JP4595367B2 - Deterioration diagnosis method and apparatus for fuel cell - Google Patents

Description

  The present invention relates to a technical field of a fuel cell degradation diagnosis method and apparatus for diagnosing degradation of a fuel cell due to, for example, assembly work or time passage.

  As one of such fuel cell deterioration diagnosis methods, a fuel cell system using an AC impedance method has been proposed (see, for example, Patent Document 1).

  According to the fuel cell system described in Patent Document 1 (hereinafter referred to as “conventional technology”), an AC signal having two different frequencies is applied to the fuel cell, and the fuel cell corresponds to each frequency. Is calculated. In the prior art, it is said that the time-dependent change of the fuel cell can be measured in real time by calculating the frequency characteristic of the impedance of the fuel cell based on the calculated impedance and obtaining the frequency characteristic curve. .

JP 2003-86220 A

  However, according to the research of the present inventors, the conventional technique has the following problems.

  The fuel cell impedance trajectory obtained by the AC impedance method is not a complete semicircle. Therefore, as shown in the prior art, even if an attempt is made to calculate the frequency characteristic curve of the impedance of the fuel cell from two measurement points, the error is extremely large and it is difficult to obtain a highly accurate result. In addition, if precise measurement is performed in the target frequency range, it is possible to obtain a highly accurate frequency characteristic curve. However, a long time is required, and the fuel cell deteriorates due to such measurement. That is, it is practically impossible to diagnose the deterioration of the fuel cell efficiently and with high accuracy by the conventional technology.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a fuel cell deterioration diagnosis method and apparatus for diagnosing fuel cell deterioration efficiently and with high accuracy.

In order to solve the above-described problem, a fuel cell deterioration diagnosis method according to the present invention is applied to a fuel cell driven at a predetermined current density, with frequencies F1, F2 (F1> F2) and F3 (F2> F3). An impedance acquisition step of acquiring at least three complex impedances respectively corresponding to the measurement frequencies in the fuel cell by applying an alternating signal of at least three measurement frequencies including
A resistance value specifying step of specifying at least three resistance values of the fuel cell respectively corresponding to the measurement frequency from the acquired complex impedance;
A diagnosis step of diagnosing deterioration of the fuel cell based on a deterioration diagnosis element that is a predetermined function of the specified resistance value, and the frequency F1 represents the resistance value that defines the complex impedance A frequency characteristic curve of the complex impedance drawn in a measurement frequency range including the measurement frequency and the first axis on a coordinate plane having a first axis and a second axis perpendicular to the first axis and representing a capacitance value Is set to a frequency corresponding to a point that defines a direct current resistance in the fuel cell, and the frequency characteristic curve is partly arcuate and the first factor is dominant. A first region and a second region partly arcuate and a second factor different from the first factor is dominant, and the frequency F2 is determined within the first region, The frequency F3 is The frequencies F2 and F3 are determined in the second region, and the frequencies F2 and F3 are frequencies corresponding to vertices of the arc or points in the vicinity of the vertices in the first region and the second region, respectively. The diagnostic elements include three deterioration diagnostic elements R1, R2-R1, and R3-2R2 + R1, where the resistance values corresponding to the frequencies F1, F2, and F3 are R1, R2, and R3, respectively. It is characterized by.

  According to the method for diagnosing deterioration of a fuel cell according to the present invention, in an impedance acquisition step, an AC signal of at least three measurement frequencies is applied to a fuel cell driven at a predetermined current density, and the measurement frequency is set to each measurement frequency. Corresponding at least three complex impedances are obtained.

  Here, the “fuel cell” according to the present invention may be a fuel cell or a fuel cell stack in which a certain number of fuel cells are stacked.

  The complex impedance is expressed by a resistance value that is a real part and a capacitance value that is an imaginary part. In the resistance value specifying step, at least three resistance values are specified for each measurement frequency. In the diagnosis step, the deterioration of the fuel cell is diagnosed based on the deterioration diagnosis element.

  Here, the “deterioration diagnostic element” is a value defined as a predetermined function of the resistance value. As long as the deterioration diagnosis element is a function of the resistance value, for example, the resistance value itself, a value obtained by performing some arithmetic operation on the resistance value, or a value calculated based on some calculation rule between a plurality of resistance values Any value is acceptable. That is, the “predetermined function” is a concept indicating a value obtained as a result of such an operation rule or the like. The number of deterioration diagnosis elements may be one or plural, and the number thereof is not limited as long as the deterioration of the fuel cell according to the present invention can be diagnosed.

  In the diagnosis step, deterioration of the fuel cell is diagnosed based on the deterioration diagnosis element. Here, the term “deterioration” according to the present invention refers to deterioration such as increase in contact resistance, insufficient gas diffusion, decrease in catalyst activity, or decrease in effective catalyst utilization rate that occurs when a fuel cell is assembled in a stack, It is defined to include all phenomena that include, or have the potential to cause, some degradation in functionality in the fuel cell, including physical or chemical degradation that occurs within the fuel cell due to the change.

  In the present invention, “diagnose” is defined as the purpose of diagnosing the deterioration state of the fuel cell qualitatively or quantitatively, or empirically, experimentally, or simulation based on a deterioration diagnosis element.

  For example, the deterioration of the fuel cell may be diagnosed by comparing a reference value for deterioration diagnosis with the value of the deterioration diagnosis element in advance. Further, by providing a plurality of such reference values, the deterioration state of the fuel cell may be diagnosed in multiple stages. Furthermore, by executing such a diagnosis for all of the fuel cells constituting the fuel cell stack and comparing the deterioration diagnosis elements obtained for each fuel cell between the cells, the deterioration or abnormality is relatively low. The process may be such that a cell estimated to be present is extracted. Such an aspect is efficient because it is possible to remove, adjust, or repair abnormal cells in the stage before actual use.

