Water electrolysis system and method for controlling water electrolysis system

Abstract

This water electrolysis system includes: a water electrolysis device including a water electrolysis cell that generates hydrogen by electrolysis; a power supply device capable of supplying, to the water electrolysis device, a drive voltage for causing electrolysis in the water electrolysis cell and a voltage having polarity opposite that of the drive voltage; and a control device that controls the driving of the power supply device. In operation stop processing for stopping the electrolysis caused by the supply of the drive voltage, the control device controls the driving of the power supply device so as to stop the supply of the drive voltage to the water electrolysis device and then supply the opposite polarity voltage to the water electrolysis device.

Description

Water electrolysis system and method for controlling the water electrolysis system

[0001] The present invention relates to a water electrolysis system and a method for controlling a water electrolysis system.

[0002] Patent Literature 1 (JP-A-2003-125999) describes a water electrolysis system and a control method thereof. It states: "The power supply unit supplies current and voltage from a DC power supply between the terminals of the water electrolysis cell. After hydrogen production is stopped, the control unit establishes a connection state in which a discharge current flows in the water electrolysis cell in a direction opposite to the direction of the current flowing during hydrogen production. The control unit performs control in a first mode in which the potential of the anode electrode is controlled to a first potential while maintaining a predetermined rate of potential decrease at the anode electrode during the generation of the discharge current." It further states: "In the first mode, when hydrogen production is stopped, the connection control unit disconnects the DC power supply using a switch on the power supply unit and connects the variable resistor using a switch. The resistance control unit controls the resistance value of the variable resistor based on information from the voltmeter to control the rate of T1216 potential decrease within a range that suppresses catalyst degradation." This makes it possible to suppress elution of the metal catalyst from the anode electrode due to rapid voltage fluctuations and voltage decrease associated with discharge after the stoppage of discharge.

[0003] JP 2023-58306 A

[0004] When a high voltage is used in a water electrolysis system, it is effective to stack water electrolysis cells to form a water electrolysis stack and further connect multiple water electrolysis stacks in series to distribute the voltage. However, a water electrolysis stack tends to retain electric charge even after the supply of voltage from a power source is stopped, and it takes time to remove the electric potential. If the electric potential is not sufficiently removed, there is a risk of electric shock or discharge when approaching the water electrolysis stack for maintenance or part replacement after operation is stopped. Furthermore, this risk is more pronounced in a configuration in which water electrolysis stacks are connected in series. Therefore, it is necessary to safely and quickly remove the electric charge remaining in the water electrolysis stack after operation is stopped and reliably drop it to ground potential.

[0005] Therefore, an object of the present invention is to provide a water electrolysis system that can quickly neutralize static electricity from water electrolysis cells when the system is shut down, and a method for controlling the water electrolysis system.

[0006] To achieve the above object, for example, the following configuration is adopted: The present application includes multiple means for achieving the above object, and one example thereof is a water electrolysis system including: a water electrolysis device including a water electrolysis cell that generates hydrogen by electrolysis; a power supply device that can supply to the water electrolysis device a drive voltage for causing electrolysis in the water electrolysis cell and a voltage of opposite polarity to the drive voltage; and a control device that controls drive of the power supply device, wherein the control device controls drive of the power supply device so as to supply the voltage of the opposite polarity to the water electrolysis device after stopping supply of the drive voltage to the water electrolysis device during an operation shutdown process for stopping generation of electrolysis due to the supply of the drive voltage.

[0007] The present invention provides a water electrolysis system and a method for controlling a water electrolysis system that can quickly neutralize static electricity from a water electrolysis cell when the system is shut down.

[0008] FIG. 1 is a configuration diagram of a water electrolysis system according to a first embodiment; FIG. 2 is a diagram for explaining a control method of the water electrolysis system according to the first embodiment; FIG. 3 is a configuration diagram of a water electrolysis system according to a second embodiment; FIG. 4 is a flowchart for explaining a control method of the water electrolysis system according to the second embodiment; FIG. 5 is a diagram (part 1) for explaining a control method of the water electrolysis system according to the second embodiment; FIG. 6 is a diagram (part 2) for explaining a control method of the water electrolysis system according to the second embodiment; and FIG. 7 is a configuration diagram of a water electrolysis system according to a third embodiment.

[0009] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. In each embodiment, elements having substantially the same function or configuration are designated by the same reference numerals, and redundant description will be omitted.

