Research On Optimization Method For Integrated System Of PV-based EV Battery Swapping And Charging Statiion

In many countries, electric vehicles (EVs) have been regarded as a type of environmentally friendly vehicles. It has been established as an effective way to promote the development of EVs to realize low-carbon economic transition and ensure energy security. Under the background of smart grid, studying the integrated mode of charging facilities and distributed photovoltaic (PV) resources is helpful to consume the renewable energy resources locally, which will improve the economy and environment benefits effectively. For the problem of solving out the optimum combination of the charging facilities and distributed photovoltaic resources, this paper studies and researches from various aspects, such as system integration mode, capacity configuration, economic operation, control strategies and experiment platform etc.Based on the expectation of consuming the renewable energy sources locally, this part analyzes the adaptiveness of the integrated system first. Combined with the adapatable electric structure of the integerated system, four typical integration modes, including distributed charging pile with PV generation, charging station with PV generation, battery swapping station with PV generation as well as large/medium battery swapping and charging station together with small scale PV generation, are proposed.Capacity optimization is a fundamental part in the design and planning of the integrated system, which takes the battery swapping and charging station as object to study. And then a multi-objective capacity optimization method is proposed. According to the energy demand of the station, the objective function and related constraints under two typical mode are established, which aims at minimizing the system operation cost and investment and maximizing the utilization of renewable energy sources. Non-dominated Sorting Genetic Algorithm-Ⅱ (NSGA-Ⅱ) is used to solve this problem. According to the analysis of the different optimization schemes, the reasonability and correctness of the established model are verified. From the analysis of the results, theses two methods can provide foundations for the plan and design of the PV-based EV battery swapping and charging stations.In view of the integrated system, optimal operation methods considering both day-ahead and real-time requirement is proposed. For the day-ahead operation optimization, based on the prediction of charging demand, the multi-objective optimal dispatch model is established. After being solved out by NSGA-Ⅱ, optimal dispatch schemes for the future 24 hours can be obtained. For the real-time operation optimization, a real-time power distribution model towards the service availability of battery swapping and charging station is proposed. When there exists great deviations in predicting the energy exchange demand, this model can regulate the charging power dynamically to guarantee the availability of the battery swapping service. According to these optimal operation models, that will improve the utilization of the renewable energy sources and lower the charging cost effectively.The optimal control model of EV charging infrastructure with renewable distributed energy sources is established through digital simulation. On the level of components, the current working principle and mode of charging and discharging machine is studied in depth. The corresponding mathematical model and control strategies are established. The existing lithium-ion battery digital simulation model is improved and a new digital simulation model is proposed which could easily spare out model parameters and set the initial value about state of charged(SOC) freely. On the level of system, for AC integrated system, a digital simulation model is established, which includes multi-group PV generation, typical charging facilities and so on. As for three possible states in the operation process, the system optimal control strategies in grid-connecting, off-grid and transitional mode is proposed.Based on the above analysis and the configuration on the primary system, design of the secondary sytem of the application platform, the physical experimental platform which including PV generation, doubly-fed induction generator(DFIG), charging facilities, EV batteries, lithium battery energy storage system, simulated loads, secondary control and monitoring devices, is established. It can realize the battery charging by renewable energy sources under both grid-connected and off-grid operation mode. With the experiment on the proposed control strategy of tie line power and the control stragegies of the seamless transiton between grid-connected and off-grid mode, correctness and effectiveness of these proposed optimal strategies are verified.