Monitoring device

Abstract

A monitoring device (120) monitors the state of reaction equipment (CS) in which a plurality of reaction cells (FC, EC) that output electrical energy or fuel as a result of an electrochemical reaction are electrically connected. The monitoring device is provided with an AC application unit (130) that applies an AC current to some of the reaction cells included in the reaction equipment, said reaction cells being defined as an application target of the AC current. The monitoring device also includes an impedance measuring unit (142) that measures the impedance of the application target on the basis of the voltage and current of the application target when the AC current is applied to the application target by the AC application unit. Furthermore, the monitoring device is provided with a state determining unit (143) that determines the state of the application target on the basis of the impedance of the application target.

Description

monitoring device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2024-126114, filed on August 1, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a monitoring device that monitors the state of a reaction device to which a plurality of reaction cells that output electric energy or fuel through an electrochemical reaction are electrically connected.

[0003] Conventionally, a fuel cell monitoring device is known that applies an alternating current to a cell stack in which multiple fuel cell units are stacked, measures the impedance of the entire cell stack, and determines the state of the cell stack based on this impedance (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2020-87764

[0005] However, when an AC current is applied to the entire cell stack to measure impedance, as in Patent Document 1, the AC current appears as unintended power pulsation in the output power of the cell stack. For example, if the amplitude of the AC current applied to the cell stack is increased to ensure accurate impedance measurement, the power pulsation also increases, which can lead to problems such as increased impact on load devices and reduced power efficiency. This is true not only for fuel cells, but also for secondary cells such as batteries.

[0006] Furthermore, in a reactor such as a water electrolysis device that outputs fuel through an electrochemical reaction, when an alternating current is applied to the entire reactor to measure impedance, pressure pulsation may occur in the fuel output from the reactor, which can cause problems such as increased vibration and noise.

[0007] An object of the present disclosure is to provide a monitoring device that can monitor the state of a reaction device while suppressing problems associated with the application of alternating current for measuring impedance.

[0008] The monitoring device of the present disclosure is a monitoring device that monitors the state of a reaction device to which a plurality of reaction cells that output electric energy or fuel by an electrochemical reaction are electrically connected, and includes: an AC application unit that applies AC to some of the reaction cells included in the reaction device as targets to which AC current is applied; an impedance measurement unit that measures the impedance of the target based on the voltage and current of the target when AC current is applied to the target by the AC application unit; and a state determination unit that determines the state of the target based on the impedance of the target.

[0009] In this way, if an alternating current is applied to some of the reaction cells included in the reactor and the impedance is measured, the state of some of the reaction cells can be monitored based on the impedance of some of the reaction cells. Furthermore, since the pulsation of the output of the reactor caused by the application of an alternating current can be suppressed compared to when an alternating current is applied to the entire reactor, problems caused by the application of an alternating current can be suppressed.

[0010] Therefore, the monitoring device of the present disclosure can monitor the state of the reaction equipment while suppressing problems associated with the application of AC current for measuring impedance.

[0011] FIG. 1 is a schematic configuration diagram of a fuel cell system including a monitoring device according to a first embodiment. FIG. 2 is an explanatory diagram illustrating an AC application unit of the monitoring device according to the first embodiment. FIG. 3 is a circuit diagram showing a voltage application circuit of the AC application unit included in the monitoring device according to the first embodiment. FIG. 4 is an explanatory diagram illustrating a configuration in which a first AC current is applied to some application targets, and a second AC current having an opposite phase to the first AC current is applied to other application targets. FIG. 5 is an explanatory diagram illustrating an error that occurs between a detected voltage at some application targets and a detected voltage at other application targets. FIG. 6 is an explanatory diagram illustrating a frequency response result of a voltage when an AC current is applied. FIG. 7 is an explanatory diagram illustrating behavior of a corrected detected voltage at some application targets and behavior of a corrected detected voltage at other application targets. FIG. 8 is a flowchart illustrating an example of a correction process performed by the monitoring device according to the first embodiment. FIG. 9 is a flowchart illustrating an example of a monitoring process performed by the monitoring device according to the first embodiment. FIG. 10 is an explanatory diagram illustrating extraction of AC components from the voltage of a cell to which AC current is applied and the voltage of a cell to which AC current is not applied in the monitoring device according to a second embodiment. FIG. 11 is an explanatory diagram illustrating non-stationary noise included in the detected voltage of a cell to which AC current is applied and non-stationary noise included in the detected voltage of a cell to which AC current is not applied. FIG. 10 is an explanatory diagram for explaining frequency response results of voltage when AC is applied to both an AC-applied cell and an AC-non-applied cell. FIG. 11 is an explanatory diagram for explaining non-stationary noise included in the detected voltage of each cell after correction processing. FIG. 12 is a flowchart showing an example of pre-processing performed by the monitoring device according to a second embodiment. FIG. 13 is a flowchart showing an example of monitoring processing performed by the monitoring device according to the second embodiment. FIG. 14 is an explanatory diagram for explaining removal of non-stationary noise included in the detected voltage of a cell to which AC is applied. FIG. 15 is a flowchart showing an example of pre-processing performed by the monitoring device according to a third embodiment. FIG. 16 is a flowchart showing an example of monitoring processing performed by the monitoring device according to the third embodiment. FIG. 17 is a schematic configuration diagram of a water electrolysis system including a monitoring device according to a fourth embodiment.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same as or equivalent to those described in the preceding embodiments will be given the same reference numerals, and their description may be omitted. Furthermore, in the embodiments, when only some of the components are described, the components described in the preceding embodiments can be applied to the remaining components. The following embodiments can be partially combined with each other, even if not specifically stated, as long as there is no particular problem with the combination.

[0013] First Embodiment This embodiment will be described with reference to Figures 1 to 9. In this embodiment, an example will be described in which a monitoring device 120 according to the present disclosure is applied to a fuel cell system 1. The fuel cell system 1 is configured as a power generation system mounted on a mobile object such as a vehicle. The fuel cell system 1 includes a cell stack CS that constitutes a fuel cell, an air supply path 10, an air discharge path 20, a hydrogen supply path 30, a hydrogen discharge path 40, a control device 100, and the like.

