Cell control system

Abstract

This invention provides a cell control system capable of estimating the degree of degradation of an electrochemical cell. [Solution] A cell control system 1 for controlling an electrochemical cell 2 for electrolyzing water or water vapor 11, comprising: a current value acquisition unit 61 for acquiring the current value of the cell current supplied to the electrochemical cell 2; a voltage control unit 31 for changing the voltage change rate ΔE, which is the rate of change of the cell voltage applied to the electrochemical cell with respect to time; a temperature control unit 32 for changing the temperature change rate ΔT, which is the rate of change of the cell temperature, which is the temperature of the electrochemical cell, with respect to time; and a degradation estimation unit 33 for estimating the degradation state of the electrochemical cell based on the current value, the voltage value of the cell voltage, and the cell temperature, wherein the voltage change rate ΔE and the temperature change rate ΔT are not 0, and the timing at which the voltage control unit 31 changes the voltage change rate ΔE and the timing at which the temperature control unit 32 changes the temperature change rate ΔT are different.

Description

Technical Field

[0001] The present invention relates to a cell control system.

Background Art

[0002] For example, as described in Patent Document 1, a hydrogen production system including an electrolytic cell stack for electrolyzing a raw material to extract hydrogen is known. When the internal resistance of the electrolytic cell stack increases due to deterioration, this hydrogen production system attempts to reduce the internal resistance of the electrolytic cell stack by increasing the temperature of the electrolytic cell stack.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the hydrogen production system described in Patent Document 1 attempts to reduce the internal resistance of the cell without estimating the deterioration state of the cells constituting the electrolytic cell stack. Therefore, there is room for improvement from the viewpoint of efficiently reducing the internal resistance of the cell.

[0005] The present invention has been made in view of such problems, and aims to provide a cell control system capable of estimating the degree of deterioration of an electrochemical cell.

Means for Solving the Problems

[0006] One aspect of the present invention is a cell control system (1) for controlling an electrochemical cell (2) for electrolyzing water or steam (11), a current value acquisition unit (61) that acquires the current value of the cell current supplied to the electrochemical cell, A voltage control unit (31) that changes the rate of change of the cell voltage applied to the electrochemical cell with respect to time, A temperature control unit (32) that changes the rate of change of the cell temperature, which is the temperature of the electrochemical cell, with respect to time, The system includes a degradation estimation unit (33) that estimates the degradation state of the electrochemical cell based on the current value, the cell voltage value, and the cell temperature. The aforementioned rate of change of voltage and the aforementioned rate of change of temperature are not 0, The cell control system is configured such that the timing at which the voltage control unit changes the rate of change of the voltage and the timing at which the temperature control unit changes the rate of change of the temperature are different. [Effects of the Invention]

[0007] With the above configuration, the timing of the cell current change in response to a change in the rate of change of voltage and the timing of the cell current change in response to a change in the rate of change of temperature can be made different. This makes it possible to distinguish and obtain the change in cell current due to a change in cell voltage and the change in cell current due to a change in cell temperature. As a result, the state of degradation of the electrochemical cell can be estimated from the respective contributions of cell voltage and cell temperature to the cell current.

[0008] As described above, according to the above embodiment, a cell control system can be provided that can efficiently reduce the internal resistance of an electrochemical cell.

[0009] The reference numerals in parentheses in the claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments later, and do not limit the technical scope of the present invention. [Brief explanation of the drawing]

[0010] [Figure 1] A block diagram showing a hydrogen production apparatus including a cell control system according to Embodiment 1. [Figure 2] A block diagram showing the storage unit according to Embodiment 1. [Figure 3] Figure showing the cell control system according to Embodiment 1. [Figure 4] Figure showing the change in cell current with respect to cell voltage when the electrochemical cell deteriorates in Embodiment 1. [Figure 5] Figure showing the change in cell current with respect to cell temperature when the electrochemical cell deteriorates in Embodiment 1. [Figure 6] Main flow showing the operation of the cell control system according to Embodiment 1. [Figure 7] Part of the flowchart showing the cell temperature control process according to Embodiment 1. [Figure 8] Part of the flowchart showing the cell temperature control process according to Embodiment 1. [Figure 9] Part of the flowchart showing the cell voltage control process according to Embodiment 1. [Figure 10] Part of the flowchart showing the cell voltage control process according to Embodiment 1. [Figure 11] Graph showing the change in cell current over time in the cell control system according to Embodiment 1. [Figure 12] Graph showing the change over time of cell voltage, cell temperature, and cell current in the first region in the cell control system according to Embodiment 1. [Figure 13] Graph showing the change over time of cell voltage, cell temperature, and cell current in the second and third regions in the cell control system according to Embodiment 1. [Figure 14] Block diagram showing a hydrogen production device including the cell control system according to Embodiment 2. [Figure 15] Block diagram showing the storage unit according to Embodiment 2. [Figure 16] Part of the flowchart showing the cell temperature control process according to Embodiment 2. [Figure 17] Part of the flowchart showing the cell temperature control process according to Embodiment 2. [Figure 18] Part of the flowchart showing the cell voltage control process according to Embodiment 2. [Figure 19] A portion of the flowchart showing the cell voltage control process according to Embodiment 2. [Figure 20] A graph showing the change in cell current over time in the cell control system according to Embodiment 2. [Figure 21] A graph showing the time-dependent changes in cell voltage, cell temperature, and cell current in the second and third regions in the cell control system according to Embodiment 2. [Modes for carrying out the invention]

[0011] (Embodiment 1) Embodiment 1 of the cell control system 1 will be described with reference to Figures 1 to 3. The cell control system 1 of this embodiment 1 controls an electrochemical cell 2 for electrolyzing water or water vapor 11. The cell control system 1 of this embodiment 1 includes a current value acquisition unit 61, a voltage control unit 31, a temperature control unit 32, and a degradation estimation unit 33.

[0012] The current value acquisition unit 61 acquires the current value of the cell current supplied to the electrochemical cell 2. The voltage control unit 31 changes the voltage change rate ΔE, which is the rate of change of the cell voltage applied to the electrochemical cell 2 with respect to time. The temperature control unit 32 changes the temperature change rate ΔT, which is the rate of change of the cell temperature, which is the temperature of the electrochemical cell 2, with respect to time. The degradation estimation unit 33 estimates the degradation state of the electrochemical cell 2 based on the current value, the cell voltage value, and the cell temperature.

[0013] The voltage change rate ΔE and the temperature change rate ΔT are not zero. The timing at which the voltage control unit 31 changes the voltage change rate ΔE and the timing at which the temperature control unit 32 changes the temperature change rate ΔT are configured to be different.

[0014] The cell control system 1 of this embodiment 1 can be used, for example, as a means to control a hydrogen production apparatus that produces hydrogen by electrolyzing water or water vapor 11 contained in a supply gas using supplied power. In this embodiment 1, a supply gas containing water vapor 11 is supplied to the cathode channel 21 of the electrochemical cell 2 shown in Figure 3, and air is supplied as the supply gas to the anode channel 22. The electrochemical cell 2 is configured to decompose the water vapor 11 and produce hydrogen gas using power supplied from a power source 51. In other words, in this embodiment 1, water is supplied to the cathode channel 21 in the form of water vapor 11.

[0015] As shown in Figure 1, the cell control system 1 comprises a control unit 3, a storage unit 4, a current value acquisition unit 61, a voltage value acquisition unit 62, and a temperature acquisition unit 63.

[0016] The control unit 3 controls the operating conditions of the electrochemical cell 2. The control unit 3 includes a voltage control unit 31, a temperature control unit 32, and a degradation estimation unit 33. The control unit 3 also includes a processor and memory. The processor can control the electrochemical cell 2, for example, by executing a control program pre-stored in the memory.

[0017] As shown in Figure 2, the memory unit 4 stores the temperature change rate ΔT, the voltage change rate ΔE, the threshold TH, and the reference data RD.

[0018] The rate of change of temperature ΔT is the rate of change of the cell temperature, which is the temperature of electrochemical cell 2, with respect to time. The rate of change of temperature ΔT is set to a non-zero value. The rate of change of temperature ΔT includes the first rate of change of temperature ΔT1, the second rate of change of temperature ΔT2, and the third rate of change of temperature ΔT3. The rate of change of temperature ΔT may include one, two, or four or more rate of change of temperature ΔT.

[0019] In this embodiment 1, the first temperature change rate ΔT1 and the third temperature change rate ΔT3 are set to positive values, while the second temperature change rate ΔT2 is set to a negative value. Furthermore, in this embodiment 1, the third temperature change rate ΔT3 is set to a value greater than the first temperature change rate ΔT1. However, the values ​​of each temperature change rate ΔT are arbitrary and may be set as appropriate.

[0020] The voltage change rate ΔE is the rate of change over time of the cell voltage applied to the electrochemical cell 2. The voltage change rate ΔE is set to a non-zero value. The voltage change rate ΔE includes a first voltage change rate ΔE1, a second voltage change rate ΔE2, and a third voltage change rate ΔE3. The voltage change rate ΔE may include one, two, or four or more voltage change rate ΔE.

[0021] In this embodiment 1, the first voltage change rate ΔE1 and the third voltage change rate ΔE3 are set to positive values, while the second voltage change rate ΔE2 is set to a negative value. Furthermore, in this embodiment 1, the third voltage change rate ΔE3 is set to a value greater than the first voltage change rate ΔE1. ​​However, the values ​​of each voltage change rate ΔE are arbitrary and may be set as appropriate.

