JP2016134287A - Fuel battery system, operation method for the same and configuration method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the influence of dispersion in performance among plural fuel batteries which are connected to one another in parallel.SOLUTION: Three fuel battery cells 18A to 18c are electrically connected to one another in parallel by electrical wires 50, 52, and successively connected in series in the order of the fuel battery cells 18A, 18B, 18C through a fuel gas pipe 30 and fuel electrode exhaust gas pipes 36, 40 so as to supply fuel in series. A fuel controller 16 can control the fuel supply amount to the fuel battery cell 18a, and a power conditioner 20 can control the magnitude of the total current corresponding to added current of the fuel battery cells 18A to 18C. An operation controller 22 controls the magnitude of the total current flowing in the electrical wires 50, 52 according to a request output, and controls the fuel supply amount to the fuel battery cell 18A at the most upstream side to the fuel amount corresponding to the total current.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fuel cell system, a fuel cell system operation method, and a fuel cell system configuration method.

  As a method for increasing the output of the fuel cell system, for example, a method of increasing the current flowing through the fuel cell by increasing the electrode area per fuel cell, and increasing the number of stacked fuel cells to increase the voltage There is a method to make it.

  However, when the electrode area of the fuel cell is increased, generally, the fuel cell tends to warp and the gas seal and electrical contact are deteriorated, and the internal gas and current are biased to adversely affect the performance. There are many problems such as restrictions on the shape and arrangement of the container for storing the fuel cells. Since there is a drawback that a large facility is required in production, there is a certain limit to increasing the electrode area of the fuel cell.

  For this reason, it is necessary to increase the number of stacked fuel cells in order to further increase the output of the fuel cell system after increasing the electrode area of the fuel cell to some extent. In addition, the small current high voltage type that gains output by reducing the current flowing through the fuel cell and stacking many sheets is larger than the large current type that increases the current by increasing the electrode area of the fuel cell. Loss due to current resistance can be reduced, which is often advantageous in terms of fuel cell performance.

  On the other hand, regarding the increase in voltage due to the increase in the number of stacked fuel cells, there is a limit to the range that can be handled by general equipment due to the withstand voltage performance of electrical wiring and various power equipment. In order to increase the voltage further, a special insulating member or thickening of the insulating member is required, which causes a problem that the size and cost of the fuel cell system increase.

  For this reason, when increasing the output of the fuel cell system, stacks in which a plurality of fuel cells are stacked are electrically connected in parallel, or a plurality of fuel cells connected in parallel are connected in series. A connection method is conceivable. By adopting such a configuration, the overall current can be increased by connecting a plurality of fuel cells in parallel while suppressing the electrode area per fuel cell to a certain level or less. High output as a whole stack can be realized without stacking one fuel cell.

  In relation to the above, Patent Document 1 discloses a configuration in which an electrolyte flow path and a fuel flow path are connected in series for all the fuel cells in a fuel cell stack system having a plurality of fuel cells.

  Patent Document 2 discloses a stack composed of one or more fuel cells, a temperature measuring device that measures the temperature of the stack, and a temperature that is electrically connected to the stack in series to adjust the temperature of the stack. A plurality of systems including a stack temperature control device are set, and each system is electrically connected in parallel, and the stacks of each system are arranged with a space between each other, and the stack temperature is determined based on the measurement result of the temperature measurement device. Techniques for controlling the adjustment device are disclosed.

JP 2009-37915 A JP 2007-250287 A

  In general, as shown in FIG. 1 as an example, the fuel cell has a characteristic that the voltage decreases due to the internal resistance as the current increases. The slope of the voltage drop with respect to the increase in current (hereinafter referred to as the `` performance '' of the fuel cell) is the environment such as the temperature of the fuel cell, the manufacturing variation of the fuel cell, the degree of deterioration of the fuel cell over time Therefore, there are individual differences for each fuel cell, and they are not always constant. When connecting fuel cells electrically in parallel, if there is a variation in performance among individual fuel cells, as shown in FIG. 2 as an example, the voltage is the same in all fuel cells, Is different for each fuel cell. In addition, the difference in current for each fuel cell changes depending on the performance variation of each fuel cell, and therefore changes over time.

  The fuel cell has a characteristic of consuming an amount of fuel proportional to the current, and the fact that there is a variation in current among individual fuel cells means that the fuel consumption in each fuel cell also varies. Means. In general, in a fuel cell, the balance between the amount of fuel supplied and the amount of fuel consumed greatly affects durability and efficiency. Specifically, if the amount of fuel consumed is too large relative to the amount of fuel supplied, the durability will be reduced, and if the amount of fuel consumed is too small relative to the amount of fuel supplied, the proportion of fuel contained in the exhaust gas of the fuel cell will be reduced. Higher efficiency decreases. Therefore, it is ideal to keep the ratio of the fuel consumption amount to the fuel supply amount high as long as the durability of the fuel cell can be ensured. However, as shown in FIG. 2, if the current consumption of each fuel cell varies, and the fuel consumption in each fuel cell varies, the ratio of the fuel supply amount to the fuel consumption in each fuel cell also increases. Variation will occur.

  Here, considering the deterioration of the durability of the fuel cell, it may be possible to give a margin to the overall fuel supply amount. In this case, even if the individual fuel cells vary in performance, Even in these fuel cells, it is possible to prevent the fuel consumption from being excessive with respect to the fuel supply amount, but this leads to a decrease in efficiency. In addition, the current flowing through each fuel cell is measured and the amount of fuel supplied to each fuel cell is sequentially controlled. Although a technique for controlling each of them in accordance with the ratio (the technique disclosed in Patent Document 2) is also conceivable, any technique causes a complicated system configuration.

  Accordingly, there is a need for a fuel cell system with a simple configuration that prevents an excessive ratio of fuel consumption to the amount of fuel supplied in each fuel cell, and that can achieve high efficiency. Note that the technique described in Patent Document 1 does not take into account the suppression of the influence of variations in the performance of individual fuel cells when a plurality of fuel cells are electrically connected in parallel.

  The present invention has been made in consideration of the above-described facts, and is a fuel cell system capable of suppressing the influence of variation in the performance of each of a plurality of fuel cells electrically connected in parallel, a method for operating the fuel cell system, and fuel The object is to obtain a battery system configuration method.

  According to a first aspect of the present invention, there is provided a fuel cell system comprising: a plurality of fuel cells that generate electricity using supplied fuel; an electrical wiring that connects the plurality of fuel cells in parallel; and a fuel that is connected in series to the plurality of fuel cells. A flow path for connecting the plurality of fuel cells in series, a current of the whole of the plurality of fuel cells flowing through the electric wiring is controlled to a magnitude corresponding to a required output, and the plurality of the fuel cells are supplied. A control unit that controls the amount of fuel supplied to the most upstream fuel cell of the flow path among the fuel cells to a fuel amount corresponding to the current of the plurality of fuel cells as a whole.

  According to the first aspect of the present invention, the fuel cell system includes a plurality of fuel cells that generate electric power from the supplied fuel, and the plurality of fuel cells are connected in parallel by electric wiring. In the first aspect of the invention, each of the plurality of fuel cells may be a fuel cell or a fuel cell stack in which a plurality of fuel cells are stacked. Here, in the first aspect of the invention, the plurality of fuel cells are connected in series by the flow paths so that the fuel is supplied in series to the plurality of fuel cells, and the control unit includes the plurality of fuels flowing in the electric wiring. The amount of fuel supplied to the uppermost fuel cell in the flow path among the plurality of fuel cells is controlled according to the current output of the plurality of fuel cells. Control the amount.

  As described above, when a plurality of fuel cells are electrically connected in parallel, the voltage is constant for each fuel cell, but the current varies according to the performance of each fuel cell (FIG. 2). See also). However, in the invention according to claim 1, since the current of the plurality of fuel cells flowing through the electric wiring is controlled to a magnitude according to the required output, the plurality of fuel cells connected in parallel electrically are Output (voltage / current) according to the required output can be obtained.

  In addition, as described above, the current consumption of each fuel cell varies depending on the performance of the individual fuel cell, and the fuel consumption also varies for each fuel cell. However, in the first aspect of the present invention, fuel is supplied in series to the plurality of fuel cells through the flow path, and the amount of fuel supplied to the most upstream fuel cell in the flow path among the plurality of fuel cells is set to the plurality of fuel cells. The fuel amount is controlled according to the current of the entire battery. As a result, the amount of fuel supplied to the uppermost fuel cell in the flow path becomes the amount of fuel corresponding to the sum of the fuel consumption in each of the plurality of fuel cells, so that the fuel consumption varies for each individual fuel cell. Even if the fuel supply amount to the fuel cell at the most downstream side of the flow path becomes too small relative to the fuel consumption amount in the fuel cell, the durability is lowered or the efficiency is lowered by being excessive. Can also be prevented.

