Water electrolysis system

Abstract

This technology provides a way to reduce the difference in current flowing through multiple water electrolysis stacks. [Solution] The water electrolysis system comprises a main power supply unit, a plurality of parallel circuits connected in parallel to the main power supply unit, a plurality of water electrolysis stacks arranged in each of the plurality of parallel circuits, and a sub-power supply unit. The sub-power supply unit is configured to be electrically mounted on some of the plurality of parallel circuits.

Description

Technical Field

[0001] The present specification relates to a water electrolysis system.

Background Art

[0002] Patent Document 1 discloses a water electrolysis system including a power supply unit, a plurality of parallel circuits arranged in parallel to each other with respect to the power supply unit, a plurality of water electrolysis stacks respectively disposed in the plurality of parallel circuits, and a control device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a plurality of water electrolysis stacks are connected in parallel to each other with respect to the power supply unit, the voltage of each water electrolysis stack becomes equal. The IV characteristic of each water electrolysis stack differs depending on the degree of deterioration and the like of each water electrolysis stack. For this reason, when a plurality of water electrolysis stacks are connected in parallel to each other with respect to the power supply unit, the current flowing through each water electrolysis stack differs. It is desired to reduce the difference between the currents respectively flowing through the plurality of water electrolysis stacks.

[0005] The present specification provides a technique capable of reducing the difference between the currents respectively flowing through a plurality of water electrolysis stacks.

Means for Solving the Problems

[0006] In a first aspect disclosed herein, the water electrolysis system may include a main power supply unit, a plurality of parallel circuits connected in parallel to the main power supply unit, a plurality of water electrolysis stacks arranged in each of the plurality of parallel circuits, and a sub-power supply unit. The sub-power supply unit may be configured to be electrically mounted on some of the plurality of parallel circuits.

[0007] According to the water electrolysis system described above, the magnitude of the current flowing through the parallel circuit can be adjusted by the auxiliary power supply unit. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks can be reduced.

[0008] In a second embodiment, the plurality of water electrolysis stacks in the first embodiment may include a first water electrolysis stack having the lowest IV characteristic for the stack current corresponding to the stack voltage, and a second water electrolysis stack having the highest IV characteristic for the stack current corresponding to the stack voltage. The auxiliary power supply unit may be electrically positioned on the parallel circuit on which the first water electrolysis stack is arranged, but may not be electrically positioned on the parallel circuit on which the second water electrolysis stack is arranged.

[0009] With the above configuration, the current flowing through the first water electrolysis stack increases compared to a configuration where the auxiliary power supply unit is not electrically positioned on the parallel circuit where the first water electrolysis stack is located. As a result, the difference between the current flowing through the first water electrolysis stack and the current flowing through the second water electrolysis stack decreases. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks can be reduced.

[0010] In a third aspect disclosed herein, the water electrolysis system may include a main power supply unit, a plurality of parallel circuits connected in parallel to the main power supply unit, and a plurality of water electrolysis stacks arranged in each of the plurality of parallel circuits, each of the plurality of water electrolysis stacks comprising a plurality of cells connected in series. Each of the plurality of water electrolysis stacks may be configured to adjust the number of cells from the plurality of cells that are electrically connected to the parallel circuit.

[0011] According to the water electrolysis system described above, the magnitude of the current flowing through the parallel circuit can be adjusted by adjusting the number of cells electrically connected to the parallel circuit. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks can be reduced.

[0012] In a fourth embodiment, in the third embodiment, each of the plurality of water electrolysis stacks may further include a first terminal, a second terminal, and a third terminal. All of the plurality of cells may be connected in series between the first terminal and the second terminal. Some of the plurality of cells may be connected in series between the first terminal and the third terminal. The remaining portion of the plurality of cells may be connected in series between the third terminal and the second terminal. In each of the plurality of parallel circuits, two of the first terminal, the second terminal, and the third terminal of the water electrolysis stack arranged in the parallel circuit may be electrically connected.

[0013] According to the above configuration, when the two terminals electrically connected to the parallel circuit are changed, the magnitude of the current flowing through the water electrolysis stack arranged in the parallel circuit changes. Therefore, the magnitude of the current flowing through the water electrolysis stack can be easily adjusted.

