DC-electrified Railway Research Articles

Design of Light-Load Regenerative Brake Control System with Load Power Estimation for DC Electrified Railways

In DC-electrified railway systems, light-load regenerative brake control prevents the occurrence of overvoltage at the filter capacitor (FC) of the traction inverter of the regenerative vehicle. However, such control can restrict regenerative power more than necessary when the distance between the powering train and regenerative train is increased, although a sufficient load exists in the electric traction system. This study clarifies the principle of the method to restrict torque current of the regenerative train based on the load power. Subsequently, a method is proposed to design the load power estimation controller.

Energy-Management Method to Reduce the Capacity of Lithium-Ion Batteries in Hybrid-Voltage-Source Three-Level Inverter for DC-Electrified Railway Vehicles

The hybrid-voltage-source three-level inverter is a traction circuit system aimed at realizing energy savings with lithium-ion batteries for direct-current-electrified railway vehicles. However, this system has the limitation of being unable to freely control the power flow of the batteries owing to the pulse width modulation. However, because this system has batteries, energy management is required for the batteries. Therefore, it is necessary to propose an energy-management method that achieves the required energy-saving effect while considering the constraints of the battery power control. In this paper, a management method is proposed to control the power flow of the batteries by determining the pulse mode of the inverter and the modulation wave offset based on the state of the charge and inverter frequency. In a 0.75-kW class mini-model verification, the effectiveness of the proposed energy-management method is then confirmed based on the state of the charge, inverter frequency, offset, and battery power. Subsequently, we evaluate the energy-saving effect of this hybrid system using a numerical simulation while considering an actual railway vehicle. In addition, the optimal capacity of the batteries is investigated. As a result, the best energy-saving effect is obtained when two of the assumed batteries are connected in series and three in parallel, and the power consumption is reduced by approximately 21%.

Control Method for Increasing Motor Power of DC-electrified Railway Vehicles with an Onboard Energy Storage System

Control Method for Increasing Motor Power of DC-electrified Railway Vehicles with an Onboard Energy Storage System

Optimal Location and Sizing of Energy Storage Systems in DC-Electrified Railway Lines Using a Coral Reefs Optimization Algorithm with Substrate Layers

This paper deals with the problem of finding the optimal location and sizing of Energy Storage Systems in DC-electrified railway lines. These devices increment the use of the regenerated energy produced by the trains in the braking phases, as they store the energy to later provide to the catenary the excess of regenerated energy, that otherwise would be lost in the rheostats. However, these infrastructures require a high initial investment that, in some cases, may question their profitability. We propose a multi-method ensemble meta-heuristic to obtain the optimal solution to the problem, with a high level of accuracy. Specifically, the Coral Reefs Optimization with Substrate Layers (CRO-SL) is proposed, an evolutionary-type approach able to run different search procedures within the same population. We will evaluate the performance of the CRO-SL in the problem, and we will show that it performs better than the best known existing meta-heuristics for this problem.

Evaluation of the Effect of Stray Current Collection System in DC-Electrified Railway System

Stray current corrosion damage is significant in DC traction power supply system (DTS). Stray current collection system including stray current collection network (SCCN) and stray current drainage device (SCDD) is designed to control the stray current. A comprehensive system integrated calculation model is established to evaluate the stray current. And the iterative power flow algorithm with simplification of DTS is proposed. The stray current distribution is calculated by multi sections rail reflux system model. The model is verified with CDEGS simulation. The influence of stray current collection system on stray current is evaluated. The result shows that the primary stray current is mainly affected by rail to SCCN resistance and the length of the line. The efficiency of collecting stray current of SCCN is mainly affected by the resistance of SCCN and the SCCN to earth resistance. While the use of SCDD deteriorates the efficiency of collecting stray current of SCCN. A site test was carried out in Chengdu Metro Line 1 to evaluate the effect of stray current collection system.

Reliability and Life Evaluation of a DC Traction Power Supply System Considering Load Characteristics

The traction power supply system is one of the most important parts of a railway system, which is responsible for providing electricity to power the running trains and other operating equipment. The performance of the power supply has a profound impact on the railway system. Therefore, it is necessary to conduct research on the reliability of the power supply system considering traction load and ensure it is highly reliable. This article introduces some reliability-related indexes based on the fault tree analysis (FTA) method and proposes a method to evaluate the system reliability of a dc-electrified railway. The effect of traction load on power supply system reliability is studied based on Institute of Electronics Engineers (IEEE) standards. A dynamic reliability and life evaluation model is built up to evaluate the reliability of traction substation and to develop a plan to reduce the operational risk of the power system. Through analysis of a practical example of the Singapore East-West line, the system reliability and remaining useful life of each traction substation are obtained. The outcome from this study provides guidance for the maintenance and future operation plan of the power system.

