JP2015220211A - Control device and control method of fuel cell - Google Patents

Abstract

A fuel cell control device and a fuel cell control method capable of suppressing control hunting and improving the durability of the fuel cell by performing suitable control. A plurality of deterioration stages set in advance based on the power value and current value of the output of the fuel cell stack are stored as deterioration stages indicating the degree of deterioration of the fuel cell stack. Next, a deterioration stage corresponding to the power value and current value of the fuel cell stack is determined based on the plurality of deterioration stages. Then, a control map corresponding to the determined deterioration stage is selected, and the fuel utilization rate is determined from the current value using the control map. [Selection] Figure 5

Description

  The present invention relates to a fuel cell control device and a fuel cell control method for controlling a fuel cell such as a solid oxide fuel cell.

2. Description of the Related Art Conventionally, for example, a solid oxide fuel cell using a solid electrolyte (solid oxide) is known as a fuel cell that generates power using, for example, fuel gas and air.
As this fuel cell, for example, a fuel cell stack in which a plurality of plate-like fuel cells each having a single cell having a fuel electrode and an air electrode on both sides of a solid electrolyte layer are stacked is used.

  In addition to the fuel cell stack, in the fuel cell, a reformer that reforms raw fuel such as city gas or kerosene into fuel gas, or a combustor that burns the remaining fuel gas and air that was not used for power generation. Etc. are used.

As one important control method for operating this type of fuel cell, a method by temperature adjustment is known (see Patent Document 1).
Specifically, in a low load region where the fuel cell itself generates little heat (due to Joule heat), the fuel utilization rate is set to a low value (that is, the fuel supply amount is increased and the ratio of the fuel supply amount necessary for power generation is increased). On the other hand, in the high load region where the heat generated by the fuel cell itself is large, the fuel utilization rate is set high (ie, the fuel supply amount is reduced and the fuel required for power generation is increased). By increasing the ratio of the supply amount to lower the combustion amount in the combustor) and increasing / decreasing the air flow rate each time, heat independence is achieved.

  That is, in the above-described conventional technology, for example, the heating effect by increasing the fuel supply amount and the cooling effect by increasing the air supply amount for power generation are used in combination to set the temperature in the fuel cell to a predetermined appropriate temperature. The fuel supply amount and the air supply amount are corrected so that the fuel utilization rate increases without causing the temperature within the fuel cell to converge to the range and the temperature within the fuel cell to be substantially out of the appropriate temperature range.

JP 2013-16356 A

  However, in the prior art, since there are so many variable parameters when performing the control as described above, the control is complicated, and so-called control hunting (for example, control parameters such as the fuel supply amount and the air supply amount undulate) There is a risk of causing the parameter to be frequently adjusted).

  When this control hunting occurs, for example, when the fuel supply amount is reduced, there is a possibility that a place where the fuel is locally depleted in the fuel battery cell may occur. When the is operated, there is a problem that the deterioration rate of the fuel cell, and hence the fuel cell, increases.

  In addition, when such complicated control is performed on a fuel cell with a large generated current, increasing the amount of air for temperature adjustment increases the power consumption of the air pump that sends air to the fuel cell. There is a risk that the amount of electric power to be generated (the amount of current drawn from the fuel cell) increases, and the deterioration of the fuel cell is promoted.

  Further, when the fuel cell is a flat type fuel cell stack, for example, when lowering the temperature of the fuel cell stack, if the air increase control and the fuel decrease control are performed simultaneously, the fuel electrode side and the air electrode side The pressure loss difference between the two may increase, which may cause accidental failures such as cell cracking.

That is, when conventional complicated control is performed, the durability of the fuel cell may be lowered, and as a result, there may be a problem that the power generation efficiency is also lowered.
The present invention has been made to solve the above-described problems, and an object of the present invention is to control a fuel cell capable of suppressing the control hunting and improving the durability of the fuel cell by performing a suitable control. And it is providing the control method of a fuel cell.

  (1) The present invention provides, as a first aspect (a control device for a fuel cell), the operation of the fuel cell that generates power using the fuel gas and the oxidant gas. In a fuel cell control device controlled based on an operating state, a plurality of deterioration stages set in advance based on a power value and a current value of the fuel cell are stored as deterioration stages indicating the degree of deterioration of the fuel cell. And determining the deterioration stage corresponding to the power value and current value of the fuel cell detected by the operating state detection means based on the plurality of deterioration stages stored in the storage means. Determination means for determining, based on the deterioration stage determined by the determination means, a determination means for determining a fuel utilization rate of the fuel cell corresponding to the deterioration stage; The flow rate of the fuel gas is calculated based on the fuel utilization rate determined by the determination means, and a predetermined amount of the fuel gas or raw fuel of the fuel gas is supplied to the fuel cell based on the calculated value. And a fuel supply control means for controlling to do so.

