Method for controlling water electrolysis system, and water electrolysis system

Abstract

Provided is a control device including: a step in which a current command value regarding current to be applied to an electrolytic stack is determined; and a step in which pure-water adjustment amount command values for adjusting the pressure or / and flow rate of water to be supplied to the electrolytic stack are determined on the basis of the current command value. The control device further includes a step A in which, when the current command value is changed from a first current command value (current command value c1) to a second current command value (current command value c2), which is a different value, and the pure-water adjustment amount command value is changed from a first pure-water adjustment amount command value (pure-water adjustment amount command value w1) to a second pure-water adjustment amount command value (pure-water adjustment amount command value w2), which is a different value, measured values of the pressure or / and flow rate are caused to reach the second pure-water adjustment amount command value from the first pure-water adjustment amount command value before a measured value of current applied from a power converter to the electrolytic stack reaches the second current command value from the first current command value.

Description

Control method for water electrolysis system and water electrolysis system

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

[0002] Unlike fossil fuels, hydrogen is a clean energy source that does not emit carbon dioxide when burned. For this reason, it has attracted attention as one of the clean energy sources needed to achieve carbon neutrality, and technological development is underway regarding the production, transportation, and use of hydrogen. In particular, hydrogen can be produced anywhere by electrolyzing water, so water electrolysis systems that can produce hydrogen by water electrolysis are attracting attention as a means of reducing energy imports and improving energy self-sufficiency, with plans to introduce them on a large scale, mainly in Europe.

[0003] The basic configuration of a water electrolysis system includes an electrolytic cell (electrolysis stack) that performs water electrolysis, a power supply (e.g., a rectifier) ​​that supplies DC power to the electrolysis stack, and a power supply that is connected to a power grid via a transformer. Furthermore, a device (defined as a pure water conditioning device in this document) is installed to supply pure water for electrolyzing water in the electrolysis stack and to recover not only the hydrogen and oxygen generated in the electrolysis stack but also the pure water not used in the electrolysis. The pure water conditioning device is equipped with a device for adjusting the pressure and flow rate of the pure water supplied to the electrolysis stack. A method for operating a pure water conditioning device for such a water electrolysis system is disclosed in Patent Document 1.

[0004] Patent Document 1 discloses a method for operating a water electrolysis device in which power feeders are provided on both sides of an electrolyte membrane, separators are laminated on the power feeders, a first flow path for supplying water is formed between one power feeder and one separator, and a second flow path for flowing hydrogen obtained by electrolysis of water as high-pressure hydrogen at a pressure higher than that of the first flow path is formed between the other power feeder and the other separator, the method comprising the steps of applying an electrolysis voltage to the water electrolysis device to perform water electrolysis, detecting fluctuations in the electrolysis voltage during the water electrolysis, and adjusting the pressure of the water supplied to the first flow path in response to the fluctuations in the electrolysis voltage.

[0005] JP 2010-180451 A

[0006] In Patent Document 1, the water pressure is adjusted based on fluctuations in the electrolysis voltage of the electrolysis stack, thereby making it possible to appropriately adjust the electrolysis state of the electrolysis stack. However, since there is a large difference between the response speed of a change in current that adjusts the voltage of the electrolysis stack and the response speed of the water pressure, the electrolysis state of the electrolysis stack may deviate from the appropriate state during a transient period in which the water pressure is adjusted in response to the current. Experiencing this transient period many times may cause deterioration of the electrolysis stack, which may require more frequent replacement of the electrolysis stack.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a water electrolysis system control method and a water electrolysis system that can reduce a difference in response speed between a current applied to an electrolysis stack and a water adjustment during a transient state.