Determining the optimum installation of energy storage systems in railway electrical infrastructures by means of swarm and evolutionary optimization algorithms

The installation of wayside Energy Storage Systems (ESSs) in DC-electrified railway systems is one of the main measures to improve their energy efficiency. They store the excess of regenerated energy produced by the trains during the braking phases and give it back to the system when necessary. Nevertheless, the big cost of the associated installation can make railway operators hesitate about the convenience of the investment. Additionally, the decisions about the configuration of the installation (locations and sizes for the ESSs) are usually based on the previous experience of the railway operators or, at best, in assessments made with simulation tools with low accuracy.This paper proposes a model to optimize the profitability of the investment. Nature-inspired optimization algorithms are applied in combination with a very realistic railway simulator. The flexibility of the nature-inspired optimization algorithms, together with their ability to successfully deal with the computationally-intensive and highly non-linear and non-convex problem posed by the realistic railway simulator, makes them the perfect choice.Three different nature-inspired optimization algorithms have been selected and compared: the Genetic Algorithm (GA) as the main exponent of the evolutionary algorithms, the Particle Swarm Optimization algorithm (PSO) as the main exponent of the swarm algorithms and the Fireworks Algorithm (FA) as another variant of the swarm algorithms. The algorithms have shown an excellent behavior, providing solutions that combine the increase of energy efficiency with a very good profitability of the installation required to obtain that increase.

Method to Design Control System of Traction Inverter of DC-electrified Railway Vehicle for an Increase in Regenerative Brake Power

Method to Design Control System of Traction Inverter of DC-electrified Railway Vehicle for an Increase in Regenerative Brake Power

Method to Design Control System of Traction Inverter of DC-electrified Railway Vehicle for an Increase in Regenerative Brake Power

Method to Design Control System of Traction Inverter of DC-electrified Railway Vehicle for an Increase in Regenerative Brake Power

Numerical Simulation to Design Light-load Regenerative Brake Control System at Load Shutdown for DC-electrified Railway Systems

Numerical Simulation to Design Light-load Regenerative Brake Control System at Load Shutdown for DC-electrified Railway Systems

Optimal energy saving in DC railway system with on-board energy storage system by using peak demand cutting strategy

A problem of peak power in DC-electrified railway systems is mainly caused by train power demand during acceleration. If this power is reduced, substation peak power will be significantly decreased. This paper presents a study on optimal energy saving in DC-electrified railway with on-board energy storage system (OBESS) by using peak demand cutting strategy under different trip time controls. The proposed strategy uses OBESS to store recovered braking energy and find an appropriated time to deliver the stored energy back to the power network in such a way that peak power of every substations is reduced. Bangkok Mass Transit System (BTS)-Silom Line in Thailand is used to test and verify the proposed strategy. The results show that substation peak power is reduced by 63.49% and net energy consumption is reduced by 15.56% using coasting and deceleration trip time control.

Evaluation and Control of Stray Current in DC-Electrified Railway Systems

In urban electric railway transit systems, rails are used to navigate trains, as well as to provide the returning path of the train's electric current to the traction power substation (TPS). Due to electrical resistance of rails and the rail-to-ground conductivity, a part of the train's returning current to the TPS flows into the ground, which is called stray current, which causes different problems such as an increase of rail potential. In this regard, a model of an electric train with a TPS, running rail, and third rail is simulated in MATLAB/Simulink. In the simulated model, the amounts of stray currents in different soil types, with and without collection mats, are compared. Afterward, to calculate the amount of stray current in the presence of the stray current control method considering different soil types through finite–element (FE) method (FEM), a UIC54 rail with insulated fastening equipment is modeled in FEMM 4.2 and analyzed with 2-D FEM. Finally, a comparison of efficiency of stray current collection mats in different soil models for both simulation in MATLAB/Simulink and FEM is also presented. The obtained results verify the accuracy of the simulated and modeled system in real conditions of electric railways.

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.

直流電気鉄道における省エネルギー化のための地上蓄電装置の電力制御

直流電気鉄道における省エネルギー化のための地上蓄電装置の電力制御

Simple Power Flow Control Method for Reducing the Power Source Capacity and Managing the Storage Energy for Hybrid Power Source Electric Vehicles

SUMMARY Electric railway vehicles require high electric power when powering and return high electric output when regenerating. Therefore, the fall in vehicle performance due to a voltage drop and the restriction on regenerative power due to a load shortage become problems in a dc-electrified railway. Therefore, energy storage devices (ESDs) are mounted on vehicles to assist the power of powering operation and to absorb the power of regeneration. In recent years, various hybrid vehicles have been studied because the performance of ESDs has become good enough for them to be mounted on vehicles. Generally, the design of the controller is a complicated problem because the vehicle operates under various running conditions. In this paper, a simple controller for ESDs is designed in the frequency domain. This controller aims at smoothing the input power and at managing the ESD energy. The proposed controller is examined under various running conditions with numerical simulations.

