Study On Energy Management Strategy And Sizing Optimization Of Onboard Hybrid Storage System For Modern Tram

Modern tram has become an important part of urban rail transit with the advantages of flexible marshalling,low cost and beautiful appearance.In recent years,more and more attention has been paid to the new non-grid power supply mode of tram,and onboard energy storage power supply technology is one of the most popular technologies.This paper focues on hybrid energy storage system(HESS)with battery and supercapacitor,which has both high power density and high energy density.The main research contents are as follows.Firstly,in order to give full play to the complementary advantages of the battery and the supercapacitor,this paper put forwards a fixed power ratio allocation strategy based on the energy interaction between the battery and the supercapacitor.With the high energy consumption demand of some sections,this strategy makes improvement on the traditional rule-based(RB)sttrategy,and makes the HESS enters the active state of battery when the supercapacitor voltage is lower than the set threshold value,and realize the energy transfer between the battery and the supercapacitor.This strategy can make the HESS achieve stable high power output,and can effectively reduce the weight of configuration.Secondly,a three-step collaborative optimization method of energy management strategy(EMS)and sizing for HESS is proposed.The first step is to improve the EMS with energy interaction.The second step is the multi-objective optimization of EMS parameters.Through the disassembly of the optimization process,the relationship between EMS and sizing and the impact on system charactersitics are clearly displayed.This method overcomes the defect that single-step sizing strategy is easy to fall into local optimization.The third step is the final optimization of capacity allocation.Based on the optimized EMS parameters,the configuration results with optimal battery lifespan and system weight are finally obtained by improved particle swarm optimization(PSO)algorithm.In this paper,the advantages of this configuration method are verified by case simulation analysis.At the same time,in order to solve the problem of low calculation efficiency in the preliminary design,this paper develops a software with EMS verification and sizing optimization,which can quickly complete the above functions.Based on the software,the reference power supply mode is quickly analyzed.Thirdly,the construction method of driving condition is proposed,and the regional characteristics is analyzed.The tram has the characteristics of varied right of way,fixed line and flexible operation,and it has similarities with both urban rail vehicles and non rail transit vehicles.Based on the analysis method of principal pomponent analysis(PCA)and K-means clustering,this paper divides the tram's driving condition into congestion condition,smooth condition and high speed condition.At the same time,based on the strong regularity of tram operation,the operation area of tram is divided according to the line conditions,and the short strokes attribution analysis is carried out through data statistics to determine whether the regions have obvious condition characteristics.Through the construction of working conditions and regional division,the HESS can be deeply optimized with the operation characteristics,and thus the operation efficiency can be further improved,and the goal of energy saving of electrified railway can be achieved.Fourthly,in order to improve the efficiency of the HESS and prolong the battery's lifespan,this paper proposes a condition adaptive strategy with real-time optimization effect.The condition adaptive strategy consists of rolling optimization strategy and RB strategy.The rolling optimization strategy forecasts the state of the tram through wavelet neural network(WNN),and optimizes the power distribution based on the dynamic programming(DP)algorithm.The condition adaptive strategy makes full use of the regional characteristics and the results of working condition analysis,and combines the advantages of the RB strategy and the optimized strategy.It can not only approach the effect of the global optimal strategy,but also realize the simplification of the strategy,ensure the stable operation of the HESS,and thus facilitate the engineering application.Finally,in order to verify the research content of this paper,a 90 kw battery-supercapacitor hybrid energy storage prototype is built.Based on the operation strategy and charging strategy proposed in this paper,the control scheme of the HESS is designed and tested to verify the dynamic characteristics of the system.And the EMSs proposed in this paper are verified by experiments to prove the effectiveness and engineering application value.