[0010] First Embodiment System Configuration Fig. 1 is a configuration diagram of a water electrolysis system 1 according to a first embodiment. The water electrolysis system 1 shown in Fig. 1 includes a water electrolysis device 10, a power supply device 20, and a control device 40. These are as follows.

[0011] [Water Electrolysis Apparatus 10] The water electrolysis apparatus 10 has water electrolysis cells that generate hydrogen gas and oxygen gas by electrolysis of pure water. The water electrolysis cells have a configuration in which an electrolyte is sandwiched between opposing electrodes. The water electrolysis apparatus 10 has a configuration in which a plurality of water electrolysis stacks 11, each of which is a stack of such water electrolysis cells, are connected in series. One water electrolysis stack 11 is configured by stacking several hundred water electrolysis cells. Although not shown in the figure, the water electrolysis apparatus 10 also includes a pure water supply tank for supplying pure water to each water electrolysis stack 11, and a separation tank for separating and dehumidifying the hydrogen gas generated by electrolysis in each water electrolysis stack 11, and supplies the dehumidified hydrogen gas to a supply destination.

[0012] When multiple water electrolysis stacks 11 are connected in series, the voltage required for hydrogen production is determined by the number of water electrolysis stacks 11 connected in series and the number and cell voltage of each water electrolysis stack 11. Therefore, when multiple water electrolysis stacks 11 are connected in series, a high voltage is applied to the water electrolysis stacks 11 to generate hydrogen gas. Furthermore, when multiple water electrolysis stacks 11 are connected in series in this manner, the amount of charge accumulated in each water electrolysis stack 11 increases, and the potential also increases depending on the number of connections. Therefore, in order to prevent electric shock or discharge during maintenance while the water electrolysis system 1 is not operating, it is necessary to remove the residual charge accumulated in the water electrolysis stack 11 and reduce the potential of the water electrolysis stack 11 to ground potential.

[0013] [Power supply device 20] The power supply device 20 is a device that supplies, to the water electrolysis device 10, a drive voltage for causing electrolysis in each water electrolysis cell constituting each water electrolysis stack 11 of the water electrolysis device 10, and a voltage of opposite polarity to the drive voltage (hereinafter referred to as a reverse voltage). The power supply device 20 includes a first DC power supply 21 and a second DC power supply 22 that are connected in parallel to the water electrolysis device 10. The power supply device 20 also includes connection switching units 31 and 32.

[0014] Of these, the first DC power supply 21 supplies a current for electrolyzing pure water to the water electrolysis apparatus 10. The second DC power supply 22 supplies a current to the water electrolysis apparatus 10 in the opposite direction to that of the first DC power supply 21.

[0015] The first DC power supply 21 and the second DC power supply 22 are variable voltage power supplies. The first DC power supply 21 applies a forward polarity voltage to the water electrolysis apparatus 10 to supply a DC current. Here, the forward polarity voltage is a drive voltage for generating electrolysis in each water electrolysis cell of the water electrolysis apparatus 10. The second DC power supply 22 applies a reverse voltage, which has a polarity opposite to that of the first DC power supply 21, to the water electrolysis apparatus 10. A ground potential is established between the first DC power supply 21 and the second DC power supply 22 and the water electrolysis apparatus 10. Note that while FIG. 1 illustrates a configuration in which the first DC power supply 21 and the second DC power supply 22 are built into the power supply apparatus 20, the first DC power supply 21 and the second DC power supply 22 may be provided as separate DC power supplies.

[0016] The connection switching units 31, 32 freely switch the connection between the water electrolysis device 10 and the first DC power source 21 and the second DC power source 22. The connection switching units 31, 32 are a first connection switching unit 31 provided between the first DC power source 21 and the water electrolysis device 10 on the side opposite to the ground potential, and a second connection switching unit 32 provided between the second DC power source 22 and the water electrolysis device 10. These connection switching units 31, 32 freely connect and disconnect the water electrolysis device 10 and the first DC power source 21 and the second DC power source 22.

[0017] [Control device 40] The control device 40 is a calculator that controls the operation of the power supply device 20. The calculator is hardware used as a so-called computer and includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The control device 40 comprehensively controls the operation of each part of the water electrolysis system 1 by having the CPU read a predetermined program from the ROM, load it into the RAM, and execute the loaded program.

