1. School of Mechatronic Engineering, Xuzhou Vocational College of Industrial and Technology, Xuzhou 221140, China;2. School of Information and Control Engineering, China University of Mining and Technology, Xuzhou 221008, China

With the increasing penetration of electric vehicles(EVs), the disordered charge and discharge behaviors bring negative impact on normal operation of power grid. Vehicle-to-grid(V2G)is an excellent solution for this problem. V2G mode based on microgrid is used for energy exchange between EVs and power grid, and multi-objective optimization model, in which minimum grid load fluctuation, maximum renewable energy utilization and maximum owners gain are taken as the optimization objectives, is established. In order to solve the optimization model, variable threshold optimization algorithm is proposed firstly, and an improved algorithm named variable charge and discharge rate optimization algorithm is proposed. The optimization results show that the two proposed algorithms could increase utilization of renewable energy, improve the imbalance between power supply and demand in the microgrid and increase benefits of EV owners through reasonable scheduling.