Here, in particular, in the diagnosis step according to the present invention, since deterioration is diagnosed based on the deterioration diagnosis element, it is not necessary to obtain an impedance frequency characteristic curve by actual measurement or calculation as in the prior art. In addition, since there are at least three measurement frequencies, the fuel cell having any frequency characteristic curve can be handled relatively, and there is no possibility of causing an error as in the prior art. In addition, it is possible to easily set the above-mentioned “predetermined function” in the deterioration diagnosis element so that such an error does not occur. Therefore, it is possible to diagnose the deterioration of the fuel cell with high efficiency and high accuracy.
Further, in the fuel cell deterioration diagnosis method according to the present invention, the frequency F1 defines the complex impedance, the first axis representing the resistance value, and the first axis representing the capacitance value and orthogonal to the first axis. A point defining the DC resistance in the fuel cell, which is an intersection of the frequency characteristic curve of the complex impedance drawn in the measurement frequency range including the measurement frequency and the first axis on a coordinate plane having two axes. Is set to a frequency corresponding to.
Such a coordinate plane is also referred to as a complex impedance plane. When plotting the complex impedance of the fuel cell on this coordinate plane, the locus of the frequency change in this plot is the “frequency characteristic curve” described here. This frequency characteristic curve is also called “Cole-Cole plot”. When this frequency characteristic curve is drawn in a certain frequency range, this curve intersects the first axis, that is, the axis defining the resistance value at a certain frequency. In this embodiment, the frequency F1 is set to a frequency corresponding to this intersection and a point that defines the direct current resistance of the fuel cell. Here, the “DC resistance” is typically a contact resistance.
The frequency F1 giving the direct current resistance is one of the frequencies that can improve the accuracy of the deterioration diagnosis because it does not change even when the fuel cell is exposed to a change with time. That is, when a change occurs in the fuel cell, the difference in resistance value specified at the frequency F1 serves as a guideline indicating the degree of deterioration as it is, so that deterioration diagnosis can be performed with high accuracy.
Note that the frequency F1 may have a property given in advance by experience or simulation, or may be given based on a frequency characteristic acquired in a certain fuel cell. In general, in a fuel cell, if the configuration, structure, or specifications are the same, the frequency characteristics of the impedance in the unused state are constant or do not differ greatly. Therefore, it is sufficient if the frequency characteristics to be used as a reference are known. It is. Therefore, there is no need to acquire frequency characteristics for each measurement as in the prior art, and deterioration of the fuel cell does not occur to the extent that it is regarded as a problem.
Further, in the fuel cell deterioration diagnosis method according to the present invention, the frequency characteristic curve includes a first region in which part of the frequency characteristic curve is circular and the first factor is dominant, and part of the frequency characteristic curve is circular in shape. A second region that is dominated by a second factor different from the one factor, the frequency F2 is determined in the first region, and the frequency F3 is determined in the second region. Is done.
The frequency characteristic curve has a complicated shape as described above, and is generally not a perfect circle. The shape of the frequency characteristic curve also changes depending on the current density when driving the fuel cell. The frequency characteristic curve includes a first region where the first factor is dominant and a second region where the second factor is dominant. Depending on how these regions overlap, The shape of the frequency characteristic also changes.
Here, the first factor is considered to be a reaction resistance when oxygen reacts in the fuel cell, for example, and the second factor is a resistance related to diffusion of oxygen in the fuel cell, for example. it is conceivable that. Depending on the current density condition, these two regions may be identifiable by, for example, a partial arc shape. Therefore, by selecting the frequencies F2 and F3 from these two regions, it becomes easy to determine what causes the deterioration of the fuel cell. As long as the frequencies F2 and F3 are selected from regions in which different factors are dominant, the current density actually used for the deterioration diagnosis of the fuel cell is not limited.
Furthermore, in the fuel cell deterioration diagnosis method according to the present invention, the frequencies F2 and F3 are frequencies corresponding to vertices of the arc or points in the vicinity of the vertices in the first region and the second region, respectively. It is.
As long as the frequencies F2 and F3 are selected from regions in which different factors are dominant, the above-mentioned effects are ensured. For example, these frequencies should be defined at the vertices of an arc appearing in each region. You can also. In this case, like the above-described DC resistance, the frequency that gives the top of the arc is preserved without being affected by the deterioration that has occurred in the fuel cell. Therefore, the error is not easily generated in the deterioration diagnosis of the fuel cell, and the highly accurate deterioration diagnosis is possible.
Note that the “vicinity vicinity” described here is not necessarily strictly a vertex, and is defined to include all points that can be recognized as the vertex of an arc in the frequency characteristic curve.
Furthermore, in the fuel cell deterioration diagnosis method according to the present invention, when the deterioration diagnosis element sets the resistance values corresponding to the frequencies F1, F2, and F3 to R1, R2, and R3, respectively, R1, It includes three degradation diagnostic elements R2-R1 and R3-2R2 + R1.
Here, R1 is the value of the DC resistance described above. Here, in particular, when F2 and F3 are selected from a region in which different factors are dominant, the degree of deterioration according to the first factor depends on the value of R2−R1, and the second degree depends on the value of R3−2R2 + R1. The degree of deterioration related to the factor can be easily diagnosed. Accordingly, it is possible to diagnose deterioration with extremely high efficiency and high accuracy.