[0014] In a fifth embodiment, in the fourth embodiment, the plurality of water electrolysis stacks may include a first water electrolysis stack having the lowest IV characteristic for the stack current corresponding to the stack voltage, and a second water electrolysis stack having the highest IV characteristic for the stack current corresponding to the stack voltage. The first water electrolysis stack may be electrically connected to the parallel circuit using the first terminal and the second terminal. The second water electrolysis stack may be electrically connected to the parallel circuit using the second terminal and the third terminal.

[0015] With the above configuration, the difference between the current flowing through the first water electrolysis stack and the current flowing through the second water electrolysis stack can be reduced compared to a configuration in which both the first and second water electrolysis stacks are connected in parallel using the first terminal and the second terminal, or the second terminal and the third terminal. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks can be reduced. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows an overview of the water electrolysis system 2 in the first embodiment, where the battery 22 is not electrically connected to the parallel circuits 14A to 14C. [Figure 2] This figure shows an overview of the water electrolysis system 2 in the first embodiment, where the battery 22 is electrically connected to the parallel circuit 14A. [Figure 3] This is a flowchart of the preparation process performed by the control device 40. [Figure 4] This figure shows an example of IV characteristics 50A~50C. [Figure 5] This figure shows an overview of the water electrolysis system 2 in the second embodiment, where the parallel circuits 14A to 14C are not electrically connected to the intermediate terminal 234. [Figure 6] This figure shows an overview of the water electrolysis system 2 in the second embodiment, where the parallel circuit 14A is electrically connected to the intermediate terminal 234. [Description of Embodiments]

[0017] (First Embodiment) As shown in Figure 1, the water electrolysis system 2 includes a power supply unit 10, a rectifier 12, a plurality of parallel circuits 14A to 14C, a plurality of water electrolysis stacks 16A to 16C, a plurality of current sensors 18A to 18C, a plurality of voltage sensors 20A to 20C, a battery 22, and a control device 40. The water electrolysis system 2 is a system that produces hydrogen by electrolyzing water.

[0018] The power supply unit 10 supplies alternating current power. As an example, the power supply unit 10 is a commercial power source or a device that converts renewable energy into alternating current power.

[0019] One end of the rectifier 12 is connected to the power supply unit 10. The other end of the rectifier 12 is connected to the plurality of parallel circuits 14A to 14C. The rectifier 12 converts the alternating current power supplied from the power supply unit 10 into direct current power. In addition, the rectifier 12 adjusts the power supplied to the plurality of parallel circuits 14A to 14C.

[0020] The plurality of parallel circuits 14A to 14C are connected to the rectifier 12 in parallel with one another.

[0021] The plurality of water electrolysis stacks 16A to 16C are respectively disposed in the plurality of parallel circuits 14A to 14C. Although not illustrated, water is supplied to the plurality of water electrolysis stacks 16A to 16C. The plurality of water electrolysis stacks 16A to 16C electrolyze the supplied water to produce hydrogen. Each of the water electrolysis stacks 16A to 16C includes a plurality of cells C connected in series, a positive terminal 30, and a negative terminal 32. All of the plurality of cells are connected in series between the positive terminal 30 and the negative terminal 32. The positive terminal 30 and the negative terminal 32 of each of the plurality of water electrolysis stacks 16A to 16C are electrically connected to the corresponding parallel circuits 14A to 14C.

[0022] Multiple current sensors 18A to 18C are each placed in multiple parallel circuits 14A to 14C. Each of the multiple current sensors 18A to 18C detects the current flowing through the multiple parallel circuits 14A to 14C, that is, the current flowing through the multiple water electrolysis stacks 16A to 16C. Similarly, each of the multiple voltage sensors 20A to 20C is each placed in multiple parallel circuits 14A to 14C. Each of the multiple voltage sensors 20A to 20C detects the stack voltage of the multiple water electrolysis stacks 16A to 16C. Hereafter, the current flowing through the water electrolysis stacks and the voltage of the water electrolysis stacks may be referred to as "stack current" and "stack voltage," respectively.

