JP6901231B2 - Fuel cell control device and fuel cell control method - Google Patents

Description

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

Conventionally, as a fuel cell that generates electricity using, for example, fuel gas and air, a solid oxide fuel cell using, for example, a solid electrolyte (solid oxide) has been known.
As the fuel cell, for example, a fuel cell stack in which a plurality of plate-shaped fuel cell cells 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 fuel cells, in addition to the fuel cell stack, a reformer that reforms raw fuel such as city gas and kerosene into fuel gas, and a combustor that burns residual fuel gas and air that have not been 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 the low load region where the fuel cell itself generates less heat (due to Joule heat), the fuel utilization rate is set low (that is, the fuel supply amount is increased and the ratio of the fuel supply amount required for power generation is increased. Decrease to increase the amount of fuel burned in the combustor), while setting the fuel utilization rate high (ie, reduce the fuel supply and fuel required for power generation) in the high load region where the fuel cell itself generates a lot of heat. By increasing the ratio of the supply amount to reduce the amount of fuel burned in the combustor) and increasing or decreasing the air flow rate each time, heat independence is achieved.

That is, in the above-mentioned conventional technique, 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 inside the fuel cell to a predetermined appropriate temperature. The fuel supply amount and the air supply amount are corrected so as to converge to the range and to increase the fuel utilization rate without the temperature inside the fuel cell deviating from the appropriate temperature range.

Japanese Unexamined Patent Publication No. 2013-16356

However, in the above-mentioned prior art, since there are a large number of fluctuation parameters when performing the above-mentioned control, the control becomes complicated, and so-called control hunting (for example, control parameters such as fuel supply amount and air supply amount are wavy, so control is performed. There was a risk of causing a condition in which the parameters had to be adjusted frequently).

When this control hunting occurs, for example, when the fuel supply amount is reduced, there may be a place where the fuel is locally depleted in the fuel cell, and the fuel cell is in such a state for a long period of time. There is a problem that the deterioration rate of the fuel cell, and eventually the fuel cell, increases when the fuel cell is operated.

In addition, when such complicated control is performed on a fuel cell with a large power generation current, if the amount of air is increased for temperature adjustment, the power consumption of the air pump that sends air to the fuel cell increases, and as a result, the fuel cell is used instead. The amount of power generated (the amount of current drawn from the fuel cell) increases, which may accelerate the deterioration of the fuel cell.

Further, when the fuel cell is a flat plate type fuel cell stack, for example, when the temperature of the fuel cell stack is lowered, if the air increase control and the fuel decrease control are performed at the same time, the fuel electrode side and the air electrode side are displayed. There is a risk that the pressure loss difference between the two will increase, causing accidental failures such as cell cracking.

That is, when the 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-mentioned problems, and an object of the present invention is a fuel cell control device capable of suppressing control hunting and improving the durability of the fuel cell by performing appropriate control. And to provide a method of controlling a fuel cell.

(1) In the first aspect (fuel cell control device) of the present invention, the operation of a fuel cell that generates power using a fuel gas and an oxidizing agent gas is detected by the operating state detecting means of the fuel cell. In a fuel cell control device controlled based on an operating state, a plurality of 10 or less types of deterioration stages set in advance based on the power value and current value of the fuel cell as deterioration stages indicating the degree of deterioration of the fuel cell. The storage means for storing the deterioration stage and the power value and the current value of the fuel cell detected by the operating state detecting means based on the plurality of deterioration stages stored in the storage means. The determination means for determining the deterioration stage, the determination means for determining the fuel utilization rate of the fuel cell corresponding to the deterioration stage based on the deterioration stage determined by the determination means, and the determination means determined by the determination means. A fuel supply that calculates the flow rate of the fuel gas based on the fuel utilization rate, and controls to supply a predetermined amount of the fuel gas or the raw material of the fuel gas to the fuel cell based on the calculated value. It is characterized by being provided with a control means.

