Energy storage systems to exploit regenerative braking in DC railway systems: Different approaches to improve efficiency of modern high-speed trains

The growing attention to environmental sustainability of transport systems made necessary to investigate the possibility of energy optimization even in sectors typically characterised by an already high level of sustainability, as in particular the railway system. One of the most promising opportunity is the optimization of the braking energy recovery, which has been already considered in tramway systems, while it is traditionally overlooked for high-speed railway systems. In this research work, the authors have developed two simulation models able to reproduce the behavior of high-speed trains when entering in a railway node, and to analyze the impact of regenerative braking in DC railway systems, including usage of energy storage systems. These models, developed respectively in the Matlab-Simscape environment and in the open source Modelica language, have been experimentally validated considering an Italian high-speed train. After validation, the authors have performed a feasibility analysis considering the use of stationary and on-board storage systems, also by taking into account capital costs of the investment and annual energy saving, to evaluate cost-effectiveness of the different solutions. The analysis has shown the possibility to improve the efficiency of high-speed railway systems, by improving braking energy recovery through the installation of such storage systems

Smart DC Grid integration in railway systems

International audienceCet article présente une nouvelle solution écologique pour récupérer l'énergie de freinage des trains par l'intégration d'un Smart DC micro-grid dans les systèmes ferroviaires. Le principe est de stocker l'excès de l'énergie de freinage dans un système de stockage hybride afin de le réutiliser pour alimenter d'autres applications non-ferroviaires qui pourraient être installées dans la station où à proximité, ce qui va améliorer l'efficacité énergétique globale du système. This paper introduces a new green solution to recover trains braking energy by integrating Smart DC micro-grid concept in railway systems. It is based on storing the excess of braking energy in a hybrid storage system and re-using it in non-railway applications such as auxiliary loads in a station or in proximity, which will increase the total energy efficiency.</p

Control of Energy Storage

Energy storage can provide numerous beneficial services and cost savings within the electricity grid, especially when facing future challenges like renewable and electric vehicle (EV) integration. Public bodies, private companies and individuals are deploying storage facilities for several purposes, including arbitrage, grid support, renewable generation, and demand-side management. Storage deployment can therefore yield benefits like reduced frequency fluctuation, better asset utilisation and more predictable power profiles. Such uses of energy storage can reduce the cost of energy, reduce the strain on the grid, reduce the environmental impact of energy use, and prepare the network for future challenges. This Special Issue of Energies explore the latest developments in the control of energy storage in support of the wider energy network, and focus on the control of storage rather than the storage technology itself

Bi-level Optimization of Sizing and Control Strategy of Hybrid Energy Storage System in Urban Rail Transit Considering Substation Operation Stability

The hybrid energy storage system (HESS) which consists of battery and ultracapacitor can efficiently reduce the substation energy cost from grid and achieve the peak shaving function, due to its characteristics of high-power density and high-energy density. The sizing of HESS affects the operation cost of whole system. Besides, operation stability (like substation peak power and voltage fluctuations) is rarely considered in urban rail transit (URT) when sizing optimization of HESS is considered. Thus, this research proposes a sizing and control strategy optimization of HESS in URT. First, the mathematic model of URT with HESS is established, which is used to simulate URT and HESS operation state by power flow analysis method. Then, based on the proposed HESS control principle, a bi-level optimization of HESS in URT is proposed. The master level aims to optimize the rated capacity and power of HESS, reducing total operational cost. Then, the HESS control strategy is optimized at slave level, reducing substation peak power and voltage fluctuations of URT. The case study is conducted based on the data of Merseyrail line in Liverpool. A comparison is also conducted, which shows that the proposed method can reduce daily operation cost by 12.68% of the substation, while the grid energy cost is decreased by 57.26%