[0023] Battery 22 is a rechargeable secondary battery. Battery 22 is configured to be electrically placed on some of the parallel circuits 14A to 14C. For example, as shown in Figure 2, battery 22 can be electrically placed on some of the parallel circuits 14A to 14C. In this embodiment, battery 22 is electrically placed on some of the parallel circuits 14A to 14C such that the difference in stack currents of the multiple water electrolysis stacks 16A to 16C is smaller than when battery 22 is not placed on any of the parallel circuits 14A to 14C. The parallel circuits on which battery 22 should be placed are determined by the battery placement determination process (see Figure 3) described later.

[0024] The control device 40 in Figure 1 is a computer composed of a CPU, ROM, RAM, etc. The control device 40 controls the operation of each component of the water electrolysis system 2.

[0025] (Preparation process; Figure 3) Referring to Figure 3, the preparation process performed by the control device 40 will be described. In this embodiment, the preparation process is for identifying the parallel circuit in which the battery 22 should be placed. When the control device 40 receives a processing start operation from an operator, it performs the process shown in Figure 3. The operator should perform the processing start operation each time a predetermined time has elapsed since the operation of the water electrolysis system 2. For example, the predetermined time is "10,000 hours".

[0026] In S10, the control device 40 applies a reference voltage Vt (see Figure 4) to each of the parallel circuits 14A to 14C.

[0027] In S12, the control device 40 identifies the largest stack current among the multiple stack currents as the reference stack current.

[0028] In S20, the control device 40 identifies one of the multiple stack currents, which is different from the reference stack current, as the target stack current.

[0029] In S22, the control device 40 determines whether the current difference, which is the difference between the reference stack current and the target stack current, is greater than or equal to a predetermined value. The predetermined value is a threshold value used to determine whether or not to electrically connect the battery 22 to the water electrolysis stack corresponding to the target stack current. The predetermined value is also information corresponding to the battery 22. If the current difference is greater than or equal to the predetermined value (YES in S22), the control device 40 proceeds to S24. On the other hand, if the current difference is not greater than or equal to the predetermined value (NO in S22), the control device 40 proceeds to S30.

[0030] In S24, the control device 40 identifies the water electrolysis stack corresponding to the target stack current and identifies the parallel circuit on which the identified water electrolysis stack is located as the target parallel circuit.

[0031] In S30, the control device 40 determines whether it has completed checking all of the one or more stack currents that are different from the reference stack current. Specifically, the control device 40 uses each of the one or more stack currents that are different from the reference stack current to determine whether the process in S20 has been executed. If the control device 40 has completed checking all of the one or more stack currents that are different from the reference stack current (YES in S30), it proceeds to S32. On the other hand, if the control device 40 has not completed checking all of the one or more stack currents that are different from the reference stack current (NO in S30), it returns to S20.

[0032] In S32, the control device 40 determines whether or not the target parallel circuit has been determined. If the target parallel circuit has been determined (YES in S32), the control device 40 proceeds to S40. On the other hand, if the target parallel circuit has not been determined (NO in S32), the control device 40 proceeds to S50.

[0033] In S40, the control device 40 displays first circuit information, including information indicating the target parallel circuit, on the display unit of the water electrolysis system 2. This allows the worker to know which parallel circuit the battery 22 should be placed in. In this case, the worker electrically places the battery 22 in the target parallel circuit. When S40 is completed, the control device 40 terminates the process shown in Figure 3.

[0034] Furthermore, in S50, the control device 40 displays second circuit information on the display unit indicating that it is not necessary to electrically connect the battery 22 to any of the parallel circuits 14A to 14C. This allows the worker to know that it is not necessary to electrically connect the battery 22 to any of the parallel circuits 14A to 14C. When S50 is completed, the control device 40 terminates the process shown in Figure 3.

[0035] (Specific case; Figure 4) Let's describe a specific case where each of the multiple IV characteristics 50A to 50C in Figure 4 corresponds to one of the multiple water electrolysis stacks 16A to 16C. In the initial state of this case, the battery 22 is not electrically connected to any of the parallel circuits 14A to 14C.

