Research On The Electric Vehicles And Energy Storage Optimal Control In Microgrid And Battery Second Use

In recent years,the development of microgrid has been paid a high attention in the world,it is seemed as an important part of the future power system.The integrated applications of renewable energy and EVs in the microgrid are helpful to increase the local consumption of renewable energy and achieve low-carbon EVs,which will improve the energy efficiency,economic and environmental benefits effectively.This paper mainly studies the optimal control of EVs and energy storage in microgrid,and puts forward energy storage optimal control strategies for different application scenarios in the microgrid coordination control and energy management layer to improve the operation performance.In addition,the retired EVs batteries second use technology has been studied to analyze technical and economic feasibility of applying retired EV batteries in second use scenario.The main research contents are as followings:(1)For the EVs charging increases the peak load of power grid and the consumption of renewable energy generations problems,the research studies on the integrated application of EVs charging and renewable energy generations by microgrid energy management to improve the energy efficiency,economy and environmental benefit of the system in DC microgrid.Firstly,the system structure and the units' function of DC microgrid are introduced,and the differences in energy conversion efficiency of DC microgrid and AC microgrid are analyzed.Then the optimized EV charging model in DC microgrid is established.In addition,an appropriate EV charging control strategy is proposed to optimize the energy management considering the different power demand scenarios in DC microgrid.The simulation results verify the proposed control strategy can synergy with renewable energy and EV charging in DC microgrid energy management,and the influence of the prediction errors on the optimal control is analyzed.(2)Photovoltaic(PV)-based battery swapping station(BSS)utilize a typical integration of consumable renewable resources to supply power for EVs.The EV battery charging and replacement service is a multi-objective optimization problem in the BSS.The energy management optimization of the DC microgrid can improve the operation performance of the BSS.First,we introduce the typical structure and operation model of PV-based BSSs.Second,three indexes are presented to evaluate operational performance.By analyzing the basic charging strategy and comparing a day-ahead operation schedule and a real-time decision-making of the BSS,a particle swarm optimization(PSO)algorithm is developed to optimize the charging operation.Finally,these three energy management operation strategies are simulated in a case study.The simulation results show that the proposed PSO strategy can effectively improve the operational performance,and results affected by the forecasting error of swapping demand are also better than the other two strategies.(3)EVs' retired batteries recycling is a weak section of China's EV industry chain,and a huge amount of used batteries recovery has become an urgent problem as the rapid development of EV industry.First,this paper analyzes the EVs'retired batteries situation in the future,and studies the main technologies in battery second use.First,the performance and causes of battery inconsistency,battery failure mechanism and influencing factors are analyzed.The evaluation methods of battery health status and residual energy test of used battery are introduced.This paper also studies the sorting,grouping and equalization techniques for the used batteries.A battery capacity decay model considering temperature,discharge depth and discharge rate is established.The value of the remaining capacity of the retired battery is analyzed,and the method of assessing the economic benefit of energy storage is given.Then,the energy storage demand is evaluated on typical applications of the power generation side,the transmission side and the user side,and the applicable scene of the battery second use is analyzed according to the technical index of the application scenario.The economic feasibility of battery second use applied to the user price management and renewable energy grid application are analyzed,and the results show that the battery second use applications are economical.(4)For the power supply shortage and operational reliability problems in microgrid,this paper studies coordination control to improve the power supply reliability.Based on the analysis of microgrid operation mode and the distributed generations control methods,grid-connected and island operation power models of microgrid are established.An optimization control strategy based on fuzzy logic control is proposed to improve the microgrid operation reliability.In grid-connected mode,the fuzzy logic control strategy considers the operation of grid-connected line and energy storage system to optimize the SOC of battery.In island mode,the fuzzy logic control strategy considers the operation of distributed generations and load to optimize the SOC of battery.The simulation case is based on the actual microgrid test platform and verifies the effectiveness of the proposed fuzzy logic control strategy in improving the power supply performances under various scenarios in microgrid.