High-speed Railway System Research Articles

Toward Traffic Patterns in High-Speed Railway Communication Systems: Power Allocation and Access Selection

In high-speed railway communication systems, the distributed antenna systems are usually employed to mitigate frequent handover and enhance the signal-to-noise ratio to receivers. In this case, jointly optimizing downlink power allocation with antenna selection (PAWAS) can enhance system energy efficiency, while the channel state and traffic density are taken into account. Besides, two typical kinds of terrains with sparse and rich scatterings and three traffic patterns including delay-sensitive, -insensitive, and hybrid traffics are investigated in this paper. We show that severe small-scale fading decreases the ergodic capacity, which is quantitatively analyzed, and proved to be proportional to the number of selected transmit antennas. In addition, in case of delay-sensitive traffic, we show that the PAWAS can be viewed as generalized channel-inversion associated with transmit antenna selection. In case of delay-insensitive traffic, we show that when multiple antennas are selected, the power allocation can be viewed as channel-inversion, whereas when single antenna is selected, it is traditional waterfilling. In case of hybrid traffic, we prove that the optimal PAWAS method can be given by separately solving the PAWAS of its delay-sensitive and -insensitive parts. Simulation results validate our theoretical results and demonstrate that proposed PAWAS can minimize the average transmit power in cases of arbitrary traffic density and channel states.

Medium-Voltage AC Static Switch Solution to Feed Neutral Section in a High-Speed Railway System

A high-speed train (HST) is a single-phase load supplied by a three-phase AC grid. The HST produces unbalanced three-line currents affecting the power quality of the grid. To balance the asymmetries on average, railway feeding sections are supplied that rotate the three phases of the grid. An electric isolation segment, called the neutral section (NS), between different sections is necessary. The HST must pass through this 1.6 km NS without power supply. In this paper, a medium-voltage AC static switch solution to feed the high-speed train in the NS is proposed. Thyristor technology is selected to design the 25 KVAC static switch. A medium-voltage power electronics procedure design is proposed to ensure proper operation in the final application. An NS operation is analyzed to identify impacts within the electric system and solution requirements are developed. Then, a low-scale prototype is used to experimentally validate the solution based on thyristor technology and the medium-voltage AC static switch is designed. Limitations on power and voltage at the Mondragon University Medium-Voltage Laboratory do not allow testing of the AC static switch at nominal conditions. A partial test procedure to test sections of the AC static switch is proposed and applied to validate the solution. Finally, experimental results for the Cordoba–Malaga (Spain) high-speed railway in real conditions with an HST crossing the NS at 300 km/h are shown.

Ultrasonic guided wave-based switch rail monitoring using independent component analysis

Switch rails are indispensable components of high speed railway systems, which have stringent nondestructive testing requirements owing to the severe operating conditions. In this article, an ultrasonic guided wave method is proposed for defect detection and localization using independent component analysis (ICA). The temperature effect is included in the data matrix by a random selection of the signals measured at different temperatures. A damage index named the average standard Euclidian distance (ASED) is used to evaluate the deviations of the test signals from the baseline signals in the feature space consisting of the independent components for the defect detection. Once the defect existence is found, defect localization is conducted by another ICA-based decomposition of a new data matrix with additional test signals for the same defect. Independent components whose coefficient vectors show a high correlation with the standard step change vector are chosen to construct the ICA-based residual signal. Then the time instance and location of the defect is determined by observing the first very high peak occurring in the residual signals. A detectability index for defect location (DIDL) is proposed. Experimental validations are performed for the defects on the foot and web of a switch rail. The results of the ASED curves clearly indicate the existence of artificial defects, and the ICA-based residual signals show the location of the defects. The proposed method is found to be superior to conventional methods such as simple baseline subtraction and optimal baseline subtraction regarding the DIDL.