[0014] The cell stack CS is a reaction device in which a plurality of reaction cells are electrically connected, and each cell outputs electric energy through an electrochemical reaction. The cell stack CS outputs electric power to a power converter PCE such as an inverter via an external circuit. The power converter PCE supplies the electric power from the cell stack CS to a load device such as a motor or a battery.

[0015] The reaction cell of this embodiment is a fuel cell FC that outputs electric energy through an electrochemical reaction between a reducing gas supplied to the anode and an oxidizing gas supplied to the cathode. The fuel cell FC is configured, for example, as a solid polymer cell, i.e., a PEFC (short for Polymer Electrolyte Fuel Cell). When hydrogen is supplied to the anode side and air is supplied to the cathode side, the fuel cell FC outputs electric energy through the electrochemical reactions shown in the following reaction formulas F1 and F2. Anode: H ２ →2H ＋ +2e － ... (F1) Cathode: 2H ＋+1 / 2O ２ +2e － →H ２ O ... (F2) The cell stack CS is connected to an air supply path 10, which is a path for supplying air to the cell stack CS, and an air discharge path 20, which flows the off-gas (i.e., off-air) of the air discharged from the cell stack CS to a muffler (not shown). An air pump 11 is provided in the air supply path 10. An air adjustment valve 21 is provided in the air discharge path 20, which adjusts the air pressure inside the cell stack CS. In addition, although not shown, a humidifier is provided in the air supply path 10 and the air discharge path 20, which humidifies the air to be supplied to the cell stack CS with water generated in the off-air. The air pump 11 and the air adjustment valve 21 are controlled based on control signals from the control device 100.

[0016] Also connected to the cell stack CS are a hydrogen supply path 30, which supplies hydrogen to the cell stack CS, and a hydrogen discharge path 40, which directs hydrogen off-gas (i.e., off-fuel) discharged from the cell stack CS to a muffler (not shown). The hydrogen supply path 30 is provided with a hydrogen tank 31 and a fuel regulating valve 32. The hydrogen discharge path 40 is provided with an exhaust valve 41, which discharges the off-fuel that has passed through the cell stack CS. The fuel regulating valve 32 and the exhaust valve 41 are controlled based on control signals from the control device 100. Although not shown, the hydrogen discharge path 40 is connected to the air discharge path 20 on the downstream side of the exhaust valve 41. As a result, the off-fuel flowing through the hydrogen discharge path 40 is diluted by mixing with off-air before being discharged from the muffler.

[0017] Next, we will explain the control device 100 that constitutes the electronic control unit of the fuel cell system 1. The control device 100 is composed of a computer including a processor and memory. The memory includes not only ROM and RAM but also auxiliary storage devices, etc. The memory is a non-transitory physical storage medium.

[0018] The control device 100 includes a control unit 110 and a monitoring device 120 that control various devices of the fuel cell system 1. The control unit 110 and the monitoring device 120 may be configured using common hardware or may be configured using separate hardware.

[0019] The control unit 110 acquires output information from various sensors, such as a stack current sensor 101 that detects the output current of the cell stack CS and a stack voltage sensor 102 that detects the output voltage of the cell stack CS. Based on the output information from the various sensors, the control unit 110 determines control signals to be output to various controlled devices, such as the air pump 11, the air regulating valve 21, the fuel regulating valve 32, and the exhaust valve 41. The control unit 110 then outputs control signals to the various controlled devices to control their operation. Furthermore, if the monitoring results of the internal state of the fuel cell FC by the monitoring device 120 indicate an abnormal state, the control unit 110 performs recovery processing to recover from the abnormal state. The control unit 110 includes, as functional units for realizing various functions, a device control unit that controls the operation of the various controlled devices and a recovery execution unit that executes recovery processing.

[0020] The monitoring device 120 is a device that monitors the internal state of the cell stack CS and is configured to include an AC application unit 130, a correction unit 141, an impedance measurement unit 142, and a state determination unit 143.

[0021] The AC application unit 130 applies AC current to some of the fuel cells FC included in the cell stack CS as application targets. The monitoring device 120 applies AC current to a predetermined number of fuel cells FC as application targets. The application targets can be set arbitrarily. For example, the application targets can include fuel cells FC located on the end side of the cell stack CS and fuel cells FC located in the center of the cell stack CS. The AC application unit 130 is connected to both ends of the fuel cells FC that are application targets, for example, as shown in FIG. 2, so that it can apply AC current to each of the fuel cells FC that are application targets.

[0022] The AC application unit 130 has a voltage application circuit 131, a cell voltage detection unit 132 that detects the cell voltage of each fuel cell FC, and an application unit 134 that has a cell current detection unit 133 that detects the cell current of each fuel cell FC, and multiple units are provided corresponding to each fuel cell FC.

[0023] As shown in FIG. 3, the voltage application circuit 131 includes an operational amplifier OP, a switch TR1, a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4. The voltage application circuit 131 is connected across the fuel cell FC so that the series connection of the switch TR1 and the first resistor R1 is electrically parallel to the fuel cell FC. A voltage waveform similar to the desired current waveform is applied to the + terminal of the operational amplifier OP of the voltage application circuit 131. The - terminal of the operational amplifier OP is connected between the switch TR1 and the first resistor R1 via the fourth resistor R4. The output of the operational amplifier OP is connected to the low potential terminal of the fuel cell FC via the second resistor R2 and to the switch TR1 via the third resistor R3.