In one aspect of the method for diagnosing deterioration of a fuel cell according to the present invention, the diagnosing step diagnoses deterioration of the fuel cell based on a comparison with a previous value of a value of the deterioration diagnosing element. .

A fuel cell often deteriorates with time regardless of the degree of time. Therefore, the impedance of the fuel cell acquired at different times changes with time. Therefore, if such a change with time can be acquired in some form, it is possible to diagnose deterioration that has occurred over time in the fuel cell. Here, if a change occurs in the impedance in the fuel cell, a change also occurs in the resistance value corresponding to this impedance, and also in the value of the deterioration diagnosis element which is a predetermined function of the resistance value. The deterioration of the fuel cell can be diagnosed based on the comparison with the previous value that defines the change over time in the value of the clogging and deterioration diagnosis element. In such a change over time, the magnitude of the time lapse is not limited in any way. For example, in an automobile or the like, it may be a timing interval for periodic inspection, or simply defined as two different times. May be. According to this aspect, it is possible to easily diagnose deterioration with time occurring in the fuel cell.

  In another aspect of the fuel cell deterioration diagnosis method according to the present invention, the diagnosis step diagnoses deterioration of the fuel cell based on a relative comparison between a value of the deterioration diagnosis element and a reference value.

  The “reference value” described here is not limited in any way as long as it can be compared with the value of the deterioration diagnosis element. If the numerical value that can be the reference value is known empirically or by simulation or the like, it may be such a numerical value, or a deterioration diagnosis element in the deterioration diagnosis performed at an arbitrary time May be the value.

  According to this aspect, it is possible to diagnose the deterioration by comparing the value of the deterioration diagnosis element with the reference value. Therefore, it is possible to diagnose the deterioration of the fuel cell clearly and promptly.

  Further, in this aspect, the reference value may be a value of the deterioration diagnosis element in the diagnosis process executed at an initial stage or a reference time.

  Here, “initial stage” refers to a stage before full-scale power generation of the fuel cell. It is possible to promptly diagnose the deterioration of the fuel cell by setting the value of the deterioration diagnosis element obtained when performing the deterioration diagnosis of the fuel cell at such a stage, for example, as a reference value or a reference value. .

In another aspect of the method for diagnosing deterioration of a fuel cell according to the present invention, the fuel cell further includes a characteristic acquisition step of acquiring the frequency characteristic curve in advance for the fuel cell, wherein the frequencies F1, F2, and F3 are acquired. Determined based on the frequency characteristic curve.

According to this aspect, in the characteristic acquisition step, the frequency characteristic curve of the impedance of the fuel cell is acquired. However, this frequency characteristic curve is for determining the frequencies F ₁ , F _2, and F ₃ , and does not promote the deterioration of the fuel cell because the acquisition of the frequency characteristic curve itself is not intended. To the extent possible. Further, after the measurement frequency is determined, it is not necessary to acquire such frequency characteristics, so there is little possibility that the fuel cell will deteriorate. On the other hand, it is very effective because an appropriate measurement frequency can be selected by determining the measurement frequency after acquiring the frequency characteristics in advance.

In another aspect of the method for diagnosing deterioration of a fuel cell in which the frequency F ₁ is a frequency corresponding to a point defining a DC resistance, the measurement frequency includes the frequency F ₄ (F ₃ > F ₄ ), and the frequency F ₄ Is a frequency corresponding to the intersection of the frequency characteristic curve and the first axis.

In this embodiment, it comprises a frequency F ₄ as the measurement frequency. Frequency F ₄ is an intersection between the frequency characteristic curve a first shaft, which is different from the intersection to the DC resistance R _1. By increasing the measurement frequency in this way, the approximation accuracy of the frequency characteristic curve is improved, so that the accuracy relating to the deterioration diagnosis of the fuel cell is further improved. When the frequency F ₄ is included in the measurement frequency in this way, assuming that the resistance value corresponding to the frequency F ₄ is R ₄ , for example, direct comparison of R ₄ is used for diagnosis of deterioration of the fuel cell. Is possible.

  In another aspect of the method for diagnosing deterioration of a fuel cell according to the present invention, when the fuel cell is deteriorated as a result of diagnosing the deterioration of the fuel cell, notification for notifying the presence of the deteriorated fuel cell The method further includes a step.

  For example, when a fuel cell is mounted in an automobile or the like, deterioration may proceed to a level where there is a problem in actual use only by periodic inspection and maintenance or inspection and maintenance based on the travel distance. It is done. In such a case, the deterioration diagnosis of the fuel cell according to the present invention may be performed in the mounted state, for example, automatically or at regular intervals.

  This aspect is particularly suitable for such cases, and when the fuel cell is in some deterioration state as a result of the deterioration diagnosis step, this is notified by the notification step, so whether or not the fuel cell has deteriorated in real time. It becomes possible to know.

