JP2008004426A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing degradation of reforming efficiency. <P>SOLUTION: The fuel cell system (100) is provided with a fuel cell (60), a reforming means (51) to generate hydrogen by reforming reaction using a reformed fuel, a cathode off-gas supply means (80) to supply the cathode off-gas of the fuel cell to the reforming means, and an O/C control means (10, 80) to carry out a first control to control O/C so that S/C+O/C≥2 and O/C may be a first prescribed value or less when the load of the fuel cell fluctuates. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of environment and can realize high energy efficiency, it has been widely developed as a future energy supply system.

  Currently, in many fuel cell systems, in a reformer, by a steam reforming reaction with a hydrocarbon fuel such as gasoline, natural gas, methanol and the like and steam and a partial oxidation reaction with oxygen and these hydrocarbon fuels, Reformed gas is generated. This reformed gas is supplied to the anode of the fuel cell. On the other hand, an oxygen-containing gas such as air is supplied to the cathode. As a result, power generation is performed in the fuel cell.

  By the way, the technique which supplies the cathode offgas containing the water which generate | occur | produced with power generation and the oxygen which was not used for power generation to a reformer is disclosed (for example, refer patent document 1). If this technique is used, it is not necessary to newly provide an apparatus for generating water vapor, so that the system can be downsized. In this technique, for the purpose of improving reforming efficiency, the amount of fuel supplied to the reformer is controlled according to the amount of residual oxygen in the cathode offgas, and the O / C ratio is maintained within the target range.

JP 2005-235583 A

  However, in the technique of Patent Document 1, the target range of the O / C ratio is unclear. Therefore, even if the O / C ratio is controlled within the target range, the reforming efficiency may decrease.

  An object of this invention is to provide the fuel cell system which can suppress a reforming efficiency fall.

  A fuel cell system according to the present invention includes a fuel cell, reforming means for generating hydrogen by a reforming reaction using reformed fuel, cathode offgas supply means for supplying cathode offgas of the fuel cell to the reforming means, O / C control means for performing first control for controlling O / C so that S / C + O / C ≧ 2 and O / C is equal to or less than a first predetermined value when the load of the fuel cell fluctuates; It is characterized by comprising. Where S represents the molar amount of water vapor supplied to the reforming means, C represents the molar amount of carbon atoms in the reformed fuel supplied to the reforming means, and O represents oxygen supplied to the reforming means. Indicates the molar amount of oxygen atoms in the gas.

  In the fuel cell system according to the present invention, the number of moles of oxygen atoms in the reforming means is twice or more the number of moles of carbon atoms. In this case, carbon is easily discharged as carbon dioxide. Thereby, carbon deposition in the reforming means can be suppressed. Moreover, since O / C becomes below a 1st predetermined value, the increase in the ratio of a partial oxidation reaction can be suppressed. In this case, excessive combustion can be suppressed. Thereby, deterioration of the reforming means can be suppressed. From the above, a reduction in reforming efficiency of the fuel cell system according to the present invention can be suppressed.

  First detection means for acquiring and / or predicting a load fluctuation range required for the fuel cell is further provided, and the O / C control means has a predetermined load fluctuation range acquired and / or predicted by the first detection means. When the value is exceeded, the first control may be performed. In this case, the influence of noise mixed in the fuel cell system according to the present invention can be ignored. Therefore, sudden changes in the fuel amount, oxygen amount, and water vapor amount due to unnecessary execution of the first control can be suppressed. As a result, destabilization of the generated hydrogen flow rate and the generated hydrogen concentration can be suppressed.

  The O / C control means may set the O / C higher as the load fluctuation range is larger. In this case, when the load increases, the temperature drop of the reforming means due to the increase in the ratio of the steam reforming reaction can be suppressed. In addition, when the load decreases, carbon deposition due to lack of water vapor can be suppressed.

  The O / C control means may end the first control when the output of the fuel cell reaches a load required for the fuel cell. In this case, unnecessary control can be prevented. In addition, the fuel cell may vary the output stepwise according to the required load. In this case, the start and end of the first control can be easily determined. The first predetermined value may be 1. In this case, excessive combustion in the reforming means can be suppressed. Thereby, deterioration of the reforming means can be suppressed.