[0024] In the voltage application circuit 131 configured in this manner, a current controlled by the switch TR1 and the operational amplifier OP flows to the negative terminal of the operational amplifier OP. The output of the operational amplifier OP operates so that the voltage applied to the positive terminal of the operational amplifier OP matches the voltage applied to the negative terminal, thereby controlling the current flowing through the first resistor R1. This causes an AC current to be applied to the fuel cell FC. The voltage application circuit 131 is able to change the frequency of the AC current applied to the fuel cell FC in a frequency range from low to high (for example, 0.01 Hz to 10 kHz) by adjusting the voltage applied to the positive terminal of the operational amplifier OP.

[0025] 4, the AC application unit 130 is configured to include a first application unit 134A and a second application unit 134B. The first application unit 134A designates some application targets as first targets and applies a first AC current to the first targets. The second application unit 134B designates other application targets as second targets and applies a second AC current to the second targets, the second AC current being in opposite phase to the first AC current. Note that while FIG. 4 illustrates a single fuel cell FC as the first target and the second target, this is not limiting, and two or more fuel cells FC may be the first target and the second target.

[0026] In this way, if the second AC current, which is in opposite phase to the first AC current applied to the first target, is applied to the second target, the AC components of the first AC current and the second AC current cancel each other out, thereby suppressing output pulsation from the cell stack CS.

[0027] Here, the first AC current is applied to the first target by a voltage application circuit 131 connected to the first target. Meanwhile, the second AC current is applied to the second target by a voltage application circuit 131 connected to the second target. In this manner, when the first AC current and the second AC current are applied to different fuel cells FC and devices, errors may occur in the gain and phase of the first AC current and the second AC current due to individual differences and deterioration of the fuel cells FC and devices. If errors occur in the gain and phase of the first AC current and the second AC current, errors also occur in the detected voltages at the first target and the second target, as shown in FIG. 5 . Such errors can cause pulsation in the output of the cell stack CS.

[0028] Therefore, the monitoring device 120 is provided with a correction unit 141 that performs correction to suppress errors caused by individual differences and deterioration of the fuel cells FC and the equipment. The correction unit 141 of this embodiment constitutes an "applied current correction unit" that corrects the AC current applied to the application target. The correction unit 141 corrects at least one of the first AC current and the second AC current so that the amplitude (i.e., gain) of the response voltage when the first AC current is applied approaches the amplitude of the response voltage when the second AC current is applied. In addition, the correction unit 141 corrects at least one of the first AC current and the second AC current so that the phase of the response voltage when the first AC current is applied is opposite to the phase of the response voltage when the second AC current is applied.

[0029] The correction unit 141, for example, compares the first AC current and the second AC current, determines the gain and phase errors that exist between them, and changes the voltage waveform to be applied to the voltage application circuit 131 so as to reduce the errors. The gain error (i.e., Δgain) between the first AC current and the second AC current can be determined by comparing the frequency response results of the voltages of the respective AC currents, as shown in FIG. 6 . Note that the correction unit 141 may also be configured to compare the first AC current and the second AC current with a predetermined AC current, determine the gain and phase errors that exist between them, and change the voltage waveform to be applied to the voltage application circuit 131 so as to reduce the errors.

[0030] The correction of the first AC current and the second AC current by the correction unit 141 reduces the error between the first AC current and the second AC current. As a result, for example, as shown in Fig. 7, the error between the response voltage at the first target and the response voltage at the second target also reduces. As a result, the pulsation of the output of the cell stack CS is suppressed.

[0031] The impedance measurement unit 142 measures the impedance of the cell stack CS based on the electrochemical impedance method. When an AC current of a predetermined frequency is applied to a fuel cell FC that is the target of application by the AC application unit 130, the impedance measurement unit 142 measures the impedance of the target of application based on the voltage and current including multiple frequencies output from the target of application.

[0032] The state determination unit 143 determines the state of the fuel cell FC to which the voltage is applied, based on the impedance of the target cell measured by the impedance measurement unit 142. The state determination unit 143 determines whether the fuel cell FC is in a state of hydrogen deficiency, oxygen deficiency, or the wet state of the electrolyte membrane, for example, based on the frequency characteristics of the impedance. The determination result of the state determination unit 143 is notified to the control unit 110. The control unit 110 controls various devices based on the determination result of the state determination unit 143.

[0033] The monitoring device 120 configured in this manner performs a correction process for the AC current applied to the fuel cells FC, and then performs a monitoring process for monitoring the fuel cells FC. The correction process and monitoring process performed by the computer that constitutes the monitoring device 120 will be described below with reference to Figures 8 and 9. The control routines shown in Figures 8 and 9 are executed by the computer that constitutes the monitoring device 120, for example, periodically or irregularly while the cell stack CS is generating electricity.

[0034] First, the correction process will be described. As shown in FIG. 8 , in step S100, the monitoring device 120 applies an AC current to a predetermined target fuel cell FC. Specifically, the monitoring device 120 applies a first AC current to a first target, which is one of the target targets, and applies a second AC current, which is opposite in phase to the first AC current, to a second target, which is another target target. Next, in step S110, the monitoring device 120 detects the current and voltage of the target fuel cell FC. Thereafter, in step S120, the monitoring device 120 executes a correction process to reduce errors caused by individual differences and deterioration of the fuel cell FC and each device. In this correction process, for example, at least one of the first AC current and the second AC current is corrected so that the amplitude of the response voltage when the first AC current is applied approaches the amplitude of the response voltage when the second AC current is applied. The correction process may be configured to correct either the first AC current or the second AC current, or may be configured to correct both the first AC current and the second AC current.

[0035] Next, the monitoring process will be described. As shown in FIG. 9, in step S200, the monitoring device 120 applies the AC current corrected by the correction process of FIG. 8 to the application targets. Specifically, the monitoring device 120 applies the corrected first AC current to a first target, which is one of the application targets, and applies the corrected second AC current to a second target. This AC application process causes the AC components of the first AC current and the second AC current to cancel each other out, thereby suppressing output pulsation from the cell stack CS.