In the first aspect, a plurality of 10 or less deterioration stages set in advance based on the power value and the current value of the fuel cell are stored in the storage means as the deterioration stages indicating the degree of deterioration of the fuel cell. Therefore, the determination means determines the deterioration stage corresponding to the detected electric power value and current value of the fuel cell based on the plurality of deterioration stages. Then, the determination means determines the fuel utilization 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 utilization rate, and based on the calculated value. Then, a predetermined amount of fuel gas or raw fuel is controlled to be supplied to the fuel cell.

That is, since the power value and the 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 the current value is obtained in advance, the detected power value and the current value are obtained. The degree of deterioration (that is, the deterioration stage) can be known from. Furthermore, the power generation state and heat generation state of the fuel cell differ depending on the deterioration stage, for example, the amount of Joule heat generated due to the increase in current is small in a state with little deterioration such as the initial stage of power generation. By setting the fuel utilization rate and adjusting the supply amount of fuel gas or raw fuel according to the fuel utilization rate, it is possible to appropriately control the power generation state and the heat generation state of the fuel cell.

In particular, in the first aspect, when determining the fuel utilization rate, a specific deterioration stage is selected from a plurality of deterioration stages of 10 types or less according to the detected power value and current value. Such a complicated control means is unnecessary, and therefore control hunting can be suppressed.

As a result, the possibility of locally depleting the fuel in the fuel cell is reduced, and the durability of the fuel cell can be greatly improved, which is a remarkable effect.
Further, in the first aspect, since the complicated control as in the conventional case is not required, the power consumption of the air pump is unlikely to increase. Therefore, the amount of current drawn from the fuel cell is unlikely to increase, and this also has the effect of improving the durability of the fuel cell.

Further, for example, even when the fuel cell is a flat fuel cell stack, the pressure loss difference between the fuel electrode side and the air electrode side when the temperature is lowered is unlikely to increase, and thus a failure such as cell cracking occurs. Has the advantage of being less likely to occur.

That is, in the first aspect, since it is not necessary to perform the conventional complicated control, that is, the control hunting can be suppressed, the durability of the fuel cell is improved, and as a result, the 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 second aspect of the present invention, 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 is characterized in that the control map corresponding to the deterioration stage determined by the determining means is selected, and the fuel utilization rate is determined 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 obtaining the fuel utilization rate from the current value of the fuel cell (the value of the current flowing through the fuel cell) (corresponding to each deterioration stage). In the means, the fuel utilization rate can be determined from the current value of the fuel cell based on the control map.

(3) In the third aspect of the present invention, each control map set according to the degree of deterioration of the fuel cell has the degree of deterioration of the fuel cell with respect to the same current value of the fuel cell. It is characterized in that the higher the degree of deterioration is, the higher the value of the fuel utilization rate is selected.

In the third aspect, a control map is prepared in which the fuel utilization rate with respect to the current value is low as a whole in a state of little deterioration such as in the initial stage of power generation, and conversely, in a state of large deterioration such as after long-term power generation. In the state, a control map is prepared in which the fuel utilization rate with respect to the current value is generally high.

That is, when the fuel cell is deteriorated, a large amount of heat generated by Joule heat due to the deterioration can be used for heat maintenance. Therefore, the fuel utilization rate can be increased by using the control map corresponding to the deterioration. it can. As a result, high power generation efficiency can be maintained even after deterioration has started in some parts.

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

Examples of the fuel cell having a parallel series structure of fuel gas include a fuel cell stack in which a plurality of fuel cell cells, which are power generation units, are stacked.
In a fuel cell stack having a parallel series structure, power generation units (fuel cell cells) constituting the fuel cell stack are electrically connected in series. By dividing the fuel gas path to be supplied to the fuel cell stack in parallel, for example, the upstream part and the downstream part, the fuel supply amount to the power generation unit is increased, and the fuel cell stack in which the power generation units are stacked is increased. Since the amount of fuel supplied to the fuel cell can be reduced, the fuel utilization rate of each fuel cell can be reduced.

