Studies On The Impacts Of Electric Vehicles Charging On The Power System And Coordinated Charging

To develop the efficient, clean electric vehicles, is an effective way to reduce fossil fuel and alleviate air pollution. In recent years, in the United States, Japan and Western Europe, electric vehicle market grows strongly and apparently, which enters into a rapid development period. In2013, with the implementation of domestic private EV subsidies, electric vehicle products will gradually increase in the next few years and there would be an explosive growth of EV market at home and abroad. The popularity of EVs will bring a negative impact on planning and operation of the grid. It’s not clear whether the existing installed capacity and the power transmission and transformation system capacity would be able to cope with new demand of charging load, with the large-scale integration of EVs. How we can improve the existing grid utilization and improve carrying capacity and minimize the negative effect brought by the charging load, without expanding the construction scale of power grid? It is necessary for us to study the negative effect and to take appropriate measures in advance, which will have an important significance in the promotion of EVs industrialization process. This thesis mainly includes the following aspects:(1) Based on the harmonic principle, three-phase bridge rectifier charger is analyzed, and models for charger and charger station has been set up, by using PSCAD as a simulation tool. The paper mainly discussed the relationship between the amplitude and phase of charger harmonic, and the output power. Four popular kinds of chargers are analyzed, especially in the power factor, cost benefits and other aspects, which provide a reference for the selection of charger. From the aspects of charging time, initial state of charging, charger characteristics are analyzed to study the probability distribution of the harmonic current and attenuation characteristics while N chargers centrally charging. Harmonic current characteristics of N chargers are simulated by simulation software PSCAD, considering charging time, initial SOC of battery. Finally, take Linyi Jiaozhuang electric vehicle charging/battery swapping station for example, APF compensation capacity has been calculated and analyzed.(2) Beginning with the analysis of influencing factors, such as battery characteristics, charge modes, driver behavior, the probability density functions of total daily trip length and charging time are deduced. The charging model is established and the optimal charging method under minimizing load variance is proposed, based on2009NHTS data and measurement results from Jiaozhuang charging station. The relationship between feeder losses and load variance is deduced, and results are presented to verify that electric vehicle charging under minimizing load variance on the grid can effectively reduce net loss. Take the10kV dual radial line of a city in Shandong for example, the impact of EVs charging on the load, voltage quality and network loss, is analyzed, under different scenarios. Results are presented to verify that electric vehicle charging under minimizing load variance on the grid can effectively reduce net loss, improve power quality and so on.(3) In this paper, a smart charging control strategy is presented, combining centralized and distributed control strategy by an aggregator. According to the negative impact on planning and operation of the power system, as is brought by the popularity of EVs, especially when implemented without control, time-of-use scheduling for EV charging has been put forward, by combining time-delay charging control and valley charging scheduling, especially considering the driver’s behavior. To some extent, the load curve can be improved, but the shortcoming of this method lies in lack of flexibility. On the premise of users’interest, intelligent charging control strategy is proposed and compared with time-of-use control strategy in this paper. The optimal scheduling scheme takes the network load variance and charging cost minimization as the optimization objective. An aggregator framework model is proposed as the means to organize charging, which combining centralized and distributed control strategy by an aggregator. The centralized optimal scheduling scheme takes the network load variance minimization as the optimization objective. The optimization goal of distributed scheduling scheme is to minimize the deviation between charging load demand and the centralized optimization results, within each dynamic sliding window, considering the actual battery constraints and EV owners’ benefits. Therefore, the dynamic control for EV charging and discharging is fulfilled. Then taking Shandong load in2015,2020,2030for example, intelligent charging control strategy, which is compared with time-of-use scheduling, is proved to be effective in reducing net loss, improving power performance.(4) An improved support vector machines prediction method is proposed and compared with conventional prediction method in this paper. The EV holdings of Shandong in2015,2020,2030are predicted by support vector machine method, providing as a quantitative basis of cost-effective analysis under different energy structure of power system. The impact and benefit brought by EV is analyzed on the premise that EV quantity is predicted accurately. Most studies at home and abroad are based on assumption or some rough prediction methods, such as the elastic coefficient method or thousand holdings method, so a more scientific and accurate prediction method is necessary. The improved support vector machines prediction method with1.68%accuracy, through the recent three years comparing data.(5) Fully considering the marginal electricity resulted from generation industry and power structure and other factors, carbon emission model for EV is established. Quantitative analysis of the environmental benefits are conducted and compared between conventional vehicle and EV considering different power structures and various levels of EV penetration. The research whether the EVs is helpful in reducing carbon emission is hot recently. In this paper, the effect of coordinated charging is analyzed from two aspects, which are short-term and long-term marginal operational cost of power supply. Based on energy structure development trends of Shandong, the energy structure is divided into three different scenarios:the traditional energy structure, the transition energy structure and new energy structure. Based on benefits analysis model, quantitative analysis of the enviroment benefits between conventional vehicle and EVs, are compared, under different charging scenarios and charging control strategies, in2015,2020,2030. The results are proved to be effective in reducing carbon emission, with energy structure transition and large-scale intergration of EVs.