  In the first aspect, the storage means stores a plurality of deterioration stages set in advance based on the power value and current value of the fuel cell as the deterioration stage indicating the degree of deterioration of the fuel cell, and the determination means Then, based on the plurality of deterioration stages, the deterioration stage corresponding to the detected power value and current value of the fuel cell is determined. Then, the determining means determines the fuel usage rate of the fuel cell corresponding to the deterioration stage, and the fuel supply control means calculates the flow rate of the fuel gas based on the fuel usage rate, and based on the calculated value. Then, control is performed so that a predetermined amount of fuel gas or raw fuel is supplied to the fuel cell.

  That is, since the power value and current value of the fuel cell correspond to the degree of deterioration of the fuel cell, if the deterioration stage corresponding to the power value and current value is obtained in advance, the detected power value and current value are determined. Thus, the degree of deterioration (that is, the deterioration stage) is known. Furthermore, since the power generation state and heat generation state of the fuel cell are different depending on the deterioration stage, such as a small amount of Joule heat generated due to current increase in a state with little deterioration at the early stage of power generation, depending on the deterioration stage, By setting the fuel usage rate and adjusting the supply amount of the fuel gas or raw fuel according to the fuel usage rate, the power generation state and heat generation state of the fuel cell can be appropriately controlled.

  In particular, in the first aspect, when determining the fuel utilization rate, a specific deterioration stage is selected from a plurality of deterioration stages corresponding to the detected power value and current value. Control means is unnecessary, and therefore control hunting can be suppressed.

As a result, there is a low possibility that the fuel is locally depleted in the fuel cell, and there is a remarkable effect that the durability of the fuel cell can be greatly improved.
Moreover, in this 1st aspect, since the complicated control like the past is unnecessary, the power consumption of an air pump cannot increase easily. Therefore, since the amount of current drawn from the fuel cell is unlikely to increase, this also has the effect of improving the durability of the fuel cell.

  Further, for example, even when the fuel cell is a flat type fuel cell stack, the pressure loss difference between the fuel electrode side and the air electrode side when the temperature is lowered is not easily expanded, and thus a failure such as cell cracking occurs. There is an advantage that is difficult to occur.

  That is, in the first aspect, since it is not necessary to perform conventional complicated control, that is, since control hunting can be suppressed, there is an effect that durability of the fuel cell is improved, and as a result, power generation efficiency is also improved.

Here, the fuel utilization rate is a value obtained by dividing the amount of fuel (A) used for power generation in the fuel cell by the amount of fuel (B) supplied to the fuel cell (that is, the ratio of A to B). is there.
(2) In the present invention, as a second aspect, the storage unit stores each control map for obtaining the fuel utilization rate from the current value of the fuel cell corresponding to each of the plurality of deterioration stages, The determining means selects the control map corresponding to the deterioration stage determined by the determining means, and determines the fuel utilization rate from the current value of the fuel cell based on the control map.

  In the second aspect, the storage means stores a control map for determining the fuel utilization rate from the current value of the fuel cell (corresponding to each deterioration stage) (the value of the current flowing through the fuel cell). In the means, the fuel utilization rate can be determined from the current value of the fuel cell based on the control map.

  (3) As a third aspect of the present invention, each control map set in accordance with the degree of deterioration of the fuel cell indicates that the degree of deterioration of the fuel cell with respect to the same current value of the fuel cell. The fuel consumption rate is set so as to be selected as the degree of deterioration is larger than when the fuel is small.

  In the third mode, for example, in a state where there is little deterioration such as in the initial stage of power generation, a control map is prepared in which the fuel utilization rate with respect to the current value is generally low. In the state, a control map having a high fuel utilization rate with respect to the current value is prepared.

  In other words, when the fuel cell is deteriorated, a large heat generation due to Joule heat resulting from the deterioration can be used for heat maintenance. Therefore, by using a control map corresponding to the deterioration, the fuel utilization rate can be increased. it can. As a result, high power generation efficiency can be maintained even after deterioration starts in some places.

(4) The present invention, as a fourth aspect, is characterized in that the fuel cell has a parallel series structure for at least the fuel gas.
The fourth aspect exemplifies the structure of the gas flow path in the fuel cell.

Examples of the fuel cell having the parallel series structure of the fuel gas include a fuel cell stack in which a plurality of fuel cells as power generation units are stacked.
In a fuel cell stack having a parallel series structure, power generation units (fuel cell) constituting the fuel cell stack are electrically connected in series. A fuel cell stack in which power generation units are stacked while increasing the amount of fuel supplied to the power generation unit by dividing the fuel gas path supplied to the fuel cell stack into two, for example, an upstream portion and a downstream portion in parallel. Therefore, the fuel supply rate of each fuel cell can be lowered.