In order to solve the above-described problem, a fuel cell deterioration diagnosis apparatus according to the present invention has frequencies F1, F2 (F1> F2) and F3 (F2> F3) for a fuel cell driven at a predetermined current density. From the acquired complex impedance, impedance acquisition means for acquiring at least three complex impedances respectively corresponding to the measurement frequency in the fuel cell by applying an alternating signal of at least three measurement frequencies including Diagnosing deterioration of the fuel cell based on a resistance value specifying means for specifying at least three resistance values of the fuel cell respectively corresponding to the measurement frequency and a deterioration diagnosis element which is a predetermined function of the specified resistance value ; and a diagnostic means for the frequency F1 defines the complex impedance, the first axis representing the resistance value, And an intersection of the frequency characteristic curve of the complex impedance drawn in the measurement frequency range including the measurement frequency and the first axis on a coordinate plane orthogonal to the first axis and having a second axis representing the capacitance value. The frequency characteristic curve is set to a frequency corresponding to a point that defines a direct current resistance in the fuel cell, and the frequency characteristic curve is a first region in which a part of the frequency characteristic curve is circular and the first factor is dominant, And a second region in which a second factor different from the first factor dominates while partly forming an arc, the frequency F2 is determined within the first region, and the frequency F3 is , Determined in the second region, and the frequencies F2 and F3 are frequencies corresponding to vertices of the arc in the first region and the second region, respectively, or points near the vertex, The deterioration diagnosis element is When the resistance value corresponding to each of the numbers F1, F2 and F3 was respectively R1, R2 and R3, characterized in that it comprises a three deterioration diagnosis element as R1, R2-R1, and R3-2R2 + R1.

  According to such a deterioration diagnosis apparatus, it is possible to execute the deterioration diagnosis as described above, and therefore it is possible to efficiently and accurately diagnose the deterioration of the fuel cell.

  Such an operation and other advantages of the present invention will be clarified by embodiments described below.

Hereinafter, a fuel cell deterioration diagnosis method according to an embodiment of the present invention will be described with reference to the drawings.
<Embodiment>
<Configuration of measurement system 100>
First, a measurement system for realizing the method for diagnosing deterioration of a fuel cell according to this embodiment will be described with reference to FIG. FIG. 1 is a circuit configuration diagram of the measurement system 100.

  In FIG. 1, a measurement system 100 is configured by connecting a fuel cell 10 to a measurement device 110 that is an example of a “fuel cell deterioration diagnosis device” according to the present invention.

  The fuel cell 10 is an example of a “fuel cell” according to the present invention, and is a cell of a polymer electrolyte fuel cell. In the present embodiment, the fuel cell 10 is a component of a fuel cell stack (not shown) in which N fuel cells 10 are stacked. Here, the fuel cell 10 will be described with reference to FIG. FIG. 2 is a cross-sectional structure diagram of the fuel battery cell 10. For example, the measuring device 110 is connected to the fuel cell 10 as shown in FIG. 1 during periodic inspection, installation, or failure of the fuel cell 10 in an inspection facility such as a service station or a home garage.

  In FIG. 2, the fuel cell 10 has an electrolyte membrane 11 made of an ion exchange membrane that spreads in a plane perpendicular to the paper surface. An anode electrode 14 composed of a catalyst layer 12 and a diffusion layer 13 is formed on one surface of the electrolyte membrane 11, and a cathode electrode 17 composed of a catalyst layer 15 and a diffusion layer 16 is formed on the other surface. The anode electrode 14, the cathode electrode 17, and the electrolyte membrane 11 sandwiched between these two electrodes form a membrane-electrode assembly 18.

  The fuel gas channel 19 is a channel for supplying fuel gas (usually hydrogen gas) to the anode electrode 14. The oxidant gas flow path 20 is a flow path for supplying an oxidant gas (usually air) to the cathode electrode 17. The fuel gas flow path 19 includes a plurality of partial flow paths extending in a direction perpendicular to the paper surface in FIG. 2 and arranged in parallel, or a single flow extending in a meandering manner in series. Consists of roads. Similarly, the oxidant gas flow path 20 includes a plurality of partial flow paths or a flow path extending in a meandering manner. Further, the fuel gas channel 19 and the oxidant gas channel 20 may extend in directions intersecting each other. The membrane-electrode assembly 18, the fuel gas channel 19 and the oxidant gas channel 20 are covered from both sides by a separator 21 for separating the fuel cell 10 from a fuel cell (not shown) adjacent thereto. Refrigerant flow paths 22 are formed at both ends of the separator 21. The refrigerant flow path 22 also includes a plurality of partial flow paths or a flow path extending in a meandering manner.

  In the above configuration, the hydrogen gas supplied to the diffusion layer 13 is separated into electrons and hydrogen ions by the catalyst layer 12. Such electrons reach the cathode electrode 17 from the anode electrode 14 through an external circuit (not shown), and hydrogen ions move to the cathode electrode 17 through the electrolyte membrane 11. On the other hand, in the cathode electrode 17, oxygen molecules in the air supplied to the diffusion layer 16 receive electrons that have passed through the external circuit and become oxygen ions, and further combine with hydrogen ions to be discharged as water. The The fuel battery cell 10 generates power in this way.

  When the above-described fuel cell stack is configured, the refrigerant flow paths 22 provided in the separator 21 face each other, that is, between the two fuel battery cells 10 adjacent to each other. Laminated to be shared.

  Returning to FIG. 1, the measuring apparatus 110 includes an AC signal source 111 and a load 112 connected in series between the anode electrode 14 and the cathode electrode 17 of the fuel cell 10, and an impedance analyzer 113 inserted in parallel with the load 112. And a deterioration diagnosis unit 114 connected to the impedance analyzer 113.

  The impedance analyzer 113 includes an impedance measuring unit 113a and a resistance value specifying unit 113b. The impedance measurement unit 113a can sequentially measure the complex impedance of the fuel cell 10 corresponding to the frequency of the AC signal source 111, and functions as an example of the “impedance acquisition unit” according to the present invention. An example of the “impedance acquisition process” according to the invention is executed.

  The resistance value specifying unit 113b can sequentially specify the resistance value corresponding to each of the complex impedances measured by the impedance measuring unit 113a, and functions as an example of the “resistance value specifying unit” according to the present invention. Alternatively, an example of the “resistance value specifying step” according to the present invention is executed.

