Water electrolysis system and its control method

Abstract

To provide a water electrolysis system capable of preventing an influence on a system voltage of a power system when electrolytic stacks are disassembled.SOLUTION: In a water electrolysis system, an alternating current-side connection terminal of a power converter is connected to an alternating current power system; a series circuit comprising at least one electrolytic stack and a circuit breaker connected to the at least one electrolytic stack is connected to a direct current-side connection terminal of the power converter; before the electrolytic stack is disconnected from a series circuit, a controller reduces the power flowing to the direct current-side connection terminal while a speed at which the power converter reduces a power flowing to the direct current-side connection terminal is set to a speed at which a difference from a reference value of an amplitude of a voltage of the alternating current power system is less than a predetermined value; and when the circuit breaker reaches a power that can disconnect an internal direct current circuit, the circuit breaker connected to the direct current circuit is disconnected, and the electrolytic stack is disconnected from the series circuit.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a water electrolysis system and a control method thereof.

Background Art

[0002] Hydrogen is a clean energy that does not emit carbon dioxide during combustion compared to fossil fuels. Therefore, as one of the clean energies for achieving carbon neutrality, it has attracted attention, and technological developments related to hydrogen production, transportation, and utilization have been promoted. In particular, regarding hydrogen production, since hydrogen can be produced anywhere by electrolyzing water, a water electrolysis system capable of producing hydrogen by water electrolysis has attracted attention as a means to reduce the amount of imported energy and improve the energy self-sufficiency rate, and large-scale introduction is planned mainly in Europe.

[0003] As the water electrolysis system is introduced on a large scale, its capacity is also increasing. The basic configuration of the water electrolysis system includes an electrolytic cell (electrolytic stack) responsible for water electrolysis, a power source (rectifier) for supplying direct current power to the electrolytic stack, and the power source is connected to the power grid via a transformer. When increasing the capacity, it can be achieved by paralleling the above basic configuration, but a large number of power sources and transformers are required, resulting in cost increases and increased occupied area as issues. To solve this problem, there is a means of connecting a group of electrolytic stacks with multiple electrolytic stacks connected to a large-capacity power source to reduce the number of power sources and transformers. In particular, a configuration in which electrolytic stacks on the direct current power side of the power source are connected in series is disclosed in Patent Document 1.

[0004] In Patent Document 1, two electrolytic stacks are connected in series, with one circuit breaker provided before and after each of them, and a circuit that bypasses the two circuit breakers is provided, and one circuit breaker is provided in the bypass circuit. This configuration is used as the minimum unit, and a configuration in which the minimum units are connected in series is disclosed. Also, when disconnecting the electrolytic stacks connected in series that constitute the minimum unit, after setting the supply amount of direct current power supplied to the minimum unit to 0, the circuit breaker of the bypass circuit is connected so that current flows through the bypass circuit, and a procedure for disconnecting the circuit breakers connected before and after the electrolytic stack is disclosed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0220620 [Overview of the project] [Problems that the invention aims to solve]

[0006] Patent Document 1 describes a technology that is effective when a part of the electrolytic stack group constituting a water electrolysis device malfunctions and the electrolytic stack is disassembled and replaced. However, there are the following problems. Since water electrolysis systems use electricity to electrolyze water, large-scale water electrolysis systems are connected to the power grid. Because a large number of water electrolysis systems are connected to the power grid, the operating state of the water electrolysis systems may affect the power grid.

[0007] As disclosed in Patent Document 1, when the DC power is reduced to zero when the electrolytic stack is disconnected, if the operation of the power supply connected to the electrolytic stack is performed abruptly, it may cause a large fluctuation in the voltage of the power system (system voltage), potentially disrupting the operation of other equipment connected to the power system.

[0008] The present invention has been made to solve the aforementioned problems and aims to provide a water electrolysis system and a control method thereof that can suppress the impact on the power system voltage when disassembling an electrolytic stack. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a water electrolysis system comprising: a power converter capable of converting alternating current and direct current to transmit and receive power between an AC-side connection terminal and a DC-side connection terminal; an electrolytic stack that electrolyzes water to generate hydrogen and oxygen; a circuit breaker connected to the DC circuit on the DC-side connection terminal side and enabling connection and disconnection of the DC circuit by an external signal or external operation; and a control device that controls the power converter and the circuit breaker, wherein the AC-side connection terminal of the power converter is connected to an AC power system, and the system comprises at least one electrolytic stack and at least one electrolytic stack A series circuit, formed by connecting the circuit breaker to a stack, is connected to the DC-side connection terminal of the power converter. The control device, before disconnecting the electrolytic stack from the series circuit, reduces the power supplied by the power converter to the DC-side connection terminal at a rate such that the difference in the amplitude of the AC power system voltage from a reference value falls below a predetermined value. When the power reaches a level that allows the circuit breaker to disconnect the internal DC circuit, the control device disconnects the circuit breaker connected to the DC circuit, thereby disconnecting the electrolytic stack from the series circuit. Other embodiments of the present invention will be described in the embodiments described later. [Effects of the Invention]

