Train Operating Conditions Research Articles

A Markov Model for Subway Composite Energy Prediction

Electric vehicles such as trains must match their electric power supply and demand, such as by using a composite energy storage system composed of lithium batteries and supercapacitors. In this paper, a predictive control strategy based on a Markov model is proposed for a composite energy storage system in an urban rail train. The model predicts the state of the train and a dynamic programming algorithm is employed to solve the optimization problem in a forecast time domain. Real-time online control of power allocation in the composite energy storage system can be achieved. Using standard train operating conditions for simulation, we found that the proposed control strategy achieves a suitable match between power supply and demand when the train is running. Compared with traditional predictive control systems, energy efficiency 10.5% higher. This system provides good stability and robustness, satisfactory speed tracking performance and control comfort, and significant suppression of disturbances, making it feasible for practical applications.

Track Map–Aided Capture of Virtual Balises: A Compatible Approach to Satellite-Based Railway Train Control

The use of a Global Navigation Satellite System (GNSS) is a significant requirement of next-generation railway train control systems. As one effective approach to integrate the GNSS positioning service into a train control system, the virtual balise (VB) solution makes it compatible with current system specifications and ensures the benefits in terms of cost efficiency and the autonomy of the train-borne subsystem. To create a VB system that performs normal balise functions, the standard VB solution suggests a capture interval (CI). However, a fixed CI cannot adapt to different train operating conditions, and thus, a full VB capture rate cannot at the same time be guaranteed with the desired spatiotemporal capturing accuracy level. In this study, a novel VB capture solution is proposed. The track map is involved in the VB capture to enable map matching of train location, interactive multiple model–based forward prediction of the next VB approaching status, and identification of the exact capture time. A field test of high-speed railway with accurately measured balises shows that the proposed approach can realize the full availability of VB capture without the difficulty of having to select a unique CI value. The capturing error and time offset are greatly reduced compared with the standard VB capture strategy using different CIs, which is significant for the future development and implementation of novel train control systems.

Traction Power Substation Load Analysis with Various Train Operating Styles and Substation Fault Modes

The simulation of railway systems plays a key role in designing the traction power supply network, managing the train operation, and making changes to timetables. Various simulation technologies have been developed to study the railway traction power network and train operation independently. However, the interactions between the load performance, train operation, and fault conditions are not fully understood. This paper proposes a mathematical modeling method to simulate the railway traction power network with a consideration of a multi-train operation, driving controls, under-voltage traction, and substation fault modes. The network voltage, power load demands, and energy consumption according to the existing operation are studied. The hotspots of the power supply network are identified based on an evaluation of the train operation and power demand. The impact of traction power substation (TPSS) outage and a short circuit on the power supply network have been simulated and analyzed. The simulation results have been analyzed and compared with those of a normal operation. A case study based on a practical metro line in Singapore is developed to illustrate the power network evaluation performance.

Properties of rubber under-ballast mat used as ballastless track isolation layer in high-speed railway

Rubber under-ballast mats (UBM) commonly used in metro traffic in China are applied in high-speed railway ballastless tracks as the isolation layer to improve the operating conditions of high-speed trains. Due to the different operating conditions between the high-speed railway and the metro traffic, the rubber UBM, used as the isolation layer in ballastless tracks, needs to be investigated furtherly. In this paper, a finite element analysis of the China Railway Track System (CRTS) III ballastless track was initially carried out, and the stress state and distribution of the rubber UBM used as the isolation layer were obtained at the service condition. Furthermore, the static, dynamic and fatigue tests of the rubber UBM samples were designed and carried out based on the analysis results. The main conclusions are as follows: under normal service conditions, the stress level of the rubber UBM is low, and it can be considered that the rubber UBM is still in the stage of linear elasticity. The material properties of the rubber UBM can be characterized by the equivalent elastic modulus, which has been determined to be 0.6 MPa by the experimental research. Furthermore, the dynamic characteristic of the rubber isolation layer exhibits a hysteresis phenomenon. The equivalent dynamic stiffness is larger than the equivalent static stiffness due to the viscoelastic characteristics of rubber material. The rubber UBM has large internal friction, high energy absorption rate and good damping performance characterized by its large loss factor. In addition, following the application of 3,000,000 repeated load, which is 1.5 times of a train axle load, the equivalent static stiffness only changes by 2%, indicating that the rubber UBM used as an isolation layer can maintain good mechanical performance under repeated loading. As such, the appropriate selection of rubber UBMs for the isolation layer in ballastless tracks can be made following the analysis and investigation of its performance characteristics.