  As a result, the amount of fuel supplied to the fuel cell stack can be reduced even after the endurance deterioration (after deterioration after long-term use), so that the overall fuel utilization rate of the fuel cell stack can be increased. Therefore, the power generation efficiency can be kept high.

The parallel series structure is a structure in which, for example, fuel gas is first introduced into a certain power generation unit (fuel cell) to generate power, and then the exhaust gas is introduced into another power generation unit to generate power.
The total fuel utilization rate is not the fuel utilization rate of each fuel cell constituting the fuel cell stack, but the overall fuel utilization rate of the entire fuel cell stack.

  (5) As a fifth aspect of the present invention, the fuel cell combusts the reformer that reforms raw fuel into the fuel gas, and the fuel gas and the oxidant gas that are not used in the power generation. At least one of the combustors is provided.

The fifth aspect illustrates a fuel cell using an auxiliary device such as a reformer or a combustor.
A reformer means that when fuel gas is supplied to a fuel cell, the raw fuel such as raw fuel gas is reformed to a composition suitable for power generation (for example, city gas or the like is a composition having more hydrogen gas components). It is a device that reforms the gas.

  (6) The present invention provides, as a sixth aspect (a fuel cell control method), the operation of the fuel cell that generates power using the fuel gas and the oxidant gas. In the control method of the fuel cell controlled based on the operating state, a plurality of deterioration stages set in advance based on the power value and current value of the fuel cell are stored as the deterioration stage indicating the degree of deterioration of the fuel cell. In addition, based on the plurality of stored deterioration stages, the deterioration stage corresponding to the power value and the current value of the fuel cell detected by the operating state detection unit is determined, and the determination is made. Based on the deterioration stage, the fuel utilization rate of the fuel cell corresponding to the deterioration stage is determined.

The sixth aspect has the same operational effects as the first aspect.
(7) In the seventh aspect of the present invention, as a seventh aspect, each control map for obtaining the fuel utilization rate from the current value of the fuel cell is stored in correspondence with each of the plurality of deterioration stages, and the determination is made. The control map corresponding to the deterioration stage is selected, and the fuel utilization rate is determined from the current value of the fuel cell based on the control map.

The seventh aspect has the same effects as the second aspect.
Hereinafter, each configuration of the present invention will be described.
The fuel gas is a gas containing a reducing agent (for example, hydrogen) serving as a fuel used for power generation of a fuel cell, and examples thereof include a reformed gas obtained by reforming a raw fuel such as a raw fuel gas. As the raw fuel, various raw fuels that can generate hydrogen by reforming, such as natural gas (for example, LNG), city gas, LPG, kerosene, methanol, biomethanol, and the like can be employed.

The oxidant gas is a gas containing an oxidant (for example, oxygen) used for power generation of the fuel cell, and examples thereof include air.
Examples of the fuel cell include a solid oxide fuel cell (SOFC) using a ZrO ₂ ceramic as an electrolyte, a solid polymer fuel cell (PEFC) using a polymer electrolyte membrane as an electrolyte, and Li-Na / K. Examples thereof include a fuel cell such as a molten carbonate fuel cell (MCFC) using a system carbonate as an electrolyte and a phosphoric acid fuel cell (PAFC) using phosphoric acid as an electrolyte.

  Examples of the fuel cell include a fuel cell as a power generation unit and a fuel cell stack including a plurality of the fuel cells (for example, stacked fuel cells). In addition, as a fuel cell, the structure provided with the single cell which laminated | stacked the fuel electrode layer, the solid electrolyte layer, and the air electrode layer integrally, for example is employable.

It is explanatory drawing which shows the whole structure of the fuel cell system of an Example. (A) is a top view which shows a fuel cell stack, (b) is explanatory drawing which divides | segments the gas flow path of a fuel cell stack into fuel gas and oxidant gas, and shows from a side surface typically. It is explanatory drawing which shows the map for calculating | requiring a degradation stage from the electric power value and electric current value of a fuel cell stack. It is explanatory drawing which shows the map for calculating | requiring a fuel utilization factor from the electric current value of a fuel cell stack, respectively in the initial stage of a driving | operation of a fuel cell stack, a middle period, and a latter period. It is a flowchart which shows the control processing implemented with a controller.

  Next, as a mode for carrying out the fuel cell control device and the fuel cell control method of the present invention, a solid oxide fuel cell control device and a solid oxide fuel cell control method will be described as examples. To do.

a) First, the overall system configuration of the solid oxide fuel cell will be described. In the following, “solid oxide form” is omitted.
As shown in FIG. 1, the fuel cell system 1 in this embodiment includes a fuel gas (for example, a reformed gas obtained by reforming a raw fuel gas such as city gas: specifically, hydrogen therein) and an oxidant gas (for example, It is a power generation unit that generates power by receiving supply of air (specifically, oxygen in the air).

