JP6335559B2 - Polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a solid polymer fuel cell including a plurality of cells each having a solid polymer electrolyte membrane sandwiched between a fuel electrode and an air electrode.

  In the polymer electrolyte fuel cell, the solid polymer electrolyte membrane and the fuel electrode and the air electrode sandwiching the polymer electrolyte membrane from both sides are wetted to increase the hydrogen ion conductivity, thereby enabling power generation. Therefore, the fuel gas supplied to the fuel electrode and the oxidant gas supplied to the air electrode are operated with humidification such as mixing water vapor. In stationary applications where long-term durability is required, operation under saturated humidification conditions in which the cell temperature and the dew points of the fuel gas and the oxidant gas are substantially the same are generally used from the viewpoint of suppressing deterioration. Under these conditions, the battery temperature is lowered during the low-load operation, and condensation water is likely to be generated. Therefore, the gas flow path necessary for the reaction is blocked, and the battery performance is deteriorated or unstable. For this reason, countermeasures for excess water discharge such as ensuring the gas flow rate in the gas flow path have been made (see Patent Document 1).

On the other hand, cost can be reduced by simplifying or eliminating the humidification function for the fuel gas and the oxidant gas. For this reason, development that suppresses cell deterioration even under non-saturated humidification conditions has been advanced (see, for example, Non-Patent Document 1).
Also, under such low humidification conditions, how efficiently the water generated by power generation can be efficiently used for wetting the cell is important in drawing out power generation performance, and optimization of the components of the cell is underway. (For example, refer nonpatent literature 2).

JP 2004-247289 A

Eiji Endoh, ECS Transactions, 16 (2), 1229, (2008) Nishikawa, Nakamura, Matsuyama, Kaoru, Proc. Of 15th Fuel Cell Symposium, 123, (2008)

  However, when the generated water accompanying power generation is efficiently used to keep the inside of the cell wet, there is a possibility that the wet state inside the cell changes due to changes in operating conditions and environment. And if the dampness is insufficient, there arises a problem that the deterioration of the cell is promoted.

When the load on the polymer electrolyte fuel cell decreases and the power generation output of the polymer electrolyte fuel cell decreases, the cell voltage in each cell of the plurality of cells constituting the polymer electrolyte fuel cell increases. When such a low-load state of the polymer electrolyte fuel cell continues (that is, when the cell voltage is high in each cell continuously), the amount of generated water is small and the deterioration of the cell due to insufficient wetting is promoted. Cheap. Further, depending on the voltage, there arises a problem that, for example, carbon constituting the air electrode is corroded.
Further, when the load on the polymer electrolyte fuel cell is increased and the power generation output of the polymer electrolyte fuel cell is increased, the cell voltage in each cell of the plurality of cells constituting the polymer electrolyte fuel cell is decreased. . If such a polymer electrolyte fuel cell is continuously in a high load state (that is, a state in which the cell voltage in each cell is low) and a state in which a large amount of water is generated by power generation continues, There is a problem in that flooding occurs in which the gas flow path is blocked by the generated water.

  As described above, if the cell voltage of each cell becomes too large or too small as the load on the polymer electrolyte fuel cell changes, the cell may fail.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a polymer electrolyte fuel cell capable of avoiding cell failure.

In order to achieve the above object, the solid polymer fuel cell according to the present invention includes a membrane electrode assembly configured by sandwiching a solid polymer electrolyte membrane between a fuel electrode and an air electrode, and the membrane electrode assembly. A fuel electrode separator that introduces fuel gas into the fuel electrode through a fuel gas flow path, and a gas separator that is provided on the air electrode side of the membrane electrode assembly and that passes through the oxidant gas flow path. A polymer electrolyte fuel cell comprising a cell stack formed by laminating a plurality of cells each having an air electrode separator for introducing an oxidant gas into an electrode, and an operation control means for controlling operation,
Voltage detecting means for measuring a cell voltage of the plurality of cells,
The operation control means is such that, among the plurality of cells, the number of cells to be subjected to the power generation operation decreases as the cell voltage of the cell performing the power generation operation measured by the voltage detection means increases.

With the above construction, can and the cell voltage of the cell where the power generating operation is determined by the voltage detecting means becomes higher (i.e., when the load on the polymer electrolyte fuel cell is decreased), the cell to be power generation operation The number is reduced. In other words, the load on the cell that is to perform the power generation operation increases, and the cell voltage of the cell that is to perform the power generation operation changes in a direction that decreases. As a result, the amount of produced water is small it is possible to suppress the generation of cell degradation and said problem by wetting shortage due avoids cell failure.

  Another characteristic configuration of the polymer electrolyte fuel cell according to the present invention is such that the operation control means is configured such that, among the plurality of cells, a cell voltage of a cell that is in a power generation operation is equal to or higher than a predetermined set lower limit voltage and a set upper limit voltage. A determination unit that determines whether or not the cell voltage is below, and when the determination unit determines that the cell voltage is higher than the set upper limit voltage, an operation cell number reduction process is performed to reduce the number of cells that perform power generation operation. When the determination unit determines that the cell voltage is lower than the set lower limit voltage, an operation cell number increase process is performed to increase the number of the cells that perform power generation operation, and the determination unit sets the cell voltage to the set lower limit voltage. An operation cell number adjusting unit that performs an operation cell number maintaining process for maintaining the number of cells that perform power generation operation as it is when it is determined that the voltage is not less than the voltage and not more than the set upper limit voltage. A.

