JP2007220315A - Fuel cell system, and method for detecting abnormal cell in it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an abnormal state in a unit cell without lowering detection accuracy of a cell voltage. <P>SOLUTION: The block voltage of a fuel cell stack 32 which is a first cell block CB1 forming a fuel cell 10 is detected by a first voltage detecting device 20, unit cells 16 composing the first cell block CB1 are divided among a plurality of second cell blocks CB2 composed of any number of unit cells, respective block voltages are detected by a plurality of second voltage detecting devices 21 respectively, the sum total V2 of the block voltages detected by a plurality of the second voltage detecting devices 21 respectively is subtracted from the block voltage V1 detected by the first voltage detecting device 20, and if the subtracted value is not more than a prescribed abnormality determining reference value, it is determined that a unit cell brought into an abnormal state exists in the first cell block which is the fuel cell stack 32. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that detects an abnormal state of a single cell that constitutes a fuel cell stack, and an abnormal cell detection method for the fuel cell system.

  A fuel cell is composed of a fuel cell stack configured by stacking a plurality of single cells in series.

  Therefore, when an abnormality occurs in one single cell, the single cells are connected in series, so that the influence affects the entire output voltage of the fuel cell stack. Therefore, a technique for determining an abnormal state of a single cell when the cell voltage decreases is disclosed.

For example, a method is disclosed in which it is determined that there is an abnormal cell that has caused a voltage drop when the voltage of a cell block composed of an arbitrary number of cells is equal to or lower than a determination reference value (Patent Document 1). reference.).
JP 2000-285945 A

  Since the general operating voltage of a single cell is about 0.6 V to 1.0 V, in order to detect the voltage of each single cell or a cell block composed of an arbitrary number of single cells, It is desirable that the voltage detection range is about 0 V to 1.5 V, which is a wider range than the operation voltage.

  However, the voltage value of an abnormal single cell is often considerably lower than the voltage detection range per single cell described above.

  Therefore, when the determination voltage for determining the abnormality of the single cell is set within the voltage detection range per unit cell as described above and the determination of the abnormality of the single cell is performed, the range in which the single cell can be stably operated originally. However, there is a problem that it is judged abnormal.

  In order to deal with such problems, if the lower limit value of the voltage detection range of the voltage detection device is expanded, digital values detected in a wide voltage detection range with a limited number of bits will be handled. This causes a new problem that the resolution of the cell voltage is lowered.

  The fuel cell system of the present invention is a first voltage detecting means for detecting a voltage of a first cell block composed of a fuel cell stack in which a plurality of unit cells each made up of a pair of electrodes arranged opposite to each other with an electrolyte membrane interposed therebetween. And a second voltage detecting means for dividing a single cell constituting the first cell block into a plurality of second cell blocks having an arbitrary number and detecting a voltage of each second cell block; When the calculation means for subtracting the sum of the second cell block voltages from the voltage of the cell block and the subtraction value subtracted by the calculation means is equal to or less than the abnormality determination reference value, the first cell block is in an abnormal state. And determining means for determining that there is a single cell.

  The abnormal cell detection method for a fuel cell system according to the present invention is a cell abnormality detection method for a fuel cell system including a fuel cell stack in which a plurality of unit cells each having a pair of electrodes arranged opposite to each other with an electrolyte membrane interposed therebetween. A first voltage detecting step for detecting a voltage of a first cell block constituted by a fuel cell stack, and a plurality of second cells comprising an arbitrary number of single cells constituting the first cell block. A second voltage detection step of dividing the block into blocks and detecting a voltage of each second cell block; a calculation step of subtracting a sum of the second cell block voltages from the first cell block voltage; and the calculation A determination step of determining that there is a single cell in an abnormal state in the first cell block when the subtraction value subtracted by the step is equal to or less than the abnormality determination reference value.

  According to the present invention, an abnormal single cell can be detected while maintaining the voltage of a single cell or cell block so that it can be detected with high resolution.

  In addition, it is not necessary to set the abnormality determination reference value within the range of the voltage detection range, and it is not determined that the single cell is in an abnormal state before it is abnormal, so the maximum range that the single cell performance allows This makes it possible to operate the fuel cell.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a fuel cell system shown as an embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the fuel cell system shown as an embodiment of the present invention includes a fuel cell 10, a first voltage detection device 20 (first voltage detection means), and a second voltage detection device 21 (second voltage). Detection means), a cooling water circulation system 30 for cooling the fuel cell 10, a fuel gas supply system 40, a fuel gas discharge system 41, an oxidant gas supply system 42, an oxidant gas discharge system 43, an inverter 26, The electric load 27 and the control unit 25 that controls the fuel cell system in an integrated manner are provided.

