Abstract:
Regenerative braking system (RBS) is a kinetic energy storage system installed in
parallel with conventional brakes in new generation of hybrid vehicles. These units
result in higher overall efficiency and reduced emissions. However, there are no
RBS systems in use for exiting local buses of Sri Lanka. Also, available RBS systems
in electric hybrid cars and similar vehicles cannot be directly fitted to the local
passenger buses due to limited capacity and cost concerns. In this background, the
aim of this research was to develop an alternative RBS applicable for passenger
busses. After a detailed literature review and conceptual designs, a flywheel based
RBS was selected mainly due to the installation, performance, maintenance and
investment concerns. Accordingly, computer modelling and simulations were
done to optimise the system configuration. Then, a physical model was fabricated
consisting of an electric motor, variable speed drive and two flywheels. In order to
simulate the regular operation of the bus, the motor was rotated at known speeds
and a primary flywheel was attached to it through a fixed gearing. During the
braking stage, the motor was disengaged from the primary flywheel and
immediately after that, a secondary flywheel was engaged with it using a variable
speed drive. During the generation cycle, the secondary flywheel was taken as the
energy source for driving the primary flywheel through the variable speed drive. In
both cases, the variable speed drive was set such that the flywheel which supplies
energy always rotates at a higher speed compared to the flywheel which absorbs
energy. Accordingly, the lab scale model resulted in 60% of breaking energy
regeneration, compared to 80% prediction by the simulations. With further
developments, the proposed system has .a higher potential to be used in real
passenger busses as an effective RBS.