  According to the above characteristic configuration, the determination unit included in the operation control unit determines whether or not the cell voltage of the cell that is in the power generation operation among the plurality of cells is equal to or higher than the predetermined set lower limit voltage and lower than the set upper limit voltage. Then, the operation cell number adjustment unit included in the operation control means performs the operation cell number reduction process when the determination unit determines that the cell voltage is higher than the set upper limit voltage, and the determination unit sets the cell voltage lower than the set lower limit voltage. If it is determined that the cell voltage is greater than the set lower limit voltage and less than the set upper limit voltage, the operation cell number maintaining process is performed. As a result, when it is determined that the cell voltage is higher than the set upper limit voltage, the number of cells is adjusted so that the cell voltage decreases to be lower than the set upper limit voltage, and it is determined that the cell voltage is lower than the set lower limit voltage. Sometimes the cell number is adjusted so that the cell voltage becomes higher than the set lower limit voltage, and if it is determined that the cell voltage is higher than the set lower limit voltage and lower than the set upper limit voltage, the cell voltage remains as it is above the set lower limit voltage and higher The number of cells is maintained so as to be equal to or lower than the voltage. In this way, the polymer electrolyte fuel cell can be operated so that the cell voltage of the cell performing the power generation operation is not less than the set lower limit voltage and not more than the set upper limit voltage.

  Still another characteristic configuration of the polymer electrolyte fuel cell according to the present invention is that the operation control means performs the process of increasing the number of operating cells and changes the inflow temperature of the cooling water flowing into the cell stack to a low temperature side. And the amount of water contained in the oxidant gas flowing into the cell stack is changed to the decreasing side, the number of operating cells is reduced, and the inflow temperature of the cooling water flowing into the cell stack is changed to the high temperature side. And the amount of water contained in the oxidant gas flowing into the cell stack is changed to the increasing side.

  According to the above characteristic configuration, when the amount of exhaust heat from the polymer electrolyte fuel cell is increased by performing the process of increasing the number of operating cells, the temperature of cooling water flowing into the cell stack is changed to the low temperature side, and the process of decreasing the number of operating cells is performed. When the amount of exhaust heat from the polymer electrolyte fuel cell decreases, the inflow temperature of the cooling water to the cell stack is changed to the high temperature side. In other words, by adjusting the cooling water inflow temperature to the cell stack, the temperature of the cell stack can be prevented from becoming excessively high even if the amount of heat exhausted from the polymer electrolyte fuel cell increases. Even if the amount of heat exhausted from the fuel cell is reduced, the temperature of the cell stack can be prevented from becoming excessively low.

In addition, if the inflow temperature of the cooling water to the cell stack is increased, the amount of water existing as a liquid in the cell stack is relatively reduced, and if the inflow temperature of the cooling water to the cell stack is decreased, the amount of water in the cell stack is The amount of water present is relatively increased. In particular, since water is generated by the power generation reaction on the air electrode side, the gas flow path is blocked with water when the inflow temperature of the cooling water into the cell stack decreases and the amount of water present as liquid water increases. Problems can occur.
However, in this feature configuration, the number of operating cells is increased, the inflow temperature of the cooling water flowing into the cell stack is changed to the low temperature side, and the amount of moisture contained in the oxidant gas flowing into the cell stack is changed to the decreasing side. Let In other words, even if the inflow temperature of the cooling water to the cell stack becomes low and the amount of water existing as a liquid in the cell stack can be relatively increased, it is included in the oxidant gas on the air electrode side. Since the amount of water to be reduced is changed to the decreasing side, the amount of water that will exist as a liquid can be prevented from greatly increasing, and the occurrence of problems such as the gas flow path being blocked with water can be suppressed. In addition, the number of operating cells is reduced, the inflow temperature of the cooling water flowing into the cell stack is changed to the high temperature side, and the amount of moisture contained in the oxidant gas flowing into the cell stack is changed to the increase side. In other words, even if the inflow temperature of cooling water to the cell stack becomes high and the amount of water present as a liquid in the cell stack can be relatively reduced, it is included in the oxidant gas on the air electrode side. Since the amount of moisture to be increased is changed to the increasing side, the cell stack can be kept moist.

It is a figure explaining the structure of a fuel cell system. It is a schematic diagram explaining the structure of a cell stack. It is a figure explaining the control mechanism of a fuel cell. It is a figure explaining the specific example of the method of adjusting the number of operation cells in 1st Embodiment. It is a graph example which shows the relationship between the electric current which flows through the cell which is performing electric power generation operation, and the cell voltage. It is a graph which shows the example of a relationship between output current and a cell voltage. It is a figure explaining the specific example of the method of adjusting the number of operation cells in 2nd Embodiment. It is a graph example which shows the relationship between the electric current which flows through the cell which is performing the electric power generation driving | operation, and the cell voltage before and after deterioration of a cell.

<First Embodiment>
The configuration of the polymer electrolyte fuel cell according to the first embodiment will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a fuel cell system, FIG. 2 is a schematic diagram illustrating a configuration of a cell stack CS, and FIG. 3 is a diagram illustrating a control mechanism of a polymer electrolyte fuel cell. It is. As shown in the figure, the fuel cell system includes a power generation unit U1 and a hot water storage unit U2. In the drawings shown in the present application, in order to facilitate understanding of the present invention, there are places where the positional relationship and size of each member are drawn differently from the original positional relationship and size.

