Wayside Energy Storage Systems Research Articles

Method of Compensating Overhead Catenary Line Voltage for Reduction of Battery Capacity at Substation Replacement by Wayside Energy Storage System

Method of Compensating Overhead Catenary Line Voltage for Reduction of Battery Capacity at Substation Replacement by Wayside Energy Storage System

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%.

Coordinated Control of the Onboard and Wayside Energy Storage System of an Urban Rail Train Based on Rule Mining

AbstractThere are three major challenges to the broad implementation of energy storage systems (ESSs) in urban rail transit: maximizing the absorption of regenerative braking power, enabling online global optimal control, and ensuring algorithm portability. To address these problems, a coordinated control framework between onboard and wayside ESSs is proposed in this study, and the related control strategy is obtained by transforming the global optimization problem into a combination of rule-based and local optimization problems. The design process of the strategy is divided into three parts: offline optimization, rule extraction, and local optimization. First, a genetic algorithm is used to optimize the charge/discharge threshold curves under typical operational conditions. Then, the rules of offline optimization results are obtained from an expert system, and the nonlinear rules are mined with local optimization methods. Finally, a coordinated strategy is presented based on the outcomes of the three parts. A power hardware-in-the-loop (PHIL) experimental platform based on RTLAB is built, and the above coordination strategy is verified based on data for the Beijing Metro Batong Line. The experimental results show that the strategy can effectively improve the energy-saving rate and reduce the regeneration failure rate substantially, with the effect being close to the offline global optimal solution. The algorithm proposed in this paper achieves near global optimal energy-saving optimization results with lower computational costs, and has strong portability, providing a good solution for the large-scale application of onboard and wayside energy storage coordination control.

Application of smart wayside object controllers to railway signalling systems for decarbonisation

In railway signalling systems, trackside equipment and signalling devices are controlled by wayside object controllers (OC). With the application of radio communication to wirelessly transmit command control and signals, the cost of cabling and installation has been significantly reduced. However, for non-electrified regional lines in rural areas, dedicated cables are still installed along the track to drive the wayside object controllers, which increases both capital and operational costs. With the development of renewable energy sources (RES) and wayside energy storage systems (ESS), a concept of smart wayside object controllers (SWOC) is proposed, which are autonomous, off-grid and powered by local renewable energy sources to reduce the related costs. To assist future system development, this work develops methods to not only calculate power and energy demand for system configuration but also estimate the life cycle cost in long-term operation. A case study based on a railway test site in Sweden is performed. This study shows that it is sufficient to use 100% local renewable energy sources to power the SWOC, trackside equipment and signalling devices. Compared with the existing system, the SWOC shows a significant cost saving in long-term operation by removing cabling and installation, reducing trackside maintenance and replacing the power supply with renewable energy power sources for decarbonisation. Therefore, the SWOC shows its significant benefits over the existing system from both economical and environmental aspects. In the end, some suggestions for future development and implementation of SWOC are given.

Environmental and Techno-economic Life Cycle Assessment of Energy Storage Systems in Railway supply system

During rush hours, catenary voltage drop is a significant issue on the 1,5kV – DC lines. Indeed, when voltage drop occures between two substations, the trains can't accelerate as they should. Among the solutions that could solve such a problem, the development of a new traditionnal substation in the middle of two others, also the integration of wayside Energy Storage Systems (ESS). This paper deals with the development on Energy Storage Systems (ESS) in the SNCF (French Railway Company) railway network. It aims to study the techno-economic interests of such innovations, also to investigate the environmental impact they could have. The assessment is based on the comparison of a traditional railway 1,5kV–DC substation and a battery-based substation.