Estimation of Stray Current From a DC-Electrified Railway and Impressed Potential on a Buried Pipe

DC-electrified traction systems are a potential source of stray current that may corrode internal and external structures and installations. The stray current intensity depends on several factors (traction current, rail insulation, concrete mat and piers resistance), that are accounted for in the proposed model. The case of a viaduct and a victim-buried pipeline is considered in detail, and the estimated impressed voltage on the pipe is compared successfully with experimental results.

An Analytical Design Method for a Regenerative Braking Control System for DC-electrified Railway Systems under Light Load Conditions

A DC-electrified railway system that is fed by diode rectifiers at a substation is unable to return the electric power to an AC grid. Accordingly, the braking cars have to restrict regenerative braking power when the power consumption of the powering cars is not sufficient. However, the characteristics of a DC-electrified railway system, including the powering cars, is not known, and a mathematical model for designing a controller has not been established yet. Hence, the object of this study is to obtain the mathematical model for an analytical design method of the regenerative braking control system. In the first part of this paper, the static characteristics of this system are presented to show the position of the equilibrium point. The linearization of this system at the equilibrium point is then performed to describe the dynamic characteristics of the system. An analytical design method is then proposed on the basis of these characteristics. The proposed design method is verified by experimental tests with a 1kW class miniature model, and numerical simulations.

Modelling the magnetic field caused by a dc-electrified railway with linearly changing leakage currents

Magnetic fields produced by dc railways can disturb operations at geomagnetic observatories. These magnetic fields consist of two parts: the ideal “full-loop” field due to the traction current in an overhead wire and in the rails, and the “leakage” field due to currents leaking from the track into the ground. Pirjola et al. (2007) present formulas with numerical examples for the magnetic field assuming a constant leakage current density between the train and the feeding substation. Lowes (2009) considers this assumption questionable. In this paper, we derive exact formulas for the magnetic field assuming that the leakage current density changes linearly being largest at the train and decreasing to zero at the substation. The Earth is considered layered. Computer codes enable calculations of the magnetic fields due to any number and configuration of the train-substation pairs at any points of observation. Numerical examples show that the value of 10 pT can easily be exceeded. An important conclusion is that the magnetic fields in the cases of a linearly changing and a constant leakage current density do not differ much. Particular attention is paid to the temporal behaviour of the magnetic field when one or two trains travel along a railway.

Fixed Energy Storage Technology Applied for DC Electrified Railway

AbstractThe fixed energy storage system solves the problem of rising energy costs by reducing primary energy consumption. Without a fixed energy storage system, the energy generated by a braking vehicle would be simply converted into waste heat by its braking resistors if no other vehicles are powered simultaneously. Because, as a rule, such synchronized braking and powering cannot be coordinated, the energy storage system stores the energy generated during braking and discharges it again when a vehicle is powered. This greatly reduces primary energy demand in the substation. However, in addition to this energy saving, the energy storage system contributes to the reduction of CO2 emissions. The energy storage system also stabilizes the system voltage. Recent years have witnessed an advance in the energy storage media technology. Developments of energy storage media, lithium ion battery, nickel‐metal hydride battery, and electric double‐layer capacitors (EDLCs) have been remarkable. This study introduces technologies of fixed energy storage system applicable for DC electrified railway in Japan, and describes two examples of charge/discharge characteristics. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Modelling the disturbance caused by a dc-electrified railway to geomagnetic measurements

Abstract Magnetic fields created by a dc-electrified railway are a nuisance to the operation of a geomagnetic observatory and also disturb other electromagnetic studies. Theoretical formulas that enable quantitative estimates of the magnetic effect of a dc railway including leakage currents in the ground are presented in this paper. They are illustrated by numerical examples. The validity of the theoretical model was verified by measurements carried out in the vicinity of a nearly north-south railway in Calgary, Canada. The earth structure in that area is approximately layered, which is an assumption included in the theoretical model. The agreement between the measured magnetic fields due to trains and the theoretical values is good. Numerical computations indicate that magnetic fields larger than the maximum allowable noise level (assumed to be about 10 pT) at today’s magnetic observatories may extend to distances of tens of kilometres from a railway. We have prepared computer programs based on the theoretical formulas in the MatLab, Octave, FORTRAN and IDL languages, in which the locations (i.e. the latitudes and the longitudes) of the point of observation, of the feeding substations and of the trains, together with the feeding and leakage currents and the heights of the feeding lines, can be given as inputs.