Traction Network Research Articles

A Practical Approach to Mitigate Low-Frequency Oscillation in Railway Electrification Systems

The low-frequency oscillation (LFO) phenomenon has frequently happened in the railway electrification systems (RES), which often caused the traction atresia of electric trains and protection malfunction of traction network. In this letter, a practical mitigation approach is presented based on impedance analysis, which indicates that changing the operation mode of the electric trains to diode-bridge rectification (DBR) circuit can mitigate the LFO because the impedance of the rectifier is increased. Then, combining the Prony technology, an online identification and mitigation approach, is proposed here for mitigating the LFO phenomenon. Experimental results verify the effectiveness of the proposed method in stabilizing voltage fluctuation of the RES. This method can also identify the oscillatory frequency and the corresponding attenuation factor.

Study on Identification Method of Voltage Sags for Traction Electric Network of High-speed Railway

In view of the important factor that the EMU can’t obtain rated voltage caused by the voltage sags of traction electric network in high-speed railway, more effective feature extraction methods of voltage sag must be established to achieve rapid identification and compensation. The recognition method combined the αβ_type orthogonal expanding phase and the instantaneous dq_, type transform, can extract accurately the key characteristics of voltage sags by using the orthogonal transformation of single-phase voltage and the coordinate transformation of spreading phase voltage. The experiment show that this method can not only identify accurately the voltage sag of the traction network, but also has the advantage of clear concept and small computation.

Development of an approach to ensure stability of the traction direct current system

The result of applying the quantitative approach to the calculation of static stability of the traction power system helped us establish that when a train runs along an actual section there emerge zones with lack of stability in terms of voltage. Exact solution to the task of evaluating the stability is extremely difficult because of the need to compute the nonlinear dependences determining the modes of operation of the traction power system and electric rolling stock. In this work, we constructed a system of four autonomous nonlinear differential equations based on experimental data that simulate the behavior of current and voltage in the contact network. We also calculated stability regions for voltage regulators in the traction network, which stabilize voltage at pantographs of electric rolling stock. The obtained stability regions of voltage regulators made it possible to estimate resource of stability and to find the most robust regulators out of those constructed. The study revealed that the non-linear regulator has better robust properties than the linear one. In this case, stability of the linear regulator is very narrow ‒ Δk=0.000004, which is an order of magnitude lower than for the non-linear regulator. When applying the non-linear regulator, voltage in the contact network stabilizes 3 times faster regardless of the place of its location. Application of the devised approach would make it possible to calculate the stability regions for various schematics of the traction network in the implementation of high-speed motion and to narrow the range of voltage fluctuations. The developed dynamic model of power consumption processes, as well as the voltage regulator, could be used when constructing an intelligent, adaptive traction power system for high-speed motion.

Unified traction power supply mode for trunk railway and urban rail transit

Based on the cophase power supply system in trunk railway and industrial frequency alternating current traction power supply system in urban rail transit, a novel unified traction power supply system of trunk railway and urban rail transit is proposed to realize the connection of trunk railway and urban rail transit with continuous power supply and no phase split. The novel traction power supply system is composed of the main substations and traction power supply networks which contain power supply networks, traction substations and traction networks. Stepped power is adopted in power supply network and traction network. Connection scheme of traction power supply networks between two adjacent main substations and its effect on suppressing equalizing current are studied. A novel contact power supply and power collection scheme is also proposed in this paper, in which contact power supply is realized by what is called “contact band”, power collection is realized by what is called “electric plough”. The advantages of contact band and electric plough are discussed. The main influencing factors of the voltage level of contact band are analyzed. The implementations of main substation traction scheme, separated power supply scheme and mixed power supply scheme are discussed. Segmented protection and state identification technology are elaborated in detail. Compared with current scheme, the novel traction power supply system proposed in this paper has many advantages and deserves further study.

