1 Overview. With the promotion and application of electric vehicles and the construction of charging stations, people's understanding of electric vehicles and charging stations is no longer limited to transportation tools and "gas stations", but they hope to develop a wider range of applications. Although most of the charging stations currently operating and under construction at home and abroad only have the single function of supplying energy to electric vehicles, the United States, Germany and other countries are already conducting research on V2G (Vehicle to Grid) related technologies. V2G refers to the two-way exchange of energy and information between electric vehicles and the power grid as a mobile energy storage unit under controlled conditions. The electric vehicle (charging station) not only obtains energy from the power grid, but also realizes the transfer of energy to the power grid when necessary. The power grid sends electricity back, thereby improving the reliability of grid operation. Electric vehicles containing distributed mobile energy storage units have the advantages of complementing the large power grid, relieving grid power supply shortages and improving grid reliability. With the development of technology, the mobile energy storage application of electric vehicle power batteries can further reduce the investment and operating costs of the power system. The combination of ultra-large power stations and decentralized micro power stations can reduce investment in transmission and distribution lines and improve the operation of the power system. safety and economy. In particular, compared with many distributed power sources, the biggest advantage of electric vehicle power battery mobile energy storage is that when a large-scale power outage occurs in a large power grid, the electric vehicle power battery mobile energy storage can still maintain normal operation, which can Improve the disaster resilience of power systems. Overall, the application advantages and feasibility of 2V2G technology are that the peak-to-valley differences of major power grids are increasing day by day, and the contradiction between the power grid's peak shaving capabilities and the objective peak shaving needs is very acute. V2G's participation in power system peak shaving is important for coping with the increasing demand for peak shaving. Serious peak load regulation issues are of extremely great significance. 2.1 Advantages of V2G technology application (1) Adjustment of capacity can be guaranteed. 90% of electric vehicles can participate in V2G services 24 hours a day. Even during peak traffic periods, more than 80% of the vehicles are parked, and private electric vehicles are parked most of the time. (2) Fast response speed. The charging and discharging of electric vehicles with bidirectional power adjustment function can reach ms level, while the traditional peaking power supply has to take into account the life of mechanical components, and the fastest response time is around s level. (3) The response power reserve margin is small. The inaccurate response of traditional peak shaving and frequency modulation to AGC signals requires a larger response power reserve margin for power grid dispatching, while V2G responds quickly and accurately to peak shaving and frequency modulation commands, which can reduce the power reserve margin. (4) High overall efficiency. The charging and discharging efficiency of the battery is higher than the average comprehensive energy efficiency of general pumped storage power station operation. (5) It has obvious social and economic benefits. Electric vehicles can take advantage of off-peak power from the grid and provide services when the grid is at its peak. 2.2 Feasibility of V2G technology application Electric vehicles/charging stations have a two-way power exchange function, which can not only transmit power to the grid (i.e., the discharge state of electric vehicles), but also absorb power from the grid (i.e., the charging state of electric vehicles); secondly, electric vehicles / The charging station has a two-way communication function and can remotely receive instructions and send power information. The peak shaving instructions are sent to the electric vehicle by the grid dispatcher through the communication network in the charging station. The response of the electric vehicle is monitored, recorded and fed back to the charging station through the communication network ( Backend management system). If electric vehicles develop to a certain scale and have relevant policy and technical support, peak shaving instructions can also be sent directly to electric vehicles through wireless communication, and the responses of electric vehicles can be monitored and recorded (the response results of each electric vehicle should also be fed back through wireless communication To the charging station background management system). Therefore, electric vehicles can achieve organized and planned peak shaving according to the requirements of the grid. 3 Basic ideas for realizing V2G peak shaving applications. Based on the peak shaving needs and the V2G statistical information of each charging station, the power grid formulates a V2G charging and discharging plan through relevant strategies and sends it to each charging station; after receiving the plan, each charging and discharging station will pass the relevant Strategies and algorithms rationally select vehicles, allocate charging and discharging power, and ensure reasonable execution of charging and discharging plans. 4. Prediction of available capacity and available time. From the perspective of grid security, V2G, as a large number of distributed power generation units with user participation, connected to the system will inevitably have a certain impact on the operation of the grid. Therefore, accurate prediction of V2G in the dispatch process Various parameters in the grid will definitely become one of the issues that the power grid dispatching and operating agencies pay attention to. Precisely because V2G has two-way interaction with user energy, its available capacity prediction problem is more complex than traditional load prediction. From a technical analysis, the available capacity of V2G energy storage can be obtained in the following two ways. (1) The user setting method means that the user sets the plan for the vehicle to participate in V2G for the next week on a weekend. The V2G operator and the backend management center use this as a standard to calculate the V2G available capacity for the next week, and give priority to the planned part in the actual charging and discharging execution. This model is similar to the contract market and real-time market models in the power market, and has good promotion prospects. (2) Using historical data for prediction, V2G capacity is closely related to weather, holidays, prices, temperatures, seasons, economic development, and the number of electric vehicles participating in V2G services. In the early stages of V2G service implementation, since there are relatively few participating vehicles, a peak-hour discharge model can be adopted. As the technology and market mature, the number of participating vehicles will gradually increase, and the historical data of V2G will gradually accumulate, so that various prediction methods can be used to predict available capacity, such as the regression analysis method, time series method, etc. commonly used in the current power system. Exponential smoothing method, gray model method, Kalman filter method and some artificial intelligence methods such as expert system, artificial neural network, fuzzy prediction and other methods. The main components of the V2G system are: battery management system (BMS), charger and discharger, V2G background management system and V2G control center. Its various functions and control relationships are as follows: (1) The V2G control center formulates V2G charging and discharging plans based on load forecast, V2G forecast and new energy power generation forecast and publishes them to each V2G background management system; the V2G control center bases on the real-time frequency of the power grid, The real-time power of new energy power generation forms real-time frequency modulation power commands and disturbance suppression commands and is sent to each V2G background management system; (2) BMS provides the maximum charge and discharge current, real-time battery power and voltage, battery charge, and battery charge to the V2G background management system through the charge and discharge machine. Discharge permission and other information; (3) The user inputs the SOC lower limit and available time information on the human-machine interface on the charger and discharger, and sends it to the V2G background management system; (4) After obtaining the above information, the V2G background management system will use the charging and discharging strategy according to the Select the charging and discharging vehicle and charging and discharging power, and control the execution of the charging and discharging machine. At the same time, the V2G background management system monitors the information of the entire charging and discharging station and feeds it back to the V2G control center. The above various information and command transmissions are completed through the communication network. 6 Conclusion With the development of the scale of electric vehicles, the development of electric vehicle charging and discharging technology and networking, and the development of smart charging station technology and management models, electric vehicles will increasingly reflect the need for clean and energy-saving transportation. The role of the power grid in providing reliable and high-quality power supply.

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