  The O / C control means may perform the first control so as not to fall below the O / C immediately before performing the first control. In this case, when the load increases, the temperature drop of the reforming means accompanying an increase in the ratio of the steam reforming reaction can be suppressed, and when the load decreases, carbon deposition due to insufficient steam can be suppressed. The O / C control means may be a pump that supplies air to the cathode of the fuel cell. In this case, it is not necessary to newly provide a device for performing O / C control of the reforming means.

  According to the present invention, carbon deposition can be suppressed and excessive combustion can be suppressed. Thereby, reduction in reforming efficiency can be suppressed.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic diagram showing an overall configuration of a fuel cell system 100 according to a first embodiment of the present invention. As shown in FIG. 1, the fuel cell system 100 includes a control unit 10, a reformed fuel tank 20, a fuel pump 30, a metering valve 40, a reformer 50, a fuel cell 60, air pumps 70 and 80, and an accelerator opening sensor. 90. The reformer 50 includes a reforming unit 51 and a heating unit 52.

  The fuel cell 60 includes a cathode 61, an anode 62, a cooling unit 63, and an ammeter 64. In this example, a hydrogen separation membrane battery was used as the fuel cell 60. Here, the hydrogen separation membrane battery is a fuel cell provided with a hydrogen separation membrane layer. The hydrogen separation membrane layer is a layer formed of a metal having hydrogen permeability. The hydrogen separation membrane battery has a structure in which the hydrogen separation membrane layer and an electrolyte having proton conductivity are laminated. Hydrogen supplied to the anode of the hydrogen separation membrane battery is converted into protons via the catalyst, moves through the proton conductive electrolyte, and combines with oxygen at the cathode to become water. The water generated at the cathode is converted into water vapor by heat generated during power generation of the hydrogen separation membrane battery.

  The control unit 10 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. The control unit 10 controls each unit of the fuel cell system 100 based on detection results given from the ammeter 64 and the accelerator opening sensor 90. Details will be described later.

  The reformed fuel tank 20 stores hydrocarbon fuel used as the reformed fuel. The fuel pump 30 supplies the reformed fuel stored in the reformed fuel tank 20 to the metering valve 40 in accordance with instructions from the control unit 10. The metering valve 40 supplies the reforming unit 51 with an amount of reformed fuel necessary for the reforming reaction in the reforming unit 51 in accordance with an instruction from the control unit 10.

  In the reforming unit 51, a reformed gas containing hydrogen is generated from the reformed fuel and a cathode off gas described later. First, a steam reforming reaction occurs by methane in the reformed fuel and steam in the cathode offgas, and hydrogen and carbon monoxide are generated. Next, a part of the generated carbon monoxide reacts with the water vapor in the cathode offgas, and hydrogen and carbon dioxide are generated. When the steam required for the steam reforming reaction is insufficient, oxygen and methane in the cathode offgas undergo a partial oxidation reaction, and hydrogen and carbon monoxide are generated.

  The reformed gas generated in the reforming unit 51 is supplied to the anode 62. At the anode 62, hydrogen in the reformed gas is converted into protons. Hydrogen that has not been converted into protons at the anode 62 and methane, carbon monoxide, and water vapor that have not reacted in the reforming unit 51 are supplied to the heating unit 52 as anode offgas.

  The air pump 70 supplies a necessary amount of air to the cooling unit 63 in accordance with instructions from the control unit 10. The air supplied to the cooling unit 63 cools the fuel cell 60 and is supplied to the heating unit 52. In the heating unit 52, a combustion reaction occurs due to the anode off gas and the air supplied from the cooling unit 63. Exhaust gas generated by the combustion reaction in the heating unit 52 is discharged outside the fuel cell system 100. Further, the combustion heat generated by the combustion reaction in the heating unit 52 is used for the steam reforming reaction in the reforming unit 51.

  The air pump 80 supplies a necessary amount of oxygen to the cathode 61 in accordance with an instruction from the control unit 10. In the cathode 61, water is generated and electric power is generated from the protons converted in the anode 62 and oxygen in the air supplied to the cathode 61. The generated electric power is stored in a storage battery (not shown) or used for a load such as a motor. The generated water becomes water vapor by the heat generated in the fuel cell 60. The air that has not reacted with the water vapor and protons generated at the cathode 61 is supplied to the reforming section 51 as a cathode off-gas and used for the steam reforming reaction and the partial oxidation reaction, respectively. Thus, since the cathode off gas can be used for the steam reforming reaction, it is not necessary to newly provide a device for generating steam.

