Abstract:
The air conditioner has a variable load to undergo a rapid change in instantaneous power consumption. The fuel cell system supplies electricity generated by reacting fuel with oxygen to the air conditioner. The fuel cell system stores the generated electricity if the instantaneous power consumption of the air conditioner is lowered and supplies the stored electricity together with the generated electricity to the air conditioner if the instantaneous power consumption is increased.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 2006-0024223, filed on Mar. 12, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a fuel cell system and an air conditioner using the same, and more particularly, to a fuel cell system, which can normally supply power to an air conditioner having a variable load that undergoes a rapid change in power consumption, and an air conditioner using the same. 
         [0004]    2. Description of the Related Art 
         [0005]    A fuel cell system is an apparatus that converts chemical energy generated through oxidation of fuel to electric energy. The fuel cell system is used as a drive source for a vehicle or is connected to an electricity system to supply power to a variety of electric devices. 
         [0006]    As described in Korean Patent Application Publication No. 2003-0078973, a conventional fuel cell system includes a reformer to generate hydrogen from fuel, a fuel cell stack to generate electric energy by reacting hydrogen with oxygen, an electric energy output unit to supply electric energy generated by the fuel cell stack to a load, and a controller to control the fuel cell system. 
         [0007]    When hydrogen and oxygen are provided to the fuel cell stack, the conventional fuel cell system causes the hydrogen and oxygen to react to generate electricity and supplies the generated electricity to a load connected to the fuel cell system. 
         [0008]    However, this conventional fuel cell system is not suitable for use with a variable load, which undergoes a rapid change in compression capacity and thus undergoes a radical change in power consumption, such as a variable-capability scroll compressor described in Korean Patent Application Publication No. 2002-0066659 or a capacity-adjustable scroll compressor of Korean Patent Application Publication No. 2005-0008475. 
         [0009]    That is, the fuel cell system generally changes the amount of electricity generated by changing the amount of fuel supplied. However, it is not possible to change the amount of electricity generated by the fuel cell stack in a short time since it takes a rather long time for the change in the amount of fuel supplied to cause a change in the amount of electricity generated. The scroll compressors described above undergo a rapid change in the power consumption in a short time since they repeat an operation with a compression capacity of 0% (unloading operation) and an operation with a compression capacity of 100% (loading operation) in a few seconds. Thus, it is difficult for the conventional fuel cell system to appropriately supply required power to such compressors. 
       SUMMARY 
       [0010]    Therefore, it is an aspect of the invention to provide a fuel cell system, which can normally supply power to a variable load that undergoes a rapid change in power consumption, and an air conditioner using the same. 
         [0011]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
         [0012]    The foregoing and/or other aspects of the present invention may be achieved by providing an air conditioner using a fuel cell system, the air conditioner having a variable load to undergo a rapid change in instantaneous power consumption, the fuel cell system supplying electricity generated by reacting fuel with oxygen to the air conditioner, wherein the fuel cell system stores the generated electricity if the instantaneous power consumption of the air conditioner is lowered and supplies the stored electricity together with the generated electricity to the air conditioner if the instantaneous power consumption is increased. 
         [0013]    The fuel cell system stores the generated electricity if the instantaneous power consumption is lower than power generated by the fuel cell system and supplies the stored electricity together with the generated electricity to the air conditioner if the instantaneous power consumption is higher than the power generated by the fuel cell system. 
         [0014]    The variable load is a variable-capacity compressor that repeats a loading operation with a compression capacity of 100% and an unloading operation with a compression capacity of 0% in cycles, an average operating ratio of the variable-capacity compressor being determined using a ratio between durations of the loading operation and the unloading operation. 
         [0015]    The power generated by the fuel cell system is determined according to the average operating ratio of the variable load. 
         [0016]    The fuel cell system includes an electrical storage to store the electricity, wherein the electrical storage has a capacity that affords a quarter or less of total power consumption required for loading and unloading operations of one cycle. 
         [0017]    The foregoing and/or other aspects of the present invention may also be achieved by providing a fuel cell system including a fuel cell to generate electricity by reacting fuel with oxygen; and an electrical storage to store the electricity generated by the fuel cell, wherein the fuel cell and the electrical storage are connected to an air conditioner having a variable load, and wherein the electricity generated by the fuel cell is stored in the electrical storage if instantaneous power consumption of the air conditioner is lowered and the electricity stored in the electrical storage, together with the electricity generated by the fuel cell, is supplied to the air conditioner if the instantaneous power consumption is increased. 
