Utilization Scheme Of Regenerative Braking Energy In Hub Traction Substation Of Electrified Railway

With the increasing networked extend of electric railways in China,a large number of hub traction substations(referred to as hubs)are formed by interweaving multiple railway lines.The characteristics of hubs can be concluded below: 1)Numerous number of power supply lines and heavy traffic density cause high traction energy consumption;2)A great number of trains with frequent start and stop create abundant regenerative braking energy;3)Regenerative braking energy which is not utilized fully at present,can be taken advantage of by various potential way.Therefore,in order to handle the problem of increasing energy consumption of electric railways,it is an urgent necessity to effectively recover and utilize the regenerative braking energy of hubs.However,the research nowadays is faced with available challenges,such as: 1)The load characteristics in the hub should be consulted to design a propriate utilization way of regenerative braking energy that corresponds to its energy characteristic;2)It is demanded to develop corresponding reasonable energy management and control strategy aiming at different power flow control equipment;3)A protection scheme attaching to the original systems is needed for security and reliability.To address the problems mentioned above,this paper established a hub regenerative braking energy utilization system and a utilization program is then planed based on the analysis of measurement load data.Energy management and control strategies are proposed with considering dynamic power feedback,and the corresponding protection system is designed.Firstly,based on the measured energy consumption data,the utilization mode of the regenerative braking energy of the hub is determined by analyzing the load characteristics of the traction power supply system of railway hubs and the 10 kV power system and revealing the inner relationship.Secondly,regenerative braking energy utilization system in a hub traction substation is designed,which combines transfer utilization,energy feed utilization and energy storage utilization.The operating principles of each system component are explored in detail.Based on the energy supply and demand relationship between various components in the system,the system energy management strategy is formulated with the goal of maximizing the reuse of regenerative braking energy and minimizing equipment power losses.On this basis,by dividing the operation mode of the system and analyzing the system power flow paths under different operation modes,a hierarchical control strategy considering dynamic power feedback is designed,where the strategy in the upper layer realizes the power flow management of the system in different operating modes and the other in the lower layer controls the converter to follow the upper layer reference commands to realize the power flow control.Furthermore,combining with available protections of hub traction substations and 10 kV power distribution stations,and on the ground of the principle that "energy utilization equipment failure does not affect the operation of the original system",the distinction is made among three levels,which are "system level","equipment level" and "early warning level",to design the protection scheme of the regenerative braking energy utilization system with hierarchical control in the hub.Finally,a simulation platform for the regenerative braking energy utilization system of the hub is built based on MATLAB/Simulink.12 operation conditions and 3 comparative operation conditions of the system are collaborated to verify the basic functions,energy management,control strategies and protection schemes of the energy utilization system.In the platform,the regenerative braking energy utilization system of the hub can realize not only several basic functions,such as bus power balance of the traction power supply system,DC bus voltage stabilization,and grid connection of the energy feed device under the unit power factor,but also effectively coordinate and control the kinetic energy in regenerative system on demand.The results indicates that the regenerative braking energy utilization system of the hub can achieve the efficient use of the regenerative braking energy of the hub and the proposed protection scheme can remove the fault in time and ensure the system operating safely.