[0008] In order to achieve the above object, the present invention provides a water electrolysis system including a power converter capable of converting AC and DC and transmitting and receiving power between an AC connection end and a DC connection end, an electrolysis stack that electrolyzes water to generate hydrogen and oxygen, a pure water conditioning device that supplies water to the electrolysis stack and recovers the hydrogen, the oxygen, and the water not used in the electrolysis, and a control device that controls the power converter and the pure water conditioning device, wherein the control device performs a step of determining a current command value to be applied to the electrolysis stack, and a step of adjusting the pressure and / or flow rate of the water supplied to the electrolysis stack based on the current command value. The method includes a step of determining a water adjustment amount command value and a step of transmitting the current command value and the pure water adjustment amount command value to the power converter and the pure water conditioning device, and is characterized in that, when changing the current command value from a first current command value to a second current command value that is a different value and changing the pure water adjustment amount command value from the first pure water adjustment amount command value to the second pure water adjustment amount command value that is a different value from the first pure water adjustment amount command value, the method further includes a step A of changing the actual measurement value of the pressure and / or the flow rate from the first pure water adjustment amount command value to the second pure water adjustment amount command value before the actual measurement value of the current applied from the power converter to the electrolysis stack reaches the second current command value from the first current command value. Other aspects of the present invention will be described in the embodiments described later.

[0009] According to the present invention, the difference in response characteristics when adjusting the current and water pressure and / or flow rate of the electrolysis stack can be reduced, and the electrolysis state of the electrolysis stack can be made appropriate.

[0010] FIG. 1 is a diagram showing the device configuration of a water electrolysis system according to an embodiment of the present invention. FIG. 2 is a diagram showing the device configuration of a pure water adjustment apparatus according to an embodiment of the present invention. FIG. 3 is a time chart showing the operation of a current and a pure water adjustment amount in a first comparative example. FIG. 4 is a time chart showing the operation of a current and a pure water adjustment amount in a second comparative example. FIG. 5 is a time chart showing a first example of operation of a current and a pure water adjustment amount according to the first embodiment. FIG. 6 is a flowchart showing the operation process of the first example of operation of a current and a pure water adjustment amount according to the first embodiment. FIG. 7 is a time chart showing a second example of operation of a current and a pure water adjustment amount according to the second embodiment. FIG. 8 is a flowchart showing the operation process of the second example of operation of a current and a pure water adjustment amount according to the second embodiment. FIG. 9 is a time chart showing a third example of operation of a current and a pure water adjustment amount according to the third embodiment. FIG. 10 is a flowchart showing the operation process of the third example of operation of a current and a pure water adjustment amount according to the third embodiment. FIG. 11 is a time chart showing a fourth example of operation of a current and a pure water adjustment amount according to the fourth embodiment. FIG. 12 is a flowchart showing the operation process of the fourth example of operation of a current and a pure water adjustment amount according to the fourth embodiment. FIG. 13 is a diagram showing the device configuration of a water electrolysis system, peripheral devices, and systems according to a fifth embodiment. FIG. 14 is a time chart showing a fifth example of operation of a current and a pure water adjustment amount according to the fifth embodiment. 10 is a flowchart showing the operation process of a fifth operation example of the current and the pure water adjustment amount according to the fifth embodiment. FIG. 11 is a time chart showing the sixth operation example of the current and the pure water adjustment amount according to the sixth embodiment. FIG. 12 is a flowchart showing the operation process of the sixth operation example of the current and the pure water adjustment amount according to the sixth embodiment. FIG. 13 is a flowchart showing the operation process of an operation mode switching operation example according to the seventh embodiment. FIG. 14 is a flowchart showing the operation process of a first operation example in the operation mode switching operation example according to the seventh embodiment. FIG. 15 is a flowchart showing the operation process of a second operation example in the operation mode switching operation example according to the seventh embodiment.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, etc. The following description shows specific examples of the contents 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 ideas disclosed in this specification. Furthermore, in all drawings used to explain the present invention, parts having the same functions are designated by the same reference numerals, and repeated explanations thereof may be omitted.

