Abstract:
A fuel cell capable of load-dependent operation is constructed such that the amount of electric power required in the fuel cell, as well as the amount of electric power supplied from a utility power source, of the amount of electric power required in a load, is precisely calculated and the driving of the fuel cell is controlled according to the amount of electric power required in the fuel cell, so that an unnecessary amount of fuel consumed in the production of electric power, thereby optimizing the operation system of the fuel cell and increasing the efficiency thereof.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a fuel cell, and more particularly to, a fuel cell capable of load-dependent operation which can maximize efficiency by adjusting the electricity produced by a fuel cell.  
         [0003]     2. Description of the Related Art  
         [0004]     In general, a fuel cell is a device for directly transforming energy of a fuel into electric energy. Such a fuel cell is a fuel cell system in which an anode and a cathode are installed on both sides of a polymer electrolyte film, and which generates electrical energy by the movement of electrons created when electrochemical oxidation of oxygen serving as a fuel occurs at the cathode (oxidized electrode or fuel electrode) and electrochemical reduction of oxygen serving as an oxidizer occurs at the cathode (reduced electrode or air electrode), which may be referred to as a kind of power generation plant.  
         [0005]     The aforementioned fuel cell is classified into an alkaline fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid electrolyte fuel cell (SOFC), a polymer electrolyte fuel cell (PEMFC), and so forth, depending on operating temperature and the type of main fuels. Among them, the electrolyte of the polymer electrolyte fuel cell is not liquid but a solid polymer membrane, which is distinguished from other fuel cell types. In the polymer electrolyte fuel cell, fuels can be used typically in such a manner that a hydrocarbon (CH) fuel, such as LNG, LPG, etc, is refined into hydrogen (H 2 ) through desulfurization, reforming reaction, and hydrogen refining process at a reforming unit, and the refined hydrogen is supplied to the fuel electrode of a stack unit.  
         [0006]      FIG. 1  is a systematic view of a PEMFC (Proton Exchange fuel cell) type fuel cell in which a hydrocarbon (CH) fuel, CH 3 OH, etc (“LPG” in the drawing), is refined into hydrogen (H 2 ) through desulfurization, reforming reaction, and hydrogen refining process at a reformer and used as a fuel.  
         [0007]     As shown therein, the prior art fuel cell includes a reforming unit  10  refining hydrogen from LNG, a stack unit  20  provided with a fuel electrode  21  connected to the reforming unit  10  to receive refined hydrogen and an air electrode  22  to receive oxygen in the air, for producing electricity and heat by an electrochemical reaction between hydrogen and oxygen, an electricity conversion unit  30  connected to the output side of the stack unit  40 , for converting electricity and supplying the same to a load, a heat exchange unit  60  supplying water to the reforming unit  10  and the stack unit  40  and cooling the reforming unit  10  and the stack unit  20 , and a control unit (not shown) electrically connected to the above-described units  10 ,  20 ,  30  and  40 , for controlling the same.  
         [0008]     The electricity conversion unit  50  includes a DC-DC converter  51  which switches a DC created in the stack unit to produce an AC and rectifies the AC to produce a DC again, and an inverter  52  which converts a DC into an AC to supply the same to an electrical appliance for AC power use.  
         [0009]     Unexplained reference numeral  20  denotes a fuel supply unit,  21  denotes a fuel supply line,  22  denotes a fuel supply pump,  30  denotes a air supply unit,  31  denotes an air supply line,  61  denotes a storage tank,  62  denotes a water circulation line,  63  denotes a radiator, and  64  denotes a water circulation pump.  
         [0010]     The above-described prior art fuel cell operates as follows.  
         [0011]     That is, a hydrocarbon fuel is reformed at the reforming unit  10  and refined into hydrogen, and the hydrogen is supplied to the fuel electrode  41  of the stack unit  40  while air is supplied to the air electrode  42  of the stack unit  40 , thereby causing an oxidation reaction at the fuel electrode  41  and a reduction reaction at the air electrode  42 . Electrons created in this process generate electricity while moving from the fuel electrode  41  to the air electrode  42 , and the DC in the electricity is switched in the DC-DC converter  51  of an electricity output unit  50  to produce an AC, the AC is stepped up or down by a coil, a transformer, a capacitance, etc. and then rectified to produce a DC again, and thereafter the inverter  52  converts the DC into the AC again and supplies it to various kinds of AC power loads.  