[0036] Next, in step S210, the monitoring device 120 calculates the current and voltage output by the first target fuel cell FC, and the current and voltage output by the second target fuel cell FC. Then, in step S220, the monitoring device 120 executes an impedance measurement process to measure the impedance of the target fuel cell FC based on the electrochemical impedance method. The monitoring device 120 of this embodiment measures the impedance of the first target based on the current and voltage output by the first target fuel cell FC, and measures the impedance of the second target based on the current and voltage output by the second target fuel cell FC.

[0037] Next, in step S230, the monitoring device 120 executes a state determination process to determine the state of the fuel cell FC to be applied, based on the impedance of the target measured by the impedance measurement unit 142. The monitoring device 120 of this embodiment determines whether the state of the first target is abnormal or not based on the impedance of the first target, and determines whether the state of the second target is abnormal or not based on the impedance of the second target. If the state of the fuel cell FC to be applied is abnormal, the monitoring device 120 notifies this fact via the control unit 110. The control unit 110 performs a recovery process to recover from the abnormal internal state of the fuel cell FC to be applied.

[0038] The monitoring device 120 described above is a device that monitors the state of a cell stack CS in which a plurality of fuel cells FC that output electrical energy through an electrochemical reaction are electrically connected. The monitoring device 120 treats some of the fuel cells FC included in the cell stack CS as targets to which AC current is applied, and includes an AC application unit 130 that applies AC current to the targets. In addition, the monitoring device 120 includes an impedance measurement unit 142 that measures the impedance of the target based on the voltage and current of the target when AC current is applied to the target, and a state determination unit 143 that determines the state of the target based on the impedance.

[0039] In this way, if an AC current is applied to some of the fuel cells FC included in the cell stack CS and the impedance is measured, the state of some of the fuel cells FC can be monitored based on the impedance of some of the fuel cells FC. Furthermore, since the pulsation of the output of the cell stack CS caused by the application of AC current can be suppressed compared to when AC current is applied to the entire cell stack CS, problems associated with the application of AC current can be suppressed. Therefore, according to the monitoring device 120 of this embodiment, the state of the cell stack CS can be monitored while suppressing problems associated with the application of AC current for impedance measurement.

[0040] The monitoring device 120 of this embodiment also has the following features: (1) The targets to which an AC current is applied are two or more fuel cells FC. The AC application unit 130 designates some of the targets as first targets and includes a first application unit 134A that applies a first AC current to the first targets. The AC application unit 130 also designates other targets as second targets and includes a second application unit 134B that applies a second AC current that is in opposite phase to the first AC current to the other targets. The impedance measurement unit 142 measures the impedances of the first target and the second target based on the voltages and currents of the first target and the second target when the first AC current is applied to the first target and the second AC current is applied to the second target.

[0041] In this way, by applying the first AC current to the first target and the second AC current to the second target in opposite phases, the AC components of the first AC current and the second AC current cancel each other out, thereby suppressing pulsation in the output of the cell stack CS and thereby reducing problems associated with the application of AC current.

[0042] (2) The monitoring device 120 includes a correction unit 141 that corrects at least one of the first AC current and the second AC current. The correction unit 141 corrects at least one of the first AC current and the second AC current so that the amplitude of the response voltage when the first AC current is applied approaches the amplitude of the response voltage when the second AC current is applied. In addition, the correction unit 141 corrects at least one of the first AC current and the second AC current so that the phase of the response voltage when the first AC current is applied is opposite to the phase of the response voltage when the second AC current is applied. This makes it easier for the AC component of the first AC current and the AC component of the second AC current to cancel each other out, thereby more effectively suppressing output pulsation from the cell stack CS.

[0043] (3) The monitoring device 120 of this embodiment monitors the fuel cells FC that output electrical energy through an electrochemical reaction between a reducing gas supplied to the anode and an oxidizing gas supplied to the cathode. This makes it possible to appropriately monitor the state of the fuel cells FC.

[0044] (Variation of First Embodiment) The impedance measurement unit 142 of the first embodiment is configured to measure the impedance of each of the first and second targets when a first AC current is applied to the first target and a second AC current is applied to the second target, but is not limited to this. The impedance measurement unit 142 may be configured to measure the impedance of one of the first and second targets when a first AC current is applied to the first target and a second AC current is applied to the second target.

[0045] As in the first embodiment, the monitoring device 120 preferably includes a correction unit 141 that corrects each AC current so that the amplitudes of the response voltages when each AC current is applied become closer and the phases of the response voltages when each AC current is applied become opposite phases, but is not limited to this. For example, the correction unit 141 may be omitted from the monitoring device 120.

[0046] Second Embodiment Next, a second embodiment will be described with reference to Figures 10 to 16. In this embodiment, differences from the first embodiment will be mainly described.

[0047] For some reason, non-steady noise, which is a non-steady noise component, may act on the cell stack CS. It is desirable to remove the non-steady noise because it affects the output voltage of the fuel cell FC to which the non-steady noise is applied.

[0048] Non-stationary noise often affects the entire cell stack CS, affecting not only the output voltage of the fuel cell FC to which the voltage is applied, but also the output voltage of other reaction cells other than the target cell. Therefore, by using the output voltages of at least some of the fuel cells FC other than the target cell, it is possible to remove the non-stationary noise from the output voltage of the target cell FC and extract the AC component corresponding to the AC current to be applied to the target cell.

[0049] Based on these considerations, the monitoring device 120 of this embodiment is configured to use the output voltages of fuel cells FC other than the target to extract an AC component corresponding to the AC current to be applied to the target from the output voltage of the target fuel cell FC. Unlike the first embodiment, the monitoring device 120 of this embodiment is configured to apply only the first AC current to the target by the AC application unit 130. Note that, below, the target fuel cell FC to be applied may be referred to as an "AC applied cell," and the other fuel cell FC to be applied may be referred to as an "AC non-applied cell."

[0050] 10 , the AC application unit 130 detects the output voltage of the AC application cell as a first voltage, and detects the output voltage of the AC non-application cell as a second voltage. The AC application unit 130 then outputs the detected voltages to the impedance measurement unit 142.

