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I.
Goal
Hybrid
Electric Vehicles (HEVs) combine two or more energy conversion technologies
(e.g., heat engines, fuel cells, generators, or motors) with one or more energy
storage technologies (e.g., fuel, batteries, super capacitors, or flywheels).
The combination of conventional and electric propulsion systems offers the
possibility of greatly reducing emissions and fuel consumption.
Using
VTB to make accurate component model and vehicle simulation is helpful to study
and make intelligent choices about efficient energy management strategies.
Simulating vehicle and component will help to increase the life of components,
improve vehicle performance, optimize vehicle system designs, and reduce
development times. Simulation modeling is critical to rapid and efficient
advanced vehicle development.
II.
System
The following system is composed of (i) a
fuel cell system as the prime source of electric power. Battery and super
capacitor bank as energy storage devices for high and intense power demands.
(ii) Buck and bi-direction DC-to-DC power converters to control power flow,
(iii) Driving pedals and steering wheel as the diver commands input, (iv) a DC
motor and mechanical part integrated as the driving part of vehicle, (v) a
common DC bus for energy distribution, and (vi) a supervisory controller to
control and balance the whole system.
System schematic is shown in Fig. 1.
Fig. 1. Schematic of HEV system in VTB
III. Some
Simulation Results
1, Acceleration and
Deceleration
In the following example of driving simulation, the vehicle is first accelerated to 29 m/s in 15 seconds, then cruises for 15 seconds at this speed, and finally decelerates and stops in another 15 seconds.
Fig. 2. Vehicle speed
Fig. 3 shows the current distribution on the DC bus to
different components. The fuel cell stack current is positive and it
increases/decreases slowly according to the internal limiter. It reaches its
maximum value of about 60 amps (about 18Kw) at the 7th second and
begins to decrease at the 30th second. During the vehicle cruising
period, the fuel cell stack supplies all the power needed by the vehicle (about
15 Kw). The battery stack delivers most of the current during the first 3
seconds then it reaches its current limit. During the cruising period the
battery stack current is nearly zero. Finally, the battery is recharged during
braking. The super capacitor delivers peak current to the vehicle during the
acceleration and accepts almost all the regenerated current during
braking.
Fig. 3. Current distribution on the DC bus to different components, driving train converter (solid), super capacitor converter (dash), battery (dot) and fuel cell converter (dash-dot).
2, Arbitrary
driving and 3D Animation
An important feature of the VTB is its advanced visualization system, which allows full motion animation of the mechanical components. This aspect of the VTB has been utilized to achieve the full motion animation of the HEV. Fig. 4 shows the 3D visualization of the performance of Hmmwv electric vehicle, including dashboard instruments, and steering wheel for user interaction.
Fig. 4. 3D visualization of the performance of Hmmwv electric vehicle
IV. Next
Step
Next
step, we will make more detailed models and improve the topology of the system,
for example, using an induction motor or a permanent magnet motor instead of DC
motor to propel the vehicle, etc. Also a real world mini HEV electric system
will be constructed and studied.