  In this fuel cell system 1, a fuel pump 5, a flow rate sensor 7, and a power generation module 15 are arranged along the supply flow path 3 of the raw fuel gas (and hence after reforming) from the upstream side. An air pump 13 is disposed in the supply channel 11, and a reforming water pump 43 is disposed in the reforming water supply channel 41.

  The power generation module 15 is disposed in a heat insulation container 17, and in the heat insulation container 17, a vaporizer 19, a reformer 21, a fuel cell stack (power generation stack) from the upstream side of the fuel gas supply channel 3. 23) A combustor 25 is arranged. In addition, a temperature sensor 27 is disposed in the fuel cell stack 23.

  In this embodiment, since the raw fuel gas (and hence the fuel gas) or air defines the upstream side and the downstream side based on the direction in which each pump 5 and 13 flows to the fuel cell stack 23, the pumps 5 and 13. The side is the upstream side, and the fuel cell stack 23 side is the downstream side.

  The fuel cell system 1 includes a controller 31 that controls the operation of the fuel cell system 1, and the controller 31 is connected to a power conditioner 33 that is an output converter.

  Here, the electric power generated in the fuel cell stack 23 is configured to be supplied to the power conditioner 33, and the electric circuit 35 reaching the power conditioner 33 (supplying electric power) from the fuel cell stack 23 is supplied to the electric circuit 35. A current sensor 37 for measuring a current (DC current) flowing through the electric circuit 35 is disposed.

Hereinafter, each configuration will be described in detail.
The fuel pump 5 is a pump that supplies raw fuel gas such as city gas to the power generation module 15 side.

  The flow rate sensor 7 is a flow meter that measures the flow rate of the raw fuel gas supplied to the power generation module 9 side by the fuel pump 5. Note that the flow rate of the fuel gas required for power generation is calculated by the controller 31, and a predetermined flow rate of the raw fuel gas is determined based on the calculation result.

The air pump 13 is a pump that supplies air, which is an oxidant gas, to the power generation module 15 side.
In the vaporizer 19, the reformed water supplied from the reformed water pump 43 is heated and vaporized to become steam, and the steam is supplied to the reformer 21. The vaporizer 19 can be used as a device that also serves as a known mixer, and the vaporizer 19 mixes raw fuel gas and water vapor.

  The reformer 21 is a device having a reforming catalyst (for example, ruthenium or nickel) inside, and the raw fuel gas introduced into the reformer 21 is steamed by the steam generated in the vaporizer 19. By reforming, a fuel gas having a higher hydrogen gas ratio (hydrogen-rich) than the raw fuel gas is generated.

As will be described later, the fuel cell stack 23 is a substantially rectangular parallelepiped device in which a plurality of plate-like fuel cells 24 (see FIG. 2B) as power generation units are stacked.
The combustor 25 is a device that mainly burns hydrogen (unreacted fuel gas) in the fuel gas discharged from the fuel cell stack 23 and oxygen in the air, and heats the fuel cell stack 23 by this combustion. can do.

The temperature sensor 27 is a sensor that is disposed on the surface (for example, a side surface) of the fuel cell stack 23 and detects the temperature of the surface.
The power conditioner 33 is an output converter that converts DC power generated by the fuel cell stack 23 into AC power and supplies the AC power to the load 39. In this power conditioner 33, in order to measure an alternating current power value, an alternating current value and an alternating voltage value can be measured.

  The output converter is not limited to the power conditioner 33 that converts the direct current output generated by the fuel cell stack 23 during power generation into an alternating current output, and converts the direct current output from the fuel cell stack 23 into a direct current output of a different voltage. It may be a DC-DC converter.

The current sensor 37 is an ammeter that measures a current (a direct current value) supplied from the fuel cell stack 23.
The controller 31 is an electronic control device provided with a known microcomputer. A signal indicating the flow rate of the fuel gas is input to the controller 31 from the flow sensor 7, a signal indicating the temperature of the fuel cell stack 23 is input from the temperature sensor 27, and the supply current of the fuel cell stack 23 is input from the current sensor 37. A signal indicating a current value is input.

  Further, as will be described later, the controller 31 indicates a current value (AC current value) and a voltage value (AC voltage value) of power supplied from the power conditioner 33 to the load 39 after being converted to AC power. A signal is input.