  As shown in FIG. 2, the fuel cell 10 includes a single fuel cell stack 32 (first cell block) in which a plurality of single cells are stacked. The fuel cell stack 32 shown in FIG. 2 will be described in detail later.

  Returning to FIG. 1 again, the configuration of the fuel cell system will be described. The fuel cell 10 generates power by a chemical reaction between fuel gas (hydrogen) supplied to the fuel electrode and oxygen in the oxidant gas (air) supplied to the oxidant electrode. The power generated by the fuel cell 10 is converted into AC power by the inverter 26 and used to drive an electric load 27 such as a motor.

  The cooling water circulation system 30 includes a cooling water circulation pipe 31, a cooling water circulation pump 28, and a radiator 29. One end of the coolant circulation pipe 31 is connected to the coolant outlet of the fuel cell 10, and the other end is connected to the coolant inlet of the fuel cell 10. The cooling water circulation pump 28 is a power source that is disposed on the cooling water circulation pipe 31 and circulates the cooling water flowing through the cooling water circulation pipe 31. The radiator 29 is disposed on the cooling water circulation pipe 31 and cools the cooling water until the temperature of the cooling water reaches a temperature suitable for cooling the temperature of the fuel cell 10.

  FIG. 2 shows a state in which the fuel cell 10 is cut along an AA section. As shown in FIG. 2, the single cell 16 is provided with a catalyst layer (not shown) on both sides of the solid polymer electrolyte membrane 13, respectively, and these are supplied with an anode 11 which is a fuel electrode to which hydrogen gas is supplied, and air. The MEA (Membrane Electrode Assembly) formed by being sandwiched between the cathode 12 which is an oxidant electrode is further sandwiched between the anode separator 14 and the cathode separator 15.

  The anode separator 14 includes a fuel gas channel 17 serving as a path for hydrogen supplied to the anode, and a cooling water channel 19 serving as a cooling water channel supplied from a cooling water circulation system. The cathode separator 15 includes an oxidant gas flow path 18 that is a flow path of air supplied to the cathode.

  Returning to FIG. 1 again, the configuration of the fuel cell system will be described. The fuel gas supply system 40 has one end connected to a hydrogen storage tank (not shown), the other end connected to a fuel gas inlet of the fuel cell 10, and supply of hydrogen as fuel gas supplied to the anode electrode side of the fuel cell 10. It becomes a route. The fuel gas discharge system 41 connects the fuel gas outlet of the fuel cell 10 and the outside, and serves as a discharge path for off-gas discharged from the fuel cell 10.

  The oxidant gas supply system 42 has one end connected to a compressor or the like (not shown), the other end connected to the oxidant gas inlet of the fuel cell 10, and air that is an oxidant gas supplied to the cathode side of the fuel cell 10. Supply route. The oxidant gas discharge system 43 connects the oxidant gas outlet of the fuel cell 10 and the outside, and serves as a path for gas discharged from the fuel cell 10.

  As shown in FIG. 3, the first voltage detection device 20 is electrically connected to both ends of the fuel cell stack 32 that is the first cell block CB <b> 1, and detects the total voltage of the fuel cell stack 32.

  The second voltage detection devices 21 (1) to 21 (n) divide the single cell 16 constituting the first cell block CB1 into a plurality of second cell blocks CB2 (1) to CB2 (n) having an arbitrary number. The voltage of each second cell block CB2 is detected.

  The block voltage of the first cell block CB1 detected by the first voltage detector 20 and the block voltage V (1) of the second cell block CB2 detected by the second voltage detectors 21 (1) to 21 (n). V (n) is output to the control unit 25, and cell abnormality is determined based on an abnormal cell detection method described later.

  Next, the abnormal cell detection method by the fuel cell system shown as an embodiment of the present invention will be specifically described.

  4 is an equivalent circuit of the fuel cell stack 32 and the first voltage detector 20 shown in FIG. Here, for the sake of explanation, it is assumed that the second cell block CB2 is composed of two single cells 16, and the first cell block CB1 is composed of 20 single cells 16 (n = 10). In addition, the voltage detection range of the second voltage detection device 21 that detects the block voltage of the second cell block CB2 is set to 0V to 3.0V. Further, an abnormality determination reference value Vm that is a determination value for determining cell abnormality of the single cell 16 held by the control unit 25 is set to −3V.

  First, the case where the fuel cell system is operating normally will be described.