[0036] First, the control device 40 applies a reference voltage Vt to each parallel circuit 14A to 14C (S10). In this case, stack currents IA to IC flow through each of the multiple water electrolysis stacks 16A to 16C. Next, the control device 40 identifies the largest stack current IC among the multiple stack currents IA to IC as the reference stack current (S12). In this case, the current difference between stack current IC and stack current IB is less than a predetermined value, and the current difference between stack current IC and stack current IA is greater than or equal to a predetermined value.

[0037] The control device 40 identifies the stack current IB as the target stack current (S20). Next, the control device 40 determines that the current difference between the reference stack current and the target stack current is not greater than or equal to a predetermined value (NO in S22). Next, the control device 40 determines that the check for the stack current IA is not complete (NO in S30).

[0038] The control device 40 identifies the stack current IA as the target stack current (S20). Next, the control device 40 determines that the current difference between the reference stack current and the target stack current is greater than or equal to a predetermined value (NO in S22). In this case, the control device 40 identifies the water electrolysis stack 16A corresponding to the target stack current and identifies the parallel circuit 14A on which the identified water electrolysis stack 16A is located as the target parallel circuit (S24). Next, the control device 40 determines that the checks for stack currents IA and IB are complete (YES in S30). The control device 40 also determines that the target parallel circuit has been determined (YES in S32). In this case, the control device 40 displays first circuit information, including information indicating the parallel circuit 14A, on the display unit of the water electrolysis system 2 (S40). As a result, as shown in Figure 2, the worker electrically places the battery 22 in the parallel circuit 14A. Furthermore, the worker should select a battery that has a voltage that makes the difference between the stack voltage Vp corresponding to the stack current IC and the reference voltage Vt zero in the IV characteristic 50A.

[0039] Subsequently, the operator performs the operation to start the water electrolysis system 2. Since the battery 22 is electrically connected to the parallel circuit 14A, the stack voltage of the water electrolysis stack 16A is increased by the voltage of the battery 22. As a result, the stack current of the water electrolysis stack 16A is larger compared to the case where the battery 22 is not electrically connected to the parallel circuit 14A. Consequently, the difference between the stack current of the water electrolysis stack 16C and the stack current of the water electrolysis stack 16A is smaller compared to the case where the battery 22 is not electrically connected to the parallel circuit 14A.

[0040] As described above, the water electrolysis system 2 comprises a power supply unit 10 (an example of a "main power supply unit"), a plurality of parallel circuits 14A to 14C connected in parallel to each other to the power supply unit 10, a plurality of water electrolysis stacks 16A to 16C arranged in each of the plurality of parallel circuits 14A to 14C, and a battery 22 (an example of a "sub-power supply unit"). The battery 22 is configured to be electrically mounted on some of the parallel circuits 14A to 14C.

[0041] According to the water electrolysis system 2 described above, the battery 22 can adjust the current flowing through the parallel circuits 14A to 14C. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks 16A to 16C can be reduced.

[0042] Furthermore, in the case of Figure 4, the multiple water electrolysis stacks 16A to 16C include a water electrolysis stack 16A (an example of the "first water electrolysis stack") having the lowest IV characteristic 50A for the stack current corresponding to the stack voltage, and a water electrolysis stack 16C (an example of the "second water electrolysis stack") having the highest IV characteristic 50C for the stack current corresponding to the stack voltage. As shown in Figure 2, the battery 22 is electrically placed on the parallel circuit 14A on which the water electrolysis stack 16A is located, but is not electrically placed on the parallel circuit 14C on which the water electrolysis stack 16C is located.

[0043] With the above configuration, the current flowing through the water electrolysis stack 16A increases. This reduces the difference between the current flowing through water electrolysis stack 16A and the current flowing through water electrolysis stack 16C. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks 16A to 16C can be reduced.

[0044] (Second example) The water electrolysis system 202 of the second embodiment will be described with reference to Figures 5 and 6. In the following, components common to both embodiments will be denoted by the same reference numerals, and their descriptions will be omitted.

