Research On Control Strategy Of Urban Rail Wayside Hybrid Energy Storage System Based On Battery SOC Tracking

With the rapid growth of China's urban rail transit operating mileage in recent years,the power consumption of urban rail systems has increased dramatically.In order to reduce the power output of the traction substation,make full use of the regenerative braking energy generated when the train is braking,and improve the voltage fluctuation of the DC traction network,an energy storage device can be introduced into the DC traction power supply system.Because the subway DC traction power supply system has a lot of regenerative braking energy,with high power and frequent braking,a high energy density lithium battery and a high power density super capacitor hybrid energy storage device can meet its characteristics and can also be used as an emergency backup power source for emergency rescue of trains when a wide area power failure occurs.Based on the traditional fixed power threshold control strategy of hybrid energy storage system,this paper considers the shorter life of lithium batteries compared to supercapacitors,dynamically adjusts the lithium battery power threshold to reduce the battery charge and discharge cycle depth.Part of the single-interval energy-saving benefits are transferred to the full life cycle of the lithium battery,thereby improving the overall revenue of the hybrid energy storage device.The paper first establishs the models of the traction substations and trains in the DC traction power supply system and analyzes the characteristics.Then it analyzes and models the lithium-ion batteries and supercapacitors in the hybrid energy storage system,and establishes the service life prediction model of the batteries,and the principle analysis and simulation verification of the control effect of the multiplexed DC/DC converter is done,which provides a theoretical basis for the study of control strategies for hybrid energy storage systems.Secondly,considering the economic benefits such as the energy saving effect of hybrid energy storage devices and the shorter cycle life of lithium batteries compared to super capacitors,this paper proposes a dynamic power threshold control strategy based on battery SOC following.This strategy effectively adjusts the lithium battery charge and discharge power threshold,regulates the lithium battery power output,reduce the depth of the lithium battery charge and discharge cycle,and effectively prolongs the battery life.At the same time,according to the characteristics of different regenerative braking energy in different departure intervals,the optimal control parameters are obtained through offline optimization of the optimization algorithm to maximize the energy-saving benefits of the hybrid energy storage device.The validity of the control strategy is verified by the multi-station and multi-vehicle simulation platform.Finally,this paper builds a prototype of a 1MW wayside lithium titanate battery-supercapacitor hybrid energy storage system,expounds the software and hardware design of the system and verifies its functionality through experiments.The experimental results show that the prototype of the hybrid energy storage system can run the dual-loop control strategy and achieve the effect of energy saving and voltage stabilization.