[0018] When the water electrolysis system 1 is in operation, the control device 40 shorts the first connection switching unit 31 and opens the second connection switching unit 32, and applies a forward polarity drive voltage to the water electrolysis device 10 from the first DC power supply 21 to supply DC current.

[0019] Furthermore, when shutting down the water electrolysis system 1, the control device 40 performs a shutdown process by controlling the drive of the power supply device 20 and the connection switching units 31, 32. The shutdown process of the water electrolysis system 1 is a process for stopping the production of hydrogen by electrolysis in the water electrolysis cells. As part of this shutdown process, the control device 40 performs sequence control including a step of applying a reverse voltage to the water electrolysis device 10 using the second DC power supply 22. Details of the shutdown process performed by the control device 40 will be described below in the section on a control method for the water electrolysis system 1.

[0020] <Control method of water electrolysis system 1> Fig. 2 is a diagram illustrating a control method of the water electrolysis system 1 according to the first embodiment. Fig. 2 is a graph showing the change over time in the voltage applied to the water electrolysis device 10 by the power supply device 20 under the control of the control device 40 shown in Fig. 1. The graph in Fig. 2 also shows the stack potential generated in the water electrolysis stack 11 of the water electrolysis device 10. The control method of the water electrolysis system 1 will be described below with reference to Fig. 2 and the above-mentioned Fig. 1.

[0021] As shown in FIG. 2 , during an operation period P1 of the water electrolysis system 1, the control device 40 supplies a forward polarity applied voltage (i.e., drive voltage V1) to the water electrolysis stack 11 from the first DC power supply 21 with the first connection switching unit 31 short-circuited and the second connection switching unit 32 open.

[0022] The control device 40 also starts reducing the drive voltage V1 from the first DC power supply 21 at the start time (T1) of the shutdown, which ends the operation period P1 of the water electrolysis system 1. This marks the start of a shutdown processing period P2 of the water electrolysis system 1. Note that the rate at which the drive voltage V1 from the first DC power supply 21 is reduced at the start time (T1) of the shutdown is set to a rate that is preset through experiments, e.g., a rate that is sufficient to prevent overcurrent. The control device 40 reduces the drive voltage V1 until the drive voltage V1 reaches 0 V at the time (T2).

[0023] As the drive voltage V1 from the first DC power supply 21 is reduced as described above, the stack potential V2 generated in the water electrolysis stack 11 also decreases. However, because each water electrolysis cell of the water electrolysis stack 11 has a configuration in which an electrolyte is sandwiched between two electrodes, forming a capacitor, an electric charge is retained in the water electrolysis cell. As a result, the rate at which the stack potential V2 decreases to ground potential is slower than the rate at which the drive voltage V1 reaches 0 V. Furthermore, even at the time T2 when the drive voltage V1 is reduced to 0 V, the stack potential V2 does not decrease to ground potential.

[0024] Therefore, after the time (T2) when the drive voltage V1 from the first DC power supply 21 is reduced to 0 V, the control device 40 opens the first connection switching unit 31 and shorts the second connection switching unit 32. Furthermore, the second DC power supply 22 is driven to supply a reverse voltage V1' to the water electrolysis stack 11. As a result, the control device 40 supplies charges of a polarity different from that during operation to the water electrolysis stack 11, recombines the charges accumulated in the water electrolysis cells of the water electrolysis stack 11, and quickly reduces the voltage of the water electrolysis stack 11 to the ground potential.

[0025] The reverse voltage V1′ applied from the second DC power supply 22 is a voltage determined in advance through experiments, and is set to a level that, for example, suppresses the occurrence of an overcurrent. The application time of the reverse voltage V1′ is also determined in advance through experiments, and is a time that is sufficient for the stack potential V2 to drop to the ground potential.

[0026] After starting to supply the reverse voltage V1′ by driving the second DC power supply 22, the control device 40 stops driving the second DC power supply 22, opens the second connection switching unit 32, and terminates the operation shutdown process of the water electrolysis system 1 at a time T3 when a set time has elapsed.

[0027] Advantages of the First Embodiment According to the first embodiment described above, when the operation of the water electrolysis system 1 is stopped, the drive voltage V1 is reduced to 0 V and then the reverse voltage V1′ is applied to the water electrolysis stack 11. This makes it possible to reliably and more quickly neutralize the stack potential V2 of the water electrolysis stack 11 to the ground potential. This makes it possible to prevent electric shock and discharge from the water electrolysis stack 11, and to safely and quickly proceed to work such as maintenance and part replacement.

