Research On Optimal Sizing And Energy Management Strategy Of On-Board Energy Storage System For Rail Transit

With the accelerating urbanization process,the increase in urban population density has brought challenges to traffic volume,speed,comfort and many other aspects.Urban rail transit has the advantages of large volume,accurate time,fast speed and be friendly to environment.Therefore,the development of urban rail transit has become a good solution to solve the problems of large population and inconvenient transportation.As one of the power supply schemes,on-board energy storage system(OESS)can realize the operation in catenary-free zone,which is much flexible,reliable and efficient.For the purpose of fully utilizing the advantages of OESS,the first-end charging operation mode could be a good choice.Then,in order to meet the requirements of power,energy,weight and cost at the same time,adopting a battery-ultracapacitor HESS is a good solution.In the context of the application of urban rail transit,this paper compares the energy efficiency of different power supply modes in order to verify the advantages of OESS in energy consumption.Then,this paper studies the energy management strategy(EMS)and sizing configuration of battery-ultracapacitor hybrid energy storage system(HESS)so that they can be optimized to increase operational efficiency and reduce whole life cycle cost.The specific work is as follows.Firstly,the existing power supply modes for urban rail vehicles are studied.Based on a three-station two-vehicle instantaneous model,combined with power profile,a dynamic mode is expanded in Matlab.The energy loss is analyzed and compared in four power supply modes of the catenary combines braking resistor,feed energy system,off-board energy storage system and completely powered by OESS.The results show that the OESS can achieve high energy efficiency.Secondly,focusing on the power distribution of HESS in first-end charging operation mode,the models of battery,ultracapacitor and DC/DC converter are established,a multi-objective control strategy considering loss,bus voltage and battery current is proposed.Then,a two-level design method contains fuzzy control(FC)and particle swarm optimization(PSO)is proposed for the weight coefficients in control function.Simulation and experimental results verified the high efficiency and feasibility of the proposed strategy.Finally,the sizing parameters and EMS parameters of HESS can affect the whole life cycle cost.Hence,when there are many variables,the multidimensional nonlinear problem appears,and the premature phenomenon is likely to occur.In this regard,this paper analyzes the life cycle cost model,combined with the existing OESS life assessment method,proposes the concept of energy distribution ratio and the method of rapid estimation of the lowest cost point.The simulation verifies that this method can effectively decouple the sizing and EMS,avoid premature phenomenon and quickly locate the optimal sizing configuration.