  As shown in FIG. 5, assuming that each single cell 16 generates power at 0.6 V, the second cell block CB2 (1) to be detected by each second voltage detection device 21 (1) to (10). Since the block voltages V (1) to V (10) of (10) are two single cells 16 connected in series, each becomes 1.2V. The control unit 25 acquires the block voltages V (1) to V (10) of the second cell block CB2 detected by each second voltage detection device 21, and calculates the sum V2. In the example shown in FIG. 5, the total block voltage V2 of the second cell block CB2 detected by the second voltage detection device 21 is 12V (= 1.2V × 10).

  Then, the control unit 25 acquires the block voltage V1 of the first cell block CB1 detected by the first voltage detection device 20, and from the acquired block voltage of the first cell block CB1, the block voltage of the second cell block CB2 Is subtracted. Here, since the fuel cell system is operating normally, the block voltage V1 of the first cell block CB1 is naturally 12V, which matches the sum V2 of the block voltages of the second cell block CB2.

  The control unit 25 compares the subtraction value obtained by subtraction in this way with the abnormality determination reference value Vm held by the control unit 25, and the subtraction value is equal to or less than the abnormality determination reference value Vm. In this case, it is determined that a cell abnormality has occurred in any of the single cells 16 of the fuel cell stack 32.

  Next, a case where some abnormality occurs in the fuel cell system will be described.

  As shown in FIG. 6, it is assumed that the single cells 16 other than the single cell 16a generate power at 0.6V, but the single cell 16a has become -3.6V due to some abnormality. At this time, the value of the second voltage detection device 21 (2) that detects the block voltage of the second cell block CB2 (2) including the single cell 16a has a voltage detection range of 0V to 3.0V. Instead of 3.6V + 0.6V = −3.0V, it becomes 0V which is the lower limit value of the voltage detection range.

  Therefore, the sum V2 of the block voltages of the second cell block CB2 detected by each second voltage detection device 21 calculated by the control unit 25 is 10.8V (= 1.2V × 9 + 0V). On the other hand, the block voltage V1 of the first cell block CB1 detected by the first voltage detection device 20 is 7.8V (= 1.2V × 9−3.0V).

  Accordingly, the subtracted value obtained by subtracting the sum V2 of the block voltages of the second cell block CB2 from the block voltage V1 of the first cell block CB1 by the control unit 25 is V1-V2 = 7.8V-10.8V = -3. 0V, which is below the abnormality determination reference value Vm, which is -3.0V. Therefore, the control unit 25 determines that an abnormality has occurred in the single cell 16 of the fuel cell stack 32.

  Thus, the control unit 25 detects the cell abnormality of the single cell 16 of the fuel cell stack 32, thereby maintaining the voltage detection range of the second cell block CB2 with high accuracy while maintaining the voltage of the second cell block CB2. It is possible to detect an abnormal state of the single cell 16 indicated as being below the lower limit value of the detection range.

  Accordingly, it is not determined that the unit cell 16 of the fuel cell stack 32 is in an abnormal state before the unit cell 16 has an abnormality. Therefore, the fuel cell stack 32, that is, the fuel cell 10 is within the maximum range permitted by the performance of the unit cell 16. Can drive.

  In the present embodiment, the second cell block CB2 is composed of two single cells 16, but the second cell block CB2 may be composed of one single cell 16. Thereby, it is possible to identify a single cell in which an abnormality has occurred.

  Here, the abnormality determination reference value Vm used when the control unit 25 determines the abnormal state of the single cell 16 of the fuel cell stack 32 is set so as to avoid a state that adversely affects the entire fuel cell 10.

  For example, the state in which the entire fuel cell 10 is adversely affected is a state in which the amount of heat generated locally in the fuel cell stack 32 has exceeded the heat amount processing capacity (cooling capacity) of the current coolant circulation system. If the amount of heat generated in the fuel cell stack 32 exceeds the current cooling capacity of the cooling water circulation system, the entire fuel cell 10 is affected, and the single cell 16 of the fuel cell stack 32 is shifted to an abnormal state. There is a possibility.

  By the way, generally, the calorific value of the fuel cell can be expressed by the following equation (1) using a load current applied to the load of the fuel cell system and a cell voltage (single cell voltage).

Fuel cell heat generation [W] = load current [A]
× (ΔH / 2F−single cell voltage) [V] (1)
(However, ΔH: Standard heat of formation, F: Faraday constant.)

  In general, the cooling capacity of the cooling system can be expressed by the following equation (2).

Cooling capacity [Wc] = cooling water flow rate [lpm] × 1000 × cooling water specific gravity [g / cc]
X Specific heat of cooling water [J / g · K] x ΔT [K] / 60 (2)
(However, ΔT: Allowable temperature difference of cooling water.)