         [0018]    The electrical storage stores the generated electricity if the instantaneous power consumption is lower than power generated by the fuel cell and supplies the stored electricity to the air conditioner if the instantaneous power consumption is higher than the power generated by the fuel cell. 
         [0019]    The variable load is a variable-capacity compressor that repeats a loading operation with a compression capacity of 100% and an unloading operation with a compression capacity of 0% in cycles, an average operating ratio of the variable-capacity compressor being determined using a ratio between durations of the loading operation and the unloading operation, and wherein the power generated by the fuel cell is determined according to the average operating ratio of the variable load. 
         [0020]    The fuel cell system further includes an electrical storage to store the electricity, wherein the electrical storage has a capacity that affords a quarter or less of total power consumption required for loading and unloading operations of one cycle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    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: 
           [0022]      FIG. 1  is a block diagram of a fuel cell system and an air conditioner using the same according to an embodiment of the present invention; 
           [0023]      FIGS. 2A and 2B  are sectional views of a variable-capacity compressor of  FIG. 1 ; 
           [0024]      FIG. 3  is a graph showing an operating ratio of the variable-capacity compressor shown in  FIGS. 2A and 2B ; 
           [0025]      FIG. 4  is a graph showing the output of an electric storage associated with the operating ratio of the variable-capacity compressor shown in  FIG. 3 ; and 
           [0026]      FIG. 5  is a block diagram of an air conditioner integrated with a fuel cell system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    Reference will now be made in detail to the 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 to explain the present invention by referring to the figures. 
         [0028]    As shown in  FIG. 1 , a fuel cell system and an air conditioner using the same according to an embodiment of the present invention include an air conditioner  20  to cool and heat a room and a fuel cell system  10  to supply electricity to the air conditioner  20 . 
         [0029]    The air conditioner  20  includes a fixed load  21  such as an outdoor heat exchanger blower fan (not shown) and an electrically-operated valve (not shown), a variable-capacity compressor  22  which is a variable load, a power supply  23  that transfers electricity supplied from the fuel cell system  10  to the outdoor heat exchanger blower fan or the variable-capacity compressor  22 , and a controller  24  that controls the operation of the air conditioner  20 . 
         [0030]    As shown in  FIGS. 2A and 2B , the variable-capacity compressor  22  includes a casing  30  having an inlet  37  and an outlet  38 , a motor  31  provided in the casing  30 , an orbiting scroll  32  that rotates by torque of the motor  31 , and a fixed scroll  34  that defines a compression space  33  between the fixed scroll  34  and the orbiting scroll  32 . A bypass pipe  35 , which connects the inlet  37  and an upper portion of the fixed scroll  34  to each other, is mounted on the casing  30 . A solenoid type Pulse Width Modulated (PWM) valve  36  is mounted on the bypass pipe  35 . 
         [0031]    In  FIG. 2A , the PWM valve  36  is closed to close the bypass pipe  35  and therefore a refrigerant supplied to the compression space  33  through the inlet  37  is compressed and discharged through the outlet  38 . This operation is a loading operation in which the compression capacity (or operating ratio) of the variable-capacity compressor  22  is 100%. In  FIG. 2B , the PWM valve  36  is opened to open the bypass pipe  35  and therefore a refrigerant supplied to the compression space  33  through the inlet  37  is not compressed and instead is supplied back to the compression space  33  through the bypass pipe  35 . This operation is an unloading operation in which the compression capacity (or operating ratio) of the variable-capacity compressor  22  is 0%. 
         [0032]    As shown in  FIG. 3 , the variable-capacity compressor  22  repeats the loading operation and the unloading operation in regular cycles. A loading operation time A and an unloading operation time B in each cycle is determined according to a required cooling capability. In  FIG. 3 , the X axis represents time and the Y axis represents the operating ratio of the variable-capacity compressor  22 . The horizontally dashed line in  FIG. 3  represents an average operating ratio of the variable-capacity compressor  22  when the variable-capacity compressor  22  operates at a duty ratio of  FIG. 3 . The average operating ratio is calculated using a formula “Average Operating Ratio=(Loading Operating Time/1 Cycle)*100”. 
