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PSL Projects : Fuel cell power sources and fuel cell hybrid power sources
Study fuel cell power sources and fuel cell involved hybrid power sources to meet power/ energy requirement for next generation portable/ mobile applications.
Twenty-first century handheld electronic devices and new generations of electric vehicles or electric airplanes have fueled a need for new high-energy, high-power, small-volume, and lightweight power sources for both military and commercial markets. Current technology batteries by themselves are insufficient to provide the long-term power (energy between refuelings) that these systems require. Fuel cells of reasonable size may provide the necessary energy, but are then unable to provide the high peak power occasionally demanded by these systems. Hybrid systems composed of fuel cells and secondary batteries combine the high energy density of fuel cells with the high power density of batteries. A fuel cell-battery hybrid system could have a number of advantages over each standalone component. Provided that the temperature was not too cold, the battery could enable instant cold-start operation since it can provide a majority of the load power requirement while the fuel cell is warming up. The battery could also condition the power output from the fuel cell to provide a voltage range that is acceptable to the equipment since most devices are already designed to accommodate the source characteristics of a battery. A hybrid system could allow both components to be of smaller dimensions and to operate with higher efficiency since neither would have to provide full load and capacity.
Fuel Cell Sources
Figs. 1, 2 and 3 show available fuel cells in the Power Sources Lab.
Fig. 1. Proton Exchange Membrane (PEM) fuel cell (rated power 1.5 KW).
Fig. 2. Proton Exchange Membrane fuel cell
(rated power 35 W).
Fig. 3. Direct Methanol fuel cell (DMFC) (rated power 20W).
Hybrid Fuel Cell/ Battery Power Sources
The simplest hybrid configuration is formed by connecting the fuel cell and the battery directly. In contrast to simple power sources (a battery alone or a fuel cell alone), such a passive hybrid demonstrates a longer run time and a higher power capability. The hybrid configuration also decreases the stress on the fuel cell and accordingly smoothes the hybrid source terminal voltage and decreases internal power losses. However, such hybrid sources have several disadvantages. First, the battery stack terminal voltage must match the nominal voltage of the fuel cell, which limits the battery pack design. Secondly, since the power distribution between the fuel cell and the battery is passively determined by the impedance characteristics of each component, the hybrid source performance may be un-necessarily limited by one of those two components. For example, the peak power capability of the hybrid may be restricted by the fuel cell when the fuel cell first reaches its safe power limit even while the output power of the battery is still well below its maximum. These disadvantages can be eliminated by interposing a DC/DC power converter between the fuel cell and the battery, creating an actively controlled hybrid source. In active hybrids, the power converter is controlled to regulate the power sharing between the fuel cell and the battery in order to maximize the advantages of each component. For example, the fuel cell and the battery can be controlled to generate the maximum power from each simultaneously; hence the peak power capability of an active hybrid can be higher than that of a passive hybrid.
Po wer Stage Design
Figs. 4-6 shows the power converters designed for hybrid
power sources in the
Fig. 4. 1.5 KW bi-directional power converter.
Fig. 5. 100 W power converter for portable applications.
Fig. 6. 200 W bi-directional power converter
Hybrid Fuel Cell Po wer Sources
Figs. 7-8 shows the hybrid power sources designed in the
Fig. 7. Hybrid power source using 1.5 KW PEM fuel cell.
Fig. 8. Hybrid power source using 35
