- Hybrid Power Technologies in Railway Vehicles and Automobiles
Hybrid Power Technologies in Railway Vehicles and Automobiles
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
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.