  The degradation diagnosis unit 114 includes an AC signal source 111, an impedance analyzer 113, a CPU (Central Processing Unit) 115 that performs higher-level control of each unit described later of the degradation diagnosis unit 114, and a memory 116. The memory 116 can store (store) the above-described resistance value of the fuel cell 10 specified by the resistance value specifying unit 113b in accordance with the control of the CPU 115, for example, a nonvolatile memory such as an HDD (Hard Disk Drive). It is a storage medium. The deterioration diagnosis unit 114 functions as an example of “diagnosis means” according to the present invention.

  The anode electrode 14 and the cathode electrode 17 may be connected to the measuring device 110 via, for example, current collecting plates provided on these two electrodes.

  Under such a configuration, an alternating current signal is applied from the alternating current signal source 111 to the fuel cell 10 driven at a constant current density, and the impedance of the fuel cell 10 at the frequency of the alternating current signal is measured by the impedance analyzer 113. Complex impedances are sequentially measured, and resistance values corresponding to the complex impedances are specified. In the deterioration diagnosis unit 114, a deterioration diagnosis process described later is executed based on this resistance value.

Note that the measurement system 100 is configured so that the CPU 115 can sequentially switch and measure the fuel cells 10 to be measured for N cells, but in FIG. 1, only a single fuel cell 10 is shown. It is shown.
<Details of degradation diagnosis processing>
<A: Details of initial deterioration diagnosis processing>
Next, details of the initial deterioration diagnosis process, which is an aspect of the deterioration diagnosis process according to the present embodiment, will be described with reference to FIG. FIG. 3 is a flowchart of the initial deterioration diagnosis process. The initial deterioration diagnosis process is, for example, a process of diagnosing initial deterioration (defect) of the N fuel cells 10 constituting the fuel cell stack before the fuel cell stack is shipped.

  In FIG. 3, first, the frequency of the AC signal source 111 for performing impedance measurement is determined (step S201). Specifically, the CPU 115 performs impedance measurement based on the AC impedance method for any one fuel cell 10. That is, step S201 is an example of the “characteristic acquisition step” according to the present invention.

  Details of step S201 will be described with reference to FIG. FIG. 4 is a schematic diagram of an impedance frequency characteristic curve 200 in the fuel cell 10.

In FIG. 4, the X-axis represents the resistance value, and the Y-axis represents the capacitance value. The frequency characteristic curve 200 intersects the X axis at the frequencies F ₁ and F ₄ , and the readings, that is, the resistance values at the respective intersections are R ₁ and R ₄ . Among these, the resistance value R ₁ that is the intersection on the high frequency side represents the direct current resistance of the fuel cell 10.

  The frequency characteristic curve 200 can be distinguished into two regions. The first region on the high frequency side is a region in which the impedance is determined mainly by the resistance of the reaction when oxygen reacts in the fuel cell 10. This is an example of a “first region in which factors are dominant”. Further, the second region on the low frequency side is a region in which the impedance is determined mainly due to the resistance when oxygen diffuses, and the “second factor is dominant according to the present invention. It is an example of a “second region”. Each of these two regions has an arc shape.

In FIG. 4, the frequency F ₂ is a frequency corresponding to the vicinity of the top of the arc in the first region, and similarly, the frequency F ₃ is a frequency corresponding to the vicinity of the top of the arc in the second region. The resistance values corresponding to the frequencies F ₂ and F ₃ are R ₂ and R ₃ , respectively.

In the present embodiment, the CPU 115 selects these three frequencies F ₁ , F ₂ and F ₃ as the measurement frequency of the fuel cell 10.

The measurement frequency may be any point on the frequency characteristic curve 200. For example, the frequency F ₄ corresponding to the resistance value R ₄ in the frequency characteristic curve 200 (that is, an example of “frequency F ₄ ” according to the present invention) may be used. However, the frequency corresponding to the point defining the direct current resistance (that is, the resistance value R ₁ ), the frequency corresponding to the apex on the arc of the first region, and the apex on the arc of the second region are the progress of deterioration. It is suitable for diagnosing deterioration with high accuracy since it is generally preserved regardless of the presence or absence of this.

  Further, in step S201, the frequency characteristic curve 200 has a property acquired for determining the measurement frequency, and the measurement frequency range and the measurement frequency interval are not limited as long as the determination is possible. . Further, such acquisition of the frequency characteristic curve 200 may be performed for only one arbitrary fuel cell 10, and therefore the deterioration of the fuel cell 10 does not proceed by the impedance measurement according to step S <b> 201. In other words, step S201 is executed within a range in which such deterioration does not proceed.

  Note that the measurement frequency may be determined in advance by, for example, simulation or the like without accompanying such actual measurement. Further, as already described, since the impedance characteristics are unlikely to differ between the fuel cells if the specifications are the same, there is data that can be substituted for the frequency characteristic curve of the impedance of the fuel cells 10 according to the present embodiment. If obtained in advance, the measurement frequency may be determined based on such data.

Returning to FIG. 3, when the measurement frequencies F ₁ , F _2, and F ₃ are determined, the CPU 115 sets a counter i indicating the fuel cell 10 to be processed to “1” (step S 202), and A counter g indicating the measurement frequency is set to “1” (step S203).

Next, the CPU 115 measures the impedance Z _g corresponding to the g th frequency (that is, the frequency F _g ) in the i th fuel cell 10 (step S204). For example, here, the impedance Z ₁ of the frequency F _{1 in} the _first fuel cell 10 is measured. Step S204 is an example of the “impedance acquisition step” according to the present invention.

