Electrolysis system and method for diagnosing electrolysis system

Abstract

To easily diagnose the state of an electrolysis stack.SOLUTION: The electrolysis system includes an electrolysis stack 10 that generates a desired gas by electrolysis of a raw material compound, a power conversion device 6 that applies a voltage to the electrolysis stack 10, a voltage sensor 7 that measures the voltage applied to the electrolysis stack 10, a diagnostic device 20 that calculates an index defined by the capacitance component of the electrolysis stack using time-series data of the voltage acquired by the voltage sensor 7 when a voltage is applied to the electrolysis stack 10 and diagnoses the state of the electrolysis stack by comparing the calculated index value with a reference value, and an output device 30 that outputs or displays the results of the diagnosis made by the diagnostic device to the outside.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolysis system and a method for diagnosing an electrolysis system. [Background technology]

[0002] Changes in energy usage toward carbon neutrality are now becoming a global trend, with transitions underway on both the power generation and energy consumption sides. Decarbonization in industry is first advanced through the electrification of heat sources. However, due to the amount of heat required and transportation demand, electrification does not necessarily solve all the problems, and expectations are rising for decarbonized fuels. Because hydrogen does not emit carbon dioxide during the combustion process, there are high expectations for the development of production technologies and technologies for its utilization. In particular, large-scale water electrolysis systems are attracting attention as a means of stably mass-producing hydrogen while suppressing carbon dioxide emissions.

[0003] Large-scale water electrolysis systems are made up of many electrolysis stacks, and for stable operation, their health must be constantly monitored and any abnormalities discovered must be dealt with promptly. However, installing many additional sensors to collect data is costly, so it is desirable to be able to make diagnoses using information that is easily obtained during operation.

[0004] Patent Document 1 discloses a technology in which the capacitance of a capacitor connected to the DC intermediate circuit of an inverter is calculated using voltage information from the initial charge generated when the inverter is started, and the calculated value is used to control the intermediate DC voltage of the inverter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-153978 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology described in Patent Document 1 is not designed to connect a load with a large capacitance component, such as an electrolysis stack, and is therefore difficult to apply to the operation of a water electrolysis stack. In recent years, there has been a demand for the development of technology to efficiently diagnose large-scale water electrolysis systems.

[0007] An object of the present invention is to provide an electrolysis system and a state diagnosis method for an electrolysis system that can easily diagnose the state of an electrolysis stack. [Means for solving the problem]

[0008] In order to solve the above problems, for example, the configurations described in the claims are adopted. The present application includes multiple means for solving the above-described problems. As one example, the electrolysis system of the present invention includes an electrolysis stack that generates a desired gas by electrolysis of a raw material compound, a power conversion device that applies a voltage to the electrolysis stack, a voltage sensor that measures the voltage applied to the electrolysis stack, a diagnostic device that calculates an index defined by the capacitance component of the electrolysis stack using time-series data of the voltage acquired by the voltage sensor when a voltage is applied to the electrolysis stack, and diagnoses the state of the electrolysis stack by comparing the value of the calculated index with a reference value, and an output device that outputs the results of the diagnosis made by the diagnostic device to the outside. [Effects of the Invention]

[0009] According to the present invention, factors that accelerate the deterioration of an electrolysis stack can be detected, enabling early countermeasures to be taken and the progression of deterioration to be suppressed. Furthermore, by detecting the deterioration state, stable operation of the system can be achieved by adjusting control conditions or replacing a deteriorated stack. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram showing an example of a diagnostic device for an electrolysis system according to a first embodiment of the present invention. [Figure 2] 4 is a flowchart showing an example of diagnostic processing according to the first embodiment of the present invention. [Figure 3] FIG. 2 is a characteristic diagram showing an example of time-series data of the voltage applied to the electrolysis stack according to the first embodiment of the present invention. [Figure 4] FIG. 1 is a circuit diagram showing an example of an equivalent circuit that simulates an initial charging circuit of an electrolytic stack according to a first embodiment of the present invention. [Figure 5] FIG. 3 is a characteristic diagram showing an example of a history of index values ​​recorded at startup according to the first embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing an example of an operation screen according to the first embodiment of the present invention. [Figure 7] FIG. 2 is a diagram showing an example of selecting an index and each electrolysis stack according to the first embodiment of the present invention. [Figure 8] FIG. 10 is a configuration diagram showing an example of a diagnostic device for an electrolysis system according to a second embodiment of the present invention. [Figure 9] 10 is a flowchart showing an example of diagnostic processing according to a second embodiment of the present invention. [Figure 10] FIG. 10 is a characteristic diagram showing an example of time-series data of the current of the electrolytic stack according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] <First embodiment> An electrolysis system and a method for diagnosing the state of an electrolysis system according to a first embodiment of the present invention will be described below with reference to FIGS.