  As described above, the invention according to claim 1 controls the currents of the plurality of fuel cells as a whole flowing through the electric wiring and also controls the amount of fuel supplied to the most upstream fuel cell in the flow path. With the configuration, it is possible to suppress a decrease in durability and efficiency due to the influence of the performance variation of each of the plurality of fuel cells electrically connected in parallel.

  In the first aspect of the invention, a configuration may be provided in which a plurality of fuel cell groups including a plurality of fuel cells connected in parallel by electric wiring and supplied with fuel in series by a flow path are provided. In this case, the plurality of fuel cell groups may be configured to be electrically connected in series and supplied with fuel in parallel, as described in claim 2, for example, or as described in claim 3. Thus, a configuration in which fuel is electrically connected in series and fuel is supplied in series may be employed.

  According to a fourth aspect of the present invention, there is provided a fuel cell system comprising: a plurality of fuel cells that generate electricity using supplied fuel; an electrical wiring that connects the plurality of fuel cells in parallel; and an output current among the plurality of fuel cells. A fuel cell having a small absolute value of the slope of the change in output voltage with respect to the change of the fuel is supplied in series in a sequence located downstream of the fuel cell having a large absolute value of the slope in the fuel flow direction. And a flow path connecting the plurality of fuel cells in series.

  In the fourth aspect of the invention, as in the first aspect of the invention, a plurality of fuel cells that generate power from the supplied fuel are connected in parallel by electric wiring, and the fuel is supplied in series to the plurality of fuel cells. As described above, a plurality of fuel cells are connected in series by flow paths. In the fourth aspect of the present invention, each of the plurality of fuel cells may be a fuel cell or a fuel cell stack in which a plurality of fuel cells are stacked.

  In the fuel cell system configured as described above, by supplying fuel to a plurality of fuel cells in series, the amount of fuel supplied to the fuel cell located upstream in the fuel flow direction is reduced downstream in the fuel flow direction. As a result, the amount of fuel supplied to the fuel cell located in the fuel cell is larger (richer), and accordingly, the fuel cell located upstream in the fuel flow direction is located downstream in the fuel flow direction. There is a difference in performance and current for each fuel cell, in which the performance is higher than that of a fuel cell, and a higher current flows in a fuel cell with higher performance than in a fuel cell with lower performance. Each fuel cell generates heat according to current and voltage. However, since fuel cells connected in parallel electrically have the same voltage, the amount of heat generated is determined according to current. Therefore, the fuel cell located on the upstream side in the fuel flow direction has a higher calorific value and the temperature is higher than the fuel cell located on the downstream side in the fuel flow direction.

  In general, as shown in FIG. 3 as an example, the fuel cell has a higher internal resistance and a higher efficiency at a higher temperature, and the internal resistance increases and the efficiency tends to decrease as the temperature decreases. However, if the temperature of the fuel cell becomes excessively high, it may adversely affect the constituent members of the fuel cell and other surrounding members, and the durability may decrease.

  The invention according to claim 4 is based on the above, and among the plurality of fuel cells, a fuel cell having a small absolute value of the slope of the change in the output voltage with respect to the change in the output current (that is, a fuel cell having high performance) A plurality of fuel cells are arranged so that the fuel is supplied in series in the order of being located downstream of the fuel cell in which the absolute value of the change of the output voltage with respect to the change is large (that is, the fuel cell having low performance). They are connected in series by a flow path. As a result, the fuel is supplied in series to the plurality of fuel cells in the order in which the variation in performance of each of the plurality of fuel cells is reduced by the difference in the amount of fuel supplied to the individual fuel cells. The variation in the temperature of the fuel cell is also equalized. Therefore, according to the fourth aspect of the present invention, it is possible to suppress a decrease in durability and efficiency due to the influence of the variation in performance of each of the plurality of fuel cells connected in parallel.

  In addition, in the invention according to claim 4, the fuel cell having a small absolute value of the slope of the change of the output voltage with respect to the change of the output current, for example, as shown in claim 5, the change of the output voltage with respect to the change of the output current. It may be a fuel cell installed in an environment where the temperature is higher than that of a fuel cell having a large absolute value of inclination. In the case where the environmental temperatures at which the plurality of fuel cells are installed are different from each other, the performance of each of the plurality of fuel cells varies due to the difference in the temperature of the installation environment. The fuel is supplied in series to the plurality of fuel cells in an order reduced by the variation in performance due to the difference in temperature of the installation environment and the difference in the amount of fuel supplied to the individual fuel cells. Therefore, the performance and temperature variations of the plurality of fuel cells can be leveled.

  According to a fourth aspect of the present invention, the fuel cell having a small absolute value of the slope of the change in the output voltage with respect to the change in the output current is, for example, as shown in the sixth aspect, the change in the output voltage with respect to the change in the output current. The fuel cell may have a larger electrode area than the fuel cell having a large absolute value of the slope.

  In general, when the electrode area of the fuel cell is increased, the current density decreases with respect to the unit current amount, so that the internal resistance decreases, and the absolute value of the slope of the change in the output voltage with respect to the change in the output current tends to be reduced. On the other hand, when the electrode area of the fuel cell is reduced, the current density increases with respect to the unit current amount, so that the internal resistance increases, and the absolute value of the slope of the change in the output voltage with respect to the change in the output current tends to increase.

  Based on the above, in the invention described in claim 6, a fuel cell having an electrode area larger than that of a fuel cell having a large absolute value of the slope of the change in the output voltage with respect to the change in the output current is obtained. The fuel cell is used as a fuel cell having a small absolute value of the change slope, and the fuel cell is serially arranged in the order of being located downstream in the fuel flow direction from the fuel cell having a large absolute value of the change of the output voltage with respect to the change of the output current. A plurality of fuel cells are connected in series by flow paths so that fuel is supplied. Thus, the variation in performance of the plurality of fuel cells due to the difference in the amount of fuel supplied to the individual fuel cells is serially connected to the plurality of fuel cells in an order that is reduced by the difference in the area of the electrodes of the individual fuel cells. As fuel is supplied, the performance and temperature variations of the plurality of fuel cells due to the difference in the amount of fuel supplied to the individual fuel cells can be leveled.

  According to a fourth aspect of the present invention, the fuel cell having a small absolute value of the slope of the change in the output voltage with respect to the change in the output current is, for example, as shown in the seventh aspect, the change in the output voltage with respect to the change in the output current. A fuel cell in which the number of stacked fuel cells is larger than that of a fuel cell having a large absolute value of inclination may be used.

  When the fuel cell has a configuration in which a plurality of fuel cells are stacked, the voltage of the fuel cell increases as the number of stacked fuel cells increases. Based on the above, according to the seventh aspect of the present invention, a fuel cell in which the number of stacked fuel cells is larger than that of a fuel cell having a larger absolute value of the slope of the change in output voltage with respect to the change in output current is obtained. An order in which the absolute value of the slope of the change in the output voltage is used as a fuel cell, and the fuel cell is located on the downstream side in the fuel flow direction from the fuel cell in which the absolute value of the change in the output voltage with respect to the change in the output current is large. A plurality of fuel cells are connected in series by flow paths so that the fuel is supplied in series.

  Accordingly, the plurality of fuel cells are arranged in an order in which the variation in performance of the plurality of fuel cells due to the difference in the amount of fuel supplied to the individual fuel cells is reduced by the difference in the number of stacked fuel cells in each fuel cell. Thus, the fuel is supplied in series, and the performance and temperature variations of the plurality of fuel cells due to the difference in the fuel supply amount to the individual fuel cells can be leveled.

  Further, in the invention according to any one of claims 4 to 7, as described in claim 8, for example, the current of the whole of the plurality of fuel cells flowing through the electric wiring is sized according to the required output. And a control unit that controls the amount of fuel supplied to the most upstream fuel cell in the flow path among the plurality of fuel cells to a fuel amount corresponding to the current of the plurality of fuel cells as a whole. You may go out. Thus, similarly to the first aspect of the invention, with a simple configuration, it is possible to suppress a decrease in durability and efficiency due to the influence of each of the performance variations of the plurality of fuel cells connected in parallel. can do.

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the flow path is switchable in order of connecting the plurality of fuel cells in series. A detection unit that detects at least one of a temperature and an output current of each of the plurality of fuel cells, and an output current based on at least one of the temperature and the output current of each of the plurality of fuel cells detected by the detection unit The plurality of fuel cells are connected in series so that the fuel cell having a small absolute value of the change in the output voltage relative to the change is positioned downstream of the fuel cell having the large absolute value of the gradient in the fuel flow direction. And a switching unit for switching the order.