  As shown in the equation (1), it can be seen that the calorific value of the fuel cell 10 is proportional to the load current. Further, the state where the heat generation amount of the fuel cell 10 exceeds the known cooling capacity of the cooling water circulation system and adversely affects the entire fuel cell 10 is a case where W> Wc. Therefore, the abnormality determination reference value Vm can be expressed by the following equation (3) using the equations (1) and (2).

Vm = ΔH / 2F−cooling water flow rate × 1000 × cooling water specific gravity × cooling water specific heat × ΔT / (60 × load current) (3)

  That is, it can be seen that the abnormality determination reference value Vm at which the single cell 16 of the fuel cell stack 32 becomes abnormal also depends on the load current. Therefore, by setting the abnormality determination reference value Vm according to the load current from the equation (3), the fuel cell stack 32, that is, the fuel cell 10 can be operated within the maximum range permitted by the performance of the single cell 16. . Accordingly, it is possible to avoid the determination of cell abnormality at a cell voltage that can be stably operated, and to reliably expand the operable range.

  Further, it can be considered that a state that adversely affects the entire fuel cell 10 does not occur unless the amount of heat generated by the fuel cell exceeds the cooling capacity of the cooling water circulation system 30. That is, it can be said that the state that adversely affects the entire fuel cell 10, that is, the state in which the single cell 16 of the fuel cell stack 32 becomes abnormal depends on the cooling capacity of the cooling water circulation system.

  The cooling capacity of the cooling water circulation system can be changed by changing the cooling water flow rate of the circulating cooling water. It can also be seen from the equation (3) that the abnormality determination reference value Vm depends on the coolant flow rate. Accordingly, by setting the abnormality determination reference value Vm according to the cooling water flow rate that determines the cooling capacity of the cooling water circulation system, the fuel cell stack 32, that is, the fuel cell 10 is operated within the maximum range permitted by the performance of the single cell 16. can do. Accordingly, it is possible to avoid the determination of cell abnormality at a cell voltage that can be stably operated, and to reliably expand the operable range.

  Next, the operation of the abnormal cell detection method of the fuel cell system will be described using the flowchart shown in FIG.

  First, in step S <b> 1, the control unit 25 starts the fuel cell system and starts operation of the fuel cell 10.

  In step S2, the control unit 25 acquires the block voltage V1 of the first cell block CB1 detected by the first voltage detection device 20 at a predetermined sampling period.

  In step S3, the control unit 25 acquires the block voltage of the second cell block CB2 detected by each of the second voltage detection devices 21 (1) to 21 (n) at a predetermined sampling period, and calculates the sum V2 thereof. calculate.

  In step S4, the control unit 25 subtracts the sum V2 of the block voltages of the second cell block CB2 acquired in step S3 from the block voltage V1 of the first cell block CB1 acquired in step S2, and an abnormality determination criterion. Compare with the value Vm. When the result of the subtraction is equal to or less than the abnormality determination reference value Vm, the control unit 25 determines that any single cell 16 of the fuel cell stack 32 is abnormal in step S5, and copes with the cell abnormality. Execute the process. Moreover, the control part 25 returns to step S2, when the result of subtraction is larger than the abnormality determination reference value Vm.

  For example, as a process corresponding to a cell abnormality, the control unit 25 determines that the fuel cell 10 is connected to the electric load 27 via the inverter 26 based on the relationship between the abnormality determination reference value Vm and the load current shown in the above equation (3). Control is made to reduce the load current to be supplied, and the amount of heat generated by the fuel cell 10 is reduced. Thereby, since the influence on the fuel cell 10 by heat generation can be avoided, the operation of the fuel cell 10 can be continued. In addition, since the fuel cell 10 can be continuously operated, the operation efficiency can be improved.

  Further, as a process corresponding to a cell abnormality, the control unit 25 increases the number of rotations of the cooling water circulation pump 28 to cool the cooling water based on the relationship between the abnormality determination reference value Vm expressed by the above-described equation (3) and the cooling water amount. The allowable heat quantity of the cooling water circulation system is increased by controlling to increase the water flow rate. Thereby, since the influence on the fuel cell 10 by heat generation can be avoided, the operation of the fuel cell 10 can be continued. In addition, since the fuel cell 10 can be continuously operated, the operation efficiency can be improved.

[Another configuration of the fuel cell 10]
As shown in FIG. 4, the fuel cell 10 used in the fuel cell system is composed of a single fuel cell stack 32. For example, as shown in FIG. 8, a plurality of fuel cell stacks 32 _n (n is a natural number). ).

