Hierarchical Control And Capacity Allocation Optimization Of Supercapacitor Energy Storage System For Urban Rail Transit

With the rapid development of socio-economic,the popularization rate of urban rail transit increases significantly,and the power consumption of the urban rail transit system is also increasing,thus energy saving has been widespread concern in the community.The application of supercapacitor energy storage system can effectively reduce the energy consumption and improve the energy conservation efficiency.Focusing on the application of supercapacitor energy storage system in urban rail transit,this thesis conducts theoreti-cal researches on three aspects,including the energy storage converter control technology,energy management strategy and supercapacitor configuration technology,and verifies the proposed research points through simulation and experiment.For the reason that regenerative braking has strong impact and randomness,the en-ergy storage device has a large intermittency in the process of recovering braking energy;and during charging and discharging process,the voltage of supercapacitor is coupled with the state of charge,which cause wide-range variation of the system' s steady-state operat-ing point,thus influencing the dynamic performance of the system.In this thesis,the small signal model is established at first,which includes the supercapacitor,the energy storage converter and train,and the influence of train current and duty cycle of the converter on the dynamic performance of the system is analyzed.Based on the voltage and current dual loop control strategy,a PI parameter optimization method of voltage loop is proposed,which considers the system tracking performance and anti-disturbance performance as the objective functions,and optimizes the control parameters at each steady-state point.The parameter optimization results are fitted with polynomial function by least square method,and are verified both in theory and by simulation.The energy recovery and release of energy storage device is affected by the train and the rectifier unit.When the constant voltage threshold method is used to control the en-ergy storage device,the control command can' t be adjusted according to the working condition of the traction power supply system,and system recovery capability descends.Based on the analysis of the characteristics of train braking process,the traction power supply system model,which includes energy storage device,train and rectifier unit,is established for the single train braking and double trains traction and braking processes,and the influence factors of energy storage energy recovery are analyzed.The charging control strategy of energy storage device based on train operating condition is also pro-posed,which can realize the maximum recovery of regenerative braking energy.Next,the influence of the rectifier output variety characteristic on discharge capacity of the storage device is analyzed,and on the basis of comprehensively considering the traction network and supercapacitor energy management,the energy storage device management state ma-chine is put forward,which implements logical and reliable energy management strategy.The capacity configuration of the supercapacitor in the urban rail energy storage sys-tem affects the cost,life and regenerative braking energy recovery rate.In this thesis,based on the thermal electrical equivalent model and three-variable life model of superca-pacitor,the influence of configuration capacity,SOC(State of Charge)ranges and current limits on the energy recovery efficiency,temperature rise and life are studied under two typical working conditions with constant power and constant current.In order to simulate the operating characteristics of energy storage devices in urban rail transit system,a sim-ulation platform for urban rail traction power supply is built.Taking into consideration of the life and cost of energy storage device,the economic benefit optimization model of the energy storage device is established,and the optimization algorithm for capacity con-figuration is presented.In the end,the optimization results are analyzed with a practical example.In order to verify the research points of this thesis,the 200kW and MW power level supercapacitor energy storage devices have been developed,which are used in laboratory and actual subway line test.The optimal control strategy of the energy storage converter and the energy management strategy are verified on the 200kW and MW level devices.Furthermore,the rate of regenerative braking energy is analyzed based on the operation data of the MW level energy storage device in actual line.The experimental results demon-strate the feasibility and effectiveness of the proposed methods.