Abstract:
A power source system comprises: a chemical reaction unit producing a gas for power generation; a generator unit reacting a part of the gas for power generation to generate power, and ejecting unreacted part in the gas for power generation as an offgas; a heating apparatus provided in the chemical reaction unit setting the chemical reaction unit to a predetermined temperature by a heat quantity by a combustion reaction using a combustion component of the offgas and the fuel for combustion; and a controller calculating a quantity of the combustion component in the offgas to control a heat quantity generated by the heating apparatus in order to maintain the predetermined temperature of the chemical reaction unit according to a calculated change of the quantity of the combustion component in the offgas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-003515, filed Jan. 11, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a power source system, a control apparatus of the power source system, and a control method of the power source system. More particularly, the present invention relates to a power source system, a control apparatus of the power source system, and a control method of the power source system, equipped with a fuel cell.  
         [0004]     2. Description of the Related Art  
         [0005]     In recent years, as an environmental problem and an energy problem have been getting popular, research and development which aim at putting a fuel cell, that have little influences on the environment (environmentally friendly), to practical use and at spreading the fuel cell have been vigorously performed. As a field to which a power source system using such fuel cell is applied, for example, a motor vehicle field can be cited. In the motor vehicle field, it has been required to put in practical use an electric vehicle using an electric motor as a drive unit in place of a gasoline engine and a diesel engine, and research and development for applying the power source system using the fuel cell as the power source unit to such electric vehicle have been vigorously performed. Consequently, the fuel cell is gradually being put in practical use and commercialized.  
         [0006]     On the other hand, there have been demands to enhance the properties and extend period of operation time concerning portable type electronic equipment, which have been conventionally driven by a secondary battery, such as a personal digital assistant, a cellular phone, a digital still camera, a digital video camera, a portable television, a note-book size personal computer and the like. For such demands, research and development to miniaturize the power source system using such fuel cell as a power source unit that replaces the secondary battery have also been vigorously performed.  
         [0007]     There is a fuel reforming type fuel cell as a fuel cell used for such a power source system. The fuel reforming type fuel cell is equipped with a chemical reaction unit such as a reformer for generating hydrogen by reforming a fuel for power generation containing a hydrocarbon compound through a chemical reaction of a catalytic reaction. In order to enhance the reaction in the chemical reaction unit efficiently, it is necessary to maintain the chemical reaction unit at a suitable predetermined temperature. As the method to maintain the chemical reaction unit at the predetermined temperature, for example, a configuration which supplies a required heat quantity using heat generation by a combustion component in the offgas ejected from a generator unit of a fuel cell and a fuel for combustion within catalyst combustor is known besides the heating by an electric heater.  
         [0008]     However, when the output power of the generator unit of a fuel cell has changed or the temperature of the generator unit has changed according to the change in power requirement due to change in load, for example, the quantity of the combustion components in an offgas ejected from the generator unit changes, and leads to change in heat quantity by combustion heat due to the change of the quantity of the combustion components in the offgas.  
         [0009]     Such change of the heat quantity is compensated by, for example, the combustion heat of the fuel for combustion, however, the catalyst combustor has a large time constant and a slow response to the injection of a fuel. Consequently, the compensation method has a problem in that it is difficult to stably control the temperature of the chemical reaction unit against a load change. Moreover, because it is difficult to control the temperature of the chemical reaction unit stably, the method also has another problem of a wasteful use of the fuel for burning.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention, regarding a power source system which is equipped with a fuel cell, has an advantage of capability for providing a power source system and a control method that can control a temperature of a chemical reaction unit stably corresponding to a load change, as well as suppress wasteful use of fuel.  