[0028] In particular, in a configuration in which a plurality of water electrolysis stacks 11, each formed by stacking water electrolysis cells, are further connected in series to increase the voltage, charge is likely to remain in the water electrolysis stack 11 located at the center of the series connection. However, by using the configuration of the first embodiment, it is possible to reliably and more quickly bring the stack potential V2 of all the water electrolysis stacks 11 to the ground potential.

[0029] As in Patent Document 1, when the water electrolysis stack is disconnected from the power source and connected to a resistor after operation has ended, the circuit is switched to the resistor side, and current flows naturally, thereby removing the charge. Therefore, when the water electrolysis stacks 11 are connected in series to a high voltage, it takes time to remove the charge. Furthermore, in this case, if the potential difference between the circuit and the water electrolysis stack after switching becomes large, there is a risk of discharge, but this risk does not occur in the configuration of the first embodiment.

[0030] Second Embodiment System Configuration Fig. 3 is a configuration diagram of a water electrolysis system 2 according to a second embodiment. The water electrolysis system 2 shown in Fig. 3 differs from the water electrolysis system 1 described using Fig. 1 in that a voltmeter 61 and an ammeter 62 are additionally provided, and in the control procedure performed by the control device 40.

[0031] A voltmeter 61 is provided in each of the plurality of water electrolysis stacks 11. An ammeter 62 is provided on the ground potential side between the water electrolysis apparatus 10 and the power supply device 20. The control device 40 controls the operation of the power supply device 20 and the connection switching units 31 and 32 based on signals from the voltmeter 61 and the ammeter 62. The control device 40 controls the power supply device 20 and the connection switching units 31 and 32 as follows.

[0032] <Control Method of Water Electrolysis System 2> FIG. 4 is a flowchart illustrating a control method of the water electrolysis system 2 according to the second embodiment, illustrating the procedure for shutting down the water electrolysis system 2 by the control device 40. FIGS. 5 and 6 are diagrams (part 1) and (part 2) illustrating a control method of the water electrolysis system according to the second embodiment. FIGS. 5 and 6 are graphs illustrating the time-dependent change in the voltage applied to the water electrolysis stack 11 by the power supply device 20 under the control of the control device 40 shown in FIG. 3 . The graphs in FIGS. 5 and 6 also illustrate the stack potential V2 of each water electrolysis stack 11 measured by each voltmeter 61 and the current value A1 measured by each ammeter 62. The stack potential V2 represents, for example, the maximum value of the values ​​measured by each voltmeter 61. The control method of the water electrolysis system 2 will be described below with reference to the flowchart in FIG. 4 and FIGS. 3, 5, and 6.

[0033] First, during an operation period P1 of the water electrolysis system 1 before starting the shutdown process, the control device 40 shorts the first connection switching unit 31 and opens the second connection switching unit 32, and supplies a forward polarity voltage (i.e., drive voltage V1) to the water electrolysis stack 11 from the first DC power supply 21. From this state, the control device 40 performs the shutdown process as follows.

[0034] [Step S101] In step S101, the control device 40 starts reducing the drive voltage V1 from the first DC power supply 21 at the start time (T1) of the shutdown, which marks the end of the operation period P1 of the water electrolysis system 1. This marks the start of a shutdown period P2 of the water electrolysis system 1. At the start time (T1) of the shutdown, the rate of change in the drive voltage V1 from the first DC power supply 21, i.e., the rate of voltage reduction, is set to a rate determined in advance by experiment, and is, for example, a rate that suppresses the occurrence of an overcurrent, as in the first embodiment.

[0035] [Step S102] In step S102, the control device 40 starts obtaining the stack potential V2 from each voltmeter 61 and the current value A1 from the ammeter 62.

[0036] [Step S103] In step S103, the control device 40 determines whether the drive voltage V1 has been reduced to 0 [V] and thus reaches drive voltage V1 = 0 [V]. In the example shown in Figures 5 and 6, at the time (T2) when the drive voltage V1 from the first DC power supply 21 reaches 0, the control device 40 determines that drive voltage V1 = 0 [V] (YES), and proceeds to step S103a. On the other hand, the control device 40 determines that drive voltage V1 is still in the process of decreasing, and that drive voltage V1 is not 0 [V] from the time (T1) when operation is stopped until the time (T2) when the drive voltage V1 reaches 0 in Figures 5 and 6 (NO), and proceeds to step S104.

