Research on the longitudinal protection of a through-type cophase traction direct power supply system based on the empirical wavelet transform

This paper proposes a longitudinal protection scheme utilizing empirical wavelet transform(EWT)for a through-type cophase traction direct power supply system,where both sides of a traction network line exhibit a distinctive boundary structure.This approach capitalizes on the boundary’s capacity to attenuate the high-frequency component of fault signals,resulting in a variation in the high-frequency transient energy ratio when faults occur inside or outside the line.During internal line faults,the high-frequency transient energy at the checkpoints located at both ends surpasses that of its neighboring lines.Conversely,for faults external to the line,the energy is lower compared to adjacent lines.EWT is employed to decompose the collected fault current signals,allowing access to the high-frequency transient energy.The longitudinal protection for the traction network line is established based on disparities between both ends of the traction network line and the high-frequency transient energy on either side of the boundary.Moreover,simulation verification through experimental results demonstrates the effectiveness of the proposed protection scheme across various initial fault angles,distances to faults,and fault transition resistances.

A preventive opportunistic maintenance method for railway traction power supply system based on equipment reliability

Conventional maintenance mode for the traction power supply system(TPSS)is to perform scheduled regular maintenance activities for power supply equipment,while such maintenance mode may result in undue maintenance tasks and low efficiency due to different degradation processes of different sorts of equipment.To address this problem,this paper introduces a preventive opportunistic maintenance(POM)method for TPSS based on equipment reliability.Firstly,a POM model is established by considering the equipment reliability degradation process based on Weibull distribution.Then,by considering the total power outage time in the planned operation cycle of TPSS as the optimization objective,the optimal maintenance scheme of TPSS is formulated by iterative method of maintenance strategies.The proposed method is verified by introducing practical maintenance strategies and fault record data of the traction transformer,circuit breaker and disconnector in an actual TPSS of a railway administration.Results show that the presented method can make full use of the existing fault data to develop a POM scheme for TPSS.It can improve maintenance efficiency and reduce power outage time,providing guidance to formulate scientific maintenance strategies for TPSS.

Industrial frequency single-phase AC traction power supply system for urban rail transit and its key technologies

To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system, an AC traction power supply system was proposed for the urban public transport such as metro and light rail transit. The proposed system consists of a main substation （MSS） and cable traction network （CTN）. The MSS includes a single-phase main traction transformer and a negative-se- quence compensation device, while the CTN includes double-core cables, traction transformers, overhead catenary system, rails, etc. Several key techniques for the proposed system were put forward and discussed, which can be summarized as （1） the power supply principle, equivalent circuit and transmission ability of the CTN, the cable-catenary matching technique, and the selection of catenary voltage level; （2） the segmentation technology and status identification method for traction power supply network, distributed and centralized protection schemes, etc.; （3） a power supply scheme for single-line MSS and a power supply scheme of MSS shared by two or more lines. The proposed industrial frequency single-phase AC traction power supply system shows an excellent technical performance, good economy, and high reliability, hence provides a new alternative for metro and urban rail transit power supply systems.

DC Traction Power Supply System Based on Modular Multilevel Converter Suitable for Energy Feeding and De-icing

A novel DC traction power supply system suitable for energy feeding and de-icing is proposed in this paper for an urban rail transit catenary on the basis of the full bridge submodule (FBSM) modular multilevel converter (MMC). The FBSM-MMC is a novel type of voltage source converter (VSC) and can directly control the output DC voltage and conduct bipolar currents, thus flexibly controlling the power flow of the urban rail transit catenary. The proposed topology can overcome the inherent disadvantages of the output voltage drop in the diode rectifier units, increase the power supply distance and reduce the number of traction substations. The flexible DC technology can coordinate multiple FBSM-MMCs in a wide area and jointly complete the bidirectional control of catenary power flow during the operation of the electric locomotive, so as to realize the local consumption and optimal utilization of the recovered braking energy of the train. In addition, the FBSM-MMCs can also adjust the output current when the locomotive is out of service to prevent the catenary from icing in winter. The working modes of the proposed topology are illustrated in detail and the control strategy is specially designed for normal locomotive operations and catenary de-icing. Simulation cases conducted by PSCAD/EMTDC validate the proposed topology and its control strategy.

FPGA-based Digital Implementation of Flexible Power Control for Three-phase to Single-phase MMC-based Advanced Co-phase Traction Power Supply System

A three-phase to single-phase modular multilevel converter based advanced co-phase traction power supply(MMC-ACTPS) system is an effective structure to address the concerns of phase splitting and poor power quality of the conventional electrified railway. Due to the large number of MMCACTPS system modules, I/O resources and computing speed have high requirements on processors. Moreover, the module capacitor balance is challenging because the sorting time is too long when the traditional sorting algorithm for voltage balance is used. To solve the above issues, a digital implementation scheme of flexible power control strategy for three-phase to single-phase MMC-ACTPS system based on field programmable gate array(FPGA), which has sufficient I/O resources, has been proposed. Due to the parallel execution characteristics of the FPGA, the execution time of the controller and the modulator can be greatly reduced compared with a digital signal processor(DSP) + FPGA or DSpace. In addition, an improved sorting algorithm is proposed to reduce the sorting time and the implementation steps are analyzed. Finally, simulation and experimental results are presented to demonstrate the effectiveness and correctness of the proposed control strategy.

A power-quality monitoring and assessment system for high-speed railways based on train-network-data center integration

In recent years,with the rapid development of high-speed railways(HSRs),power interruptions or disturbances in traction power supply systems have become increasingly dangerous.However,it is often impossible to detect these faults immediately through single-point monitoring or collecting data after accidents.To coordinate the power quality data of both traction power supply systems(TPSSs)and high-speed trains(HSTs),a monitoring and assessing system is proposed to access the power quality issues on HSRs.By integrating train monitoring,traction substation monitoring and data center,this monitoring system not only realizes the real-time monitoring of operational behaviors for both TPSSs and HSTs,but also conducts a comprehensive assessment of operational quality for train-network systems.Based on a large number of monitoring data,the field measurements show that this real-time monitoring system is effective for monitoring and evaluating a traction-network system.

Overview of Resilient Traction Power Supply Systems in Railways with Interconnected Microgrid

In recent years,the achievement of a renewable and sustainable traction power supply system(TPSS)in the rail sector has become a significant challenge.Focusing on this issue,this paper firstly provides a comprehensive overview and classification of the state-of-art TPSSs in DC and AC railway.Then,together with low voltage(LV)DC,medium voltage(MV)DC,LV AC,and hybrid AC/DC interconnected microgrid(IMGs),various architectures of resilient TPSSs are proposed for renewable energy integration into DC and AC railway.The resilient TPSS offers on-site access and local consumption of renewable sources alongside railways and guarantees a sustainable power supply in the case of grid disturbances and failures,e.g.,voltage unbalance,harmonic and violent fluctuation,power outage,and extreme events in the wake of natural disasters and extreme weather.This approach also helps facilitate the development of the next generation TPSSs for enhanced flexibility and sustainability.Then,based on a comparative analysis of different resilient TPSSs,a brief outlook of the future trend is given.Finally,it is concluded that resilient TPSS provides a universal solution for both renewable energy integration and high-quality power supply against grid disturbances and failures.