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2006-01-0218
A Hybrid Powertrain Provided with an
Emulated Fuel Cell System and a Battery Pack: Experimental Results
藏戏教案
Marco Santoro, Manlio Pasquali and Gianfranco Pagni
ENEA Rearch Center “Casaccia”
Luca Solero
University of Rome “ROMA TRE”
Reprinted From: Applications of Fuel Cells in Vehicles 2006
(SP-2006)
2006 SAE World Congress
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April 3-6, 2006
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ABSTRACT
The increasing concern about polluting emissions of vehicles, the cost and the limited availability of
petroleum are urging many rearchers in the world to develop innovative and more energy-efficient traction powertrains. In order to improve the energy conversion efficiencies into the vehicle, auto manufacturers are looking at new energy-storage-system technologies and fuel converters with great interest. The University of Rome“ROMA TRE” and ENEA (the Italian National Agency for New Technologies, Energy and the Environment) have jointly developed and tested a Fuel Cell Emulator, able to feed a vehicle powertrain just like an actual fuel cell should do. Aim of this work was to substitute the fuel cell with a much more reliable device and test different powertrain layouts and control strategies. This approach allows comparing different powertrains by simply resizing their components. INTRODUCTION
Comprehensive studies (e.g. [1]) have compared veral powertrain layouts and technologies to a reference conventional vehicle - provided with gasoline engine and automatic transmission - over many driving schedules. The cycles with low power demand (low speed or stop-and-go operations) appear to be the most suitable for hybrid operations. The results are logical considering the sources of savings for hybrid vehicles: regenerative braking, no engine idling, and better powertrain efficiency at low power demands.
When considering the introduction of advanced vehicles, a complete well-to-wheel evaluation must b
e performed to determine the potential impact of a technology on carbon dioxide and Green Hou Gas (GHGs) emissions. A well-to-wheels (WTW) analysis of a vehicle/fuel system covers all stages of the fuel cycle, from energy feedstock recovery (well) to energy delivery at the vehicle’s wheels. A WTW analysis is also referred to as a fuel-cycle analysis. Considering fuel economies for the different vehicle’s configurations on the U.S. Combined cycle (including FUDS and FHDS) it is clear that substantial gains can be achieved through dielisation or hybridisation. The results considering well-to-pump (WTP), pump-to-wheels (PTW) and WTW powertrain efficiencies for the combined cycle imply that: • Dielisation can increa the efficiency by more than 20%,
• Hybridisation alone leads to an improvement of more than 30%,
• Dielisation and hybridisation lead to an improvement of more than 50%,
• A gain of more than 150% can be obtained with the hybrid fuel cell. The hybrid fuel cell configuration combines high fuel-cell-system efficiency and regenerative braking to achieve the highest fuel economy.
Considering the energy loss during the NEDC (New European Driving Cycle) cycle for each component for the configurations considered, the same analysis shows that the engine is, by far, the
least efficient of the components (accounts for more than 75% of the total loss for the reference ca). Fuel cell vehicles lo only half the energy of the best parallel ca. Moreover, a hybrid fuel cell powertrain consumes less energy than a system containing only a fuel cell. The weight advantage of the fuel cell system is not sufficient to compensate for the loss in regenerative energy. Fuel cell vehicles supported by an energy storage system achieve the highest fuel economy. This is why regenerative braking energy may be stored and the fuel cell can often operate in high-efficiency regions.
Other studies [2] pointed out that on a fixed time budget, vehicle miles travelled by vehicle vary inverly with the average driving speed. In other words, personal vehicles bad in congested urban areas may accumulate fewer miles of driving per year than suburban-bad vehicles. Thus, owners of hybrid vehicles living in congested areas may drive less than hybrid owners living in suburban area, nullifying the large fuel economy
2006-01-0218
A Hybrid Powertrain Provided with an Emulated Fuel Cell
System and a Battery Pack: Experimental Results
Marco Santoro, Manlio Pasquali and Gianfranco Pagni
ENEA Rearch Center “Casaccia”
Luca Solero
糖醋鲤鱼做法University of Rome “ROMA TRE”Copyright © 2006 SAE International
advantage they hold over comparable conventional vehicles. Nonetheless, we believe that the extensive u of hybrid vehicles should dramatically improve the air quality in urban areas. This is th
anks to the degrees of freedom the powertrains are provided with which allow to design low tailpipe-emission vehicles especially conceived for urban traffic.
Becau of their high efficiency and low emissions,fuel cell vehicles are undergoing extensive rearch and development. A clean vehicle, such as a fuel cell vehicle, does not mean that there are no emissions from a well-to-wheel perspective. When producing hydrogen from reforming at a station, fuel cell vehicles have a lower advantage in terms of efficiency and emissions. Emerging methods for generating hydrogen by exploiting renewable energy sources (e.g. [3]) will soon allow considering fuel-cell-propelled vehicles as actual Zero Emission Vehicles (ZEVs).