[0022] The threshold TH is a predetermined numerical value set relative to the current value of the cell current. The threshold TH includes a first threshold TH1 and a second threshold TH2. The threshold TH may include one or more threshold THs. In this embodiment 1, the first threshold TH1 is set to a value greater than the second threshold TH2. However, the value of each threshold TH is arbitrary and may be set as appropriate.

[0023] The temperature control unit 32 changes the rate of temperature change ΔT based on the current value supplied to the electrochemical cell 2 and the threshold value TH (see Figure 13). The temperature control unit 32 changes the rate of temperature change ΔT by selecting one of the first rate of temperature change ΔT1, the second rate of temperature change ΔT2, and the third rate of temperature change ΔT3. In this embodiment 1, the temperature control unit 32 changes the rate of temperature change ΔT when the current value supplied to the electrochemical cell 2 falls below the first threshold value TH1. More specifically, when the current value supplied to the electrochemical cell 2 falls below the first threshold value TH1, the temperature control unit 32 changes the rate of temperature change ΔT from the first rate of temperature change ΔT1 or the second rate of temperature change ΔT2 to the third rate of temperature change ΔT3.

[0024] Furthermore, the temperature control unit 32 controls the temperature of the electrochemical cell 2 so that it remains below the upper limit temperature Tmax (see Figures 12 and 13). This prevents degradation from occurring due to excessively high temperatures in the electrochemical cell 2.

[0025] The time interval at which the temperature control unit 32 controls the cell temperature of the electrochemical cell 2 can be arbitrarily set, for example, in seconds, minutes, hours, days, weeks, etc. In this embodiment 1, since the hydrogen production apparatus is controlled, it is preferable to perform temperature control at relatively long time intervals, for example, the temperature control of the electrochemical cell 2 can be performed in hours or days.

[0026] The voltage control unit 31 changes the voltage rate of change ΔE based on the voltage value of the cell voltage applied to the electrochemical cell 2 and the threshold value TH (see Figure 13). The voltage control unit 31 changes the voltage rate of change ΔE by selecting one of the first voltage rate of change ΔE1, the second voltage rate of change ΔE2, and the third voltage rate of change ΔE3. In this embodiment 1, the voltage control unit 31 changes the voltage rate of change ΔE when the current value supplied to the electrochemical cell 2 falls below the second threshold value TH2. Specifically, the voltage control unit 31 changes the voltage rate of change ΔE from the first voltage rate of change ΔE1 or the second voltage rate of change ΔE2 to the third voltage rate of change ΔE3 when the current value supplied to the electrochemical cell 2 falls below the second threshold value TH2.

[0027] The voltage control unit 31 according to this embodiment 1 controls the voltage value so that it is less than or equal to the thermal neutral voltage Vn (see Figure 13). The thermal neutral voltage Vn is the voltage value at which endothermic and exothermic reactions balance when electrolysis of water or water vapor 11 is performed in the electrochemical cell 2.

[0028] If the electrolysis of water or water vapor 11 is performed at a voltage value greater than the thermal neutral voltage Vn, an exothermic reaction will proceed. This is preferable from the viewpoint that the heat necessary for the electrolysis reaction is obtained by the reaction. However, a cooling device and refrigerant are required separately to cool the electrochemical cell 2. Furthermore, it is difficult to precisely control the electrolysis reaction in the exothermic reaction region.

[0029] On the other hand, if the electrolysis of water or water vapor 11 is performed at a voltage value smaller than the thermal neutral voltage Vn, an endothermic reaction will proceed. For this reason, a heating device and heat source are required to heat the electrochemical cell 2. However, from the viewpoint of controlling the electrolysis reaction, heating can be used to promote the electrolysis reaction, and heating can be stopped or cooling can be used to suppress the electrolysis reaction. Therefore, performing the electrolysis of water or water vapor 11 at a voltage value smaller than the thermal neutral voltage Vn is preferable because it allows for precise control of the electrolysis reaction.

[0030] The time interval at which the voltage control unit 31 controls the cell voltage of the electrochemical cell 2 can be arbitrarily set, for example, in seconds, minutes, hours, days, weeks, etc. In this embodiment 1, since the hydrogen production apparatus is controlled, it is preferable to perform voltage control at relatively long time intervals, for example, the voltage control of the electrochemical cell 2 can be performed in hours or days.

[0031] The degradation estimation unit 33 estimates the degradation state of the electrochemical cell 2 based on the current value supplied to the electrochemical cell 2, the voltage value of the cell voltage applied to the electrochemical cell 2, and the cell temperature of the electrochemical cell 2. The degradation estimation unit 33 will be described in detail later.

[0032] The cell control system 1 of this embodiment 1 includes a cell stack 20 formed by stacking multiple electrochemical cells 2. In the cell stack 20, the multiple electrochemical cells 2 are electrically connected in series. In the cell stack 20, the multiple electrochemical cells 2 are stacked in the direction Z (see Figure 3) of the arrangement of the cathode channel 21, electrolyte 23, and anode channel 22 in the electrochemical cell 2. Furthermore, the multiple electrochemical cells 2 are sandwiched between a pair of end plates (not shown) located at both ends of the arrangement direction Z in the cell stack 20.

[0033] The cell stack 20 is housed within a housing 15 covered with thermal insulation. The housing 15 is for maintaining the electrochemical cell 2 at a temperature suitable for the electrolysis of water vapor 11. A temperature control unit 151 for adjusting the temperature of the cell stack 20 is housed within the housing 15. The temperature control unit 151 can be, for example, an electric heater or a heat exchanger. The control unit 3 controls the temperature control unit 151 to, for example, set the temperature of the electrochemical cell 2 to 500-600°C. However, the temperature range of the electrochemical cell 2 is not limited to the above range and can be set arbitrarily.

[0034] The cell control system 1 has a power supply 51 that supplies power to the cell stack 20. The power supply 51 supplies the electrochemical cell 2 with the power necessary for the electrolysis of water vapor 11.

[0035] The cell control system 1 includes a cathode supply channel 53 that supplies supply gas to the cathode channel 21 of the electrochemical cell 2, and an anode supply channel 54 that supplies supply gas to the anode channel 22 of the electrochemical cell 2. In this embodiment 1, the cathode supply channel 53 supplies supply gas containing water vapor 11 to the cathode channel 21, and the anode supply channel 54 supplies air, which is the supply gas, to the anode channel 22. The cathode supply channel 53 is provided with a flow rate adjustment unit 531 that adjusts the flow rate of the supply gas supplied to the cathode channel 21. The flow rate adjustment unit 531 can be, for example, a solenoid valve. The anode supply channel 54 is also provided with an air pump 541 for supplying pressurized air to the anode channel 22. The control unit 3 adjusts the flow rate of the gas supplied to the cathode channel 21 and the anode channel 22, as well as the pressure inside the cathode channel 21 and the anode channel 22, by controlling the flow rate adjustment unit 531 and the air pump 541.

[0036] Furthermore, the cell control system 1 includes a cathode discharge channel 57 through which the gas discharged from the cathode channel 21 flows, and an anode discharge channel 58 through which the gas discharged from the anode channel 22 flows.

[0037] The cell control system 1 of this embodiment 1 has an inert gas supply path 55 that supplies an inert gas, which is the supply gas, to the electrochemical cell 2. The inert gas supply path 55 is connected to a cathode supply path 53 and an anode supply path 54, and is configured to supply inert gas to the cathode path 21 and the anode path 22, respectively. The inert gas supply path 55 is provided with flow rate adjustment units 551 and 552 that adjust the flow rate of the inert gas supplied to the cathode path 21 or the anode path 22. The flow rate adjustment units 551 and 552 can be, for example, solenoid valves. The control unit 3 adjusts the flow rate of the inert gas supplied to the cathode path 21 or the anode path 22 by controlling the flow rate adjustment units 551 and 552.

[0038] The cell control system 1 of this embodiment 1 includes a hydrogen supply channel 56 for supplying hydrogen gas, which is the supply gas, to the cathode channel 21. The hydrogen supply channel 56 is connected to the cathode supply channel 53. The hydrogen supply channel 56 is also provided with a flow rate adjustment unit 561 for adjusting the flow rate of hydrogen gas supplied to the cathode channel 21. The flow rate adjustment unit 561 can be, for example, a solenoid valve. The hydrogen supply channel 56 is intended to suppress oxidation of the cathode diffusion layer 242 and the cathode reaction layer 241, described later, and prevent deterioration by supplying hydrogen gas to the cathode channel 21 as needed. The control unit 3 adjusts the flow rate of hydrogen gas supplied to the cathode channel 21 by controlling the flow rate adjustment unit 561.

[0039] The cell control system 1 includes a return channel 571 that branches off from the cathode discharge channel 57 and connects the cathode discharge channel 57 and the cathode supply channel 53. The return channel 571 is a channel for supplying water vapor 11 and hydrogen discharged to the cathode discharge channel 57 without being decomposed by the electrochemical cell 2 back to the cathode channel 21 as supply gas. The return channel 571 is equipped with a pump 572 for supplying the supply gas from the cathode discharge channel 57 to the cathode channel 21 via the cathode supply channel 53. The control unit 3 adjusts the flow rate of the supply gas from the cathode discharge channel 57 supplied to the cathode channel 21 by controlling the pump 572.