         [0011]     In order to achieve the aforementioned advantage, power source system of the present invention comprises: a chemical reaction unit receiving supply of fuel for power generation to produce a gas for power generation; a generator unit receiving supply of the gas for power generation, reacting a part of the gas for power generation to generate power, and ejecting unreacted part in the gas for power generation as an offgas; a heating apparatus provided in the chemical reaction unit, receiving supply of the offgas and a fuel for combustion, and setting the chemical reaction unit to a predetermined temperature by a heat quantity generated by a combustion reaction using a combustion component in the offgas and the fuel for combustion; a flow meter measuring a flow rate of the gas for power generation supplied to the generator unit; a calculator calculating the quantity of the combustion component in the offgas based on a value of a flow rate of the gas for power generation supplied to the generator unit, the value of the flow rate measured by the flow meter, and a value of power generated by the generator unit; and a controller controlling a heat quantity generated by the heating apparatus in order to maintain the predetermined temperature of the chemical reaction unit according to a change of the quantity of the combustion component in the offgas, the quantity calculated by the calculator. Here, the fuel for combustion is made of the fuel for power generation.  
         [0012]     The heating apparatus comprises a first heating unit receiving the supply of the offgas to generate a heat quantity by a combustion reaction using the combustion component in the offgas, and a second heating unit receiving a supply of the fuel for combustion to generate a heat quantity by the combustion reaction of the combustion component in the fuel for combustion; and the control unit controls the heat quantity generated by the second heating unit according to the quantity of the combustion component in the offgas, the quantity calculated by the calculator.  
         [0013]     The power source system further comprises an air quantity controller controlling an air quantity supplied to the generator unit, the chemical reaction unit and every unit requiring air introduction of the heating apparatus according to a change of the value of the power generated by the generator unit so that the air quantity is close to a bare minimum of quantity.  
         [0014]     The fuel for power generation is a hydrocarbon material containing a hydrogen atom, and the chemical reaction unit is equipped with a reforming unit which at least generates a gas including a specific fuel component containing hydrogen as the gas for power generation from the fuel for power generation by a predetermined catalytic reaction. The chemical reaction unit may further be equipped with a by-product removing unit removing a by-product produced by the catalytic reaction.  
         [0015]     The generator unit is equipped with a fuel cell generating power by an electrochemical reaction using the gas for power generation.  
         [0016]     The calculator comprises a section for calculating a hydrogen quantity contained in the gas for power generation according to the value of the flow rate of the gas for power generation supplied to the generator unit, the value measured by the flow meter; and a section for calculating a quantity of the hydrogen in the offgas based on the calculated value of the hydrogen contained in the gas for power generation and a value of a hydrogen utilization rate according to a generated power in the generator unit.  
         [0017]     The power source system further comprises a voltage converter converting output power of the generator unit into an output voltage to supply the output voltage to a load, and the generator unit controls a quantity of power generated according to a change of required power based on an operation state of the load. Additionally, the generator unit comprises a current measuring instrument measuring an output current value of the generator unit through the voltage converter or a converter converting an output of the voltage converter into an output current value of the generator unit, wherein the calculator calculates the quantity of the combustion component in the offgas based on a quantity of the flow rate of the gas for power generation measured by the flow meter and an output current value of the generator unit obtained by the current measuring instrument or the converter.  
         [0018]     In order to achieve the aforementioned advantage, control apparatus of the present invention comprises: the power source system including at least: a chemical reaction unit receiving supply of fuel for power generation to produce a gas for power generation; a generator unit receiving the gas for power generation, reacting a part of the gas for power generation to generate power, and ejecting unreacted part in the gas for power generation as an offgas; and a heating apparatus receiving supply of the offgas and a fuel for combustion, and setting the chemical reaction unit to a predetermined temperature by a heat quantity generated by a combustion reaction using a combustion component in the offgas and the fuel for combustion, and the control apparatus comprising: a flow meter measuring a flow rate of the gas for power generation supplied to the generator unit; a calculator calculating the quantity of the combustion component in the offgas based on a value of a flow rate of the gas for power generation, the value of the flow rate measured by the flow meter, and a value of power generated by the generator unit; and a controller controlling a heat quantity generated by the heating apparatus in order to maintain a temperature of the chemical reaction unit according to a change of the quantity of the combustion component in the offgas, the quantity calculated by the calculator.  