On the other hand, the controller 31 outputs a control signal for controlling the operations of the fuel pump 5, the air pump 13, and the power conditioner 33.
Further, the controller 31 is connected with a fuel pump 5 for supplying fuel gas to the fuel cell stack 23, an air pump 13 for supplying air, and an air-fuel mixture pump (not shown) for supplying fuel mixture to the start burner. These operations are controlled by a control signal from the controller 31.

  Further, as described above, the controller 31 receives the current value (A1) (direct current at the output of the fuel cell stack 23) from the current sensor 37, and the power conditioner 33 receives the AC current value (A2). An AC voltage value (V2) is input.

The controller 31 is a control device for the fuel cell system of the present invention, and functions as a storage unit, a determination unit, a determination unit, and a fuel supply control unit of the present invention.
b) Next, the configuration of the fuel cell stack 23 will be briefly described.

  As shown in FIG. 2A, the fuel cell stack 23 is a rectangular parallelepiped device in which plate-like fuel cells 24 are stacked (for example, nine stages in the vertical direction in FIG. 2B). The tenth first to tenth bolts 41a to 41j (and the respective nuts 43) penetrating the stack 23 in the stacking direction are integrally fixed.

  Further, the fuel cell 24 is a so-called fuel electrode support membrane type fuel cell 24. Although not shown, the fuel cell 24 is formed of a well-known fuel electrode (disposed so as to be in contact with the fuel flow path) and (for example, made of zirconia). ) A solid electrolyte body and an air electrode (arranged so as to be in contact with the air flow path).

As shown in FIG. 2B, the fuel cell stack 23 has a parallel series structure in the flow path of the fuel gas.
Specifically, the fuel gas introduced from the outside of the stack into the through hole 45h of the eighth bolt 41h is introduced into the fuel flow path of the fifth to ninth fuel cells 24e to 24i, and the through hole of the third bolt 41c. It is configured to be introduced into the fuel flow path of the first to fourth fuel cells 24a to 24d via 45c and discharged out of the stack via the through hole 45b of the second bolt 41b.

  On the other hand, the air introduced from the outside of the stack into the through hole 45j of the tenth bolt 41j is introduced into the air flow path of each of the fuel cells 24a to 24i and discharged out of the stack through the through hole 45e of the fifth bolt 41e. It is configured to be.

c) Next, the principle of controlling the fuel cell system 1 will be described.
-According to research by the present inventors, it has been found that there is a correlation between the degree of deterioration of the fuel cell stack 23 and the output (ie, power value and current value) of the fuel cell stack 23. Specifically, it is known that there is a relationship as shown in FIG. 3 between the degree of deterioration and the power value and current value. The map shown in FIG. 3 is stored in the memory of the controller 31.

  In addition, the degree of deterioration usually correlates with the operation time of the fuel cell stack 23, and it is known that the deterioration proceeds as the operation time becomes longer. It is. However, although the deterioration tends to increase as the operation time becomes longer, it varies depending on the operation state. Therefore, it is considered preferable to judge the degree of deterioration based on the power value and the current value rather than the operation time.

  Specifically, when the operating conditions are constant, as shown in FIG. 3, there is a characteristic that the power value that can be generated is large but the current value is small in the initial stage of operation. The power value and the current value that can be generated in this way have a characteristic that they are almost medium, and the latter part of the operation has a characteristic that the power value that can be generated is smaller but the current value is larger than that in the middle period.

  For example, as shown in the following Table 1, the relationship between the generated power (power value) corresponding to the degree of deterioration and the current value shows the initial value (5000 hours or less from the start of power generation) even if the current value is the same generated power. And the middle period (above 5000 hours from the start of power generation and less than 40000 hours) and the latter period (above 40000 hours from the start of power generation and less than or equal to 90000 hours), there is a tendency to increase from the initial period to the middle period and later.

従って、このような特徴から、電力値と電流値とに基づいて、現在、燃料電池スタック２３がどの程度劣化しているかを判断することができる。

Therefore, based on such characteristics, it is possible to determine how much the fuel cell stack 23 is currently deteriorated based on the power value and the current value.

  In the present embodiment, as the deterioration stage indicating the degree of deterioration, three types of deterioration stages are set in the initial stage, the middle period, and the latter stage (the degree of sequential deterioration is large) according to the degree of the deterioration degree. Two or more kinds of deterioration stages may be set. However, if too many deterioration stages are set, the control becomes complicated. For example, 10 or less types are preferable.

  Further, as described above, since the power value that can be generated varies depending on the degree of deterioration, an upper limit value of the output power of the power conditioner 33 is provided for each deterioration stage, and the controller 31 sets the power conditioner 33 to the upper limit value. Control not to exceed.

