Research On Coordinated Charging And Discharging Strategies Of Electric Vegicles

Now, with the growing global energy shortage, global warming and environmental pollution problems, the world concerns more about energy conservation and emission reduction. Electric vehicles (EVs) are driven by electricity instead of oil, with low noise, high energy efficiency and multi-source electric energy. Compared with the gasoline fuelled vehicles, EVs can help reduce travel costs and greenhouse gas emissions. Becoming an important way to ease the shortage of oil and improve the environment, EVs are considered to be the future of the automotive industry. Thus, countries all over the world pay more attention to promote the development of electric vehicles.The number of EVs connecting to electrical systems is expected to grow rapidly, presenting a potential burden on the systems. EVs can work both as loads and distributed resources, and be idle for the most time of a day. Through vehicle-to-grid (V2G) technology which realize a two-way flow of energy between EVs and the grids, EVs can help smooth the load curve,enhance the security, reliability and economics of the grids. Thus, the deployment of charging and discharging of EVs has become a hot spot recently.On the basis of a large number of research results at home and abroad, a load model of different types of EVs is built, taking into account the population of EVs, the battery characteristics of EVs and the behaviors of EV owners. Then, according to the development of electricity market, the relevant concepts of economic dispatch problems are introduced. At last, two coordinated charging and discharging strategies of EVs joining in economic dispatch problems and one strategy under the influence of charging and discharging prices are proposed in this paper.Firstly, an aggregator of many EVs working as an interruptible load (IL) joins the electrical power system. A corresponding economic dispatch model is proposed, whose objective includes generating cost, reserve cost, emission cost and so on, considering the uncertainties of load fluctuations, wind power outputs and fault outages of generator. Secondly, based on the load characteristics of EVs, an economic dispatch model involved with the schedulable EVs is developed. Monte Carlo simulation and particle swarm optimization (PSO) are applied to solve these two models. The simulation results show that EVs can help improve the economics of the systems and optimize the allocation of generators. Finally, a coordinated charging and discharging model of a single EV is established, taking charging and discharging prices, battery characteristics and expected battery conditions into account. On the basis of load characteristics of EVs, the impacts of EVs on the voltage deviations, the load fluctuations and the power losses of the systems are discussed. The simulation results show that the reasonable price is very important for the reliability and economics of a system.