[0010] According to the present invention, the impact on the power system voltage when disassembling an electrolytic stack can be suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the apparatus configuration of a water electrolysis system according to the first embodiment. [Figure 2] This figure shows the apparatus configuration of the electrolytic stack group according to the first embodiment. [Figure 3] This is a time chart showing the system operation and grid voltage during the disconnection of the comparative example. [Figure 4] This is a time chart showing the system operation and grid voltage during disconnection according to the first embodiment. [Figure 5]This is a flowchart showing the disassembly process of the electrolytic stack according to the first embodiment. [Figure 6] This is a time chart showing the system operation and grid voltage during operation when the system load factor is increased after the disconnection is performed according to the first embodiment. [Figure 7] This is a time chart showing the operation process that increases the system load ratio after the decoupling is performed according to the first embodiment. [Figure 8] This figure shows the apparatus configuration of a water electrolysis system according to the second embodiment. [Figure 9] This is a time chart showing the system operation and grid voltage during disconnection according to the second embodiment. [Figure 10] This figure shows another apparatus configuration of the water electrolysis system according to the second embodiment. [Figure 11] This is a flowchart showing the disassembly process of the electrolytic stack according to the second embodiment. [Figure 12] This is a time chart showing the system operation and grid voltage during operation when the system load factor is increased after disconnection in the second embodiment. [Figure 13A] This flowchart shows the operation process for increasing the system load rate after the decoupling is performed in the second embodiment. [Figure 13B] This flowchart shows the operation process for increasing the system load ratio after the decoupling is performed in the second embodiment. [Figure 14] This figure shows the apparatus configuration (part 1) of the electrolytic stack group constituting the water electrolysis system according to the first and second embodiments. [Figure 15] This figure shows the apparatus configuration (part 2) of the electrolytic stack group constituting the water electrolysis system according to the first and second embodiments. [Figure 16] This figure shows the apparatus configuration (part 3) of the electrolytic stack group constituting the water electrolysis system according to the first and second embodiments. [Figure 17] This figure shows the schematic configuration of the water system, hydrogen system, and oxygen system of the water electrolysis system according to the present invention.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings and the like. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions. Various changes and modifications can be made by those skilled in the art within the scope of the technical idea disclosed in this specification. Also, in all the drawings for explaining the present invention, those having the same function are denoted by the same reference numerals, and the repeated description thereof may be omitted.

[0013] <<First Embodiment>> Hereinafter, a first embodiment for carrying out the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 is a diagram showing the device configuration of the water electrolysis system 100 according to the first embodiment. In the water electrolysis system 100, an electrolysis stack group 11 is connected to the DC-side connection terminal 12b of a power converter 12, and the operating states of the electrolysis stack group 11 and the power converter 12 are adjusted by a controller 150 (control device).

[0014] The controller 150 is configured to include, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), etc. The controller 150 is realized by a predetermined program (control program) stored in the ROM being developed in the RAM and executed by the CPU. The program mentioned here is for causing a computer to execute a control method.

[0015] Figure 17 is a diagram showing the schematic configuration of the water system, hydrogen system, and oxygen system of the water electrolysis system 100 according to the embodiment. The water electrolysis system 100 mainly consists of an electrolysis stack 101, a hydrogen gas tank 102, an oxygen gas tank 103, water piping 106, hydrogen gas piping 107, oxygen gas piping 108, a water pump 109, a large cooler 110, a water flow rate adjustment valve 111, a small cooler 112, a hydrogen gas tank pressure adjustment valve 113, an oxygen gas tank pressure adjustment valve 114, an electrolysis stack hydrogen gas pressure adjustment valve 115, an electrolysis stack oxygen gas pressure adjustment valve 116, an oxygen gas / water separation tank 117, an electrolysis stack water pressure adjustment valve 118, a hydrogen gas / water separation tank 119, and a water tank 120. Figure 17 is an example of a water electrolysis system other than the proton permeable type, and as shown in the water electrolysis system 100, there are two water supply systems, and water is also supplied to the hydrogen electrode side.

[0016] The hydrogen production process for water electrolysis system 100 is shown below. Water is supplied from the water tank 120 to the oxygen electrode and hydrogen electrode sides of individual electrolytic stacks 101 by the water pump 109. Hydrogen and oxygen are generated by electrolyzing water by applying a predetermined voltage to the electrolytic stacks 101. The generated hydrogen is separated in the hydrogen gas / water separation tank 119, adjusted to a predetermined pressure by the electrolytic stack hydrogen gas pressure regulating valve 115, and collected in the hydrogen gas tank 102 via the hydrogen gas piping 107. There, the hydrogen gas is adjusted to a predetermined pressure by the hydrogen gas tank pressure regulating valve 113, and the hydrogen gas 104 is supplied to the outside. The water separated in the hydrogen gas / water separation tank 119 is adjusted to a predetermined pressure by the electrolytic stack water pressure regulating valve 118, collected in the water tank 120, and supplied again to the electrolytic stacks 101 via the water pump. The water piping 106 connected to the discharge side of the water pump 109 is branched into two systems, configured to supply water to the electrolytic stacks 101 separately.

[0017] The generated oxygen, along with the unelectrolyzed water, is discharged from the electrolysis stack 101, separated in the oxygen gas / water separation tank 117, adjusted to a predetermined pressure by the electrolysis stack oxygen gas pressure regulating valve 116, collected in the oxygen gas tank 103 via the oxygen gas piping 108, adjusted to a predetermined pressure by the oxygen gas tank pressure regulating valve 114, and the oxygen gas 105 is supplied to the outside. The water separated in the oxygen gas / water separation tank 117 is adjusted to a predetermined pressure by the electrolysis stack water pressure regulating valve 118, collected in the water tank 120, and supplied again to the electrolysis stack 101 via the water pump. Although the power supply lines are not shown in Figure 17, the electrolysis stack 101 is connected to a general DC power supply to provide the power necessary for water electrolysis. The number of electrolysis stacks 101 in the water electrolysis system 100 changes depending on the capacity of the water electrolysis system 100; as the capacity increases, the number of electrolysis stacks 101 in the water electrolysis system 100 also increases.

[0018] The water electrolysis system 100 is equipped with an electrolytic stack hydrogen gas pressure regulating valve 115 and an electrolytic stack oxygen gas pressure regulating valve 116, but this is not the only water electrolysis system that is equipped with these, and some water electrolysis systems do not. General electrolytic stacks 101 have variations in characteristics and variations in electrolysis voltage due to degradation, so even when the same current is applied, differences in resistance values ​​result in differences in electrolysis efficiency.