[0045] As shown in Figure 5, the water electrolysis system 202 does not have a battery. The water electrolysis stacks 216A to 216C each include a plurality of cells C connected in series, a positive terminal 30, a negative terminal 32, and an intermediate terminal 234. The intermediate terminal 234 is the positive terminal. In a modified example, the intermediate terminal 234 may be the negative terminal. All of the plurality of cells C are connected in series between the positive terminal 30 and the negative terminal 32. A portion of the plurality of cells C are connected in series between the positive terminal 30 and the intermediate terminal 234. The remaining portion of the plurality of cells C are connected in series between the intermediate terminal 234 and the negative terminal 32. In this embodiment, the number of cells C connected in series between the positive terminal 30 and the intermediate terminal 234 is less than the number of cells C connected in series between the intermediate terminal 234 and the negative terminal 32. Two of the positive terminal 30, negative terminal 32, and intermediate terminal 234 of the water electrolysis stacks arranged in the parallel circuits 14A to 14C are electrically connected to each parallel circuit. Specifically, for example, the positive terminal 30 and negative terminal 32 of the water electrolysis stacks 216A to 216C, or the intermediate terminal 234 and negative terminal 32 of the water electrolysis stacks 216A to 216C are electrically connected to each parallel circuit 14A to 14C.

[0046] (Preparation process; Figure 3) The control device 40 in this embodiment also performs the preparation process shown in Figure 3. The preparation process in this embodiment is for identifying the parallel circuit that should utilize the intermediate terminal 234. In the initial state shown in Figure 3, each of the multiple parallel circuits 14A to 14C is electrically connected to the intermediate terminal 234 and the negative terminal 32 of the water electrolysis stack arranged in the parallel circuit.

[0047] In this embodiment, the first circuit information in S40 is information to inform the worker of the water electrolysis stack whose positive terminal 30 should be used. Therefore, the worker who sees the first circuit information electrically connects the target parallel circuit to the positive terminal 30 and negative terminal 32 of the water electrolysis stack corresponding to the target parallel circuit. In addition, one or more parallel circuits other than the target parallel circuit are electrically connected to the intermediate terminal 234 and negative terminal 32 of the water electrolysis stack arranged in the parallel circuit.

[0048] Furthermore, in this embodiment, the second circuit information in S50 indicates that the intermediate terminal 234 should be used for all parallel circuits. Therefore, an operator who sees the second circuit information electrically connects each of the multiple parallel circuits 14A to 14C to the positive terminal 30 and negative terminal 32 of the water electrolysis stack arranged in the parallel circuit. With this configuration, the operating efficiency of the water electrolysis system 2 can be improved compared to a configuration in which each of the multiple parallel circuits 14A to 14C is electrically connected to the intermediate terminal 234 and negative terminal 32 of the water electrolysis stack arranged in the parallel circuit.

[0049] (Specific case; Figure 4) Let's describe a specific case where each of the multiple IV characteristics 50A to 50C in Figure 4 corresponds to one of the multiple water electrolysis stacks 216A to 216C. In the initial state of this case, each of the multiple parallel circuits 14A to 14C is electrically connected to the intermediate terminal 234 and the negative terminal 32 of the water electrolysis stack arranged in the parallel circuit.

[0050] Similar to the first embodiment, the control device 40 identifies the parallel circuit 14A as the target parallel circuit.

[0051] Then, the control device 40 displays first circuit information, including information indicating the parallel circuit 14A, on the display unit of the water electrolysis system 2 (S40). As a result, as shown in Figure 6, the worker electrically connects the parallel circuit 14A to the positive terminal 30 and negative terminal 32 of the water electrolysis stack 216A, and electrically connects the parallel circuits 14B and 14C to the intermediate terminal 234 and negative terminal 32 of the water electrolysis stacks 216B and 216C.

[0052] Subsequently, the worker performs an operation to start the water electrolysis system 2. Since the parallel circuit 14A is electrically connected to the positive terminal 30 and the negative terminal 32, the stack current of the water electrolysis stack 216A is larger compared to a configuration in which the parallel circuit 14A is electrically connected to the intermediate terminal 234 and the negative terminal 32. As a result, the difference between the stack current of the water electrolysis stack 216C and the stack current of the water electrolysis stack 216A is reduced.