[0012] [Electrolysis system configuration] FIG. 1 shows the configuration of an electrolysis system according to a first embodiment of the present invention. The electrolysis stack 10 included in the electrolysis system receives power from an AC system 1 after conversion. That is, AC power from an AC system 1 is stepped down by a transformer 2 and then supplied to a power converter 6 via a harmonic filter 5. The power converter 6 converts the supplied AC power into DC power and supplies it to an electrolysis stack 10. Although only one electrolysis stack 10 is shown in FIG. 1 , in an actual electrolysis system, multiple electrolysis stacks 10 are installed depending on the scale of the electrolysis system, and DC power is supplied to each of the electrolysis stacks 10.

[0013] Electromagnetic switches 3a and 3b and a charging resistor 4 are installed between the transformer 2 and the harmonic filter 5. During the initial charging of the smoothing capacitor of the power conversion device 6 and the capacitance component of the electrolytic system, only the electromagnetic switch 3a is turned on, connecting the transformer 2 and the harmonic filter 5 via the charging resistor 4. After the initial charging is complete, the electromagnetic switch 3b is turned on, bypassing the charging resistor 4 and connecting the transformer 2 and the harmonic filter 5.

[0014] The electrolysis stack 10 electrolyzes a raw material compound using supplied DC power to produce a desired gas. For example, the electrolysis stack 10 can produce hydrogen by electrolyzing water. The voltage applied to the electrolytic stack 10 by the power converter 6 is measured by a voltage sensor 7. Time-series data of the voltage measured between the input terminals of the electrolytic stack 10 is sent to a diagnostic device 20 and used to diagnose the electrolytic stack 10.

[0015] The diagnostic device 20 may be a device having an independent housing, or may be integrated with the power conversion device 6. Alternatively, the diagnostic device 20 may be implemented as software in a control computer for the power conversion device 6. When the diagnostic device 20 is implemented as software on a control computer, for example, as shown in FIG. 1, the diagnostic device 20 includes a CPU (Central Processing Unit) 21, a memory 22, a storage 23, an input / output unit 24, and a communication interface 25, all of which are connected to each other by a bus line. The CPU 21 executes a program stored in the memory 22 or the storage 23 .

[0016] The memory 22 is configured as, for example, a RAM (Random Access Memory), and stores computer programs and calculation result data, and also provides the CPU 21 with a work area necessary for each process. In this embodiment, the CPU 21 executes a program, and a processing unit for diagnosing the state of the electrolysis stack 10 is configured in a work area in the memory 22. The storage 23 is configured by a hard disk drive (HDD) or a solid state drive (SSD), and stores computer programs as well as data required for calculations and calculation result data.

[0017] The input / output unit 24 performs input processing of measured values ​​from sensors and the like, and also performs output processing of display data and the like. The communication interface 25 performs communication processing with external devices, servers, etc. via a predetermined network, for example, transmitting the diagnosis results to an external terminal. Note that configuring diagnostic device 20 using a computer with the configuration shown in FIG. 1 is just one example, and for example, part or all of the processing may be configured using hardware such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0018] [Diagnosis processing by diagnostic equipment] FIG. 2 is a flowchart showing the electrolysis system diagnostic process performed by the diagnostic device 20 according to this embodiment. First, the electrolysis system turns on only the electromagnetic switch 3a to start initial charging of the electrolysis stack 10 via the charging resistor 4 (step S100). This initial charging occurs when the electrolysis system is first started up after installation, but may also occur when the system is restarted after a certain period of downtime due to maintenance or the like. The timing for performing the initial charging here may vary depending on whether the electrolytic stack 10 is started from a state where no charge has accumulated in the capacitance component, or whether the voltage is lowered below a threshold to temporarily suspend electrolysis, and then the voltage is raised to resume electrolysis.

