Application Of Hybrid Energy Storage System In Urban Rail Transit

As a kind of comfortable means of transportation with high-speed,safe and stable operation,large passenger capacity and basically free from weather change,urban rail transport industry is developing quickly,which has become one of the important factors to measure the urbanization process.However,the frequent braking or deceleration of urban rail train will generate a large amount of regenerative braking energy.Supposing that the section of energy can be utilized effectively,the urban rail transport industry will enter a new stage of development.Aiming at the regenerative braking energy generated in the running process of urban rail train,there are currently three ways to absorb energy: resistance consumption type,inverter feedback type and energy storage type.In the light of the comparative analysis of system structure,working principle,advantages and disadvantages of these three energy utilization methods,the energy storage type is finally selected to recycle the regenerative braking energy.This way not only can ensure the safe and stable operation of urban rail train but also can raise the utilization rate of energy,and the way will not produce harmonic pollution to the AC power grid.Firstly,the equivalent circuit model of 24 pulse uncontrolled rectifier unit in traction substation,equivalent circuit model of DC traction network,urban rail train model are analyzed and established.Moreover,a simulation model is built for verification,and the results show that the 24-pulse uncontrolled rectifier can basically meet the requirements of the urban rail transit power supply system.Secondly,according to the performance analysis of several energy storage elements,the combination of super capacitor and lead-acid battery is selected as the energy storage device of the power supply system.Two bidirectional DC/DC converters are used to connect the energy storage elements to the DC traction network bus in parallel.By analyzing the working principle of bidirectional DC/DC converter,the small signal model of the equivalent circuit of energy storage device in different modes is established to prepare for the next control strategy.Stabilizing bus voltage of DC traction network by voltage outer loop control strategy,and this module outputs the reference power of the hybrid energy storage device.Based on the first-order low-pass filtering method,the optimal allocation of reference power is achieved by using the state of charge partition management of super capacitor.And this method can protect the state of charge of the super capacitor.Using traditional limit management to manage the state of charge of the lead-acid battery.This module can output the reference current of each energy storage element.The current inner loop control strategy determines the working mode of the system by comparing the magnitude of the reference current and the actual current and then outputting drive pulses.Finally,the simulation model of power allocation of the first-order low-pass filter and the optimal power allocation model based on the sub-regional management of the state of charge of super capacitor are built on the Matlab/Simulink platform to verify the presented control strategy.The results show that the presented control strategy can reduce the fluctuation of bus voltage of DC traction network and keep it in normal range.In addition,compared with the first-order low-pass filter power allocation method,the optimal power allocation method can protect the state of charge of the super capacitor.Ensure that the super capacitor can discharge more and charge less in high state of charge,and charge more and discharge less in low state of charge.