[0012] <Water Electrolysis System> Fig. 1 is a diagram showing the configuration of a water electrolysis system 100 according to an embodiment of the present invention. In the water electrolysis system 100, an electrolysis stack group 11 is connected to a DC connection end 12b of a power converter 12, and pure water is electrolyzed into hydrogen and oxygen in response to a current applied from the power converter 12 to the electrolysis stack group 11. A pure water adjustment device 13 is connected to the electrolysis stack group 11, and pure water is supplied through a pipe 13a. Hydrogen generated in the electrolysis stack group 11 and pure water not used for water electrolysis are recovered through a pipe 13b. Oxygen generated in the electrolysis stack group 11 and pure water not used for water electrolysis are recovered through a pipe 13c. The water electrolysis system 100 also includes a controller 15 (control device), which detects and adjusts the operating states of the electrolysis stack group 11, the power converter 12, and the pure water adjustment device 13.

[0013] The controller 15 is configured with, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. The controller 15 is realized by a predetermined program (control program) stored in the ROM being loaded into the RAM and executed by the CPU. The program here is for causing a computer to execute a control method.

[0014] The water electrolysis system 100 has a configuration in which a transformer 7 is connected to an AC connection end 12 a of a power converter 12, the transformer 7 is connected to a switch 3, and the switch 3 is connected to a grid 4. By adjusting the power converter 12, electric power is supplied from the grid 4 to the components of the water electrolysis system 100.

[0015] The controller 15 included in the water electrolysis system 100 has a function of receiving information output from an external device 5. The external device 5 may be, for example, a power supply facility or a power consumption facility installed in the vicinity of the water electrolysis system 100, a control device that comprehensively manages the power supply facility or the power consumption facility, an instruction from an organization that manages the state of a wide-area power grid, or electricity market trading information (electricity market information), for example, a spot electricity price.

[0016] Furthermore, the controller 15 also has a function of acquiring external information such as the water electrolysis system 100 and the system voltage, and determines the operating state of the water electrolysis system 100 based on various pieces of information.

[0017] Here, the types of electrolysis stacks constituting the electrolysis stack group 11 are broadly divided into alkaline and solid polymer types, and in this embodiment, a case where a solid polymer type water electrolysis stack is used as the electrolysis stack is assumed. The solid polymer type has a superior response speed compared to the alkaline type, and is suitable as a water electrolysis system that follows fluctuations in renewable energy. Furthermore, the size of the solid polymer type electrolysis stack can be made smaller than that of the alkaline type, and therefore it is suitable as a system that requires space saving, such as being installed offshore near an offshore wind power generation system.

[0018] 2 is a diagram showing the configuration of the pure water preparation device 13 included in the water electrolysis system 100. A flow rate-adjustable valve 135 is connected to a pipe 13b through which hydrogen and pure water discharged from the electrolysis stack group 11 are transported. A gas-liquid separator 131 that separates hydrogen and pure water is connected downstream of the valve 135. A pure water tank 138 that stores the pure water discharged from the gas-liquid separator 131 is connected downstream of the gas-liquid separator 131. A water pump 139 that pressurizes and transports the pure water is connected downstream of the pure water tank 138. A valve 137 that adjusts the flow rate of the pure water supplied to the electrolysis stack group 11 is connected downstream of the water pump 139. The pure water is supplied to the electrolysis stack group 11 via a pipe 13a. A pressure-adjusting valve 132 is connected to the gas-liquid separator 131 to adjust the internal pressure of the gas-liquid separator 131 and to supply hydrogen to the outside of the water electrolysis system 100 via a pipe 132a. A flow rate-adjustable valve 136 is connected to a pipe 13c through which oxygen and pure water discharged from the electrolysis stack group 11 are transported, and a gas-liquid separator 133 that separates oxygen from pure water is connected downstream of the valve 136. The pure water discharged from the gas-liquid separator 133 is transported downstream of the gas-liquid separator 133 to a pure water tank 138. A pressure-regulating valve 134 is connected to the gas-liquid separator 133, which adjusts the internal pressure of the gas-liquid separator 133 and supplies oxygen to the outside of the water electrolysis system 100 via a pipe 134a.