  In addition, in this embodiment, in order to control the supply amount of fuel gas, as shown in FIG. 4, three types of control maps, an initial map, a medium-term map, and a late-term map, are stored. The fuel cell (ie, the fuel cell stack 23) shown in FIG. 3 is used by switching according to the deterioration stage indicating the degree of deterioration. The control map shown in FIG. 4 is stored in the memory of the controller 31.

  For example, as shown in the following Table 2, the relationship between the current value according to the degree of deterioration and the fuel utilization rate shows that the control map is different between the initial stage, the middle stage, and the latter stage even when the current value is the same. The fuel utilization rate is set so as to increase in the middle and later stages from the initial stage.

具体的には、本実施例では、図４に示すように、初期の劣化ステージにおける電流値と燃料利用率との関係を示す初期マップと、中期の劣化ステージにおける電流値と燃料利用率との関係を示す中期マップと、後期の劣化ステージにおける電流値と燃料利用率との関係を示す後期マップとの３種類の制御マップが設定されている。

Specifically, in the present embodiment, as shown in FIG. 4, an initial map showing the relationship between the current value and the fuel utilization rate in the initial deterioration stage, and the current value and the fuel utilization rate in the medium deterioration stage. Three types of control maps are set: a medium-term map that shows the relationship, and a late-time map that shows the relationship between the current value and the fuel utilization rate in the later-stage deterioration stage.

  Therefore, in this embodiment, based on the relationship (map) shown in FIG. 3, the current degree of deterioration (deterioration stage) is determined from the power value and current value, and the degree of deterioration obtained from the determination result is determined. Accordingly, each control map shown in FIG. 4 is selected, and the fuel utilization rate is determined from the current value using each control map.

  Specifically, the initial map is a map in which the fuel utilization rate increases as the current value increases, but the increase rate of the fuel utilization rate is set to be smaller than that of the other control maps. This is because the degree of deterioration is small in 5000 hours or less (so-called initial stage) from the start of operation, and therefore, the amount of Joule heat generated due to power generation (due to deterioration or the like) is small even under the same operation conditions.

  Therefore, in this case, by reducing the fuel utilization rate, the ratio of the fuel supply amount necessary for power generation is reduced, and the combustion amount in the combustor 25 is increased. As a result, the operating temperature of the fuel cell stack 23 can be maintained at a predetermined operating temperature.

  The medium-term map is a map in which the fuel utilization rate increases as the current value increases. The increase rate of the fuel utilization rate is set larger than the initial map (described later) and smaller than the later map. Yes. This is because the degree of deterioration is moderate (compared to the initial and later stages) at 40,000 hours or less (so-called mid-stage) from the start of operation. Therefore, even under the same operating conditions, joules accompanying power generation (due to deterioration, etc.) This is because the amount of heat generated is also moderate.

  Therefore, in this case, by setting the fuel utilization rate to a medium level, the ratio of the fuel supply amount necessary for power generation is set to a medium level, and the combustion amount in the combustor 25 is set to a medium level. As a result, the operating temperature of the fuel cell stack 23 can be maintained at a predetermined operating temperature.

  Further, the late map is a map in which the fuel utilization rate increases as the current value increases, but the increase rate of the fuel utilization rate is set larger than that of the other control maps. This is because the degree of deterioration is large at 90000 hours or less (so-called late stage) from the start of operation, and therefore, the amount of Joule heat generated due to power generation (due to deterioration or the like) is large even under the same operation conditions.

  Therefore, in this case, by increasing the fuel utilization rate, the ratio of the fuel supply amount necessary for power generation is increased, and the combustion amount in the combustor 25 is decreased. As a result, the operating temperature of the fuel cell stack 23 can be maintained at a predetermined operating temperature.

  The maps in FIGS. 3 and 4 can be obtained in advance by experiments or the like, but the current value and voltage value (power value) used for the setting are such as those of sensors that actually measure those values. Set using output.

  That is, for example, when each map is set using the output (current value or power value) for the load 39, the deterioration stage is determined and the fuel utilization rate is actually determined using the output for the load 39. .

d) Next, the procedure of the control process performed by the controller 31 will be described.
As shown in FIG. 5, in step (indicated by S in FIG. 5) 100, the current value (DC current) of the output of the fuel cell stack 23 is obtained based on the signal from the current sensor 37.

Further, the voltage value (AC voltage) and current value (AC current) of the output to the load 39 are obtained from the power conditioner 33.
Here, the power value can be calculated from the voltage value and the current value. For example, the power value (W1) can be calculated from the DC current value (A1) and the voltage value (V2) (average of AC). Alternatively, the power value (W2) can be calculated from the current value (A2) (AC averaged) and the voltage value (V2) (AC averaged).

In addition, what current value and electric power value should be used should just employ | adopt the value used when each map of FIG. 3, FIG. 4 was set as mentioned above.
In the subsequent step 110, the degree of deterioration (deterioration stage) is determined from the power value and current value obtained in step 100 using the map shown in FIG.