  The ammeter 64 detects the current generated by the power generation reaction in the fuel cell 60 and gives the detection result to the control unit 10. The accelerator opening sensor 90 detects the opening of an accelerator (not shown) and gives the detection result to the control unit 10. Hereinafter, the O / C control of the reforming unit 51 by the control unit 10 at the time of load fluctuation will be described.

First, the control unit 10 determines whether or not a load required for the fuel cell 60 (hereinafter referred to as a required load Preq) is varied based on the detection result of the accelerator opening sensor 90. When it is determined that there is a change in the required load Preq, the control unit 10 controls the air pump 80 so as to satisfy the following formula (1).
S / C + O / C ≧ 2 (1)
Here, S indicates the molar amount of water vapor supplied to the reforming unit 51. C indicates the molar amount of carbon atoms in the reformed fuel supplied to the reforming unit 51. O represents the molar amount of oxygen atoms in the oxygen gas supplied to the reforming unit 51.

  Since 1 mol of oxygen is contained in 1 mol of water vapor, if an amount of water vapor, reformed fuel, and oxygen satisfying the formula (1) is supplied to the reforming unit 51, carbon in the reforming unit 51 The number of moles of oxygen atoms that have not reacted with is more than twice the number of moles of carbon atoms that have not reacted with oxygen. In this case, carbon is easily discharged as carbon dioxide. Thereby, carbon deposition in the reforming part 51 can be suppressed.

Here, the partial oxidation reaction is an exothermic reaction. Therefore, if the ratio of the partial oxidation reaction is rapidly increased, the reforming portion 51 may be deteriorated due to excessive combustion. Therefore, in this embodiment, the control unit 10 controls the air pump 80 so as to satisfy the following formula (2) in addition to the formula (1).
O / C ≦ X (2)
X is a value determined so that the reforming part 51 does not deteriorate due to excessive combustion. In this embodiment, X = 1. Hereinafter, the reason why O / C is 1 or less will be described.

  FIG. 2 is a diagram illustrating a relationship between O / C and the temperature in the reforming unit 51. The vertical axis on the left side in FIG. 2 indicates the temperature in the reforming unit 51, the vertical axis on the right side in FIG. 2 indicates the hydrogen concentration in the reforming unit 51, and the horizontal axis in FIG. The temperature was measured at a plurality of locations in the reforming unit 51. As shown in FIG. 2, when O / C = 1.0, the temperature of the reforming part 51 was 800 ° C. or lower at any location. On the other hand, when O / C = 1.5, there was a portion exceeding 800 ° C. in the reforming section 51. In this case, it is considered that excessive combustion occurs in the reforming section 51. From the above, by setting O / C to 1.0 or less, it is possible to suppress deterioration of the reforming unit 51 due to excessive combustion.

  Thus, by controlling O / C so as to satisfy the expressions (1) and (2), it is possible to suppress carbon deposition in the reforming part 51 and to suppress deterioration of the reforming part 51. Can do. Therefore, a reduction in reforming efficiency of the fuel cell system 100 can be suppressed. In the system using oxygen and water vapor in the cathode off-gas for the reforming reaction as in the fuel cell system 100 according to the present embodiment, the S / C can be freely set because the water vapor amount depends on the power generation amount of the fuel cell 60. Can not be controlled. Therefore, O / C control is effective to satisfy the expressions (1) and (2).

  Note that the control unit 10 may perform the O / C control so as not to fall below the O / C immediately before the O / C control is performed. In this case, when the load increases, the temperature drop of the reforming means accompanying an increase in the ratio of the steam reforming reaction can be suppressed, and when the load decreases, carbon deposition due to insufficient steam can be suppressed.

  Subsequently, the O / C control by the control unit 10 will be specifically described. First, the control unit 10 receives the accelerator opening Acc from the accelerator opening sensor 90. The control unit 10 calculates the required load Preq based on the received accelerator opening Acc. In this case, the control unit 10 calculates the required load Preq using the map shown in FIG. FIG. 3 is a diagram illustrating an example of the relationship between the accelerator opening Acc and the required load Preq. The vertical axis in FIG. 3 indicates the required load Preq, and the horizontal axis in FIG. 3 indicates the accelerator opening Acc. As shown in FIG. 3, the required load Preq increases in proportion to the accelerator opening Acc.