Diagnostics of the 3 Kv DC Traction Power Network

The railway traction network line is one of the technical elements ensuring proper operation of railway traffic. Due to its technical function and specificity, it is an essential element of the railway infrastructure. That is, why diagnostics of traction networks is a very important issue. In the article, the authors presented issues related to the diagnostics of 3kVDC traction networks. An analysis of traction network faults for a group of power supply areas was also presented. Additionally, calculations of damage indicators in a selected, representative power supply area are presented. On the basis of made an analysis authors proposed solutions aimed at minimizing breakdowns in traction networks.

Influence Study on Electric Vehicle-traction Network System Considering Pantograph Arcing

This article analyzes the influence of pantograph arcing phenomenon on the electrical quantity which is related equipment of traction power supply system. The Mayer arc model was improved by taking into account arc dissipation power, arc diameter, transverse blowing arc and so on, based on this, modeling was performed, the traction power supply system such as AT doublewire traction network model and CRH3 EMU load model was described mathematically later on, and simulation analysis was ultimately achieved using MATLAB/Simulink software. The study results show that the pantograph arcing phenomenon causes the harmonic components that are the voltage and current of the traction network to increase, at the same time, making the performance indexes of the DC-side voltage of the CRH3 EMU rectifier to change.

Impedance-Based Harmonic Instability Assessment in a Multiple Electric Trains and Traction Network Interaction System

This paper presents an impedance-based method to systematically investigate the interaction between multiple trains and a traction network, focusing on evaluating the harmonic instability problem. First, the interaction mechanism of the multitrain and the traction network is represented as a feedback interconnection of the two subsystems, i.e., an equivalent output impedance of the traction network and an equivalent input admittance of the multitrain. Then, the harmonic instability is evaluated through a series of pole-zero diagrams drawn from the closed-loop transfer matrix of the multitrain and network system. The interaction system is unstable, and the harmonic instability will happen if there are some high-frequency poles of the closed-loop system locating in the right-half plane. This method is used for analyzing the harmonic instability phenomena, the characteristics, influential factors, and potential mitigation schemes. The theoretical results are further validated by the simulations and experiments.

Vehicle-Grid System Stability Analysis Based on Norm Criterion and Suppression of Low-Frequency Oscillation With MMC-STATCOM

In recent years, low-frequency oscillation (LFO) events sometimes occur between the traction network and the electric motive units (EMUs) in vehicle-grid systems of a high-speed railway when multiple EMUs access the traction network. Some measures have been taken from the vehicle side to suppress LFO by changing the control parameters or control strategies of the converters. This paper presents a proposed scheme of suppressing LFO by applying a static synchronous compensator (STATCOM) to the traction network. The stability of the vehicle-grid system is first analyzed using the norm criterion. Next, for unstable vehicle-grid systems, the approach of utilizing a modular multilevel converter STATCOM (MMC-STATCOM) connected to the grid is proposed to suppress the LFO. Further, when the MMC-STATCOM is connected to the grid, the parameter sensitivity analysis is implemented in detail; the analysis results indicate that the MMC-STATCOM-based approach operates well in suppressing LFO, regardless of the change of the system parameters. The simulation results validate the stability analysis and the efficient suppression of LFO for the vehicle-grid system.

Determination of the Parameters of a Compensating Unit in a Traction Power Supply System with a Booster Transformer

The energy relations in a traction ac power supply system including a power multifunctional booster transformer with a nonsinusoidal current and voltage at the current collector of electric rolling stock are considered. The expediency of the selection and regulation of the compensating unit connected to the compensating winding of the transformer based on the minimum exchange energy determined by the presence of the capacity and inductive energy storages is shown. Generating the reactive energy, the booster transformer reduces the voltage losses in the power supply system due to decreasing the primary current. In addition, due to the effects of the bootstrap and series capacity, it exceeds the voltage in the traction network and, therefore, increases the voltage at the current collector of the electric rolling stock. The proposed coefficient of efficiency of the compensating unit allows selecting its capacity with a sufficient accuracy to ensure the optimal operation mode of the traction power supply system, which is on average 15–20% less than the capacity determined using the existing method.

