Environmental Engineering Reference
In-Depth Information
systems for regenerative breaking. They could be also used alone in a vehicle, but
the best use of these components is in hybrid configurations for giving out energy
during accelerations and receiving it during braking in a rapid way. Moreover,
super capacitors are safer than flywheels, as they do not present problems of
mechanical breakdown and gyroscopic effects; however, other devices such as
power electronics converters are generally required to step up and down the
voltage.
Several research studies have been carried out with super capacitors playing a
significant role in the management of energy on board [
41
-
45
].
5.5 Hybrid Propulsion Systems
A generic hybrid vehicle is powered by at least two different power sources on
board. There are many possible variations of hybrid vehicles depending on
thetypeofsourceandthemechanicaland electric connections among them.
The battery pack play a key role in any type of hybrid vehicle, and has to be
designed taking into account that battery duty cycle and therefore depth and
frequency of discharge is dependant on the hybrid configuration chosen for the
vehicle. In hybrid configurations for which the battery storage system is used to
assist energy sources on board only during acceleration, hill climbing and slow-
speed moving, the battery remains in the same state of charge for most of its
life, and thus deep discharges do not happen very often. This way of operate for
batteries tends to make the battery life longer that those used for pure electric
drives or hybrid configurations with a small storage system where the power is
mainly supplied by the energy source on board, such as a motor-generator with
a thermal engine or a fuel cell system. On the other hand, vehicles with a low
energy storage system require a high recharging rate during regenerative
braking, which is a characteristic satisfied by storage systems with a high
specific power.
These considerations are closely examined in the following sections, where
different type of hybrid vehicles are described, starting from those already com-
mercially diffused (HTEV) up to hydrogen fuel cell electric vehicles (HFCEV),
passing through less usual solutions, such as vehicles using solar energy or
alternative storage systems [
3
,
4
].
5.5.1 Hybrid Thermal Electric Vehicles
Hybrid vehicles equipped with an internal combustion engine, batteries and an
electric motor/generator (HTEV) is the most commonly studied and experimented.
The basic configurations for HTEVs are the series hybrid and the parallel
hybrid, which are shown in the Figs.
5.17
and
5.18
, respectively [
1
]. In the series