  FIG. 4 is a diagram illustrating another example of the relationship between the accelerator opening Acc and the required load Preq. The vertical axis in FIG. 4 indicates the required load Preq, and the horizontal axis in FIG. 4 indicates the accelerator opening Acc. As shown in FIG. 4, the required load Preq increases stepwise as the accelerator opening Acc increases. That is, the values that can be taken by the required load Preq are limited to a plurality of predetermined values. In this case, control of the amount of hydrogen and the amount of oxygen necessary for the power generation reaction is facilitated.

  Next, the control unit 10 can determine that the required load Preq has changed when the required load Preq has a value different from the previous required load Preq_o. When the absolute value of the difference between the required load Preq and the previous required load Preq_o is larger than a predetermined value (for example, 20% of the maximum output of the fuel cell 60), it may be determined that the required load Preq has changed. . In this case, the influence of noise mixed in the fuel cell system 100 can be ignored. Therefore, rapid changes in the fuel amount, oxygen amount, and water vapor amount due to unnecessary execution of the O / C control can be suppressed. As a result, destabilization of the generated hydrogen flow rate and the generated hydrogen concentration can be suppressed. When the required load Preq varies stepwise as shown in FIG. 4, it becomes easy to determine the variation of the required load.

  When it is determined that the required load Preq has fluctuated, the control unit 10 calculates a target amount of reformed fuel to be supplied to the reforming unit 51 (hereinafter, fuel target flow rate Qf_t). In this case, the control unit 10 calculates the fuel target flow rate Qf_t using the map shown in FIG. FIG. 5 is a diagram illustrating an example of the relationship between the required load Preq and the fuel target flow rate Qf_t. The vertical axis in FIG. 5 represents the fuel target flow rate Qf_t, and the horizontal axis in FIG. 5 represents the required load Preq.

  As shown in FIG. 5, the fuel target flow rate Qf_t increases as the required load Preq increases. On the high load side, the increase ratio of the fuel target flow rate Qf_t with respect to the increase ratio of the required load Preq is large. This is because the reforming efficiency generally decreases on the high load side.

Next, based on the detection result of the ammeter 64, the control unit 10 calculates the flow rate of water vapor contained in the cathode offgas (hereinafter, estimated water vapor flow rate Stm (mol / s)). The controller 10 can calculate the estimated water vapor flow rate Stm using the following equation (3).
Stm = (power generation current × number of stacked cells) / (2 × 96485) (3)
In Equation (3), the generated current is the current detected by the ammeter 64, the number of stacked cells is the number of cells stacked in the fuel cell 60, and 96485 is the Faraday constant.

  Next, the control unit 10 calculates a predicted S / C value (hereinafter referred to as predicted S / C) when the reformed fuel having the fuel target flow rate Qf_t is supplied to the reforming unit 51. In this case, the control unit 10 can calculate the predicted S / C from the fuel target flow rate Qf_t and the estimated water vapor flow rate Stm.

  Next, the control unit 10 obtains a target O / C (hereinafter, control target O / C) in the reforming unit 51. In this case, the control target O / C is obtained so as to satisfy the above formulas (1) and (2). In this case, carbon deposition in the reforming unit 51 can be suppressed, and excessive combustion in the reforming unit 51 can be suppressed.

  Moreover, the control part 10 may obtain | require control target O / C using the map of FIG. FIG. 6 is a map showing the relationship between the predicted S / C and the control target O / C. The vertical axis in FIG. 6 represents the control target O / C, and the horizontal axis in FIG. 6 represents the predicted S / C. As illustrated in FIG. 6, the control unit 10 may set the control target O / C to the minimum value when the predicted S / C is 2.0. This is because when the predicted S / C is 2.0, carbon deposition can be suppressed even if the ratio of the partial oxidation reaction is small. In addition, when the predicted S / C is smaller than 2.0, the control unit 10 increases the control target O / C. This is for suppressing carbon deposition. Furthermore, the control unit 10 increases the control target O / C even when the predicted S / C is larger than 2.0. This is because when the ratio of the steam reforming reaction, which is an endothermic reaction, increases, the temperature of the reforming unit 51 decreases.