As a result, even after durability deterioration (after long-term use and deterioration), the amount of fuel supplied to the fuel cell stack can be reduced, so that the total fuel utilization rate of the fuel cell stack can be increased, and finally. The power generation efficiency can be maintained 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 for each fuel cell that constitutes the fuel cell stack, but the total fuel utilization rate for the entire fuel cell stack.

(5) In the fifth aspect of the present invention, the fuel cell burns a reformer that reforms raw fuel into the fuel gas, the fuel gas that has not been used for the power generation, and the oxidizing agent gas. It is characterized by having at least one of the combustors.

The fifth aspect illustrates a fuel cell using an auxiliary device such as a reformer or a combustor.
When supplying fuel gas to a fuel cell, the reformer reforms the raw fuel such as raw material fuel gas into a composition more suitable for power generation (for example, the composition of city gas or the like having a higher hydrogen gas component). It is a device that reforms to the gas of.

(6) In the sixth aspect (fuel cell control method) of the present invention, the operation of the fuel cell that generates power using the fuel gas and the oxidant gas is detected by the operating state detecting means of the fuel cell. In the fuel cell control method controlled based on the operating state, a plurality of 10 or less types of deterioration stages set in advance based on the power value and the current value of the fuel cell as deterioration stages indicating the degree of deterioration of the fuel cell. The deterioration stage is stored, and 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 detecting means is determined. Based on the determined deterioration stage, the fuel utilization rate of the fuel cell corresponding to the deterioration stage is determined.

The sixth aspect has the same effect as the first aspect.
(7) As a seventh aspect of the present invention, each control map for obtaining the fuel utilization rate from the current value of the fuel cell is stored in accordance 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.

This seventh aspect has the same effect 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) which is 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 material, various raw materials capable of producing hydrogen by reforming, for example, natural gas (for example, LNG), city gas, LPG, kerosene, methanol, biomethanol and the like can be adopted.

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

Further, examples of the fuel cell include a fuel cell that is a power generation unit and a fuel cell stack that includes a plurality of fuel cell cells (for example, a stack of fuel cell cells). As the fuel cell, for example, a configuration including a single cell in which a fuel electrode layer, a solid electrolyte layer, and an air electrode layer are integrally laminated can be adopted.

It is explanatory drawing which shows the whole structure of the fuel cell system of an Example. (A) is a plan view showing the fuel cell stack, and (b) is an explanatory view schematically showing the gas flow path of the fuel cell stack from the side surface by dividing the gas flow path into the fuel gas and the oxidant gas. It is explanatory drawing which shows the map for obtaining the deterioration stage from the electric power value and the current value of a fuel cell stack. It is explanatory drawing which shows the map for obtaining the fuel utilization rate from the current value of the fuel cell stack in the early stage, the middle stage, and the late stage of the operation of a fuel cell stack, respectively. It is a flowchart which shows the control process performed by a controller.

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

a) First, the entire system configuration of the solid oxide fuel cell will be described. In the following, the "solid oxide type" will be omitted.
As shown in FIG. 1, the fuel cell system 1 in the present embodiment includes a fuel gas (for example, a reformed gas obtained by reforming a raw material fuel gas such as city gas: hydrogen in the reformed gas) and an oxidant gas (for example, hydrogen in the reformed gas). Air: Specifically, it is a power generation unit that generates power by being supplied with (oxygen in it).

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

The power generation module 15 is arranged in the heat insulating container 17, and the vaporizer 19, the reformer 21, and the fuel cell stack (power generation stack) are contained in the heat insulating container 17 from the upstream side of the fuel gas supply flow path 3. ) 23, the combustor 25 is arranged. Further, a temperature sensor 27 is arranged on the fuel cell stack 23.