[0019] When charging starts in step S100, a charging current flows into the smoothing capacitor of the power converter 6 and the capacitance component of the electrolytic stack 10, and the voltage rises as charge accumulates. Generally, the capacitance component of the electrolytic stack has a larger capacity than the smoothing capacitor of the power converter, so the time constant of the voltage rise is roughly proportional to the value of the capacitance component of the electrolytic stack 10. Note that charging may start when charge remains in the smoothing capacitor of the power converter 6 or the capacitance component of the electrolytic system.

[0020] Next, the diagnostic device 20 performs a voltage acquisition process to acquire the measurement value of the voltage sensor 7 and time-series data of the voltage applied to the electrolysis stack 10 (step S101). Figure 3 shows an example of acquired voltage time series data. As shown in Figure 3, as time passes from t1 to t2 to t3, the detected voltage value increases from v1 to v2 to v3, but the rate of increase slows as the voltage increases. The time constant τ of the voltage increase increases as the capacitance component increases, assuming other conditions are the same. As shown in Figure 3, when the time constant τ is larger than the reference value τ0 (τ>τ0), the rate at which the voltage rises decreases. On the other hand, when the time constant τ is smaller than the reference value τ0 (τ<τ0), the rate at which the voltage rises increases.

[0021] 2, the diagnostic device 20 calculates an index defined by the capacitance component of the electrolytic stack 10 (step S102). The index here is the time constant of the change in voltage applied to the electrolytic stack 10. FIG. 4 shows an equivalent circuit simulating the initial charging circuit of the electrolysis stack 10. DC voltage V eWhen resistance R and capacitance C are connected in series to a power supply via a switch SW, the voltage V applied to capacitance C rises with a time constant τ = RC, as shown in equation 1. Here, the voltage value at time t = t0 is V0. If we assume that the resistance is constant, the time constant τ is proportional to the capacitance C. Therefore, if the time constant or a function of the time constant can be obtained from time-series data, it can be used as an index defined by capacitance.

[0022]

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[0023] If the sampling interval of the voltage time series data is T, then at each time t k can be written as in [Equation 2]. By substituting these into [Equation 1] and rearranging them, we obtain [Equation 2] and [Equation 3], which show the voltages V1 and V2 at times t1 and t2. Furthermore, by transforming [Equation 4] using [Equation 3], we get [Equation 5]. The same goes for subsequent times, which can be written as in [Equation 6].

[0024]

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[0025]

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[0026]

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[0027]

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[0028]

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[0029] By transforming equation [6], equation [7] and equation [8] are obtained. In this way, the time constant τ and e -T / τ This calculation may be performed using only the initial data where the voltage rise rate is large. Alternatively, a moving average may be taken to suppress the influence of noise.

[0030]

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[0031]

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[0032] 2, the diagnostic device 20 determines a reference value to be used for comparison (step S103). When an appropriate amount of water is supplied to the electrolysis stack 10, the value of the capacitance component depends on the water temperature. Therefore, it is preferable to store the reference value as a function of the water temperature and adjust the reference value according to the water temperature at each time.

[0033] Next, the diagnostic device 20 compares the calculated index with a reference value to diagnose the state of the electrolysis stack 10 (step S104). If the calculated index deviates from the reference value by more than a predetermined percentage, or if it deviates from a predetermined range set around the reference value, the diagnostic device 20 determines that some abnormality has occurred in the electrolysis stack 10.

[0034] Fig. 5 shows an example of how the calculated index changes over time. The vertical axis of Fig. 5 represents the index, and the horizontal axis represents time. The plot points (black circles) of the characteristics shown in Fig. 5 represent the times when the diagnostic device 20 measured the index. In the example of Fig. 5, the indices obtained up to the seventh measurement are within the normal range (within the range of reference values), but the indices from the eighth to tenth measurements are out of the normal range and in an abnormal state. The diagnostic device 20 detects such abnormalities in the indices.

[0035] If the diagnosis by the diagnostic device 20 estimates that the capacitance is smaller than normal, an insufficient amount of water or an abnormally low temperature is suspected. Since it is known that carrying out electrolysis when the amount of water is insufficient accelerates the deterioration of the electrolysis stack, the diagnostic device 20 adjusts the amount of water so that an appropriate amount is supplied. Conversely, if the capacitance is estimated to be larger than normal, there is a possibility that the amount of water is excessive or the temperature is abnormally high. Therefore, the diagnostic device 20 can detect an excess or shortage of water amount or an abnormal temperature based on the diagnosis results. If the temperature falls outside the appropriate range, deterioration of the electrolysis stack will also accelerate, so it is desirable for the diagnostic device 20 to take action as soon as possible to bring the water volume within the appropriate range.

