Senthilnathan Mariappan ABB Motion, Traction Untersiggenthal, Switzerland, email@example.com
Of all transport modes, rail is one of the most electrified and is a sustainable alternative to other transport modes, both in terms of energy use and carbon emissions per passenger-kilometer or ton-kilometer. In fact, trains are significantly more efficient than cars and trucks even when they are powered by fossil fuels. The rail business is also an exception in the transport sector in that it has consistently reduced its emissions while increasing passenger and freight volumes.
Nevertheless, the railway sector is striving toward further improvements in energy efficiency and lower carbon footprint so that it can maintain its environmental advantage and become the backbone of a sustainable, multimodal and safe transport system.
Further, the pace of electrification is too slow in many countries for various reasons. Therefore, it is essential to find alternative solutions that either eliminate the need for fossil-fuel-powered rail vehicles or, at the very least, lower their carbon footprint, since complete electrification of the railway network is not always economically feasible. →01.
Alternative traction systems in railways
Alternative low-carbon traction systems with embedded onboard ESSs are becoming integral to the transition toward sustainable transportation solutions. The increasing adoption of these technologies across a broad spectrum of applications from light rail vehicles to heavy haul locomotives and infrastructure maintenance vehicles not only helps to decarbonize rail transport but also delivers other benefits, including lower total cost of ownership (TCO) when compared to incumbent combustion engine-based solutions. Further, they help to improve the operational performance of the vehicle, provide more flexibility and lower capital investment in infrastructure.
Application diversity in railway applications
An onboard ESS can be used as the main energy source in battery electric vehicles and enable them to operate over non-electrified sections. In hybrid vehicles, the ESS works as a buffer storage and provides peak power that helps to reduce the installed power of the primary power source, be it the diesel engine or a fuel cell, and allows the recuperation of braking energy. Further, peak shaving helps to operate the primary power source more often at its maximum efficiency point and reduce fuel consumption.
In diesel-hybrid applications, the presence of an onboard ESS further helps to reduce harmful emissions when the vehicle is at a station by utilizing the energy stored in the batteries to feed auxiliary loads and accelerate the vehicle out of the station.
In vehicles operating with a DC catenary supply, the use of an ESS helps to maximize the recuperation of braking energy in networks with receptivity limitations, stabilize the line voltage due to peak shaving – which allows a network density increase without costly infrastructure upgrades – and reduce the rail-to-ground potential.
Meeting all these demands calls for robust and reliable traction batteries that can deliver the required performance with maximum safety and reliability over a long service life that can extend up to 15 years or more.
Characteristics necessary for rolling stock traction batteries
Performance requirements for rolling-stock traction batteries are more demanding than those of an electric car due to the operating environment, applied stress levels and utilization level. To put this in context, most electric cars are typically parked for around 95 percent of their lifetime and cover under 100,000 km in 10 years. In contrast, a typical commuter train has an operational lifetime of around 30 to 35 years, is in operation for 16 to 18 hours a day, 350 days a year and travels 1,000,000 km in under five years. These factors result in a cumulative stress on the battery that is around 20 times higher than that for an electric car battery. Furthermore, traction batteries must also offer a high level of inherent safety, provide high availability, avoid performance drop-off during hot or cold days, have a long lifetime and have high power capabilities (in both charge and discharge) over wide temperature and state-of-charge (SoC) ranges.
These considerations mean that the selection of rolling stock traction batteries must not be made exclusively using cost per kWh or specific energy as key performance indicators (KPIs). Instead, purchasing decisions must be based on the expected TCO over the vehicle’s lifetime and place emphasis on selecting a battery that can operate reliably under harsh environmental conditions.
Modular high-performance batteries
To address these requirements, ABB has developed BORDLINE ESS – a high-performance Li-ion battery based on ABB’s deep technological knowledge and domain expertise honed over years of experience in the railway sector.
To ensure high quality and reliability, BORDLINE battery packs are based on modular hardware and software building blocks. This approach allows a high level of standardization at both the battery module and pack level without compromising the flexibility required to tailor solutions according to OEM needs and ensure a faster time to market →02-03.