In this embodiment, the upstream side and the downstream side are defined based on the direction in which the raw fuel gas (hence, the fuel gas) or air flows from the pumps 5 and 13 to the fuel cell stack 23, so that the pumps 5 and 13 are used. The side is the upstream side, and the fuel cell stack 23 side is the downstream side.

Further, 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 conversion device.

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 (supplying electric power) from the fuel cell stack 23 to the power conditioner 33. , A current sensor 37 that measures the current (DC current) flowing through the electric circuit 35 is arranged.

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. The flow rate of the fuel gas required for power generation is calculated by the controller 31, and the flow rate of the predetermined 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 well-known mixer, and the vaporizer 19 mixes the raw material fuel gas and steam.

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

As will be described later, the fuel cell stack 23 is a substantially rectangular parallelepiped device in which a plurality of plate-shaped fuel cell cells 24 (see FIG. 2B), which are 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 the combustion heats the fuel cell stack 23. can do.

The temperature sensor 27 is a sensor that is arranged 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 conversion device that converts the DC power generated by the fuel cell stack 23 into AC power and supplies it to the load 39. In this power conditioner 33, in order to measure the AC power value, the AC current value and the AC voltage value can be measured.

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

The current sensor 37 is an ammeter that measures the current (direct current value) supplied from the fuel cell stack 23.
The controller 31 is an electronic control device including a well-known microcomputer. A signal indicating the flow rate of fuel gas is input from the flow rate sensor 7, a signal indicating the temperature of the fuel cell stack 23 is input from the temperature sensor 27, and a signal indicating the temperature of the fuel cell stack 23 is input from the current sensor 37. A signal indicating the 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 the power supplied from the power conditioner 33 to the load 39 after being converted into AC power. The signal is input.

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

Further, as described above, the current value (A1) (direct current at the output of the fuel cell stack 23) is input to the controller 31, and the alternating current value (A2) is input from the power conditioner 33. The 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 means, a determination means, a determination means, and a fuel supply control means 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 device in which plate-shaped fuel cell cells 24 are laminated (for example, 9 steps in the vertical direction of FIG. 2B), and is a fuel cell. The stack 23 is integrally fixed by ten first to tenth bolts 41a to 41j (and nuts 43) penetrating the stack 23 in the stacking direction.

The fuel cell 24 is a so-called fuel cell support film type fuel cell 24, which is not shown, but is composed of a well-known fuel cell (arranged so as to be in contact with the fuel flow path) and (for example, zirconia). ) It has a solid electrolyte and an air electrode (arranged so as to be in contact with the air flow path).

Further, 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 8th bolt 41h is introduced into the fuel flow path of the 5th to 9th fuel cell cells 24e to 24i, and is introduced into the through hole of the 3rd bolt 41c. It is configured to be introduced into the fuel flow path of the first to fourth fuel cell cells 24a to 24d via 45c and discharged out of the stack through 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 10th volt 41j is introduced into the air flow path of each fuel cell 24a to 24i and discharged to the outside of the stack through the through hole 45e of the 5th volt 41e. It is configured to be.

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

Further, the degree of deterioration usually has a correlation with the operating time of the fuel cell stack 23, and it is known that the deterioration progresses as the operating time becomes longer. Therefore, the standard time is shown in Table 1. There is. However, although the deterioration tends to increase as the operating time increases, it varies depending on the operating conditions. Therefore, it is considered desirable to judge the degree of deterioration based on the power value and the current value rather than the operating time.

Specifically, when the operating conditions are constant, as shown in FIG. 3, there is a feature that the power value that can be generated is large but the current value is small at the initial stage of operation, and in the middle stage of operation, compared to the initial stage. The power value and current value that can be generated are almost medium, and in the latter half of operation, the power value that can be generated is smaller but the current value is larger than in the middle stage.