[0040] The cell control system 1 includes a temperature acquisition unit 63 for measuring the cell temperature of the electrochemical cell 2. The cell temperature information acquired by the temperature acquisition unit 63 is transmitted to the control unit 3. The temperature acquisition unit 63 can be, for example, a thermocouple or a resistance thermometer. If the temperature acquisition unit 63 is a sheathed thermocouple, for example, the cell temperature of the electrochemical cell 2 can be measured by inserting the sheathed thermocouple inside the end plates (not shown) provided at both ends of the cell stack 20 in the Z direction.

[0041] The cell control system 1 includes a pressure acquisition unit (not shown) that measures the pressure in the cathode channel 21 and the anode channel 22. The pressure acquisition unit can be installed, for example, in the electrochemical cell 2 to directly measure the pressure in the cathode channel 21 and the anode channel 22. The pressure information acquired by the pressure acquisition unit is transmitted to the control unit 3. The pressure acquisition unit can also be installed, for example, in the cathode supply channel 53, cathode discharge channel 57, anode supply channel 54, and anode discharge channel 58. In this case, for example, the magnitude of the pressure in the cathode supply channel 53, cathode discharge channel 57, anode supply channel 54, and anode discharge channel 58 can be considered as the magnitude of the pressure in the cathode channel 21 and the anode channel 22, and control such as degradation diagnosis can be performed. The control unit 3 can also calculate the magnitude of the pressure in the cathode channel 21 and the anode channel 22 based on the magnitude of the pressure in the cathode supply channel 53, the anode supply channel 54, etc.

[0042] The cell control system 1 has a flow rate acquisition unit (not shown) that measures the flow rate of the supply gas flowing through the cathode channel 21 and the anode channel 22. The flow rate information of the supply gas acquired by the flow rate acquisition unit is transmitted to the control unit 3. The flow rate acquisition unit can be provided, for example, in the cathode supply channel 53 and the anode supply channel 54. In this case, the flow rates of the cathode supply channel 53 and the anode supply channel 54 can be considered as the flow rates of the cathode channel 21 and the anode channel 22. The control unit 3 can also calculate the flow rates of the cathode channel 21 and the anode channel 22 based on the flow rates of the cathode supply channel 53 and the anode supply channel 54. The flow rate acquisition unit can be, for example, a mass flow meter, a volumetric flow meter, etc. Furthermore, since the volumetric flow rate of the supply gas containing water vapor 11 flowing through the cathode channel 21 changes easily with temperature and pressure, when using a volumetric flow meter as the flow rate measurement unit, it is preferable to convert it to a mass flow rate and use it for controlling the electrochemical cell 2. In other words, it is preferable to convert the volumetric flow rate, which is the measurement data from the volumetric flow meter, into a mass flow rate based on the measurement data from the temperature acquisition unit 63 and the pressure measurement unit, and use this for controlling the electrochemical cell 2.

[0043] The voltage value acquisition unit 62 acquires the voltage value of the cell voltage applied to the electrochemical cell 2. The voltage value acquisition unit 62 transmits the acquired cell voltage information to the control unit 3.

[0044] The current value acquisition unit 61 acquires the current value of the cell current supplied to the electrochemical cell 2. The current value acquisition unit 61 is located in the conductive path connecting the power supply and the electrochemical cell 2. The current value acquisition unit 61 transmits the acquired cell current information to the control unit 3.

[0045] Next, the electrochemical cell 2 will be described based on Figure 3. In this embodiment 1, the electrochemical cell 2 is a solid oxide type cell. That is, in this embodiment 1, the electrochemical cell 2 is an SOEC (Solid Oxide Electrolysis Cell). The electrolyte 23 is made of solid oxide ceramic and contains oxide ions (O 2- It has conductivity of ). The electrolyte 23 can be made using, for example, yttria-stabilized zirconia, perovskite-type oxide, yttria-partially stabilized zirconia, etc. The SOEC has a negative temperature resistance characteristic in which the electrical resistance of the electrochemical cell 2 decreases as the cell temperature increases.

[0046] The electrochemical cell 2 comprises a porous cathode reaction layer 241 provided on one side in the alignment direction Z of the electrolyte 23, and a porous cathode diffusion layer 242 provided between the cathode reaction layer 241 and the cathode channel 21. In this embodiment 1, the cathode reaction layer 241 contains a catalyst such as nickel to promote the decomposition reaction of water vapor 11. The cathode diffusion layer 242 has the function of diffusing water vapor 11 from the cathode channel 21 to the cathode reaction layer 241, and also has the function of diffusing hydrogen gas produced by electrolysis from the cathode reaction layer 241 to the cathode channel 21. The cathode reaction layer 241 and the cathode diffusion layer 242 can be made of materials such as metals or metal compounds.

[0047] Furthermore, the electrochemical cell 2 comprises a porous anode reaction layer 251 provided on the other side of the alignment direction Z in the electrolyte 23, and a porous anode diffusion layer 252 provided between the anode reaction layer 251 and the anode channel 22. In this embodiment 1, the anode reaction layer 251 contains a catalyst for promoting the generation of oxygen gas. The anode diffusion layer 252 has the function of diffusing the oxygen gas generated in the anode reaction layer 251 from the anode reaction layer 251 to the anode channel 22. The anode reaction layer 251 and the anode diffusion layer 252 can be made of materials such as metals and metal compounds. In addition, the anode reaction layer 251 can contain, for example, a perovskite-type oxide as a catalyst.

[0048] Next, the electrolysis of water vapor 11 in the electrochemical cell 2 will be described. In this embodiment 1, the water vapor 11 supplied to the cathode channel 21 passes through the cathode diffusion layer 242 and reaches the cathode reaction layer 241, where "H2O + 2e - →H2+O 2- The electrolytic reaction of "" takes place in the anode reaction layer 251. 2- → 1 / 2O2 + 2e - The following reaction takes place: In other words, in the cathode reaction layer 241, water vapor 11 is electrolyzed to produce hydrogen gas and oxide ions (O 2- Hydrogen gas is generated. The hydrogen gas diffuses into the cathode channel 21. The oxide ions move through the electrolyte 23 to the anode channel 22, where they are oxidized in the anode reaction layer 251 to become oxygen gas, which then diffuses into the anode channel 22. The hydrogen gas produced by this electrolytic reaction is discharged from the cathode channel 21 to the cathode discharge channel 57, and the generated oxygen gas is discharged from the anode channel 22 to the anode discharge channel 58.

[0049] The degradation estimation unit 33 will be explained with reference to Figures 4 and 5. When the electrochemical cell 2 degrades, its internal resistance increases. For example, when the electrolysis reaction of water or water vapor 11 is performed at a constant voltage, the cell current supplied to the electrochemical cell 2 decreases as the electrochemical cell 2 degrades and its internal resistance increases.

[0050] Furthermore, for example, if the electrolysis reaction of water or water vapor 11 is carried out with a constant current, the cell voltage applied to the electrochemical cell 2 increases due to the deterioration of the electrochemical cell 2, which increases the internal resistance of the electrochemical cell 2.

[0051] On the other hand, as described above, electrochemical cell 2 has a negative temperature resistance characteristic. Therefore, increasing the operating temperature of electrochemical cell 2 improves various reactivity processes in electrochemical decomposition and the ionic conductivity of the electrolyte, resulting in a decrease in the internal resistance of electrochemical cell 2.

[0052] As described above, when electrochemical cell 2 is operated, the internal resistance changes due to changes in cell current and cell voltage caused by degradation, as well as temperature changes. Therefore, simply examining the contribution of cell voltage to cell current (the amount of change in cell current corresponding to the change in cell voltage) makes it difficult to determine whether the changes in cell current and cell voltage are due to degradation of electrochemical cell 2 or to a decrease in the operating temperature of electrochemical cell 2.

[0053] Therefore, in this embodiment 1, the state of degradation of the electrochemical cell 2 is estimated from the contributions of the cell voltage value and the cell temperature to the cell current. This will be schematically explained below.

[0054] Figure 4 schematically shows the characteristics of the electrochemical cell 2 when the rate of change of cell temperature ΔT is set to the first rate of change of temperature ΔT1, and the rate of change of cell voltage ΔE is set to the first rate of change of voltage ΔE1. ​​In Figure 4, the horizontal axis represents the cell voltage applied to the electrochemical cell 2, and the vertical axis represents the cell current supplied to the electrochemical cell 2.

[0055] The white circles in Figure 4 represent data showing the relationship between cell current and cell voltage when electrochemical cell 2 is not degraded or when the cell temperature of electrochemical cell 2 is relatively high. The solid line L1 passing through the white circles is an approximation curve L1 generated by a known method. However, the approximation curve includes an approximation straight line.

[0056] The black circles in Figure 4 represent data showing the relationship between cell current and cell voltage when electrochemical cell 2 is degraded or when the cell temperature of electrochemical cell 2 is relatively low. In other words, the data with black circles are experimental data suggesting degradation of electrochemical cell 2. The dashed line L2 passing through the data with black circles is the approximation curve L2 for the data with black circles. However, the approximation curve includes the approximation straight line.

