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 has not only been limited to transportation tools and “gas stations”, but to develop a wider range of applications. Although most of the charging stations currently operating and under construction at home and abroad have only a single function for 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 electric vehicle as a mobile energy storage unit to realize the bidirectional exchange of energy and information with the grid under controlled conditions. The electric vehicle (charging station) not only obtains energy from the grid, but also realizes the electric vehicle (charging station) when necessary. The grid reverses power transmission, thereby improving the reliability of the grid operation.

Electric vehicles with distributed mobile energy storage units have the advantages of being complementary to large power grids, alleviating grid power shortages and improving grid reliability. With the development of technology, electric vehicle power battery mobile energy storage applications can further reduce the investment and operating costs of power systems. The combination of ultra-large power plants and decentralized micro-power plants can reduce investment in transmission and distribution lines and improve power system operation. 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 mobile vehicle power battery mobile energy storage can still maintain normal operation. Improve the resilience of the power system.

2 V2G technology application advantages and feasibility

Overall, the peak-to-valley difference between the major power grids is increasing day by day. The contradiction between the peak-shaving capacity of the power grid and the objective peak-shaving needs is very sharp. V2G's participation in power system peak-shaving is extremely important for dealing with increasingly severe peak-shaping problems. Great significance.

2. 1 Advantages of V2G technology application

(1) Adjusting the capacity can be guaranteed. On the 1st, 24 hours, 90% of electric vehicles can participate in V2G services. Even at the peak of traffic, more than 80% of vehicles are parked, and most of the private electric vehicles are in a state of suspension.

(2) Fast response. The electric vehicle with two-way power regulation can charge and discharge up to the ms level, while the traditional peak-shaving power supply takes into account the life of the mechanical components, and the response time is also the fastest at the s level.

(3) The response power reserve margin is small. The traditional peaking and frequency modulation of the AGC signal does not require an accurate response power reserve margin. The V2G responds quickly and accurately to the peaking and frequency modulation commands, which can reduce the power reserve margin.

(4) High overall efficiency. The charge and discharge efficiency of the battery is higher than the average integrated energy efficiency of the general pumped storage power station.

(5) It has obvious social and economic benefits. Electric vehicles can take advantage of grid electricity and provide services when the grid is at its peak.

2. 2 Feasibility of V2G technology application

The electric vehicle/charging station has a power bidirectional exchange function, which can transmit power to the grid (ie, the electric vehicle discharge state), and can also absorb power from the grid (ie, the electric vehicle charging state). Second, the electric vehicle/charging station has two-way communication function. The command can be remotely received and the power transmission information is transmitted. The peaking command is dispatched by the power grid to the electric vehicle through the communication network in the charging station, and the response of the electric vehicle is monitored, recorded, and fed back to the charging station (backstage management system) through the communication network. If the electric vehicle develops to a certain scale, with relevant policies and technical support, the peaking command can also be directly sent to the electric vehicle through wireless communication, and the response of the electric vehicle can be monitored and recorded (the response results of each electric vehicle should also be feedback through wireless communication). Give the charging station background management system). Therefore, electric vehicles can achieve organized and planned peak shaving according to grid requirements.

3 Basic ideas for implementing V2G peaking application

According to the peaking demand and according to the V2G statistical information of each charging station, the grid will issue a V2G charging and discharging plan to each charging station through relevant strategies. After receiving the plan, each charging and discharging station will select the vehicle and allocate the charging through relevant strategies and algorithms. Discharge power, ensure that the charge and discharge plan is implemented properly. A schematic diagram of V2G participating in system peaking is shown in Figure 1.

Figure 1 Schematic diagram of V2G participation in system peak shaving

Figure 1 Schematic diagram of V2G participation in system peak shaving

4 Forecast of available capacity and available time

From the perspective of grid security, V2G as a user-participating distributed power generation unit will inevitably have a certain impact on the operation of the grid. Therefore, it is necessary to accurately predict the various parameters of V2G in the scheduling process. One of the concerns of grid dispatching operators. Because V2G has the interaction of two-way interaction with user energy, the prediction problem of available capacity is more complicated than traditional load forecasting. From the technical analysis, the available capacity of V2G energy storage can be obtained in the following two ways.

(1) User-set method

Refers to the user's plan to participate in V2G for the next week on a weekend. The V2G operator and the back-end management center use this as the standard to calculate the V2G available capacity for the next week, and execute the plan part preferentially in the actual charge and discharge execution. This model is similar to the contract market and real-time market model in the power market, and has a good promotion prospect.

(2) Ways of using historical data for forecasting

The capacity of V2G is closely related to the number of V2G services involved in weather, holidays, prices, temperature, seasons, and economic development. In the early stage of the V2G service implementation, since the participating vehicles were relatively small, it was possible to use the peak discharge model. With the maturity of technology and market, 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 the available capacity, such as the regression analysis method and time series method commonly used in power systems. Exponential smoothing method, grey model method, Kalman filtering method and some artificial intelligence methods such as expert system, artificial neural network, fuzzy prediction and other methods.

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