  The power generation unit U1 has a polymer electrolyte fuel cell as a combined heat and power generation device that generates heat and electricity together. The polymer electrolyte fuel cell includes a membrane electrode assembly 40 configured by sandwiching a polymer electrolyte membrane 10 between a fuel electrode 11 and an air electrode 12, and a fuel electrode 11 side of the membrane electrode assembly 40. A fuel electrode separator 13 that introduces fuel gas into the fuel electrode 11 through the gas flow path 13a, and the air electrode 12 side of the membrane electrode assembly 40 are provided, and the oxidant gas is supplied to the air electrode 12 through the oxidant gas flow path 14a. And a cell stack CS formed by laminating a plurality of cells C each having an air electrode separator 14 for introducing air. Further, as shown in FIG. 3, the polymer electrolyte fuel cell includes an operation control means 36 for controlling its own operation. The operation control system is configured to control the operation of the fuel cell system.

In the present embodiment, hydrogen as a fuel gas and air (oxygen) as an oxidant gas are supplied to the polymer electrolyte fuel cell.
Hydrogen as the fuel gas is generated when the reformer 8 provided in the power generation unit U1 reforms raw fuel containing hydrocarbons. In the example shown in FIG. 1, raw fuel gas (city gas or the like) mainly composed of methane (CH ₄ ) is supplied to the reformer 8 through the raw fuel gas supply path 6 and reformed. The resulting fuel gas mainly composed of hydrogen is supplied to the cell C through the fuel gas supply path 7. In addition, air as an oxidant gas is also supplied to the cell C through the oxidant gas supply path 1.

  A fuel electrode side humidifier 4 is provided in the middle of the fuel gas supply path 7 to humidify the fuel gas supplied to the cell C. An air electrode side humidifier 2 is provided in the middle of the oxidant gas supply path 1 to humidify the oxidant gas supplied to the cell C. Various existing humidifiers can be used for the fuel electrode side humidifier 4 and the air electrode side humidifier 2. The operation control means 36 controls the operations of the fuel electrode side humidifier 4 and the air electrode side humidifier 2. Specifically, the operation control means 36 adjusts the dew points of the fuel gas and the oxidant gas by controlling the temperatures at the humidified portions of the fuel electrode side humidifier 4 and the air electrode side humidifier 2. For example, when the operation control means 36 increases the temperature at the humidifying portion of the fuel electrode side humidifier 4, the amount of water contained in the fuel gas can be increased (that is, the dew point of the fuel gas is increased). .

  In addition, the fuel gas after being used for the power generation reaction in the cell C (hereinafter also referred to as “exhaust fuel gas”) is supplied to the combustor 9 via the exhaust fuel gas passage 5. In addition, air (oxygen) is supplied through the oxidant gas supply path 1a. Then, the exhaust fuel gas is combusted in the combustor 9 and the combustion heat is transmitted to the reformer 8, whereby the reforming reaction in the reformer 8 is promoted. Then, the exhaust gas discharged from the combustor 9 and the air after being used for the power generation reaction in the cell C are discharged to the outside of the power generation unit U1 through the exhaust gas path 3. FIG. 1 shows a state in which exhaust fuel gas and air are mixed in advance and then supplied to the combustor 9 (a state in which the exhaust fuel gas passage 5 is connected to the oxidant gas supply passage 1a). However, the exhaust fuel gas and air may be separately supplied to the combustor 9.

  In the cell C, the fuel electrode separator 13 is provided on the fuel electrode 11 side of the membrane electrode assembly 40, and the air electrode separator 14 is provided on the air electrode 12 side of the membrane electrode assembly 40. Then, the fuel gas is introduced into the fuel electrode 11 through the fuel gas channel 13 a formed in the fuel electrode separator 13, and the oxidant gas is introduced into the air electrode 12 through the oxidant gas channel 14 a formed in the air electrode separator 14. Is done. In the example shown in FIG. 1, one cell C includes a fuel electrode separator 13 in which a fuel gas groove 13a serving as a fuel gas passage 13a through which fuel gas flows is formed on one surface, and an oxidant on one surface. An air electrode separator 14 in which an oxidant gas groove serving as an oxidant gas flow path 14a through which gas flows is formed and a cooling water groove through which cooling water flows is formed on the other surface; a membrane electrode assembly 40; It is configured using. Then, in one cell C, the fuel gas is introduced into the fuel electrode 11 by making one surface of the fuel electrode separator 13 in which the fuel gas groove is formed relative to the fuel electrode 11 of the membrane electrode assembly 40, The oxidant gas is introduced into the air electrode 12 by making one surface of the air electrode separator 14 in which the groove for the oxidant gas is formed facing the air electrode 12 of the membrane electrode assembly 40. . In the cell stack CS, the other surface of the air electrode separator 14 in which the cooling water groove of one cell C is formed is connected to the other surface of the fuel electrode separator 13 in which the groove for fuel gas of the other cell C is not formed. A plurality of cells C are sequentially stacked so as to face the surface.