[0051] The impedance measurement unit 142 extracts an AC component corresponding to the AC current to be applied to the application target based on a first voltage detected as the output voltage of the AC application cell and a second voltage detected as the output voltage of the AC non-application cell.The impedance measurement unit 142 measures the impedance of the AC application cell based on the AC component extracted from the first voltage detected as the output voltage of the AC application cell.

[0052] Here, the first voltage and second voltage are detected by different cell voltage detection units 132. Due to individual differences and deterioration of the fuel cell FC and the cell voltage detection unit 132, for example, as shown in Fig. 11, differences may occur in the non-stationary noise appearing in the first voltage and the second voltage. Such errors may be a factor that prevents the extraction of the AC component contained in the first voltage.

[0053] Therefore, the impedance measurement unit 142 of this embodiment is configured to perform correction to suppress differences in non-stationary noise caused by individual differences, deterioration, etc. between the fuel cells FC and the cell voltage detection unit 132. That is, the impedance measurement unit 142 corrects at least a portion of the AC current, first voltage, and second voltage applied to the AC application cells so as to remove non-stationary noise acting on the entire cell stack CS. The impedance measurement unit 142 corrects the AC current based on the difference in frequency characteristics between the first voltage and the second voltage when AC current is applied so as to reduce differences in non-stationary noise caused by individual differences, deterioration, etc. between the fuel cells FC and the cell voltage detection unit 132. Note that differences in non-stationary noise caused by individual differences, deterioration, etc. appear as differences in the frequency characteristics of the first voltage and the second voltage when AC current is applied to both the AC application cell and the AC non-application cell, for example, as shown in FIG. 12 . Therefore, by comparing the frequency characteristics of the first voltage and the second voltage when AC current is applied to each cell, it is possible to reduce the difference in non-stationary noise that occurs due to individual differences and deterioration of the fuel cell FC and the cell voltage detection unit 132. By performing such processing, for example, as shown in Fig. 13, the difference between the non-stationary noise contained in the first voltage and the non-stationary noise contained in the second voltage is reduced. As a result, it is possible to appropriately remove the non-stationary noise contained in the output voltage of the AC powered cell.

[0054] Next, an example of control processing such as pre-processing and monitoring processing executed by the computer constituting the monitoring device 120 will be described with reference to Figures 14 and 15. The control routines shown in Figures 14 and 15 are executed by the computer constituting the monitoring device 120 periodically or irregularly while the cell stack CS is generating power, for example.

[0055] First, regarding the pre-processing, as shown in FIG. 14 , in step S100A, the monitoring device 120 applies a predetermined AC current to both the AC-applied cell and the AC-non-applied cell. In the pre-processing, AC currents of the same phase may be applied to the AC-applied cell and the AC-non-applied cell, or, as in the first embodiment, AC currents of opposite phases may be applied to the AC-applied cell and the AC-non-applied cell. Next, in step S110A, the monitoring device 120 detects the frequency characteristics of each cell to which AC current is applied. Specifically, the monitoring device 120 detects the voltage of the AC-applied cell as a first voltage and the voltage of the AC-non-applied cell as a second voltage, and further detects the difference in frequency characteristics between the first voltage and the second voltage when AC current is applied. Then, in step S120A, the monitoring device 120 calculates an AC correction value that can reduce the difference in non-stationary noise caused by individual differences, deterioration, etc., based on the difference in frequency characteristics between the first voltage and the second voltage when AC current is applied.

[0056] Next, regarding the monitoring process, as shown in FIG. 15 , in step S200A, the monitoring device 120 applies the AC current corrected by the correction process of FIG. 14 to the AC-applied cells. In this monitoring process, no AC current is applied to the AC-non-applied cells. Next, in step S210A, the monitoring device 120 detects the voltage of the AC-applied cells as a first voltage and the voltage of the AC-non-applied cells as a second voltage. Then, in step S220A, the monitoring device 120 performs a process to remove non-stationary noise contained in the first voltage, which is the response voltage of the AC-applied cells. In this process, for example, the second voltage is subtracted from the first voltage to extract an AC component with reduced influence of non-stationary noise. This allows, for example, as shown in FIG. 16 , to use the non-stationary noise contained in the second voltage to remove the non-stationary noise contained in the first voltage and appropriately extract an AC component corresponding to the first AC current. In addition, in the monitoring device 120 of this embodiment, the processor performs processes such as using the second voltage to remove noise components corresponding to non-stationary noise from the first voltage after the detected voltage detected by the cell voltage detection unit 132 is AD converted and input to the processor.

[0057] Next, in step S230A, the monitoring device 120 measures the impedance of the fuel cell FC to be the voltage application target based on the electrochemical impedance method. Specifically, the monitoring device 120 executes an impedance measurement process. The impedance of the AC applying cell is measured based on the first voltage in which the influence of non-stationary noise has been reduced and the current output by the AC applying cell.

[0058] Next, in step S240A, the monitoring device 120 executes a state determination process for determining the state of the AC application cell based on the impedance of the application target measured by the impedance measurement unit 142. The specific process of the state determination process is the same as that described in the first embodiment, and therefore, description thereof will be omitted.

[0059] The rest of the configuration is the same as that of the first embodiment. The monitoring device 120 of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration common to or equivalent to that of the first embodiment.

[0060] The monitoring device 120 of this embodiment also has the following features: (1) The monitoring device 120 utilizes noise components contained in the second voltage of the non-target AC application cell to remove noise components that act on the entire cell stack CS from the first voltage of the AC application cell, and can extract AC components that correspond to the AC current to be applied to the AC application cell. The AC components extracted in this manner are less affected by noise components that act on the entire cell stack CS, and are therefore suitable for measuring the impedance of the AC application cell.

[0061] (2) The impedance measurement unit 142 of this embodiment corrects the AC current applied to the AC-applied cells so as to remove noise components that affect the entire cell stack CS. This reduces the influence of noise components that affect the entire cell stack CS, allowing the impedance of the AC-applied cells to be measured appropriately.

