Research On The Energy Storage Characteristics Of Electric Vehicles And Its Allocation Method

With the rise of the shortage of fossil fuel and environmental problems, large quantity of environmentally friendly renewable energy is adopted to the power grid. The renewable energy has brought plenty of energy resources to the grid as well as the challenges of reliability and quality problems caused by its randomness and volatility. The rapid development of the electric vehicles, which is attracting more and more attention, provides a feasible solution to theses problems. On the one hand, the electric vehicles use electricity as their major power sources. So there is no pollution problems because of its zero emissions. On the other hand, the electric vehicles use battery to store energy which potentially can be allocated as energy storage of the grid. If the electric vehicles are dispatched effectively, they may become a promising form of energy storage without highly investment.This dissertation mainly researches on the characteristics of electric vehicles which can be divided into three main themes. The first theme is the estimation of charging and discharging load of the electric vehicles. Many researches are done based on Monte Carlo methods in different dimensions. The second theme is to evaluate the dispatchable capacity of electric vehicles. The concept of accessing probability is innovatively invented for the evaluation of dispatchable power and energy. The final theme is energy storage configuration method for electric vehicles. The methods proposed are respectively aiming at peak load shifting and valley load filling or smoothing the fluctuation of renewable energy. The researches proposed in the dissertation are summarised as follows:1. Various types of electric-vehicle batteries are introduced and their characteristics are compared through the explanation of their principles. The electric-vehicle batteries are combined into groups in order to enhance the total power and capacity when used in the electric vehicles. The temporal and spatial characteristics of electric vehicles are detailedly analyzed and described in the form of probability model. This part of research provides the data and model basis for the later simulations. Then the concept of Vehicle-to-Grid technology is introduced along with its realization method.2. The estimation of ownership of vehicles is proposed based on the Logistic curve fitting method. What’s more, least absolute deviation method is used to avoid the influence of outliers in the data. Then the charging load of a demonstration district is estimated based on the Monte Carlo methods. Both the summer and winter’s charging load are estimated in order to arrange the upgrade plan of the transformers in the district. Afterwards, the fast charging load in typical cities are also estimated. The simulation results indicate that the charging load of the electric vehicles will greatly increase the electricity consumption and peak-valley difference. At last, the characteristic of discharging is also analyzed.3. The accessing probability of electric vehicles is invented according to reliability theory. This concept used in the dissertation changes the temporal and spatial characteristics into regular pattern when studying on the large scale of electric vehicles. Based on the accessing propability, dispatchable capacity of different types of electric vehicles is defined and evaluated through probability theory. The dispatchable capacity consists of dispatchable charging load, discharging load, charging energy and discharging energy. The simulation results indicate that electric vehicles does have some potential to be dispatched. And the dispatchable potential is very helpful to the planning, configuration and real-time dispatch of the grid. Some further study is also done about the impact of demand-side management on the dispatchable capacity.4. The principle of peak load shifting and valley load filling with electric vehicles is innovatively analyzed through the relation between the charging states and load curve. The principle is analyzed in one period first and then in several sequent periods. The possibility of failure of peak load shifting is also analyzed. After the study of principles, a configuration method of the electric vehicles is proposed aiming at decreasing the peak-valley difference. The goal of the configuration is decided by the cutting line and area method. The method can fulfill the charging requirement as well as configure enough electric vehicles to accomplish the task of decreasing the peak-valley difference.5. By improving the traditional configuration methods of energy storage to stabilize the fluctuation of renewable energy, a configuration method applied for the electric vehicles is proposed. The method identifies the goal of smoothing through Fourier transform, and then configure enough electric vehicles to achieve the goal. The simulations not only accomplish the task of smoothing the short-term output of wind power with private electric vehicles, but also find out long-term collaborative solutions with wind power with the help of various types of electric vehicles.