Effects of friction-based fixed bearings on seismic performance of high-speed railway simply supported girder bridges and experimental validation

This study investigated the seismic performance of simply supported girder bridges with a span length of 32 m. Those bridges were a common part in China’s high-speed railway system and used spherical bearings to connect girders and piers. First, a finite element model of the scaled bridge with a geometrical similarity ratio of 1:8 was established by OpenSees. Second, five seismic damage states of fixed bearings and piers were defined based on the deformation failure criterion. Finally, an incremental dynamic analysis and a pseudo-dynamic test were performed to evaluate the effects of friction-based fixed bearings on the seismic response and damage state of bearings and piers. Results show that the sliding of friction-based fixed bearings effectively restricts the force transmitting between piers and girders, and reduces the seismic damage of piers. Those bearings with a small friction coefficient lead to a large relative displacement between piers and girders, while those bearings with a large friction coefficient cause a large seismic force exceeding the yield load of piers. Therefore, an appropriate friction coefficient of friction-based fixed bearing should be determined to achieve an optimal seismic performance of bridge according to the specific conditions of bridge and ground motion inputs.

The reduced fluctuation in the electromagnetic forces of a coreless HTS linear synchronous motor

Two types of high temperature superconducting (HTS) linear synchronous motors (LSMs), which could be potentially used as the traction system of high speed railway were demonstrated in this work. One has a stator made of traditional ferromagnetic yoke and three-phase copper windings and the other has a coreless type stator. Different from the permanent magnet motor, the mover of the HTS LSM was made by HTS coils, which can provide high-intensity magnetic field. The HTS coils were electrically connected in series and powered by DC currents to behave as permanent magnets. To comprehensively study the developed HTS LSMs, finite-element models were established to predict its performance in terms of normal force and thrust force. To validate the simulation model, we designed and fabricated a three-dimensional force-measuring system, which could be used to measure the thrust and normal force of the HTS LSMs under different conditions. This work provides some basic knowledge for the study of the HTS LSM with coreless stator.

Effects of vertical ground motions on seismic vulnerabilities of a continuous track-bridge system of high-speed railway

A continuous bridge in high-speed railway is close to several known faults in China. Those faults, respectively at different distances from the bridge site, will produce different ground motions with the different ratios of vertical component to the horizontal component at the bridge site. It is necessary to identify the influence of vertical ground motions on the seismic responses and vulnerabilities of the track-bridge system. This paper solved this problem by carrying out an incremental dynamic analysis (IDA) and a further seismic fragility analysis on a widely used continuous bridge in China. The results show that the damage probabilities of most bridge and track components increase along with the increase of vertical part in ground motions. This trend is significant for the sliding layer of track part in the longitudinal direction and the piers of bridge part in any direction, however, insignificant for the bearings of bridge part in any direction. Moreover, this trend is more significant for the track part across the girder gap due to the different seismic responses of adjacent bridges. The seismic design of track-bridge system should rigorously take the vertical part of ground motions into account.

Low-Frequency Stability Analysis of Single-Phase System With $dq$-Frame Impedance Approach—Part II: Stability and Frequency Analysis

Nowadays, the power electronics-based systems sometimes present the low-frequency instability owing to the interaction between the power converters and the grid, such as the low-frequency oscillation (LFO) happening in the single-phase vehicle-grid (electric multiple units (EMUs)-traction power grid) systems of high-speed railway. To address this problem, the impedance-based stability analysis method is adopted. Given the grid impedance and the $dq$-frame converter impedance in the EMUs, several popular impedance-based stability analysis methods are compared, and their features and applicability are summarized. The generalized Nyquist stability criterion is then applied to more cases to validate the proposed impedance model for the single-phase converters, and excels in good estimation of the stability boundary and oscillation frequency. The analysis results are validated by the simulation and dSPACE tests. Through the comprehensive analysis in this paper, the mechanism of LFO in high-speed railway system is further elucidated, and it is suggested that the negative impedance of the converters will contribute to the LFO.