Model-based investigation of an uncontrolled LTO wayside energy storage system in a 750 V tram grid

Wayside energy recovery systems (WERS) can increase energy efficiency in DC railway grids. Almost all commercial systems connect energy storage system and grid via power electronics, and most studies investigate this approach. Power electronics increase complexity, space demand, and investment costs.Our work presents a novel concept for an application in 750 V grids: a direct grid-coupled, uncontrolled WERS based on a commercial lithium-ion-titanate-oxide (LTO) cell.We present a detailed simulation model to investigate the application of the novel concept on tramline 112 in Oberhausen/Mulheim (Germany). Field measurements on two vehicles support the investigations. We consider the auxiliaries’ specific behaviour and use measured traction power profiles as simulation input. As a result, the application of the proposed WERS could save around 182,500 kWh per year. Economic operation is thus possible with a service life of two years at investment costs of less than 53,000 €.

Optimal Siting and Sizing of Wayside Energy Storage Systems in a D.C. Railway Line

The paper proposes an optimal siting and sizing methodology to design an energy storage system (ESS) for railway lines. The scope is to maximize the economic benefits. The problem of the optimal siting and sizing of an ESS is addressed and solved by a software developed by the authors using the particle swarm algorithm, whose objective function is based on the net present value (NPV). The railway line, using a standard working day timetable, has been simulated in order to estimate the power flow between the trains finding the siting and sizing of electrical substations and storage systems suitable for the railway network. Numerical simulations have been performed to test the methodology by assuming a new-generation of high-performance trains on a 3 kV direct current (d.c.) railway line. The solution found represents the best choice from an economic point of view and which allows less energy to be taken from the primary network.

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.

A Dual-Stage Modeling and Optimization Framework for Wayside Energy Storage in Electric Rail Transit Systems

In this paper, a dual-stage modeling and optimization framework has been developed to obtain an optimal combination and size of wayside energy storage systems (WESSs) for application in DC rail transportation. Energy storage technologies may consist of a standalone battery, a standalone supercapacitor, a standalone flywheel, or a combination of these. Results from the dual-stage modeling and optimization process have been utilized for deducing an application-specific composition of type and size of the WESSs. These applications consist of different percentages of energy saving due to regenerative braking, voltage regulation, peak demand reduction, estimated payback period, and system resiliency. In the first stage, sizes of the ESSs have been estimated using developed detailed mathematical models, and optimized using the Genetic Algorithm (GA). In the second stage, the respective sizes of ESSs are simulated by developing an all-inclusive model of the transit system, ESS and ESS management system (EMS) in MATLAB/Simulink. The mathematical modeling provides initial recommendations for the sizes from a large search space. However, the dynamic simulation contributes to the optimization by highlighting the transit system constraints and practical limitations of ESSs, which impose bounds on the maximum energy that can be captured from decelerating trains.

Hierarchical Optimization of an On-Board Supercapacitor Energy Storage System Considering Train Electric Braking Characteristics and System Loss

In order to absorb the regenerative braking energy of trains, supercapacitor energy storage systems (ESS) are widely used in subways. Although wayside ESS are widely used, because of the influence of no-load voltage, and so on, a wayside ESS cannot absorb all the regenerative braking energy in some special cases, and the brake resistor is still activated, which leading to the wasting of energy. In order to completely replace the on-board brake resistor, this paper configures a certain on-board super-capacitor, and based on a DC-side series super-capacitor topology, proposes a hierarchical optimization energy management strategy (EMS). The EMS is divided into three layers: Firstly, the strategy can increase the inverter-side voltage in a short time without changing the traction network voltage, and improve the train braking characteristic curve by utilizing the short-time overvoltage capability of the inverter and the motor; Secondly, by coordinated control with a wayside supercapacitor, the residual regenerative braking energy can be absorbed even in special cases; Finally, based on loss calculation and current prediction, this strategy can effectively reduce the system loss by adjusting the DC voltage on the inverter-side. The proposed control strategy is validated through RT-LAB experiment, and the experimental results agree well with the theory.