[0019] The means for adjusting the pressure of the pure water supplied to the electrolysis stack group 11 are as follows. A first means for adjusting the pressure can be achieved by adjusting the internal pressure of the gas-liquid separators 131, 133 using the pressure adjustment valves 132, 134. A second means for adjusting the pressure can be achieved by adjusting the output pressure of the water pump 139. A third means for adjusting the pressure can be achieved by simultaneously implementing the first means for adjusting the pressure and the second means for adjusting the pressure. In the following embodiments, the pressure of the pure water is adjusted by any of the means for adjusting the pressure.

[0020] The means for adjusting the flow rate of pure water supplied to the electrolysis stack group 11 are as follows. A first means for adjusting the flow rate can be achieved by adjusting the opening of valves 135 and 136. A second means for adjusting the flow rate can be achieved by adjusting the opening of valve 137. A third means for adjusting the flow rate can be achieved by simultaneously implementing the first and second means for adjusting the flow rate. In the following embodiments, the pressure of pure water is adjusted by any of the pressure adjusting means described above.

[0021] 3 to 6, a first operation example of a control method for changing the current supplied to the electrolytic stack group 11 and the pure water adjustment amount will be described. Note that, hereinafter, the pure water adjustment amount is defined as the pressure and / or flow rate of the pure water. Furthermore, the active power command value p1 and the active power command value p2, the current command value c1 and the current command value c2, and the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 will be described in the case where each command value 1 is greater than each command value 2 (c1 > c2, w1 > w2). However, this is not a limitation, and a similar operation method is also performed when each command value 1 is smaller than each command value 2 (c1 < c2, w1 < w2).

[0022] Fig. 3 is a time chart showing the relationship between current and pure water adjustment amount in a first comparative example. That is, Fig. 3 is a time chart showing an example of the relationship between current and pure water adjustment amount in a comparative example in which an embodiment of the present invention is not applied, used for comparative purposes to explain the embodiments of the present invention. The horizontal axis of Fig. 3 represents time, and the vertical axis represents, from the top of the figure, the active power command value required for the water electrolysis system 100, the current applied to the electrolysis stack group 11, and the pure water adjustment amount. The upper part of the figure indicates a higher active power command value, a larger current, and a larger pure water adjustment amount, respectively. Note that the current includes a command value shown by a solid line and an actual measurement value shown by a dashed line, and the pure water adjustment amount also includes a command value shown by a solid line and an actual measurement value shown by a dashed line.

[0023] The electrolytic stack group 11 is composed of multiple electrolytic stacks, and generally, the electrolytic stacks are connected in parallel to a power source to control the current of each electrolytic stack. On the other hand, when multiple electrolytic stacks are connected in series, the current is constant in all the electrolytic stacks connected in series. When control is performed in response to a change in the active power command value, the sum of the power of each electrolytic stack is controlled to match the active power command value.

[0024] In the first comparative example, it is assumed that the active power command value requested of the water electrolysis system 100 is maintained at active power command value p1 from time t0 to time t1, and then the active power command value p1 is decreased to active power command value p2 from time t1 to time t2, and the active power command value p2 is maintained from time t2 onwards.

[0025] Note that time t1 may be the time when the change in the active power command value begins, or time t1 may be determined after detecting or receiving a change in the active power command value at a timing prior to time t1.

[0026] In the first comparative example, the current command value and the pure water adjustment amount command value are decreased from time t1 to time t2 in accordance with changes in the active power command value. As the current command value changes from current command value c1 to current command value c2, the actual measured value of the current decreases from time t1 and coincides with current command value c2 at time t3. Furthermore, as the pure water adjustment amount command value changes from pure water adjustment amount command value w1 to pure water adjustment amount command value w2, the actual measured value of the pure water adjustment amount begins to decrease from time t1 and coincides with pure water adjustment amount command value w2 at time t4.