  In the invention according to claim 9, at least one of the temperature and the output current of each of the plurality of fuel cells is detected by the detection unit, and the switching unit detects the temperature and the output current of each of the plurality of fuel cells detected by the detection unit. Based on at least one of the above, the fuel cell in which the absolute value of the slope of the change in the output voltage with respect to the change in the output current is smaller than a predetermined value is located downstream of the fuel cell in which the absolute value of the slope is large in the fuel flow direction In this way, the order of connecting a plurality of fuel cells in series is switched.

  As a result, the absolute value (fuel cell performance) of the slope of the change in the output voltage with respect to the change in the output current of each of the plurality of fuel cells due to the difference in the degree of deterioration with time of each of the plurality of fuel cells. If there is a difference, this difference is detected as a variation in at least one of the temperature and output current of each of the plurality of fuel cells, and a fuel cell in which the absolute value of the slope of the change in output voltage with respect to the change in output current is smaller than a predetermined value Since the order of connecting the plurality of fuel cells in series is switched so that the fuel cell has a larger absolute value of the slope than the fuel cell in the flow direction of the fuel, the degree of deterioration with time of each of the plurality of fuel cells is changed. Even when the performance of the plurality of fuel cells varies due to the difference or the like, it is possible to suppress a decrease in durability and efficiency.

  According to a tenth aspect of the present invention, there is provided a method of operating a fuel cell system in which a plurality of fuel cells that generate electricity using supplied fuel are connected in parallel by electric wiring, and fuel is connected in series to the plurality of fuel cells by flow paths. And the current of the plurality of fuel cells flowing through the electrical wiring is controlled to a magnitude corresponding to a required output, and is supplied to the most upstream fuel cell in the flow path among the plurality of fuel cells. The amount of fuel to be controlled is controlled to the amount of fuel corresponding to the current of the whole of the plurality of fuel cells. Therefore, as in the first aspect of the invention, it is electrically connected in parallel with a simple configuration. It can suppress that durability and efficiency fall by the influence of the dispersion | variation in each performance of a some fuel cell.

  According to a eleventh aspect of the present invention, there is provided a fuel cell system configuration method in which a plurality of fuel cells that generate power using supplied fuel are connected in parallel by electric wiring, and among the plurality of fuel cells, a change in output current is detected. The plurality of fuel cells are supplied in series in the order in which the fuel cells having a small absolute value of the change in the output voltage are positioned downstream of the fuel cell having the large absolute value of the gradient in the fuel flow direction. In the same manner as in the invention of claim 4, due to the influence of variation in the performance of each of the plurality of fuel cells electrically connected in parallel, It can suppress that durability and efficiency fall.

  The present invention has an effect that the influence of variation in performance of each of the plurality of fuel cells electrically connected in parallel can be suppressed.

It is a diagram which shows an example of the current-voltage characteristic of a fuel cell. It is a diagram which shows an example of the change according to the performance of the current-voltage characteristic of a fuel cell. It is a diagram which shows an example of the change according to the temperature of the current-voltage characteristic of a fuel cell. 1 is a schematic configuration diagram of a fuel cell system according to a first embodiment. It is a flowchart which shows the fuel cell system operation control process in 1st Embodiment. It is a schematic block diagram which shows the other structure of a fuel cell system. It is a schematic block diagram which shows the other structure of a fuel cell system. It is a schematic block diagram of the fuel cell system which concerns on 2nd Embodiment. It is a schematic block diagram of the fuel cell system which concerns on 3rd Embodiment. It is a schematic block diagram of the fuel cell system which concerns on 4th Embodiment. It is a schematic block diagram of the fuel cell system which concerns on 5th Embodiment. It is a flowchart which shows the fuel cell system operation control process in 5th Embodiment. It is a schematic block diagram of the fuel cell system as a comparative example of this invention.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 4 shows a fuel cell system 10A according to the first embodiment. The fuel cell system 10A includes a reformer 12, a burner 14, a fuel controller 16, three fuel cells 18A to 18C, a power conditioner 20, and an operation control unit 22 as main components.

  The reformer 12 is connected to the other end of a source gas pipe 28 having one end connected to the fuel controller 16. One end of a reforming water supply pipe 24 is connected to the reformer 12, and a pump 26 is provided in the middle of the reforming water supply pipe 24. Reformed water is supplied to the reformed water supply pipe 24, and the supplied reformed water is sent to the downstream side (the reformer 12 side) by the pump 26 and supplied to the reformer 12. The pump 26 is electrically connected to the operation control unit 22, and the driving of the pump 26 is controlled by the operation control unit 22.

  The reformer 12 is steam-reformed using the reformed water (steam) supplied through the reformed water supply pipe 24 by using the reformed water (steam) supplied through the reformed water supply pipe 24 by being heated by the burner 14. Then, fuel gas containing hydrogen gas is generated. The fuel gas generated by the reformer 12 is supplied via the fuel gas pipe 30 to the fuel battery cell 18A located at the uppermost stream in the fuel gas flow direction.

  The fuel controller 16 is connected to a gas source (not shown) via the raw material gas pipe 23. A raw material gas (hydrocarbon fuel) from which sulfur compounds are adsorbed and removed by the desulfurizer is supplied to the fuel controller 16 from a gas source through a raw material gas pipe 23. The fuel controller 16 is connected to the reformer 12 via the raw material gas pipe 28 as described above. That is, the fuel controller 16 is connected to the fuel cell 18 </ b> A via the raw material gas pipe 28, the reformer 12 and the fuel gas pipe 30. The fuel controller 16 is electrically connected to the operation control unit 22. The fuel controller 16 can control the amount of fuel gas (fuel supply amount) supplied from the reformer 12 to the fuel electrode of the fuel cell 18 </ b> A via the fuel gas pipe 30. The amount of fuel supplied to the fuel electrode of the fuel cell 18 </ b> A via the mass device 12 is controlled by the operation control unit 22. Specifically, the operation control unit 22 controls the amount of source gas supplied from the fuel controller 16 to the reformer 12 (source gas supply amount), thereby supplying fuel to the fuel electrode of the fuel cell 18A. Control the amount. The operation control unit 22 controls the amount of reforming water supplied to the reformer 12 by the pump 26 to an amount that is sufficient for steam reforming in the reformer 12 according to the fuel supply amount.

  Further, one end of an oxidizing gas supply pipe 32 is connected to the fuel cell 18 </ b> A, and a blower 34 is provided in the middle of the oxidizing gas supply pipe 32. The oxidizing gas (air) is supplied to the oxidizing gas supply pipe 32, and the supplied oxidizing gas is sent to the fuel cell 18A side by the blower 34 and supplied to the air electrode of the fuel cell 18A. The blower 34 is electrically connected to the operation control unit 22, and the drive of the blower 34 is controlled by the operation control unit 22.

The fuel cells 18 </ b> A to 18 </ b> C have the same configuration, and include an electrolyte layer, and a fuel electrode and an air electrode that are respectively stacked on the front and back surfaces of the electrolyte layer. An oxidizing gas (air) is supplied to the air electrode (cathode electrode). In the air electrode, as shown by the following formula (1), oxygen and electrons in the oxidizing gas react to generate oxygen ions. The generated oxygen ions reach the fuel electrode through the electrolyte layer.
(Air electrode reaction)
1 / 2O ₂ + 2e ⁻ → O ²⁻ (1)

On the other hand, at the fuel electrode, as shown by the following formulas (2) and (3), oxygen ions that have passed through the electrolyte layer react with hydrogen and carbon monoxide in the fuel gas, and water (water vapor) and carbon dioxide. Carbon and electrons are generated. Electrons generated in the fuel electrode move from the fuel electrode to the air electrode through an external circuit, and are thus generated in the fuel cells 18A to 18C. In addition, each fuel cell generates heat with the above reaction during power generation.
(Fuel electrode reaction)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (2)
CO + O ²⁻ → CO ₂ + 2e ⁻ (3)

  One end of a fuel electrode exhaust pipe 36 and an air electrode exhaust pipe 38 is connected to the fuel cell 18A, and the other end of the fuel electrode exhaust pipe 36 and the air electrode exhaust pipe 38 is connected to the fuel cell 18B. The fuel electrode exhaust gas containing unreacted hydrogen gas, water, carbon monoxide and carbon dioxide discharged from the fuel electrode of the fuel cell 18A is supplied to the fuel electrode of the fuel cell 18B via the fuel electrode exhaust pipe 36. The oxidizing gas discharged from the air electrode of the fuel cell 18A is supplied to the air electrode of the fuel cell 18B via the air electrode exhaust pipe 38.

  Fuel cells include solid polymer fuel cells (PEFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), and solid oxide fuel cells depending on the type of electrolyte. Although there are several types such as (SOFC), in the first embodiment, the fuel cells 18A to 18C may be any of the above types of fuel cells.