At the core of each battery pack are modules equipped with high-power prismatic lithium-ion cells that incorporate a lithium titanium oxide (LTO) anode. Batteries with an LTO anode are an ideal choice for rolling-stock applications as they offer high inherent safety (such as tolerance to abuse), a long cycle life, fast charging capability, excellent lifetime (even at 35 °C) and good low-temperature performance. LTO batteries also allow operation over a wide SoC without power restriction.
The battery module features a patented liquid-cooling concept that helps to maximize battery performance and lifetime in even the most demanding applications. The cells are laser welded, a fusion process with less heat input to the cell. The process is precise, highly repeatable and ensures a very stable electrical connection with low contact resistance. Laser welding minimizes contact degradation over the cell lifetime due to the reduced risk of oxidation or corrosion between cell tabs and bus bars.
Benefits of standardized modular building blocks
ESSs based on standardized and modular building blocks offer several advantages, including:
• Scalability: The voltage and energy of the ESS can be easily set according to customer needs. This design approach results in a minimal set of modules that can cover many applications.
• Higher availability: Failure in one battery pack will not result in failure of the total system. The vehicle can continue operation after the faulty pack is isolated.
• Excellent safety: In the unlikely event of a thermal runaway, it is limited to and contained within a single sub-pack within the larger system. At the same time, the design and cell selection in BORDLINE ESS make a thermal runaway event very unlikely to start with.
• Faster service: Individual packs can be exchanged instead of having to dismount the entire system from the train.
• Flexibility: The battery system can be easily adapted to changing needs by increasing or reducing the number of packs, even in operating fleets.
• Versatility: The standardized system can be integrated flexibly and easily into the train – on the roof, underfloor, or in the machine room, with only adaptations to the mounting interfaces. →04.
Production and testing of modules
The battery modules are produced on a semi-automated production line in Baden, Switzerland that includes robots for pick and place →05, laser welding and quality checks. Burn-in test results and other relevant parameters are recorded and fed into a remote condition monitoring system to establish the basis for monitoring field performance.
Digital solutions enhance customer value
To further enhance customer value, ABB has developed a suite of remote service solutions that ensure optimal utilization of the ESS, offer an overview of the installed base and carry out a cross-fleet analysis. Analysis of field data provides valuable insights into the current health of the battery and can be used to identify and implement corrective actions or make informed decisions regarding optimization and safety. Remote access to field data also speeds up troubleshooting and implementation of corrective measures.
ABB has successfully delivered or is delivering high-performance traction batteries to more than 550 railway vehicles with references covering the entire range of railway applications. Two such examples are presented below.
Battery electric trains for northern Germany
ABB is working on an order for the Swiss rail vehicle manufacturer Stadler to deliver energy-efficient traction converters and ESSs for the operator Nahverkehrsverbund Schleswig-Holstein GmbH (NAH.SH) in northern Germany. ABB’s traction components will be installed on 55 new bi-mode electric multiple units that will operate on a partially electrified network on which the longest unelectrified route is around 80 km →06. The use of high-performance batteries ensures that the vehicle has the same performance in both electric and battery mode.
Bi-mode hybrid trains for Trenitalia
ABB is delivering BORDLINE ESS and DC-DC converters to Hitachi Rail’s Masaccio Hybrid Bi-Mode Multiple Units being delivered to Trenitalia. The ESSs for the 70 trains are primarily intended for storing the energy regenerated during braking while operating in diesel mode. The stored energy will be re-used to provide motive power support to the vehicle during the acceleration phase and to feed onboard auxiliary loads at specified station stops, thereby removing the need to operate the diesel engine and thus reduce local emissions.
Accelerating the transition to a low-carbon future
Globally, the railway industry is working to improve energy efficiency and meet emissions targets that will further strengthen its position as the most efficient and environmentally friendly mode of transport. The technologies required to deliver significant improvements are not only available but also proven. Furthermore, with BORDLINE, the need for high-performance, long-life and safe traction batteries is no longer an Achilles heel for the rolling stock industry.