When the impedance _{Z g} is measured, CPU 115 identifies the resistance value _{R g} corresponding to _{Z g} (step S205), and stores that value in the memory 116 (step S206). In the memory 116, the resistance value R _g is stored as a resistance value corresponding to the g-th frequency in the i-th fuel cell 10. Step S205 is an example of the “resistance value specifying step” according to the present invention.

  Next, the CPU 115 increments the counter g by “1” (step S207), and at the same time, the impedance measurement is performed for the three measurement frequencies determined in step S201 as to whether the value of the counter g is “4”. It is determined whether or not the processing has been completed (step S208).

If there is a frequency that has not been measured (step S208: NO), the CPU 115 returns the process to step S204, and the process from step S204 to step S208 is repeated. Thus, in the i-th fuel cell 10, the resistance value _{R g} corresponding to all the measurement frequency _(F 1, _{F 2} and _{F 3)} is stored in the memory 116 (step S208: YES), the CPU 115, from resistance value _{R g} stored in the memory 116, it calculates a degradation diagnostic element (step S209). It should be noted that R _g stored in the memory 116 at this time is the DC resistance R ₁ , the resistance value R ₂ corresponding to the vertex of the arc in the first region, and the vertex of the arc in the second region. that is the resistance value R ₃ equivalent.

In the present embodiment, the deterioration diagnosis element is defined as “R ₁ ”, “R ₂ −R ₁ ”, and “R ₃ −2R ₂ + R ₁ ” using these R ₁ , R _2, and R ₃ . When the calculation of these three deterioration diagnosis elements is completed, the CPU 115 stores these values in the memory 116. (Step S210). The memory 116 stores the stored deterioration diagnosis element value as the deterioration diagnosis element value for the i-th fuel cell 10. The deterioration diagnosis element is not limited to the embodiment exemplified here, and may be a value expressed as a function of the resistance value _Rg . However, the deterioration diagnosis element according to the present embodiment is effective because the factor of deterioration can be specified to some extent. As the measurement frequency, when the above-mentioned frequency F ₄ is further selected by comparing the resistance value R ₄ corresponding to the frequency F ₄ directly, it may determine the presence or absence of degradation.

  Next, the CPU 115 increments the counter i by “1” and whether the value of the counter i is “N + 1”, that is, whether the calculation of the deterioration diagnosis element has been completed for all N fuel cells 10. It is determined whether or not (step S212).

  When there is a fuel cell 10 that has not been subjected to the calculation of the deterioration diagnosis element (step S212: NO), the CPU 115 returns the process to step S203 and performs the processes from step S203 to step S212 in all N pieces. Repeat for the fuel cell 10. When the calculation of the deterioration diagnosis elements is completed for the N fuel cells 10 and they are stored in the memory 116 in a form individually associated with the fuel cells 10 (step S212: YES), the CPU 115 Then, the values of the deterioration diagnosis elements are compared among all the fuel cells 10 (step 213).

  The CPU 115 diagnoses whether there is a deteriorated cell based on the comparison result of the deterioration diagnosis element values (step S214). When diagnosing deterioration, the CPU 115 calculates an average value of the values of the individual deterioration diagnosis elements among all N cells. It is diagnosed that the fuel cell 10 having the deterioration diagnosis element having a large deviation from the average value is deteriorated. Note that the criterion for deterioration diagnosis in step S214 may be any as long as it is made based on comparison of deterioration diagnosis elements. A reference value for deterioration diagnosis is given in advance by empirical or simulation, and deterioration diagnosis may be performed by comparing the reference value with the value of the deterioration diagnosis element of each cell. Further, the magnitude of the deviation used for the deterioration diagnosis may be freely determined.

  The deterioration of the fuel cell 10 that is found as a result of the diagnosis in this way is different from the deterioration over time due to actual use, for example, and is mainly caused by the initial deterioration that occurs in each fuel cell 10 when the fuel cell 10 is assembled in the stack. It is. Examples of such initial deterioration include deterioration such as an increase in contact resistance, insufficient gas diffusion, a decrease in catalyst activity, or a decrease in catalyst utilization efficiency. Step S214 is an example of the “diagnostic process” according to the present invention.

  When the CPU 115 diagnoses that there is no deteriorated fuel cell 10 (step S214: NO), the CPU 115 determines the value of the deterioration diagnosis element of each fuel cell 10 currently stored in the memory 116 as a reference. Is stored again as the value of the deterioration diagnosis element (step S218).

  Further, when the CPU 115 determines that there is a deteriorated fuel cell 10 (step S214: YES), the CPU 115 notifies the outside of the existence of the fuel cell 10 determined to be deteriorated (step S215). At this time, information (for example, a cell number or the like) specifying the fuel cell 10 determined to be deteriorated is notified together. That is, step S215 is an example of the “notification process” according to the present invention.

  The fuel cell 10 notified of the deterioration is re-diagnosed (step S217) after being repaired or replaced, for example (step S216). Specifically, the process from step S203 to step S210 is re-executed only for the cell, and the average value of the deterioration diagnosis element values between cells is newly calculated based on the newly obtained deterioration diagnosis element value. Is calculated and deterioration is diagnosed. Such a process is repeated until it is diagnosed that there is no deteriorated cell. Note that, in order to prevent complication of the drawing, in FIG. 3, a portion related to the repetition of the rediagnosis process is omitted.