[0057] Figure 5 schematically shows the characteristics of the electrochemical cell 2 when the rate of change of cell temperature ΔT is set to the first rate of change of temperature ΔT1 and the rate of change of cell voltage ΔE is set to the first rate of change of voltage ΔE1. ​​In Figure 5, the horizontal axis represents the cell temperature of the electrochemical cell 2, and the vertical axis represents the cell current supplied to the electrochemical cell 2.

[0058] The white circles in Figure 5 represent data showing the relationship between cell current and cell temperature when electrochemical cell 2 is not degraded or when the cell temperature of electrochemical cell 2 is relatively high. The solid line L3 passing through the white circles is an approximation curve L3 generated by a known method. However, the approximation curve includes an approximation straight line.

[0059] The black circles in Figure 5 represent data showing the relationship between cell current and cell temperature when electrochemical cell 2 is degraded or when the cell temperature of electrochemical cell 2 is relatively low. In other words, the data with black circles are experimental data suggesting degradation of electrochemical cell 2. The dashed line L4 passing through the data with black circles is the approximation curve L4 for the data with black circles. However, the approximation curve includes the approximation straight line.

[0060] As shown in Figure 4, when the rate of change of cell temperature ΔT is set to the first rate of change of temperature ΔT1, and the rate of change of cell voltage ΔE is set to the first rate of change of voltage ΔE1, if the cell current decreases from the value indicated by the white circle to the value indicated by the black circle, it is difficult to determine whether the decrease in cell current is due to the deterioration of electrochemical cell 2 or to the decrease in the temperature of electrochemical cell 2.

[0061] Therefore, as shown in Figure 5, when the rate of change of cell temperature ΔT is set to the first rate of change of temperature ΔT1, and the rate of change of cell voltage ΔE is set to the first rate of change of voltage ΔE1, and the electrochemical cell 2 is not degraded, data showing the relationship between cell current and cell temperature is stored in the storage unit 4 as reference data RD.

[0062] If a decrease in cell current occurs, and the relationship between the decrease in cell current and the cell temperature of electrochemical cell 2 changes along the approximation curve L3 (see white arrow), then it can be inferred that the decrease in cell current is due to a decrease in the cell temperature of electrochemical cell 2.

[0063] On the other hand, if the decrease in cell current does not follow the approximation curve L3 (see black arrow), it can be inferred that the decrease in cell current is due to the deterioration of electrochemical cell 2. In this way, the state of deterioration of electrochemical cell 2 can be estimated from the contributions of cell voltage and cell temperature to the cell current.

[0064] Figures 4 and 5 describe the case where the rate of change of cell temperature ΔT is set to the first rate of change of temperature ΔT1 and the rate of change of cell voltage ΔE is set to the first rate of change of voltage ΔE1. ​​However, the combination of the rate of change of temperature ΔT and the rate of change of voltage ΔE is not limited to the above. In this embodiment 1, the relationship between cell current and cell temperature, and the relationship between cell current and cell voltage, when the first rate of change of temperature ΔT1, the second rate of change of temperature ΔT2, and the third rate of change of temperature ΔT3 are set for each of the first rate of change of voltage ΔE1, the second rate of change of voltage ΔE2, and the third rate of change of voltage ΔE3, are stored in the storage unit 4 as reference data RD.

[0065] However, the reference data RD may be measured data, or it may be data estimated through simulation. It may also be data converted based on measured data to accommodate changes in operating conditions.

[0066] The degradation estimation unit 33 estimates the degradation state of the electrochemical cell 2 based on the voltage value acquired by the voltage value acquisition unit 62, the cell temperature acquired by the temperature acquisition unit 63, the current value acquired by the current value acquisition unit 61, and the reference data RD.

[0067] In this embodiment 1, the timing at which the voltage control unit 31 changes the voltage rate of change ΔE and the timing at which the temperature control unit 32 changes the temperature rate of change ΔT are configured to be different. This allows the state of degradation of the electrochemical cell 2 to be estimated as follows. For example, suppose the state changes from one in which the temperature of the electrochemical cell 2 is controlled by a first temperature rate of change ΔT1 and the voltage of the electrochemical cell 2 is controlled by a first voltage rate of change ΔE1, to a state in which the cell temperature of the electrochemical cell 2 is controlled by a first temperature rate of change ΔT1 and the cell voltage of the electrochemical cell 2 is controlled by a third voltage rate of change ΔE3. Then, the cell current in the state in which the electrochemical cell 2 is controlled by a first temperature rate of change ΔT1 and a first voltage rate of change ΔE1 can be compared with the cell current in the state in which the electrochemical cell is controlled by a first temperature rate of change ΔT1 and a third voltage rate of change ΔE3. Furthermore, the reference data RD corresponding to the above operating conditions, which is stored in the storage unit 4, can be compared with this. This allows us to estimate the degradation state of electrochemical cell 2 based on more data, thereby improving the accuracy of the estimation regarding the degradation of electrochemical cell 2.

[0068] Note that the above-mentioned combinations of temperature change rate ΔT and voltage change rate ΔE are merely examples, and any combination of temperature change rates ΔT1 to ΔT3 and voltage change rates ΔE1 to ΔE3 is arbitrary.

[0069] The degradation estimation unit 33 may continuously estimate the degradation state of the electrochemical cell 2 while the electrochemical cell 2 is operating. Alternatively, the degradation estimation unit 33 may estimate the degradation state of the electrochemical cell 2 at regular intervals or at arbitrary intervals while the electrochemical cell 2 is operating. Furthermore, the degradation estimation unit 33 may estimate the degradation state of the electrochemical cell 2 at the timing when the temperature control unit 32 changes the rate of temperature change ΔT, or when the voltage control unit 31 changes the rate of voltage change ΔE.

[0070] Next, the control of the electrochemical cell 2 by the control unit 3 will be explained with reference to Figures 6 to 13.

[0071] Figure 6 shows the main flow of the cell control system 1 according to this embodiment 1. When the cell control system 1 is started, the cell temperature control process S1 and the cell voltage control process S2 are executed. The cell temperature control process S1 and the cell voltage control process S2 are executed in parallel.

[0072] Figure 7 shows a flowchart of the cell temperature control process S1. When the cell temperature control process S1 is executed, the temperature control unit 32 sets the initial cell temperature Ti (S101, see Figure 12). The temperature control unit 32 sets the initial cell temperature Ti to a value lower than the upper limit temperature Tmax of the electrochemical cell 2. In this embodiment, the initial temperature Ti is set to 500°C. However, the value of the initial temperature Ti can be set arbitrarily. Also, the upper limit temperature Tmax of the electrochemical cell 2 can be set arbitrarily. The upper limit temperature Tmax of the electrochemical cell 2 may be, for example, the temperature at which the degradation rate of the electrochemical cell 2 due to temperature becomes significantly large. In this embodiment 1, the upper limit temperature Tmax of the electrochemical cell 2 is set to 600°C. The temperature control unit 32 also sets the initial temperature Ti to at least the temperature at which water vapor 11 can be electrolyzed.

[0073] Next, in S102, the temperature acquisition unit 63 acquires the temperature of the electrochemical cell 2. The temperature acquisition unit 63 transmits the acquired cell temperature to the temperature control unit 32.

[0074] The temperature control unit 32 determines whether the received cell temperature is less than or equal to the upper limit temperature Tmax of the electrochemical cell 2 (S103). If the cell temperature is less than or equal to the upper limit temperature Tmax of the electrochemical cell 2 (S103:Y), the temperature control unit 32 performs control to increase the cell temperature at a first temperature change rate ΔT1 (S108, see Figure 12). As described above, since the SOEC constituting the electrochemical cell 2 has a negative resistance temperature characteristic, the electrical resistance value of the electrochemical cell 2 decreases as the cell temperature rises. After step S108 is executed, the process returns to S102 in Figure 7 to obtain the temperature of the electrochemical cell 2.

[0075] If the cell temperature is not below the upper limit temperature Tmax of the electrochemical cell 2 (S103:N), the temperature control unit 32 performs control to reduce the cell temperature at the second temperature change rate ΔT2 (S104, see Figure 13). This changes the rate of change of the cell temperature of the electrochemical cell 2. As described above, the second temperature change rate ΔT2 is set to a negative value. By keeping the temperature of the electrochemical cell 2 below the upper limit temperature Tmax, the deterioration of the electrochemical cell 2 can be suppressed (see Figures 12 and 13).

[0076] As described above, since electrochemical cell 2 has a negative temperature resistance characteristic, the internal resistance of electrochemical cell 2 increases as the cell temperature decreases.

[0077] Next, the current value acquisition unit 61 acquires the current value of the current supplied to the electrochemical cell 2 (S105). The current value acquisition unit 61 transmits the acquired current value to the temperature control unit 32 of the control unit 3.

[0078] The temperature control unit 32 determines whether the transmitted current value is less than or equal to the first threshold TH1 (S106). If the current value is not less than or equal to the first threshold TH1 (S106:N), the process returns to S104 in Figure 7.

[0079] If the current value is less than or equal to the first threshold TH1 (S106:Y), the temperature control unit 32 increases the cell temperature at the third temperature change rate ΔT3 (S107, see Figure 13). As described above, the third temperature change rate ΔT3 is set to a larger value than the first temperature change rate ΔT1. Therefore, the rate of increase in the temperature of the electrochemical cell 2 controlled based on the third temperature change rate ΔT3 is greater than when controlled based on the first temperature change rate ΔT1.