  The cell C is sequentially stacked in the Y-axis direction shown in FIG. The cell stack CS extends from the upstream side to the downstream side along the stacking direction of the cells C (that is, extends along the Y-axis direction), and the fuel gas supply through which the fuel gas supplied to the cell stack CS flows. Manifold part 15, oxidant gas supply manifold part 17 through which oxidant gas supplied to cell stack CS flows, fuel gas discharge manifold part 16 through which fuel gas discharged from cell stack CS flows, and exhaust from cell stack CS And an oxidant gas discharge manifold portion 18 through which the oxidant gas flows. A fuel gas supply path 7 is connected to the fuel gas supply manifold section 15, whereby fuel gas is supplied to the cell stack CS. The oxidant gas supply passage 1 is connected to the oxidant gas supply manifold section 17 so that the oxidant gas is supplied to the cell stack CS. The exhaust gas passage 5 is connected to the fuel gas discharge manifold section 16, whereby the fuel gas (exhaust fuel gas) after being used for the power generation reaction in the cell C is discharged from the cell stack CS. The exhaust gas passage 3 is connected to the oxidant gas discharge manifold portion 18 so that the oxidant gas after being used for the power generation reaction in the cell C is discharged from the cell stack CS.

  Inside each cell C, the fuel gas flow path 13a connects between the fuel gas supply manifold section 15 and the fuel gas discharge manifold section 16, and the oxidant gas flow path 14a is connected to the oxidant gas supply manifold section 17. The oxidant gas discharge manifold portion 18 is connected. In the fuel gas supply manifold section 15, the fuel gas flows into the fuel gas flow path 13 a while flowing from the upstream side to the downstream side, and in the oxidant gas supply manifold section 17, the oxidant gas flows from the upstream side. It flows into the oxidant gas flow path 14a while flowing toward the downstream side. In the example shown in FIG. 2, in order to simplify the drawing, in the cell C, the fuel gas flow path 13a is formed in a straight line shape along the X-axis direction, and the oxidant gas flow path 14a is straight along the Z-axis direction. Although a schematic diagram is illustrated as being formed in a shape, the shape of the fuel gas flow path 13a and the shape of the oxidant gas flow path 14a inside the cell C can be freely designed. For example, in one cell C, the fuel gas flow path 13a can be formed so that the fuel gas flows in the positive direction of the X axis as a whole while meandering in the XZ plane. Further, in one cell C, the oxidant gas flow path 14a can be formed so that the oxidant gas flows in the positive direction of the Z axis as a whole while meandering in the XZ plane. . Further, in the example shown in FIG. 2, description of the cooling water is omitted.

  The cooling water described above plays a role of cooling the cell C and also plays a role of recovering exhaust heat from the cell C. In the present embodiment, the cooling water flows through the cooling water circulation path 19. In the middle of the cooling water circulation path 19, the cooling water flow path 20 in the cell stack CS, the cooling water heat exchanger 21, and the cooling water pump 22 are provided. The energized cooling water is circulated while flowing through the cell stack CS (cooling water flow path 20) and the cooling water heat exchanger 21 in order. Moreover, the hot water stored in the hot water storage tank 25 provided in the hot water storage unit U <b> 2 flows into the cooling water heat exchanger 21 through the exhaust heat recovery path 23. As a result, in the cooling water heat exchanger 21, heat exchange is performed between the cooling water flowing through the cooling water circulation path 19 and the hot water flowing through the exhaust heat recovery path 23. The flow rate of hot water in the exhaust heat recovery path 23 is adjusted by controlling the output of the exhaust heat recovery pump 24 provided in the middle of the exhaust heat recovery path 23. The operation of the cooling water pump 22 and the exhaust heat recovery pump 24 is controlled by the operation control means 36.

  In the hot water storage tank 25 provided in the hot water storage unit U2, hot water at a relatively high temperature is stored in the upper part, and hot water at a relatively low temperature is stored in the lower part. Specifically, the exhaust heat recovery path 23 is provided so as to connect the lower part of the hot water storage tank 25 and the upper part of the hot water storage tank 25, and the cooling water heat exchanger 21 is provided therebetween. As a result, the relatively low temperature hot water stored in the lower part of the hot water storage tank 25 is heated up to the cooling water heat exchanger 21 through the exhaust heat recovery path 23, and the heated temperature is relatively increased. Hot hot water returns to the upper part of the hot water storage tank 25 and flows in.

  A hot water supply passage 27 is connected to the upper part of the hot water storage tank 25 to supply hot water for hot water supply such as a kitchen or a bath. In addition, a water supply path 26 is connected to the lower part of the hot water storage tank 25 so that hot water is replenished to the hot water storage tank 25.

  Next, operation control of the polymer electrolyte fuel cell will be described. As will be described in detail below, the operation control unit 36 performs operation control to change the number of cells C to be in power generation operation according to the cell voltage of the cell C that is performing power generation operation among the plurality of cells C. .

  The polymer electrolyte fuel cell includes a connection state switching unit 31 that selectively switches an electrical connection state between the plurality of cells C and the power output circuit unit 32 for each cell C, and a fuel gas supply manifold unit 15. A gas inflow state adjusting unit for adjusting an inflow state of the fuel gas to the fuel gas passage and the inflow state of the oxidant gas from the oxidant gas supply manifold unit to the oxidant gas passage; Here, the power output circuit unit 32 operates to output power corresponding to the load power by the power load unit.