         [0019]     The fuel for power generation is a hydrocarbon material containing a hydrogen atom, and the calculator comprising: a section for calculating a quantity of hydrogen contained in the gas for power generation according to a value of the flow rate of the gas for power generation supplied to the generator unit; and a section for calculating a quantity of hydrogen in the offgas based on a calculated value of the hydrogen contained in the gas for power generation and a value of a hydrogen utilization rate according to a generated power in the generator unit.  
         [0020]     The control apparatus further comprises an air quantity controller controlling an air quantity supplied to the generator unit, the chemical reaction unit and every unit requiring air introduction of the heating apparatus according to the value of the power generated by the generator unit so that the air quantity is close to a bare minimum of quantity.  
         [0021]     In order to achieve the aforementioned advantage, a control method of a power source system, including the power source system composed of: a chemical reaction unit receiving supply of fuel for power generation to produce a gas for power generation; a generator unit receiving supply of the gas for power generation, reacting a part of the gas for power generation to generate power, and ejecting unreacted part in the gas for power generation as an offgas; and a heating apparatus receiving supply of the offgas and a fuel for combustion, and setting the chemical reaction unit to a predetermined temperature by a heat quantity generated by a combustion reaction using a combustion component in the offgas and the fuel for combustion, and the method comprising the steps of: calculating the quantity of the combustion component in the offgas based on a flow rate of the gas for power generation supplied to the generator unit, and a value of power generated by the generator unit; and controlling a heat quantity generated by the heating apparatus in order to maintain a temperature of the chemical reaction unit steady according to a change of the quantity of the combustion component in the offgas, the quantity calculated in a step to calculate the quantity of the combustion component in the offgas.  
         [0022]     The step of calculating the quantity of the combustion component in the offgas comprises steps of: calculating a quantity of hydrogen contained in the gas for power generation according to a value of the flow rate of the gas for power generation supplied to the generator unit; and calculating a quantity of hydrogen in the offgas based on a value of a hydrogen utilization rate according to a generated power in the generator unit, and a calculated quantity of hydrogen contained in the gas for power generation.  
         [0023]     The control method further comprises a step of controlling an air quantity supplied to the generator unit, the chemical reaction unit and every unit requiring air introduction of the heating apparatus according to the value of the power generated by the generator unit so that the air quantity is close to a bare minimum of quantity.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a block diagram showing the configuration of a power source system of a first embodiment according to the present invention;  
         [0025]      FIG. 2  is a flowchart showing the operation of the offgas control processing in the present embodiment;  
         [0026]      FIG. 3  is a graph showing a relation between the output voltages of a generator unit and a hydrogen utilization rates; and  
         [0027]      FIG. 4  is a flowchart showing the operation of the air quantity control processing in a second embodiment of the power source system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Hereinafter, details of a power source system, a control apparatus of the power source system, and a control method of the power source system according to the present invention are described based on the embodiments shown in the drawings.  
       First Embodiment  
       [0029]     First, a first embodiment of the power source system according to the present invention is described.  
         [0000]     (1) Configuration  
         [0030]      FIG. 1  is a block diagram showing the configuration of the power source system of the first embodiment according to the present invention.  
         [0031]     The power source system is composed of a control unit (control apparatus)  130 , a DC/DC converter (voltage converter)  160  and a fuel cell system  200 .  
         [0032]     The fuel cell system  200  is equipped with a reactor unit  100  equipped with a chemical reaction unit, a generator unit (generator cell)  120 , a methanol tank  140 , a water tank  150 , pumps P 1 -P 3 , drivers D 1 -D 3 , valves V 1 -V 7 , flow meters F 1 -F 8  and the like.  
         [0033]     The reactor unit  100  is composed of a combustion fuel evaporator  101 , an electric heater and thermometer  102 , a reformed fuel evaporator  103 , an electric heater combined with thermometer  104 , a CO remover (by-product removing unit)  105 , an electric heater combined with thermometer  106 , a reformer (reforming unit)  107 , an electric heater combined with thermometer  108 , a methanol catalyst combustor (heater: first heater)  109  and an offgas catalyst combustor (heater: second heater)  110 . Here, the CO remover  105  and the reformer  107  constitute the chemical reaction unit.  
