DC Electric Railway Systems Research Articles

Modelling a DC Electric Railway System and Determining the Optimal Location of Wayside Energy Storage Systems for Enhancing Energy Efficiency and Energy Management

Global demand for fossil fuels is highly increasing, necessitating energy efficiency to be enhanced in transitioning to low-carbon energy systems. Electric railways are highly efficient in reducing the transportation demand for fossil fuels as they are lightweight and their energy demand can be fed by renewable energy resources. Further, the regenerative braking energy of decelerating trains can be fed to accelerating trains and stored in onboard energy storage systems (ESSs) and stationary ESSs. It is fundamental to model electric railways accurately before investigating approaches to enhancing their energy efficiency. However, electric railways are challenging to model as they are nonlinear, resulting from the rectifier substations, overvoltage protection circuits, and the unpredictability and uncertainty of the load according to the train position. There have been few studies that have examined the ESS location’s impact on improving the energy efficiency of electric railways while using specialised simulation tools in electric railways. However, no single study exists that has studied the location impact of stationary ESSs on the energy efficiency of electric railways while the trains are supported by onboard ESSs. Given these goals and challenges, the main objective of this work is to develop a model using commercial software used by industry practitioners. Further, the energy saving is aimed to be maximised using stationary ESSs installed in optimal locations while trains are supported by onboard ESSs. The model includes trains, onboard ESSs, rail tracks, passenger stations, stationary ESSs, and traction power systems involving power lines, connectors, switches, sectioning, and isolators. In this article, a test scenario is presented comprising two trains running on a 20 km with three passenger stations and two substations. The trains and track are modelled in OpenTrack simulation software (Version 1.9) while the power system is modelled in OpenPowerNet simulation software (Version 1.11). The two simulation tools are used in the railway industry and can produce realistic results by taking into account the entire electrical network structure. A stationary ESS is added on the wayside and moved in steps of 1 km to obtain the optimal location before investigating the impact of stationary ESSs on the performance and energy management of onboard ESSs. It is found that the energy saving when installing a stationary ESS at the optimal location is 56.05%, the peak-power reduction of Substation 1 is 4.37%, and the peak-power reduction of Substation 2 is 18.67%.

A new distributed voltage control method for MVDC electric railway systems with renewable energy sources

The medium voltage DC (MVDC) electric railway system is one of the most interesting options for future high-speed rail (HSR) lines. The dc voltage control is one of the most critical challenges of MVDC electric railway systems due to various reasons such as simultaneous, continuous and considerable changes in the power and location of trains, regenerative brake energy of trains, long power lines, the application of ESS’s and RES’s. In this paper, a voltage control, i.e., the optimal-voltage voltage-power (OVVP) control method, is presented for MVDC electric railway systems. OVVP control method is a practical, reliable, automatic, and modular distributed voltage control method. The proposed voltage control method satisfies the nearest voltage to the nominal value in each node and the smoothest voltage profile in different MVDC electric railway systems. Although the analyses carried out in this paper analytically prove the significant performance of the presented voltage control method, different challenging scenarios are considered to verify OVVP control method more. In addition, the results of the proposed voltage control method are successfully validated by GAMS software.

Medium‐voltage DC electric railway systems: A review on feeding arrangements and power converter topologies

Medium‐voltage DC electric railway systems: A review on feeding arrangements and power converter topologies

Correction to: PSO-Based Initial SOC and Capacity Optimization for Stationary Energy Storage Systems in DC Electric Railway System

Correction to: PSO-Based Initial SOC and Capacity Optimization for Stationary Energy Storage Systems in DC Electric Railway System

PSO-Based Initial SOC and Capacity Optimization for Stationary Energy Storage Systems in DC Electric Railway System

PSO-Based Initial SOC and Capacity Optimization for Stationary Energy Storage Systems in DC Electric Railway System

TransEnergy – a tool for energy storage optimization, peak power and energy consumption reduction in DC electric railway systems

