Research On Control Strategies For Dynamic Setting Of Supercapacitor Voltage Threshold In Urban Rail Energy Storage Systems

With the rapid progress of society and economy,rail transit has continuously brought convenience to people because of its large passenger capacity,low pollution and fast speed.Due to the short distance between the stations of rail transit and frequent acceleration and braking,the urban rail needs to absorb energy during acceleration,which will reduce the voltage of the traction network;when the urban rail decelerates and brakes,the energy generated by the braking will cause the voltage of the traction network to rise high.How to optimize the traction and braking characteristics,reduce energy release and improve energy absorption utilization has become a hot issue in urban rail research.Under this research background,an energy storage system with supercapacitors was introduced into the urban rail system to adjust the relationship between the energy storage system and the traction network voltage,coordinate energy release and absorption between the two sets of energy storage systems,and deal with traction network voltage fluctuations.Start research.First,analyze the characteristics of rail transit regenerative braking,mathematically analyze rail transit traction substations and traction drive systems,build a 24-pulse rectifier circuit and a permanent magnet synchronous motor simulation model,build a rail transit simulation platform without energy storage system,and simulate urban rail The voltage of the traction network changes under a complete operating condition.Then,analyze the energy storage mechanism,model and capacity selection of the supercapacitor,build a supercapacitor simulation model,discuss the supercapacitor constant current charging and discharging characteristics,and apply the bidirectional DC-DC converter(Bi-directional DC-DC converter under different charging and discharging working modes)Converter(abbreviated as BDC)performs mathematical analysis,and simultaneously analyzes the voltage and current double closed-loop control system,supercapacitor charge and discharge current limiting model and energy storage system work switching problems.Finally,due to the complicated and variable urban rail with energy storage system,non-linearity,large traction network voltage change range and serious energy waste,the traditional control strategy adopts voltage and current double closed-loop control system,because it does not consider the actual state change and supercapacitor in actual operation State of Charge(SOC)leads to relatively low accuracy in model prediction and unsatisfactory control effect.To solve this problem,this paper adopts fuzzy control strategy to connect the double super capacitor SOC and the urban rail to the energy storage system.The distance L is used as an input for fuzzy modeling,expert knowledge and experience are used to write fuzzy rules,and the super capacitor voltage threshold is output through a fuzzy controller.The use of Mamdani type fuzzy controller can realize that the output does not require an accurate model;the use of TS type fuzzy controller output is expressed in multiple forms,which can avoid defuzzification errors,in which the polynomial coefficients are determined by the least squares method,and the urban rail is built using Matlab / Simulink The simulation model of the dynamic setting of the voltage threshold of the supercapacitor of the energy storage system.Comparison and analysis show that the voltage amplitude of the traction network under the fuzzy control strategy is smaller than that under the traditional control strategy.Fuzzy control can dynamically set the charge and discharge voltage threshold of the dual energy storage system,coordinate the energy flow between the dual energy storage systems,and control the energy release and absorption of the energy storage system during urban rail acceleration and braking,thereby achieving stable traction The purpose of the grid voltage.Based on the principle of optimal energy-saving effect and balanced utilization degree of energy storage system,the fuzzy controller has the potential errors when manually setting parameters and writing fuzzy rules.The Adaptive Neuro-Fuzzy Ingerence System(ANFIS)has The self-learning ability of ANFIS controller is used to train and model a largenumber of experimental data to improve the accuracy of the prediction mode.The simulation model of the dynamic setting of the super capacitor voltage threshold of the urban rail energy storage system is built using Matlab / Simulink software.The voltage amplitude of the traction network under the adaptive neural fuzzy network control strategy is smaller than that under the fuzzy control strategy.The ANFIS control strategy can dynamically set the charge and discharge voltage threshold of the energy storage system,coordinate and cooperate with the dual energy storage system to release and absorb energy under the acceleration and braking conditions of the urban rail,and overall improve the traction network voltage regulation and energy saving effect.