         [0034]     The combustion fuel evaporator  101  evaporates the methanol (fuel for combustion) injected from the methanol tank  140  with the pump P 1 , and sends it out to the methanol catalyst combustor  109 . The flow rate of the methanol injected into the combustion fuel evaporator  101  is adjusted by the valve V 1 , and is measured with the flow meter F 1 . The electric heater combined with thermometer  102  functions as an electric heater to heat the combustion fuel evaporator  101 , and also functions as a thermometer to measure the temperature of the combustion fuel evaporator  101  by detecting the resistance of the combustion fuel evaporator  101 .  
         [0035]     The reformed fuel evaporator  103  evaporates the methanol (fuel for power generation) injected from the methanol tank  140  with the pump P 1 , and the water injected from the water tank  150  with the pump P 3 . The reformed fuel evaporator  103  sends the evaporated methanol and water out to the reformer  107 . The flow rate of the methanol injected into the reformed fuel evaporator  103  is adjusted by the valve V 2 , and is measured with the flow meter F 2 . The flow rate of the water injected into the reformed fuel evaporator  103  is adjusted by the valve V 3 , and is measured with the flow meter F 3 . The electric heater combined with thermometer  104  functions as an electric heater to heat the reformed fuel evaporator  103 , and also functions as a thermometer to measure the temperature of the reformed fuel evaporator  103  by detecting the resistance of the reformed fuel evaporator  103 .  
         [0036]     The reformer  107  generates a reformed gas (gas for power generation) containing hydrogen by a catalytic reaction of the evaporated water and the evaporated methanol supplied from the reformed fuel evaporator  103 .  
         [0037]     The CO remover  105  mixes the air introduced by the air pump P 2  and the reformed gas generated by the reformer  107 , removes the carbon monoxide as a by-product generated by the catalytic reaction of the reformer  107  from the reformed gas according to a selective oxidation reaction, and supplies the mixed gas to the generator unit  120 . The air flow rate introduced into the CO remover  105  is adjusted by the valve V 4 , and is measured with the flow meter F 4 .  
         [0038]     The electric heater combined with thermometer  106  functions as an electric heater to heat the CO remover  105 , and also functions as a thermometer to measure the temperature of the CO remover  105  by detecting the resistance of the CO remover  105 .  
         [0039]     The electric heater combined with thermometer  108  functions as an electric heater to heat the reformer  107 , and also functions as a thermometer to measure the temperature of the reformer  107  by detecting the resistance of the reformer  107 .  
         [0040]     The methanol catalyst combustor  109  mixes the evaporated fuel supplied from the combustion fuel evaporator  101  and the air introduced by the air pump P 2 , and performs catalytic combustion of the mixed gas to heat the chemical reaction unit of the reactor unit  100  with the combustion heat. The air flow rate introduced into the methanol catalyst combustor  109  is adjusted by the valve V 5 , and is measured with the flow meter F 5 .  
         [0041]     The offgas catalyst combustor  110  mixes the offgas (unreacted reformed gas containing hydrogen) ejected from the generator unit  120  and the air introduced with an air pump P 2 , and performs catalytic combustion of the mixed gas to heat the whole reaction unit  100  by the combustion heat. The air flow rate introduced into the offgas catalyst combustor  110  is adjusted by the valve V 6 , and is measured with the flow meter F 6 . Incidentally, although the present embodiment is configured so as to supply methanol from the methanol tank  140  to the reformed fuel evaporator  103  and the combustion fuel evaporator  101 , and a part of the fuel for power generation is used as a fuel for combustion, the present invention is not limited to such configuration. The fuel for combustion may be supplied from another dedicated tank. Moreover, the fuel for power generation and the fuel for burning may be made of different materials.  