[0062] (Variation of Second Embodiment) Unlike the first embodiment, the monitoring device 120 of the second embodiment is configured so that the AC application unit 130 applies only a first AC current to the application targets, but is not limited to this. For example, as in the first embodiment, the monitoring device 120 may be configured so that some application targets are designated as first targets and the first AC current is applied to the first targets, while other application targets other than the first targets are designated as second targets and a second AC current having an opposite phase to the first AC current is applied to the second targets. This also applies to the following embodiments.

[0063] As in the second embodiment, it is desirable that the impedance measurement unit 142 corrects the AC current applied to the AC-applied cells so as to remove noise components that act on the entire cell stack CS, but this is not necessarily required.

[0064] Third Embodiment Next, a third embodiment will be described with reference to Figures 17 and 18. In this embodiment, differences from the second embodiment will be mainly described.

[0065] The monitoring device 120 of this embodiment is configured to correct at least one of the first voltage output by the AC applied cell or the second voltage output by the AC non-applied cell so as to remove noise components that affect the entire cell stack CS. Specifically, the monitoring device 120 corrects at least one of the first voltage and the second voltage based on the difference in frequency characteristics between the first voltage and the second voltage so as to reduce the difference in non-stationary noise that occurs due to individual differences and deterioration of the fuel cell FC and the cell voltage detection unit 132. The pre-processing and monitoring processing performed by the monitoring device 120 of this embodiment will now be described with reference to FIGS. 17 and 18 .

[0066] First, regarding the preprocessing, as shown in FIG. 17 , in step S100B, the monitoring device 120 applies a predetermined AC current to both the AC-applied cells and the AC-non-applied cells. Next, in step S110B, the monitoring device 120 detects the frequency characteristics of each cell to which the AC current is applied. Then, in step S120B, the monitoring device 120 calculates a correction value for one of the first voltage and the second voltage, which can reduce the difference in non-stationary noise caused by individual differences, deterioration, etc., based on the difference in frequency characteristics between the first voltage and the second voltage when the AC current is applied. Note that the preprocessing may be performed to calculate a correction value for either the first voltage or the second voltage, or may be performed to calculate correction values ​​for both the first voltage and the second voltage.

[0067] Next, the monitoring process will be described. As shown in FIG. 18 , in step S200B, the monitoring device 120 applies a predetermined AC current to the AC-applied cells. In this monitoring process, no AC current is applied to the AC-non-applied cells. Next, in step S210B, the monitoring device 120 detects the voltage of the AC-applied cells as a first voltage and detects the voltage of the AC-non-applied cells as a second voltage. Then, in step S215B, the monitoring device 120 executes a correction process to correct at least one of the first voltage and the second voltage so as to remove noise components that affect the entire cell stack CS. In this correction process, at least one of the first voltage and the second voltage detected in step S210B is corrected using a correction value for one of the first voltage and the second voltage obtained in the preprocessing.

[0068] Next, in step S220A, the monitoring device 120 performs a process to remove non-stationary noise contained in the first voltage, which is the response voltage of the AC powered cell. This process involves, for example, subtracting the second voltage from the first voltage obtained through the correction process to extract an AC component with reduced influence of non-stationary noise. In the monitoring device 120 of this embodiment, the processor performs a process to remove noise components corresponding to non-stationary noise from the first voltage using the second voltage after the detected voltage detected by the cell voltage detection unit 132 is AD converted and input to the processor. Next, in step S230B, the monitoring device 120 measures the impedance of the AC powered cell using an electrochemical impedance method. Then, in step S240B, the monitoring device 120 performs a state determination process to determine the state of the AC powered cell. The processes in steps S230B and S240B are similar to the processes in steps S220A and S230A described in the second embodiment, and therefore will not be described again.

[0069] The remaining features are the same as those of the second embodiment. The monitoring device 120 of this embodiment can obtain the same effects as those of the second embodiment, which are achieved by a configuration common to or equivalent to that of the second embodiment. The monitoring device 120 of this embodiment also has the following features: (1) The impedance measurement unit 142 of this embodiment corrects one of the first voltage and the second voltage so as to remove noise components acting on the entire cell stack CS. This reduces the effects of noise components acting on the entire cell stack CS, allowing the impedance of the AC-powered cells to be measured appropriately.

[0070] (Variation of the Third Embodiment) In the second and third embodiments, the impedance measurement unit 142 is configured to perform processes such as noise removal by the processor after the detected voltage detected by the cell voltage detection unit 132 is AD converted and input to the processor. However, this is not limited to this. For example, the impedance measurement unit 142 may perform processes such as noise removal using an analog differential circuit before the detected voltage detected by the cell voltage detection unit 132 is AD converted. In this case, memory usage and the processor load can be reduced. Furthermore, the impedance measurement unit 142 may perform processes such as noise removal after frequency conversion of the detected voltage detected by the cell voltage detection unit 132 using a frequency converter (not shown). In this case, memory usage and the processor load can be significantly reduced. Note that the frequency conversion of the detected voltage detected by the cell voltage detection unit 132 may be performed by either hardware or software within the processor.

[0071] Fourth Embodiment Next, a fourth embodiment will be described with reference to Fig. 19. In this embodiment, differences from the first embodiment will be mainly described.

[0072] In this embodiment, an example will be described in which a monitoring device 120A according to the present disclosure is applied to a water electrolysis system 1A. As shown in Fig. 19 , the water electrolysis system 1A is configured as a system for producing fuel by electrolyzing water. The water electrolysis system 1A includes a cell stack CS in which multiple electrolysis cells EC are electrically connected, a water supply path 10A, a circulation path 20A, a fuel discharge path 30A, a control device 100A, and the like.

[0073] The cell stack CS constitutes an electrolysis device. The cell stack CS is a reaction device in which multiple reaction cells are electrically connected, and each cell outputs electrical energy through an electrochemical reaction. The cell stack CS is supplied with power from a power source PW via an external circuit.