[0019] In the water electrolysis system 100 shown in Figure 17, the electrolysis voltage of each individual electrolysis stack is measured, and the electrolysis stack with a high electrolysis voltage is reduced by adjusting the electrolysis stack hydrogen gas pressure adjustment valve 115 and the electrolysis stack oxygen gas pressure adjustment valve 116. This reduces the reaction resistance, thereby lowering the voltage of the electrolysis stack with a high voltage and reducing the voltage difference with other electrolysis stacks, thereby increasing the electrolysis efficiency and enabling operation.

[0020] The electrolytic stack hydrogen gas pressure regulating valve 115 and the electrolytic stack oxygen gas pressure regulating valve 116 are constantly monitored to prevent backflow due to pressure differences with other electrolytic stacks. A control algorithm is provided to control the pressure in both gas tanks by controlling the hydrogen gas tank pressure regulating valve 113 and the oxygen gas tank pressure regulating valve 114 according to the situation.

[0021] Returning to Figure 1, the controller 150 is also equipped with a function to take in information about the water electrolysis system 100, as well as external information such as grid voltage and grid voltage amplitude, and determines the operating state of the water electrolysis system 100 based on various information. The water electrolysis system 100 is connected to the power system 5 via a switch 4 that adjusts connection and disconnection, with transformers 2 and 3 connected to the AC side connection terminal 12a of the power converter 12. The power system 5 may be a three-phase AC system or a single-phase AC system. Depending on the power system 5, the configuration of transformers 2 and 3, switch 4, and the water electrolysis system 100 changes. The power converter 12 is equipped with a function to convert the AC power supplied from the power system 5 into DC power and supply DC power to the DC side connection terminal 102b.

[0022] Figure 2 is a diagram showing the device configuration of the electrolytic stack group 11 according to the first embodiment. Figure 2 shows an example of the configuration of the electrolytic stack group 11 that constitutes the water electrolysis system 100. The configuration consists of six strings, each with one circuit breaker 7 connected before and after the electrolytic stack 6, connected in parallel to the DC terminals 1011 and 1012, which are terminals connected to the DC side connection terminal 12b of the power converter 12 (six strings connected in parallel). In the first embodiment, the electrolytic stack group 11 has six in parallel, but it is not limited to this, and the number of parallel connections may be other than six. Below, in the first embodiment, a method for disconnecting the electrolytic stack 6A included in the string indicated as group A from among the six parallel connected strings will be described. Situations requiring disconnection include, but are not limited to, detection of abnormalities in the electrolytic stack 6, operation testing, and maintenance. Incidentally, in Figure 2, the "series circuit" consists of one electrolytic stack 6 and circuit breakers 7, 7 provided on the positive and negative sides of this electrolytic stack, respectively. In this respect, the string is a "series circuit".

[0023] The control method (control process) for disconnecting the electrolytic stack 6A from the electrolytic stack group 11 will be explained below using Figures 3 to 7. Figure 3 is a time chart showing the system operation and grid voltage during disconnection of a comparative example. Specifically, Figure 3 shows a time chart of the system operation and grid voltage during disconnection in a comparative example where the first embodiment is not applied, used as a comparative explanation of the first embodiment. The horizontal axis of Figure 3 represents time, and the vertical axis, from top to bottom, represents the system load factor, the amplitude of the grid voltage, and the connection status of group A. The top of the figure indicates a system load factor of 100%, a grid voltage amplitude greater than the appropriate value, and a connection status of group A that indicates it is connected, respectively. Here, the system load factor represents the power factor supplied to the water electrolysis system, and 100% indicates that it matches the rated value. Furthermore, the amplitude of the grid voltage has an appropriate range, and the grid operator sends instructions to the operating status of the equipment connected to the power grid, and the operator who manages those equipment adjusts it so that it is kept within the appropriate range.

[0024] In the comparative example, it is assumed that the system load factor is reduced by decreasing the DC power supplied by the power converter 12 of the water electrolysis system 100 to the electrolysis stack group 11 from time t1 to time t2, thereby disconnecting the electrolysis stack 6A (see Figure 2) as quickly as possible.

[0025] In this case, the system load rate can be rapidly reduced to a state where the electrolytic stack 6A is disconnected, resulting in a system load rate of 0%, and the connection state of group A can be disconnected at time t2. However, the AC power supplied from the power grid 5 to the AC side connection terminal 12a of the power converter 12 of the water electrolysis system 100 drops sharply, and the power grid 5 momentarily becomes surplus. As shown in the middle of Figure 3, the amplitude of the grid voltage may increase and deviate from the appropriate range. Such changes in the amplitude of the grid voltage may cause equipment connected to the power grid 5 to malfunction because it deviates from the grid voltage state required for its operation. In the worst case, the supply and demand balance of the power grid 5 may be disrupted, potentially leading to a widespread power outage in the power grid 5.

[0026] Figure 4 is a time chart showing the system operation and grid voltage during disconnection according to the first embodiment. The horizontal and vertical axes of the figure are the same as in Figure 3, so their explanation is omitted. In Figure 4, the state of the comparative example shown in Figure 3 is shown by a dashed line, and the state of the first embodiment is shown by a solid line. In the first embodiment, the system load factor is reduced at time t1 by reducing the DC power supplied to the electrolysis stack group 11 by the power converter 12 provided in the water electrolysis system 100. While the system load factor is being reduced, the amplitude of the grid voltage is monitored, and the rate at which the system load factor is reduced is determined so that the amplitude of the grid voltage does not exceed an appropriate range, and the system load factor is reduced to L1. This L1 is the system load factor at which circuit breakers 7A1 and 7A2 (see Figure 2) can transition to the disconnected state. In order to perform disconnection as quickly as possible, group A is disconnected at the L1 stage before the system load factor becomes 0%, but after the system load factor becomes L1, the power to circuit breakers 7A1 and 7A2 is cut off so that the connection state of group A is disconnected. In the first embodiment, the electrolytic stack 6A can be quickly disconnected while keeping the amplitude of the system voltage change below an appropriate range.