         [0012]     Here, if the overall load is greater than the amount of electricity created in the fuel cell, the amount of electricity required for the overall load is supplemented by using a utility power source.  
         [0013]     However, in the above-described prior art fuel cell, in a case where a fuel cell is used as a power source in homes or buildings, a load in actual use varies every hour, and this may lead to overproduction or underproduction. For instance, part of electronic appliances used in homes is for temporary use, and the amount of electricity used increases when such electronic appliances are in use, while the amount of electricity used decreases when they are not in use. In this case, particularly, in the countries or regions where the sale of electricity is not permitted, if the amount of electricity produced in a fuel cell is not increased or decreased depending on a change in the overall load, this results in the production of unnecessary electricity or it becomes necessary to prepare a fuel cell having an overcapacity in consideration of such a change, thereby incurring unnecessary costs.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0014]     Therefore, the present invention has been made in consideration of the above problems of the prior art fuel cell, and has as its object to provide a fuel cell capable of load-dependent operation which can adjust an electricity output depending on the variation of a load in actual use.  
         [0015]     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a fuel cell, including: a fuel supply unit; an air supply unit; a stack unit connected to the fuel supply unit via a fuel supply line to receive hydrogen and connected to the air supply unit via a fuel supply line to receive oxygen, thereby creating an electrical energy and a thermal energy by an electrochemical reaction between hydrogen and oxygen; an electricity conversion unit for converting the electrical energy created in the stack unit so as to be supplied to a load; an electric power metering unit for detecting both a residual amount of electric power left after the electricity conversion unit supplies electricity to a load and a supplementary amount of electric power supplied through a utility power source; and a control unit electrically connected to the electric power metering unit, and calculating the difference between the residual amount of electric power and supplementary amount of electric power detected by the electric power metering unit to control the electricity output of the stack unit.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0017]     In the drawings:  
         [0018]      FIG. 1  is a systematic view of one example of a prior art fuel cell;  
         [0019]      FIG. 2  is a systematic view of one example of a fuel cell according to the present invention; and  
         [0020]      FIG. 3  is a sequential view showing a load-dependent control procedure in the fuel cell of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Hereinafter, a fuel cell capable of load-dependent operation according to the present invention will be described with reference to one embodiment which is illustrated in the accompanying drawings.  
         [0022]      FIG. 2  is a systematic view of one example of a fuel cell according to the present invention.  FIG. 3  is a sequential view showing a load-dependent control procedure in the fuel cell of the present invention.  
         [0023]     As shown therein, the fuel cell according to the present invention includes a reforming unit  110  refining hydrogen from LNG, a fuel supply unit  120  connected to the reforming unit  110  and supplying refined hydrogen to a fuel electrode to be described later, an air supply unit  130  supplying air in the atmosphere to an air electrode to be described later, a stack unit  140  provided with a fuel electrode  141  to receive hydrogen and an air electrode  142  to receive oxygen from the air, for producing electricity and heat by an electrochemical reaction between hydrogen and oxygen, an electricity conversion unit  150  connected to the output side of the stack unit  140 , for supplying electricity to a load, a heat exchange unit  160  supplying water to the reforming unit  110  and the stack unit  140  and cooling the reforming unit  110  and the stack unit  140 , an electric power metering unit  170  detecting both a residual amount of electric power left after the electricity conversion unit  150  supplies electricity to a load and a supplementary amount of electric power supplied through a utility power source, and a control unit  180  calculating the difference between the residual amount of electric power and supplementary amount of electric power detected by the electric power metering unit  170  to control the electricity output of the stack unit  140 .  
         [0024]     The fuel supply unit  120  and the air supply unit  130  have a fuel supply line  121  and an air supply line  131 , respectively, that are connected to the fuel electrode and air electrode  142  of the stack unit  140 . A fuel supply pump  122  and an air supply pump  132  are provided, respectively, at middle portions of the fuel supply line  121  and air supply line  131 , so as to adjust the supply amount of a fuel and the supply amount of air. Here, the fuel supply pump  122  may be installed at a forward flow side of the reforming unit  110  or at a backward flow side of the reforming unit  110 .  