The connection state switching unit 31 is configured using a plurality of relay circuits 30. Each relay circuit 30 connects the fuel electrode 11 and the air electrode 12 of one cell C constituting the cell stack CS. When all the relay circuits 30 are switched to the disconnected state, no current flows through the relay circuits 30, so that the output currents of all the cells C connected in series flow to the power output circuit unit 32. become. On the other hand, when the relay circuit 30 that connects the fuel electrode 11 and the air electrode 12 of a specific cell C is switched to the connected state, a current flows through the relay circuit 30, that is, the corresponding cell C Will bypass the current. If the number of cells C in power generation operation changes, the amount of fuel gas and the amount of oxidant gas required for the power generation reaction in the cell stack CS also change, but the amount of fuel gas supplied to the cell stack CS The flow rate can be controlled using the flow rate controller 38, and the flow rate of the oxidant gas can be controlled using the flow rate controller 39. The operation of the relay circuit 30 and the power output circuit unit 32 is controlled by the operation control means 36. The operation of the flow controller 38 and the flow controller 39 is controlled by the operation control means 36.
Further, a voltmeter 29 for measuring a cell voltage that is an output voltage of each cell C is provided. The plurality of voltmeters 29 constitute voltage detection means 29A.

  In the present embodiment, the gas inflow state adjusting unit 35 includes a partition plate 33 illustrated in FIG. 2 and a partition plate control unit 34 that controls the position of the partition plate 33. The partition plate 33 includes four plate-like members as the side portions 33a and one plate-like member as the bottom portion 33b, and the side portions 33a are vertically attached to the sides of the rectangular bottom portion 33b. It has become. When the gas flow direction in the fuel gas supply manifold section 15 and the oxidant gas supply manifold section 17 is a forward direction, the partition plate 33 is mounted from the downstream side to the upstream side, and the stacking direction of the cells C It is configured to be capable of translation along (the Y-axis direction in FIG. 2). Each of the four side portions 33a can be inserted between the manifold and the cell C from the downstream side in the stacking direction of the cells C toward the upstream side. The four side portions 33a are provided between the fuel gas supply manifold portion 15 and the cell stack CS, between the oxidant gas supply manifold portion 17 and the cell stack CS, and between the fuel gas discharge manifold portion 16 and the cell stack CS. In the meantime, it can be inserted between the oxidant gas discharge manifold 18 and the cell stack CS. When the side portion 33a of the partition plate 33 is inserted between the manifold and the cell stack CS, the fuel gas flow path 13a of the cell C from the manifold is inserted in the portion where the side portion 33a of the partition plate 33 is inserted. And the inflow of gas to the oxidant gas flow path 14a is blocked. That is, by moving the partition plate 33 in parallel along the stacking direction of the cells C, the inflow state of the fuel gas from the fuel gas supply manifold portion 15 to the fuel gas flow path 13a and the oxidant gas supply manifold portion 17 The inflow state of the oxidant gas to the gas flow path 14a can be adjusted. In the configuration of the partition plate 33 of the present embodiment, the side portions 33a move as a unit. Therefore, by moving the partition plate 33, the fuel gas channel 13a and the oxidant gas channel of the cell C from the manifold are moved. The shutoff timing and start timing of the gas inflow to 14a are the same. The operation of the gas inflow state adjusting unit 35 is controlled by the operation control means 36.

  FIG. 4 is a diagram illustrating a specific example of a method for adjusting the number of operating cells. The movement of the partition plate 33 with respect to the cell stack CS as shown in FIG. 4 is common to both the fuel gas and the oxidant gas. Therefore, in FIG. 4, the reference numbers of the members relating to the oxidant gas are given in parentheses. As shown in the figure, when the partition plate 33 is moved in the negative direction of the Y-axis (that is, when the partition plate 33 is moved from the state shown in FIG. 4A to the state shown in FIG. 4B), the fuel The number of cells C into which the gas flows in and the number of cells C into which the oxidant gas flows in decrease, and accordingly, the number of cells C that can perform power generation operation decreases. On the other hand, when the partition plate 33 is moved in the positive direction of the Y axis (that is, when the partition plate 33 is moved from the state shown in FIG. 4B to the state shown in FIG. 4A), the fuel The number of cells C into which gas flows in and the number of cells C into which oxidant gas flows in increase, and accordingly, the number of cells C that can perform power generation operation increases.

FIG. 5 is a graph example showing the relationship between the current flowing through the cell C performing the power generation operation and the cell voltage. As shown in the figure, when the load of the cell stack CS is reduced (that is, when the current flowing through the cell C performing the power generation operation is reduced), the cell voltage is increased. It is not preferable to continuously operate for a long time in a state where the amount of generated water is small because it causes deterioration of the cell C. In such a case, if the number of the cells C performing the power generation operation is decreased, the current flowing through the cells C performing the power generation operation is relatively increased in order to obtain an equivalent output. The cell voltage also decreases.
Conversely, when the load on the cell stack CS increases (that is, when the current flowing through the cell C performing power generation increases), the cell voltage decreases. In such a case, if the number of cells C performing power generation operation is increased, the current flowing through the cells C performing power generation operation is relatively decreased, so that the cell voltage of those cells C also increases. become.

