Research On Energy Management Strategy Of Urban Rail Wayside Hybrid Energy Storage System Based On Improved Ⅰ-Ⅴ Droop Curve Adjustment

In recent years,urban rail transit has developed rapidly,and the energy consumption of urban rail system traction has increased sharply.The addition of energy storage devices can reduce the energy consumption of train operation and reduce or avoid regeneration failure.Because the urban rail system has a large demand for energy and power,a hybrid energy storage system of lithium batteries and supercapacitors is adopted.Due to the high energy storage of the battery,the hybrid energy storage device can also be used as a backup power source to provide emergency traction energy for the train in the event of a power supply failure.For the energy management strategy research of ground hybrid energy storage,most of the focus is on internal battery and supercapacitor power distribution,ignoring the influence of external charge and discharge threshold on internal power distribution.Based on the traditional voltage and current dual closed-loop control strategy,this paper considers the characteristics of the urban rail system and the characteristics of energy storage components,integrates external and internal control into one level,and correlates the internal current with the external voltage.In order to improve the energy saving rate of the system,the control strategy of the ground hybrid energy storage system of battery and supercapacitor is optimized.The paper firstly models the substation and the train in the urban rail system,builds a simulation platform for the urban rail transit traction power supply system,analyzes the energy flow characteristics of the train at different departure intervals,and analyzes the control effect of the energy storage device under different capacities and powers,and then proposed the necessity of a hybrid energy storage system.According to the relationship between the train and the state of the hybrid energy storage device,the energy flow is divided into 7 situations,and the microscopic analysis is carried out.According to the voltage suppression effect of the traction network,the interaction of trains,and the influence of no-load network voltage fluctuations,the control effects of the 3 energy management strategies are analyzed to provide a theoretical basis for the subsequent proposal of energy management strategies for hybrid energy storage systems.Secondly,considering the operation characteristics of urban rail trains and the characteristics of energy storage components of hybrid energy storage devices,this paper proposes an energy management strategy based on improved Ⅰ-Ⅴ droop curve adjustment.This strategy combines the external charge and discharge threshold with the internal charge and discharge current of the battery and supercapacitor,sets different starting voltages for the battery and supercapacitor,and makes the charging current increase with the increase of the network voltage,and the discharge current increases with the decrease of the network voltage,which realizes the fluctuation of the network voltage within a certain range and increases the train interaction energy.According to the analysis of the influence of train operating conditions and charging and discharging control parameters,the adjustment principle of the control parameters is determined,and the parameters are optimized on this basis,so that the starting voltage difference varies linearly according to the departure interval.And according to the use range of the supercapacitor and the energy consumption of the braking resistor under the initial parameters,adjust the minimum allowable voltage to achieve optimal control of the energy storage element.While reducing the braking resistance loss,it also increases the utilization rate of supercapacitors,reduces the utilization rate of batteries,and improves the overall performance of the energy storage device.The effectiveness of the proposed control strategy is verified by a multi-station and multi-vehicle simulation platform based on actual lines.Finally,the 1MW ground lithium titanate battery and supercapacitor hybrid energy storage device developed in this paper was used in the field tests at Liyuan Station on the Batong Line of the Beijing Metro.The performance of the energy storage device was verified by night single train experiment.The daytime experiment verifies the problems existing in the traditional control strategy.Then,the proposed energy management strategy based on the improved Ⅰ-Ⅴ current curve adjustment was verified by a ground battery and capacitor energy storage system control strategy verification experiment platform.