         [0033]    The controller  24  determines the duty ratio of the loading and unloading operation times according to a required cooling capability and opens or closes the PWM valve  36  according to the duty ratio. The controller  24  also calculates the average operating ratio of the variable-capacity compressor  22  using the average operating ratio calculation formula described above. 
         [0034]    The fuel cell system  10  includes an oxygen supply  11 , a fuel supply  12 , a reformer  13 , a fuel cell  14 , an electrical storage  15 , and a controller  16 . The oxygen supply  11  supplies oxygen to the fuel cell  14  and the fuel supply  12  supplies fuel to the reformer  13 . This fuel may be gaseous fuel such as natural gas or methane or liquid fuel such as methanol or hydrazine. The reformer  13  generates hydrogen by heating the fuel and provides the hydrogen to the fuel cell  14 . 
         [0035]    The fuel cell  14  includes a number of unit cells (stack) (not shown). Each unit cell includes an electrolyte membrane (not shown), an air electrode (cathode) (not shown), and a fuel electrode (anode) (not shown). When hydrogen is supplied to the fuel electrode, it is separated into hydrogen ions and electrons. The hydrogen ions are moved to the air electrode through the electrode membrane and the electrons are moved to the air electrode through an external circuit. In the air electrode, oxygen supplied to it reacts with hydrogen ions to form water. Thus, in each unit cell, oxygen reacts with hydrogen to generate electricity and water. 
         [0036]    Since the fuel cell  14  is connected to the power supply  23  of the air conditioner  20 , electricity generated at the fuel cell  14  is provided to the air conditioner  20 . The power generated by the fuel cell  14  is determined according to the average operating ratio of the variable-capacity compressor  22 . More specifically, the level of power that is generated by the fuel cell  14  is determined to be a level which affords (or covers) power consumption required for the variable-capacity compressor  22  and power consumption required for the fixed load  21  when the variable-capacity compressor  22  operates at the average operating ratio. 
         [0037]    Consequently, as the loading operation time ratio of the variable-capacity compressor  22  increases, the average operating ratio increases and therefore the power generated by the fuel cell  14  increases. On the other hand, as the loading operation time ratio of the variable-capacity compressor  22  decreases, the average operating ratio decreases and therefore the power generated by the fuel cell  14  decreases. 
         [0038]    The electrical storage  15  includes a super capacitor and a secondary battery and is connected to the fuel cell  14  and the power supply  23  of the air conditioner  20 . As shown in  FIG. 4 , the electrical storage  15  receives and stores electricity generated by the fuel cell  14  when the variable-capacity compressor  22  is in unloading operation and discharges the stored electricity to the air conditioner  20  when the variable-capacity compressor  22  is in loading operation. In  FIG. 4 , the X axis represents time and the Y axis represents the output of the electrical storage. 
         [0039]    When the variable-capacity compressor  22  is in an unloading operation, power generated by the fuel cell  14  is higher than power consumption by the air conditioner  20  and therefore a small portion of the electricity generated by the fuel cell  14  is provided to the air conditioner  20  to drive the fixed load  21  or the like of the air conditioner  20  and the remaining portion is stored in the electrical storage  15 . On the other hand, when the variable-capacity compressor  22  is in a loading operation, power consumption by the air conditioner  20  is higher than power generated by the fuel cell  14  and therefore not only the electricity generated by the fuel cell  14  but also the electricity stored in the electrical storage  15  are provided to the air conditioner  20  to allow the air conditioner  20  to operate normally. 
         [0040]    The capacity of the electrical storage  15  is sufficient if it has a level which affords only a quarter of the power consumption required for a one-cycle operation of the variable-capacity compressor  22 . An operation pattern which requires the electrical storage  15  to supply the highest power to the air conditioner  20  corresponds to the case where the loading operation time and the unloading operation time are equal. In this case, the electrical storage  15  has to supply a quarter of the power consumption required for a one-cycle operation of the variable-capacity compressor  22  to the air conditioner  20  in the loading operation of each cycle. Accordingly, it is preferable to select the capacity of the electrical storage  15  to have an appropriate level based on the cycle (or period) of the variable-capacity compressor  22 . 