As shown in FIG. 8, when the number of fuel cell stacks is increased in the fuel cell 10 and a plurality of fuel cell stacks _32n are provided, the first cell block CB1 to be measured by the first voltage detection device 20 is changed. By using a plurality of fuel cell stacks 32 _n connected in series, the function of the first voltage detection device 20 is, for example, power for monitoring power generated by the fuel cell 10 normally provided in the fuel cell system. The monitoring device 50 can be substituted. Thereby, it is not necessary to newly install the first voltage detection device 20, and the fuel cell system can be reduced in size and cost.

As shown in FIG. 8, even when the fuel cell 10, the control unit 25, as in the flowchart shown in FIG. 7, by detecting the cell abnormality of the fuel cell stack 32 _n of the single cell 16, the While maintaining the voltage detection range of the two-cell block CB2 with high accuracy, it is possible to detect an abnormal state of the single cell 16 indicated as a cell voltage equal to or lower than the lower limit value of the voltage detection range of the second cell block CB2.

Therefore, before the single cell 16 of the fuel cell stack 32 _n is causing an abnormality, the abnormality because the state is it is eliminated determined that the fuel cell stack 32 to the maximum extent the performance of the single cell 16 allows _n, that the fuel The battery 10 can be operated.

  The above-described embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and various modifications can be made depending on the design and the like as long as the technical idea according to the present invention is not deviated from this embodiment. Of course, it is possible to change.

It is a principal part schematic block diagram of the fuel cell system shown as embodiment of this invention. It is a figure for demonstrating the structure of a single cell. It is a figure for demonstrating the structure of a fuel cell stack provided with a 1st voltage detection apparatus and a 2nd voltage detection apparatus. It is the figure which showed the equivalent circuit of the voltage detection apparatus. It is the figure which showed the equivalent circuit of the voltage detection apparatus in case the fuel cell system is operate | moving normally. It is the figure which showed the equivalent circuit of the voltage detection apparatus when a fuel cell system is not operating normally. It is a flowchart for demonstrating abnormal cell detection processing operation. It is a figure for demonstrating another structure of a fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell 16 Single cell 16a Single cell 20 1st voltage detection apparatus 21 2nd voltage detection apparatus 25 Control part 29 Radiator 30 Cooling water circulation system 32 Fuel cell stack 32 _n Fuel cell stack

Claims (10)

A fuel cell in which a plurality of unit cells each composed of a pair of electrodes arranged opposite to each other with an electrolyte membrane interposed therebetween;
A first voltage detecting means for detecting a voltage of a first cell block composed of a plurality of single cells among the plurality of single cells;
A second voltage detecting means for detecting a voltage of each of a plurality of second cell blocks composed of one or more single cells obtained by dividing the first cell block;
Arithmetic means for subtracting the sum of the voltages of the second cell block from the voltage of the first cell block;
A fuel cell system comprising: a determination unit that determines that the single cell in an abnormal state exists in the first cell block when a subtraction value subtracted by the calculation unit is equal to or less than an abnormality determination reference value. . The fuel cell system according to claim 1, wherein the abnormality determination reference value is changed according to a load current of the fuel cell system. A cooling means for cooling the fuel cell with cooling water;
The fuel cell system according to claim 1, wherein the abnormality determination reference value is changed according to a flow rate of the cooling water. The fuel cell system according to claim 3, wherein the flow rate of the cooling water is increased when it is determined that the single cell in an abnormal state exists in the first cell block. 5. The load current of the fuel cell system is reduced when it is determined that the single cell in an abnormal state exists in the first cell block. 6. Fuel cell system. The fuel cell system according to any one of claims 1 to 5, wherein the first cell block includes one fuel cell stack. The fuel cell system according to any one of claims 1 to 5, wherein the first cell block includes two or more fuel cell stacks. The fuel cell system according to any one of claims 1 to 7, wherein the second cell block is a single cell. The fuel cell system according to any one of claims 1 to 7, wherein the second cell block includes two or more single cells. A method for detecting an abnormal cell in a fuel cell system comprising a fuel cell stack in which a plurality of unit cells each having a pair of electrodes arranged opposite to each other with an electrolyte membrane interposed therebetween,
A first voltage detecting step of detecting a voltage of a first cell block constituted by the fuel cell stack;
A second voltage detecting step of detecting a voltage of a second cell block constituting the first cell block;
Subtracting the sum of the voltages of the second cell block from the voltage of the first cell block;
And a determination step of determining that the single cell in an abnormal state exists in the first cell block when a subtraction value subtracted by the calculation step is equal to or less than an abnormality determination reference value. Abnormal cell detection method.

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