[0027] Figure 5 is a flowchart showing the disassembly process S100 of the electrolytic stack 6A according to the first embodiment. The process shown in the flowchart in Figure 5 is implemented in the controller 150 (see Figure 1). Figure 2 will be referred to as appropriate in the explanation of the process.

[0028] After deciding to disconnect the electrolytic stack 6A, in step S101, the system load factor is reduced by decreasing the DC power supplied from the DC-side connection terminal 102b of the power converter 12, and the process moves to step S102. In the following step S102, the system monitors whether the amplitude of the grid voltage is below the appropriate range. If it exceeds the appropriate range (step S102, No), the process moves to step S103; if it is below the appropriate range (step S102, Yes), the process moves to step S104. In step S103, the power at the DC-side connection terminal 102b of the power converter 12 is adjusted to slow the rate at which the system load factor decreases, so that the amplitude of the grid voltage is below the appropriate range, and the process returns to step S102. The appropriate range is, for example, the range in which the difference from the reference value of the voltage amplitude of the AC power system is below a predetermined value. The predetermined value can be set to any value that achieves the objective. For example, it is advisable to set a value smaller than the value set by the power system operator, or a value that takes safety margins into consideration.

[0029] In step S104, it is determined whether the system load rate allows for the disconnection of circuit breakers 7A and 7B of group A. If disconnection is possible (step S104, Yes), the process proceeds to step S105. If disconnection is not possible (step S104, No), the process returns to step S102. In the subsequent step S105, the DC power at the DC-side connection terminal 102b of the power converter 12 is adjusted to stop the decrease in the system load rate, and the process proceeds to step S106. In step S106, circuit breakers 7A and 7B of group A are disconnected, and the series of processes is completed.

[0030] The following describes a method for increasing the system load rate again after the decoupling is performed according to the first embodiment. Figure 6 is a time chart showing the system operation and grid voltage during operation to increase the system load factor after disconnection according to the first embodiment. The horizontal and vertical axes of the figure are the same as in Figures 3 and 4, so their explanation is omitted. Also, the state of group A before disconnection up to time t3 is the same as in Figure 4, so its explanation is omitted. When this embodiment is applied, at time t3 the connection state of group A is disconnected, that is, after the circuit breakers 7A1 and 7A2 are moved to the disconnected state (after the electrolytic stack 6A is electrically disconnected from the DC circuit by circuit breaker 7), the power converter 12 is adjusted to maintain the system load factor at L1 until time t4. After time t4 until time t5, the DC power at the DC side connection terminal 12b of the power converter 12 is adjusted to increase the system load factor toward L2 (the power supply to the DC side connection terminal 12b of the power converter 12 is increased). At this time, the rate of increase of the system load factor is determined so that the amplitude of the grid voltage does not deviate from the appropriate range.

[0031] The system load factor L2 is the system load factor that the electrolytic stack group 11 allows after the electrolytic stack 6A is disconnected from the electrolytic stack group 11, and in the first embodiment, it represents a system load factor of 5 / 6 of 100%. However, this value of L2 is not limited to this, as it is determined by factors such as the configuration of the electrolytic stack group 11, the state of the multiple electrolytic stacks 6, the overall state of the water electrolysis system 100, and maintenance.

[0032] Figure 7 is a time chart showing the operation process S200 that increases the system load rate after the decoupling is performed according to the first embodiment. Of the flowchart shown in Figure 7, the processes from step S101 to step S106 are the same as those shown in Figure 5, so a detailed explanation is omitted.

[0033] After performing step S106, step S201 adjusts the power converter 12 to increase the system load factor. In the following step S202, it is determined whether the amplitude of the grid voltage is below the appropriate range. If it exceeds the appropriate range (step S202, No), the process moves to step S203; if it is below the appropriate range (step S202, Yes), the process moves to step S204. In step S203, the power converter 12 is adjusted to slow down the rate of increase of the system load factor so that the amplitude of the grid voltage is below the appropriate range, and the process returns to step S202. In step S204, it is determined whether the system load factor (L2 in the first embodiment) required after disconnecting group A has been reached. If it has not been reached (step S204, No), the process returns to step S202 while maintaining the increase in the system load factor; if it has been reached (step S204, Yes), the process moves to step S205. In step S205, the increase in the system load factor is stopped, and the series of operations ends.

[0034] By applying the first embodiment described above to the water electrolysis system 100, the electrolytic stacks 6 of the electrolytic stack group 11 can be quickly disconnected without hindering the stabilization of the system by keeping the amplitude of the system voltage below an appropriate range.

[0035] <<Second Embodiment>> A second embodiment for carrying out the present invention will be described below with reference to Figures 8 to 13. Figure 8 shows the configuration of the water electrolysis system 100A according to the second embodiment. Only the power converter 12A differs from that in Figure 1, so the explanation of functions other than the power converter 12A is omitted.

[0036] The power converter 12A is a self-commutated power converter that has the function of converting AC power supplied from the power system 5 to the AC side connection terminal 12a into DC power and supplying DC power to the DC side connection terminal 12b, and also has the function of sending and receiving reactive power with the power system 5. Furthermore, the method for disconnecting the electrolytic stack 6A of group A (see Figure 2) in the electrolytic stack group 11 will be described below.

[0037] Figure 9 is a time chart showing the system operation and grid voltage during disconnection according to the second embodiment. The horizontal axis of Figure 9 represents time, and the vertical axis, from top to bottom, represents the system load factor, the amplitude of the grid voltage, the connection status of group A, and the reactive power transmitted and received between the power grid 5 and the power converter 12A provided in the water electrolysis system 100. The top of the figure represents a system load factor of 100%, a grid voltage amplitude greater than the appropriate value, a connection status of group A being connected, and the transmission of reactive power, respectively. The definitions of the appropriate ranges for the system load factor and the amplitude of the grid voltage are the same as in the first embodiment, so an explanation is omitted.