  If the deterioration stage indicates the initial stage of operation, the process proceeds to step 120. If the deterioration stage indicates the middle period of operation, the process proceeds to step 130. If the deterioration stage indicates the latter period, the process proceeds to step 140.

In step 120, since it is the initial stage of operation, the fuel utilization rate is obtained from the current value using the initial map of FIG.
In step 130, since the operation is in the middle period, the fuel utilization rate is obtained from the current value using the medium-term map in FIG. 4B.

Further, in step 140, since it is the latter period of operation, the fuel utilization rate is obtained from the current value using the latter period map of FIG.
In subsequent step 150, a fuel supply amount (specifically, a raw fuel supply amount that is a supply amount of raw fuel gas) is calculated from the fuel utilization rate obtained in each step in accordance with the operating state.

  Specifically, for example, between a direct current value Ia [A] generated from the fuel cell stack 23 and a fuel flow rate (fuel gas flow rate) Qa [mol / sec] supplied to the fuel cell stack 23, In general, the following equation (1) holds.

Ia = nFQa (1)
(N: number of electrons contributing to the reaction, F: Faraday constant [C / mol])
From this equation (1), the fuel flow rate Qa required to generate the desired current Ia is calculated.

  The fuel supply amount (fuel gas supply amount) Qb supplied to generate power while maintaining the heat self-sustained by the fuel cell stack 23 is expressed by the following equation (2) using the fuel utilization rate Uf [%]. It can be calculated.

Qb = 100 × Qa / Uf (2)
The raw fuel supply amount Q [L / min] can be calculated by the following equation (3) using the Qb.
Q = M × Qb (3)
In the above formula (3), M is a constant determined by the raw fuel type.

That is, the raw fuel supply amount Q [L / min] is calculated by the equations (1), (2), and (3).
In the following step 160, the operation of the fuel pump 5 is controlled so as to supply the fuel supply amount calculated in step 150 (that is, the raw fuel supply amount Q), and this processing is temporarily ended.

e) Next, the effect of the present embodiment will be described.
In the present embodiment, a plurality of deterioration stages set in advance based on the power value and current value of the fuel cell stack 23 are stored as deterioration stages indicating the degree of deterioration of the fuel cell stack 23. Based on the deterioration stage, a deterioration stage corresponding to the (detected) power value and current value of the fuel cell stack 23 is determined. Then, the fuel usage rate of the fuel cell stack 23 is determined using each control map corresponding to the deterioration stage, the flow rate of the raw fuel gas is calculated based on the fuel usage rate, and based on the calculated value. , A predetermined amount of raw fuel gas (and thus a reformed fuel gas) is supplied to the fuel cell stack 23.

  That is, in this embodiment, when setting the fuel utilization rate, a specific deterioration stage is selected from a plurality of deterioration stages corresponding to the detected power value and current value, and each control corresponding to the deterioration stage is selected. Since the map is used, complicated control means as in the prior art is unnecessary, and therefore control hunting can be suppressed.

As a result, the possibility that the fuel is locally depleted in the fuel cell 24 is reduced, and the durability of the fuel cell stack 23 can be greatly improved.
Further, since complicated control as in the prior art is unnecessary, the power consumption of the air pump 13 is unlikely to increase. Therefore, since the amount of current flowing through the fuel cell stack 23 is difficult to increase, the durability of the fuel cell stack 23 is also improved from this point.

  Further, even when the fuel cell 24 is a flat type fuel cell stack 23, the pressure loss difference between the fuel electrode side and the air electrode side when the temperature is lowered is difficult to increase, and therefore, a failure such as cell cracking occurs. There is an advantage that is difficult to occur.

  That is, in this embodiment, since it is not necessary to perform conventional complicated control, that is, since control hunting can be suppressed, the durability of the fuel cell stack 23 is improved, and as a result, the power generation efficiency is also improved. .

  Further, in this embodiment, in a state where there is little deterioration at the initial stage of power generation, a control map with a low fuel utilization rate with respect to the current value is prepared. In the state, a control map having a high fuel utilization rate with respect to the current value is prepared.

  That is, when the fuel cell stack 23 is deteriorated, a large heat generation due to Joule heat resulting from the deterioration can be used for heat maintenance. Therefore, by using the control map corresponding to the deterioration described above, the fuel utilization rate is increased. can do. As a result, high power generation efficiency can be maintained even after deterioration starts in some places.

