Research On Charging/Discharging Strategy For Electric Vehicles Under Micro-Grid Economic Operation

At present, due to the increasingly intense contradictions between the rapid growth of electricity demand, energy shortages and environmental degradation, so the technology of distributed generation has been widely concerned. But the large-scale development of distributed generation is limited by its diversity, indirectness and complexity. As an important part of the construction of smart grid, microgrid can effectively solve the problem caused by a large number of distributed power generation equipment connected to the grid, and improve the reliability and flexibility of the interconnection between the power grid and distributed generation equipment. In addition, with the widespread use of electric vehicles, the charge/discharge behavior of electric vehicles is random and dispersion, the security and stability operation of the grid is facing a new challenge.At first, the private electric vehicle is taken as the object of the research. Based on the survey and statistics of the travel habits and travel characteristics of the traditional car owners, the mathematical model of the charging start time and the daily travel distance of the electric vehicle are proposed. Based on this, two charging/discharging strategies of electric vehicle are proposed. Then, considering the micro-grid economic operation and the charging/discharging cost of electric vehicle, a new bi-level optimization model is presented for coordinating the charging/discharging schedules of the PEVs base on the theory of bi-level optimization. The upper-level optimization model takes the minimum operation cost of the microgrid as the objective, and the lower-level optimization model takes the maximum charging and discharging cost of electric vehicle as objective. For NP-hard problem of bi-level optimization, we transform the bi-level programming formulation into a single-level program with equilibrium constraints by its Karush–Kuhn–Tucker optimality conditions. Simulation results show that the proposed charge/discharge strategy can reduce the operation cost of the microgrid and the charge discharge cost of the electric vehicle, so the validity and feasibility of the model are verified.On this basis, vehicle routing problem is introduced and the logistics distribution electric vehicle is taken as the object of the research. A collaborative optimization model of electric vehicle driving paths and charge discharge strategy is proposed. For minimum the overall operating costs of the microgrid which including the energy exchange cost of the microgrid, the fast charge cost of the electric vehicle and the loss of the battery, the model decides the driving path, the fast charge time and the charge and discharge power of electric vehicle, which based on the forecast value of the output of the wind turbine, the forecast value of user load and the distribution task of the distribution company. Then adapting the hybrid coding adaptive imperialist competition algorithm to solve the proposed model, the simulation results show that the proposed method can control electric car to complete the task distribution, at the same time, effectively enhance the absorptive capacity of microgrid for renewable energy generation and vastly reduced the operation cost of microgrid.