         [0042]     The generator unit  120  has one or a plurality of generator cell structures, each including a fuel electrode formed on one surface of an electrolyte film MEA and an air electrode formed on the other surface, and generates electric power by an electrochemical reaction of hydrogen, which is supplied to the fuel electrode and is contained in the reformed gas supplied from the CO remover  105  after removing CO, and oxygen in the air supplied to the air electrode is introduced by the air pump P 2 . Moreover, the generator unit  120  supplies unreacted reformed gas, which has not been used for the electrochemical reaction, to the offgas catalyst combustor  110 . The flow rate of the reformed gas supplied to the generator unit  120  after removing CO is measured with the flow meter F 8 .  
         [0043]     The DC/DC converter  160  receives the supply of the electric power generated by the generator unit  120 , and is connected to a load such as electric equipment and the like. The DC/DC converter  160  generates an output voltage of a predetermined voltage based on the electric power supplied from the generator unit  120 , and supplies the output voltage to the load. The DC/DC converter  160  includes a secondary battery  160   a  holding at least a part of the electric power generated by the generator unit  120 . For example, at the time of starting the system, at the time of an overload, or the like, the DC/DC converter  160  generates the output of the predetermined voltage with the stored power of the secondary battery  160   a . At the time of the stationary operation of the system, the DC/DC converter  160  performs switching regulation of the output power of the generator unit  120  to a constant voltage and supply it to an external load, as well as charge the secondary battery  160   a . Here, the electric power generated by the generator unit  120  is suitably adjusted according to the changes (load changes) of the requested power based on the operation state of the load connected through the DC/DC converter  160 . Moreover, the DC/DC converter  160  may be equipped with a configuration (current measuring instrument) measuring the output current value Ico of the generator unit  120  through the DC/DC converter  160  directly, or may be equipped with the configuration (converter) converting the output of the DC/DC converter  160  into the output current value Ico of the generator unit  120 .  
         [0044]     The control unit  130  is equipped with a CPU, a ROM, a RAM, an A/D converter, a D/A converter, and the like, and controls the operation of each unit of the system. Specifically, the CPU executes various control programs stored in ROM and the like, and controls so that the reactor unit  100  is in the predetermined operation state. For example, the output FO of each unit flow meters F 1 -F 8  described above, temperature measurement value of the electric heater combined with thermometers  102 ,  104 ,  106  and  108 , and the like are obtained by means such as A/D conversion, as well as output current value Ico of the generator unit  120  is obtained through the DC/DC converter  160  by means such as A/D conversion. Subsequently, according to the values obtained, valve drive signals VD driving the valves V 1 -V 7  of each unit described above, driver control signals CD controlling the drivers D 1 -D 3  driving the pumps P 1 -P 3 , heater drive signals of the electric heaters and thermometers  102 ,  104 ,  106  and  108 , and the like are generated by the CPU to control so that the reactor unit  100  is in the predetermined operation state. Incidentally, the control program stored in the ROM of the control unit  130  and the like includes offgas control processing and air quantity control processing in each embodiment, both of which will be described later.  
         [0045]     Moreover, table data used for the offgas control processing, which will be described later, is stored in the ROM of the control unit  130 .  
         [0000]     (2) Operation  
         [0046]     Next, the operation of the offgas control processing executed by the control unit  130  is described as the operation of the power source system in the configuration described above.  
         [0047]      FIG. 2  is a flowchart showing the operation of the offgas control processing of the present embodiment.  
         [0048]     The offgas control processing shown in  FIG. 2  is executed by an interruption at every predetermined time, for example, by the timer interrupter by CPU of the control unit  130 .  
         [0049]     First, at interruption execution timing, the CPU of the control unit  130  executes the program of the offgas control processing stored in the ROM or the like, and proceeds the processing to Step SA 1  shown in  FIG. 2  to measure a reformed gas flow rate Frg supplied from the CO remover  105  to the generator unit  120 . The reformed gas flow rate Frg is measured by an output FO of the flow meter F 8 .  