[0036] In addition to these factors that accelerate deterioration, if deterioration progresses in such a way that the effective electrode area of ​​the electrolytic stack 10 becomes smaller, the capacitance component decreases, and if deterioration progresses in such a way that the inter-electrode distance becomes smaller, the capacitance component increases. Therefore, the diagnostic device 20 can also detect such deterioration states. In this case, the diagnostic device 20 may individually accumulate historical data of multiple electrolytic stacks 10 and detect deviations from the trends of each individual electrolytic stack 10 and differences from other electrolytic stacks 10 using a machine learning technique.

[0037] Finally, diagnostic device 20 outputs the diagnostic result to the outside via output device 30 (step S105). If output device 30 is a display device, the diagnostic result is displayed. Alternatively, output device 30 may transmit the diagnostic result to another terminal.

[0038] When a maintenance person for the electrolysis system detects a factor that accelerates deterioration based on the output of the diagnosis result, the maintenance person for the electrolysis system promptly takes measures to resolve the factor, thereby suppressing the progression of deterioration of the electrolysis stack 10. Furthermore, when a deterioration state is detected, the maintenance person for the electrolysis system adjusts the control conditions to reduce the amount of electrolysis reaction, thereby extending the life of the electrolysis stack 10.

[0039] Conversely, a maintenance person for the electrolysis system may increase the amount of electrolysis reaction on the assumption that a deteriorated stack will be replaced in the near future. Instead of a maintenance person operating the electrolysis system, a control device (not shown) for the electrolysis system may acquire the diagnosis results of the diagnosis device 20 and automatically make adjustments to extend the life of the electrolysis stack 10 or increase the amount of electrolysis reaction on the assumption that the deteriorated electrolysis stack 10 will be replaced.

[0040] Fig. 6 shows an example of an operation screen displayed on a display device serving as the output device 30. The example in Fig. 6 is an operation screen for diagnosing the electrolytic stack 10 in conjunction with the start-up of the electrolysis system. As shown in Fig. 6, the operation screen displays a start button for starting the electrolysis system, a stop button for stopping the electrolysis system, and the like.

[0041] The operation screen has a status display field and a diagnostic result display field. The status display field displays a status indicating the operating state of the electrolysis system. In the example of FIG. 6, the status display field displays "Startup completed." The diagnostic device 20 is configured to perform a diagnosis at startup, and the results of the diagnosis are displayed in the diagnostic result display field. In the example of FIG. 6, the diagnostic result display field displays "Within normal range."

[0042] If the diagnostic result of the diagnostic device 20 indicates an abnormality, details of the abnormality, such as "deterioration of the electrolytic stack," are displayed in the diagnostic result display field. The diagnostic result may be configured to display a more detailed deterioration state. For example, details such as how to adjust the control conditions to extend the lifespan may be displayed. Furthermore, the diagnostic device 20 may estimate the excess or deficiency of the water volume based on the diagnostic result, and the output device 30 may display the estimated excess or deficiency of the water volume.

[0043] As described above, according to the electrolysis system of this embodiment, it is possible to detect factors that accelerate deterioration of the electrolysis stack and the state of deterioration at an early stage and take measures against them, thereby realizing an electrolysis system that can be stably operated.

[0044] Because the electrolysis system includes a plurality of electrolysis stacks 10, the diagnostic device 20 individually diagnoses each of the plurality of electrolysis stacks 10. Based on the individual diagnostic results of the diagnostic device 20, a maintenance technician for the electrolysis system can select an electrolysis stack 10 for which maintenance is to be performed. For example, as shown in FIG. 7, assume that five electrolytic stacks 10, designated stack No. 1 to stack No. 5, are installed as the electrolytic stacks 10, and stack No. 1 and stack No. 4 are within the normal range, while stack No. 2, stack No. 3, and stack No. 5 are abnormal.

[0045] In this case, the diagnostic device 20 assigns the stack No. 5, which is the stack that deviates the most from the normal range, the first inspection priority among the five electrolytic stacks 10. In addition, the diagnostic device 20 assigns the stack No. 3, which is the stack that deviates the second most from the normal range, the second inspection priority, and the stack No. 2, which is the stack that deviates the third most from the normal range, the third inspection priority.

