Research On Capacity Optimization And Energy Management Strategy Of Urban Rail Transit On-board And Wayside Energy Storage System

With the rapid development of energy storage technology,energy storage methods have become the mainstream solution of the problem of urban rail regenerative energy utilization worldwide,including two types of applications: wayside and on-board.Since either wayside energy storage system or on-board energy storage system can effectively reduce the probability of regenerative braking recovery failure on the premise of ensuring the energy saving rate,in order to improve the utilization rate of regenerative braking energy,this paper proposes to replace the braking resistors with the on-board energy storage system,combined with the wayside energy storage system,absorbs regenerative braking energy and stabilizes the voltage of the traction network,effectively suppressing the occurrence of regenerative braking recovery failure.This paper mainly focuses on the application of the on-board and wayside energy storage system,conducts theoretical research on the establishment of the equivalent model,the optimization of capacity allocation,and the control strategy of charging and discharging thresholds,and carries out simulation verification according to the actual urban rail line.First of all,an equivalent model of urban rail transit DC traction power supply system including traction substations,trains,and energy storage systems is established.Through power flow analysis,it is verified that due to the limitation of transmission distance,pure wayside energy storage systems cannot recover all regeneration braking energy,even if the capacity is infinite.The residual regenerative braking energy will cause the DC traction grid voltage to rise,so that regenerative recovery failure occurs.The on-board and wayside energy storage system proposed in this paper can better solve this problem.The use of a small-capacity on-board energy storage system can recover the remaining regenerative braking energy that cannot be recovered by the pure wayside energy storage system.Furthermore,for the capacity configuration optimization of multi energy coupling system such as urban rail transit,the overall benefit needs to be considered.The capacity configuration optimization algorithm of on-board and wayside energy storage system proposed in this paper uses the non dominated genetic algorithm with elite strategy to realize the multi-objective and multivariable optimization of economic benefit rate and energy saving rate.The on-board energy storage system has the ability to provide emergency traction energy for trains.The traditional multi-objective optimization algorithm transforms the artificial weighting calculation of the objective function into a single objective function for optimization.However,the non dominated genetic algorithm can avoid the irrationality of artificially defining the weight through the congestion calculation.Compared with the pure wayside energy storage,the case study shows that the optimized capacity configuration results in an energy-saving rate of8.41% and an economic benefit rate of 6.57%.The optimization results of capacity configuration lay a foundation for the subsequent research on energy management strategy of energy storage system.Lastly,because the traditional fixed threshold control strategy has a significant difference in energy saving effect when the DC grid voltage fluctuates,this paper proposes a threshold control strategy that combines offline optimization and online optimization.Under the condition of headway,the reference value of charge and discharge threshold is optimized offline by genetic algorithm,and the offline optimization result is used as the initial condition of online optimization.When the train is running,if the no-load voltage rises and the reference threshold can no longer effectively recover and release the braking energy of the energy storage system,the online control strategy corrects the charging and discharging threshold by calculating the recovered energy value of the energy storage system.The simulation analysis based on the actual operation of the subway line shows that the online optimization control strategy can complete the correction of the charging and discharging threshold within 4to 7 headways.The threshold control strategy can make the energy storage system effectively suppress the adverse effects caused by no-load voltage fluctuations,and ensure the good energy saving effect of the energy storage system.