Abstract Electrified railways are large users of electrical power at a time when grid supply conversion to renewable energy production is making supply to the grid less predictable and environmental concerns demand reduction in energy use. These developments make it desirable to control and reduce both total energy usage and peak power demand of railway systems. While AC systems have a well-developed ability to regenerate power to the grid, high transmission losses in DC systems make local storage of energy a more attractive option. A model has been created integrating a versatile and configurable database-driven generic rail network model with a power supply network representative of DC electric railways. The work is intended as a high-level design tool to explore system wide behaviors prior to detailed final design modelling of specific technologies. To validate our method, predictions of train motion and power demand have been compared with data from the Merseyrail network in the UK. Simulating a full day of traffic for the Wirral Line of Merseyrail (237 services on two routes) with the assumption of energy storage being available at each electrical sub-station revealed the dependence of storage effectiveness on the timetable and traffic density at specific locations. The model is combined with a genetic algorithm to optimise system parameters (storage size, charge/discharge power limits, timetable, train driving style/trajectory) and also enables identification of cases in which poorly specified storage technology would have little impact on peak power and energy consumption.

Novel Cooperative Controller Design of Heterogeneous Energy Storages for Economic Applications in Electric Railway Systems

Owing to the consistently increased request about efficiency improvement through utilization of regenerative energy from braking railway vehicle in the DC electric railway systems, there are a lot of researches about energy storage applications. However, the feasibility of ESS technology application is usually limited by economic factors rather than technical factors of it. Therefore, this paper proposes the application of heterogeneous energy storage system based on ramp-rate-considered cooperative controller in order to improve economics. The heterogeneous combination of energy storage devices with different technical advantages can gives a more economical solution to respond to individual specifications required by the system. A ramp-rate-considered cooperative controller for the heterogeneous ESS application is presented numerically, and effectiveness of the proposed method has been verified through electromagnetic transient simulation.

Overview of DC and AC Electric Railway Systems Considering Energy Efficiency Enhancement Methods

In this paper both DC and AC railway electric power feeding systems are reviewed and discussed. The advantage and disadvantage of these systems are also compared. One major problem of such systems is that they take the lion share of electricity consumption compared to non-traction systems. Therefore, most of the new technologies focus on enhancing Energy efficiency of railway systems. This paper discusses the main operation methodologies for reducing the consumption of electric traction systems. These methods include using renewable energy resources (RER), such as solar Photovoltaic (PV) panels and wind turbines, and regenerative braking. Moreover, the most common energy storage devices such as batteries, super-capacitors and flywheels. They are used in railway systems for storing the excess energy from RER or the return energy during regenerative braking (Batteries, super-capacitors and flywheel) are also explained. In addition, challenges of the right storage system selection for specific applications are briefly discussed.

Hardware-in-the-Loop Simulation on Fault Current Limiting Operation of RE-123 Coated Conductors Under the Influence of Spatial Inhomogeneity

We have investigated transient behavior of RE-123 coated conductors in fault current limiting operation based on experimental hardware-in-the-loop simulation (HILS). Fault current limiting function of superconducting electric power application is attractive to maximize the potential of power system; such a function can be realized by the transition to the resistive state of superconducting wire. However, the phenomena is relatively complicated: nonlinear current transport properties varying with time-dependent temperature rise. Furthermore, from practical point of view, the influence of spatially homogeneity of cooling and local critical current properties in RE-123 coated conductors must be clarified for reliable operation. To demonstrate this, we developed HILS system using real-time digital simulator. Fault current limiting operation was successfully demonstrated for dc electric railway system. This method enabled us to evaluate the real-time responses of RE-123 coated conductors such as nonlinear properties and thermal behaviors under a power grid network. In particular, we applied RE-123 coated conductors with spatially inhomogeneous cooling and local critical currents to the experiment to understand the influences of them on the fault current limiting and recovery functions. Furthermore, such transient phenomena were successfully described by an electrically and thermally coupled analysis taking into account of temperature dependent nonlinear transport properties of the RE-123 coated conductors based on the percolation transition model. The method and findings will become crucial for effective and reliable designs of superconducting fault current limiters.

