delay that EVs access charging stations is reduced,the probability that EVs complete charging increases,and the utilization ratio of each charging station is close to 100%.Besides,with the SMA,the total average system utility of EVs and charging stations increases,and the satisfactory ratio of EV users also rises.In the V2 G system in the smart grid,EVs with surplus electricity are entitled to feed back their electricity to the grid when the grid is in the peak period.The third issue is how to design incentive mechanism to encourage a large number of EVs to offer electricity feedback service to decrease the peak-to-valley value and enhance the stability of the grid.Since most private cars are not in use in most time and one EV can feed back only a small amount of electricity compared to the amount of electricity that the grid demands,we propose the two-level group-selling based auction mechanism.The proposed auction mechanism can guarantee all biddings are truthfulness,and we also prove that the mechanism posses other important economic properties,such as incentive rationality and ex-post balance.Numerical results show the two-level group-selling based auction mechanism could help the grid reduce the operation cost,and meanwhile offer incentives to EVs which offer electricity feedback services.The last issue is to joint study the problem of EV charging and electricity feedback,and we suggest constructing the cooperative charging and discharging system in parking lots.Frequent charging and discharging will consume EV users a lot of waiting time and is not conducive to the stability of the grid.EVs with surplus electricity and EVs which need charging in the same parking lot can be pairs.We apply many-to-many matching model to formulate the problem and design the Pareto Optimal Matching Algorithm(POMA)to find the optimal matching between these two sets of EVs.Numerical results indicate that the trading volume of electricity increases with the proposed POMA which is helpful to enhance the stability of the grid in the peak period.Meanwhile,the transaction price of electricity between charging EVs and discharging EVs is always not lower than the reserved price of discharging EVs,which offer incentives to discharging EVs to participate in the proposed system.