[0038] In the second embodiment, the response of the water electrolysis system 100 regarding the system load factor and the connection status of group A from time t0 to time t1, and the reduction of the system load factor by the power converter 12A reducing the DC power at the DC side connection terminal 12b from time t1 are the same as in the first embodiment. However, as shown in the bottom row of Figure 9, the power converter 12A is characterized by receiving reactive power from the power system 5.

[0039] In the second embodiment, the rate of decrease in the system load factor is determined based on the amplitude of the grid voltage, and the power converter 12A receives reactive power from the power system 5, thereby reducing the fluctuation range of the grid voltage associated with the decrease in the system load factor from time t1 compared to the first embodiment. As a result, while in the first embodiment the decrease in the system load factor was carried out over a period from time t1 to time t3, in the second embodiment the decrease in the system load factor is shortened to a period from time t1 to time t3a, and the connection state of group A can be disconnected at time t3a. Note that time t3a is earlier than time t3. As a result, in the second embodiment, even when disconnecting the electrolytic stack 6A, the increase in the amplitude of the grid voltage can be suppressed and the amplitude of the grid voltage can be kept below an appropriate range, and disconnection can be performed more quickly than in the first embodiment.

[0040] Figure 10 shows another configuration of the water electrolysis system 100 according to the second embodiment. In Figure 8, the power converter 12A is shown to receive reactive power, but this is not the only option. As shown in Figure 10, although the power converter 12 of the water electrolysis system 100 does not have the function of sending and receiving reactive power, similar to the first embodiment, if a peripheral device 21 connected in parallel with the water electrolysis system 100 to the power system 5 is capable of sending and receiving reactive power to and from the power system 5, the peripheral device 21 may perform the reactive power adjustment shown in Figure 9.

[0041] Here, the peripheral device 21 may be a reactive power compensation device such as an SVC (Static Var Compensator) or STATCOM (Static synchronous Compensator), or it may be a device equipped with a self-commutated power converter such as a PCS (Power Conditioning System).

[0042] Furthermore, although Figure 10 shows the peripheral device 21 connected to the power system 5 via transformers 2 and 3, this is not the only option, and the connection location may be on the power system 5 side. In this case, the controller 150 and the peripheral device 21 adjust the reactive power while exchanging information about each other's status using communication means.

[0043] Figure 11 is a flowchart of the electrolytic stack disassembly process S300 according to the second embodiment. Refer to Figure 2 as appropriate. After determining when to begin disconnecting the electrolytic stack 6A, step S301 executes a process to reduce the DC power at the DC-side connection terminal 12b of the power converter 12A to lower the system load factor, and then proceeds to step S302. Step S302 executes a process to receive reactive power from the power converter 12A, and then proceeds to step S303. Step S303 determines whether the amplitude of the grid voltage is below the appropriate range. If it exceeds the appropriate range (step S303, No), proceeds to step S304; if it is below the appropriate range (step S303, Yes), proceeds to step S306. Step S304 performs a process to reduce the rate at which the system load factor decreases, and then proceeds to step S305. Step S305 executes a process to increase the received reactive power, and then returns to S303, which is the process of monitoring changes in the grid voltage.

[0044] In step S306, it is determined whether circuit breakers 7A1 and 7A2 of group A can be disconnected. If they can be disconnected (step S306, Yes), the process proceeds to step S307. If they cannot be disconnected (step S306, No), the process waits until the system load rate decreases and disconnection becomes possible, then returns to step S303. In step S307, the process of stopping the system load rate is executed, and the process proceeds to step S308. In step S308, in order to disconnect the electrolytic stack 6A of group A, circuit breakers 7A1 and 7A2 are moved to the disconnected state, and then the series of processes ends.

[0045] In the following section, using Figures 12 and 13, we will describe an operating method (operating process) for increasing the system load rate of the water electrolysis system 100 after disconnecting group A from the electrolysis stack group 11.

[0046] Figure 12 is a time chart showing the system operation and grid voltage during operation to increase the system load factor after disconnection in the second embodiment. The horizontal and vertical axes of Figure 12 are the same as in Figure 9, so a detailed explanation is omitted. Also, the system state and grid state from time t0 to time t3a are the same as in Figure 9, so a detailed explanation is omitted.

[0047] At time t3a, the connection state of group A is disconnected, and the system load factor is maintained at L1 until time t4a. At time t4a, the DC power at the DC-side connection terminal 12b of power converter 12A is increased to raise the system load factor until it reaches L2, the system load factor at which the water electrolysis system 100 can operate after disconnecting group A. At this time, the rate of increase in the system load factor from time t4a to time t5a is determined based on the amplitude of the grid voltage, but is set to a value that keeps the amplitude of the grid voltage below the appropriate range. In parallel, from time t4a to time t5a, reactive power is transmitted from the AC-side connection terminal 12a of power converter 12A to the power system 5, thereby keeping the amplitude of the grid voltage below the appropriate range.

[0048] As explained in Figure 9, the power converter 12A is responsible for transmitting reactive power. However, this is not the only option. As shown in Figure 10, if peripheral devices 21 (SVC or STATCOM) connected in parallel with the water electrolysis system 100 to the power system 5 are capable of transmitting and receiving reactive power to and from the power system 5, the peripheral devices 21 may perform the reactive power adjustment shown in Figure 12.

[0049] In the second embodiment, when the system load ratio is reduced and group A is disconnected from the electrolytic stack group 11, the period of reduction in the system load ratio can be made shorter than the period t3-t1, which is t3a-t1. Similarly, when increasing the system load ratio, the period can be made shorter than the period t5-t4 in the first embodiment, which is t5a-t4a. Thus, the second embodiment allows for a faster recovery of the system load ratio than the first embodiment.

[0050] Figures 13A and 13B are flowcharts of the operation process S400 that increases the system load rate after decoupling in the second embodiment. The processes from step S301 to step S308 are the same as in Figure 11, so a detailed explanation is omitted.

