Patent Application
20080044694
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. The thicknesses of layers or regions shown in the drawings are exaggerated for clarity.
Referring to
The fuel cell 20 may have a stack structure, in which the fuel cell 20 and the switch 25 are connected in the above-described manner. The switch 25, which is to control a current flow between the first through fifth unit cells 20a-20e, is maintained in an open state while the fuel cell 20 is normally operated, for example, when supplying power to a load 35. However, when power is not supplied from the fuel cell 20 to the load 35, the operation of the fuel cell 20 is stopped, or the load 35 is removed, the switch 25 is cycled ON and OFF (closed and open) until a residual fuel remaining in membrane-electrode assemblies (MEAs) of the first-fifth unit cells 20a-20e reaches a given amount. The switch 25 may be cycled ON and OFF until a residual fuel remaining between a fuel cartridge (not shown), mounted on the fuel cell 20, is completely or substantially consumed. During the cycling of the switch 25, an OFF time T, for which the switch 25 is maintained in an OFF state, is longer than an ON time t, for which the switch 25 is maintained in an ON state (T>t). Since the first through fifth unit cells 20a-20e are short-circuited when the switch 25 is turned ON (closed), the temperature of the fuel cell system may rapidly increase. Hence, the ON time t of the switch 25 should be short enough to prevent the temperature increase from affecting the fuel cell system and/or physically damaging the MEA. However, since the ON time t is dependent on various manufacturing conditions and characteristics of the MEA, a ratio t/T may be greater than zero and less than one, according to the characteristics of the MEA. For example, the ratio of t/T may be in the range 0<(t/T)<1, or in the range 0<(t/T)<0.7.
The operation of the switch 25 is controlled by a circuit unit 30 (control unit). The circuit unit 30 determines whether the switch 25 is in the ON state or the OFF state, by detecting whether the fuel cell 20 is operating and/or whether the fuel cell 20 is connected to the load 35. The circuit unit 30 can controls the ON and OFF times t and T of the switch 25, according to preset times. When the switch 25 is turned ON, the circuit unit 30 detects whether the temperature of the fuel cell system 100 exceeds a preset temperature. When the temperature of the fuel cell system 100 exceeds the preset temperature, due to the ON state of the switch 25, the circuit unit 30 may reduce the ON time t and increase the OFF time T, to constantly maintain the total time taken to consume the residual fuel remaining in the fuel cell 20. When the load 35 is connected to the fuel cell 20 during the ON and OFF cycling operation of the switch 25, the circuit unit 30 detects the connection of the load 35 with the fuel cell 20 and causes the switch 25 to be maintained in the opened (OFF) state.
The circuit unit 30 may include a first controller (not shown) that controls the ON and OFF operation (cycling) of the switch 25. The first controller selectively applies a pulse signal to the switch 25, so that the switch 25 can be cycled ON and OFF. The switch 25 can be maintained in the ON state when the pulse signal is applied to the switch 25 from the first controller. Alternatively, the switch 25 may be maintained in the OFF state when the pulse signal is applied to the switch 25 from the first controller. The cathode of the fifth cell 20e is connected to a first terminal of the load 35, via the circuit unit 30. The anode of the first unit cell 20a is connected to a second terminal of the load 35, via the circuit unit 30. The load 35 may be an electronic device that can use a primary or secondary cell as a power source. Examples of the load 35 include a mobile phone, a game player, an MP3 player, a personal digital assistant (PDA), a global positioning system (GPS), digital multimedia broadcasting (DMB), a camcorder, a camera, and the like.
While the fuel cell system 100, shown in
In detail, referring to
The fuel cell system 200 includes a circuit unit 40 (control unit). The cathode of the fifth unit cell 20e and the fifth switch 25e are connected to a first terminal of the load 35, via the circuit unit 40. The anode of the first unit cell 20a and the first switch 25a are connected to a second terminal of the load 35, via the circuit unit 40.
When the load 35 is separated from the fuel cell system, or when the operation of the fuel cell 20 is stopped while the load 35 is attached to the fuel cell system, the first through fifth switches 25a-25e are switched ON and OFF in a cycling operation, to consume the residual fuel (or a portion thereof) remaining in the MEAs of the first through fifth unit cells 20a-20e and/or to consume the residual fuel remaining between the cartridge and the MEA. The cycling operation may be repeated until the residual fuel is completely consumed. Also, the cycling operation may be repeated until a voltage of each of the first through fifth unit cells 20a-20e reaches a reference voltage, for example, 0.1 V. In the present exemplary embodiment, the voltage is an open circuit voltage (OCV) measured when the first through fifth switches 25a-25e are in an opened state, during the cycling operation of the first through fifth switches 25a-25e. Since the first through fifth unit cells 20a-20e are short-circuited when the first through fifth switches 25a-25e are closed, an ON time t1, for which the first through fifth switches 25a-25e are maintained in a closed state, can be shorter than an OFF time T1, for which the first through fifth switches 25a-25e are maintained in the opened state. For example, a ratio of the ON time t1 to the OFF time T1 (t1/T1) may be greater than 0 and less than 1, according to the characteristics of the MEA, that is, in the range 0<(t1/T1)<1. The ON time t1 for which the first through fifth switches 25a-25e are maintained in the closed state may be shortened or lengthened, under the control of the circuit unit 40. For example, the time t1 may be changed by a second controller (not shown) that is included in the circuit unit 40. The second controller can controls the cycling operation of the first through fifth switches 25a-25e. The second controller of the circuit unit 40 can control the first through fifth switches 25a-25e to perform the cycling operation by applying a pulse signal to the first through fifth switches 25a-25e, like the first controller of the fuel cell system of
The cycling operation of the first through fifth switches 25a-25e may be performed by using a number of different cycling methods. In a first cycling method, the first through fifth switches 25a-25e may be simultaneously switched ON and OFF. For example, the switches 25a-25e are all switched ON or OFF as a group, which can be referred to as a group cycle or group cycling.