Hardware-in-the-Loop Simulation of Superconducting Devices for DC Electric Railway Systems Based on a Real-Time Digital Simulator

We have developed a hardware-in-the-loop (HIL) simulation setup to analyze superconducting devices for dc electric railway systems. When such superconducting devices are to be installed into a larger system, it is indispensable to characterize their behavior, i.e., their interaction with the system, to assure their reliability in all operating conditions. This is challenging when using full-scale superconducting devices and real power systems because many types of operation and fault cannot be easily demonstrated. Numerical simulation may compensate for that, but complete modeling of superconducting devices has often been difficult because of complicated electromagnetic behavior due to nonlinear transport properties, the transition between superconducting and normal states, and so on. In this paper, we have established an HIL simulation setup by the combination of superconducting hardware and a real-time digital simulator (RTDS). They communicate information about the instantaneous current and voltage values to each other every 50 $\upmu$ s. This enables us to simulate the interaction between superconducting devices and the system for many kinds of operation and fault. Furthermore, it is not necessary to use a full-scale superconducting device, as the signal level from/to the RTDS can be scaled. This will be very attractive for understanding the behavior of a superconducting device by studying a small prototype before developing the full-scale one.

Regenerative Energy Control of DC Electric Railway Based on Solid State Transformer

Regenerative energies are generated by regenerative braking of train. Regenerative energies might cause the problem of power quality such as the voltage drop and malfunction of the power conversion device in the electric railway system. For these reasons, many researches have studied to solve these problems. In this paper, we modeled DC electric railway system based on the solid state transformer that is composed of voltage source converter (VSC) and bi-directional DC-DC converter for controlling the regenerative energy. In order to verify the performance of the proposed electric railway system, electric railway system is modeled by using real time simulator OP5600. In addition, the controller of solid state transformer is implemented by using DSP, TMS320F28335.

전압형 컨버터와 EDLC의 협조 제어에 의한 직류전기철도 회생에너지 이용률 및 전압 제어 능력 향상

In the DC electric railway system, the effective use of regenerative break energy is an important issue. Since regenerative break energy causes voltage rise or drop in the system, it should be also solved effectively. To solve the problems, applying electric double layer capacitor (EDLC) or voltage source converter (VSC) to the DC electric railway system has been studying. In this paper, the coordination of EDLC and VSC is proposed to solve the problem effectively with its coordinated control algorithm. The proposed method is tested to show its feasibility using Matlab/Simulink.

직류도시철도 시스템에서 저장장치 단위 용량 당 에너지 절감 효과 분석 연구

직류도시철도 시스템에서 저장장치 단위 용량 당 에너지 절감 효과 분석 연구

Characteristic Analysis of DC Electric Railway Systems with Superconducting Power Cables Connecting Power Substations

The application of superconducting power cables to DC electric railway systems has been studied. It could leads to an effective use of regenerative brake, improved energy efficiency, effective load sharing among the substations, etc. In this study, an electric circuit model of a DC feeding system is built and numerical simulation is carried out using MATLAB-Simulink software. A modified electric circuit model with an AC power grid connection taken into account is also created to simulate the influence of the grid connection. The analyses have proved that a certain amount of energy can be conserved by introducing superconducting cables, and that electric load distribution and concentration among the substations depend on the substation output voltage distribution.

鉄道用超電導ケーブルの冷却システム

DC electric railway systems are widely used in Japan, including in metropolitan areas. However, they have some problems, such as limited use of regenerative brakes and energy losses. In order to solve those problems, and to attain the energysavings essential for next-generation electric railway systems, we have been studying the feasibility of applying superconducting power cables to DC electric feeder systems. In this study, the design and specifications of a cooling system which are required for the superconducting cables for railway systems are shown.

