| The railway is the main artery of the national economy,critical infrastructure and major livelihood projects.It is one of the backbones and main modes of transportation of the integrated transportation system.Its status and role in China's economic and social development are of vital importance.Railway transportation has the comparative advantages of large volume,low energy consumption,and low emissions.It is recognized as one of the most environmentally friendly transportation methods,but it is also a large energy consumer.With the increase in population worldwide and the rapid development of electrified railways,the energy consumption of the railway industry will continue to increase further.Therefore,in today's era of increasing global demand for resources and increasingly prominent environmental problems,it is essential to realize energy conservation,emission reduction and green development of electrified railway systems.Electric locomotive will generate a large amount of regenerative braking energy(RBE)during the braking process.China has many railway lines and the terrain along the railway is complex,which makes China's railways contain a lot of RBE.If the RBE generated by electric locomotives can be sufficiently and efficiently used inside the railway traction power supply network,which can not only reduce the energy consumption of railway transportation and ensure the economical and efficient operation of the traction power supply system,but also reduce the carbon emissions of China's and even the global railway transportation industry,thereby making a great contribution to the environment-friendly society.In order to improve the utilization rate of RBE generated by electric locomotives,alleviate the pressure on public power grids,and reduce the operating costs of transportation companies,this paper proposed an intelligent system for RBE utilization of railway locomotives.This system can collect the data of traction power grid in real time,and use intelligent optimization algorithms for analysis and calculation to form the optimal control decision of the full-line RBE.This decision can control the cooperative operation of multiple bidirectional power electronic converters,realizing the sufficient utilization of RBE in the traction power supply system and reducing the cost of locomotive power consumption.In addition,the system can also realize the functions of improving the power quality of the traction power supply system,cutting peaks and filling valleys,using clean energy,active voltage control of the contact network,and using as a railway emergency power supply.It can further improve the intelligence level of the railway traction power supply system and promote the construction of smart railway grids.First,the subject background,research significance,and current research status at home and abroad are summarized.The current railway energy consumption level and the ability of electric locomotives to generate RBE are analyzed,and the results shown that the recovery and utilization of railway locomotive RBE would be of great significance for the energy conservation and consumption reduction of electrified railways.The existing schemes of RBE utilization for electric locomotives are summarized,and the advantages,disadvantages and application limitations of each RBE utilization scheme are introduced.Based on this,with respect to the bottlenecks of existing RBE utilization schemes and the characteristics of railway traction power supply systems,an intelligent system for RBE utilization of railway locomotives is proposed.The system has the advantages of high RBE utilization rate,high reliability,and high level of intelligence.Then the basic working principle and working mode of the proposed energy utilization system are introduced,and the mathematical model of the energy utilization system is established.The structure composition and working mode of the energy utilization system are introduced,and the ability of the energy utilization system to utilize RBE is analyzed.The model of traction power supply system with energy utilization system is built,including the traction substation,traction network,and power transferring device.By using this model,the voltage,harmonic voltage and harmonic current distributed on each conductor in the traction network during RBE transmission can be analyzed,thereby predicting the impact of RBE on the traction power supply system during transmission.Furthermore,the control strategies of power transferring device(PTD),energy-storage-based power transferring device(EPTD)and control strategy of central controller are given.From the perspective of the overall function of the device,the control strategies of PTD and EPTD for regulating RBE are given.A high-power PTD and EPTD topology is selected.with respect to the cascaded H-bridge structure in the rectifier side of this topology,a capacitor voltage balance control strategy based on capacitor energy feedback is proposed to balance the DC-side capacitor voltage in each bridge.In order to ensure the stability of high-power PTD and EPTD operation,the power transmission range limits are analyzed theoretically,and and the overall control strategy of high-power PTD and EPTD for regulating RBE is given.A centralized control strategy for RBE utilization in the overall traction power supply system is proposed to control the coordinated operation of all PTDs and EPTDs,so as to achieve the efficient utilization of RBE in the overall line.Next,in order to improve the economy and efficiency of the proposed energy utilization system,and maximize the potential of the proposed energy utilization system,some optimization control strategies are further proposed and other functions of the energy utilization system are developed.The control strategy of energy utilization system for improving power quality is given,and the control method and compensation current detection method for improving power quality under different working conditions are analyzed.the capacity of EPTD when improving power quality is analyzed,and the influence of RBE and energy storage system on the EPTD capacity is discussed.Then,combined with the characteristics of the energy utilization system structure,a capacity optimization method of using PTD to share the reactive power compensated by EPTD is proposed to reduce the operation capacity of EPTD.Then,in order to improve the reliability of the energy utilization system,a centralized-decentralized control strategy is proposed,which can quickly restore the utilization ability of the RBE of the energy utilization system in the event of a failure,thereby enhancing the ability of the energy utilization system to withstand the failure.An capacity optimization method of energy storage system based on statistic method is proposed to configure the capacity of the energy storage system,thereby realizing the cost-effective operation of the energy utilization system.Other functions of the energy utilization system,including peak cutting and valley filling,clean energy utilization,active voltage control of the contact grid,and railway emergency power supply,are developed,thereby further improving the intelligence of the traction power supply system.Finally,the theory proposed in this paper is verified by simulation and experiment.The simulation model of traction power supply system,PTD and EPTD is built by using Matlab / simulink simulation platform.By the use of the above models,the control strategy of adjusting RBE and the control strategy of improving power quality based on PTD and EPTD are verified.A small power experimental prototype is built to verify the capacitor voltage balance control strategy and power transmission range limits proposed in this paper.In addition,the centralized control strategy,centralized-decentralized control strategy,and the capacity optimization configuration method of energy storage system are verified in Matlab.The results of simulation and experiment prove the correctness of the research in this paper. |
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