  Further, one end of a fuel electrode exhaust pipe 40 and an air electrode exhaust pipe 42 is connected to the fuel cell 18B, and the other end of the fuel electrode exhaust pipe 40 and the air electrode exhaust pipe 42 is connected to the fuel cell 18C. Yes. The fuel electrode exhaust gas containing unreacted hydrogen gas, water, carbon monoxide and carbon dioxide discharged from the fuel electrode of the fuel cell 18B is supplied to the fuel electrode of the fuel cell 18C through the fuel electrode exhaust pipe 40. The oxidizing gas discharged from the air electrode of the fuel cell 18B is supplied to the air electrode of the fuel cell 18C via the air electrode exhaust pipe 42.

  As described above, the fuel cell system 10A according to the first embodiment includes the fuel gas pipe 30, the fuel cell 18A to 18C, so that the fuel is supplied in series in the order of the fuel cells 18A, 18B, and 18C. The fuel electrode exhaust pipes 36 and 40 are connected in series. The fuel cells 18A to 18C are examples of a plurality of fuel cells in the present invention, and the fuel gas pipe 30 and the fuel electrode exhaust pipes 36 and 40 are examples of flow paths in the present invention.

  Further, one end of a fuel electrode exhaust pipe 44 is connected to the fuel cell 18C, and the other end of the fuel electrode exhaust pipe 44 is connected to the burner 14. The fuel electrode exhaust gas containing unreacted hydrogen gas, water, carbon monoxide, and carbon dioxide discharged from the fuel electrode of the fuel battery cell 18B is supplied to the burner 14 via the fuel electrode exhaust pipe 44. The oxidizing gas discharged from the air electrode of the fuel cell 18C is discharged out of the system through the air electrode exhaust pipe 46 having one end connected to the fuel cell 18C.

  The burner 14 mixes and burns the fuel electrode exhaust gas supplied from the fuel cell 18 </ b> C via the fuel electrode exhaust gas pipe 44 with air, and heats the reformer 12. Further, the exhaust gas generated by the combustion in the burner 14 is discharged out of the system through a burner exhaust pipe 48 having one end connected to the burner 14.

  The fuel cells 18 </ b> A to 18 </ b> C are electrically connected in parallel because the fuel electrodes are connected to each other via the electrical wiring 50 and the air electrodes are connected to each other via the electrical wiring 52. Has been. When power generation is performed in the fuel cells 18A to 18C, a current obtained by adding the currents flowing through the fuel cells 18A to 18C to the electrical wirings 50 and 52 (this current is the "multiple fuel cells in the present invention"). Current ”), and hereinafter referred to as an overall current. The electric wirings 50 and 52 are examples of the electric wiring in the present invention.

  The electrical wirings 50 and 52 are connected to the power conditioner 20, respectively, and the power conditioner 20 is electrically connected to the operation control unit 22. The power conditioner 20 can control the magnitude of the total current flowing through the electric wirings 50 and 52, and the magnitude of the total current flowing through the electric wirings 50 and 52 is controlled by the operation control unit 22 via the power conditioner 20. The The electric wirings 50 and 52 are connected to a power load (not shown) via a transformer (not shown), and the power (voltage / current) generated by the fuel cells 18A to 18C is converted from DC to AC or voltage conversion. It is supplied to the power load through the transformation process such as, and consumed.

  In addition, the power conditioner 20 and the operation control part 22 are an example of the control part in this invention with the fuel controller 16 demonstrated previously.

  Next, the operation of the first embodiment will be described. When the power of the fuel cell system 10A is turned on and the operation start of the fuel cell system 10A is instructed, the operation control unit 22 performs the fuel cell system operation control process shown in FIG.

  In step 200 of the fuel cell system operation control process, the operation control unit 22 detects the power consumption of the power load, and calculates the output power required for the fuel cell system 10A based on the detected power consumption. . In the next step 202, the operation control unit 22 calculates an output current (total current flowing through the electrical wirings 50 and 52) from the output power calculated in step 200. In the fuel cell system 10A, since the fuel cells 18A to 18C are electrically connected in parallel, the DC power voltage output from the fuel cell system 10A is constant, and the output current is obtained by dividing the output power by the output voltage. Is calculated.

  In the next step 204, the operation control unit 22, based on the output current calculated in step 202, the fuel supply amount and the air supply amount to the fuel cell 18 </ b> A located at the uppermost stream in the fuel gas flow direction, The amount of reforming water supplied to the reformer 12 is calculated.

  The amount of fuel supply is defined as F, where I is the total amount of electrons that can be reacted by the supplied fuel, and I is the amount of electrons generated by the current that reacts with the fuel. From the balance between durability and efficiency of the fuel cells 18A-18C, When the optimum value of F is assumed to be, for example, I / F = 80%, the output current can be substituted for I where I / F = 80%, and F can be calculated as the fuel supply amount. The fuel supply amount calculated by this calculation is obtained by substituting the output current (the sum of the currents flowing through the individual fuel cell units 18A to 18C) for I, so the fuel amount corresponding to the output current, that is, the individual fuel cell unit The fuel supply amount corresponds to the sum of the fuel consumption in the cells 18A to 18C. The air supply amount and the reforming water supply amount can be obtained from the calculated fuel supply amount.

  In the next step 206, the operation control unit 22 outputs to the power conditioner 20 a control signal for controlling the total current flowing through the electric wirings 50 and 52 to the output current calculated in step 202, and the most upstream fuel cell 18A. A control signal for controlling the fuel supply amount to the fuel supply amount calculated in step 204 is output to the fuel controller 16, and the air supply amount to the fuel cell 18 A is controlled to the air supply amount calculated in step 204. A signal is output to the blower 34, and a control signal for controlling the supply amount of reforming water to the reformer 12 to the reforming water supply amount calculated in step 204 is output to the pump 26.

  In the next step 208, the operation control unit 22 determines whether or not an instruction to end the operation of the fuel cell system 10A is given. If the determination is negative, the process returns to step 200, and steps 200 to 208 are repeated until the determination of step 208 is affirmed. When the end of the operation of the fuel cell system 10A is instructed, the determination in step 208 is affirmed and the fuel cell system operation control process is ended.

  As described above, in the fuel cell system 10A, since the three fuel cells 18A to 18C are electrically connected in parallel, the currents flowing through the individual fuel cells 18A to 18C are the individual fuel cells 18A to 18A. It will vary according to the performance of 18C. However, in the fuel cell system 10A, the total current flowing in the electric wirings 50 and 52 is controlled to a magnitude corresponding to the required output, so that the three fuel cells 18A to 18C as a whole have outputs (voltages) corresponding to the required output.・ Current can be obtained.

  Further, as the current flowing through the individual fuel cells 18A to 18C varies depending on the performance of the individual fuel cells 18A to 18C, the fuel consumption also varies for each individual fuel cell 18A to 18C. Become. However, in the fuel cell system 10A, fuel is supplied in series to the fuel cells 18A to 18C by the fuel gas pipe 30 and the fuel electrode exhaust pipes 36, 40, and the amount of fuel supplied to the most upstream fuel cell 18A is set. The fuel amount is controlled according to the total current. As a result, the amount of fuel supplied to the most upstream fuel cell 18A becomes the amount of fuel corresponding to the sum of the fuel consumption in each of the fuel cells 18A to 18C. Therefore, for each individual fuel cell 18A to 18C. Even if the fuel consumption varies, the fuel supply amount to the most downstream fuel battery cell 18C becomes too small relative to the fuel consumption in the fuel battery cell 18C, so that the durability decreases or becomes excessive. This can also prevent the efficiency from decreasing.

  The operation of the fuel cell system 10A according to the first embodiment will be further described. In the following description, as shown in FIG. 13, a fuel cell system 300 configured to supply fuel in parallel from the fuel controller 16 to the fuel cells 18A to 18C is used as a comparative example. In FIG. 13, the reformer 12, the burner 14, the operation control unit 22 and the like are not shown.

  In the fuel cell system 300 according to the comparative example, the fuel gas pipe 302 is branched into three on the downstream side of the fuel controller 16 and is connected to the fuel cells 18A to 18C, respectively, and is parallel to the fuel cells 18A to 18C. It is the structure where fuel is supplied to. In this case, the fuel controller 16 adjusts the total fuel supply amount to the fuel cells 18A to 18C, and the fuel supply amount to the individual fuel cells 18A to 18C is the pressure loss in the fuel cells 18A to 18C. It is distributed at a substantially constant rate (for example, equally divided). On the other hand, since the fuel cells 18A to 18C are electrically connected in parallel, the current flowing through the individual fuel cells 18A to 18C is determined according to the performance of the individual fuel cells 18A to 18C.

  In the fuel cell system 300 according to the comparative example, when the fuel consumption in the individual fuel cells 18A to 18C varies, the ratio between the fuel supply amount and the fuel consumption in the individual fuel cells 18A to 18C also varies. Occurs.