[0051] After step S308, which is the process of disconnecting group A from electrolytic stack group 11, step S401 is performed to adjust the DC power at the DC-side connection terminal 12b of power converter 12A to increase the system load factor, and then the process moves to step S402. In step S402, the process of transmitting reactive power from the AC-side connection terminal 12a of power converter 12A is performed, and then the process moves to step S403. In step S403, it is determined whether the amplitude of the grid voltage is below the appropriate range, and if it exceeds the appropriate range (step S403, No), the process moves to step S404, and if it is below the appropriate range (step S403, Yes), the process moves to step S406. In step S404, the process of reducing the rate of increase of the system load factor is performed, and then the process moves to step S405. In step S405, the process of increasing the power of the transmitted reactive power is performed, and then the process returns to step S403.

[0052] In step S406, it is determined whether the system load percentage after disconnection reaches L2. If it has not reached L2 (step S406, No), it waits and returns to step S403. If it has reached L2 (step S406, Yes), it proceeds to step S407. In step S407, after executing a process to stop the increase in the system load percentage, it proceeds to step S408. In step S408, the transmission of reactive power is stopped, and the series of processes ends.

[0053] By applying the second embodiment of the present invention described above to the water electrolysis system 100, fluctuations in the power system voltage of the power system 5 can be minimized when the electrolysis stack 6 is disconnected from the electrolysis stack group 11. In particular, by adding a function to adjust reactive power compared to the first embodiment, the time until the electrolysis stack 6 is disconnected can be shortened.

[0054] In the first and second embodiments described above, the electrolytic stack group 11 was described as a configuration in which electrolytic stacks 6, as shown in Figure 2, are connected in parallel, but the configuration is not limited to this.

[0055] Figure 14 shows the device configuration (1) of the electrolytic stack group constituting the water electrolysis system according to the first and second embodiments. Figure 15 shows the device configuration (2) of the electrolytic stack group constituting the water electrolysis system according to the first and second embodiments. Figure 16 shows the device configuration (3) of the electrolytic stack group constituting the water electrolysis system according to the first and second embodiments.

[0056] For example, as shown in Figure 14, the configuration may involve connecting multiple electrolytic stacks 6 in series in a string in parallel, and operating circuit breakers 7B1 and 7B2 to disconnect the electrolytic stacks 6B1, 6B2, and 6B3 of group B. In the case of Figure 14, when increasing the system load after disconnecting group B, since three electrolytic stacks are disconnected, L2 becomes 3 / 6 = 1 / 2 of 100%. Incidentally, in Figure 2 mentioned above, there was one electrolytic stack 6 in one string (series circuit), but in the example of Figure 14, one string has three electrolytic stacks 6 in series (three electrolytic stacks 6 are connected in a chain).

[0057] Another example, as shown in Figure 15, is a configuration in which many units, each consisting of a string of one electrolytic stack 6 and two circuit breakers 7 connected in parallel, are connected in series, and circuit breakers 7C1 and 7C2 are operated to disconnect the electrolytic stack 6C of group C. In the case of Figure 15, when the system load rate is increased after disconnecting group C, L2 becomes half of 100%. This is because the configuration of electrolytic stack group 11 consists of three configurations of electrolytic stacks 6 connected in parallel, connected in series. After disconnecting electrolytic stack 6C from group C, the number of parallel electrolytic stacks in the parallel circuit that included group C decreases from two to one. As a result, the current capacity of the parallel circuit that included group C is determined by the electrolytic stack 6 that is not disconnected, and therefore the current capacity of electrolytic stack group 11 also becomes half of 100%.

[0058] Another example is a configuration in which multiple units are connected in series, each unit consisting of one electrolytic stack 6 and two circuit breakers 7, with a circuit breaker 7D3 connected to a bypass circuit, as shown in Figure 16. Circuit breakers 7D1, 7D2, and 7D3 are operated to disconnect the electrolytic stack 6D of group D. In the case of Figure 16, circuit breaker 7D3 is energized when the electrolytic stack 6D is disconnected. Furthermore, when increasing the system load factor after disconnecting group D, L2 becomes 5 / 6 of 100%.

[0059] Even if the configuration of the electrolytic stack group 11 is as shown in Figures 14 to 16, by applying the embodiment of the present invention, it becomes possible to quickly disassemble the electrolytic stack 6 while suppressing the impact on the power system 5.

[0060] The water electrolysis system 100 according to this embodiment is a water electrolysis system comprising: a power converter 12 capable of converting AC and DC to send and receive power between an AC-side connection terminal 12a and a DC-side connection terminal 12b; an electrolysis stack 6 that electrolyzes water to generate hydrogen and oxygen; a circuit breaker 7 connected to a DC circuit on the DC-side connection terminal side, which enables connection and disconnection of the DC circuit by an external signal or external operation; and a control device (e.g., controller 150) that controls the power converter and the circuit breaker 7. The AC-side connection terminal 12a of the power converter 12 is connected to an AC power system, and a series circuit consisting of at least one electrolysis stack 6 and at least one electrolysis stack 6 connected to a circuit breaker 7 is connected to the DC-side connection terminal 12b of the power converter 12.

[0061] The control device is characterized in that, before disconnecting the electrolytic stack 6 from the series circuit, the power converter 12 reduces the power it supplies to the DC-side connection terminal at a rate such that the difference in the voltage amplitude of the AC power system from a reference value falls below a predetermined value, thereby reducing the power supplied to the DC-side connection terminal 12b, and when the power reaches a level that allows the circuit breaker 7 to disconnect the internal DC circuit, the circuit breaker 7 connected to the DC circuit is disconnected, thereby disconnecting the electrolytic stack 6 from the series circuit.

[0062] According to this embodiment, in a water electrolysis system with multiple electrolytic stacks connected, even when some of the electrolytic stacks are disconnected, the impact on the power system voltage of the connected power grid can be suppressed, thereby reducing additional costs related to measures to suppress fluctuations in the power grid.