[0037] [Step S103a] In step S103a, the control device 40 switches the voltage applied to the water electrolysis stack 11 to the reverse voltage V1'. At this time, the control device 40 opens the first connection switching unit 31 and shorts the second connection switching unit 32. The control device 40 also drives the second DC power supply 22 to supply the reverse voltage V1' to the water electrolysis stack 11. At this time, the control device 40 increases the reverse voltage V1' at a predetermined rate of change, i.e., a predetermined voltage increase rate. Then, the process proceeds to step S104.

[0038] [Step S104] In step S104, the control device 40 determines whether the current value A1 acquired in step S102 is within the range of the current threshold Ith. The current threshold Ith is a value set for the absolute value of the current value A1 flowing in the reverse direction relative to the current value A1 measured during the operation period P1. If the current value A1 acquired in step S102 does not exceed the current threshold Ith, the control device 40 determines that the current value A1 is within the range of the current threshold Ith (YES) and proceeds to step S105. On the other hand, if the current value A1 acquired in step S102 exceeds the current threshold Ith, the control device 40 determines that the current value A1 is not within the range of the current threshold Ith (NO) and proceeds to step S104a.

[0039] In the example shown in Fig. 5, it is determined that the current is not within the range of the current threshold Ith (NO) at the first time point T11. In the example shown in Fig. 6, it is determined that the current is not within the range of the current threshold Ith (NO) at the first time point T11 and the third time point T13.

[0040] [Step S104a] In step S104a, the control device 40 reduces the rate of change of the voltage applied to the water electrolysis stack 11. Before step S103a, this rate of change is the rate of decrease of the drive voltage V1. In the example shown in FIG. 6 , this corresponds to the reduction in the rate of change of the drive voltage V1 after the first time point T11.

[0041] On the other hand, after step S103a is executed, this change rate is the increase rate of the reverse voltage V1′, which corresponds to the decrease in the change rate of the reverse voltage V1′ after the first time point T11 in the example shown in Fig. 5, and corresponds to the decrease in the change rate of the reverse voltage V1′ after the third time point T13 in the example shown in Fig. 6.

[0042] [Step S105] In step S105, the control device 40 determines whether the rate of change of the stack potential V2, which began to be acquired in step S102, is equal to or greater than a threshold. At this time, the control device 40 stores in advance a threshold value for the rate of change of the stack potential V2. This threshold value is set, for example, to a value that prevents the stop processing period P2 from being longer than necessary. If it is determined that the rate of change of the stack potential V2 is equal to or greater than the threshold value (YES), the process proceeds to step S106. On the other hand, if it is determined that the rate of change of the stack potential V2 is not equal to or greater than the threshold value (NO), the process proceeds to step S105a.

[0043] [Step S105a] In step S105a, the control device 40 increases the rate of change of the voltage applied to the water electrolysis stack 11. Before step S103a, this rate of change is the rate of decrease of the drive voltage V1. In the example shown in FIG. 6 , this rate of change corresponds to the increase in the rate of change (decrease rate) of the drive voltage V1 from the second time point T12 onwards. On the other hand, after step S103a, this rate of change is the rate of change of the reverse voltage V1′.

[0044] [Step S106] In step S106, the control device 40 determines whether the stack potential V2, which the control device 40 started acquiring in step S102, is the ground potential. If it is determined that the stack potential V2 is the ground potential (YES), the process proceeds to step S107. In the example shown in FIG. 5, the stack potential V2 is determined to be the ground potential (YES) from the second time point T12 onwards, and in the example shown in FIG. 6, the stack potential V2 is determined to be the ground potential (YES) from the fourth time point T14 onwards. On the other hand, if the control device 40 determines that the stack potential V2 is not the ground potential (NO), the process returns to step S103 and repeats the subsequent steps.

