What effect does electric vehicle charge and discharge have on electric power system?

Research background

At present, with the increasing penetration rate of electric vehicles, unregulated free charge and discharge poses a threat to the power grid. For example, the transformer overload, network loss increase, etc., can use the corresponding control and scheduling strategy to eliminate and suppress, and at the same time achieve peak filling, eliminate renewable energy and other functions. This paper discusses the load characteristics and load model of electric vehicle, expounds its influence on power system from four aspects, and briefly introduces the corresponding optimal scheduling control strategy.

Effect of Electric Vehicle Charging on Electric Power System

Considering the free randomness of the charging behavior of electric car owners: In time, the uncertainty of the electric car reaching the specific time of the charging station, the different battery status leads to the uncertainty of the charging time; Space, due to the uncertainty of people's travel needs lead to the randomness of the location of electric vehicles. All kinds of uncertainty makes the safe and stable operation of the power grid will be subjected to greater tests. For the power fluctuation problem of intermittent renewable energy, the technology related to the use of energy storage to smooth the fluctuations and participate in peak adjustment has been studied, and electric vehicles are idle for most of the day and can be regarded as distributed energy storage. The renewable energy that eliminates excess energy and sends electricity to it at the peak of the grid, and at the same time it can optimize the economy of wind power grid.

Power quality

Electric vehicle battery charging is a nonlinear load, and its access will also increase the corresponding charging equipment containing a large number of electric electronic devices. Harmonics will be generated during the charging process. PWM rectifier + DC/DC charging machine and corresponding control strategy will be adopted. The harmonic can be limited to a lower level, but it is limited by capacity, cost, etc., and can not be widely used. In the actual operation of the power grid, in order to ensure that the power quality of the grid is up to the standard, the automobile charging station will consider providing compensation and filtering devices in the relevant distribution system.

Load Balance

The widespread use of electric vehicles and the large number of connections to the grid may lead to a larger partial load on the distribution network. Obviously, different electric vehicle penetration rate, resulting in different daily peak load increment corresponding to the use of effective models and strategies to eliminate the impact. In the paper, the general load, distributed power supply, electric vehicle etc. in distribution network have been divided into layers, the coordination scheduling control model has been established, and the dynamic optimization control of electric vehicle charge and discharge has been realized.

Power Capacity Planning

After the electric vehicle is connected to the power grid, it must adjust the corresponding power installed capacity and power transmission equipment to cope with the pressure of the power generation and transmission and distribution system caused by the increase in load. At the same time, this load change will put forward higher requirements for the power supply installed capacity and line capacity of the power grid.

Effect of Electric Vehicle Discharge on Electric Power System

The study found that EV access to the network is more economical than the construction of peak adjustment power plants or units. At present, there are also relevant documents to study the feasibility and potential benefits of V2G technology. The concept of interconnection of vehicle networks will bring new compensation concepts. If we adopt correct and reasonable scheduling and guidance, using electric vehicles to absorb excess renewable energy and calm fluctuations will help to achieve a balance between supply and demand. At the same time, it can expand the power market, reduce the peak gap, and provide backup for the power system. However, there is no mature research on the integrated scheduling strategy of electric vehicles with consideration of electricity price factors such as orderly charging and coordination with renewable, or participation in FM, as rotary backup, etc., and it needs to be further explored and developed.

Conclusion

In this paper, the adverse effects of electric vehicle free charging and discharging behavior on power system, such as Transformer overload and network loss increase, are described from four aspects of system reliability, power quality, load balance and power supply capacity. It also expounds the good benefits that will be brought after connecting to the power grid according to the reasonable scheduling plan, such as cutting peak filling and eliminating excess renewable energy. At the same time, the influence factors and probability model of charging load are summarized, which provides reference for future research.

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