[0063] The control method for a water electrolysis system of this embodiment comprises a power converter 12 capable of converting AC and DC to send and receive power between an AC-side connection terminal 12a and a DC-side connection terminal 12b, an electrolysis stack 6 that electrolyzes water to generate hydrogen and oxygen, a circuit breaker 7 connected to the DC circuit on the DC-side connection terminal 12b and enabling connection and disconnection of the DC circuit by an external signal or external operation, and a control device (e.g., controller 150) that controls the power converter 12 and the circuit breaker 7, wherein the AC-side connection terminal 12a of the power converter 12 is connected to an AC power system, and at least one An electrolytic stack 6 and a series circuit formed by connecting a circuit breaker 7 to at least one of the electrolytic stacks 6 are connected to the DC-side connection terminal 12b of the power converter 12. Before disconnecting the electrolytic stack 6 from the series circuit, the power converter 12 reduces the power it supplies to the DC-side connection terminal 12b at a rate such that the difference in the voltage amplitude of the AC power system from a reference value falls below a predetermined value. When the power reaches a level that allows the circuit breaker 7 to disconnect the internal DC circuit, the circuit breaker 7 connected to the DC circuit is disconnected, thereby disconnecting the electrolytic stack 6 from the series circuit.

[0064] The water electrolysis system 100 shown in Figure 17 above comprises a plurality of water electrolysis stacks (e.g., electrolysis stack 101) connected in series with a DC power supply, a first tank (e.g., hydrogen gas tank 102) for storing hydrogen produced by the water electrolysis stacks, a second tank (e.g., oxygen gas tank 103) for storing oxygen produced by the water electrolysis stacks, a first hydrogen pressure regulating valve (e.g., hydrogen gas tank pressure regulating valve 113) for regulating the pressure of hydrogen produced by the entire plurality of water electrolysis stacks, and a first oxygen pressure regulating valve for regulating the pressure of oxygen produced by the entire plurality of water electrolysis stacks. The system is characterized by comprising a valve (for example, an oxygen gas tank pressure regulating valve 114), a second hydrogen pressure regulating valve (for example, an electrolytic stack hydrogen gas pressure regulating valve 115) for regulating the pressure of hydrogen produced in individual water electrolysis stacks, a second oxygen pressure regulating valve (for example, an electrolytic stack oxygen gas pressure regulating valve 116) for regulating the pressure of oxygen produced in individual water electrolysis stacks, and a control device (for example, a controller 150) for controlling the opening and closing of the first hydrogen pressure regulating valve, the first oxygen pressure regulating valve, the second hydrogen pressure regulating valve, and the second oxygen pressure regulating valve.

[0065] Furthermore, the water electrolysis system 100 includes a voltage measuring instrument (not shown) in each electrolysis stack 101, and a control device that has information on the specified voltage range and the warning voltage range. The control device has a function to calculate the pressure of hydrogen gas 104 or oxygen gas 105 to reduce the voltage to the specified voltage range when the voltage of the electrolysis stack 101 measured by the voltage measuring instrument reaches the warning voltage range.

[0066] Furthermore, the water electrolysis system 100 has the following features: each electrolytic stack 101 is equipped with a voltage measuring instrument (not shown), and the control device has information on the specified voltage range and the warning voltage range. When the voltage of the electrolytic stack 101 measured by the voltage measuring instrument reaches the warning voltage range, the control device adjusts the opening and closing of the electrolytic stack hydrogen gas pressure adjustment valve 115 or the electrolytic stack oxygen gas pressure adjustment valve 116 corresponding to the electrolytic stack 101, thereby lowering the pressure of the hydrogen gas 104 or oxygen gas 105 in the electrolytic stack 101.

[0067] Furthermore, the water electrolysis system 100 includes a pressure measuring instrument (not shown) in each electrolysis stack 101 for measuring the gas pressure of the electrolysis stack 101, and a control device that has information on the specified pressure range and the warning pressure range. When the gas pressure measured by the pressure measuring instrument reaches the warning pressure range, the control device adjusts the opening and closing of the electrolysis stack hydrogen gas pressure adjustment valve 115 or the electrolysis stack oxygen gas pressure adjustment valve 116 corresponding to the electrolysis stack 101 to lower the pressure of the oxygen gas 105 or hydrogen gas 104 in the electrolysis stack 101.

[0068] Furthermore, the water electrolysis system 100 further comprises a temperature measuring instrument (not shown) for measuring the temperature of individual electrolytic stacks 101 or the temperature of water discharged from individual electrolytic stacks 101, a water supply pump 109 (liquid supply device) for supplying water to the entire set of electrolytic stacks 101, a large cooler 110 (first cooler) for adjusting the temperature of the water supplied to the entire set of electrolytic stacks 101, a water flow rate adjustment valve 111 (valve) and a small cooler 112 (second cooler) provided in the water piping 106 (supply piping) between the water supply pump 109 or the large cooler 110 and the electrolytic stacks 101, and a control device for controlling the water supply pump 109, the large cooler 110, the small cooler 112 and the water flow rate adjustment valve 111, wherein the control device has the function of opening the water flow rate adjustment valve 111 corresponding to the electrolytic stack 101 or cooling the water supplied to the electrolytic stack 101 with the small cooler 112 corresponding to the electrolytic stack 101 when the temperature of any of the individual electrolytic stacks 101 changes. [Explanation of Symbols]