Influence factors analysis of rail potential in urban rail transit

Rail potential is affected by a variety of influence factors in the urban rail transit. This paper proposes a state space average (SSA) model of the traction power system to explore the effects caused by the traction network resistance, inductance, capacitance and rail-to-ground resistance. The SSA model solutions prove that the traction network inductance and capacitance have significant influences on rail potentials. Moreover, based on the SSA model, the rail potential distribution of a metro line during the train timetable period is obtained for rail protections, which is conductive to improve the reliability of the traction power system.

МОДЕЛИРОВАНИЕ ЭЛЕКТРОМАГНИТНЫХ ПОЛЕЙ В ИСКУССТВЕННЫХ СООРУЖЕНИЯХ ЖЕЛЕЗНОДОРОЖНОГО ТРАНСПОРТА

The PURPOSE of the study is development of methods and tools for modeling electromagnetic fields when passing a tractive network in artificial constructions of railway transport. METHODS. The study employs the methods for determining the modes of traction power supply systems (TPSS) using phase coordinates, which are based on the models of elements in the form of lattice equivalent circuits with a fully-meshed topology. These models and methods are implemented in the program complex Fazonord providing simulation of the TPSS modes of different types as well as determination of strengths of an electromagnetic field created by tractive networks of these traction power supply systems. When calculating the strengths the elements of artificial constructions have been simulated by the sets of grounded wires. RESULTS. The article presents the simulation results of electromagnetic safety conditions in the traction networks on the sections of railroads located in artificial constructions including galleries, bridges, tunnels. The metal work of these structures significantly affects a distribution pattern of electromagnetic field strengths in space. This fact is explained by the presence of the grounded conducting objects (which transform the tunnels, galleries and bottom-road bridges into limited spaces) and remoteness of the Earth's surface when moving on the deck-type bridges. CONCLUSION. The simulation results of electromagnetic fields in the engineering structures of railway transport show that at the height of 1.8 m from railroad tracks the deck-type bridge has the greatest electric and magnetic fields the strengths of which are higher than in the open space. The tunnel, gallery and the bottom-road bridge are characterized by smaller strengths and lower flows of electromagnetic energy, which is due to the closeness of the screening metal works of these constructions to the catenary system. The energy is transferred by an electromagnetic field in tunnels, on galleries and bottom-road bridges in a limited space between the catenary system and grounded constructions located nearby.

Peculiarities of Measurements of AC Traction Current Asymmetry in Rail Lines

Up to half of failures in the operation of rail circuits and automatic locomotive signaling at the sections of railways with ac electric traction occurs due to the disturbances caused by the traction current asymmetry in the rail lines. Since the primary source of this asymmetry is the asymmetry of resistances of rail threads within the rail circuits, the measurements of the resistance of elements of each rail thread make it possible to not only define the traction current asymmetry, but also to find the elements, the resistances of which go beyond the limits of the norm. The traction current asymmetry can also be measured directly; however, the measurement results depend as well on the conditions of their being carried out—on the temperature of rails and the magnitude of alternating traction current in them. This is explained by the fact that the asymmetry of resistances of rail threads of rail line is formed owing to an asymmetric increase in them in the transient electrical resistances in the joints of rail links and in the choke bridges. These transient resistances depend on ambient temperature and traction currents in rail threads slightly. As a result, when decreasing the temperature of the rails of P65 type from +40 to –40°C, the asymmetry of resistances of rail threads taking into account their mutual inductance increases by 2.2—2.4 times, while increasing the traction current in rails, for example, by three times causes almost the same asymmetry increase. The influence of mutual inductance of rail threads with the contact wire leads to a decrease in the traction current asymmetry in the rail line. The mutual inductance of rail threads with high-voltage lines of longitudinal power supply that are placed on the contact line supports can increase or decrease this asymmetry, depending on which of the rail threads has less resistance. All these factors should be taken into account both when measuring the asymmetry of resistances of rail threads or the asymmetry of alternating traction current in them and when extrapolating these data to other operating conditions of the rail traction network by the rail temperature or by the magnitude of currents in rail threads, contact wires, and high-voltage lines.