Low-Frequency Stability Analysis of Single-Phase System With dq-Frame Impedance Approach—Part I: Impedance Modeling and Verification

The utilization of a large number of power electronic converters in the high-speed railway system results in the low-frequency instability for the single-phase vehicle-grid system. In order to probe into the problem, the impedance-based approach is adopted. This paper focuses on the dq-frame impedance modeling and verification of the single-phase converters in the electric multiple units. The closed-loop input impedance modeling methods for both single converter and interleaved converters considering the second-order generalized integrator-based phase-locked loop (PLL) are put forward. Then, the dq-frame impedance measurement method for single-phase systems based on the Hilbert transform is proposed, and the modeling approach is verified by the frequency-domain simulations on the switching models. The good agreement of the model and simulation illustrates that the modeling method is suitable and accurate enough until half of the switching frequency. It is elucidated that the single-phase rectifier's impedance has the off-diagonal characteristic and the negative-impedance characteristic on the dd channel at low frequencies. Moreover, both the current and voltage controls have influences on the negative impedance shaping, while PLL does not.

Itinerary choice and advance ticket booking for high-speed-railway network services

This paper formulates and examines the passenger flow assignment (itinerary choice) problem in high-speed railway (HSR) systems with multiple-class users and multiple-class seats, given the train schedules and time-varying travel demand. In particular, we take into account advance booking cost of travelers in the itinerary choice problem. Rather than a direct approach to model advance booking cost with an explicit cost function, we consider advance booking cost endogenously, which is determined as a part of the passenger choice equilibrium. We show that this equilibrium problem can be formulated as a linear programming (LP) model based on a three-dimension network representation of time, space, and seat class. At the equilibrium solution, a set of Lagrange multipliers for the LP model are obtained, which are associated with the rigid in-train passenger capacity constraints (limited numbers of seats). We found that the sum of the Lagrange multipliers along a path in the three-dimension network reflects the advance booking cost of tickets (due to advance/early booking to guarantee availability) perceived by the passengers. Numerical examples are presented to demonstrate and illustrate the proposed model for the passenger assignment problem.

Parallel Intelligent Systems for Integrated High-Speed Railway Operation Control and Dynamic Scheduling

The information exchange gap between current operation control and dynamic scheduling in high-speed railway systems (HRSs) still exists, and this gap has hindered the further integrative improvement of HRSs. This paper aims to explore a feasible solution to bridging the information exchange gap for further improving the efficiency of HRSs, with the parallel intelligent systems for integrated HRS operation control and dynamic scheduling first analyzed and constructed using the ACP approach, that is, "artificial systems" (A), "computational experiments," (C) and "parallel execution" (P). Then, on the basis of the constructed parallel intelligent systems, experiments on several typical scenarios in HRSs are conducted to achieve a set of control and management strategies for actual HRSs. Experimental results show that a number of powerful tools provided by the proposed parallel intelligent systems can be utilized not only to study the current HRSs, but also to further undertake research on integrated operation control and dynamic scheduling for HRSs.

Model-based correlation between change of electrical resistance and change of dislocation density of fatigued-loaded ICE R7 wheel steel specimens

Abstract Weight-optimized component design as well as a reliable estimation of the lifetime of metallic materials and components require a comprehensive understanding of fatigue processes and a systematic investigation of the underlying fatigue behavior. This becomes even more important when designing highly loaded components such as wheels of high-speed passenger railway systems. Typically, mechanical stress-strain hysteresis measurements and increasingly different types of temperature and electrical resistance measurements are used to characterize the fatigue behavior and fatigue processes. Here, electrical resistance measurements provide significant information as they allow the detection of microstructural changes, e. g., through changes in dislocation density and structure. In addition, electrical resistance measurements can be considered in load increase and constant amplitude tests with inserted load-free sequences and in service load tests to characterize damage progress. In this paper, characteristic values of the change in electrical resistance were determined for ICE R7 wheel steel specimens and correlated with dislocation density, which was load- and cycle-dependent and determined through transmission electron microscopy.

Optimization of the Synergies Between Preparation of High-Speed Railway Train Running Diagram and Station Route Allocation Plan

Abstract Introduction. Station route allocation plan is an important extension of the train running diagram and the both are closely intertwined so the overall research on the synergetic preparation method is more beneficial in improving the preparation quality of the train running diagram and providing better service for passengers. Therefore, the research topic has practical significance. Methodology. Based on extensive literatures, this paper studies the synergetic preparation method of train running diagram and station route allocation plan in detail and analyses their association for providing a theoretical basis for the synergetic preparation method. Results. This work introduces the synergetic, analyses the systematic characteristics of the operation organization system of high speed railway and puts forward the optimization strategy of train running diagram and station route allocation plan. Conclusions. The work provides the solution for the preparation of the train running diagram and station route allocation plan by solving the examples based on the relevant optimization factors, such as train running in districts and train arrangement.