Impact on railway infrastructure of wayside energy storage systems for regenerative braking management: a case study on a real Italian railway infrastructure

Today, in the railway sector there is considerable interest in studying the best ways of exploiting train braking energy, in order to achieve a reduction in energy costs and better stabilisation of grid voltage. Among the various on-board or wayside measures proposed, one of the most promising solutions is based on using wayside energy storage systems (WESSs). A WESS is a storage installation which can be integrated into mass transit systems in urban areas as well as into long-distance railway lines. It can operate as a smart storage system able to provide relevant benefits in terms of recovering surplus regeneration braking energy, voltage stabilisation, reduction of peak power demand. For these purposes, an effective and flexible simulator is essential to provide all the elements needed to focus and compare feasible configurations and operations. This study examines the problem of introducing the WESS technology in real railway infrastructure. It proposes a method based on a simulator of the WESS system integrated into the infrastructure and carries out the results of dynamic simulations referring to real operating data of the system and vehicles. The results highlight the performance of the WESS in terms of energy and power exchange, also discussing economic aspects.

A Dual-Objective Substation Energy Consumption Optimization Problem in Subway Systems

Maximizing regenerative energy utilization is an important way to reduce substation energy consumption in subway systems. Timetable optimization and energy storage systems are two main ways to improve improve regenerative energy utilization, but they were studied separately in the past. To further improve energy conservation while maintaining a low cost, this paper presents a strategy to improve regenerative energy utilization by an integration of them, which determines the capacity of each Wayside Energy Storage System (WESS) and correspondingly optimizes the timetable at the same time. We first propose a dual-objective optimization problem to simultaneously minimize substation energy consumption and the total cost of WESS. Then, a mathematical model is formulated with the decision variables as the configuration of WESS and timetable. Afterwards, we design an ϵ -constraint method to transform the dual-objective optimization problem into several single-objective optimization problems, and accordingly design an improved artificial bee colony algorithm to solve them sequentially. Finally, numerical examples based on the actual data from a subway system in China are conducted to show the effectiveness of the proposed method. Experimental results indicate that substation energy consumption is effectively reduced by using WESS together with a correspondingly optimized timetable. Note that substation energy consumption becomes lower when the total size of WESS is larger, and timetable optimization further reduces it. A set of Pareto optimal solutions is obtained for the experimental subway line—based on which, decision makers can make a sensible trade-off between energy conservation and WESS investment accordingly to their preferences.

Modeling and Simulation of DC Electric Rail Transit Systems With Wayside Energy Storage

Electric rail transit systems are large consumers of electricity, which face challenges related to improving their overall energy efficiency. Although various solutions have been proposed to achieve this target, it is not feasible to implement and test all of them. Since finding the solution that is most appropriate to a given system is typically a site-specific problem, an accurate, validated, and reliable simulation tool is crucial. In this paper, a simulation model for studying wayside energy storage systems in dc electric rail transit system is presented. The proposed model provides a reliable tool for analyzing the behavior of the transit system during intervals that span from a small fraction of time (milliseconds) up to 24 h. In order to validate the proposed simulation model, its results were compared with real measurements of a standard subway system.

Energy storage sizing methodology for mass-transit direct-current wayside support: Application to French railway company case study

In the context of direct-current electrified railway systems, power supply quality issues are a major concern for the railway network operators. Indeed, after signaling systems and track equipment, voltage issues may be the most challenging factor for the capacity of a direct-current railway line. These issues and the high cost of new substations motivate the implementation of wayside energy storage systems to support the system. Since an appropriate sizing methodology is a key step towards an energy storage system implementation in a railway line, in this paper a sizing methodology is presented in detail. As hypothesis, the sizing methodology is defined such that the storage system is able to support the railway line under projected conditions of the rolling stock traffic, along with other technical criteria relevant to the railway operator. A real-time simulation oriented, direct-current railway network modeling approach is proposed and exploited in this sizing methodology. Using this modeling method, the optimal energy storage sizing formulation is described. The objective function to minimize is the trade-off between energy storage capacity and charging power. The proposed sizing method is applied to a real railway line with known power supply quality issues. This case study is introduced by analyzing real voltage measurements on two key sites of the line over several days. Then, the sizing methodology is applied and the results are discussed for the study case, defining the minimal technical requirements to install. The obtained minimal technical requirements for the storage system are considered by the operator to take a cost-effective decision in contrast with the reinforcement of the line with new substations.