[0045] [Step S107] In step S107, the control device 40 performs a process to stop the reverse voltage V1'. Note that in the example shown in FIGS. 5 and 6 , as the drive voltage V1 decreases from the start time (T1) of the operation shutdown, the stack potential V2 generated in the water electrolysis stack 11 also decreases. However, as described in the first embodiment, the rate at which the stack potential V2 decreases to ground potential is slower than the rate at which the drive voltage V1 reaches 0 [V]. Therefore, at the time (T2) when the drive voltage V1 = 0, the stack potential V2 has not reached ground potential (0 [V]). After the drive voltage V1 is switched to the reverse voltage V1', the stack potential V2 reaches ground potential. Therefore, in step S107, the reverse voltage V1' is applied to the water electrolysis stack 11.

[0046] As the process of stopping the reverse voltage V1', the control device 40 reduces the reverse voltage V1' to 0 V at a preset rate and terminates the process. Note that the rate of change of the reverse voltage V1' at this time is set to a preset rate such that, for example, the current value A1 in the water electrolysis stack 11 quickly becomes zero.

[0047] <Advantages of the Second Embodiment> According to the second embodiment described above, when the water electrolysis system 2 is shut down, the drive voltage V1 is reduced to zero volts and then the reverse voltage V1' is applied to the water electrolysis stack 11. Therefore, the same advantages as those of the first embodiment can be obtained. Furthermore, in the second embodiment, when the water electrolysis system 2 is shut down, the drive voltage V1 and the reverse voltage V1' are controlled based on the current value remaining in the water electrolysis stack 11 and the stack potential V2, thereby preventing a reverse overcurrent from occurring in the water electrolysis device 10. This makes it possible to prevent damage to the water electrolysis device 10 due to the generation of an overcurrent.

[0048] Third Embodiment System Configuration Fig. 7 is a configuration diagram of a water electrolysis system 3 according to a third embodiment. The water electrolysis system 3 according to the third embodiment shown in Fig. 7 is a modification of the water electrolysis system 1 according to the first embodiment, and differs in the configuration of a power supply device 20'.

[0049] That is, the power supply device 20' has a plurality of (here, two) DC power supplies 23 connected in series in the same direction, and a connection switching unit that can freely switch the voltage supplied from the DC power supplies 23 to the water electrolysis device 10 between a drive voltage V1 and a reverse voltage V1'. In addition, there is a ground potential between the two DC power supplies 23.

[0050] In this power supply device 20′, a wiring 30 extending from the positive electrode of the DC power supply 23 is bifurcated and connected to both sides of the water electrolysis device 10. In addition, in the power supply device 20′, a wiring 30′ extending from the negative electrode of the DC power supply 23 is bifurcated and connected to both sides of the water electrolysis device 10.

[0051] A first branch 30a of the wiring 30 connected to the positive electrode side of the power supply device 20' is provided with a first connection switching unit 31 that can freely connect and disconnect between the power supply device 20' and one side of the water electrolysis device 10. Furthermore, a second branch 30b of the wiring 30 connected to the positive electrode side of the power supply device 20' is provided with a second connection switching unit 32 that can freely connect and disconnect between the power supply device 20' and the other side of the water electrolysis device 10.

[0052] A first branch 30a' of the wiring 30' connected to the negative electrode side of the power supply device 20' is provided with a third connection switch 33 that can freely connect and disconnect the power supply device 20' and one side of the water electrolysis device 10. Furthermore, a second branch 30b' of the wiring 30' connected to the negative electrode side of the power supply device 20' is provided with a fourth connection switch 34 that can freely connect and disconnect the power supply device 20' and the other side of the water electrolysis device 10.

[0053] In the water electrolysis system 3, the control device 40 controls the driving of the power supply device 20′ and the first connection switching unit 31 to the fourth connection switching unit 34. The operation shutdown process performed by the control device 40 is described in detail below.

[0054] <Method of controlling water electrolysis system 1> During operation of the water electrolysis system 3, the control device 40 applies a voltage from the power supply device 20′ while shorting the first connection switching unit 31 and the fourth connection switching unit 34 and opening the second connection switching unit 32 and the third connection switching unit 33. This causes a forward drive voltage V1 to be supplied to the water electrolysis device 10. In this case, the drive voltage V1 applied to the water electrolysis device 10 is twice as high as that in the first embodiment.

[0055] Furthermore, when the operation of the water electrolysis system 3 is stopped, the control device 40 opens the first connection switching unit 31 and the fourth connection switching unit 34 and shorts the second connection switching unit 32 and the third connection switching unit 33 after the forward polarity drive voltage V1 from the power supply device 20' has been reduced to zero [V]. The control device 40 also applies a voltage to the water electrolysis device 10 from the power supply device 20'. This causes a reverse polarity voltage (hereinafter referred to as reverse voltage V1') to be supplied to the water electrolysis device 10.