Spatial Magnetic-Field Description Method Aimed at 2 × 25 kV Auto-Transformer Power Supply System in High-Speed Railway

Complete and accurate spatial magnetic field description is the premise of effectively assessing the power supply capability of a high-speed railway (HSR). Its evaluation indicators are the current distributions and the integrated impedance of traction network. This paper proposes a spatial magnetic-field description method for the auto-transformer (AT) power supply system. Due to the limitations of previous approaches, all the real loop circuits of the AT system are considered for structuring a loop circuit matrix. At first, different description processes are divided, respectively, into those for the right side and the left side of the load. Then, considering that two types of return conductors exist in an AT system, a certain current ratio deduced in existing studies is introduced. As the introduced current ratio of the left side of the load is approximate, an iterative scheme is adopted. By constantly adjusting current ratio to satisfy a constraint condition of circuit voltages, accurate traction network impedance is obtained. Last, in order to verify the effectiveness of the proposed description method, two real-life experiments in a Chinese HSR line are performed, which indicate that the proposed method can not only directly reflect complete and accurate current distribution, but also deduce the exact traction network integrated impedance.

The evolutionary mechanism of high-speed railway system based on hypernetwork theory

Railway system as an important transportation pattern can improve regional economic growth and accelerate the development of transportation structure. In this paper, we propose an evolving model to describe the evolutionary mechanism of high-speed railway system by using hypernetwork theory. The stations are represented as nodes while the lines are represented as hyperedges. The evolving process includes two ingredients: growing and linking which is driven by both random and preferential attachment. We analytically deduce the node hyperdegree distribution which is shown to follow a shifted power-law distribution. Furthermore, we test the impact of parameters on the model. Then the empirical investigations of China Railway High-speed (CRH) are demonstrated which can be explained by the proposed model. The model can reveal the macro characteristics of railway system and provide reference for the further development of high-speed railway.

Dynamic Channel Model With Overhead Line Poles for High-Speed Railway Communications

In order to develop reliable communication links for high-speed railway (HSR) systems, accurate models for the propagation channel are required. The radio channel properties in HSR scenarios are different from those in cellular scenarios not only due to the high velocity, but also due to the special construction elements and the type of surroundings along the train lines. This letter focuses on the influence of overhead line poles along the railway on the HSR communication channel. The overhead line poles affect the line-of-sight communication path periodically, and also act as static and periodic scatterers along railway lines. We performed a measurement campaign at a carrier frequency of 2.4 GHz on the Guangzhou-Shenzhen dedicated high-speed train line in China. Based on the measurement result we propose a dynamic channel model considering periodic poles for HSR communication.

Fatigue life analysis of dropper used in pantograph-catenary system of high-speed railway

Dropper is an important component of pantograph-catenary system employed in high-speed railway. The cyclic stress in dropper can lead to the fatigue failure during operation. The study of the fatig...

Computer vision–based automatic rod-insulator defect detection in high-speed railway catenary system

Maintenance of catenary system is a crucial task for the safe operation of high-speed railway systems. Catenary system malfunction could interrupt railway service and threaten public safety. This article presents a computer vision algorithm that is developed to automatically detect the defective rod-insulators in a catenary system to ensure reliable power transmission. Two key challenges in building such a robust inspection system are addressed in this work, the detection of the insulators in the catenary image and the detection of possible defects. A two-step insulator detection method is implemented to detect insulators with different inclination angles in the image. The sub-images containing cantilevers and rods are first extracted from the catenary image. Then, the insulators are detected in the sub-image using deformable part models. A local intensity period estimation algorithm is designed specifically for insulator defect detection. Experimental results show that the proposed method is able to automatically and reliably detect insulator defects including the breakage of the ceramic discs and the foreign objects clamped between two ceramic discs. The performance of this visual inspection method meets the strict requirements for catenary system maintenance.