[0074] The reaction cell of this embodiment is an electrolysis cell EC that outputs fuel (e.g., hydrogen) through an electrochemical reaction of a reducing agent supplied to the anode. The electrolysis cell EC is configured, for example, as a solid polymer cell. When water, which is a reducing agent, is supplied to the anode side while power is supplied from a power source PW, the electrolysis cell EC outputs hydrogen through the electrochemical reactions shown in the following reaction formulas F3 and F4. Anode: H ２ O → 2H ＋ +1 / 2O ２ +2e － ... (F3) Cathode: 2H ＋ +2e － →H ２ ...(F4) The cell stack CS is connected to a water supply path 10A, which supplies water to the cell stack CS, and a circulation path 20A, which circulates water discharged from the anode side of the cell stack CS. The water supply path 10A is provided with a water pump 11A, a first gas-liquid separator 12A, and an adjustment valve 13A. The first gas-liquid separator 12A is provided at the junction of the water supply path 10A and the circulation path 20A. The first gas-liquid separator 12A separates oxygen and water discharged from the anode side and flowing through the circulation path 20A. The first gas-liquid separator 12A discharges the separated oxygen to the outside and outputs the separated water to the water supply path 10A. The water pump 11A and the adjustment valve 13A are controlled based on control signals from a control device 100A.

[0075] A fuel discharge path 30A, through which hydrogen generated by separation through electrolysis of water in the cell stack CS flows, is also connected to the cell stack CS. The fuel discharge path 30A is provided with a second gas-liquid separator 31A, a back-pressure control valve 32A that adjusts the pressure on the cathode side inside the cell stack CS, and a fuel tank 33A that stores fuel. The second gas-liquid separator 31A separates the fuel and water discharged from the cathode side. The second gas-liquid separator 31A discharges the separated fuel to the fuel tank 33A and discharges the separated water to the cathode side of the cell stack CS. The back-pressure control valve 32A is controlled based on a control signal from the control device 100A.

[0076] Next, the control device 100A constituting the electronic control unit of the water electrolysis system 1A will be described. The control device 100A is configured by a computer including a processor and memory. The memory is a non-transitory tangible storage medium. Specifically, the control device 100A includes a control unit 110A that controls various devices in the water electrolysis system 1A and a monitoring device 120A. The control unit 110A and the monitoring device 120A may be configured by common hardware or separate hardware.

[0077] The control unit 110A acquires output information from various sensors, such as a stack current sensor 101 that detects the output current of the cell stack CS and a stack voltage sensor 102 that detects the output voltage of the cell stack CS. Based on the output information from the various sensors, the control unit 110A determines control signals to be output to various controlled devices, such as the water pump 11A, the regulating valve 13A, and the back pressure regulating valve 32A. The control unit 110A then outputs control signals to the various controlled devices to control their operation. Furthermore, if the monitoring results of the internal state of the electrolytic cell EC by the monitoring device 120A indicate an abnormal state, the control unit 110A performs recovery processing to recover from the abnormal state.

[0078] The monitoring device 120A is a device that monitors the internal state of the cell stack CS. The monitoring device 120A is configured to include an AC application unit 130A, a correction unit 141A, an impedance measurement unit 142A, and a state determination unit 143A. The AC application unit 130A, the correction unit 141A, the impedance measurement unit 142A, and the state determination unit 143A are configured in the same manner as in the first embodiment. Therefore, in this embodiment, descriptions of the AC application unit 130A, the correction unit 141A, the impedance measurement unit 142A, and the state determination unit 143A will be omitted.

[0079] The water electrolysis system 1A of this embodiment is otherwise similar to that of the first embodiment. Similar to the first embodiment, the water electrolysis system 1A of this embodiment can obtain the same effects as those of the first embodiment, which are achieved by a configuration common to or equivalent to that of the first embodiment.

[0080] The water electrolysis system 1A of this embodiment also has the following features: (1) The reaction cell monitored by the monitoring device 120 is the electrolytic cell EC that outputs fuel through an electrolytic reaction of a reducing agent supplied to the anode. This allows the state of the electrolysis device to be appropriately monitored based on the impedance of the electrolytic cell EC to which AC current is applied.

[0081] (Variation of the Fourth Embodiment) In the fourth embodiment, an example of monitoring an electrolytic cell EC that electrolyzes water vapor and outputs hydrogen as fuel has been described, but the gases etc. supplied to the electrolytic cell EC are not limited to those described above and may be different from those described above.

[0082] Furthermore, although the electrolytic cell EC of the fourth embodiment is configured such that water is supplied as a reducing agent to the anode of the electrolytic cell EC, this is not limiting. The electrolytic cell EC may be partially different from the above-described electrolytic cell EC.

[0083] Other Embodiments Although typical embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as follows.

[0084] In the above-described embodiment, an example was described in which the monitoring device 120 of the present disclosure is applied to a polymer electrolyte fuel cell FC or an electrolytic cell EC. However, the application of the monitoring device 120 is not limited to this, and it can also be applied to reaction cells other than polymer electrolyte fuel cells. The monitoring device 120 can also be applied to, for example, solid oxide fuel cells FC or electrolytic cells EC. Note that the solid oxide electrolytic cell EC may be configured to use, for example, a mixed gas of water vapor and carbon dioxide as a reducing agent, electrolyze the reducing agent, and output methane as fuel.

[0085] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle.

[0086] In the above-described embodiments, when numerical values ​​such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless they are specifically stated as essential or are clearly limited to a specific number in principle.

[0087] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., the shapes, positional relationships, etc. are not limited to those unless otherwise specified or when they are fundamentally limited to specific shapes, positional relationships, etc.

[0088] The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor with one or more dedicated hardware logic circuits. The controller and method of the present disclosure may be implemented on one or more special-purpose computers configured with a processor and memory programmed to perform one or more functions in combination with a processor configured with one or more hardware logic circuits. The computer program may also be stored on a computer-readable non-transitory tangible storage medium as instructions executed by a computer.