[0046] Furthermore, for stacks No. 1 and No. 4, which are within the normal range, stack No. 4, which has a relatively large change from the reference value within the normal range, will be given the fourth inspection priority, and stack No. 1, which is closest to the reference value, will be given the fifth inspection priority. By having the diagnostic device 20 display such inspection priorities, the person in charge of maintaining the electrolysis system knows the order in which to inspect the electrolysis stack 10, enabling appropriate and stable operation of the electrolysis stack 10.

[0047] When a plurality of electrolysis stacks 10 are installed in this manner, a predetermined number of the electrolysis stacks 10 may be periodically suspended in order to extend the life of the electrolysis stacks 10. When the electrolysis stacks 10 are restarted after suspension, charging of the electrolysis stacks 10 occurs again, and therefore, if the diagnosis is performed at that timing, the diagnostic device 20 can periodically diagnose all of the electrolysis stacks.

[0048] In addition, if the historical data of multiple electrolytic stacks 10 are individually accumulated and deviations from the trends of each individual electrolytic stack 10 or differences from other electrolytic stacks 10 are detected using machine learning techniques, the diagnostic device 20 may determine inspection priorities based on the detected differences in trends, etc.

[0049] <Second embodiment> Next, an electrolysis system and a state diagnosis method for an electrolysis system according to a second embodiment of the present invention will be described with reference to Figures 8 to 10. In Figures 8 to 10, parts corresponding to those in Figures 1 to 7 described in the first embodiment are given the same reference numerals, and duplicated explanations will be omitted.

[0050] [Electrolysis system configuration] FIG. 8 shows the configuration of an electrolysis system according to a second embodiment of the present invention. The electrolysis system of this embodiment differs from the electrolysis system of the first embodiment in that, as sensors for measurement, in addition to a voltage sensor 7 that measures the voltage applied to the electrolysis stack 10, a current sensor 8 that measures the current flowing into the electrolysis stack 10 is also installed. The diagnostic device 20′ acquires both the voltage measured by the voltage sensor 7 and the current measured by the current sensor 8, directly derives the value of the capacitance component of the electrolytic stack, and diagnoses the electrolytic stack 10. The other configurations of the electrolysis system are the same as those of the electrolysis system shown in FIG.

[0051] [Diagnosis processing by diagnostic equipment] FIG. 9 is a flowchart showing the electrolysis system diagnostic process performed by the diagnostic device 20' according to this embodiment. First, the electrolysis system turns on only the electromagnetic switch 3a to start initial charging of the electrolysis stack 10 (step S200). The initial charging here is the first time the electrolysis stack 10 is charged, as in the first embodiment, but it may also be when the electrolysis system is restarted after a certain period of downtime due to maintenance or the like. When this initial charging begins, a charging current flows into the smoothing capacitor of the power converter 6 and the capacitance component of the electrolytic stack 10, and as charge accumulates, the voltage rises while the current decreases.

[0052] Then, the diagnostic device 20' acquires time series data of the voltage applied to the electrolytic stack 10 and time series data of the current flowing into the electrolytic stack 10 from the voltage sensor 7 and the current sensor 8 (step S201). Figure 10 shows the concept of the acquired time-series current data. The vertical axis in Figure 10 represents current, and the horizontal axis represents time. As Figure 10 shows, the current reaches its highest value I0 at charging start time t0, and gradually decreases to I1, I2, I3, and so on as time passes (t1, t2, t3, and so on).

[0053] 10, when the time constant τ is larger than the reference value τ0 (τ>τ0), the current decreases slowly. On the other hand, when the time constant τ is smaller than the reference value τ0 (τ<τ0), the current decreases quickly. The time-series data of the voltage detected by the voltage sensor 7 has the characteristics shown in FIG.

[0054] Returning to the explanation of the flowchart in Fig. 9, the diagnostic device 20' calculates an index defined by the capacitance component of the electrolytic stack 10 based on the acquired time-series data of voltage and time-series data of current (step S202). In this embodiment, the value of the capacitance component itself serves as the index. In this case, in the equivalent circuit shown in Fig. 4, the amount of charge stored in the capacitance C is described by Equation 9.

[0055]

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[0056] There are various methods for calculating the integral term shown in equation (9), but assuming execution on a device with limited processor performance and memory capacity, we will describe the case where the trapezoidal rule, which is one of the simplest methods, is applied. The capacitance value can be found using equation (10). This calculation may be performed using only the initial data with a large current decrease rate. Alternatively, the following formula (11) may be used as a separate calculation formula. In these formulas, T is the sampling interval.