  The rate of increase in the control target O / C relative to the change in the predicted S / C may be smaller when the predicted S / C decreases from 2.0 than when the predicted S / C increases from 2.0. preferable. This is because if the ratio of the partial oxidation reaction is increased more than necessary when the ratio of the steam reforming reaction is small, the temperature of the reforming unit 51 increases rapidly. Note that the amount of increase in the control target O / C may be set larger as the load increase amount applied to the fuel cell 60 is larger. This is because the decrease width of S / C becomes large. From the above, appropriate O / C control according to the load situation is possible. Even when the map of FIG. 6 is used, it is necessary to satisfy the relationships of the expressions (1) and (2).

  Next, the control unit 10 controls the metering valve 40 so that the flow rate of the reformed fuel supplied to the reforming unit 51 becomes the fuel target flow rate Qf_t. The control unit 10 may reduce the variation in the supply amount of the reformed fuel when the current reformed fuel flow rate (hereinafter referred to as the current flow rate Qf) approaches the fuel target flow rate Qf_t. . This is because the flow rate of the fuel supplied to the reforming unit 51 easily converges to the fuel target flow rate Qf_t. Details will be described below.

  First, it is determined whether or not the load on the fuel cell 60 increases. In this case, the control unit 10 determines that the load on the fuel cell 60 increases if the fuel target flow rate Qf_t is larger than the current flow rate Qf, and decreases the load on the fuel cell 60 if the fuel target flow rate Qf_t is equal to or less than the current flow rate Qf. Judge that. When it is determined that the load of the fuel cell 60 increases, the control unit 10 calculates the reformed fuel flow rate supplied to the reforming unit 51. In this case, the control unit 10 uses the map of FIG.

  FIG. 7 is a diagram showing the relationship between the amount of change in the reformed fuel necessary for the reforming unit 51 and the correction value of the reformed fuel amount (hereinafter referred to as the correction value map (Qf_t−Qf)). The horizontal axis in FIG. 7 indicates the amount of change in the reformed fuel, and the vertical axis in FIG. 7 indicates the correction value map (Qf_t−Qf). As shown in FIG. 7, the correction value map (Qf_t−Qf) is a constant value smaller than “Qf_t−Qf” when the amount of change in the reformed fuel is equal to or less than the first predetermined value. When the fluctuation amount of the fuel exceeds the first predetermined value, it increases in proportion to the fluctuation amount of the reformed fuel, and when the fuel fluctuation amount exceeds the second predetermined value, a value larger than “Qf_t−Qf” is shown.

  The control unit 10 controls the metering valve 40 so that the reformed fuel having a smaller flow rate between the fuel target flow rate Qf_t and the current flow rate Qf + correction value map (Qf_t−Qf) is supplied to the reforming unit 51. In this case, when the fluctuation amount of the reformed fuel is in the range of the second predetermined value or more, the flow rate of the reformed fuel supplied to the reforming unit 51 is set to the fuel target flow rate Qf_t. On the other hand, when the fluctuation amount of the reformed fuel becomes equal to or less than the second predetermined value, the reformed fuel amount supplied to the reforming unit 51 is set to a value smaller than the fuel target flow rate Qf_t. Thereby, a sudden change in the amount of reformed fuel supplied to the reforming unit 51 can be suppressed.

  When it is determined that the load on the fuel cell 60 decreases, the control unit 10 calculates the reformed fuel flow rate to be supplied to the reforming unit 51. In this case, the control unit 10 uses the map of FIG. FIG. 8 is a diagram showing the relationship between the amount of change in reformed fuel required for the reforming unit 51 and the correction value of the reformed fuel amount (hereinafter referred to as a correction value map (Qf−Qf_t)). The horizontal axis in FIG. 8 indicates the amount of change in the reformed fuel, and the vertical axis in FIG. 8 indicates the correction value map (Qf−Qf_t). As shown in FIG. 8, the correction value map (Qf−Qf_t) shows a constant value smaller than “Qf−Qf_t” when the amount of change in the reformed fuel is equal to or smaller than the third predetermined value. When the fluctuation amount of the fuel exceeds the third predetermined value, it increases in proportion to the fluctuation amount of the reformed fuel, and when it exceeds the fourth predetermined value, a value larger than “Qf−Qf_t” is shown.

