Multi-objective optimal scheduling of a DC micro-grid consisted of PV system and EV charging station

Integration of PV system and EV charging station is a typical way of spot utilization of renewable resources. Research on multi-objective optimal scheduling of a DC micro-grid consisted of PV system and EV charging station is proposed in this paper. Based on the structure of the DC micro-grid and function of each component, mathematical model of the multi-objective optimization for scheduling, which takes the cost of electricity purchasing and energy circulation of storage batteries as objective functions, is built and then solved with NSGA-II. Constraints including EVs' charging time, the range of the charging/discharging power and SOC (state of charge) of the storage batteries, power supply rate of the distribution network and system power balance are considered in this model. A certain case is studied and verifies the model's rationality. Compared with an instant charging plan, the optimal scheme is superior in reducing cost and energy circulation.

I. Introduction

Compared to traditional vehicles driven with gasoline or other fuel, EVs charged through the charging infrastructure, which is connected directly to the electricity grid, will produce not much less amount of indirect carbon emission and cannot alleviate the dependence on fossil fuels [1]. In this case, to realize actual low carbon, two solutions can be adopted: one is to develop the renewable energy power generation system, schedule collaboratively the charging of electric vehicles and the electricity generating of renewable energy, and improve the electricity grid's ability to absorb renewable energy[2]; the other is to directly set up the link between charge-discharge facilities and distributed renewable energy power generation system, and realize the spot utilization of renewable energy [3], [4]. In the city environment, a DC micro-grid consisted of EV charging station and PV system is a typical way in realizing the spot utilization. Related demonstration project construction have been carried out in many places in both inland and abroad, in order mainly to validate key technologies that have something to do with PV device and the EV charging infrastructure. Few researches have been done focused on optimal scheduling. After the large-scale use of EVs, in order to make the micro-grid to a full use, reasonable optimal scheduling strategy is needed to carry out according to the specific condition of PV system and charging demand. At present, the researches on similar system mainly focus on capacity configuration and so on. Ref. [5] aims at reducing the investment of system operation, and optimizing the capacity configuration of power plant containing complementary power generation with wind turbine and PV. To meet the demand of charging load, a feed-in shift method is adopted in [6] to optimize configuration on do integrated power generation system with three renewable energy including wind, PV and water, gives priority to wind and PV, coordinates the use of water, and charge the EVs together.