         [0025]     The stack unit  140  has the fuel electrode  141  and the air electrode  142  arranged with an electrolyte film interposed there between, and a separator plate (not shown) with a fuel flow path and an air flow path is installed on the outer surface of the fuel electrode  141  and air electrode  142  to form unit cells. The unit cells are stacked in layers to comprise the stack unit  140 .  
         [0026]     The electricity conversion unit  150  includes a DC-DC converter  151  which switches a DC created in the stack unit  140  to produce an AC and rectifies the AC to produce a DC again, and an inverter  152  which converts a DC into an AC to supply the same to an electrical appliance for AC power use.  
         [0027]     The electric power metering unit  170  includes a meter  171  installed between the electricity conversion unit  150  of the fuel cell and the utility power source, for detecting an amount of electric power used of various kinds of loads, a first electric power sensor  172  installed at the output terminal of the electricity conversion unit  150 , for detecting an amount of electric power produced through the electricity conversion unit  150  and transmitting a signal to the control unit  180 , and a second electric power sensor  173  installed between the meter  171  and the load, for detecting a residual amount of electric power left after supplied to various kinds of loads through the fuel cell and a supplementary amount of electric power supplied to various kinds of loads from the utility power source.  
         [0028]     The first electric power sensor  172  and the second electric power sensor  173  may be comprised of a current sensor for sensing current, or a hybrid sensor for sensing both current and voltage.  
         [0029]     The control unit  180  is electrically connected to the fuel supply pump  121  and the air supply pump  131  so that the amount of fuel and air supply can be adjusted depending on the difference between the residual amount of electric power and the supplementary amount of electric power. Data can be exchanged by directly reading the first electric power sensor  172 , or by using a communication protocol.  
         [0030]     Unexpected reference numeral  161  denotes a storage tank,  162  denotes a water circulation line,  163  denotes a radiator, and  164  denotes a water circulation pump.  
         [0031]     In the drawings, like reference numerals have been used throughout to designate identical elements.  
         [0032]     The operational effects of a fuel cell capable of load-dependent operation are as follows.  
         [0033]     That is, if the stack unit  140  reacts by a command from the control unit  180 , the stack unit  140  generates electricity and heat, and the electricity is utilized as electrical energy required at homes or offices through the electricity conversion unit  150 , while the heat is utilized as heat energy in conjunction with a room heating or hot water system.  
         [0034]     At this time, part of electrical appliances connected to the fuel cell for receiving electricity is for temporary use. Thus, the amount of electric power required in the overall load may be greater or less than the amount of electric power produced in the fuel cell according to the user&#39;s frequency of use. Accordingly, in the present invention, the control unit  180  of the fuel cell continuously manages the electricity output and the use amount of electric power, and always allows an appropriate amount of electricity to be produced in the fuel cell.  
         [0035]     For instance, as shown in  FIGS. 2 and 3 , the first electric power sensor  172  detects an amount of electric power produced in the fuel cell, the second electric power sensor  173  detects a residual amount of electric power left after supplied to the overall load or a supplementary amount of electric power supplied to the load from a utility power source because the amount of electric power produced through the fuel cell does not cover the overall load, and the control unit  180  compares a current amount of electric power production detected from the first electric power sensor  172  with the values detected from the second electric power sensor  173  to calculate an appropriate amount of electricity to be produced in the fuel cell, adjusts the opening and closing amount of the fuel supply pump  122  and air supply pump  132  so as to increase or decrease the amount of fuel and air supply as much as an increment or decrement thereof. Also, the DC-DC converter  151  and inverter  152  of the electricity conversion unit  150  are commanded to increase or decrease the output amount of electric power, thereby always allowing the fuel cell to produce an appropriate amount of electricity.  
         [0036]     Subsequently, the fuel cell produces as much an amount of electric power as a load actually requires, so that an unnecessary amount of fuel consumed in the production of electric power, thereby optimizing the operation system of the fuel cell and increasing the efficiency thereof.