In a second cycling method, the first through fifth switches 25a-25e may be independently operated in a sequence (sequential cycling). For example, the second cycling operation may be performed by turning the switches 25a-25e ON and OFF, one at a time, in a sequence, i.e., in a sequential cycle. A sequential cycle can comprise any suitable sequence, for example, a numerical sequence, a reverse numerical sequence, an arbitrary sequence, or a random sequence.
For example, when a sequential cycle comprises the reverse numerical sequence, the first through fifth switches 25a-25e are operated starting with the fifth switch 25e and proceeding in reverse numerical order to the first switch 25a, such that only a single switch is switched ON at a time. In detail, the reverse numerical sequence starts when only the fifth switch 25e is maintained in the ON state for a given time t1, while the first through fourth switches 25a-25d are maintained in the OFF state. Next, only the fourth switch 25d is maintained in the ON state for a given time t1, while the first through third switches 25a-25c and the fifth switch 25e are maintained in the OFF state. Next, only the third switch 25c is maintained in the ON state for a given time t1, while the first and second switches 25a and 25b and the fourth and fifth switches 25d and 25e are maintained in an OFF state. Next, only the second switch 25b is maintained in the ON state for a given time t1, while the first switch 25a and the third through fifth switches 25c-25e are maintained in the OFF state. Next, only the first switch 25a is maintained in the ON state for a given time t1, while the second through fifth switches 25b-25e are maintained in an OFF state, thereby completing a cycle If the residual fuel remaining in the MEAs of the first through fifth unit cells 20a-20e is not completely consumed in this process, the cycle may be repeated.
In other exemplary embodiments, the order of operation of the switches in a sequential cycle can be any order, so long as each switch 25a-25e is switched ON and OFF once per cycle. When a sequential cycle comprises the numerical sequence the switches 25a-25e may be sequentially operated starting with the first switch 25a and proceeding in numerical order to the fifth switch 25e, similar to when the sequential cycle comprises a reverse numerical sequence.
When a sequential cycle comprises the arbitrary sequence, the order in which the switches 25a-25e are switched ON and OFF can be any order, so long as only a single switch is switched ON at a time, and the order is maintained in successive cycles. When a sequential sequence comprises the random sequence, the order in which the switches 25a-25e are switched ON and OFF can vary from cycle to cycle successive cycles, so long as each switch is operated once during each of the cycles.
A third cycling method comprises dividing the switches 25a-25e into a number of groups, then sequentially cycling each group. For example, the first through fifth switches 25a-25e are divided into at least two groups, such as, a first group comprising the third through fifth switches 25c-25e, and a second group comprising the switches 25a-25b. The switches of the first group may be sequentially cycled, and at the same time the switches of the second group can be cycled using a sequential cycle. In this way a switch of the first group and a switch of the second group can be turned ON at the same time.
A fourth cycling method, according to an aspect of the present invention, comprises dividing the switches 25a-25e into first and second groups, the switches of both of the groups are then group cycled. For example, the switches of the first group are all turned ON, while the switches of the second group are all turned OFF, and then the switches of the second group are turned ON while the switches of the first group are turned OFF.
Aspects of the present invention encompass cycling methods that comprise any combination of the above-mentioned cycling methods.
Referring to
The voltage can be a total voltage, which is a voltage of all of the cells 20a-20e, i.e., a voltage measured when the first through fifth switches 25a-25e are in the OFF state. When the total voltage reaches a reference voltage, a cycling operation(s) of the cells 20a-20e is stopped. For example, in the cycling operations of the first and second switch groups 50 and 60, when the total voltage reaches the reference voltage, the cycling operations of the first switch group 50 and the second switch group 60 are stopped.
The voltage of the first through fifth unit cells 20a-20e can be measured as group voltages when the switches 25a-25e are divided into switch groups. The group voltages can relate to unit cells associated with the switches of the respective switch groups. For example, a first group voltage of the first switch group 50 can be detected when the switches 25c-25e are OFF, and a second group voltage of the second switch group 60 can be detected when the switches 25a-25b are OFF. When either the first or the second group voltage reaches a reference voltage, a cycling operation applied thereto can be stopped, while a cycling operation associated with the other switch group is repeated. For example, when the first group voltage reaches a reference voltage, but the second group voltage does not reach the reference voltage, a cycling operation of the first switch group 50 is stopped, and a cycling operation of the second switch group 60 is repeated. The cycling operation of the second switch group can be stopped when the second group voltage reaches the reference voltage.