Calculation and Optimization of Propulsion Force of a Real-Scale REBCO Magnet for EDS Train

Electrodynamic suspension (EDS) train has the unique advantages of excellent levitation and guidance stabilities, large levitation gap, and so on. All of these merits make it a promising candidate for the future ultra-high-speed transportations, in which the high-temperature superconducting (HTS) linearly synchronous driving motor (LSM) plays an important role because of the decrease of energy consumption of HTS magnet. This paper, which serves as a fundamental study on the HTS synchronous driving system of EDS train, is aimed to calculate the propulsion force of LSM and optimize the propulsion fluctuation. First, in order to define the operating current of LSM, the critical current of a real-scale REBCO coil was numerically estimated using the so-called T-A model. Second, based on the Neumann formula and virtual displacement method, an analytic model to estimate the propulsion force of LSM was established and verified by comparing results with a finite-element method (FEM) numerical model. Finally, by resorting to the validated analytic model, the geometric parameters of propulsion coil were optimized, and then using the optimal parameters, the maximum electromagnetic forces of LSM under different operating conditions of EDS train were calculated. It was found that the linearly driving system inherently keeps robust driving stability to the lateral and normal displacements.

<b>Development of a Telecommunication and Train Operation Simulator for Radio Communication Train Control</b>

When bringing radio communication train control systems into service, it is essential to establish conditions that will allow stable radio communications, and take into account train operating conditions. As such a radio telecommunications and train operations simulator to forecast train operation was developed, that takes into account radio wave propagation and telecommunications networks. In addition, using the simulator, a system design flow chart was designed to ensure that certain basic criteria are met. This paper describes the simulator, and the design flow chart, and presents the results from a case study carried out using the simulator.

Analysis and Adaptive Mitigation Scheme of Low-Frequency Oscillations in AC Railway Traction Power Systems

The diffusion of modern electric trains equipped with high-power voltage-source converters has introduced new dynamic interactions with the ac traction power system that may create unexpected low-frequency oscillations (LFOs). This paper presents for the first time a detailed analysis of the operating conditions of electric trains and a traction network, revealing that specific changes in the operating conditions of the train-network system are responsible for the oscillations and may lead to instability. The study is carried out with an analytical dynamic model considering the transient direct current control and focuses on evaluating how the mismatch between the parameters of the controller and the controlled object of the train-network system affects the system dynamics and stability. It is shown that the retuning of controller parameters improves the dynamic performance and the stability of the train-network system, and hence an adaptive mitigation method is proposed to mitigate LFOs adopting a new design of the controller with minimal change and cost to the original system, which provides a simple solution to guide engineering practice in railway traffic. Simulations and experimental results are presented to fully validate the proposed method.

Train distance and speed estimation using multi sensor data fusion

The accurate distance and speed estimates of train and individual coaches are necessary for the safe operation of the high-speed train system. Often, the train system does not rely on a single sensor for its distance and speed measurements as the sensors are susceptible to diverse operating conditions such as snow, rain, fog, tunnel, hilly region, slip, slide, etc. Hence, the information from a combination of sensors which can complement each other under certain operating conditions is required for the correct estimation. For distance measurements, Global Navigation Satellite System (GNSS) and balise are generally used. For speed sensing, the combination of wheel sensor, radar and GNSS are chosen. The diversity of sensors in terms of sampling rate and noise characteristics, etc. greatly affect the overall estimation accuracy and reliability if the measurements are used directly. Hence, this work presents a probabilistic weighted fusion algorithm which is based on the nonlinear longitudinal train dynamic model. The fusion algorithm combines the state estimates from distributed and sensor-specific extended Kalman filters. The effectiveness of the proposed fusion algorithm is demonstrated on the simulated sensor measurements along with a wide range of noises, spurious measurements, train operating conditions and track environmental disturbances.

Prediction and mitigation of train-induced vibrations of large-scale building constructed on subway tunnel

Among all the recent improvements in the railway industry, ground vibration remains an important showstopper in metropolitan cities. In some particular cases, significant levels of vibration are felt by residents. The role of engineers is to propose mitigation solutions and to ensure that they are efficient in the long-term. This paper presents a numerical study of a large-scale building close to underground networks. A two-step time-frequency prediction method for train-induced vibrations of a superstructure is proposed in this work. In the first step, the spatial train-track coupled dynamic model in time domain is established and then simulated to obtain the vertical and lateral rail supporting forces (fastener forces). In the second step, the discrete Fourier Transform (DFT) of fastener forces are taken as the external loads of a finite element (FE) model of the track-tunnel-soil-building system to solve the building vibrations. On this basis, train-induced vibrations of the large-scale building are predicted under different train operation conditions, and two relevant standards are adopted to evaluate the building vibrations. Further, a base isolation measure, that consists in installing steel springs between the superstructure and the base, is employed to mitigate excessive building vibration. Results show that the underground train and track interaction could result in over-limit building vibrations. The train moving with a higher speed will deteriorate track vibration level and leads to more serious extent of over-limit vibrations of the larger-scale building. The base isolation measure can effectively reduce the excessive building vibrations, and also ensures the train-induced vibrations of the building to satisfy the relevant standard requirements under the worst train operation conditions.