[0089] [Aspects of the present disclosure] [First aspect] A monitoring device for monitoring the state of a reaction device (CS) to which a plurality of reaction cells (FC, EC) that output electric energy or fuel by electrochemical reaction are electrically connected, the monitoring device comprising: an AC application unit (130) that applies AC current to some of the reaction cells included in the reaction device as targets to which AC current is applied; an impedance measurement unit (142) that measures the impedance of the target based on the voltage and current of the target when AC current is applied to the target by the AC application unit; and a state determination unit (143) that determines the state of the target based on the impedance of the target. [Second Aspect] The monitoring device according to the first aspect, wherein the application targets are two or more of the reaction cells, the AC application unit includes: a first application unit (134A) that defines some of the application targets as first targets and applies a first AC current to the first targets, and a second application unit (134B) that defines other application targets than the first targets as second targets and applies a second AC current that is in opposite phase to the first AC current to the second targets, and the impedance measurement unit measures the impedances of the first target and the second target based on the voltages and currents of the first target and the second target when the first AC current is applied to the first target and the second AC current is applied to the second target. [Third Aspect] The monitoring device according to the first aspect, wherein the application targets are two or more of the reaction cells, the AC application unit includes: a first application unit (134A) that defines some of the application targets as first targets and applies a first AC current to the first targets, and a second application unit (134B) that defines other application targets than the first targets as second targets and applies a second AC current to the second targets, the second AC current being in opposite phase to the first AC current, and the impedance measurement unit measures the impedance of the first targets based on the voltage and current of the first targets when the first AC current is applied to the first targets and the second AC current is applied to the second targets.[Fourth Aspect] The monitoring device according to the second or third aspect, further comprising an applied current correction unit (141) that corrects at least one of the first AC current and the second AC current so that an amplitude of a response voltage when the first AC current is applied and an amplitude of a response voltage when the second AC current is applied approach each other and a phase of the response voltage when the first AC current is applied and a phase of the response voltage when the second AC current is applied are opposite in phase. [Fifth Aspect] The monitoring device according to any one of the first to fourth aspects, wherein the impedance measurement unit extracts an AC component corresponding to the AC current to be applied to the application target based on a first voltage detected as an output voltage of the reaction cell to be applied and a second voltage detected as an output voltage of at least a part of the reaction cell other than the application target, and measures the impedance of the application target based on the AC component. [Sixth Aspect] The monitoring device according to the fifth aspect, wherein the impedance measurement unit corrects at least a part of the AC current, the first voltage, and the second voltage so as to remove noise components acting on the entire reaction device. [Seventh Aspect] The monitoring device according to any one of the first to sixth aspects, wherein the reaction cell is a fuel cell (FC) that outputs electric energy through an electrochemical reaction of a reducing gas supplied to an anode and an oxidizing gas supplied to a cathode. [Eighth Aspect] The monitoring device according to any one of the first to sixth aspects, wherein the reaction cell is an electrolysis cell (EC) that outputs fuel through an electrolytic reaction of a reducing agent supplied to an anode.

Claims

1. A monitoring device for monitoring the state of a reaction device (CS) to which a plurality of reaction cells (FC, EC) that output electric energy or fuel by electrochemical reaction are electrically connected, the monitoring device comprising: an AC application unit (130) that applies AC current to some of the reaction cells included in the reaction device as targets to which AC current is applied; an impedance measurement unit (142) that measures the impedance of the target based on the voltage and current of the target when AC current is applied to the target by the AC application unit; and a state determination unit (143) that determines the state of the target based on the impedance of the target.

2. The monitoring device according to claim 1, wherein the application targets are two or more of the reaction cells, the AC application unit includes: a first application unit (134A) that defines some of the application targets as first targets and applies a first AC current to the first targets, and a second application unit (134B) that defines other application targets as second targets and applies a second AC current that is in opposite phase to the first AC current to the second targets, and the impedance measurement unit measures the impedances of the first target and the second target based on the voltages and currents of the first target and the second target when the first AC current is applied to the first target and the second AC current is applied to the second target.

3. The monitoring device according to claim 1, wherein the application targets are two or more of the reaction cells, the AC application unit includes: a first application unit (134A) that defines some of the application targets as first targets and applies a first AC current to the first targets, and a second application unit (134B) that defines other application targets as second targets and applies a second AC current that is in opposite phase to the first AC current to the second targets, and the impedance measurement unit measures the impedance of the first targets based on the voltage and current of the first targets when the first AC current is applied to the first targets and the second AC current is applied to the second targets.

4. A monitoring device as described in claim 2 or 3, comprising an applied current correction unit (141) that corrects at least one of the first AC current and the second AC current so that the amplitude of the response voltage when the first AC current is applied approaches the amplitude of the response voltage when the second AC current is applied, and the phase of the response voltage when the first AC current is applied is opposite to the phase of the response voltage when the second AC current is applied.

5. The monitoring device according to claim 1 or 2, wherein the impedance measuring unit extracts an AC component corresponding to the AC current to be applied to the target based on a first voltage detected as the output voltage of the reaction cell to be applied and a second voltage detected as the output voltage of at least a part of the reaction cell other than the target, and measures the impedance of the target based on the AC component.

6. The monitoring device according to claim 5, wherein the impedance measuring unit corrects at least a portion of the AC current, the first voltage, and the second voltage so as to remove noise components acting on the entire reaction device.

7. The monitoring device according to claim 1 or 2, wherein the reaction cell is a fuel cell (FC) that outputs electrical energy through an electrochemical reaction between a reducing gas supplied to the anode and an oxidizing gas supplied to the cathode.

8. The monitoring device according to claim 1 or 2, wherein the reaction cell is an electrolytic cell (EC) that outputs fuel through an electrolytic reaction of a reducing agent supplied to an anode.

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