Emergency Control Systems in the Uninterrupted Traction Power Supply of Subways

Traction dc power supply systems with a traditional feed voltage of 825 V are part of the basic transport infrastructure of metropolitan cities. The development of electrified railroads has resulted in the mainstream use of these systems. There are many works about their strengths and weaknesses; however, modern circumstances make it necessary to operate and upgrade these systems, maintain their usability, and improve their efficiency. New rolling stock with asynchronous engines is being launched for subway service with increased loads and travel speeds. In these conditions, one of the main features of maintaining the course of transportation is to guarantee uninterrupted power supply of electric rolling stock. This can be made possible through appropriate and timely responses by maintenance personnel, power dispatchers, automation and emergency control systems. The microprocessor systems used at the modern level of technological development have been embodied in intelligent terminals of feeder lines of electric traction networks used in subway service. Their algorithmic part must be improved and upgraded for compliance with the current realities of subway service by integrating emergency control equipment algorithms, full-scale analysis of analog processes in the electric traction network, discrete signals of automatic controls and telemechanics, and states and switches of cross-connect equipment, which must facilitate increased automation of the traction substation and make it completely unattended.

Brake Voltage Following Control of Supercapacitor-Based Energy Storage Systems in Metro Considering Train Operation State

The utilization of a supercapacitor energy storage system (ESS) to store regenerative braking energy in urban rail transit can achieve an energy-saving effect. This paper proposes a brake voltage following energy management strategy of ESS to adjust the charging and discharging threshold voltage based on the analysis of train operation states. The energy storage device state of charge is considered to realize the maximum usage of the ESS. First of all, the mathematical model of the dc traction power system, which encompasses the train, ESS, and traction substation, is established. Then, the energy allocation influence factors are analyzed, in particular for the double train structure. Second, under the different conditions, with the real-time monitoring of the traction network voltage and the train status, an energy management state machine is determined. Meanwhile, a set of effective state switching schemes is given to achieve the transformation of the energy management states. In the end, both the simulations using actual line data and main track field experiments prove the rationality and validity of the proposed management strategy.

An Approach to Suppress Low Frequency Oscillation in the Traction Network of High-Speed Railway Using Passivity-Based Control

The traction blockade in depots of multiple electric multiple units (EMUs) is generally considered to be caused by the voltage low frequency oscillation (LFO) of the high-speed railway traction network. As a possible solution, a strategy using single-phase EMUs rectifiers with passivity-based control (PBC) is proposed in this paper. First, the mathematical model of the four-quadrant pulse width modulation rectifier is constructed based on the port controlled Hamiltonian with dissipation. Next, with the insertion of damping, the new energy function can be minimized at the equilibrium point of the system, which enables the derivation of the rectifier control law based on the interconnection and damping assignments PBC. Comparison of simulation results with those of the traditional proportional integral (PI) scheme, autodisturbance rejection control and multivariable control verifies that the proposed PBC controller has better dynamic and static performance. Among all strategies considered, the resulting line current has the least total harmonic distortion, and the dc-link voltage of single-phase EMUs rectifier has the least oscillation and the shortest adjustment time, when using the PBC. Meanwhile, the simulations of multi-EMUs accessed a traction network show that the proposed method significantly suppresses the voltage LFO of the traction network. Finally, the LFO signal modal analysis is performed using the fast Fourier transform and the estimating signal parameters via the rotational invariance techniques. It indicates that PBC can suppress the symmetrical frequency components and effectively reduce the third, fifth, and other harmonic components compared with the PI control in EMUs.