[0080] As described above, since electrochemical cell 2 has a negative temperature resistance characteristic, increasing the temperature of electrochemical cell 2 will decrease its internal resistance.

[0081] When step S107 is executed, the temperature acquisition unit 63 acquires the temperature of the electrochemical cell 2 (S109). The temperature acquisition unit 63 transmits the acquired cell temperature to the temperature control unit 32.

[0082] The temperature control unit 32 determines whether the received cell temperature is less than or equal to the upper limit temperature Tmax of the electrochemical cell 2 (S110). If the cell temperature is less than or equal to the upper limit temperature Tmax of the electrochemical cell 2 (S110:Y), the process returns to S107 and the cell temperature is increased by the third temperature change rate ΔT3.

[0083] If the cell temperature is not below the upper limit temperature Tmax of the electrochemical cell 2 (S110:N), step S111 in Figure 8 is executed. In step S111, the current value acquisition unit 61 acquires the current value of the current supplied to the electrochemical cell 2. The current value acquisition unit 61 transmits the acquired current value to the temperature control unit 32 of the control unit 3.

[0084] The temperature control unit 32 determines whether the transmitted current value is less than or equal to the second threshold TH2 (S112). If the current value is not less than or equal to the second threshold TH2 (S112:N), the process returns to S104 in Figure 7.

[0085] If the current value is less than or equal to the second threshold TH2 (S112:Y), the temperature control unit 32 determines that the electrochemical cell 2 has reached the end of its lifespan (S113). This is because, when the cell temperature is not less than or equal to the upper limit temperature Tmax of the electrochemical cell, if the current value is less than or equal to the second threshold TH2, it is determined that the electrochemical cell 2 has reached the end of its lifespan and is unable to perform the desired performance. Based on this, the temperature control unit 32 terminates the cell temperature control process S1.

[0086] Next, the cell voltage control process S2 will be described with reference to Figure 9. Figure 9 shows a flowchart of the cell voltage control process S2. When the cell voltage control process S2 is executed, the voltage control unit 31 sets the initial cell voltage Vi (S201, see Figure 12). The voltage control unit 31 sets the initial voltage Vi to a value lower than the thermal neutral point voltage Vn. In this embodiment 1, the thermal neutral point voltage Vn is set to 1.28V per electrochemical cell 2. However, the initial voltage Vi can be set to any value. The voltage control unit 31 also sets the initial voltage Vi to a voltage at least high enough to electrolyze water vapor 11.

[0087] Next, in S202, the voltage value acquisition unit 62 acquires the voltage value applied to the electrochemical cell 2. The voltage value acquisition unit 62 transmits the acquired cell voltage to the voltage control unit 31.

[0088] The voltage control unit 31 determines whether the received cell voltage is less than or equal to the thermal neutral voltage Vn (S203). If the cell temperature is less than or equal to the thermal neutral voltage Vn (S203:Y), the voltage control unit 31 performs control to increase the cell temperature at a first voltage change rate ΔE1 (S208, see Figure 12). After step S208 is performed, the process returns to S202 in Figure 9 to obtain the voltage value of the voltage applied to the electrochemical cell 2.

[0089] If the cell voltage is not below the thermal neutrality voltage Vn (S203:N), the voltage control unit 31 performs control to reduce the cell voltage by the second voltage change rate ΔE2 (S204). This changes the rate of change of the cell voltage of the electrochemical cell 2. As described above, the second voltage change rate ΔE2 is set to a negative value. By keeping the voltage of the electrochemical cell 2 below the thermal neutrality voltage Vn, the electrolysis reaction of water or water vapor 11 in the electrochemical cell 2 can be precisely controlled.

[0090] Next, the current value acquisition unit 61 acquires the current value supplied to the electrochemical cell 2 (S205). The current value acquisition unit 61 transmits the acquired current value to the voltage control unit 31 of the control unit 3.

[0091] The voltage control unit 31 determines whether the transmitted current value is less than or equal to the second threshold TH2 (S206). If the current value is not less than or equal to the second threshold TH2 (S206:N), the process returns to S204 in Figure 9.

[0092] If the current value is less than or equal to the second threshold TH2 (S206:Y), the voltage control unit 31 increases the cell voltage at the third voltage change rate ΔE3 (S207, see Figure 13). As described above, the third voltage change rate ΔE3 is set to a larger value than the first voltage change rate ΔE1. ​​Therefore, the rate of increase in the voltage of the electrochemical cell 2 controlled based on the third voltage change rate ΔE3 is greater than when controlled based on the first voltage change rate ΔE1.

[0093] When step S207 is executed, the voltage acquisition unit 62 acquires the voltage of the electrochemical cell 2 (S209). The voltage acquisition unit 62 transmits the acquired cell voltage to the voltage control unit 31.

[0094] The voltage control unit 31 determines whether the received cell voltage is less than or equal to the thermal neutral point voltage Vn (S210). If the cell voltage is less than or equal to the thermal neutral point voltage Vn (S210:Y), the process returns to S207, and the cell voltage is increased by the third voltage change rate ΔE3.

[0095] If the cell voltage is not less than or equal to the thermal neutral voltage Vn (S210:N), step S211 in Figure 10 is executed. In step S211, the current value acquisition unit 61 acquires the current value of the current supplied to the electrochemical cell 2. The current value acquisition unit 61 transmits the acquired current value to the voltage control unit 31 of the control unit 3.

[0096] The voltage control unit 31 determines whether the transmitted current value is less than or equal to the second threshold TH2 (S212). If the current value is not less than or equal to the second threshold TH2 (S212:N), the process returns to 204 in Figure 9.

[0097] If the current value is less than or equal to the second threshold TH2 (S212:Y), the voltage control unit 31 determines that the electrochemical cell 2 has reached the end of its lifespan (S213). This is because, when the cell voltage is not less than or equal to the thermal neutral point voltage Vn, which is the upper limit voltage of the electrochemical cell 2 in this embodiment, the current value being less than or equal to the second threshold TH2 indicates that the electrochemical cell 2 has reached the end of its lifespan and is unable to perform the desired performance. Based on this, the voltage control unit 31 terminates the cell voltage control process S2.

[0098] Next, the operation of this embodiment 1 will be described with reference to Figures 11 to 13. However, the mode of operation of this embodiment 1 is not limited to the following description.

[0099] Figure 11 schematically shows the relationship between cell current and time when the electrochemical cell 2 according to this embodiment 1 is operated. The operation of the electrochemical cell 2 can be divided into a first region, a second region, and a third region based on time.

[0100] The first region is the period from when the electrochemical cell 2 starts operating until the cell temperature of the electrochemical cell 2 is no longer below the upper limit temperature Tmax, or the cell voltage is no longer below the thermal neutral voltage Vn. When the electrochemical cell 2 starts operating, the cell current is supplied to the electrochemical cell 2 at an initial current Ii. As described above, when the electrochemical cell 2 starts operating, the voltage control unit 31 controls the cell voltage with a first voltage change rate ΔE1, and the temperature control unit 32 controls the cell temperature with a first temperature change rate ΔT1. Therefore, when the electrochemical cell 2 starts operating, the cell current increases from the initial current Ii as time progresses.

[0101] As the operating time of electrochemical cell 2 elapses, electrochemical cell 2 begins to degrade. When electrochemical cell 2 degrades, the cell current begins to decrease even if the cell temperature and cell voltage increase. Therefore, in the first region, the cell current follows an upward-convex curve.

[0102] The duration of the first period is not particularly limited and can be set arbitrarily, and can be calculated from the design life of the electrochemical cell 2. For example, the duration of the first period can be set to any period from one year to five years. In the first period, the electrochemical cell 2 is temperature-controlled based on the first rate of temperature change ΔT1 and voltage-controlled based on the first rate of voltage change ΔE1. ​​Therefore, since the rate of temperature change ΔT and the rate of voltage change ΔE are not changed frequently, the operating conditions of the electrochemical cell 2 can be stabilized.

[0103] For example, if the duration of the first period is set to one year and the range of cell temperature change is set to 500°C to 600°C, the first temperature change rate ΔT1 will be a temperature increase of 100°C over one year. Specifically, the first temperature change rate ΔT1 will be 0.27°C / day. Also, for example, if the duration of the first period is set to five years and the range of cell temperature change is set to 500°C to 600°C, the first temperature change rate ΔT1 will be a temperature increase of 100°C over five years. Specifically, the first temperature change rate ΔT1 will be 0.05°C / day. It is preferable to set the first temperature change rate ΔT1 to between 0.05°C / day and 0.27°C / day.

[0104] The third temperature change rate ΔT3 is a larger value than the first temperature change rate ΔT1, and is preferably set to 0.5°C / day to 1.0°C / day, and more preferably to 1.0°C / day to 5.0°C / day.

[0105] The second temperature change rate ΔT2 is a negative value, preferably set to -1.0°C / day to -0.5°C / day, and more preferably to -2.0°C / day to -1.0°C / day.

[0106] Furthermore, the first voltage change rate ΔE1 is preferably set to 0.05V / day to 0.15V / day, and more preferably to 0.15V / day to 0.25V / day.

[0107] The third voltage change rate ΔE3 is a larger value than the first voltage change rate ΔE1, and is preferably set to 0.25V / day to 0.35V / day, and more preferably to 0.35V / day to 0.45V / day.