[0057]

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[0058]

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[0059] Steps S202 to S205 in Fig. 9 are the same as steps S102 to S105 in Fig. 2. That is, diagnostic device 20' determines a reference value to be used for comparison (step S203).

[0060] Next, the diagnostic device 20′ compares the calculated index with a reference value to diagnose the state of the electrolysis stack 10 (step S204). If the calculated index deviates from the reference value by more than a predetermined percentage, or if it deviates from a predetermined range set around the reference value, the diagnostic device 20′ determines that some abnormality has occurred in the electrolysis stack 10. In this embodiment, the diagnostic device 20' may also apply a machine learning technique to individually accumulate historical data of a plurality of electrolytic stacks and detect deviations or differences from the trends of each individual stack. Finally, the diagnostic device 20' outputs the diagnostic results to the outside from the output device 30 (step S205).

[0061] According to this embodiment, the value of the capacitance component of the electrolysis stack 10 can be directly derived, which enables quantitative diagnosis and realizes an electrolysis system that can be operated more stably.

[0062] <Modification> It should be noted that the embodiments described so far have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described.

[0063] In addition, the configuration diagrams shown in Figures 1 and 8 only show control lines and information lines that are considered necessary for explanation, and do not necessarily show all control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected. Furthermore, the flowcharts shown in FIGS. 3 and 9 are also examples, and as long as the processing results are the same, the order of some of the processing may be changed or multiple processes may be executed simultaneously.

[0064] Furthermore, the electrolysis system diagnostic device 20, 20′ described in each of the above-described embodiments may be configured by implementing a program that executes the processing shown in the flowchart of Fig. 3 or Fig. 9, and in this case, the program is prepared in the memory 22 or storage 23 in the computer shown in Fig. 1. Alternatively, the program executed by the computer functioning as the electrolysis system diagnostic device 20, 20′ may be stored in an external memory, an IC card, an SD card, an optical disk, or other recording medium, and transferred to the computer that functions as the electrolysis system diagnostic device 20, 20′. [Explanation of symbols]

[0065] REFERENCE SIGNS LIST 1...AC system, 2...transformer, 3a, 3b...electromagnetic switch, 4...charging resistor, 5...harmonic filter, 6...power conversion device, 7...voltage sensor, 8...current sensor, 10...electrolytic stack, 20, 20'...diagnostic device, 21...CPU, 22...memory, 23...storage, 24...input / output unit, 25...communication interface, 30...output device

Claims

1. an electrolysis stack for producing a desired gas by electrolysis of a feed compound; a power converter that applies a voltage to the electrolysis stack; a voltage sensor that measures the voltage applied to the electrolysis stack; a diagnostic device that calculates an index defined by a capacitance component of the electrolytic stack using time-series data of the voltage acquired by the voltage sensor when a voltage is applied to the electrolytic stack, and diagnoses the state of the electrolytic stack by comparing the calculated index value with a reference value; an output device that outputs or displays the results of the diagnosis made by the diagnostic device; Electrolysis system.

2. The index is the time constant of the voltage change applied to the electrolytic stack. The electrolysis system of claim 1 .

3. The index is proportional to the value of the capacitance component of the electrolytic stack. The electrolysis system of claim 1 .

4. The electrolysis stack produces hydrogen by electrolysis of water. The electrolysis system of claim 1 .

5. The diagnostic device detects whether the amount of water supplied to the electrolysis stack is excessive or insufficient. The electrolysis system of claim 1 .

6. The diagnostic device detects a temperature abnormality in the electrolysis stack. The electrolysis system of claim 1 .

7. The diagnostic device accumulates historical data for multiple electrolysis stacks individually and detects deviations or differences from individual trends using machine learning techniques. The electrolysis system of claim 1 .

8. A current sensor is provided to measure the current flowing into the electrolysis stack. The electrolysis system of claim 1 .

9. A diagnostic method for an electrolysis system for diagnosing an electrolysis stack that produces a desired gas by electrolysis of a raw material compound, comprising: a voltage acquisition process for acquiring a voltage applied to the electrolysis stack when the electrolysis stack generates the gas; an electrolytic stack diagnosis process for calculating an index defined by a capacitance component of the electrolytic stack using time-series data of the voltage acquired in the voltage acquisition process, and diagnosing the state of the electrolytic stack by comparing the value of the obtained index with a reference value. Diagnostic methods for electrolytic systems.

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