         [0041]    The controller  16  controls the fuel cell system  10  and, particularly, controls power generated by the fuel cell  14 . When it is necessary to determine the power generated by the fuel cell  14 , the controller  16  performs data communication with the controller  24  of the air conditioner  20  to confirm the average operating ratio of the variable-capacity compressor  22  and then determines the power generated by the fuel cell  14  according to the confirmed average operating ratio. To accomplish this, the controller  16  previously stores data regarding the levels of power generated by the fuel cell in association with the average operating ratios of the variable-capacity compressor  22 . When the power generated by the fuel cell  14  has been determined, the controller  16  controls the fuel supply  12  and the reformer  13  to allow the fuel cell  14  to output a target generated power. 
         [0042]      FIG. 5  shows an air conditioner integrated with a fuel cell system. Since the air conditioner  40  of  FIG. 5  includes a fuel cell system, one controller  24  controls both the air conditioner  40  and the fuel cell system. Accordingly, it is not necessary to perform data communication between the controllers  16  and  24  as shown in  FIG. 1 . 
         [0043]    In  FIG. 5 , a fuel cell  14 , an electrical storage  15 , a fixed load  21 , and a variable-capacity compressor  22  are all connected to an electricity system  50  so that the fuel cell  14  or the electrical storage  15  may provide electricity to the electricity system  50  or the electricity system  50  may supply commercial electricity to the fixed load  21  or the variable-capacity compressor  22  when needed. A description of other components is similar to that of  FIG. 1 . 
         [0044]    The following is a description of how a fuel cell system and an air conditioner using the same according to the present invention operate. If the user of the air conditioner  20  sets a target temperature and inputs an operation command to the air conditioner  20 , then the controller  24  of the air conditioner  20  calculates a required cooling capability based on the difference between the target temperature and the room temperature. The controller  24  then sets loading and unloading operation times (duty ratio) of the variable-capacity compressor  22  according to the calculated cooling capability. Here, power consumption required for the air conditioner  20  is not high and therefore the fuel cell  14  is not activated and the electrical storage  15  provides a small amount of electricity to the air conditioner  20 . 
         [0045]    When the duty ratio has been set, the controller  24  of the air conditioner  20  calculates an average operating ratio of the variable-capacity compressor  22  using an average operating ratio calculation formula and performs data communication with the controller  16  of the fuel cell system  10  to inform the controller  16  of the average operating ratio. The controller  16  of the fuel cell system  10  determines power generated by the fuel cell system  10  with reference to the data regarding the levels of power generated by the fuel cell in association with the average operating ratios of the variable-capacity compressor. The controller  16  then controls the fuel supply  12  and the like to allow the fuel cell system  10  to output a target generated power. 
         [0046]    When the fuel cell system  10  outputs a generated power corresponding to the average operating ratio of the variable-capacity compressor  22 , the controller  16  of the fuel cell system  10  performs data communication with the controller  24  of the air conditioner  20  to inform the controller  24  of that fact. Then, the controller  24  of the air conditioner  20  causes the variable-capacity compressor  22  to perform the loading or unloading operation while opening or closing the PWM valve  36  according to the duty ratio. 
         [0047]    When the variable-capacity compressor  22  is in loading operation, the power generated by the fuel cell  14  alone does not afford power consumption by the air conditioner  20  and therefore electricity stored in the electrical storage  15  is additionally supplied to the air conditioner  20 . On the other hand, when the variable-capacity compressor  22  is in unloading operation, the power generated by the fuel cell  14  exceeds the power consumption required for the air conditioner  20  and therefore the surplus power is stored in the electrical storage  15 . 
         [0048]    Although the air conditioner applied to the present invention has been exemplified by an air conditioner having a variable-capacity compressor in the above description, the present invention can be applied to any other type of air conditioner that undergoes a rapid change in the power consumption, for example an inexpensive air conditioner that repeatedly turns on and off its compressor at intervals of several minutes. 
         [0049]    As is apparent from the above description, the present invention allows even a fuel cell system with a low rate of output change to normally supply power to an air conditioner that undergoes a rapid change in the power consumption. 
         [0050]    In addition, in the present invention, the capacity of the electrical storage only has to afford up to a quarter of the power consumption required for a one-cycle operation of the variable-capacity compressor. This allows the fuel cell system to use a small-capacity electrical storage, thereby reducing the manufacturing the cost and size of the fuel cell system. 
         [0051]    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 these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.