         [0050]     Subsequently, in Step SA 2 , a hydrogen quantity content Crh in the reformed gas is calculated from a measured reformed gas flow rate Frg. Here, in the case the reformed gas was produced by reforming methanol through a steam reform reaction, it is known that the hydrogen contained in the reformed gas is about 75%, and the remaining 25% of the reformed gas is carbon dioxide. Therefore, the hydrogen quantity content Crh can be calculated from reformed gas flow rate Frg×0.75. The calculated value is stored in a register Crh.  
         [0051]     Subsequently, in Step SA 3 , the output current value Ico of the generator unit  120  is directly measured from the DC/DC converter  160  with a current measuring instrument, or the output current value Ico of the generator unit  120  is obtained by converting the output of the DC/DC converter  160  with a converter, and the value of the output current value Ico is stored in a register Ico.  
         [0052]     Next, the processing proceeds to Step SA 4 . Here, the quantity of the hydrogen consumed by the electrochemical reaction for power generation by the generator unit  120  is proportional to the value of an output current. When the value of the output current is Ico, it is known that the quantity of the hydrogen consumed in the generator unit  120  Cgh can be calculated by formula (1). Therefore the residual hydrogen quantity in the offgas Rgh can be obtained by subtracting the hydrogen quantity consumed in the generator unit  120  Cgh from the hydrogen quantity content Crh of the reformed gas. That is, by assigning the output current Ico of the generator unit  120  stored in the register Ico into the following formula (1), the hydrogen quantity consumed in the generator unit  120  Cgh is calculated. Successively, as shown in a formula (2), the hydrogen quantity consumed in the generator unit  120  Cgh calculated by the formula (1), is substracted from the hydrogen quantity content Crh of the reformed gas, and the residual hydrogen quantity in the offgas Rgh is calculated. The calculated value is stored in a register Rgh. 
 
 Cgh= 22.4 ×Ico× 60/ F/ 2  (1) 
 
 Rgh=Cr−Cgh   (2) 
 
         [0053]     Here, in the formula (1), 22.4[L]×Ico[A]×60[sec]/F/2 represents a hydrogen consumption quantity, and F represents the Faraday constant (96485.3415 [C/mol]).  
         [0054]     When the residual hydrogen quantity in the offgas Rgh is obtained in this way, the processing proceeds to Step SA 5 . Here, it is supposed that the residual hydrogen quantity calculated in the previous time is stored in a resister Rgl. Then, by subtracting a residual hydrogen quantity Rgh, which is calculated this time and stored in a register Rgh, from the previous residual hydrogen quantity Rgl, a difference value Dhg of the residual hydrogen quantity in the offgas from the previous time to this time is calculated and the difference value Dhg is stored into a register Dhg.  
         [0055]     Next, in Step SA  6 , the difference value Dhg of the residual hydrogen quantity in the offgas stored in the register Dhg, and the present setting value V 1   b  of the valve V 1  adjusting the quantity of the methanol supplied to the methanol catalyst combustor  109  through the combustion fuel evaporator  101  is read out. Then a new setting value V 1   b N of the valve V 1  is read out from a methanol quantity adjusting valve setting table T 1  stored in the ROM of the control unit  130 , by using the difference value Dhg and the setting value V 1   b  as addresses.  
         [0056]     Here, the methanol quantity adjusting valve setting table T 1  is a table in which the values of suitable setting values V 1   b N, obtained by experiments, of the valve V 1  are saved, which values are necessary for controlling the heating value of the methanol catalyst combustor  109  so as to maintain the temperature of the reactor unit  100  to be constant, regarding various combinations of each value, when the difference value Dhg of the residual hydrogen quantity in the offgas takes various values to each value of the various setting value V 1   b  of the valve V 1 .  
         [0057]     Subsequently, in Step SA 7 , the valve drive signal VD is generated corresponding to the new setting value V 1   b N, which has been read out in Step SA 6  mentioned above, and supplied to the valve V 1 .  