AIM OF THE WORK
Aim of our work was the realization of a fuel cell emulator able to generate the voltage/current relationship the fuel cell would supply,and investigate different control approaches of a hybrid powertrain containing a battery pack. The emulator has to be a much more reliable “fuel converter” than the actual fuel cell. During testing, the emulator has been constrained to operate in steady state conditions, i.e. the fuel cell current rate has been continuously monitored and constrained.
A major European automobile manufacturer has provided us with a Simulink model of a 60-kW PEM fuel cell (Fig. 1). The model is mostly empirical,relying on fuel cell component input/output relationships measured in the laboratory and quasi-static, using data collected in steady state tests. Most of the data are contained in look-up tables. By changing the number of elementary cells in the model, we have modified the size of the fuel cell, and we have therefore tested and compared the behavior of different-size fuel cells.
We have modified at ENEA labs in Rome a battery cycler, i.e. an AC/DC converter that is able to charge and discharge a battery pack according to a chon voltage/current law. Such modified battery charger can be driven from external signals, calculated by the model
described above.
Fig. 1: 60kW PEM fuel cell
THE POWERTRAIN
We have shown in previous papers [4, 5] the availability and effectiveness of our Multi Input Power Electronic Converter (MIPEC). This device manages the bidirectional power flow from three different sources for feeding a traction drive (Fig. 2).
Fig.2: MIPEC manages the power flowing from a Battery
Storage Unit (BSU), an UltraCapacitor tank (UC) and the Fuel Cell (FC) to the Traction Drive The powertrain does not contain any ultracapacitor and therefore just two inputs of MIPEC can work in this test.The fuel cell system has been emulated thanks to the battery cycler (3-pha AC/DC converter) and a suitable DC link capacitive filter. An x86 real time microprocessor platform (PC 104) regulates the output voltage of the FC emulator as function of the output DC current and the operating temperature.
The microprocessor controls the emulator on the basis of the fuel cell model: at a given current generated by the emulator, the instantaneous output voltage can differ on dependence - this is evident at low-load currents - on the operating conditions (Fig. 3).
Fuel Cell Voltage vs. Current
10
20
30
40
50
60
70
80
90
大话西游语录100
110
120广阔天地
130
140
150
Current [A]
Fig.3:Minimum, mean and maximum fuel cell Voltage
vs. mean supplied Current The powertrain is completed by a VRL A battery pack and a traction drive (induction motor with peak power of 30kW and continuous power of 15kW), coupled to a
four-quadrant-operation dynamometer (Fig. 4).
Fig. 4: 15kW continuous-, 30kW peak-power traction
drive, mechanically coupled to dynamometer
HOW THE TEST BENCH OPERATES
Fig. 5: Layout of the powertrain under testing
Referring to Fig. 5, PC104 microprocessor and boards, with a time step of 0.1s x
Calculate hydrogen consumption, fuel cell temperature and voltage in dependence on the current requested
容易紧张怎么办
x Drive the cycler by imposing the voltage the fuel cell would supply
x Calculate the batteries state of charge and their maximum allowable current
x
Calculate and nd to the MIPEC DSP the maximum current and the maximum current rate the fuel cell could meet
x Acquire fuel-cell emulator current and voltage x
Acquire batteries current and voltage
纸鸢飞
淑女头像The MIPEC DSP x
Receives information from the PC104 microprocessor concerning maximum fuel cell current, maximum battery current, maximum rate of the fuel cell current
x
Drives MIPEC switching devices (i.e. calculates their duty cycles length) and thus determines the current flows from batteries and fuel cell.
Torque and speed from the drive are acquired with a time step of 1s during testing.
Main aim of the powertrain control strategy -this algorithm is implemented in the PC104 boards -is to
limit the fuel cell power rate. This result can be gained by introducing an energy storage system which allows supporting the rapid change of power flows over the driving schedule. Moreover, the VRL A battery pack allows recovering energy during vehicle braking and coastdown.
The adoption of a hybrid configuration allows decreasing the cost of the powertrain: a fuel cell of lower size - supported by an energy storage system - can feed a vehicle with the same performance that should be met by a vehicle provided with a full-size one.
Varying the quantity of elementary cells in the model we have rescaled the fuel cell size and tested the behavior of powertrains propelled by a 7-, 15-, and 22-kW fuel cell,with the same battery pack at three different initial SOC values.
Fig.6shows how the powertrain power flows are qualitatively managed. When the vehicle accelerates, the fuel cell meets the power request (Pload ) like a