For example, as shown in Table 1 below, the relationship between the generated power (power value) corresponding to the degree of deterioration and the current value shows that the current value is the initial (5000 hours or less from the start of power generation) even if the generated power is the same. In the middle period (more than 5,000 hours from the start of power generation and less than 40,000 hours) and the second half (more than 40,000 hours from the start of power generation and less than 90,000 hours), it tends to increase from the early stage to the middle stage and the latter stage.

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, from such a feature, it is possible to determine how much the fuel cell stack 23 is currently deteriorated based on the electric power value and the current value.

In this embodiment, as the deterioration stage indicating the degree of deterioration, three types of deterioration stages of early stage, middle stage, and late stage (the degree of deterioration is large in sequence) are set according to the degree of deterioration. Two or four or more deterioration stages may be set. However, if too many deterioration stages are set, control becomes complicated, so for example, 10 or less are preferable.

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

-In addition, in this embodiment, in order to control the fuel gas supply amount, as shown in FIG. 4, three types of control maps, an initial map, a medium-term map, and a late-term map, are stored, and this control map is stored. , The fuel cell (that is, the fuel cell stack 23) shown in FIG. 3 is switched and used 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 Table 2 below, the relationship between the current value and the fuel utilization rate according to the degree of deterioration is shown. The fuel utilization rate is set to increase in the middle and late stages rather than in the early stages.

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 this 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-term deterioration stage are shown. Three types of control maps are set: a medium-term map showing the relationship and a late map showing the relationship between the current value and the fuel utilization rate in the late deterioration stage.

Therefore, in this embodiment, the current degree of deterioration (deterioration stage) is determined from the power value and the current value based on the relationship (map) shown in FIG. 3, and the degree of deterioration obtained by the determination result is determined. Each control map shown in FIG. 4 is selected accordingly, 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 rate of increase in the fuel utilization rate is set smaller than that of 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, even under the same operating conditions, the amount of Joule heat generated (due to deterioration or the like) due to power generation is small.

Therefore, in this case, by reducing the fuel utilization rate, the ratio of the fuel supply amount required for power generation is lowered, 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.

In addition, the medium-term map is a map in which the fuel utilization rate increases as the current value increases, but the rate of increase in the fuel utilization rate is set larger than that of the initial map (described later) and smaller than that of the late map. There is. This is because the degree of deterioration is moderate (compared to the early and late stages) within 40,000 hours or less (so-called mid-term stage) from the start of operation, and therefore, even under the same operating conditions, the joules associated with 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 required 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 latter map is a map in which the fuel utilization rate increases as the current value increases, and the rate of increase in the fuel utilization rate is set larger than that of other control maps. This is because the degree of deterioration is large in 90,000 hours or less (so-called late stage) from the start of operation, and therefore, even under the same operating conditions, the amount of Joule heat generated (due to deterioration or the like) is large due to power generation.

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

The maps of FIGS. 3 and 4 can be obtained in advance by experiments or the like, but the current value and voltage value (electric power value) used for the setting can be obtained by a sensor or the like that actually measures those values. Set using the 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 100 (indicated by S in FIG. 5) 100, the current value (direct 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 the 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 (AC averaged) voltage value (V2). Alternatively, the power value (W2) can be calculated from the (averaged alternating current) current value (A2) and the (averaged alternating current) voltage value (V2).

As for which current value or power value to use, as described above, the value used when each of the maps of FIGS. 3 and 4 is set may be adopted.
In the following step 110, the degree of deterioration (deterioration stage) is determined from the power value and the current value obtained in the step 100 by using the map shown in FIG.

Here, if the deterioration stage indicates the initial stage of operation, the process proceeds to step 120, if the deterioration stage indicates the middle stage of operation, the process proceeds to step 130, and if the deterioration stage indicates the latter stage, 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. 4 (a).
Further, in step 130, since the operation is in the middle stage, the fuel utilization rate is obtained from the current value by using the medium-term map of FIG. 4 (b).