         [0058]     Thereby, the valve V 1  adjusts the quantity of the methanol supplied to the methanol catalyst combustor  109  through the combustion fuel evaporator  101  according to the new setting value V 1   b N. That is, the opening and closing control of the valve V 1  according to the setting value V 1   b N is performed so that the difference value Dhg becomes “0.” For example, when the residual hydrogen quantity Rgh increases and the heating value of the offgas catalyst combustor  110  increases, the CPU closes the valve V 1  so as to decrease the quantity of the methanol supplied to the combustion fuel evaporator  101  to offset the increase of the heating value. On the other hand, when the residual hydrogen quantity Rgh decreases and the heating value of the offgas catalyst combustor  110  decreases, the CPU controls to open the valve V 1  to increase the quantity of the methanol supplied to the combustion fuel evaporator  101  so as to compensate the decrease in the heating value.  
         [0059]     Subsequently, the processing proceeds to Step SA 8 , and stores the value of the register Rgh into the resister Rgl. Then, the residual hydrogen quantity Rgh calculated this time is updated as the previous value Rgl, and ends the processing.  
         [0060]     By repeatedly executing the offgas control processing described above approximately 1-20 times/sec by the timer interrupter for example, the heating value of the methanol catalyst combustor  109  is increased or decreased by adjusting the quantity of the methanol (fuel for combustion) which is supplied to the burning fuel evaporator  101  to follow the residual hydrogen quantity Rgh in the offgas which changes every moment. Consequently, it becomes possible to control the temperature of the reformer unit to maintain the temperature stably, corresponding to load changes.  
         [0061]     Moreover, it also becomes possible to suppress the wasteful use of the methanol (fuel for combustion) in the methanol catalyst combustor  109  by controlling the heating value of the methanol catalyst combustor  109  appropriately.  
       Second Embodiment  
       [0062]     Next, a second embodiment of the power source system according to the present invention is described.  
         [0063]     Since the configuration of the second embodiment is almost the same as that of the first embodiment shown in  FIG. 1 , detailed description of the configuration is omitted.  
         [0064]     The second embodiment is different from the first embodiment described above in that the quantity of air supplied to each unit of the fuel cell system  200  (the CO remover  105 , the methanol catalyst combustor  109 , the offgas catalyst combustor  110 , and the generator unit  120 ) which needs air introduction, is controlled according to the output current Ico of the generator unit  120 .  
         [0065]      FIG. 3  is a graph showing a relation between the output voltages of the generator unit  120  and hydrogen utilization rates.  
         [0066]     As apparent from the graph representing the relation between the output voltages of the generator unit  120  and the hydrogen utilization rates (a characteristic when a cell temperature is 80° C.), which is shown in  FIG. 3 , for example, when the generator unit  120  is generating electricity at an output voltage of Vc, the hydrogen utilization rate is approximately 81%, and the offgas contains only the residual hydrogen of 19%. On the other hand, when the generator unit  120  generates electricity at an output voltage of Vn, the hydrogen utilization rate becomes 30%, and 70% of hydrogen remains in the offgas.  
         [0067]     That is, if the hydrogen utilization rate falls by lowering the generated electricity output of the generator unit  120 , the quantity of the reacting hydrogen inevitably decreases, and the quantity of the oxygen consumption of the generator unit  120  also falls consequently. Moreover, due to the decrease, the air quantity required by each of the CO remover  105 , the methanol catalyst combustor  109  and the offgas catalyst combustor  110  also decreases.  
         [0068]     Therefore, the air quantity to be supplied to each unit of the fuel cell system  200  which requires air introduction (the CO remover  105 , the methanol catalyst combustor  109 , the offgas catalyst combustor  110 , and the generator unit  120 ) may be suitably controlled, that is, it may be controlled to be approach a suitable quantity necessary for the reaction (bare minimum of quantity). Since the necessary air quantity decreases especially at the time of lowering the generated electricity output, it is possible to lower the drive voltage of the air pump P 2  to decrease the supplying air quantity. Thereby, the air beyond necessity is not supplied to the generator unit (generator cell) while reducing power consumption, and the drying of the electrolyte film MEA of the generator unit can be prevented.  
         [0069]     Hereinafter, the air quantity control processing by an air quantity controller which embodies such operations is described.  FIG. 4  is a flowchart showing the operation of the air quantity control processing in the second embodiment of the power source system according to the present invention.  
