Research On Energy Management Strategy Of Tram Hybrid Energy Storage System Based On Pseudospectrum Method

Modern tram is an effective part of urban rail transit with friendly environment and large passenger capacity.The tram loaded with energy storage has been widely developed due to its low investment cost and no impact on urban landscape.However,a single energy storage element can not meet the high-power and energy consumption operation requirements of the tram.The HESS composed of energy storage elements with complementary characteristics can well match the operation requirements of the tram through the optimization of capacity configuration and EMS.Therefore,the research on capacity allocation and EMS optimization of hybrid energy storage system is very important for efficient and energy-saving operation of trams.In this paper,the capacity allocation and EMS optimization of the hybrid energy storage system composed of lithium titanate battery and supercapacitor are studied.Firstly,the HESS of tram is modeled,and the boundary conditions of the hybrid energy storage system are analyzed.On the basis of comparing the advantages and disadvantages of different topological structures of hybrid energy storage system,the semi-active battery structure with small energy consumption and light weight is selected.Based on the HPPC experimental manual,the Rint model and the first-order model of lithium titanate battery are identified.The power curve of the tram is constructed by traction calculation,and the boundary conditions of the hybrid energy storage system are analyzed,which lays the foundation for the optimization of capacity allocation and energy management strategy.Secondly,to solve the coupling problem between energy management strategy and capacity allocation,a new capacity allocation algorithm based on improved convex optimization algorithm is proposed.Based on the analysis of the original convex optimization algorithm,an improved convex optimization algorithm is proposed,which can get the multi-objective non dominated solution set,and the redundancy of energy and power is analyzed to improve the robustness of the capacity allocation result.From the perspective of energy consumption and mass,the single energy storage system and hybrid energy storage system are compared,and the advantages and disadvantages of single energy storage system and hybrid energy storage system are analyzed.Thirdly,aiming at the problem that the global optimal result cannot be transformed into real-time control strategy,this paper proposes an adaptive multi-mode dynamic proportional control strategy applied to hybrid energy storage system.Taking the system efficiency as the optimization objective,the pseudospectral method is used to optimize the power distribution between lithium battery and super capacitor.According to the optimization results,the input variables and the decision variables obtained from the optimization are modal analyzed,and the dynamic proportional control strategy suitable for online is extracted.Furthermore,in order to make the control strategy change adaptively with the change of the actual operation state,an adaptive multi-mode dynamic proportional control strategy is proposed.By comparing dynamic programming with pseudospectral method,the optimization performance and cumulative error of different algorithms are analyzed.Finally,based on the experimental platform of hybrid energy storage system,the function of fixed proportion method and adaptive dynamic proportion control strategy is verified.By comparing the fixed proportion strategy with the adaptive dynamic proportion control strategy,the superiority of the power allocation method proposed in this paper is verified.Through the comparative analysis of the adaptive multi-mode dynamic proportional control strategies under different initial conditions,the adaptability of the control strategy proposed in this paper is verified.