Adaptive control method to manage SOC for energy storage in DC electric railways

Incorporating energy storage systems (ESSs) into electric railways has been shown to be advantageous for energy saving and power quality enhancement. For DC railways, the connection method of the ESS to the track may impose restrictions on charging and discharging the ESS to control the state of charge (SOC). Without management of the SOC, the ESS is shown in this study to reach minimum or maximum limits, reducing its effectiveness due to unavailability. Whilst it is possible to oversize the capacity of ESS, this incurs increased costs and requires more physical space. The main objective of this study is to propose and validate a control algorithm that prevents the ESS from reaching the maximum or minimum SOC limits whilst maintaining the benefits of the system. The main concept of the proposed control method is to dynamically update the voltage and current setpoints of the ESS to manage its SOC. The control algorithm is implemented in the MATLAB software and the simulation results are validated against experimental results, using a track emulator and supercapacitor. The findings demonstrate that, with appropriate dynamic charge/discharge control, the SOC levels can be adequately managed and no external load or source is required

A Review of Developments in Electrical Battery, Fuel Cell and Energy Recovery Systems for Railway Applications: a Report for the Scottish Association for Public Transport

This report outlines the current status of batteries, hydrogen fuel cells and short-term energy storage systems for railway and tramway applications. The report includes discussion of issues associated with regenerative braking and the recovery of energy that would otherwise be dissipated as heat during braking. As well as feeding energy back to the supply grid, as in the case of conventional electrified rail systems, energy recovery may also be achieved using batteries, supercapacitors, flywheels or hydraulic devices and developments in each of these areas are reviewed. The advantages of hybrid systems that involve combinations of different power sources and energy storage methods are emphasised and some associated design optimisation issues are discussed. For each of the developments mentioned, there is a brief account given of some transport applications in the United Kingdom and elsewhere. This is a rapidly developing field and operating experience with vehicles currently entering service in various countries will provide important additional insight within the next two or three years

Energy management and control strategies for the use of supercapacitors storage technologies in urban railway traction systems

In recent years the need to reduce global energy consumption and CO2 emissions in the environment, has been involved even in the railways sector, aimed at the highly competitive concept of new vehicles/transportation systems. The requirements hoped by the operating companies, particularly as concerns tramway and metro-train systems, are increasingly focused on products with so far advanced features in terms of energy and environmental impact. In order to accomplish this possible scenario, this could be put into effects in technological subsystems and critical components, which are able to fulfill not only functional and performance requirements, but also regarding the new canons of energy saving. On the other hand, the regional and national energetic political strategies impose a continuous effort in the eco-sustainability and energy saving direction both for the vehicles and for the infrastructure management. In this scenario, the thesis aims to fill the gap in the technical literature and deals with improving the energy efficiency of urban rail transport systems by proposing both design methodologies and effective control strategies for supercapacitor-based energy storage systems, to be installed on-board urban rail vehicles or along the rail track. Firstly, a deep, rigorous and comprehensive study on the factors which affect energy issues in a DC-electrified urban transit railway system is carried out. Then a widespread overview of the currently available strategies and technologies for recovery and management of braking energy in urban rail is presented, also by providing an assessment of their main advantages and disadvantages alongside a list of the most relevant scientific studies and well established commercial solutions. Afterwards, some effective control strategies for the optimal energy management of the supercapacitor-based energy storage system have been studied. Extensive simulations have been performed with the aim of validating the proposed techniques by employing a methodology which is based on tests carried out by means of scale models of the real systems. A wide range of experimental tests has been developed and carried out on a laboratory-scale simulator for a typical urban service railway vehicle, in order to fully confirm the theoretical performances, validity, and feasibility of the studied controls, and quantify the technical and economic advantages obtained in terms of global energy saving, voltage regulation, power compensation and infrastructure power loss reduction. The overall goal of this study is to gain an understanding of the methods and approaches for assessing the use of supercapacitor storage systems in urban rail transit oriented to the optimization of the energy saving and the reduction of the vehicle energy consumption, for whatever technological solutions are adopted