[0053] As described above, the water electrolysis system 202 comprises a power supply unit 10, a plurality of parallel circuits 14A to 14C connected in parallel to each other to the power supply unit 10, and a plurality of water electrolysis stacks 216A to 216C arranged in the plurality of parallel circuits 14A to 14C, each of which comprises a plurality of cells C connected in series. Each of the plurality of water electrolysis stacks 216A to 216C is configured to adjust the number of cells C from the plurality of cells C that are electrically connected to the parallel circuits 14A to 14C.

[0054] According to the water electrolysis system 202 described above, the magnitude of the current flowing through the parallel circuits 14A to 14C can be adjusted by adjusting the number of cells C electrically connected to the parallel circuits. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks 216A to 216C can be reduced.

[0055] Furthermore, each of the multiple water electrolysis stacks 216A to 216C is further equipped with a positive electrode terminal 30 (an example of a "first terminal"), a negative electrode terminal 32 (an example of a "second terminal"), and an intermediate terminal (an example of a "third terminal"). All of the multiple cells C are connected in series between the positive electrode terminal 30 and the negative electrode terminal 32. Some of the multiple cells C are connected in series between the positive electrode terminal 30 and the intermediate terminal 234. The remaining portion of the multiple cells C are connected in series between the intermediate terminal 234 and the negative electrode terminal 32. In each of the multiple parallel circuits 14A to 14C, two of the positive electrode terminal 30, negative electrode terminal 32, and intermediate terminal 234 of the water electrolysis stack arranged in the parallel circuit are electrically connected.

[0056] According to the above configuration, when the two terminals connected to the parallel circuits 14A to 14C are changed, the magnitude of the current flowing through the water electrolysis stack arranged in the parallel circuit changes. Therefore, the magnitude of the current flowing through the water electrolysis stack can be easily adjusted.

[0057] Furthermore, in the cases shown in Figures 4 and 6, the multiple water electrolysis stacks 216A to 216C include a water electrolysis stack 216A having the lowest IV characteristic 50A for the stack current corresponding to the stack voltage, and a water electrolysis stack 216C having the highest IV characteristic 50C for the stack current corresponding to the stack voltage. The water electrolysis stack 216A is connected to the parallel circuit 14A using the positive terminal 30 and the negative terminal 32. The water electrolysis stack 216C is connected to the parallel circuit 14C using the negative terminal 32 and the intermediate terminal 234.

[0058] With the above configuration, compared to a configuration in which both the water electrolysis stack 216A and the water electrolysis stack 216C are connected in parallel using the positive terminal 30 and the negative terminal 32, or the negative terminal 32 and the intermediate terminal 234, the difference between the current flowing through the water electrolysis stack 216A and the current flowing through the water electrolysis stack 216C can be reduced. Therefore, the difference between the currents flowing through each of the multiple water electrolysis stacks 216A to 216C can be reduced.

[0059] The specific examples of the technology disclosed in this specification have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples described above.

[0060] (First modified example) In the first and second embodiments, the number of parallel circuits, water electrolysis stacks, etc. may be two or four or more.

[0061] (Second Modification) In the first embodiment, the water electrolysis system 2 may have a switching mechanism for switching between a connected state in which the battery 22 is electrically connected to the parallel circuit and a disconnected state in which the battery 22 is not electrically connected to the parallel circuit. For example, the switching mechanism is a relay. In this modification, after S30 of the preparation process in Figure 3, the control device 40 may switch the switching mechanism corresponding to the target parallel circuit to the connected state and switch the switching mechanism corresponding to parallel circuits other than the target parallel circuit to the disconnected state. In this modification, S40 and S50 in Figure 3 can be omitted.

[0062] (Third Modification) In the first embodiment, the battery 22 may be configured to be electrically arranged in two parallel circuits.

[0063] (Fourth Modification) In the first and second embodiments, steps S14 to S30 in Figure 3 can be omitted. In this modification, the control device 40 may determine the parallel circuit in which water electrolysis stacks other than the water electrolysis stack corresponding to the reference stack current are arranged as the target parallel circuit.

[0064] (Fifth Modification) In the first embodiment, the water electrolysis system 2 may include multiple batteries.