[0108] The second voltage change rate ΔE2 is a negative value, preferably set to -0.2V / day to -0.1V / day, and more preferably to -0.3V / day to -0.2V / day.

[0109] The second region is the period from when the cell temperature of the electrochemical cell 2 is no longer below the upper limit temperature Tmax, or when the cell voltage is no longer below the thermal neutral voltage Vn, until the cell current no longer increases above the second threshold TH2. In this second region, the voltage control unit 31 changes the voltage change rate ΔE, and the temperature change rate ΔT is also changed. As a result, the cell current is controlled to be above the second threshold TH2 while repeatedly increasing and decreasing.

[0110] The third region is the region in which the cell current does not increase above the second threshold TH2, even when the voltage control unit 31 controls the cell voltage and the temperature control unit 32 controls the cell temperature. In the third region, the cell current of the electrochemical cell 2 cannot be increased above the second threshold TH2, so it is determined that the electrochemical cell 2 has reached the end of its lifespan. Therefore, the operation of the electrochemical cell 2 is stopped.

[0111] The following provides a detailed explanation of each area.

[0112] Figure 12 shows an example of the first region. From top to bottom, Figure 12 shows graphs illustrating the relationship between cell voltage and time, the relationship between cell temperature and time, and the relationship between cell current and time.

[0113] The cell voltage is initially applied to electrochemical cell 2 when it is operating, with an initial voltage Vi. Subsequently, the cell voltage increases at a first voltage change rate ΔE1 (S208 in Figure 9).

[0114] When the electrochemical cell 2 is in operation, its cell temperature is set to an initial temperature Ti. Subsequently, the cell temperature increases at the first current change rate (S108 in Figure 7). The cell temperature reaches the upper limit temperature Tmax at time t0. In this embodiment 1, the period from the start of operation of the electrochemical cell 2 to time t0 when the cell temperature reaches the upper limit temperature Tmax is defined as the first region.

[0115] When the cell temperature reaches the upper limit temperature Tmax, the temperature control unit 32 reduces the cell temperature at the second temperature change rate ΔT2 (S104 in Figure 7).

[0116] However, if the cell voltage reaches the thermal neutral voltage Vn earlier than the cell temperature reaches the upper limit temperature Tmax, the end of the first region is defined as the point at which the cell voltage reaches the thermal neutral voltage Vn.

[0117] When the electrochemical cell 2 is operating, an initial current Ii is supplied to the electrochemical cell 2. Subsequently, as the cell voltage increases and the cell temperature rises, the cell current also increases.

[0118] As the operating time of electrochemical cell 2 increases, the degradation of electrochemical cell 2 progresses. As a result, even if the cell voltage and cell temperature increase, the cell current begins to decrease. Consequently, the cell current curve in the first region is convex upwards.

[0119] Next, Figure 13 shows examples of the second and third regions. From top to bottom, Figure 13 shows graphs illustrating the relationship between cell voltage and time, the relationship between cell temperature and time, and the relationship between cell current and time. The start of time on the horizontal axis is t0, which is the end of the first region and the beginning of the second region.

[0120] During the interval from time t0 to time t1, the cell voltage increases at a first voltage change rate ΔE1. ​​The cell temperature decreases at a second temperature change rate ΔT2. The cell current reaches a first threshold TH1 at time t1. The temperature control unit 32 increases the cell temperature at a third temperature change rate ΔT3 (S107 in Figure 7).

[0121] During the interval from time t1 to time t2, the cell voltage increases at a first voltage change rate ΔE1. ​​The cell current begins to increase after time t1 has elapsed. This is because the response of the cell current is slightly delayed even when the cell temperature begins to increase at a third temperature change rate ΔT3. The cell temperature rises at the third temperature change rate ΔT3 and reaches the upper limit temperature Tmax at time t2. The temperature control unit 32 decreases the cell temperature at a second temperature change rate ΔT2 (S104 in Figure 7).

[0122] In the interval from time t2 to time t3, the cell voltage increases at a first voltage change rate ΔE1, reaching the thermal neutral voltage Vn at time t3. The voltage control unit 31 decreases the cell voltage at a second voltage change rate ΔE2 (S204 in Figure 9). The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases with a slight delay from time t2. This is because the response of the cell current to the change in cell temperature is delayed.

[0123] During the interval from time t3 to time t4, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases and reaches a first threshold TH1 at time t4. The temperature control unit 32 increases the cell temperature at a third temperature change rate ΔT3 (S107 in Figure 7).

[0124] During the interval from time t4 to time t5, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature increases at a third temperature change rate ΔT3. At time t5, the cell voltage reaches the upper temperature limit Tmax. The temperature control unit 32 decreases the cell temperature at a second temperature change rate ΔT2 (S104 in Figure 7). The cell current begins to increase with a slight delay after time t4 has elapsed.

[0125] In the interval from time t5 to time t6, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current begins to decrease with a slight delay after time t5 has elapsed. At time t6, the cell current reaches the first threshold TH1. The temperature control unit 32 increases the cell temperature at a third temperature change rate ΔT3 (S107 in Figure 7).

[0126] Between time t6 and time t7, the cell current decreases at a second voltage change rate ΔE2. The cell temperature increases at a third temperature change rate ΔT3. The cell temperature reaches its upper limit temperature Tmax at time t7. The temperature control unit 32 reduces the cell temperature at a second temperature change rate ΔT2 (S104 in Figure 7). The cell current decreases between time t6 and time t7. This is because the degradation of the electrochemical cell 2 has progressed, making it difficult to increase the cell current by increasing the cell temperature.

[0127] During the interval from time t7 to time t8, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases during the interval from time t7 to time t8. At time t8, the cell current reaches a second threshold TH2. The voltage control unit 31 increases the cell voltage at a third voltage change rate ΔE3 (S207 in Figure 9).

[0128] Between time t8 and time t9, the cell voltage increases at a third voltage change rate ΔE3. At time t9, the cell voltage reaches the thermal neutral voltage Vn. The voltage control unit 31 decreases the cell voltage at a second voltage change rate ΔE2 (S204 in Figure 9). The cell temperature decreases between time t8 and time t9. The cell current increases from time t8. The cell current responds quickly to changes in cell voltage. The cell current increases until time t9.

[0129] During the interval from time t9 to time t10, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases during the interval from time T9 to time t10. At time t9, the cell current decreases rapidly in line with the decrease in cell voltage. At time t10, the cell current reaches the first threshold TH1. The temperature control unit 32 increases the cell temperature at a third temperature change rate ΔT3 (S107 in Figure 7).

[0130] In the interval from time t10 to time t11, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature increases at a third temperature change rate ΔT3. The cell temperature reaches the upper limit temperature Tmax at time t11. The temperature control unit 32 decreases the cell temperature at a second voltage change rate ΔE2 (S204 in Figure 9). The cell current decreases in the interval from time t10 to time t11n. This is because the electrochemical cell 2 has deteriorated, and the cell current cannot be increased by raising the cell temperature.

[0131] During the interval from time t11 to time t12, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases during the interval from time t11 to time t12. The cell current reaches a second threshold TH2 at time t12. The voltage control unit 31 increases the cell voltage at a third voltage change rate ΔE3 (S207 in Figure 9).

[0132] In the interval from time t12 to time t13, the cell voltage increases at a third voltage change rate ΔE3. The cell voltage reaches the thermal neutral point voltage Vn at time t13. The voltage control unit 31 decreases the cell voltage at a second voltage change rate ΔE2 (S204 in Figure 9). The cell temperature decreases at a second temperature change rate ΔT2. The cell current increases rapidly at time t12 and continues to increase until time t13.

[0133] During the interval from time t13 to time t14, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases during the interval from time t13 to time t14. At time t14, the cell current reaches a second threshold TH2. The voltage control unit 31 increases the cell voltage at a third voltage change rate ΔE3 (S207 in Figure 9).

[0134] Between time t14 and time t15, the cell voltage increases at a third voltage change rate ΔE3. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases between time t14 and time t15. This is because the electrochemical cell 2 is deteriorating, and increasing the cell voltage does not increase the cell current.

[0135] The period from time t0 to time t15 is designated as the second region. In the second region, the operation of the electrochemical cell 2 is controlled by the voltage control unit 31 and the temperature control unit 32.

[0136] After time t15, the cell voltage decreases at the second voltage change rate ΔE2. The cell temperature decreases at the second temperature change rate ΔT2. The cell current continues to decrease. After time t15, no conditions are set to increase the cell voltage and cell temperature, so the cell current will continue to decrease. However, even if the cell voltage and cell temperature were increased, the degradation of electrochemical cell 2 has already progressed, so an increase in cell current cannot be expected. In other words, at time t15, it is determined that electrochemical cell 2 has reached the end of its lifespan (S113 in Figure 8, S213 in Figure 10). The period after time t15 is considered the third region.

[0137] The degradation estimation unit 33 may continuously estimate the degradation state of the electrochemical cell 2 while the electrochemical cell 2 is operating. Alternatively, the degradation estimation unit 33 may estimate the degradation state of the electrochemical cell 2 at regular intervals or at arbitrary intervals while the electrochemical cell 2 is operating. Furthermore, the degradation estimation unit 33 may estimate the degradation state of the electrochemical cell 2 at each time point from t0 to t15. With this, the operation of the cell control system 1 of this embodiment 1 is completed.