Ultrasonic guided wave focusing in waveguides with constant irregular cross-sections

As essential components of a high-speed railway system, switch rails can be easily damaged by sophisticated operating conditions. Therefore, precise online detection for switch rails is necessary. Methods based on ultrasonic guided waves are ideal candidates for structural integrity of the switch rails, which are natural waveguides with irregular cross-sections. However, energy decentralization in the wave propagation severely restricts detectability. Phased array systems have been developed and implemented to steer and focus acoustic energy in waveguides of ordinary cross-sections such as pipes and plates. This paper proposes a method for ultrasonic guided wave focusing in waveguides with constant irregular cross-sections. We analyzed the characteristics of the guided waves generated by partial loadings based on a semi-analytical finite element method (SAFEM). An algorithm was developed for calculating the amplitude weights and time delays required to modulate excitation signals. Two coefficients were defined to evaluate the wave focusing results, namely the half area coefficient (HAC) and half energy coefficient (HEC). Numerical simulations to verify the proposed method were carried out for a switch rail base with a constant irregular cross-section. The results demonstrate that the guided acoustic beam has been effectively steered to focus at the pre-determined locations with enhanced acoustic wave energy. Furthermore, the influence of various factors on guided wave focusing was studied. Excitation signals of low center frequencies with narrow bandwidths are recommended for ideal focusing results.

Comparing China's urban systems in high-speed railway and airline networks

Although the Chinese high-speed railway (HSR) entered the transportation market at a late stage in 2003, its networks have become the world's largest and are currently even growing faster than airline networks. Using the 2013 origin/destination (O/D) passenger flow data instead of commonly used scheduled data, we compare the spatial configurations of the Chinese national urban system in both high-speed railway and airline networks. The results show that HSR-dominant cities and links are located mainly in the middle and eastern parts of China, offering regional connections, whereas air-dominant cities and links are evenly distributed across the whole of China and predominantly offer interregional connections. This is mainly because HSR networks are more focused on connections to cities with high socio-economic performance and are more restricted by the geographical distance between linked cities than the airline networks. Furthermore, HSR networks promote agglomeration economies within cities located along the trunk lines in specific regions, whereas airline networks contribute to more balanced urban development in China. These dimensions indicate that the configuration of urban systems in HSR networks differ largely from that of air networks when measured in terms of passenger flows.

Dual-Connectivity Prevenient Handover Scheme in Control/User-Plane Split Networks

A control/user (C/U) plane-split network, where macro- and microevolved Node Bs (eNBs) are responsible for C/U-planes, respectively, is a potential 5G solution to address the problems experienced by high-speed railway communication systems such as frequent handovers (HOs), low system capacity, and low data rate. The C-plane transition occurs during an intermacro eNB HO to reduce the frequency of HOs. However, the intermacro-eNB HO in a C/U-plane-split network is prone to handover failures (HOFs) and long service interruption time similar to the traditional long-term evolution-advanced (LTE-A) HO without improvements because it is similar to an LTE-A HO between macro-eNBs from the perspective of C-plane transition. In this paper, we realize a C/U-plane-split network using the LTE-A dual-connectivity (DC) technique and propose a dc-based prevenient HO (PHO) scheme to improve the robustness of the intermacro-eNB HO. The proposed scheme specifically is an a priori method and uses the transmit diversity based on the dc technique to reduce the risk of HOFs and the long service interruption time. Further, we first develop the analytical expressions for HO performance for PHO and LTE-A HO, where HOFs are aligned with the LTE-A specifications such that they are defined as the association between the radio link monitor and HO processes. The analytical results are verified against simulation results. Through simulations, we compare PHO with LTE-A HO and the representative schemes of the previous literature in a variety of mobility performance metrics (such as the averages of the successful HO rate, the HOF rate, the radio link failure rate, the ping-pong rate, and the service interrupt time). The results confirm that the proposed scheme achieves superior performance in the key metrics of the successful HO rate and service interrupt time.