  Specifically, in the fuel cell system 300, although the total value (total current) of the current flowing through the fuel cells 18A to 18C and the total amount of fuel supplied to the fuel cells 18A to 18C can be controlled, the current and fuel The supply amount cannot be controlled for each of the individual fuel cells 18A to 18C. Here, for example, when the total value of the total current and the fuel supply amount is controlled so that I / F = 80%, if the situation satisfies F1: F2: F3 = I1: I2: I3, I1 / F1 = I2 / F2 = I3 / F3 = I / F = 80%, and the ratio between the fuel supply amount and the fuel consumption amount of the fuel cells 18A to 18C becomes a target value.

  However, if the current ratio of the fuel cells 18A to 18C deviates from the ratio of the fuel supply amount (F1: F2: F3 ≠ I1: I2: I3), any of I1 / F1, I2 / F2, and I3 / F3 If one or more of the fuel cells exceeds the target value I / F = 80%, the one or more fuel cells 18 having the I / F exceeding the threshold value may possibly be damaged due to oxidation of the fuel electrode or the like. . In addition, since the ratio of the fuel consumption to the fuel supply amount is always excessive in one or more fuel cells 18, there is a possibility that durability may be reduced.

  As an example, in the fuel cell system 300 according to the comparative example, the current ratio of the fuel cells 18A to 18C is I1: I2: I3 = 9: 8: 7, and the fuel is equally distributed to the fuel cells 18A to 18C. (That is, F1: F2: F3 = 1: 1: 1), and I / F = 80% is assumed to be ideal from the balance between durability and efficiency of the fuel cell. In the fuel cell system 300, when the ratio of the total current and the total amount of fuel supply is controlled to 80% under the above conditions, I1 / F1 = 90%, I2 / F2 = 80%, I3 / F3 = 70%, and the fuel consumption is excessive in the fuel cell 18A. Further, in order to suppress an excessive fuel consumption state and to make In / Fn ≦ 80% in all the fuel cells, it is necessary to set I / F = 71%, and the efficiency of the fuel cell system 300 as a whole Will lead to a significant drop in

  On the other hand, in the fuel cell system 10A according to the first embodiment, the ratio of the total current and the fuel supply amount (the fuel supply amount to the most upstream fuel cell 18A) under the above conditions is I / F = When controlled to 80%, the fuel cell 18A alone has I1 / F = 30%, the fuel cells 18A and 18B have (I1 + I2) / F = 57%, and the total of the fuel cells 18A-18Cn has (I1 + I2 + I3) / F = 80%, and there is no fuel cell in which the fuel consumption is excessive. In addition, since the total amount of the fuel cells 18A to 18C consumes 80% of the fuel supply amount, an ideal high efficiency can be obtained. This is universally true regardless of the number of fuel cells and the variation in current among the plurality of fuel cells.

  In addition, assuming that a case where the fuel cell 18A to 18C electrically connected in parallel has undergone a significant performance degradation due to damage or the like, the fuel cell in which a significant performance degradation has occurred. Almost no current flows through the cell 18, and the remaining fuel cell compensates for that amount. In the fuel cell system 300 according to the comparative example, the fuel is also supplied to the fuel cell 18 in which the performance is greatly deteriorated in the same manner as the other fuel cells 18 under the above-described assumption conditions. It is discharged in vain without being done. Further, in other normal fuel cells 18, the fuel supply amount does not increase even though it is necessary to increase the current up to the amount of the fuel cells 18 in which the significant performance degradation has occurred.

  In contrast, in the fuel cell system 10A according to the first embodiment, all the fuel is supplied to the most upstream fuel cell 18A, and the fuel supplied to the fuel cell 18A is supplied to the fuel cells 18B and 18C. Since the fuel cells are sequentially supplied, even if the fuel cells 18 in which no current flows are generated in the fuel cells 18A to 18C, the fuel not consumed in the fuel cells 18 is supplied to the subsequent fuel cells 18. Since the fuel cells 18 in the subsequent stage are effectively consumed, it is possible to prevent the fuel cells 18 in the subsequent stage from running out of fuel and the wasteful release of fuel.

  Next, another configuration of the fuel cell system according to the present invention will be described. FIG. 6 shows a fuel cell system 10B, and FIG. 7 shows a fuel cell system 10C. 6 and 7, illustration of the reformer 12, the burner 14, the operation control unit 22, and the like is omitted.

  In both the fuel cell system 10B shown in FIG. 6 and the fuel cell system 10C shown in FIG. 7, p (p ≧ 2) fuel cells 18 are electrically connected in parallel by electric wiring 60, and p fuels S (s ≧ 2) units in which the battery cells 18 are connected in parallel are electrically connected in series by the electric wiring 60. The basic concept of the fuel supply to the individual fuel cells 18 is the same as that of the fuel cell system 10A, and the fuel supply pipe 62 (or fuel) is connected to the p fuel cells electrically connected in parallel. The fuel is supplied in series by the supply pipe 64). However, between the s units electrically connected in series, fuel may be supplied in parallel by the fuel supply pipe 62 as in the fuel cell system 10B shown in FIG. Like the fuel cell system 10C shown in the figure, the fuel may be supplied in series by the fuel supply pipe 62, or the part to which the fuel is supplied in parallel and the part to be supplied in series can be mixed. is there.

As described above, current distribution (current variation or current gradient) can occur in the p fuel cells electrically connected in parallel. Therefore, supplying fuel in series improves efficiency and durability. Achieve both. On the other hand, the s number of units electrically connected in series have the same total current in all the units. Therefore, like the fuel cell system 10B shown in FIG. Even in the configuration of distributing (in the configuration of FIG. 6, it is preferable to provide an orifice in order to suppress fluctuations in the distribution ratio, and for example, it is preferably fixed to equal distribution, etc.), the ratio between the fuel supply amount and the fuel consumption amount varies. It is possible to use the fuel effectively. Of course, the fuel can be effectively used even in a configuration in which fuel is supplied in series to each of the s units as in the fuel cell system 10C shown in FIG.

  FIG. 6 is an example of the fuel cell system according to claim 2, and FIG. 7 is an example of the fuel cell system according to claim 3.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 8 shows a fuel cell system 10D according to the second embodiment. In FIG. 8, the reformer 12, the burner 14, the operation control unit 22, and the like are not shown. The fuel cell system 10D includes six fuel cells 18A to 18F. Fuel cell 18A-18F is arrange | positioned in the inside of the cell storage container 70 in order from one end part. In the fuel cells 18A to 18F, the three fuel cells 18A to 18C are electrically connected in parallel by the electric wiring 72 connected to the power conditioner 20, and the three fuel cells 18D to 18F are connected. 18F is electrically connected in parallel, and units of the fuel cells 18A to 18C and units of the fuel cells 18D to 18F are connected in series.

  The fuel cells 18A to 18F are supplied with fuel in parallel to the units of the fuel cells 18A to 18C and the units of the fuel cells 18D to 18F through the fuel supply pipe 74 having one end connected to the fuel controller 16. The The fuel supply pipe 74 supplies fuel in series in the order of the fuel cells 18A, 18B, and 18C (in the order from one end portion of the cell container 70 to the central portion) in the units of the fuel cells 18A to 18C. In the units of the fuel cells 18D to 18F, the fuel is serially connected in the order of the fuel cells 18F, 18E, and 18D (from the other end of the cell container 70 toward the center). Connected to be supplied.

  The operation of the second embodiment will be described. When fuel is supplied in series to the plurality of fuel cells 18, the amount of fuel supplied to the upstream fuel cells 18 is larger (richer) than the amount of fuel supplied to the downstream fuel cells 18. Accordingly, the performance of the upstream fuel cell 18 is higher than that of the downstream fuel cell 18, and a larger current flows. Since the fuel cells 18 electrically connected in parallel have the same voltage, the amount of heat generated is determined according to the current, and the upstream fuel cell 18 has a larger amount of heat than the downstream fuel cell 18 and has a higher temperature. Get higher.

  On the other hand, when a plurality of fuel cells 18 are arranged in the cell container 70 as in the second embodiment, generally, the arrangement position of the fuel cells 18 in the cell container 70 is the cell container 70. As the temperature approaches the side wall surface, the heat dissipation of the fuel cell 18 increases and the temperature tends to decrease. Conversely, as the distance from the side wall surface increases, the heat dissipation of the fuel cell 18 decreases and the temperature tends to increase. is there.