Possibilities of using a superconducting energy storage in DC power systems of traction network

Implementation of dynamic energy storage technology and its integration with the power system represents another important step in the development of the energy sector. This article discusses the advancement of superconducting energy storage technologies and the possibilities of their use in power engineering as well as other branches of industry. It also presents the perspective of applications of superconducting energy storage type SMES (Superconducting Magnetic Energy Storage) both for commercial and industrial applications and their impact on power grid. The article analyzes the functions that systems can use with the use of a superconductor in the power system. The functionality of SMES systems has been analyzed in particular from the point of view of its use in railways.

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.

Low-Frequency Oscillation Suppression of the Vehicle–Grid System in High-Speed Railways Based on H∞ Control

Recently, a traction blockade in the depots of numerous electric multiple units (EMUs) of high-speed railways has occured and resulted in some accidents in train operation. The traction blockade is caused by the low-frequency oscillation (LFO) of the vehicle–grid (EMUs–traction network) system. To suppress the LFO, a scheme of EMUs line-side converter based on the H∞ control is proposed in this paper. First, the mathematical model of the four-quadrant converter in EMUs is presented. Second, the state variables are determined and the weighting functions are selected. Then, an H∞ controller based on the dq coordinate is designed. Moreover, compared with the simulation results of traditional proportional integral (PI) control, auto-disturbance rejection control (ADRC) and multivariable control (MC) based on Matlab/Simulink and the RT-LAB platform, the simulation results of the proposed H∞ control confirm that the H∞ controller applied in EMUs of China Railway High-Speed 3 has better dynamic and static performances. Finally, a whole cascade system model of EMUs and a traction network is built, in which a reduced-order model of a traction network is adopted. The experimental results of multi-EMUs accessed in the traction network indicate that the H∞ controller has good suppression performance for the LFO of the vehicle–grid system. In addition, through the analysis of sensitivity of the H∞ controller and the traditional PI controller, it is indicated that the H∞ controller has better robustness.

Train–Network Interactions and Stability Evaluation in High-Speed Railways–Part I: Phenomena and Modeling

This paper presents an impedance-based model to systematically investigate the interaction performance of multiple trains and traction network interaction system, aiming to evaluate the serious phenomena, including low-frequency oscillation (LFO), harmonic resonance, and harmonic instability. The train–network interaction mechanism is therefore studied, and one presents a detailed coupling model for investigating the three interactive phenomena and their characteristics, influential factors, analysis methods, and possible mitigation schemes. In Part I of the two-part paper, the measured waveforms of such three phenomena are first characterized to indicate their features and principles. A unified framework of the train–traction network system for investigating the three problems is then presented. In order to reveal the interaction mechanism, all-frequency impedance behaviors of the electric trains and traction network are equally modeled. In which, an impedance-based input behavior of the train is fully investigated with considering available controllers and their parameters in DQ -domain. The entire traction network, including traction transformer, catenary, supply lines, is represented in a frequency-domain nodal matrix. Furthermore, the impedance–frequency responses of both electric train and traction network are measured and validated through frequency scan method. Finally, a generalized train–network simulation and experimental system are conducted for verifying the theoretical results of the two-part paper.

Train–Network Interactions and Stability Evaluation in High-Speed Railways—Part II: Influential Factors and Verifications

Low-frequency oscillation (LFO), harmonic resonance, and harmonic instability phenomena in high-speed railways (HSRs) result from the interactions between multiple electric trains and the traction network. A train–network interaction system and a unified impedance-based model are therefore presented to reveal the mechanism of these three phenomena in Part I of the two-part paper. Part II of the paper presents and compares the detailed simulation and experiment results to investigate the available possible influential factors, verifications, and discussions of the three phenomena. The influential factors include the following: 1) four-quadrant converter (4QC) parameters involving the control parameters of the current controller (CC), the voltage controller (VC), and the phase-locked loop (PLL); 2) network parameters involving the utility power system, traction transformer, primary/secondary supply lines, catenary lines, and autotransformers (ATs); and 3) different numbers and positions of trains and railway lines will also be considered and discussed. In order to validate the theoretical results, the time-domain simulation and experiment system have been conducted. Finally, the differences and the relations among the three phenomena are discussed.