Therefore, in the present embodiment, the operation control means 36 determines whether or not the cell voltage of the cell C that is in the power generation operation among the plurality of cells C is equal to or higher than a predetermined set lower limit voltage V _L1 and lower than a set upper limit voltage V _H1. When the determination unit 36a and the determination unit 36a determine that the cell voltage is higher than the set upper limit voltage V _H1 (that is, the load on the cell stack CS has decreased), the number of cells C that perform power generation operation is decreased. When the determination unit 36a determines that the cell voltage is lower than the set lower limit voltage V _L1 (that is, the load on the cell stack CS has increased), the number of cells C that perform power generation operation is increased. performed the number of operating cells increased processing for, when the cell voltage by the determination unit 36a is determined to set the lower limit voltage is V _L1 or more and less than the set upper limit voltage V _H1, while the number of cells C to the power generation operation of the current And a number of operating cells regulating portion 36b which performs the operation cell number of sustain process of lifting. Here, the “cell voltage” can be set as appropriate, such as the average value of the cell voltages of the cell C performing the power generation operation, the maximum value or the minimum value of the cell voltages of the cell C performing the power generation operation. Moreover, it has the memory | storage part 36c which memorize | stores the operation control means 36 and the information to handle.

  Then, the operation cell number adjustment unit 36b of the operation control means 36 performs the fuel cell supply from the fuel gas supply manifold unit 15 in order from the cell C on the upstream side of the cells C that are not performing the power generation operation as the operation cell number increase process. The operation of the gas inflow state adjusting unit 35 is controlled so as to start the inflow of the fuel gas into the gas channel 13a and the inflow of the oxidant gas from the oxidant gas supply manifold unit 17 to the oxidant gas channel 14a. The operation of the connection state switching unit 31 is controlled so that the cell C to be generated and operated is connected to the power output circuit unit 32, and among the cells C that are performing the generation operation as the operation cell number reduction process In order from the cell C on the downstream side, inflow of fuel gas from the fuel gas supply manifold section 15 to the fuel gas flow path 13a and from the oxidant gas supply manifold section 17 to the oxidant gas The operation of the gas inflow state adjusting unit 35 is controlled so as to stop the inflow of the oxidant gas into the flow path 14a, and the connection state is switched so that the cell C to be operated for power generation is connected to the power output circuit unit 32. The operation of the unit 31 is controlled.

FIG. 6 shows the cell voltage, the number of operating cells, the output power (referred to as “output” in FIG. 6), the coolant temperature, the dew point of the reaction gas, and the output current (referred to as “current” in FIG. 6). It is an example of a graph which shows a typical transition. As shown in FIG. 6, the operating cell number adjustment unit 36b determines the number of cells C that are in power generation operation when the determination unit 36a determines that the cell voltage is higher than the set upper limit voltage V _{H1 at} time t1 and time t2. The number of operation cells to be reduced is being reduced. By performing the operation cell number reduction process, the cell voltage decreases after time t1 and after time t2.
In addition, when the determination unit 36a determines that the cell voltage is lower than the set lower limit voltage V _{L1 at} the time t3 and the time t4, the operation cell number adjustment unit 36b increases the number of the operation cells C to increase the number of the cells C that perform the power generation operation. Increase processing is performed. By performing the operation cell number increasing process, the cell voltage increases after time t3 and after time t4.

It is possible to appropriately set how many cells C the power generation operation number is increased when the number of operation cells is increased and how many cells C the power generation operation number is decreased when the operation cell number is decreased. is there. For example, a setting for increasing and decreasing by one is possible, and a setting for increasing and decreasing by plural is also possible.
Alternatively, the target number of operating cells (that is, the power generation operation) may be determined according to the following Equation 1 with reference to the current number of operating cells. However, in the following formula 1, the target number of operation cells is an integer value of 1 or more and the maximum number of operation cells or less. The output power is output power at the power output circuit unit 32, and the operation control means 36 acquires the value of the output power from the power output circuit unit 32.

[Formula 1]
Target number of operating cells = Current number of operating cells x (Output power when set upper limit voltage or lower than set lower limit voltage / Output power when setting the current number of operating cells)

If the number of operating cells increases, the amount of exhaust heat increases as viewed in the entire cell stack CS, and the temperature of the cooling water flowing through the cooling water circulation path 19 and flowing into the cell stack CS increases. Therefore, in the present embodiment, the operation control unit 36 performs an operation cell number increase process and changes the inflow temperature of the cooling water flowing into the cell stack CS to the low temperature side. Specifically, the operation control unit 36 changes the flow rate of the exhaust heat recovery pump 24 to the increasing side, thereby changing the temperature of the cooling water flowing through the cooling water circulation path 19 to the decreasing side and flowing into the cell stack CS. The cooling water inflow temperature can be changed to the low temperature side. At this time, the operation control means 36 can obtain information on the inflow temperature of the cooling water flowing into the cell stack CS with reference to the measurement result of the thermometer 28 provided in the middle of the cooling water circulation path 19.
On the other hand, when the number of operating cells decreases, the amount of exhaust heat decreases as viewed in the entire cell stack CS, and the temperature of the hot water recovered by exhaust heat decreases. Therefore, in the present embodiment, the operation control means 36 performs the operation cell number reduction process and changes the inflow temperature of the cooling water flowing into the cell stack CS to the high temperature side. Specifically, the operation control means 36 changes the flow rate of the exhaust heat recovery pump 24 to the decreasing side, thereby changing the inflow temperature of the cooling water flowing into the cell stack CS to the high temperature side and recovering the exhaust heat. Increase the temperature of hot water.