Superconducting Power Cable Application in DC Electric Railway Systems

A superconducting power cable is a prospective application of high-temperature superconductors. Although power cables using Bi2223 or YBCO wires have been developed in the world so far mainly for utility grid application, we focus attention on railway application of a superconducting power cable. We have studied how to introduce superconducting power cables effectively and economically to a dc electric railway. Numerical analysis models based on the MATLAB-Simulink are constructed for a dc electric feeder system of singe- and double-track railways. Tractive force and train resistance characteristics are modeled. Energy saving by the superconducting power cable is investigated with the influences of the number of substations, the train operation interval, etc., taken into account. The results show that the superconducting power cables can improve regeneration rate and system energy saving, and reduce the substation capacity very effectively. It will be also an advantage that if the transportation capacity of a railway line needs to be increased, the introduction of superconducting cables could achieve it without changing the existing substations along the line.

Application of Superconducting Power Cables to DC Electric Railway Systems

Abstract For novel design and efficient operation of next-generation DC electric railway systems, especially for their substantial energy saving, we have studied the feasibility of applying superconducting power cables to them. In this paper it is assumed that a superconducting power cable is applied to connect substations supplying electric power to trains. An analysis model line was described by an electric circuit, which was analyzed with MATLAB-Simulink. From the calculated voltages and currents of the circuit, the regenerative brake and the energy losses were estimated. In addition, assuming the heat loads of superconducting power cables and the cryogenic efficiency, the energy saving of the total system was evaluated. The results show that the introduction of superconducting power cables could achieve the improved use of regenerative brake, the loss reduction, the decreased number of substations, the reduced maintenance, etc.

Basic Characteristics of the Contact Wire Breaking by the Arc between the Contact Wire and the Pantograph

The contact wire breaking accident caused by the arc between the contact wire and the pantograph happens rarely in the DC electric railway system. The contact wire breaking phenomenon is discussed and investigated based on the experimental data performed 30 years ago. The material of the contact strip and the contact wire has changed, however, and the breaking characteristics of the contact wire caused by the arc should be different. In this paper, the contact wire breaking characteristics are carefully investigated using the recent materials. It is cleared that the breaking index of 750As is approximately appropriate in the limited condition and the other breaking condition is summarized based on the experimental data more than 400 times.

Distribution of the traction return current in ac and dc electric railway systems

The problem of the determination of the real distribution of the return current in electric railway traction systems is considered. One or more conductors (depending on the specific supply system) are purposely set up to carry the traction return current flowing from the rolling stock axles back to the supply (i.e., substation); yet, part of the return current flows through signalling conductors (disturbing current) and through the earth, depending on the value of the electric parameters of the system, on the circuit arrangement, and on the relative position of the supply, the rolling stock, and signalling devices. The amplitude (as a percentage of the total return current) of the disturbing current may be high enough to cause interference to signalling. This work investigates the behavior of the return current in AC and DC electric railway systems, on the basis of a reference system for the variation of the most important electrical parameters. The definition of the transfer function between the return current and the signalling circuit variables is an important element for the compatibility analysis between train detection systems, rolling stock and infrastructure, to promote the cross-acceptance of rolling stock in Europe and abroad.

Application of Electric Double-layer Capacitors for Energy Storage on Electric Railway

The methods to stabilize power sources, which are the measures against voltage drop, power loading fluctuation, regeneration power lapse and so on, have been important issues in DC feeding circuits. Therefore, an energy storage medium that uses power efficiently and reduces above-mentioned problems is much concerned about. In recent years, development of energy storage medium is remarkable for drive-power supplies of electric vehicles. A number of applications of energy storage, for instance, battery and flywheel, have been investigated so far. A large-scale electric double-layer capacitor which is rapidly charged and discharged and offers long life, maintenance-free, low pollution and high efficiency, has been developed in wide range. We have compared the ability to charge batteries and electric double-layer capacitors. Therefore, we carried out fundamental studies about electric double-layer capacitors and its control. And we produced a prototype of energy storage for the DC electric railway system that consists of electric double-layer capacitors, diode bridge rectifiers, chopper system and PWM converters. From the charge and discharge tests of the prototype, useful information was obtained. This paper describes its characteristics and experimental results of energy storage system.