  The control unit 10 controls the metering valve 40 so that the reformed fuel having a flow rate larger than the target fuel flow rate Qf_t and the current flow rate Qf−correction value map (Qf−Qf_t) is supplied to the reforming unit 51. . In this case, when the variation amount of the reformed fuel is in the range of the fourth predetermined value or more, the flow rate of the reformed fuel supplied to the reforming unit 51 is set to the fuel target flow rate Qf_t. On the other hand, when the fluctuation amount of the reformed fuel becomes equal to or smaller than the fourth predetermined value, the reformed fuel amount supplied to the reforming unit 51 is set to a value larger than the fuel target flow rate Qf_t. Thereby, a sudden change in the amount of reformed fuel supplied to the reforming unit 51 can be suppressed.

  Next, the control unit 10 controls the air pump 80 so that the O / C in the reforming unit 51 becomes the control target O / C. The control unit 10 ends the O / C control when the reformed fuel flow rate supplied to the reforming unit 51 reaches the fuel target flow rate Qf_t. The control unit 10 may end the O / C control when the output of the fuel cell 60 reaches the required load Preq. In this case, when the output of the fuel cell 60 fluctuates step by step as shown in FIG. 4, it is prepared to determine the end of the O / C control. This is because the output of the fuel cell 60 does not fluctuate unnecessarily.

  Next, an example of a flowchart when the control unit 10 performs O / C control of the fuel cell system 100 will be described. FIG. 9 is a diagram showing an example of the flowchart. The control unit 10 executes the flowchart of FIG. 9 every 100 ms, for example. First, as shown in FIG. 9, the control unit 10 calculates a required load Preq based on the accelerator opening obtained from the accelerator opening sensor 90 (step S1). In this case, the control unit 10 uses the map of FIG.

  Next, the control unit 10 determines whether or not the absolute value of the difference between the required load Preq and the previous required load Preq_o exceeds the load change determination value k (step S2). In the present embodiment, the load change determination value k is 20% of the maximum output of the fuel cell 60. When it is determined in step S2 that the absolute value of the difference between the required load Preq and the previous required load Preq_o exceeds the load change determination value k, the control unit 10 indicates that the O / C control is being executed. Set the flag. Specifically, the control unit 10 substitutes 1 for the variable Preq_flg (step S3).

  Next, the control unit 10 calculates the fuel target flow rate Qf_t based on the required load Preq (step S4). In this case, the control unit 10 uses the map of FIG. Next, the control unit 10 calculates the estimated water vapor flow rate Stm based on the current value acquired from the ammeter 64 (step S5). Next, the control unit 10 calculates a predicted S / C from the fuel target flow rate Qf_t and the estimated water vapor amount Stm (step S6). Next, the control unit 10 calculates a control target O / C based on the predicted S / C (step S7). In this case, the control unit 10 uses the map of FIG.

  Next, the control unit 10 determines whether or not the fuel target flow rate Qf_t is larger than the current flow rate Qf (step S8). When it is determined in step S8 that the fuel target flow rate Qf_t is larger than the current flow rate Qf, the control unit 10 is smaller than either the fuel target flow rate Qf_t and the current flow rate Qf + correction value map (Qf_t−Qf) shown in FIG. The flow rate is set to the current flow rate Qf, and the metering valve 40 is controlled so that the reformed fuel of the current flow rate Qf is supplied to the reforming unit 51 (step S9). When it is not determined in step S8 that the fuel target flow rate Qf_t is larger than the current flow rate Qf, the control unit 10 determines which of the fuel target flow rate Qf_t and the current flow rate Qf-correction value map (Qf-Qf_t) shown in FIG. The larger flow rate is set as the current flow rate Qf, and the metering valve 40 is controlled so that the reformed fuel of the current flow rate Qf is supplied to the reforming unit 51 (step S10).