  As described above, the second embodiment utilizes the fact that the temperature of the fuel battery cell 18 varies depending on the position of the fuel battery cell 18 in the cell storage container 70, and the units of the fuel battery cells 18A to 18C. Is connected to the fuel supply pipe 74 so that the fuel is supplied in series in the order of the fuel cells 18A, 18B, 18C, that is, from the side wall surface of the cell container 70. In addition, for the units of the fuel cells 18D to 18F, the fuel supply pipe 74 is provided so that the fuel is supplied in series in the order of the fuel cells 18F, 18E, 18D, that is, from the side of the side wall of the cell container 70. Connected.

  With the above configuration, the fuel cells 18A and 18F arranged at positions where the temperature in the container 70 is lowered increase the amount of heat generated by increasing the fuel supply amount, while the temperature in the container 70 becomes higher. Since the calorific value is reduced by reducing the fuel supply amount for the arranged fuel battery cells 18C and 18D, the temperature distribution and current distribution of the fuel battery cells 18A to 18F in the cell container 70 may be leveled. The efficiency and durability of the fuel cell system 10D can be improved.

  Further, in the second embodiment, on the premise that the temperature of the fuel cell 18 is different depending on the distance between the arrangement position of the fuel cell 18 in the cell container 70 and the side wall surface of the cell container 70, Although the order of supplying the fuel to the fuel cells 18 has been determined, the present invention is not limited to this. For example, in the cell container 70, the temperature of a fuel cell having a small distance from the vicinity of the heat radiating surface or the surroundings of the air input path tends to be low, and the temperature of a fuel cell having a small distance from the burner 14 tends to be high. As described above, when the temperature distribution of the fuel cell 18 in the cell container 70 has a small correlation with the distance from the side wall surface, according to the actual temperature distribution of the fuel cell 18 in the cell container 70. Needless to say, the order of supplying the fuel to the fuel cells 18 may be determined.

  When a plurality of fuel cells 18 are prepared, the prepared plurality of fuel cells 18 often have variations in performance (current-voltage characteristic slopes: see FIGS. 1 to 3) due to manufacturing variations. . For this reason, in the second embodiment, in arranging the six fuel cells 18A to 18F in the cell storage container 70, instead of randomly arranging the fuel cells 18A to 18F, individual fuel cells 18A to 18F are arranged in advance. Each of the performances of the fuel cells 18A to 18F is measured, and the variation in the performance of the individual fuel cells 18A to 18F due to manufacturing variation or the like, the temperature distribution in the cell accommodation container 70, and the like. The change of the performance of the fuel cell 18 according to the arrangement position of the fuel cell 18 (see FIG. 3), and the fuel cell 18 according to the fuel supply sequence caused by the difference in the fuel supply amount to the individual fuel cells 18 Considering the change in performance comprehensively, in the operation state of the fuel cell system 10, the variation in the performance of the individual fuel cells is minimized, so that the inside of the cell container 70 of each fuel cell 18. Select location position, it may be selected to supply order of fuel to each fuel cell 18.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 9 shows a fuel cell system 10E according to the third embodiment. In FIG. 9, the reformer 12, the burner 14, the operation control unit 22, and the like are not shown. As described above, when fuel is supplied in series to the plurality of fuel cells 18, the upstream fuel cells 18 generate more heat and have a higher temperature than the downstream fuel cells 18.

  As shown in FIG. 9, the fuel cell system 10E according to the third embodiment reduces the temperature variation of the fuel cells 18 depending on the fuel supply order to the plurality of fuel cells 18. The electrode area of the upstream fuel cell 18A is made smaller than the electrode area of the fuel cells 18B and 18C, and the electrode area of the most downstream fuel cell 18C is made larger than the electrode area of the fuel cells 18A and 18B. .

  In general, the larger the electrode area of the fuel battery cell 18, the lower the current density with respect to the unit current amount, so that the internal resistance decreases. The internal resistance tends to increase due to increased density. For this reason, when fuel is supplied in series to the fuel cells 18 electrically connected in parallel, as described above, the electrode area of the downstream fuel cell 18 is increased, and the upstream fuel cell 18 is increased. Since the internal resistance of the downstream fuel cell 18 can be relatively decreased with respect to the upstream fuel cell 18, the current distribution of the fuel cells 18A to 18C can be reduced. In addition, the temperature distribution can be made uniform, and the efficiency and durability of the fuel cell system 10E can be improved.

The concept of calculating the electrode area necessary to make the current distribution and temperature distribution of the fuel cells 18A to 18C uniform will be described below. The internal resistance of the fuel cell 18 is expressed by the following equation (4).
ΔV = η + IR (4)
Where ΔV is the amount of voltage drop with respect to the open electromotive force, η is the polarization resistance of the fuel cell, R is the ohmic resistance of the fuel cell, and I is the current value. From the equation (4), the current flowing through the fuel cell is expressed by the following equation (5).
I = (ΔV−η) / R (5)
Both the polarization resistance η and the ohmic resistance R of the fuel cell change depending on the electrode area. The polarization resistance η also changes depending on the fuel concentration (fuel supply amount). Since the polarization resistance η decreases as the fuel concentration increases, assuming that fuel is supplied to the fuel cells 18A to 18C in the order shown in FIG. 9, η1 <η2 <η3.

On the other hand, since the fuel cells 18A to 18C are electrically connected in parallel, the voltage drop amounts ΔV of the fuel cells 18A to 18C are equal. Therefore, if the electrode areas of the fuel cells 18A to 18C are the same and the ohmic resistance R is equal, I1>I2> I3 and current distribution occurs. Therefore, the current distribution can be reduced by adjusting the electrode area of the fuel battery cell 18C to be larger while the electrode area of the fuel battery cell 18C is adjusted to be larger so that R1>R2> R3. Specifically, it is preferable to adjust the electrode area so as to satisfy the following expression (6), but the effect of reducing the current distribution and the temperature distribution can be obtained simply by approaching the expression (6).
(ΔV−η1) / R1 = (ΔV−η2) / R2 = (ΔV−η3) / R3 (6)

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 10 shows a fuel cell system 10E according to the fourth embodiment. In FIG. 10, the reformer 12, the burner 14, the operation control unit 22, and the like are not shown. Instead of the fuel cells 18 in the embodiments described so far, a plurality of fuel cell stacks 120 (see FIG. 10) in which a plurality of fuel cells 18 are stacked are prepared, and the plurality of fuel cell stacks 120 are electrically connected in parallel. In addition, when the fuel is supplied in series, the upstream fuel cell stack 120 in the fuel flow direction generates more heat and the temperature is higher than the downstream fuel cell stack 120.

  As shown in FIG. 10, the fuel cell system 10F according to the fourth embodiment reduces the temperature variation of the fuel cell stack 120 depending on the fuel supply sequence to the plurality of fuel cell stacks 120. The number of stacks of the fuel cells 18 in the upstream fuel cell stack 120A is made smaller than the number of stacks of the fuel cells 18 in the fuel cell stacks 120B and 120C, and the number of stacks of the fuel cells 18 in the most downstream fuel cell stack 120C is reduced. More than the number of stacked fuel cells 18 in the fuel cell stacks 120A and 120B.

  The voltage of the entire fuel cell stack 120 becomes higher as the number of stacked fuel cells 18 increases. For this reason, when supplying fuel in series to a plurality of fuel cell stacks 120 electrically connected in parallel, as described above, the number of stacked fuel cells 18 in the upstream fuel cell stack 120 is reduced, By increasing the number of stacked fuel cells 18 in the downstream fuel cell stack 120, the voltage of the downstream fuel cell stack 120 can be relatively increased with respect to the upstream fuel cell stack 120. Therefore, the current distribution and temperature distribution of the fuel cell stacks 120A to 120C can be made uniform, and the efficiency and durability of the fuel cell system 10F can be improved.

The concept of calculating the number of stacks of the fuel cells 18 necessary for making the current distribution and temperature distribution of the fuel cell stacks 120A to 120C uniform will be described below. The voltage of the entire fuel cell stack in which a plurality of fuel cells are stacked is expressed by the following equation (7).
V = N (V _OCV −η−IR) (7)
Where V is the voltage of the entire fuel cell stack in which a plurality of fuel cells are stacked, N is the number of stacked fuel cells, V _OCV is the open electromotive force per fuel cell, and η is 1 of the fuel cells. The polarization resistance per sheet, R is the ohmic resistance per sheet of fuel cells, and I is the current value. From the equation (7), the current of the fuel cell is expressed by the following equation (8).
I = (V _OCV −V / N−η) / R (8)

  The polarization resistance η varies depending on the fuel concentration. Since the polarization resistance η becomes smaller as the fuel becomes thicker, as shown in FIG. 10, if fuel is supplied in series to the fuel cell stacks 120A to 120C, η1 <η2 <η3. On the other hand, since the fuel cell stacks 120A to 120C are electrically connected in parallel, the voltage V has the same value as the fuel cell stacks 120A to 120C. Therefore, assuming that the number N of stacked fuel cells in the fuel cell stacks 120A to 120C is the same, the characteristics of the individual fuel cells are the same, and the ohmic resistance R is the same value, I1> I2> I3. As a result, a current distribution is generated, and a temperature distribution is also generated. Therefore, while reducing the number N1 of the fuel cell stacks 18 in the fuel cell stack 120A, the current distribution is adjusted by adjusting the number N3 of the fuel cell stacks 120C in a large amount so that N1 <N2 <N3. In addition, the temperature distribution can be reduced.