  Further, when the inflow temperature of the cooling water to the cell stack CS is increased, the amount of water existing as a liquid in the cell stack CS is relatively reduced, and when the inflow temperature of the cooling water to the cell stack CS is decreased, the cell stack CS The amount of water present as a liquid in the inside increases relatively. In particular, since water is generated by the power generation reaction on the air electrode 12 side, if the inflow temperature of the cooling water to the cell stack CS is lowered and the amount of water existing as liquid water is increased, the gas flow path is water. Problems such as blockage can occur. Therefore, in the present embodiment, the operation control means 36 performs the operation cell number increasing process, changes the inflow temperature of the cooling water flowing into the cell stack CS to the low temperature side as described above, and flows into the cell stack CS. The amount of water contained in the oxidant gas is changed to the decreasing side using the air electrode side humidifier 2. That is, even if the inflow temperature of the cooling water into the cell stack CS is lowered and the amount of water existing as a liquid in the cell stack CS can be relatively increased, the oxidant is present on the air electrode 12 side. Since the amount of water contained in the gas has been changed to the decreasing side, the amount of water that will exist as a liquid can be prevented from increasing significantly, and problems such as the gas flow path being blocked by water can be prevented. Can be suppressed. Similarly, the operation control means 36 performs a process for reducing the number of operating cells, changes the inflow temperature of the cooling water flowing into the cell stack CS to the high temperature side as described above, and changes the oxidizing gas into the cell stack CS. The amount of water contained is changed to the increase side using the air electrode side humidifier 2. In other words, even when the temperature of the cooling water flowing into the cell stack CS becomes high and the amount of water existing as a liquid in the cell stack CS can be relatively reduced, the oxidant is present on the air electrode 12 side. Since the amount of water contained in the gas is changed to the increasing side, the inside of the cell stack CS can be kept wet.

Second Embodiment
The polymer electrolyte fuel cell of the second embodiment is different from the above embodiment in the configuration of the gas inflow state adjusting unit 35. Although the structure of the polymer electrolyte fuel cell of 2nd Embodiment is demonstrated below, description is abbreviate | omitted about the structure similar to the said embodiment.

  FIG. 7 is a diagram illustrating a specific example of a method for adjusting the number of operating cells. As shown in the drawing, in the second embodiment, the partition plate 37 included in the gas inflow state adjusting unit 35 allows and blocks the flow of gas inside the fuel gas supply manifold unit 15 and the oxidant gas supply manifold unit 17. It is comprised with the plate-shaped member. Moreover, the partition plate control part 34 mentioned above can switch the attitude | position of each partition plate 37 using drive mechanisms (not shown), such as a motor. By the control from the partition plate control unit 34, each partition plate 37 is either in a gas flow allowance state allowing the gas flow to the downstream side or a gas flow cut-off state blocking the gas flow to the downstream side. Can be switched to

The gas flow allowable state is a state where the surface direction of the partition plate 37 is parallel to the gas flow direction in the fuel gas supply manifold portion 15 and the oxidant gas supply manifold portion 17. In this state, the gas can flow along the surface direction of the partition plate 37 without being obstructed by the partition plate 37 inside the fuel gas supply manifold portion 15 and the oxidant gas supply manifold portion 17.
On the other hand, the gas flow cut-off state is a state in which the surface direction of the partition plate 37 is orthogonal to the gas flow direction in the fuel gas supply manifold portion 15 and the oxidant gas supply manifold portion 17. In this state, in the fuel gas supply manifold portion 15 and the oxidant gas supply manifold portion 17, the gas flow is blocked by the partition plate 37, and the gas does not flow downstream from the partition plate 37 (that is, The flow of gas downstream is blocked by the partition plate 37).

  As described above, the operation cell number adjusting unit 36b of the operation control means 36 performs the fuel gas supply manifold in order from the cell C on the upstream side of the cells C not performing the power generation operation as the operation cell number increasing process. The operation of the gas inflow state adjusting unit 35 is started so as to start the inflow of the fuel gas from the unit 15 to the fuel gas channel 13a and the inflow of the oxidant gas from the oxidant gas supply manifold unit 17 to the oxidant gas channel 14a. Controlling the operation of the connection state switching unit 31 so that the cell C to be operated for power generation is connected to the power output circuit unit 32, and performing the power generation operation as the operation cell number reduction process In order from the cell C on the downstream side of C, the inflow of fuel gas from the fuel gas supply manifold section 15 to the fuel gas flow path 13a and the oxidizing gas supply manifold section 17 The operation of the gas inflow state adjusting unit 35 is controlled so as to stop the inflow of the oxidant gas to the oxidant gas flow path 14a, and the cell C for generating operation is connected to the power output circuit unit 32. The operation of the connection state switching unit 31 is controlled.

  In the present embodiment, the partition plate 37 provided in the fuel gas supply manifold portion 15 and the partition plate 37 provided in the oxidant gas supply manifold portion 17 may be operated at the same timing or separately. You may operate at the timing.

<Another embodiment>
<1>
In the above embodiment, the configuration of the fuel cell system can be changed as appropriate.
For example, a transformer, a carbon monoxide remover, or the like may be additionally provided in the power generation unit U1 shown in FIG. That is, in the example shown in FIG. 1, the example in which the reformed gas (gas containing hydrogen as a main component) generated by the reformer 8 is supplied to the cell C of the polymer electrolyte fuel cell is shown. The carbon monoxide contained in the reformed gas is transformed into carbon dioxide using a transformer, and the monoxide remaining in the reformed gas after the transformation treatment is performed using a carbon monoxide remover. You may change so that it may supply to the cell C, after removing carbon.
In addition, the configuration of each gas channel, the configuration of the cooling water channel, the configuration of the hot water channel, and the like shown in FIG.