Further, in step 140, since it is the latter stage of the operation, the fuel utilization rate is obtained from the current value by using the latter stage map of FIG. 4 (c).
In the following step 150, the fuel supply amount (specifically, the raw material fuel supply amount which is the raw material fuel gas supply amount) is calculated from the fuel utilization rate obtained in each step according to the operating state.

Specifically, for example, between the DC current value Ia [A] generated from the fuel cell stack 23 and the fuel flow rate (fuel gas flow rate) Qa [mol / sec] supplied to the fuel cell stack 23, Generally, 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.

Then, the fuel supply amount (fuel gas supply amount) Qb supplied for power generation while the fuel cell stack 23 maintains thermal independence is calculated by the following equation (2) using the fuel utilization rate Uf [%]. Can be calculated.

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

That is, the raw material fuel supply amount Q [L / min] is calculated by the above 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 the step 150 (that is, the raw fuel supply amount Q), and this process is temporarily terminated.

e) Next, the effects of this embodiment will be described.
In this embodiment, as the deterioration stages indicating the degree of deterioration of the fuel cell stack 23, a plurality of deterioration stages set in advance based on the power value and the current value of the fuel cell stack 23 are stored, and the plurality of deterioration stages are stored. Based on the deterioration stage, the deterioration stage corresponding to the power value and the current value of the (detected) fuel cell stack 23 is determined. Then, the fuel utilization 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 utilization rate, and the flow rate of the raw fuel gas is calculated based on the calculated value. , A predetermined amount of raw material fuel gas (hence, a fuel gas obtained by reforming the raw material 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 according 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 conventional case is not required, and therefore control hunting can be suppressed.

As a result, the possibility of locally depleting fuel in the fuel cell 24 is reduced, and the durability of the fuel cell stack 23 can be greatly improved, which is a remarkable effect.
Further, since the complicated control as in the conventional case is not required, the power consumption of the air pump 13 is unlikely to increase. Therefore, the amount of current flowing through the fuel cell stack 23 is unlikely to increase, and this also has the effect of improving the durability of the fuel cell stack 23.

Further, even when the fuel cell 24 is a flat plate 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 unlikely to increase, and thus a failure such as cell cracking occurs. Has the advantage of being less likely to occur.

That is, in this embodiment, since it is not necessary to perform the conventional complicated control, that is, the 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 such as at the beginning of power generation, a control map is prepared in which the fuel utilization rate with respect to the current value is low as a whole, and conversely, there is large deterioration such as after long-term power generation. In the state, a control map is prepared in which the fuel utilization rate with respect to the current value is generally high.

That is, when the fuel cell stack 23 is deteriorated, a large amount of heat generated by Joule heat due to the deterioration can be used for heat maintenance. Therefore, by using the control map corresponding to the above-mentioned deterioration, the fuel utilization rate can be increased. can do. As a result, high power generation efficiency can be maintained even after deterioration has started in some parts.

Further, 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 two, for example, an upstream portion and a downstream portion in parallel, so that the amount of fuel supplied to each fuel cell 24 can be increased and the fuel cell can be used. 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, even after the durability is deteriorated (after being used for a long period of time and deteriorated), the amount of fuel supplied to the fuel cell stack 23 can be reduced, so that the total fuel utilization rate of the fuel cell stack 23 can be increased. Ultimately, the power generation efficiency can be maintained high.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be carried out in various modes without departing from the present invention.
(1) For example, the fuel cell includes a solid oxide fuel cell (SOFC), a polymer electrolyte fuel cell (PEFC), a molten carbonate fuel cell (MCFC), a phosphoric acid fuel cell (PAFC), and the like. Fuel cells can be 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 utilization rate, the output (DC current, DC voltage) of the fuel cell stack is used as the power conditioner. May be obtained by using a separately provided current meter or voltmeter, or may use the output (AC current, AC voltage) obtained from the power conditioner.