         [0070]     The air quantity control processing shown in  FIG. 4  is executed by an interruption at every predetermined time, for example, by the timer interrupter of the CPU of the control unit  130 .  
         [0071]     First, at interruption execution timing, the CPU of the control unit  130  executes the program of the air quantity control processing stored in the ROM and the like, and proceeds its processing to Step SB 1  shown in  FIG. 4 . The CPU directly measures the output current value Ico of the generator unit  120  from the DC/DC converter  160  with a current measuring instrument, or the CPU converts the output of the DC/DC converter  160  to obtain the value of the output current value Ico of the generator unit  120  with a converter. Then, the CPU stores the value of the output current value Ico in the register Ico.  
         [0072]     Subsequently, in Step SB 2 , the optimum air pump drive voltage Vap corresponding to the output current Ico stored in the register Ico is read out from an air pump drive table T 2 .  
         [0073]     Here, the air pump drive table T 2  is a table in which the experimentally obtained values of the air pump drive voltage Vap are saved, at which values the optimum air supplying quantity to the value of each output current Ico is produced, using various values of output currents Ico as reading addresses.  
         [0074]     Subsequently, in Step SB 3 , the CPU supplies the driver control signal CD corresponding to the air pump drive voltage Vap obtained at Step SB 2  mentioned above to the driver D 2  of the air pump P 2 . Thereby, the air pump P 2  is set so as to produce the optimum air supplying quantity.  
         [0075]     Subsequently, in Step SB 4 , each of setting values corresponding to the output current Ico stored in the register Ico, a generator unit air valve setting value Vac, a CO remover air valve setting value Var, a methanol catalyst combustor air valve setting value Vam, and an offgas catalyst combustor air valve Vaf are read out from a valve drive table T 3 .  
         [0076]     Here, the valve drive table T 3  is a table in which the experimentally obtained valve setting values Vas, Var, Vam and Vaf are saved, at which the valves supplies the optimum air quantities to each unit of the fuel cell system  200  requiring air introduction (the generator unit  120 , the CO remover  105 , the methanol catalyst combustor  109  and the offgas catalyst combustor  110 ) to the value of each output current Ico, using the various values of output currents Ico as reading addresses.  
         [0077]     Subsequently, the processing proceeds to Step SB 5 , and the valve drive signal VD is generated corresponding to each of the valve setting values Vac, Var, Vam and Vaf read at Step SB 4  mentioned above. Then, the generated valve drive signal VD is supplied to each of the corresponding valves V 4 -V 7 , and completes the processing. Thereby, each of the valves V 4 -V 7  is adjusted to supply the optimum air quantity (bare minimum).  
         [0078]     By repeatedly executing the air quantity control processing described above every fixed period by the timer interrupter, the air quantity supplied to each unit of the fuel cell system  200  which requires air introduction (the CO remover  105 , the methanol catalyst combustor  109 , the offgas catalyst combustor  110  and the generator unit  120 ) is set as a suitable quantity (bare minimum of quantity) necessary for the reaction of each unit according to the output current Ico of the generator unit  120 . In particular, since the necessary air quantity decreases at the time of lowering the generated output, the drive voltage of the air pump P 2  can be lowered to decrease the air supplying quantity. Thereby, power consumption can be reduced, and the improvement in the energy efficiency for the whole system can be achieved as a result by fuel conservation, and a long period of operation can be enabled. Furthermore, since the air more than necessary is not supplied to the generator unit (generator cell), it is also possible to prevent drying of the electrolyte film MEA of the generator unit.  
         [0079]     Incidentally, although only the air quantity control processing is performed in the present embodiment, the present invention is not limited to this embodiment. An aspect of also using the offgas control processing by the first embodiment described above may be used together with the air quantity control processing. In that case, it becomes possible to control the temperature of the reactor unit to be stably constant within dealing with load changes, while enabling the long period of operation by the improvement in energy efficiency of the whole system by fuel conservation and the prevention of the drying of the electrolyte film of the generator unit (generator cell).