Specifically, it is preferable to adjust the number of stacks of fuel cells for each stack so as to satisfy the following equation (9). Is obtained.
V / N1 + η1 = V / N2 + η2 = V / N3 + η3 (9)
In the above equation (9), it is assumed that the characteristics of the individual fuel cells are the same and the ohmic resistance R is the same value. However, the characteristics of the fuel cells differ for each stack due to differences in temperature environment. If there is, the stacking number N of fuel cells for each stack may be adjusted so as to satisfy the following equation (10).
(V _OCV -V / N1-η1) / R1
= (V _OCV -V / N2-η2) / R2
= (V _OCV -V / N3 -η3) / R3 (10)

  In the second embodiment, the current distribution of the fuel cells 18A to 18C is changed according to the fuel supply sequence according to the temperature distribution of the fuel cells 18 according to the arrangement position in the cell container 70. In addition, the aspect of reducing the temperature distribution has been described. Moreover, 3rd Embodiment demonstrated the aspect which reduces the current distribution and temperature distribution of fuel cell 18A-18C by changing the electrode area of fuel cell 18A-18C according to the supply order of fuel. Furthermore, in the fourth embodiment, the current distribution and temperature distribution of the fuel cells 18A to 18C are reduced by changing the number of stacked fuel cells in the fuel cell stacks 120A to 120C in accordance with the fuel supply order. Explained. However, the present invention is not limited to the embodiment described above, and an embodiment using a combination of at least two of the three embodiments is also included in the scope of the right of the present invention.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 11 shows a fuel cell system 10G according to the fifth embodiment. In addition, illustration of the reformer 12, the burner 14, etc. is abbreviate | omitted in FIG. As shown in FIG. 11, the fuel cell system 10G includes two fuel cells 18A and 18B. The other end of the pipe 72 whose one end is connected to the fuel controller 16 is connected to the three-way valve 78. One ends of pipes 74 and 76 are connected to the three-way valve 78, the other end of the pipe 74 is connected to the fuel supply side of the fuel cell 18A, and the other end of the pipe 76 is the fuel supply side of the fuel cell 18B. It is connected to the. The three-way valve 78 is switched to a state a where the pipe 72 communicates with the pipe 74 or a state b where the pipe 72 communicates with the pipe 76. The three-way valve 78 is connected to the operation control unit 22, and the operation control unit 22 controls switching between the states a and b.

  One end of a pipe 82 is connected to the fuel discharge side of the fuel cell 18 </ b> A, the pipe 82 is branched into a pipe 84 and a pipe 86 on the way, and the other end of the pipe 84 is connected to a three-way valve 80. Yes. Further, one end of a pipe 92 is connected to the fuel discharge side of the fuel cell 18B, the pipe 92 is branched into a pipe 94 and a pipe 96 on the way, and the other end of the pipe 94 is connected to the three-way valve 80. Yes. One end of a fuel electrode exhaust pipe 44 is connected to the three-way valve 80. The three-way valve 80 is switched to a state “a” where the pipe 94 communicates with the fuel electrode exhaust pipe 44 or a state “b” where the pipe 84 communicates with the fuel electrode exhaust pipe 44. The three-way valve 80 is connected to the operation control unit 22, and the operation control unit 22 controls switching between the states a and b.

  The other end of the pipe 86 is connected to the three-way valve 88, the other end of the pipe 96 is connected to the three-way valve 88, and one end of the pipe 98 is connected to the three-way valve 88. The three-way valve 88 switches to a state a where the pipe 86 communicates with the pipe 98 or a state b where the pipe 96 communicates with the pipe 98. The three-way valve 88 is connected to the operation control unit 22, and the operation control unit 22 controls switching between the states a and b.

  The other end of the pipe 98 is connected to the three-way valve 90, and one ends of the pipes 110 and 112 are connected to the three-way valve 90. The other end of the pipe 110 is connected to the middle part of the pipe 74, and the other end of the pipe 112 is connected to the middle part of the pipe 76. The three-way valve 90 is switched to a state “a” where the pipe 98 communicates with the pipe 112 or a state “b” where the pipe 98 communicates with the pipe 110. The three-way valve 90 is connected to the operation control unit 22, and the operation control unit 22 controls switching between the states a and b.

  Further, a current sensor 114 is provided at a position where the current of the fuel battery cell 18A can be detected in the electrical wiring 50, 52 connecting the fuel battery cells 18A, 18B and the power conditioner 20, and the fuel battery cell. A current sensor 116 is provided at a position where the current of 18B can be detected. The current sensors 114 and 116 are connected to the operation control unit 22, and the currents of the fuel cells 18 </ b> A and 18 </ b> B detected by the current sensors 114 and 116 are input to the operation control unit 22.

  Further, temperature sensors 102 and 104 are provided in the fuel cells 18A and 18B. The temperature sensors 102 and 104 are connected to the operation control unit 22, and the temperatures of the fuel cells 18 </ b> A and 18 </ b> B detected by the temperature sensors 102 and 104 are input to the operation control unit 22. The temperature sensors 102 and 104 and the current sensors 114 and 116 are examples of the detection unit in the present invention.

  The operation control unit 22 performs a first operation state in which the three-way valves 78, 80, 88, 90 are respectively switched to the state a with respect to the three-way valves 78, 80, 88, 90, or the three-way valves 78, 80, 88, 90. Is controlled to switch to the second operating state that switches to state b.

  In the first operating state, after fuel is supplied from the fuel controller 16 to the fuel cell 18A, the fuel electrode exhaust gas from the fuel cell 18A is supplied to the fuel cell 18B, and the fuel electrode from the fuel cell 18B is supplied. Exhaust gas is discharged to the fuel electrode exhaust pipe 44. Further, in the second operating state, after fuel is supplied from the fuel controller 16 to the fuel cell 18B, the fuel electrode exhaust gas from the fuel cell 18B is supplied to the fuel cell 18A, and from the fuel cell 18A. The fuel electrode exhaust gas is discharged to the fuel electrode exhaust gas pipe 44.

  In the fifth embodiment, the pipes 72, 74, 76, 82, 84, 86, 92, 94, 98, 110, 112 and the three-way valves 78, 80, 88, 90 are flow paths according to claim 9. The operation control unit 22 is an example of a switching unit according to claim 9. In addition, as the fuel cells 18A and 18B in the fifth embodiment, a low temperature operation type fuel cell, for example, a solid polymer type or phosphoric acid type fuel cell is suitable.

  The operation of the fifth embodiment will be described. When the fuel cell system 10G is installed, the operation control unit 22 is instructed whether to operate in the first operation state or the second operation state. The operation state instruction at this time may be an operation state set in advance by default, or as described in the second embodiment, the fuel is first supplied to the fuel cells 18 disposed in a lower temperature environment. If the electrode areas of the fuel cells 18A and 18B are different from each other as described in the third embodiment, the fuel cell 18 having a larger electrode area can be selected later. The operating state in which fuel is supplied may be selected, or the performance of the fuel cells 18A and 18B is measured in advance, and the performance is higher (the absolute value of the slope of the current-voltage characteristic is smaller). In addition, an operation state in which fuel is supplied later may be selected, or an operation state may be selected by combining the above selection methods.

  When the installation of the fuel cell system 10G is completed, the fuel cell system 10G is turned on, and the operation start of the fuel cell system 10G is instructed, the operation control unit 22 performs the fuel cell system operation control process shown in FIG. Do.

  In the fuel cell system operation control process shown in FIG. 12, first, in step 210, the operation control unit 22 determines whether or not 1 is set in the switching flag. Note that the switching flag is stored in the nonvolatile memory of the operation control unit 22, and is set to 0 when the fuel cell system 10G is installed. If the determination in step 210 is negative, the process proceeds to step 200, and the processes in steps 200 to 206 are performed. Steps 200 to 206 are the same as the processing described in the first embodiment, and thus the description thereof is omitted.

  In the next step 216, the operation control unit 22 acquires the temperature and current of the fuel cells 18A and 18B of the fuel cell system 10G from the temperature sensors 102 and 104 and the current sensors 114 and 116, and acquires the acquired fuel cells 18A. , 18B, it is determined whether or not the order of supplying the fuel to the fuel cells 18A, 18B is switched.