[0056] The rate at which the drive voltage V1 is reduced and the supply and stop of the reverse voltage V1' when the operation of the water electrolysis system 3 is stopped may be the same as in the first embodiment.

[0057] The configuration of the third embodiment as described above provides the same advantages as those of the first embodiment. Furthermore, even when the operating voltage of the water electrolysis device 10 is high, the potential of the water electrolysis device 10 can be controlled after the operation of the water electrolysis system 3 is stopped. Furthermore, the third embodiment can be combined with the second embodiment, and the effects of the second embodiment can be achieved by combining them.

[0058] The present invention is not limited to the above-described embodiments and modifications, and includes various other modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0059] REFERENCE SIGNS LIST 1, 2, 3... Water electrolysis system 10... Water electrolysis device 11... Water electrolysis stack 20, 20'... Power supply device 21... First DC power supply 22... Second DC power supply 23... DC power supply 31... First connection switching unit 32... Second connection switching unit 33... Third connection switching unit 34... Fourth connection switching unit 40... Control device 61... Voltmeter 62... Ammeter A1... Current value V1... Drive voltage V1'... Reverse voltage V2... Stack potential

Claims

1. A water electrolysis system comprising: a water electrolysis device having a water electrolysis cell that generates hydrogen by electrolysis; a power supply device that can supply to the water electrolysis device a drive voltage for causing electrolysis in the water electrolysis cell and a voltage of opposite polarity to the drive voltage; and a control device that controls the drive of the power supply device, wherein, during an operation shutdown process for stopping the generation of electrolysis due to the supply of the drive voltage, the control device controls the drive of the power supply device so that the voltage of the opposite polarity is supplied to the water electrolysis device after stopping the supply of the drive voltage to the water electrolysis device.

2. The water electrolysis system according to claim 1, wherein the water electrolysis device is configured by connecting a plurality of water electrolysis stacks in series, each stack comprising the water electrolysis cells.

3. The water electrolysis system according to claim 1, wherein the power supply device comprises: a first DC power supply that supplies the drive voltage to the water electrolysis device; a second DC power supply that is connected in parallel to the first DC power supply and supplies the voltage of opposite polarity to the water electrolysis device; and a connection switching unit that can freely switch the connection between the water electrolysis device and the first DC power supply and the second DC power supply.

4. The water electrolysis system according to claim 1, wherein the power supply device comprises: a plurality of DC power sources connected in series; and a connection switching unit that can freely switch the voltage supplied from the plurality of DC power sources to the water electrolysis device between the drive voltage and the voltage of the opposite polarity.

5. The water electrolysis system according to claim 1, wherein when the control device stops the supply of the drive voltage to the water electrolysis device during the operation shutdown process, the control device stops the supply of the drive voltage at a preset voltage reduction rate.

6. The water electrolysis system according to claim 1, wherein the control device supplies a preset voltage when supplying the reverse polarity voltage to the water electrolysis device during the operation shutdown process.

7. The water electrolysis system according to claim 1, further comprising: a voltmeter for measuring the potential of the water electrolysis device; and an ammeter for measuring the current flowing through the water electrolysis device.

8. The water electrolysis system according to claim 7, wherein the control device controls a rate of reduction of the drive voltage based on the measured values ​​of the voltmeter and the ammeter when stopping the supply of the drive voltage to the water electrolysis device during the operation shutdown process.

9. The water electrolysis system according to claim 7, wherein when the control device supplies the reverse polarity voltage to the water electrolysis device during the operation shutdown process, the control device controls the reverse polarity voltage based on the measurement value of the ammeter.

10. A method for controlling a water electrolysis system including a water electrolysis device having a water electrolysis cell that generates hydrogen by electrolysis, and a power supply device that can supply to the water electrolysis device a drive voltage for causing electrolysis in the water electrolysis cell and a voltage of opposite polarity to the drive voltage, wherein, by controlling the drive of the power supply device with a control device, in an operation shutdown process for stopping the generation of electrolysis caused by the supply of the drive voltage, the control device stops the supply of the drive voltage to the water electrolysis device and then supplies the voltage of opposite polarity to the water electrolysis device.

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