A strategy for utilization of regenerative energy in urban railway system by application of smart train scheduling and wayside energy storage system

Nowadays, electric railway system is known as an efficient and environmentally friendly solution for transportation system. Many developing countries have been expanding their railway systems to support the growth of transport demand. Even though railway system can utilize energy efficiently, its operation still requires bulk of energy. Therefore, management of multiple energy sources is an important issue for railway planning and operation. The advent of modern railway technologies provides regenerative braking system which can recover considerable energy from brake operation. Management of regenerative energy becomes a key for enhancing railway operation. This paper presents a strategy for utilizing regenerative energy in urban railway system by adjusting train operating schedule and employing wayside energy storage system. Optimizing train schedule aims to increase the degree of regenerative energy usage and applying super capacitor as temporary energy storage will manage the surplus of regenerative energy. By integrating appropriate train scheduling and energy storage system, energy management can be more flexible and effective leading to improvement of energy-saving operation. The numerical case study of Bangkok Rapid Transit System was performed and evaluated to reflect the improvement of utilizing regenerative energy.

Control of Energy Storage

In the attempt to tackle the issue of climate change, governments across the world have agreed to set global carbon reduction targets. [...]

A Power Control Method to Save Energy for Wayside Energy Storage Systems in dc‐Electrified Railway System

SUMMARYThe introduction of wayside energy storage systems is effective for the recovery of regenerative brake energy in dc‐electrified railways. However, considering the cost of their deployment, it is preferable to maximize the energy saving effect with a minimum capacity of the energy storage devices (ESDs). In this paper, we propose a power control method that can improve the energy saving effect while managing the energy of the ESDs. The proposed method is implemented by controlling the filter capacitor voltage of the line side of the power converter for the ESDs depending on their energy and the line voltage of the overhead contact line to which they are connected. Next, the proposed method is verified by numerical simulations and experimental tests with a 1 kW class downsized model.

Control Strategies with Dynamic Threshold Adjustment for Supercapacitor Energy Storage System Considering the Train and Substation Characteristics in Urban Rail Transit

Recuperation of braking energy offers great potential for reducing energy consumption in urban rail transit systems. The present paper develops a new control strategy with variable threshold for wayside energy storage systems (ESSs), which uses the supercapacitor as the energy storage device. First, the paper analyzes the braking curve of the train and the V-I characteristics of the substation. Then, the current-voltage dual-loop control method is used for ESSs. Next, in order to achieve the best energy-saving effect, the paper discusses the selection principle of the charge and discharge threshold. This paper proposes a control strategy for wayside supercapacitors integrated with dynamic threshold adjustment control on the basis of avoiding the onboard braking chopper’s operation. The proposed control strategy is very useful for obtaining good performance, while not wasting any energy in the braking resistor. Therefore, the control strategy has been verified through simulations, and experimental tests, have been implemented on the Batong Line of Beijing subway using the 200 kW wayside supercapacitor energy storage prototype. The experimental results show that the proposed control is capable of saving energy and considerably reducing energy consumption in the braking resistor during train braking.

Line-Voltage Control Based on Wayside Energy Storage Systems for Tramway Networks

This paper presents a control strategy for the power flow management of a wayside energy storage system based on a supercapacitor technology installed in a tramway network. The control is based on the management in real time of voltage levels at catenary point connections in order to optimize the energy flow among the running tramcars and substations with the goals of improving the energy saving and reducing the voltage drops in the supply network. The suggested control algorithm was experimentally validated using a laboratory-scale model to verify the effectiveness of the strategy. A lithium-ion capacitor module with 72 series-connected laminated cells of the JSR Micro ULTIMO type was used. Thus, an emulation of a real tramway network in the city of Naples (ANM) was implemented to evaluate the potential impact in terms of costs/benefits of the next installation on the ANM network.

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