  Specifically, for example, the above-described determination is performed when, for example, the temperature of the fuel cell 18 that is currently downstream in the fuel flow direction (currently the fuel cell 18 to which fuel is supplied later) is currently upstream. This can be done by determining whether the temperature is lower than a predetermined threshold value than the temperature of the fuel cell 18 on the side (the fuel cell 18 to which the fuel has been supplied first).

  Further, specifically, the determination is made, for example, when the current of the fuel cell 18 that is currently downstream in the fuel flow direction (currently the fuel cell 18 to which fuel is supplied later) is Can be performed by determining whether the current is lower than a predetermined threshold value or more than the current of the fuel cell 18 on the upstream side (the fuel cell 18 to which fuel has been supplied first).

  If the determination in step 216 is negative, the process proceeds to step 208. The determination in step 208 is negative until the end of the operation of the fuel cell system 10G is instructed, and the process returns to step 210. Therefore, the process of the operation control unit 22 while the determination in step 216 is negative is the same as that in the first embodiment.

  Further, a certain period has elapsed since the installation of the fuel cell system 10G. For example, the degree of deterioration with time of the fuel cell 18 during this period is greatly different between the fuel cell 18A and the fuel cell 18B. In such a case, the temperature of the fuel cell 18 that is currently downstream is lower than the temperature of the fuel cell 18 that is currently upstream, or is currently downstream. A state may occur in which the current of the fuel cell 18 being lower than the current of the fuel cell 18 currently on the upstream side is lower than the threshold value. Further, in the state where at least one of the temperature and the current is different by a threshold value or more as described above, there is a concern that the fuel cell 18 that is currently on the upstream side is deteriorated.

  For this reason, when at least one of the temperature and current of the fuel cell 18 currently on the downstream side is lower than the temperature of the fuel cell 18 currently on the upstream side by a threshold value or more, The determination at step 216 is affirmed and the routine proceeds to step 218. In step 218, the operation control unit 22 sets 1 to the switching flag, and proceeds to step 208.

  When the switching flag is set to 1 in step 218, the determination in step 210 is affirmed and the routine proceeds to step 212. In step 212, the operation control unit 22 switches to the second operation state if the current operation state is the first operation state, and changes to the first operation state if the current operation state is the second operation state. By switching, the fuel cell 18 that supplies the fuel first is replaced among the fuel cells 18A and 18B. Further, in the next step 214, the operation control unit 22 sets the switching flag to 0 and returns to step 210.

  By the above processing, when the degree of deterioration of the fuel cell 18 with time is greatly different between the fuel cell 18A and the fuel cell 18B, or the order of the performance of the fuel cells 18A, 18B is changed over time. Even in the case of a change to the fuel cell system, the difference in current and temperature of the fuel cells 18A and 18C can be reduced, and the deterioration of the efficiency and durability of the fuel cell system 10G over time can be suppressed.

  In the fifth embodiment, the case where there are two fuel cells 18 has been described. Needless to say, the present invention is also applicable to the fuel cell system 10 provided with a larger number of fuel cells 18. Moreover, although 5th Embodiment demonstrated the aspect which detects indirectly the absolute value of the inclination of the change of the output voltage with respect to the change of the output current of the fuel cell 18 by detecting the temperature of the fuel cell 18. However, the present invention is not limited to this, and a configuration that directly detects the absolute value of the slope of the change in the output voltage with respect to the change in the output current of the fuel battery cell 18 by detecting the output current of each fuel battery cell 18. It is also possible to adopt.

  Moreover, the fuel cell in each embodiment mentioned above is only an example of the fuel cell in this invention, it replaces with the fuel cell in each embodiment except 4th Embodiment, and the fuel cell which laminated | stacked multiple fuel cells. Needless to say, a stack may be used.

  Further, the fuel cell system described in each of the above-described embodiments is merely an example of the present invention. For example, in the above-described embodiment, the fuel cell system having the configuration in which the reformer and the burner are provided has been described. However, the reformer and the burner are not necessary if the fuel cell system is supplied with fuel from the outside. An example of a fuel cell system to which fuel is supplied from the outside is a fuel cell system mounted on a moving body such as a vehicle. Thus, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications and applications are possible without departing from the spirit of the present invention.

10A, 10B, 10C, 10D, 10E, 10F, 10G ... Fuel cell system, 16 ... Fuel controller (control unit), 18A, 18B, 18C, 18D, 18E, 18F ... Fuel cell (fuel cell), 20 ... Power conditioner (control part), 22 ... Operation control part (control part), 30 ... Fuel gas pipe (flow path), 36, 40 ... Fuel electrode exhaust pipe (flow path), 50, 52, 60, 72 ... Electricity Wiring, 62, 64, 74 ... fuel supply pipe (flow path), 72, 74, 76, 82, 84, 86, 92, 94, 98, 110, 112 ... piping (flow path), 78, 80, 88, 90 ... Three-way valve (flow path), 102, 104 ... Temperature sensor (detection unit)

Claims (11)

A plurality of fuel cells that generate electricity using the supplied fuel;
Electrical wiring connecting the plurality of fuel cells in parallel;
A flow path connecting the plurality of fuel cells in series so that fuel is supplied in series to the plurality of fuel cells;
The amount of fuel supplied to the most upstream fuel cell in the flow path among the plurality of fuel cells is controlled by controlling the current of the plurality of fuel cells flowing through the electrical wiring to a magnitude corresponding to a required output. A control unit that controls the amount of fuel in accordance with the current of the entire plurality of fuel cells;
Including fuel cell system.   A plurality of fuel cell groups including a plurality of fuel cells connected in parallel by the electrical wiring and supplied in series by the flow path, the plurality of fuel cell groups being electrically connected in series and in parallel The fuel cell system according to claim 1, wherein fuel is supplied.   A plurality of fuel cell groups including a plurality of fuel cells connected in parallel by the electrical wiring and supplied in series by the flow path, the plurality of fuel cell groups are electrically connected in series, and in series The fuel cell system according to claim 1, wherein fuel is supplied. A plurality of fuel cells that generate electricity using the supplied fuel;
Electrical wiring connecting the plurality of fuel cells in parallel;
Among the plurality of fuel cells, an order in which a fuel cell having a smaller absolute value of a change in output voltage with respect to a change in output current is located on the downstream side of the fuel flow direction than a fuel cell having a larger absolute value of the gradient. A flow path connecting the plurality of fuel cells in series so that the fuel is supplied in series at
Including fuel cell system.   The fuel cell system according to claim 4, wherein the fuel cell having a small absolute value of the slope is a fuel cell installed in an environment where the temperature is higher than that of the fuel cell having a large absolute value of the slope.   5. The fuel cell system according to claim 4, wherein the fuel cell having a small absolute value of the slope is a fuel cell having an electrode area larger than that of the fuel cell having a large absolute value of the slope.   5. The fuel cell system according to claim 4, wherein the fuel cell having a small absolute value of the slope is a fuel cell in which the number of stacked fuel cells is larger than that of the fuel cell having the large absolute value of the slope.   The amount of fuel supplied to the most upstream fuel cell in the flow path among the plurality of fuel cells is controlled by controlling the current of the plurality of fuel cells flowing through the electrical wiring to a magnitude corresponding to a required output. The fuel cell system according to any one of claims 4 to 7, further comprising a control unit configured to control the amount of fuel according to the current of the plurality of fuel cells as a whole. The flow path can be switched in order to connect the plurality of fuel cells in series,
A detector that detects at least one of a temperature and an output current of each of the plurality of fuel cells;
Based on at least one of the temperature and output current of each of the plurality of fuel cells detected by the detection unit, a fuel cell having a small absolute value of the slope of the change in output voltage relative to the change in output current is an absolute value of the slope. A switching unit that switches the order in which the plurality of fuel cells are connected in series so that the fuel cell is located downstream of the larger fuel cell in the fuel flow direction;
The fuel cell system according to any one of claims 1 to 8, further comprising: A plurality of fuel cells that generate electricity with the supplied fuel are connected in parallel by electric wiring,
Supplying fuel in series by flow paths to the plurality of fuel cells;
The amount of fuel supplied to the most upstream fuel cell in the flow path among the plurality of fuel cells is controlled by controlling the current of the plurality of fuel cells flowing through the electrical wiring to a magnitude corresponding to a required output. A method of operating a fuel cell system, comprising controlling the amount of fuel according to the current of the plurality of fuel cells as a whole. A plurality of fuel cells that generate electricity with the supplied fuel are connected in parallel by electric wiring,
Among the plurality of fuel cells, an order in which a fuel cell having a smaller absolute value of a change in output voltage with respect to a change in output current is located on the downstream side of the fuel flow direction than a fuel cell having a larger absolute value of the gradient. A method for configuring a fuel cell system, comprising: connecting the plurality of fuel cells in series by a flow path so that fuel is supplied in series.