  Furthermore, in this embodiment, the fuel cell stack 23 has a parallel series structure for the fuel gas. In the parallel-series structure, the fuel gas path supplied to the fuel cell stack 23 is divided into, for example, an upstream part and a downstream part in parallel, so that the fuel supply amount to each fuel cell 24 is increased and the fuel cell is increased. Since the amount of fuel supplied to the stack 23 can be reduced, the fuel utilization rate of each fuel cell 24 can be lowered.

  As a result, the amount of fuel supplied to the fuel cell stack 23 can be reduced even after endurance deterioration (after being used and deteriorated for a long time), so that the total fuel utilization rate of the fuel cell stack 23 can be increased, Ultimately, the power generation efficiency can be kept high.

Needless to say, the present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the scope of the present invention.
(1) For example, as a fuel cell, a solid oxide fuel cell (SOFC), a polymer electrolyte fuel cell (PEFC), a molten carbonate fuel cell (MCFC), a phosphoric acid fuel cell (PAFC), etc. A fuel cell is mentioned.

  (2) As the current value and power value (voltage value used for calculating the power value) used for determining the deterioration stage and determining the fuel usage rate, the output (DC current, DC voltage) of the fuel cell stack is used as the power conditioner. Alternatively, it may be obtained using an ammeter or a voltmeter provided separately, or an output (AC current, AC voltage) obtained from a power conditioner may be used.

(3) Although the reformer and the combustor are used in the above embodiment, the present invention can be applied to a fuel cell system without a reformer or a combustor.
(4) It should be noted that the present invention does not use, for example, a vaporizer or a reformer (that is, does not generate a fuel gas such as hydrogen by reforming the raw fuel gas). The present invention can be applied to an apparatus that uses a fuel gas such as hydrogen and supplies the fuel gas to a fuel cell stack by a pump or the like.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 5 ... Fuel pump 13 ... Air pump 17 ... Power generation module 21 ... Reformer 23 ... Fuel cell stack 25 ... Combustor 27 ... Temperature sensor 31 ... Controller 33 ... Power conditioner 37 ... Current sensor

Claims (7)

In a fuel cell control device that controls the operation of a fuel cell that generates power using fuel gas and an oxidant gas based on the operating state of the fuel cell detected by the operating state detection means,
Storage means for storing a plurality of deterioration stages set in advance based on the power value and current value of the fuel cell as a deterioration stage indicating the degree of deterioration of the fuel cell;
Determination means for determining the deterioration stage corresponding to the power value and current value of the fuel cell detected by the operating state detection means based on the plurality of deterioration stages stored in the storage means;
Determining means for determining a fuel utilization rate of the fuel cell corresponding to the deterioration stage based on the deterioration stage determined by the determining means;
The flow rate of the fuel gas is calculated based on the fuel utilization rate determined by the determining means, and a predetermined amount of the fuel gas or the raw fuel of the fuel gas is supplied to the fuel cell based on the calculated value. Fuel supply control means for controlling so as to
A fuel cell control device comprising: The storage means stores each control map for obtaining the fuel utilization rate from the current value of the fuel cell, corresponding to each of the plurality of deterioration stages,
The determining means selects the control map corresponding to the deterioration stage determined by the determining means, and determines the fuel utilization rate from the current value of the fuel cell based on the control map. The fuel cell control device according to claim 1.   Each control map set according to the degree of deterioration of the fuel cell shows that the degree of deterioration is larger than the case where the degree of deterioration of the fuel cell is small with respect to the same current value of the fuel cell. The fuel cell control device according to claim 2, wherein the fuel cell utilization rate is set to be selected.   The said fuel cell is provided with the parallel series structure about the said fuel gas at least, The control apparatus of the fuel cell of any one of Claims 1-3 characterized by the above-mentioned.   The fuel cell includes at least one of a reformer that reforms raw fuel into the fuel gas and a combustor that burns the fuel gas and the oxidant gas that have not been used in the power generation. The fuel cell control device according to claim 1, wherein the control device is a fuel cell control device. In a fuel cell control method for controlling the operation of a fuel cell that generates power using a fuel gas and an oxidant gas based on the operating state of the fuel cell detected by the operating state detecting means,
As the deterioration stage indicating the degree of deterioration of the fuel cell, a plurality of deterioration stages set in advance based on the power value and current value of the fuel cell are stored,
Based on the plurality of stored deterioration stages, determine the deterioration stage corresponding to the power value and current value of the fuel cell detected by the operating state detection means,
A fuel cell control method, comprising: determining a fuel utilization rate of the fuel cell corresponding to the deterioration stage based on the determined deterioration stage. Corresponding to each of the plurality of deterioration stages, each control map for obtaining the fuel utilization rate from the current value of the fuel cell is stored,
7. The fuel cell according to claim 6, wherein the control map corresponding to the determined deterioration stage is selected, and the fuel utilization rate is determined from the current value of the fuel cell based on the control map. Control method.

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