重载列车运行工况仿真与试验比较研究

重载列车运行工况仿真与试验比较研究

An approach for pillow plate heat exchangers design for single-phase applications

Pillow-plate heat exchangers (PPHEs) represent a novel equipment type. For their application in industry, reliable preliminary design techniques are required. In this article, the existing methods for heat exchangers design are analysed and the approach for selecting the PPHE design with minimal heat transfer area is proposed. It is based on the mathematical model of thermal and hydraulic PPHE behaviour, in which the overall heat transfer coefficient and pressure drop in PPHEs are expressed through the fluid velocity. The estimation of fluid velocities in PPHE channels is based on the condition that the predefined allowable pressure drop is fully exploited. Two case studies for water heating and crude oil preheat train operating conditions are discussed, in which the flowrates of the fluids on the hot and cold sides differ significantly. The PPHE design with minimal heat transfer area for the considered case studies is presented, with specified pillow-plate geometry parameters and distance between pillow-plate panels. The resulting pressure drops and velocities in PPHEs channels as well as the obtained heat transfer surface areas are compared with existing data for chevron-type plate heat exchangers (PHEs) designed for the same operating conditions. This comparison shows that PPHEs have higher velocities in channels, longer plates and lower heat transfer area. It can be concluded that PPHEs can be successfully used for operating conditions, under which the flow rates for hot and cold fluid are significantly different and the application of chevron-type PHEs with single-pass arrangement is complicated.

The Braking Behaviors of Cu-Based Metallic Brake Pad for High-Speed Train Under Different Initial Braking Speed

The purpose of this research was to study the braking behaviors of Cu-based composite pad under real operating conditions of high-speed train. A series of pad-on-disk braking tests was performed with the initial braking speed (IBS) from 80 to 380 km/h. Results showed that the coefficient of friction (COF) of the brake pad demonstrated a three-stage feature with the increase in IBS. It decreased from 0.395 to 0.358 with the increase in IBS from 80 to 200 km/h, then increased to 0.398 when IBS reached 320 km/h; and fell again to 0.379 at 380 km/h. Similarly, the pad also displayed three wear regimes as IBS increased, i.e., (1) mild wear (80–160 km/h), (2) moderate wear (200–250 km/h), and (3) severe wear (300–380 km/h). Surface morphologies and phase analyses indicate that the evolution of the COF mainly depends upon the state of friction film. The formation or completion of friction film regularly contributes to a lower COF and wear rate, while the destruction of friction film results in a higher COF and wear rate. Besides, the “lubricants” induced by high braking temperature are also responsible for the change in the COF. As IBS increased, the key wear mechanisms changed from abrasion, plowing, and oxidation to delamination at 250 km/h.

Evaluation of Stray Current From a DC-Electrified Railway With Integrated Electric–Electromechanical Modeling and Traffic Simulation

Leakage currents from a dc-electrified railway requires careful consideration throughout the life time of the railway. The design objective is to minimize the current leakage from the railway return path (the running rails for a dc-electrified railway, with possibly additional conductors in parallel for ac-electrified systems). For this objective to be met, the design needs to account for foreseeable misuse during the construction phase (i.e., the lack of independence between the earthing system and the stray current collection system, due to space and construction exigencies in a viaduct) and degradation of insulation due to ageing and poor maintenance. Perhaps, more importantly, other influences, such as the train characteristics, time tabling, headway, multiple train movement, etc., need consideration to determine the worst case leakage current and, thus, the ability to define appropriate mitigations with respect to stray current management. In this paper, we describe the implementation of an integrated model for the assessment of stray current for a dc-electrified railway, in which these factors are considered. We provide an analysis of the stray current magnitude under worst case train operating conditions (i.e., multiple trains with a 90-s headway accelerating) and highlight factors that determine the efficiency of the stray current collection system. The integrated model presented enables a detailed assessment of all factors impacting the stray current magnitude, as well as an assessment of the overall performance of the stray current collection system.

Passive Filter Design for China High-Speed Railway With Considering Harmonic Resonance and Characteristic Harmonics

In order to make high-speed trains (HSTs) lighter and more reliable, LC or LCL high-pass filters, which are widely adopted to mitigate high-order harmonics, are not installed in most of China HSTs. Therefore, the harmonic problem is a concern, because of the significant adverse impacts it has on the tractive drive system of the train and power quality of the utility system. The harmful harmonic distortions in high-speed railways (HSRs) are mainly caused by harmonic resonance and massive characteristic harmonics emission. This paper presents the results of harmonic assessment and harmonic filter design for a typical HSR line in China. Harmonic penetration analysis (HPA) is implemented and carried out to determine the harmonic distorted types for a wide range of possible train-operating conditions in a timetable. Both statistical field test and numerical calculation are used in passive filter design for HSRs. A C-type filter is designed here to address these typical harmonic distortions. The studies will be validated by detailed simulations based on the train timetable by counting the 95% index of the 24-h profile of harmonic results.

The Development Of A Neural Network-based Multi-function Protection Relay

The protection of DC traction circuits from fault conditions is a difficult task. The paper describes the development of a neural network to be used in a multifunction protection relay. The neural network developed can discriminate between normal train operation and short-circuit conditions on the DC traction supply. The neural network provides fault protection and location. The neural network was trained and tested using both simulated and actual data. The paper presents results showing that the neural network can discriminate between faults on a DC traction system and the normal operation of both camshaft and chopper controlled rolling stock. Conclusions are given on the advantages and disadvantages of using neural networks, along with their possible use in also locating a fault.