  Next, the control unit 10 determines whether or not the fuel target flow rate Qf_t is equal to the current flow rate Qf (step S11). When it is determined in step S11 that the fuel target flow rate Qf_t is equal to the current flow rate Qf, the control unit 10 sets a flag indicating that the O / C control has ended. Specifically, the control unit 10 substitutes 0 for the variable Preq_flg (step S12). Next, the control unit 10 substitutes the required load Preq for the previous required load Preq_o (step S13). Next, the control unit 10 calculates a cathode air flow rate Qc to be supplied to the cathode 61 based on the current flow rate Qf, the control target O / C, and the required load Preq, and the air at the cathode air flow rate Qc is supplied to the cathode 61. Thus, the air pump 80 is controlled (step S14). Thereafter, the control unit 10 ends the operation.

  If it is not determined in step S2 that the absolute value of the difference between the required load Preq and the previous required load Preq_o exceeds the load change determination value k, the control unit 10 determines whether or not the variable Preq_flg is 1. Determination is made (step S15). When it is determined in step S15 that the variable Preq_flg is 1, the control unit 10 performs the operation of step S8. If it is not determined in step S15 that the variable Preq_flg is 1, the control unit 10 ends the operation. When it is determined in step S11 that the fuel target flow rate Qf_t is equal to the current flow rate Qf, the control unit 10 performs the operation of step S14.

  Thus, O / C can be appropriately controlled by executing the flowchart of FIG. Thereby, a reduction in reforming efficiency of the fuel cell system 100 can be suppressed.

  In this embodiment, the reforming unit 51 corresponds to the reforming unit, the air pump 80 corresponds to the cathode off-gas supply unit, the control unit 10 and the air pump 80 correspond to the O / C control unit, and the accelerator opening sensor 90 Corresponds to the first detection means, and the O / C control corresponds to the first control.

1 is a schematic diagram showing an overall configuration of a fuel cell system according to a first embodiment of the present invention. It is a figure which shows the relationship between O / C and the temperature in a modification part. It is a figure which shows an example of the relationship between an accelerator opening and a request | requirement load. It is a figure which shows the other example of the relationship between an accelerator opening and a request | requirement load. It is a figure which shows an example of the relationship between request | requirement load and fuel target flow volume. It is a map which shows the relationship between prediction S / C and control target O / C. It is a figure which shows the relationship between the variation | change_quantity of the reformed fuel required for a reforming part, and the correction value of reformed fuel quantity. It is a figure which shows the relationship between the variation | change_quantity of the reformed fuel required for a reforming part, and the correction value of reformed fuel quantity. It is a figure which shows an example of the flowchart at the time of a control part performing O / C control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Control part 40 Metering valve 50 Reformer 51 Reformer 60 Fuel cell 61 Cathode 62 Anode 70, 80 Air pump 90 Accelerator opening sensor 100 Fuel cell system

Claims (8)

A fuel cell;
Reforming means for generating hydrogen by a reforming reaction using the reformed fuel;
Cathode offgas supply means for supplying cathode offgas of the fuel cell to the reforming means;
O / C control means for performing a first control for controlling the O / C so that S / C + O / C ≧ 2 and O / C is not more than a first predetermined value when the load of the fuel cell fluctuates; A fuel cell system comprising:
Where S represents the molar amount of water vapor supplied to the reforming means, C represents the molar amount of carbon atoms in the reformed fuel supplied to the reforming means, and O represents the modified amount. The molar amount of oxygen atoms in the oxygen gas supplied to the mass means is shown. First detection means for acquiring and / or predicting a fluctuation range of a load required for the fuel cell;
The O / C control means performs the first control when the fluctuation range of the load acquired and / or predicted by the first detection means exceeds a predetermined value. Fuel cell system. 3. The fuel cell system according to claim 1, wherein the O / C control unit sets the O / C higher as the fluctuation range of the load is larger. The O / C control means ends the first control when the output of the fuel cell reaches a load required for the fuel cell. Fuel cell system. 5. The fuel cell system according to claim 1, wherein the output of the fuel cell varies stepwise according to a required load. 6. The fuel cell system according to any one of claims 1 to 5, wherein the first predetermined value is 1. The fuel cell system according to any one of claims 1 to 6, wherein the O / C control means performs the first control so as not to fall below the O / C immediately before the first control is performed. The fuel cell system according to claim 1, wherein the O / C control means is a pump that supplies air to a cathode of the fuel cell.

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