[0069] 2,3 Transformers 4 Switch 5 Power system (AC power system) 6 Electrolytic Stack 7 Circuit breaker 21 Peripheral devices (peripheral devices capable of transmitting and receiving reactive power) 11 Electrolytic Stack Group 12,12A Power Converter 12a AC side connection terminal 12b DC side connection terminal 100,100A Water Electrolysis System 101 Electrolytic Stack (Water Electrolytic Stack) 102 Hydrogen gas tank (Tank 1) 103 Oxygen gas tank (tank 2) 104 Hydrogen gas 105 Oxygen gas 106 Water Piping 107 Hydrogen gas piping 108 Oxygen gas piping 109 Water supply pump 110 Large cooler 111 Water flow control valve 112 Small cooler 113 Hydrogen gas tank pressure regulating valve (first hydrogen pressure regulating valve) 114 Oxygen gas tank pressure regulating valve (first oxygen pressure regulating valve) 115 Electrolytic Stack Hydrogen Gas Pressure Regulating Valve (Second Hydrogen Pressure Regulating Valve) 116 Electrolytic Stack Oxygen Gas Pressure Regulating Valve (Second Oxygen Pressure Regulating Valve) 117 Oxygen gas / water separation tank 118 Electrolytic Stack Water Pressure Regulating Valve 119 Hydrogen gas / water separation tank 120 water tank 150 Controller (Control Device) 1011,1012 DC terminal S100, S300 Decompression process S200, S400 operation processing

Claims

1. A water electrolysis system comprising: a power converter capable of converting alternating current to direct current and transmitting and receiving power between an AC-side connection terminal and a DC-side connection terminal; an electrolytic stack that generates hydrogen and oxygen by electrolyzing water; a circuit breaker connected to the DC circuit on the DC-side connection terminal and capable of connecting and disconnecting the DC circuit by an external signal or operation; and a control device that controls the power converter and the circuit breaker, The AC-side connection terminal of the power converter is connected to an AC power grid. A series circuit comprising at least one electrolytic stack and the circuit breaker connected to at least one electrolytic stack is connected to the DC side connection terminal of the power converter. The control device is Before disconnecting the electrolytic stack from the series circuit, the power converter reduces the power it supplies to the DC connection terminal at a rate such that the difference in the voltage amplitude of the AC power system from a reference value falls below a predetermined value, while reducing the power supplied to the DC connection terminal. When the circuit breaker reaches a power level that allows it to disconnect the internal DC circuit, the circuit breaker connected to the DC circuit is disconnected, thereby disconnecting the electrolytic stack from the series circuit. A water electrolysis system characterized by the following features.

2. A water electrolysis system according to claim 1, When reducing the power at the DC-side connection terminal of the power converter before disassembling the electrolytic stack, reactive power is received from the AC power system. A water electrolysis system characterized by the following features.

3. A water electrolysis system according to claim 2, The power converter is the one that receives the reactive power from the AC power system. A water electrolysis system characterized by the following features.

4. A water electrolysis system according to claim 2, The device that receives the reactive power from the AC power system is connected in parallel with the water electrolysis system and is capable of sending and receiving reactive power to and from the AC power system. A water electrolysis system characterized by the following features.

5. A water electrolysis system according to claim 1, After the circuit breaker electrically disconnects the electrolytic stack from the DC circuit, the power supply to the DC connection terminal of the power converter is increased. A water electrolysis system characterized by the following features.

6. A water electrolysis system according to claim 1, The control device is While reducing the power supplied to the DC-side connection terminal, the power converter receives information regarding the voltage of the AC power system, and if the difference in the amplitude of the AC power system voltage from a reference value exceeds a predetermined value, the power converter reduces the rate at which it reduces the power supplied to the DC-side connection terminal. A water electrolysis system characterized by the following features.

7. A water electrolysis system according to any one of claims 1 to 6, A water electrolysis system characterized in that two or more of the series circuits are connected in series to the DC side connection terminal of the power converter.

8. A water electrolysis system according to any one of claims 1 to 6, A water electrolysis system characterized in that two or more of the series circuits are connected in parallel to the DC side connection terminal of the power converter.

9. A water electrolysis system according to any one of claims 1 to 6, A water electrolysis system characterized in that two or more of the series circuits are connected in series and in parallel to the DC side connection terminal of the power converter.

10. A control method for a water electrolysis system comprising: a power converter capable of converting alternating current to direct current and transmitting and receiving power between an AC-side connection terminal and a DC-side connection terminal; an electrolytic stack that generates hydrogen and oxygen by electrolyzing water; a circuit breaker connected to the DC circuit on the DC-side connection terminal side and enabling connection and disconnection of the DC circuit by an external signal or external operation; and a control device that controls the power converter and the circuit breaker, The AC-side connection terminal of the power converter is connected to an AC power grid. A series circuit comprising at least one electrolytic stack and the circuit breaker connected to at least one electrolytic stack is connected to the DC side connection terminal of the power converter. Before disconnecting the electrolytic stack from the series circuit, the power converter reduces the power it supplies to the DC connection terminal at a rate such that the difference in the voltage amplitude of the AC power system from a reference value falls below a predetermined value, while reducing the power supplied to the DC connection terminal. When the circuit breaker reaches a power level that allows it to disconnect the internal DC circuit, the circuit breaker connected to the DC circuit is disconnected, thereby disconnecting the electrolytic stack from the series circuit. A method for controlling a water electrolysis system, characterized by the features described above.

11. A method for controlling a water electrolysis system according to claim 10, When reducing the power at the DC-side connection terminal of the power converter before disassembling the electrolytic stack, reactive power is received from the AC power system. A method for controlling a water electrolysis system, characterized by the features described above.

12. A method for controlling a water electrolysis system according to claim 11, The power converter is the one that receives the reactive power from the AC power system. A method for controlling a water electrolysis system, characterized by the features described above.

13. A method for controlling a water electrolysis system according to claim 11, The device that receives the reactive power from the AC power system is connected in parallel with the water electrolysis system and is capable of sending and receiving reactive power to and from the AC power system. A method for controlling a water electrolysis system, characterized by the features described above.

14. A method for controlling a water electrolysis system according to claim 10, After the circuit breaker electrically disconnects the electrolytic stack from the DC circuit, the power supply to the DC connection terminal of the power converter is increased. A method for controlling a water electrolysis system, characterized by the features described above.

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