(3) In the above embodiment, a reformer and a combustor are used, but the present invention can also be applied to a fuel cell system without a reformer or a combustor.
(4) In the present invention, for example, as a raw fuel gas without using a vaporizer, a reformer, or the like (that is, instead of reforming the raw fuel gas to generate a fuel gas such as hydrogen). It can be applied to a device that uses a fuel gas such as hydrogen and supplies the fuel gas to the fuel cell stack by a pump or the like.

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 (4)

In a fuel cell control device that controls the operation of a fuel cell that generates electricity using a fuel gas and an oxidant gas based on the operating state of the fuel cell detected by the operating state detecting means.
The fuel cell, I SOFC der flat-plate comprises a combustor for burning said fuel gas not used in the power generation and the oxidant gas,
As a deterioration stage indicating the degree of deterioration of the fuel cell, a storage means for storing a plurality of deterioration stages of 10 or less types set in advance based on the electric power value and the current value of the fuel cell, and a storage means.
A determination means for determining the deterioration stage corresponding to the electric power value and the current value of the fuel cell detected by the operating state detecting means based on the plurality of deterioration stages stored in the storage means.
Based on the deterioration stage determined by the determination means, fuel utilization is a value obtained by dividing the amount of fuel used for the power generation of the fuel cell corresponding to the deterioration stage by the amount of fuel supplied to the fuel cell. The means of determining the rate and
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 the raw material of the fuel gas is supplied to the fuel cell based on the calculated value. Fuel supply control means to control
It is a fuel cell control device equipped with
The storage means is configured to store 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 determination means is configured to select the control map corresponding to the deterioration stage determined by the determination means, and determine the fuel utilization rate from the current value of the fuel cell based on the control map.
Each of the control maps set according to the degree of deterioration of the fuel cell is a case where the degree of deterioration is larger than the case where the degree of deterioration of the fuel cell is smaller than the case where the degree of deterioration of the fuel cell is smaller than the case where the current value of the same fuel cell is the same. The higher the fuel utilization rate is selected, the more
The fuel utilization rate reduces the amount of combustion in the combustor as the fuel utilization rate increases.
A fuel cell control device characterized by this. The fuel cell control device according to claim 1, wherein the fuel cell has a parallel series structure for at least the fuel gas. The fuel cell, the control device of the fuel cell according to claim 1 or claim 2, characterized in that with a reformer for reforming raw fuel to the fuel gas. In a fuel cell control method that controls the operation of a fuel cell that generates electricity using a fuel gas and an oxidant gas based on the operating state of the fuel cell detected by the operating state detecting means.
The fuel cell, I SOFC der flat-plate comprises a combustor for burning said fuel gas not used in the power generation and the oxidant gas,
As a deterioration stage indicating the degree of deterioration of the fuel cell, a plurality of 10 or less types of deterioration stages set in advance based on the electric power value and the current value of the fuel cell are stored.
Based on the plurality of stored deterioration stages, the deterioration stage corresponding to the electric power value and the current value of the fuel cell detected by the operating state detecting means is determined.
Based on the determined deterioration stage, the fuel utilization rate, which is a value obtained by dividing the amount of fuel used for the power generation of the fuel cell corresponding to the deterioration stage by the amount of fuel supplied to the fuel cell, is determined. And
The flow rate of the fuel gas is calculated based on the fuel utilization rate, and a predetermined amount of the fuel gas or the raw fuel of the fuel gas is controlled to be supplied to the fuel cell based on the calculated value. ,
It ’s a fuel cell control method.
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 is stored.
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.
Each of the control maps set according to the degree of deterioration of the fuel cell is a case where the degree of deterioration is larger than the case where the degree of deterioration of the fuel cell is smaller than the case where the degree of deterioration of the fuel cell is smaller than the case where the current value of the same fuel cell is the same. The higher the fuel utilization rate is selected, the more
The fuel utilization rate reduces the amount of combustion in the combustor as the fuel utilization rate increases.
A fuel cell control method characterized by this.

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