Finally, if it is diagnosed that there is no deterioration for all N fuel cells, the process proceeds to step S218. The CPU 115 stores the value of the deterioration diagnosis element in each fuel cell 10 at that time in the memory 116 as the value of the final deterioration diagnosis element, that is, the value of the reference deterioration diagnosis element, and the initial deterioration diagnosis process is performed. finish.
<B: Details of the deterioration diagnosis process over time>
In addition to the initial deterioration as described above, the fuel battery cell 10 deteriorates to some extent with time. Next, a time-dependent deterioration diagnosis process, which is another aspect of the deterioration diagnosis process according to the present embodiment, for diagnosing such deterioration over time will be described with reference to FIG. FIG. 5 is a flowchart of the deterioration diagnosis process with time. In the figure, the same parts as those in FIG. In addition, the timing at which the deterioration diagnosis process with time is executed differs depending on the specification application and usage status of the fuel cell 10 or the fuel cell stack.

  In FIG. 5, the process from step S202 to step S210 is the same as that in FIG. In the time-dependent deterioration diagnosis process, the measurement frequency is equal to the above-described initial deterioration diagnosis process, and therefore it is not necessary to determine the measurement frequency again.

  In FIG. 5, when the deterioration diagnosis element for the i-th fuel cell 10 is stored in the memory 116 (step S <b> 210), the CPU 115 stores the reference deterioration diagnosis element for the fuel cell 10 stored in the memory 116. Is compared with the value of the deterioration diagnosis element (step S301), and it is diagnosed whether or not the i-th fuel cell 10 is deteriorated (step S302). At this time, the diagnosis of deterioration is performed based on the deviation between the value of the deterioration diagnosis element obtained at that time and the value of the reference deterioration diagnosis element. In addition, the standard value of the deviation determined that the fuel cell 10 is deteriorated may be given in advance as a reference value.

  When it is diagnosed that the i-th fuel cell 10 is deteriorated (step S302: YES), the CPU 115 temporarily stores the cell number in the memory 116 (step S303) and shifts the process to step S211. Let On the other hand, when it is determined that the i-th fuel cell 10 has not deteriorated (step S302: NO), the process proceeds to step S211 as it is.

  When the counter i is incremented in step S211, it is determined whether or not there has been a diagnosis of deterioration over time for all N fuel cells 10 (step S212). If there is a fuel cell 10 that has not been diagnosed for deterioration over time (step S212: NO), from step S203 until all N fuel cells 10 are diagnosed for the presence of deterioration over time. When the process up to step S212 is repeated and the presence or absence of deterioration over time is diagnosed for all N fuel cells 10 (step S212: YES), the CPU 115 stores the deterioration over time stored in the memory 116. The number of the fuel cell 10 diagnosed as being present is notified to the outside (step S215), and the temporal deterioration diagnosis process ends. That is, the time-dependent deterioration diagnosis process is different from the initial deterioration diagnosis process mainly in that a comparison related to the deterioration diagnosis is performed in one fuel cell 10.

  Here, the value of the deterioration diagnosis element is compared with the value of the reference deterioration diagnosis element described above, but the comparison target is not limited to this. For example, when the time deterioration diagnosis process is repeatedly performed as in a periodic inspection, the value of the deterioration diagnosis element obtained in the previous time deterioration diagnosis process may be used as a comparison control.

  Here, with reference to FIG. 6, a time-dependent deterioration diagnosis process will be supplementarily described. FIG. 6 is a diagram showing the result of executing the deterioration diagnosis process with time on the complex plane. 6 is a complex impedance plane similar to FIG.

FIG. 6 shows the result of the time-dependent deterioration diagnosis process performed at any time T _A , T _B and Tc for any fuel cell 10 constituting the fuel cell stack. In the figure, R ₁ , R ₂ and R ₃ obtained at time T _A are R _1A , R _2A and R _3A , respectively, and similarly, R _1B , R _2B and R _3B , at time T _B , and _R 1C at time _{T C, R 2C,} and _{R 3C} are obtained respectively.

  As shown in FIG. 6, the result of executing the temporal deterioration diagnosis process according to the present embodiment is shown as scattered points on the complex impedance plane. Therefore, compared with the case where the frequency characteristic curve as shown in FIG. 4 is repeated for each deterioration diagnosis process or for each fuel cell 10, the processing time required for the deterioration diagnosis of the fuel cell 10 is 1/5. It is about 1/10, and efficient diagnosis of deterioration is possible.

Also, as shown in FIG. 4, F ₁ represents the direct current resistance of the fuel cell 10, F ₂ is a measurement frequency selected from the first region, and F ₃ is a measurement selected from the second region. Because of the frequency, the deterioration of the fuel cell 10 can be diagnosed with high accuracy by the value of the deterioration diagnosis element generated from these resistance values.

For example, if the difference between R _1A and R _1C is large, that is, the contact resistance in the fuel cell 10 is deteriorated, and if the difference between R _2A -R _1A and R _2C -R _1C is large, the first factor That is, it can be diagnosed that some deterioration relating to the reaction of oxygen is in progress. Furthermore, if the difference between R _3A -2R _2A + R _1A and R _3C -2R _2C + R _1C is large, it can be diagnosed that the second factor, that is, some deterioration relating to oxygen diffusion is in progress.

  In this way, by selecting the measurement frequency from a region where the main dominating factors are different, it is possible not only to diagnose the presence / absence of deterioration of the fuel cell 10 but also to specify the deterioration factor to some extent. This makes it possible to take appropriate measures according to the deterioration factors.

  For example, when the fuel cell stack is mounted on the vehicle, it is difficult to perform the deterioration diagnosis at an arbitrary timing. In such a case, the measuring device 110 may be mounted on the car. This on-board measuring device 110 can continuously monitor the deterioration of the fuel cell.

