Optimization Of Electric Vehicle’s Charging And Discharging And Coordination Of Profit Chain

Electric vehicle (EV) has been an important transition direction for transportation field because of its energy conservation and emission reduction benefits. EV charging behavior is mainly dominated by EV users. When an EV connects to the power grid, it will generate stochastic power load and influence the operation of power grid. Besides, the power structure of China is dominated by coal, so the stochastic charging behavior will shift the saved carbon emissions on the transportation side to generation side, then the EVs cannot realize environmental benefits. Therefore, it is important to put emphasis on studying and optimizing charging behavior when developing EVs, so that the development mode can be more reasonable and sustainable. In addition, many stakeholders will join the process of EV charging, including generators, power grids, charging operators and EV users. For optimizing the charging behavior of users, it is essential to coordinate the interests among each stakeholder, so as to form an external incentive to guide users’charging behavior. Based on different EV charging modes, this paper is aimed at forming a charging optimization strategy and coordination mechanism of interest chain for ensuring ordered charging and discharging. Currently, China is strongly promoting the electrification process on the public transportation field. Considering the similarity with private EVs and the availability of operation data, this paper puts more emphasis on the charging behavior and charging optimization strategy of electric taxis.The study of EV’s charging behavior is the foundation of that of ordered charging optimization strategy. Firstly, analyses of practical charging behavior for all days, weekdays and weekends are conducted in Section 2. Trough on-the-spot investigation and research, the data of electric taxis in Shenzhen and Hainan has been collected. Then, distribution fittings for charging starting time as well as charging duration are built based on Gaussian mixture model and the optimum fitting model is selected by Bayesian Information Criteria. Furthermore, charging general rule model is obtained after the fitting model is verified via Monte Carlo Method. Moreover, concerning EV ownership, charging times, charging power, charging efficiency and other factors, an EV charging demand model is constructed to determine the charging power load generated by EVs. In addition, for analyzing the benefits of EV charging, a power grid operation efficiency analysis model and carbon emission reduction analysis model are built respectively in Section 3. Via case studies of multiple regions, the results show that power load of present charging behavior will increase the pressure for the operation of power grid. While it is obvious that EV owns environmental advantages compared with internal combustion vehicles. Meantime, the benefits of EV charging show diversity among multiple regions.The charging behavior optimization strategy is the premise to realize the EV energy conservation and emissions reduction benefits. Focusing on this, this paper conducts charging optimization for direct charging mode and battery swapping mode in Section 4 and Section 5, respectively. Under direct charging mode, charging optimization model is built respectively from the view of different stakeholders, including power grid, charging operator and EV users. Power grid gives priority to balance load fluctuation, together with minimizing extrinsic motivation. Operators set goals to maximize the charging income under time-of-use electricity fee and charging service fee. EV users would be eager to minimize the charging cost accordingly. Then three charging strategies are gained. Through analysis, it shows that optimized charging load will improve comprehensive benefits compared with practical charging load, and the strategy formed from power grid’s perspective works the best. For comparing the energy conservation and carbon emission reduction effect of these charging loads, an energy-saving scheduling optimization model is constructed, which sets the lowest cost of coal as the goal from the view of generators. The results show that the three optimized charging loads can reduce the volume of thermal power generation, improve the efficiency of thermal power coal consumption, and increase the clean energy power generation compared with the present charging mode. Under the battery swapping mode, an ordered battery swapping mode is raised which is premised on avoiding the peak load period, busy taxis’ operation period and drivers’rest period. Trough constructing the efficiency analysis model for power grid side, the ordered swapping mode is verified to be able to increase the benefits for power grid. Moreover, considering wind power connecting to power grid, thermal units operation constraints, transmission constraints, battery swapping station operation constraints and charging and discharging power constraints, a power economic dispatch model is built to analyze the energy conservation benefits of EVs under this mode. The results show that ordered battery swapping mode, EV volume and charging and discharging strategy of operators will jointly influence the energy saving and emission reduction benefits for generation side.Whether it can realize a win-win situation between heterogeneous subjects among interest chain is closely related to the realization of the orderly EV charging and discharging, and any stakeholder suffers economic loss will hinder the healthy development of the EV charging market. Economic problems have been the bottlenecks for the further and large-scale development of battery swapping mode. Compared with direct charging mode, battery swapping mode owns several obvious advantages. It is more suitable for providing power to taxis, orderly controlling charging and discharging due to battery’s centralized management, as well as improving benefits for energy system, however its operators can hardly balance the budget owing to the large upfront investment. Based on the demand side, Section 6 firstly finds potential operators and accordingly operation mode, then builds investment cost analysis model from the perspective of operators and constructs charging cost analysis model from the perspective of users. Moreover, the marginal benefit condition of carrying out battery swapping service for operators and the marginal cost condition of accepting this service for EV users are obtained. Through the comparison of these two boundary conditions, the economic results of each operation model could be obtained. In addition, sensitivity analysis is carried out of several key factors influencing the economic efficiency of battery swapping mode, including battery lifetime, weight of vehicle, the discount rate, the volume of EV discharging and the price of discharging, et al.Establishment of an inner coordination and balance among the charging profit chain is the mechanism safeguard of EV’s orderly charging and discharging. Around the goal of EV charging and discharging in an orderly way, and realizing the benefit improvement for related parties, Section 7 further studies the intrinsic mechanism for promoting interest chain to achieve coordination. Under the direct charging mode, based on the sequential game idea, interest optimization models are constructed from the perspective of each stakeholder, and the coordination of profit chain is achieved through price linkage. When realizing the balance state, the charging power load leads to a peak cut and avoids new peak load during load valley and flat period. In addition, the generation and power grid’s earnings rise, users’charging costs decline, wind power generation capacity improves and highly efficient thermal power units’competitiveness is more apparent under the coordination situation. Under the battery swapping mode, a contract mechanism is built between power grid and charging operators, and operators and users follow the "principal-agent" relation. By setting several charging and discharging prices and time of use battery service fee, Section 7 aims to explore a coordination balance point among profit chain for battery swapping mode. Results show that taking same charging and discharging price and smaller changes of peak-valley battery swapping service fee can safeguard the benefits of all parties and achieve a sustainable operation of the profit chain.