Electric vehicles with the characteristics of cleanliness and energy storage have broad application prospects. However

in order to solve the drawback of short driving mileage

electric vehicle charging stations should be available on the expressways. The battery-swapping mode is employed in the electric vehicle charging stations for centralized management of batteries. Firstly

a bi-level economic dispatch model is developed. The objective function is to minimize the total cost in the upper level

and optimize the network loss in the lower level

respectively. Secondly

based on the proposed model

a new method is presented. In the upper level

the total output of the centralized charging stations and the thermal power units are optimized for every moment using the particle swarm optimization method. The power output of each thermal power unit is allocated for every moment by the integrative sensitivity. In the lower level

the power output of each centralized charging station is optimized for every moment and allocated by network loss sensitivity. Finally

numerical examples based on an improved IEEE 30-bus tested system show that the method proposed is accurate and effective

which can satisfy the economic requirements while obviously improving the calculation speed.