[0065] (Sixth Modification) In the second embodiment, the water electrolysis system 2 may have a switching mechanism for switching between a first connection state in which the parallel circuit is electrically connected to the positive terminal 30 and the negative terminal 32, and a second connection state in which the parallel circuit is electrically connected to the intermediate terminal 234 and the negative terminal 32. In this modification, the control device 40 may, after S30 of the preparation process in Figure 3, switch the switching mechanism corresponding to the target parallel circuit to the first connection state, and switch the switching mechanism corresponding to parallel circuits other than the target parallel circuit to the second connection state. In this modification, S40 and S50 in Figure 3 can be omitted.

[0066] (Seventh Modification) In the second embodiment, each water electrolysis stack 216A to 216C may have four or more terminals.

[0067] (Eighth Modification) In the second embodiment, the positive terminal 30 and the negative terminal 32 are configured such that the number of cells C connected in series between the positive terminal 30 and the negative terminal 32 can be changed. In this modification, the intermediate terminal 234 can be omitted.

[0068] (9th Modification) In the second embodiment, the worker who has seen the second connection information may electrically connect each of the multiple parallel circuits 14A to 14C to the intermediate terminal 234 and the negative terminal 32 of the water electrolysis stack arranged in the parallel circuit.

[0069] (Tenth Modification) In the first and second embodiments, the worker may identify the target parallel circuit using multiple stack currents relative to a reference voltage.

[0070] Furthermore, the technical elements described herein or in the drawings demonstrate technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technologies illustrated herein or in the drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of symbols]

[0071] 2: Water electrolysis system, 10: Power supply unit, 12: Rectifier, 14A~14C: Parallel circuit, 16A~16C: Water electrolysis stack, 18A~18C: Current sensor, 20A~20C: Voltage sensor, 22: Battery, 30: Positive terminal, 32: Negative terminal, 40: Control device, 202: Water electrolysis system, 216A~216C: Water electrolysis stack, 234: Intermediate terminal

Claims

1. A water electrolysis system, Main power supply unit, A plurality of parallel circuits connected in parallel to each other to the main power supply unit, Multiple water electrolysis stacks arranged in each of the aforementioned multiple parallel circuits, Sub-power supply unit and Equipped with, The auxiliary power supply unit is configured to be electrically positioned on some of the parallel circuits among the plurality of parallel circuits. Water electrolysis system.

2. The plurality of water electrolysis stacks include a first water electrolysis stack having the lowest IV characteristics for the stack current corresponding to the stack voltage, and a second water electrolysis stack having the highest IV characteristics for the stack current corresponding to the stack voltage. The auxiliary power supply unit is electrically positioned on the parallel circuit on which the first water electrolysis stack is arranged, but is not electrically positioned on the parallel circuit on which the second water electrolysis stack is arranged. The water electrolysis system according to claim 1.

3. A water electrolysis system, Main power supply unit, A plurality of parallel circuits connected in parallel to each other to the main power supply unit, A plurality of water electrolysis stacks arranged in the plurality of parallel circuits, each of the plurality of water electrolysis stacks comprising a plurality of cells connected in series, comprising: Each of the plurality of water electrolysis stacks is configured to allow adjustment of the number of cells among the plurality of cells that are electrically connected to the parallel circuit. Water electrolysis system.

4. Each of the aforementioned water electrolysis stacks further comprises a first terminal, a second terminal, and a third terminal. All of the multiple cells are connected in series between the first terminal and the second terminal. A portion of the plurality of cells is connected in series between the first terminal and the third terminal. The remaining portion of the plurality of cells is connected in series between the third terminal and the second terminal. In each of the plurality of parallel circuits, two of the first, second, and third terminals of the water electrolysis stack arranged in the parallel circuit are electrically connected. The water electrolysis system according to claim 3.

5. The plurality of water electrolysis stacks include a first water electrolysis stack having the lowest IV characteristics for the stack current corresponding to the stack voltage, and a second water electrolysis stack having the highest IV characteristics for the stack current corresponding to the stack voltage. The first water electrolysis stack is electrically connected to the parallel circuit using the first terminal and the second terminal. The water electrolysis system according to claim 4, wherein the second water electrolysis stack is electrically connected to the parallel circuit using the second terminal and the third terminal.

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