[0138] Next, the effects of this embodiment 1 will be described. The cell control system 1 according to this embodiment 1 controls an electrochemical cell 2 for electrolyzing water or water vapor 11. The cell control system 1 includes a current value acquisition unit 61, a voltage control unit 31, a temperature control unit 32, and a degradation estimation unit 33. The current value acquisition unit 61 acquires the current value of the cell current supplied to the electrochemical cell 2. The voltage control unit 31 changes the voltage change rate ΔE, which is the rate of change of the cell voltage applied to the electrochemical cell 2 with respect to time. The temperature control unit 32 changes the temperature change rate ΔT, which is the rate of change of the cell temperature, which is the temperature of the electrochemical cell 2, with respect to time. The degradation estimation unit 33 estimates the degradation state of the electrochemical cell 2 based on the current value, the voltage value of the cell voltage, and the cell temperature. The voltage change rate ΔE and the temperature change rate ΔT are not zero. The timing at which the voltage control unit 31 changes the voltage change rate ΔE and the timing at which the temperature control unit 32 changes the temperature change rate ΔT are configured to be different.

[0139] According to this embodiment 1, the timing at which the cell current changes in response to a change in the voltage rate of change ΔE and the timing at which the cell current changes in response to a change in the temperature rate of change ΔT can be made different. This makes it possible to distinguish and obtain the change in cell current due to a change in cell voltage and the change in cell current due to a change in cell temperature. As a result, the state of degradation of the electrochemical cell 2 can be estimated from the respective contributions of cell voltage and cell temperature to the cell current.

[0140] The voltage control unit 31 according to this embodiment 1 controls the voltage value to be less than or equal to the thermal neutral voltage Vn, which is the voltage value at which heat absorption and heat generation are balanced. This allows the electrochemical cell 2 to be operated in the heat absorption region. As a result, the deterioration of the electrochemical cell 2 can be suppressed compared to when the electrochemical cell 2 is operated in the heat generation region.

[0141] The temperature control unit 32 according to this embodiment 1 controls the cell temperature so that it is below the upper limit temperature Tmax of the electrochemical cell 2. This makes it possible to suppress the deterioration of the electrochemical cell 2 due to temperature rise.

[0142] The temperature control unit 32 according to this embodiment 1 is configured to change the temperature change rate ΔT when the current value supplied to the electrochemical cell 2 falls below a first threshold TH1. The voltage control unit 31 according to this embodiment 1 is configured to change the voltage change rate ΔE when the current value falls below a second threshold TH2, which is different from the first threshold TH1. As a result, by simply making the first threshold TH1 and the second threshold TH2 different, the timing at which the voltage control unit 31 changes the voltage change rate ΔE and the timing at which the temperature control unit 32 changes the temperature change rate ΔT can be made different.

[0143] In this embodiment 1, the first threshold TH1 is greater than the second threshold TH2. The response speed of the voltage value when controlling the voltage value is faster than the response speed of the cell temperature when controlling the cell temperature. Therefore, when the current value falls below the second threshold TH2, the cell current can be quickly increased by changing the voltage change rate ΔE.

[0144] (Embodiment 2) Next, Embodiment 2 will be described with reference to Figures 14 and 15. Note that, unless otherwise specified, reference numerals used in Embodiment 2 and later that are the same as those used in the previously described embodiments represent the same components as those in the previously described embodiments.

[0145] As shown in Figure 14, the control unit 3 according to this embodiment 2 includes a supply gas control unit 34. The supply gas control unit 34 controls the supply conditions of the supply gas supplied to the electrochemical cell 2. The supply gas includes air, inert gas, hydrogen, and water vapor 11. The supply conditions include the ratio of each component gas constituting the supply gas, the temperature of each supply gas, the flow rate, etc.

[0146] The supply gas control unit 34 receives the degradation status of the electrochemical cell 2 from the degradation estimation unit 33 and can change the supply conditions of the supply gas based on the degradation status of the electrochemical cell 2.

[0147] Examples of modifying the supply conditions of the supply gas include, for instance, controlling the oxygen concentration in the supply gas (increasing the concentration of inert gas mixed with air) or controlling the fuel utilization rate (increasing the ratio of water vapor in the hydrogen-water vapor mixture). The choice of which supply conditions to modify and how to modify them is arbitrary.

[0148] This section describes the control method for lowering the oxygen concentration in the supply gas. Specifically, the oxygen partial pressure in the anode channel 22 is reduced by flowing a gas other than air, such as nitrogen or helium, through the anode channel 22. In other words, an inert gas is supplied from the inert gas supply channel 55 (see Figure 14) to the anode channel 22 via the anode supply channel 54. As a result, the oxygen concentration of the gas supplied to the anode channel 22 becomes lower than the oxygen concentration of air, which is 21%. This makes it easier for the oxygen gas generated in the anode reaction layer 251 to disperse to the anode channel 22 and to be released to the outside through the anode channel 22, thereby reducing the overvoltage of the electrochemical cell 2. As a result, the cell current of the electrochemical cell 2 can be increased.

[0149] Furthermore, by reducing the fuel utilization rate (increasing the ratio of water vapor 11 in the hydrogen and water vapor 11 mixture), the reactivity to water vapor 11 can be improved, and the overpotential of the cathode reaction layer can be reduced. As a result, the cell current of the electrochemical cell 2 can be increased.

[0150] As shown in Figure 15, the storage unit 4 in this second embodiment stores the third threshold value TH3. The third threshold value TH3 is set to a smaller value than the first threshold value TH1 and the second threshold value TH2 described in Embodiment 1. The supply gas control unit 34 changes the supply conditions for the supply gas when the current value becomes less than or equal to the third threshold value TH3.

[0151] Figure 16 shows a flowchart of the cell temperature control process S1 according to this second embodiment. In the cell temperature control process S1 of this second embodiment, steps S101 to S108 are the same as steps S101 to S108 in Figure 7, so redundant explanations are omitted.

[0152] When step S107 is executed, the current value acquisition unit 61 acquires the current value of the cell current (S120). The current value acquisition unit 61 transmits the acquired current value to the supply gas control unit 34.

[0153] The supply gas control unit 34 determines whether the transmitted current value is less than or equal to the third threshold TH3 (S121). If the cell current value is less than or equal to the third threshold TH3 (S121:Y), the supply gas control unit 34 changes the supply conditions for the supply gas (S122). This increases the cell current.

[0154] Once step S122 is executed, the process returns to S105 in Figure 16.

[0155] On the other hand, if the cell current value is not below the third threshold TH3 (S121:N), the process returns to S107 in Figure 16. As a result, the temperature control unit 32 increases the cell temperature at the third temperature change rate ΔT3.

[0156] After step S107 is performed, the temperature control unit 32 performs step S123 in Figure 17 in parallel with step 120. In step S123, the temperature acquisition unit 63 acquires the temperature of the electrochemical cell 2. The temperature acquisition unit 63 transmits the acquired temperature to the temperature control unit 32.

[0157] The temperature control unit 32 determines whether the received cell temperature is less than or equal to the upper limit temperature Tmax of the electrochemical cell 2 (S124). If the cell temperature is less than or equal to the upper limit temperature Tmax of the electrochemical cell 2 (S124:Y), S107 in Figure 16 is executed.

[0158] If the cell temperature is not below the upper limit temperature Tmax of the electrochemical cell 2 (S124:N), the current value acquisition unit 61 acquires the current value of the current supplied to the electrochemical cell 2 (S125). The current value acquisition unit 61 transmits the acquired current value to the temperature control unit 32 of the control unit 3.

[0159] The temperature control unit 32 determines whether the transmitted current value is less than or equal to the third threshold TH3 (S126). If the current value is not less than or equal to the third threshold TH3 (S126:N), the process returns to S104 in Figure 16.

[0160] If the current value is less than or equal to the third threshold TH3 (S126:Y), the temperature control unit 32 determines that the electrochemical cell 2 has reached the end of its lifespan (S127). This is because, when the cell temperature is not less than or equal to the upper limit temperature Tmax of the electrochemical cell, if the current value is less than or equal to the third threshold TH3, it is determined that the electrochemical cell 2 has reached the end of its lifespan and is unable to perform the desired performance. Based on this, the temperature control unit 32 terminates the cell temperature control process S1.

[0161] Figure 18 shows a flowchart of the cell voltage control process S2 according to this second embodiment. In the cell voltage control process S2 of this second embodiment, steps S201 to S208 are the same as steps S201 to S208 in Figure 9, so redundant explanations are omitted.

[0162] When step S207 is executed, the current value acquisition unit 61 acquires the current value of the cell current (S220). The current value acquisition unit 61 transmits the acquired current value to the supply gas control unit 34.

[0163] The supply gas control unit 34 determines whether the transmitted current value is less than or equal to the third threshold TH3 (S221). If the cell current value is less than or equal to the third threshold TH3 (S221:Y), the supply gas control unit 34 changes the supply conditions for the supply gas (S122). This increases the cell current.

[0164] Once step S222 is executed, the process returns to S205 in Figure 18.

[0165] On the other hand, if the cell current value is not below the third threshold TH3 (S221:N), the process returns to S207 in Figure 18. As a result, the voltage control unit 31 increases the cell voltage at the third voltage change rate ΔE3.

