| dc.description.abstract | Efficient energy storage and cost-effective solutions are vital for electric vehicle applications.
As it is widely known, the battery pack of an electric vehicle is a significant component that
determines the range and price of the electric vehicle mostly. The recent trend in electric vehicles is
using Li-Ion battery packs as the primary energy source. However, Li-Ion battery technology is still
immature and its cost is higher than other battery solutions. Although the range of recent electric
vehicles has been improved significantly with this recent battery type, their range is still less than
conventional vehicles and their market price is almost twice of a gasoline fueled-vehicle. This has
brought about new electric powertrain configurations to increase the vehicle energy efficiency.
Regenerative braking is a feature that increases the energy efficiency of an electric vehicle by
capturing the kinetic energy and storing it in the electrical energy storage unit. This unique feature
leads to drive some extra miles with an electric vehicle. However, the round-trip efficiency of the
regenerative braking is quite low in applications. The powertrain components in an electric vehicle
have more than 90% efficiency values. Improving the efficiency of the electrical machine or the
power processor unit would not increase the regenerative braking efficiency because of the overall
energy efficiency chain. In addition, regenerative braking has a power limitation that is the rated
electrical power. Because of these reasons, if we would like to improve the range of an electric
vehicle, we need to increase the regenerative braking capability. Energy form conversions should
be avoided and mechanical form of the energy in the vehicle should be kept the same as much as
possible.
In this study, we introduced a magnetically coupled three-port electric machine, the transmotor.
The transmotor consists of two mechanical ports that are decoupled and an electrical port for
the power processor unit connection. In vehicle applications, the first mechanical port can be
connected wheels. The second mechanical port in the machine can be connected a mechanical
energy storage device such as a flywheel. Hence, the structure of the transmotor creates two
mechanical paths for the energy exchange. This two-path energy exchange feature can be used to
enhance the regenerative braking capability of electric powertrains.
We developed a new powertrain configuration for electric vehicles that is called Flywheel
Transmotor (FWT) powertrain. Application of the transmotor and a flywheel in an electric powertrain
was presented. This new powertrain configuration was applied in a commercial electric
vehicle, Nissan Leaf 2012 that is currently in the electric vehicle market. Simulation models were
developed for the existing powertrain of the vehicle and flywheel transmotor powertrain. Standard
drive cycles were used to run simulations. Simulation results of the new powertrain configuration
were presented and compared with the conventional Nissan Leaf 2012 powertrain simulation results.
Effect of the new parameters that are flywheel moment of inertia and flywheel initial speed
was investigated. Performance tests were also performed and outcomes were presented. We optimized
the flywheel powertrain configuration of Nissan Leaf 2012 with the acquired simulation
data.
According to simulation results, the range of the Nissan Leaf 2012 can be increased by 14.2%
with flywheel transmotor powertrain configuration. In addition, the rated electrical power of the
traction motor and power electronics can be decreased by 25%. In other words, a Nissan Leaf
2012 can travel 14.2% more with a smaller electric power rating compared to its original powertrain.
The required flywheel weight for this powertrain is around 1-2% of the vehicle weight.
The stored energy in the flywheel is 2-3% of the battery pack energy. The control complexity of
the new powertrain configuration is less compared to existing electric flywheel powertrains in the
literature. Since we only utilize one electric motor/generator and one power electronics circuit in
the powertrain, it is a cheaper and more reliable solution than other flywheel powertrain applications.
The flywheel transmotor powertrain can be a competitive alternative for existing electric
powertrains by providing a better regenerative braking capability. | en |