<2>
In the above embodiment, the set lower limit voltage V _L1 and the set upper limit voltage V _H1 illustrated in FIG. 5 may be changed according to the deterioration state of the cell C. This is because the IV curve indicating the relationship between the current flowing through the cell performing the power generation operation and the cell voltage shifts to the low voltage side (downward in the figure) due to the deterioration of the cell C, and is set accordingly. This is because it is also necessary to shift the lower limit voltage V _L1 and the set upper limit voltage V _H1 .

FIG. 8 is a graph example showing the relationship between the current flowing through the cell performing the power generation operation and the cell voltage before and after the deterioration of the cell. Such an IV curve indicates that the output power is increasing at the start of the polymer electrolyte fuel cell, the output power is decreasing at the time of stopping, or otherwise, the minimum output power to the maximum output power or the maximum output power to the minimum output. It can be acquired when the output is changed to power at once. Here, the set lower limit voltage V _L2 and the set upper limit voltage V _H2 are voltages at which the output power before and after the shift (W = V × I) becomes equal. That is, the operation control means 36 can derive the set lower limit voltage V _L2 and the set upper limit voltage V _H2 after changing according to the deterioration state of the cell C from the relationship of the following formula 2.

[Formula 2]
V _H1 × I _H1 = V _H2 × I _H2
V _L1 × I _L1 = V _L2 × I _L2

<3>
In the said 1st Embodiment, although the partition plate 33 which has each side part 33a demonstrated the example which moves integrally, you may comprise each side part 33a so that a movement is possible separately. Specifically, the fuel gas side portion 33a (the side portion 33a inserted between the fuel gas supply manifold portion 15 and the cell stack CS, the fuel gas discharge manifold portion 16 and the cell stack CS is inserted). And the side portion 33a on the oxidant gas side (the side portion 33a inserted between the oxidant gas supply manifold portion 17 and the cell stack CS, and the oxidant gas discharge manifold portion 18). And the side portion 33a) inserted between the cell stack CS and the cell stack CS. The fuel gas side partition plate 33 (side portion 33a) and the oxidant gas side partition plate 33 (side portion 33a) are configured separately, and the operation control means 36 controls each movement separately. It can be so. For example, when the operation control means 36 shuts off the inflow of gas from the manifold to the fuel gas flow path 13a and the oxidant gas flow path 14a of the cell C, first, the oxidant gas side partition plate 33 (side portion 33a). To control the operation of the partition plate 33 (side portion 33a) on the fuel gas side to control the gas flow into the fuel gas channel 13a. It is also possible to perform a process that blocks the inflow.

<4>
In the above embodiment, the cooling water may or may not flow through the cell C that is not performing the power generation operation.

  The present invention can be used for a polymer electrolyte fuel cell capable of avoiding cell failure.

DESCRIPTION OF SYMBOLS 10 Solid polymer electrolyte membrane 11 Fuel electrode 12 Air electrode 13 Fuel electrode separator 13a Fuel gas flow path 14 Air electrode separator 14a Oxidant gas flow path 36 Operation control means 36a Determination part 36b Operation cell number adjustment part 40 Membrane electrode assembly C Cell CS Cell stack VH1 Setting upper limit voltage VH2 Setting upper limit voltage VL1 Setting lower limit voltage VL2 Setting lower limit voltage

Claims (3)

A membrane electrode assembly comprising a solid polymer electrolyte membrane sandwiched between a fuel electrode and an air electrode, and a fuel gas introduced into the fuel electrode through a fuel gas flow path provided on the fuel electrode side of the membrane electrode assembly A plurality of cells having a fuel electrode separator and an air electrode separator that is provided on the air electrode side of the membrane electrode assembly and introduces an oxidant gas into the air electrode through an oxidant gas flow path. A polymer electrolyte fuel cell comprising a cell stack and an operation control means for controlling operation,
Voltage detecting means for measuring a cell voltage of the plurality of cells,
The operation control means is a polymer electrolyte fuel cell that reduces the number of cells to be operated for power generation as the cell voltage of the cells that are performing the power generation operation measured by the voltage detection means among the plurality of cells increases. . The operation control means includes
A determination unit that determines whether or not the cell voltage of a cell that is in a power generation operation among the plurality of cells is equal to or higher than a predetermined set lower limit voltage and lower than or equal to a set upper limit voltage;
When the determination unit determines that the cell voltage is higher than the set upper limit voltage, an operation cell number reduction process is performed to reduce the number of the cells that perform power generation operation, and the cell voltage is set to the set lower limit voltage by the determination unit. When it is determined that the voltage is lower, the number of operating cells is increased to increase the number of the cells that are in power generation operation, and the determination unit determines that the cell voltage is equal to or higher than the set lower limit voltage and lower than the set upper limit voltage. 2. The polymer electrolyte fuel cell according to claim 1, further comprising an operation cell number adjusting unit that performs an operation cell number maintaining process for maintaining the number of the cells that perform power generation operation as they are. The operation control means includes
While performing the process of increasing the number of operating cells, changing the inflow temperature of the cooling water flowing into the cell stack to a low temperature side, and changing the amount of water contained in the oxidant gas flowing into the cell stack to the decreasing side,
A process for reducing the number of operating cells, changing an inflow temperature of cooling water flowing into the cell stack to a high temperature side, and changing an amount of water contained in the oxidant gas flowing into the cell stack to an increase side. Item 3. The polymer electrolyte fuel cell according to Item 2.

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