[0166] After step S207 is performed, the voltage control unit 31 performs step S223 in Figure 19 in parallel with step 220. In step S223, the voltage value acquisition unit 62 acquires the voltage value of the voltage applied to the electrochemical cell 2. The voltage value acquisition unit 62 transmits the acquired voltage value to the voltage control unit 31.

[0167] The voltage control unit 31 determines whether the received cell voltage is less than or equal to the thermal neutral point voltage Vn of the electrochemical cell 2 (S224). If the cell voltage is less than or equal to the thermal neutral point voltage Vn of the electrochemical cell 2 (S224:Y), S207 in Figure 18 is executed.

[0168] If the cell voltage is not less than or equal to the thermal neutral point voltage Vn of the electrochemical cell 2 (S224:N), the current value acquisition unit 61 acquires the current value of the current supplied to the electrochemical cell 2 (S225). The current value acquisition unit 61 transmits the acquired current value to the voltage control unit 31 of the control unit 3.

[0169] The voltage control unit 31 determines whether the transmitted current value is less than or equal to the third threshold TH3 (S226). If the current value is not less than or equal to the third threshold TH23 (S226:N), the process returns to S204 in Figure 18.

[0170] If the current value is less than or equal to the third threshold TH3 (S226:Y), the voltage control unit 31 determines that the electrochemical cell 2 has reached the end of its lifespan (S227). This is because, when the cell voltage is no longer less than or equal to the thermal neutral point voltage Vn, which is the upper limit voltage for use of the electrochemical cell 2 in this embodiment 2, the current value being less than or equal to the third threshold TH3 indicates that the electrochemical cell 2 has reached the end of its lifespan and is unable to perform the desired performance. Based on the above, the voltage control unit 31 terminates the cell voltage control process S2.

[0171] Next, the operation of this second embodiment will be described with reference to Figures 20 and 21. However, the mode of operation of this second embodiment is not limited to the following description.

[0172] Figure 20 schematically shows the relationship between cell current and time when the electrochemical cell 2 according to this second embodiment is operated. This second embodiment differs from the first embodiment in that the third threshold value TH3 is shown on the vertical axis.

[0173] The following provides a detailed explanation of each area.

[0174] Since the first region is the same as in Embodiment 1, we will omit any redundant explanations.

[0175] Figure 21 shows an example of the second and third regions according to this second embodiment. The period from time t0 to time t15 is the same as in the first embodiment, so redundant explanations are omitted.

[0176] During the interval from time t15 to time t16, the cell voltage decreases at the second voltage change rate ΔE2. The cell temperature decreases at the second current change rate. The cell current decreases during the interval from time t15 to time t16, and at time t16, it reaches the third threshold TH3. The supply gas control unit 34 changes the supply conditions of the supply gas.

[0177] Between time t16 and time t17, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current increases from a point after time t16 due to the change in the supply conditions of the supply gas. This is because the response of the cell current to the change in the supply conditions of the supply gas is slightly delayed. The cell current increases above the second threshold TH2 and the first threshold TH1. Subsequently, the cell current begins to decrease because the electrochemical cell 2 has already deteriorated, and the cell voltage, cell current, and temperature have all decreased. As a result, the cell current curve becomes convex upwards between time t16 and time t17. The cell current reaches the first threshold TH1 at time t17. The temperature control unit 32 increases the cell temperature at a third temperature change rate ΔT3 (S107 in Figure 16).

[0178] During the interval from time t17 to time t18, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature increases at a third temperature change rate ΔT3. The cell current decreases during the interval from time t17 to time t18 because the electrochemical cell 2 is deteriorating. At time t18, the cell current reaches the second threshold TH2. The voltage control unit 31 increases the cell voltage at a third voltage change rate ΔE3 (S207 in Figure 18).

[0179] During the interval from time t18 to time t19, the cell voltage increases at a third voltage change rate ΔE3. The cell temperature increases at a third temperature change rate ΔT3. At time t19, the cell temperature reaches the upper limit temperature Tmax. The temperature control unit 32 decreases the cell temperature at a second temperature change rate ΔT2 (S104 in Figure 16). The cell current increases during the interval from time t18 to time t19.

[0180] In the interval from time t19 to time t20, the cell voltage increases at the third temperature change rate ΔT3. The cell voltage reaches the thermal neutral voltage Vn at time t20. The voltage control unit 31 decreases the cell voltage at the second voltage change rate ΔE2 (S204 in Figure 18). The cell temperature decreases at the second temperature change rate ΔT2. The cell current follows an upward-convex curve in the interval from time t19 to time t20.

[0181] In the interval from time t20 to time t21, the cell voltage decreases at a second temperature change rate ΔT2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current decreases in the interval from time t20 to time T21, reaching a second threshold TH2 at time t21. The voltage control unit 31 increases the cell voltage at a third voltage change rate ΔE3 (S207 in Figure 18).

[0182] During the interval from time t21 to time t22, the cell voltage increases at a third voltage change rate ΔE3. The cell voltage reaches the thermal neutral point voltage Vn at time t22. The voltage control unit 31 decreases the cell voltage at a second voltage change rate ΔE2 (S204 in Figure 18). The cell temperature decreases at a second temperature change rate ΔT2. The cell current remains almost unchanged from time t21 to time t22 due to the degradation of the electrochemical cell 2.

[0183] Between time t22 and time t23, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. Between time t22 and time t23, the cell current decreases. At time t23, the cell current reaches a third threshold TH3. The supply gas control unit 34 changes the supply conditions of the supply gas.

[0184] Between time t23 and time t24, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current increases slightly after time t23. Then, between time t23 and time t24, the cell current changes from increasing to decreasing, forming an upward-convex curve. The cell current reaches the third threshold TH3 at time t24. The supply gas control unit 34 changes the supply conditions of the supply gas.

[0185] Between time t24 and time t25, the cell voltage decreases at a second voltage change rate ΔE2. The cell temperature decreases at a second temperature change rate ΔT2. The cell current continues to decrease between time t24 and time t25 due to the degradation of electrochemical cell 2 (S127 in Figure 17, S227 in Figure 19). That is, at time t24, it is determined that electrochemical cell 2 has reached the end of its lifespan. The period after time t24 is considered the third region.

[0186] The degradation estimation unit 33 may continuously estimate the degradation state of the electrochemical cell 2 while the electrochemical cell 2 is operating. Alternatively, the degradation estimation unit 33 may estimate the degradation state of the electrochemical cell 2 at regular intervals or at arbitrary intervals while the electrochemical cell 2 is operating. Furthermore, the degradation estimation unit 33 may estimate the degradation state of the electrochemical cell 2 at each time point from t0 to t25. With the above, the operation of the cell control system 1 of this embodiment 2 is completed.

[0187] Next, the effects of this second embodiment will be described. The cell control system 1 according to this second embodiment further includes a supply gas control unit 34 that controls the supply conditions of the supply gas supplied to the electrochemical cell 2. The supply gas control unit 34 changes the supply conditions of the supply gas when the current value falls below a third threshold TH3, which is smaller than the first threshold TH1 and the second threshold TH2. This makes it possible to change the supply conditions of the supply gas according to the deteriorated parts of the electrochemical cell 2. As a result, it is possible to perform control according to the deteriorated parts of the electrochemical cell 2.

[0188] The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from its spirit. [Explanation of symbols]

[0189] 1: Cell control system, 2: Electrochemical cell, 11: Water vapor, 31: Voltage control unit, 32: Temperature control unit, 33: Degradation estimation unit, 61: Current value acquisition unit, ΔE: Voltage change rate, ΔT: Temperature change rate

Claims

1. A cell control system (1) for controlling an electrochemical cell (2) for electrolyzing water or water vapor (11), A current value acquisition unit (61) acquires the current value of the cell current supplied to the electrochemical cell, A voltage control unit (31) that changes the rate of change of the cell voltage applied to the electrochemical cell, which is the rate of change of the cell voltage with respect to time, A temperature control unit (32) that changes the rate of change of the cell temperature, which is the temperature of the electrochemical cell, with respect to time, The system includes a degradation estimation unit (33) that estimates the degradation state of the electrochemical cell based on the current value, the cell voltage value, and the cell temperature. The aforementioned rate of change of voltage and the aforementioned rate of change of temperature are not zero. A cell control system configured such that the timing at which the voltage control unit changes the rate of change of the voltage and the timing at which the temperature control unit changes the rate of change of the temperature are different.

2. The cell control system according to claim 1, wherein the voltage control unit controls the voltage value to be less than or equal to the thermal neutral voltage (Vn), which is the voltage value at which heat absorption and heat generation are balanced.

3. The cell control system according to claim 1, wherein the temperature control unit controls the cell temperature so that it is below the upper limit temperature (Tmax) of the electrochemical cell.

4. The temperature control unit is configured to change the rate of temperature change when the current value supplied to the electrochemical cell falls below a first threshold (TH1). The cell control system according to claim 1, wherein the voltage control unit is configured to change the voltage change rate when the current value falls below a second threshold (TH2) that is different from the first threshold.

5. The cell control system according to claim 4, wherein the first threshold is greater than the second threshold.

6. moreover, The system includes a supply gas control unit (34) that controls the supply conditions of the supply gas supplied to the electrochemical cell, The cell control system according to claim 4 or 5, wherein the supply gas control unit changes the supply conditions of the supply gas when the current value falls below a third threshold (TH3) which is smaller than the first threshold and the second threshold.

Images