McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams

Hybrid Power Technologies in Railway Vehicles and Automobiles

Literature Review

The hybridisation of propulsion systems in hybrid electric vehicles (HEVs), in both railway and automotive applications, involve the implementation of the most efficient combination between power sources and energy storage devices.  The choice of power sources available for HEVs is wide and varied.  Salmasi (2007) suggests that, in terms of the power sources, the term HEV is commonly associated with an internal combustion engine and an electric motor that also serves the role of an electrical generator.

With regards to the energy storage devices in HEVs, the laws of Thermodynamics dictate that useful energy obtained from an energy store is always less than the quantifiable energy originally supplied into it.  Further to this, as discussed by Henning, et al. (2005), technology currently does not provide an energy store boasting the best in energy density (kWh/kg) and power density (kW/kg) - in terms of per unit mass, in this context.

The viability of hydrogen fuel cells in automobile HEVs was the research focus by Schofield, et al. (2005), where two high peak power ZEBRA batteries and a 6kW hydrogen Proton Exchange Membrane Fuel Cell (PEMFC) were the energy sources for driving a zero emission London Taxi.  The viability of fuel cells in automobiles is questioned due to their extremely poor regulation with load and inability to benefit from braking energies.  Restricting the physical dimensions, namely mass and volume, of the fuel cell within reasonable limits as determined by the power requirements of the vehicles drive train thereby imposes the buffering of the dynamic peak power requirements of the vehicle by a secondary energy source. The implemented energy management system was therefore required to ensure all dynamic demands of power were taken from an on-board battery.

While the utilisation of flywheel technology was easily achieved in railway applications, their implementation in automobiles is much more complicated as they tend to operate as gyroscopes with an angular momentum acting inline with the forces acting on the automobile in question and typically of a similar order of magnitude.  The solution to this problem requires the mounting of the flywheel within a number of gimbals so as to decouple the vehicles dynamic translation from that imposed by the angular momentum of the flywheel.

Related Links
To Top