04-05-2013, 12:41 PM
A HYBRID VEHICLE CONFIGURATION WITH ZERO EMISSION
A HYBRID VEHICLE.pdf (Size: 316.55 KB / Downloads: 38)
Abstract
The search for alternatives to
petroleum economy, in automotive field,
must satisfy the energy requirements and
to offer, at least, the same performance
than conventional vehicles. This work
proposes a vehicle configuration that
satisfies its real energy requirements and
also obtains a zero level of noxious
emissions. This topology is constituted by
a fuel cell, a battery and a bank of ultra
capacitors. Once the energetic supply is
guaranteed, the second problem consists
on the power delivery control strategy. The
importance of this control is to optimize
the hybrid vehicle components operation
mode. By means of simulations, this work
shows the deficiencies of current control
systems with respect to the supply and the
energetic efficiency. Moreover, it suggests
using a fuzzy control in the proposed
topology in order to optimize the
efficiency. This control policy is currently
being developed by the author.
Key words: electric vehicle, fuel cell,
fuzzy
Introduction
The traditional fuels, as the derivatives of
the oil, present a larger number of
disadvantages than advantages. Besides
the political, social and economic conflicts
that have happened in the last decades, it is
necessary to add real facts as the high level
of emission of carbon dioxide and carbon
monoxide and the direct consequences on
the planet as the thaw of the glacial ones,
the floods, the acid rains and the
greenhouse effect. The Transport Sector
produces 22 % of the emission of CO2
calculated between 1300 and 7700 million
tons per year. From the point of view of
the safety, the petrol and combustible
diesel oil, that even being more used, are
also the most dangerous in case of
accident. In order to improve the fuel
consumption, to reduce the noxious
emissions, as well as to offer a more
economic vehicle without sacrificing
neither the security nor the performance,
hybrid technology is being object of study
and development in the framework of
automotive industry. Control “Hybrid”
concept is often used for those
configurations of vehicles which result
from a combination between an internal
combustion engine and an electric motor,
and also for those vehicles that, using only
an electric motor, have another element
that provides additional energy to the
battery. There are two different basic
topologies in electrical hybrid vehicles.
Series hybrid
The total energy on board results
from the combination of two or more
power sources (figure 1). The internal
combustion engine (ICE) connects to a
generator (GEN) to produce electrical
power. This electric power is stored in a
battery (BAT). The electrical motor (EM)
works with AC current, so an inverter
(INV) is necessary to turn the DC current
to AC current. The electric motor supplies
the traction power to wheels across a
mechanical differential gear. Therefore, the
traction is obtained from an only central
electric motor. The continuous arrows
indicate the energy flow, and the
discontinuous arrow for regenerative
braking flow. The regenerative braking is a
method to take advantage of the vehicle’s
kinetic energy during the braking.
Parallel hybrid
This topology is a combination of traction
systems: an electric motor and an internal
combustion engine work
Jointly (figure 2). The power distribution
is just mechanical. The internal
combustion engine connects directly to a
gear box (GB) to produce mechanical
power. The energy stored by the battery
converts to AC by a inverter. Then the
electric motor transforms the electric
power to mechanical power. There are
three working ways: 1- the gear box can
receive power from two sources (internal
combustion engine and battery), 2-
someone of the sources is off, 3- the
internal combustion engine drives only the
electric machine to charge the battery. The
continuous arrows indicate the energy
flow, and the discontinuous arrow for
regenerative braking flow.
SIMULATIONS
National Renewable Energy
Laboratory (NREL) has developed a
vehicles simulator called ADVISOR
(Advanced Vehicle Simulator), which is
available since 1998 [4]. In this simulator,
we can find an electric hybrid vehicle
model with a fuel cell. The additional
energy sources are only a battery. The
simulation tests were carried out with a
1380 kg vehicle and a driving cycle named
CYC_CLEVELAND that is similar to a
road cycle. Figure 6 shows that there are
differences between the demanded and the
reached velocity, whose maximum values
are around 30 km/h. This fact is caused by
the energetic insufficiency presented in the
vehicle configuration.
CONCLUSIONS
Several simulations show that the hybrid
vehicle composed of a fuel cell and a
battery is not enough to guarantee the
energy supply. Nevertheless, the
configuration composed of the three
energy sources (the fuel cell, battery and
bank of ultracapacitors) reduces the
difference between the demanded and the
supplied power. It is also showed that fuel
cell does not work in the maximum energy
efficiency range, and so a new control
strategy is justified. Due to this reason, this
new control strategy is being developed by
the authors. Because of the very nonlineal
behaviour of the components of the
electric system, as well as the complexity
of a suitable control so as to the system
works efficienly, fuzzy control policies are
being developed. These policies are based
on machine learning of models by neurofuzzy
techniques and on no-lineal control
strategies.