In the above described cycling operations of the first and second switch groups 50 and 60, when the first and second switches 25a and 25b of the second switch group 60 are simultaneously turned ON and OFF (group cycled), the first and second switches 25a and 25b of the second switch group 60 may be replaced with a single switch 28, as shown in
The first through fifth unit cells 20a-20e generate a maximum current when the voltage per cell reaches an ideal operation point, where the potentials of the anodes and the cathodes of the respective first through fifth unit cells 20a-20e are equal to each other. A larger current generation results in a larger fuel consumption. Hence, in the cycling operations of the switches 25 and 25a-25e of the fuel cell system of any of
Referring to
The first through fifth switches 54a-54e may perform the same function as the switches 25a-25e of
When a power required by the load 35 is greater than power supplied by the fuel cell 52, the secondary cell 58 supplies a power corresponding a difference therebetween, to the load 35. Accordingly, when the power required by the load 35 is sufficiently supplied by the fuel cell 52, the secondary cell 58 may be in a standby state. An input end of the secondary cell 58 is connected to an output end of the battery charger 62. An output end of the secondary cell 58 is connected to an input end of the converter 56. The ninth and tenth switches 54i and 54j are disposed on a wire 70 connecting the output end of the secondary cell 58 and the input end of the converter 56. The ninth and tenth switches 54i and 54j cut off or pass a current flowing from the secondary cell 58 to the converter 56, according to a signal of a control unit (not shown). The seventh through tenth switches 54g-54j may be power metal oxide field effect transistors. When the secondary cell 58 is operated to supply power to the load 35, the ninth and tenth switches 54i and 54j are in an ON state. However, while the secondary cell 58 is charged by the battery charger 62, the ninth and tenth switches 54i and 54j are in an OFF state.
A method of operating the fuel cell 52 of the fuel cell system of
A first method is performed by fully charging the secondary cell 58, and when there is still a residual fuel, cycling ON and OFF the first through fifth switches 54a-54e, or the sixth switch 54f. The first through fifth switches 54a-54e may be cycled ON and OFF in the same manner as described in the case of the first through fifth switches 25a-25e of
Referring to
A second method of operating the fuel cell 52 of the fuel cell system 80 of
Referring to the second graph G22 of
Referring to
The charging of the secondary cell 58 in the first method may be continued without interruption, until the voltage of the fuel cell 52 drops below a predetermined value. However, the charging of the secondary cell 58 in the second method may not be completed at one time, and if so, may be periodically or non-periodically repeated until the voltage of the fuel cell 52 drops below the predetermined value. The residual fuel is consumed by short-circuiting the unit cells 52a-52e of the fuel cell 52 between a charging of the secondary cell 58 and a next charging of the secondary cell 58.
The first and second methods consume the residual fuel of the fuel cell 52 by simultaneously short-circuiting the unit cells 52a-52e in the fuel cell 52, or arbitrarily or sequentially short-circuiting one or more of the unit cells 52a-52e in the fuel cell 52, that is, by turning ON and OFF the first through fifth switches 52a-52e or the sixth switch 52f, according to any cycling methods a described therein. When the residual fuel of the fuel cell 52 is consumed by turning ON and OFF the first through fifth switches 52a-52e or the sixth switch 52f, the seventh switch 54g is maintained in an OFF state.
As described above, the fuel cell system, according to aspects of the present invention, employs one or more switches between the fuel cell and the load, as means for short-circuiting the whole fuel cell, or selectively short-circuiting the unit cells. The fuel cell system, according to aspects of the present invention, also employs a circuit unit to control the operation of the switch.
Since the fuel cell system repeatedly performs the ON and OFF operation (cycling operation) on one or more of the switches, in such a manner that the ON time (short-circuit time) is shorter than the OFF time, the residual fuel remaining in the fuel cell or between the cartridge and the MEA of the fuel cell can be safely and rapidly consumed, while controlling a temperature increase of the fuel cell system.
As a result, fuel leakage can be prevented, the MEA can be prevented from being exposed to highly concentrated fuel under no load, and the residual fuel remaining in the cartridge can be removed when the cartridge needs to be replaced with a new one. Also, since the fuel is consumed due to the short circuiting of the unit cells included in the fuel cell, the configuration of the fuel cell system can be simplified. Since the residual fuel can be consumed by repeating the short circuiting, the temperature of the fuel cell can be prevented from rising, and water that is stored for reuse can be prevented from evaporating.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention. For example, various switches, for example transistors, or any other suitable switching devices, may be used as switches 25, 25a-25e, and 28. Also, instead of turning ON a switch during a short time for a plurality of times in order to consume the residual fuel the OFF time may be increased. That is, the OFF time may vary according to a time lapse. Also, the switch controller may be installed outside the circuit unit. Accordingly, the spirit and scope of the present invention is not defined by the embodiments explained above but by the following claims.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-77775 | Aug 2006 | KR | national |
| 2007-49943 | May 2007 | KR | national |