  The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and deterioration of the fuel cell accompanying such changes. Diagnostic methods and devices are also within the scope of the present invention.

1 is a configuration circuit diagram of a measurement system 100 according to an embodiment of the present invention. 1 is a cross-sectional structure diagram of a fuel cell 10 according to an embodiment of the present invention. It is a flowchart of the initial stage deterioration diagnosis process which concerns on embodiment of this invention. It is a schematic diagram of the frequency characteristic curve 200 which concerns on an initial stage deterioration diagnosis process. It is a flowchart of a time-dependent deterioration diagnostic process which concerns on embodiment of this invention. It is the figure which represented the result of the time degradation diagnosis process on the complex plane.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 100 ... Measurement system, 110 ... Measuring apparatus, 111 ... AC signal source, 112 ... Load, 113 ... Impedance analyzer, 113a ... Impedance measuring part, 113b ... Resistance value specific | specification part, 114 ... Deterioration diagnostic part, 115 ... CPU, 116 ... memory. 200: Frequency characteristic curve.

Claims (8)

By applying an AC signal of at least three measurement frequencies including frequencies F1, F2 (F1> F2) and F3 (F2> F3) to a fuel cell driven at a predetermined current density, the fuel cell An impedance acquisition step of acquiring at least three complex impedances respectively corresponding to the measurement frequencies;
A resistance value specifying step of specifying at least three resistance values of the fuel cell respectively corresponding to the measurement frequency from the acquired complex impedance;
Diagnosing deterioration of the fuel cell based on a deterioration diagnosis element that is a predetermined function of the identified resistance value , and
The frequency F1 is a measurement including the measurement frequency on a coordinate plane having a first axis representing the complex impedance and representing a resistance value, and a second axis perpendicular to the first axis and representing a capacitance value. A frequency characteristic curve drawn in a frequency range and an intersection of the frequency characteristic curve of the complex impedance and the first axis, and set to a frequency corresponding to a point defining a direct current resistance in the fuel cell;
The frequency characteristic curve includes a first region in which a part is circular and the first factor is dominant, and a second factor that is partly circular and is different from the first factor is dominant. Has two regions,
The frequency F2 is determined in the first region,
The frequency F3 is determined in the second region,
The frequencies F2 and F3 are frequencies corresponding to vertices of the arc or points in the vicinity of the vertices in the first region and the second region, respectively.
The deterioration diagnosis element includes three deterioration diagnosis elements R1, R2-R1, and R3-2R2 + R1 when the resistance values corresponding to the frequencies F1, F2, and F3 are R1, R2, and R3, respectively. Include
A method for diagnosing deterioration of a fuel cell. 2. The fuel cell deterioration diagnosis method according to claim 1, wherein the diagnosis step diagnoses deterioration of the fuel cell based on a comparison of a value of the deterioration diagnosis element with a previous value . 2. The fuel cell deterioration diagnosis method according to claim 1, wherein the diagnosis step diagnoses deterioration of the fuel cell based on a relative comparison between a value of the deterioration diagnosis element and a reference value. 3. The fuel cell deterioration diagnosis method according to claim 3, wherein the reference value is a value of the deterioration diagnosis element in the diagnosis step executed at an initial stage or a reference time. The fuel cell further includes a characteristic acquisition step of acquiring the frequency characteristic curve in advance,
The method for diagnosing deterioration of a fuel cell according to any one of claims 1 to 4 , wherein the frequencies F1, F2, and F3 are determined based on the acquired frequency characteristic curve. The measurement frequency includes a frequency F4 (F3> F4),
Said frequency F4 is the fuel cell process of degradation diagnosis according to claim 1, any one of 5, which is a frequency corresponding to the intersection between the said frequency characteristic curve first axis. The fuel result of diagnosing the deterioration of the battery, when the fuel cell is deteriorated, the deteriorated the presence of the fuel cell are from claim 1, characterized by further comprising a notification step of notifying 6 The fuel cell deterioration diagnosis method according to any one of the preceding claims. By applying an AC signal of at least three measurement frequencies including frequencies F1, F2 (F1> F2) and F3 (F2> F3) to a fuel cell driven at a predetermined current density, the fuel cell Impedance acquisition means for acquiring at least three complex impedances respectively corresponding to the measurement frequencies;
Resistance value specifying means for specifying at least three resistance values of the fuel cell respectively corresponding to the measurement frequency from the acquired complex impedance;
Diagnostic means for diagnosing degradation of the fuel cell based on a degradation diagnostic element that is a predetermined function of the identified resistance value , and
The frequency F1 is a measurement including the measurement frequency on a coordinate plane having a first axis representing the complex impedance and representing a resistance value, and a second axis perpendicular to the first axis and representing a capacitance value. A frequency characteristic curve drawn in a frequency range and an intersection of the frequency characteristic curve of the complex impedance and the first axis, and set to a frequency corresponding to a point defining a direct current resistance in the fuel cell;
The frequency characteristic curve includes a first region in which a part is circular and the first factor is dominant, and a second factor that is partly circular and is different from the first factor is dominant. Has two regions,
The frequency F2 is determined in the first region,
The frequency F3 is determined in the second region,
The frequencies F2 and F3 are frequencies corresponding to vertices of the arc or points in the vicinity of the vertices in the first region and the second region, respectively.
The deterioration diagnosis element includes three deterioration diagnosis elements R1, R2-R1, and R3-2R2 + R1 when the resistance values corresponding to the frequencies F1, F2, and F3 are R1, R2, and R3, respectively. Include
A fuel cell deterioration diagnosis device characterized by the above.

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