For the first time in human history, more than half the world’s population now live in cities. By 2030, 5 billion people are expected to live in high density urban areas. This migration can have positive consequences to the environment as large cities are more energy efficient. A New York City resident’s carbon foot print is 30% that of a suburban or rural counterpart. However, this population density also throws up a serious set of challenges.
Careful urban planning is needed to optimise high-demand land and space for various uses including housing, work space, parks and green surfaces and parking. Transportation systems must be integrated, effective, sustainable and affordable to reduce/eliminate the need for personal cars. There must be systems in place to reduce pollution, greenhouse gases, NOx (nitrogen oxide) emissions, particulates, and heat island effects from buildings and vehicles. Natural resources have to be managed to enable the reuse of refuse material and minimise water and energy consumption.
The International Energy Agency (IEA) predicts that transport energy use and emissions will increase by over 50% by 2030 and more than double by 2050. In the UK, nearly 21% of the country’s CO2 is generated by domestic transport, dominated by passenger cars.
Hybrid Power
Governments are now funding initiatives to counter these challenges. One that has been identified by the Intergovernmental Panel on Climate Change (IPCC) is hybrid propulsion. When trialled in buses and trucks it has resulted in improved fuel consumption and CO2 and greenhouse gas emissions reduced by 20% to 40%.
Achieving and delivering a heavy-duty hybrid solution that addresses the demand for sustainability is a complex task which can be approached in several ways. At the same time, organisations investing in these new technologies need to realise a return on investment while providing a product that meets all the expectations of the end users, including affordability. This means that the product must provide the best performance in terms of fuel efficiency, reliability, reduced emissions, lower operating costs, passenger comfort, and lower noise, while keeping the cost of its production as low as possible.
When planning an urban rail system, it must be remembered that the largest element in the overall life cycle cost of a fleet of trains is the energy consumed for train propulsion. In many western European countries and in North America, that electricity is mostly generated using fossil fuel and nuclear-based power generators.
In an urban environment, light rail vehicles can be more popular and hence more justifiable if a solution can be found that minimises or eliminates the implementation of costly, unsightly and maintenance-prohibitive overhead power lines and catenaries in specific areas.
Considering the above, there is a considerable opportunity to reduce overall emissions, cost and our dependence on fossil fuels.
Varied technologies
In order to achieve transportation systems sustainability, a variety of technologies need to co-exist. Technology and product development strategies must maximise the benefits derived from investment in advanced power management and propulsion systems. Production volumes have to be increased to drive down unit cost, and improved reliability will reduce the need for complex and expensive product maintenance and field support.
Different companies, with different cultures and pedigrees, have varying views on the best way to achieve a balanced equation of cost vs. performance. BAE Systems has 60 years of expertise in power management and control for commercial and military aircraft, so its engineers can think at the system level to develop hybrid propulsion solutions. Achieving a sustainable solution requires a complete understanding of its purpose and the way it is used, its support in the field, a whole-life cost that would be acceptable to the marketplace and how it will evolve in the next 20 to 50 years. Other important considerations include an understanding of the politics that shapes the various global markets, local environmental and energy policies, and the acquisition processes of such vehicles and fleets.
Potential adjacent markets and applications for components have to be considered for both subsystems and perhaps the entire system as well. Using the same components in different market sectors will increase volumes and have a beneficial effect on both costs and return on investment. Light rail, renewable energy and military hardware are examples of adjacent markets that can use the same technologies.
Many facets
The intimate understanding of this multi-faceted puzzle allows the most appropriate team members to be brought together, including supply chain, vehicle OEMs, end-users, policy makers and local communities. This philosophy was the foundation that supported BAE Systems’ continued investment in developing, maturing and delivering a range of hybrid propulsion and power management solutions, branded as HybriDrive®, for buses, trucks, and light and heavy rail applications.
The result of this systematic approach is a family of components and subsystems that are flexible in nature and that can be integrated in various ways to support each application. Such components include:
• Liquid cooled high torque and power density electric power generators and traction motors that are based on induction and/or permanent magnet technology. These electric machines are scalable in torque and power by changing their axial length and are designed to meet both stringent military and commercial requirements.
• IGBT (Insulated Gate Bipolar Transistor) and MOSFET (Metal Oxide Semiconductor Field-Effect Transistor) based liquid cooled state-of-the-art Power electronics converters (inverters and DC-DC converters) scalable in power via the addition or removal of power stages that meet the needs of commercial and military vehicles.
• Advanced energy storage systems that utilise a variety of chemistries and technologies (nanophosphate lithium-iron power cell based, ultra-capacitor based, lead-acid and others) combining liquid and air-cooled solutions as well as rugged designs to meet stringent shock, vibration and other harsh operational conditions.
• Advanced energy and power management algorithms that ensure an optimised system operation through an intelligent energy and power flow between the various subsystems. Such algorithms include Energy Storage System State of Charge management, vector control of traction motors and generators and prime mover engine management controls.
• Battery chargers developed to support the needs of electric vehicles as well as plug-in hybrid vehicles.
Benefits
Detailed analyses carried out to assess and quantify the benefits of introducing the above advanced and matured technology into the rail industry showed very enticing results. For example, the introduction of an on-board energy storage system that is optimised for a specific set of duty cycles and train sizes leads to an improvement of 15% to 30% in energy consumption on LRV, metros, and DMU type trains. This also reduces the number of power sub-stations that are required. The energy storage system can provide an additional 20% to 70% additional power through the “booster effect”, improving train acceleration by up to 30% from 0 to 100 km/hr, and that in turn can lead to reduced headways. Overall, the reduction in energy consumption can decrease CO2 emissions by 15% to 30%.
As an example, a tramway that needs to operate catenary-free for a distance of 2 km or more while supporting functions such as air-conditioning can be powered with three BAE Systems HybriDrive® Series ESS modules integrated in parallel. Such a solution including all the required protection and distribution devices, as well as cables, cooling, and support structure needs, will weigh 1600 kg and will occupy a total of approximately 3m3. The achieved small volume and weight will make the introduction of this technology attractive to the rail market whilst taking advantage of economies of scale to reduce acquisition costs as modules are already in production and in use in buses.
BAE Systems has a long legacy of proven technology development and commercialisation deployed in a variety of applications and adjacent industries. Trends in the energy market, as well as strong global urbanisation, require the introduction of cleaner, greener, fuel and energy efficient power management and propulsion technologies to support the rapid development and deployment of sustainable people and goods transport systems. Hybrid power systems are one way to achieve this.
