Environmental Engineering Reference
In-Depth Information
yield the lowest overall efficiency in a WTW context due to limitations of internal
combustion engine technology. Hydrogen fuel powered vehicles have the highest
WTW efficiency due to a much more efficient fuel cell (60-70% versus 20-40%
for gasoline or diesel fuels) even though their production process fuel cycle is less
efficient.
Modelling the vehicle system is essential in a TTW energy analysis in parti-
cular because of the large number of different powertrain configurations and
technologies available. At the US National Renewable Energy Laboratory, one of
the seven national laboratories under the DOE, a mathlab program ADVISOR has
been developed that assists users in performance and economy predictions of
arbitrary hybrid vehicle architectures. ANL has developed a powerful simulation
tool called PSAT for powertrain systems analysis toolkit [6]. With PSAT users can
estimate the vehicle wheel torque necessary to track operator inputs or to follow a
regulated drive cycle speed versus time programme. With PSAT, driveline com-
ponents such as engine throttle, clutch displacements, gear selection and brakes are
all modelled so that a realistic energy picture of vehicle operations is obtained.
With PSAT, users can select from some 150 vehicle configurations, including
hybrid and fuel cell power plants. Vehicle architectures include two wheel drive,
four wheel drive and combinations as well as the ability to model transient vehicle
modes. Figure 9.3 is an illustration of PSAT's capability.
Forward modelling (driver-to-wheels) more realistically predicts system dynamics,
transient component behaviour and vehicle response.
Commands from a powertrain controller to obtain the desired vehicle speed
More accurately represents component dynamics (e.g. engine starting and warm-up,
shifting, clutch engagement ...)
Allows for advanced (e.g. physiological) component models
Allows for the development of control strategies that can be used in hardware-in-the-loop
or vehicle testing
Small time steps enhance accuracy
Figure 9.3 ANL powertrain systems analysis toolkit: PSAT (from Reference 6 with
permission)
In a full simulation environment the PSAT core model shown in Figure 9.3 can
be manipulated to include parallel hybrid M/G and controller, and the engine could
be replaced with a fuel cell power plant and ancillaries. The modular structure
admits relative ease of adding or removing functional blocks because the interfaces
are standard and well documented. During a simulation a higher level controller
representing the vehicle systems control sits atop a hierarchy consisting of ICE and
transmission powertrain controller, or a fuel cell plant and auxiliary control, or even
a BEV control architecture and virtually everything in between. PSAT is a forward-
looking model (i.e. not a programme follower) that accepts driver input commands