[0027] In this case, the response speed of the current is faster than the response speed of the pure water adjustment amount, so there is a time lag before each actual measured value matches each command value 2 (the actual measured value of the current matches the current command value c2 at time t3, and the actual measured value of the pure water adjustment amount matches the pure water adjustment amount command value w2 at time t4).

[0028] Such a difference in response speed may cause the state near the electrolytic membrane of the electrolysis stack group 11 to be in an inappropriate state. When the current is reduced as shown in FIG. 3 , the change in the measured pure water adjustment amount is slower than the decrease in the measured current, causing the area near the electrolytic membrane to be more supercooled than the steady state, which may increase the resistance and result in poor water electrolysis efficiency. Conversely, when the measured current is increased, the increase in the pure water adjustment amount relative to the increase in current may be slower, which may result in insufficient discharge of generated hydrogen gas and oxygen gas, resulting in a relative decrease in the electrolytic membrane area, or a decrease in the amount of pure water supplied, which may cause overheating near the electrolytic membrane, potentially accelerating deterioration of the electrolytic membrane. Repeatedly experiencing such a state with different response speeds may result in increased power loss and deterioration of the electrolytic stack.

[0029] The pure water adjustment amount (pure water adjustment amount command value) may be pressure, flow rate, or pressure and flow rate, but is the same in all cases (this also applies to Figures 4 and 5 described below).

[0030] FIG. 4 is a time chart showing the relationship between the current and the pure water adjustment amount in the second comparative example. The horizontal and vertical axes in the diagram are the same as those in FIG. 3 , and therefore their explanations are omitted. FIG. 4 illustrates an example of operation in which the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 are equal. For example, by adjusting the pure water adjustment amount command values ​​w1 and w2 to match the current when the current is at the rated value and increasing the pure water adjustment amount regardless of the current, it is possible to avoid the accumulation of generated gas near the electrolytic membrane and overheating, which may occur in the example in FIG. 3 . However, constantly maintaining a high pure water adjustment amount requires power, and the electrolytic resistance increases due to supercooling of the electrolytic membrane, which may reduce the electrolytic efficiency of the water electrolysis system 100 (increase in loss).

[0031] First Embodiment FIG. 5 is a time chart showing a first operational example of the current and pure water adjustment amount according to the first embodiment. The horizontal and vertical axes in the diagram are the same as those in FIG. 3 , and therefore their explanations are omitted. In FIG. 5 , in order to eliminate the delay in the response speed of the actual measured value of the pure water adjustment amount relative to the response speed of the actual measured value of the current, the pure water adjustment amount command value is immediately changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w2 at time t1, when the active power command value starts to change from active power command value p1 to active power command value p2. This allows the actual measured value of the pure water adjustment amount to be changed from time t1 and matched with the pure water adjustment amount command value w2 by time tA, which is earlier than time t3, when the actual measured value of the current matches the current command value c2 (the actual measured value of the pure water adjustment amount reaches the pure water adjustment amount command value w2 earlier than time t3). That is, the controller 15, which is a control device, executes step A. This allows the conditions around the electrolytic membrane to be maintained in a more appropriate state than in the first comparative example described above.

[0032] That is, step A is a step in which, when changing the current command value from the first current command value (current command value c1) toward a second current command value (current command value c2) which is a different value, and changing the pure water adjustment amount command value from the first pure water adjustment amount command value (pure water adjustment amount command value w1) toward a second pure water adjustment amount command value (pure water adjustment amount command value w2) which is a different value, the actual measured value of the pressure and / or flow rate is made to reach the second pure water adjustment amount command value from the first pure water adjustment amount command value before the actual measured value of the current applied from the power converter 12 to the electrolytic stack group 11 reaches the second current command value from the first current command value.

[0033] On the other hand, in the case of Comparative Example 1 shown in Fig. 3, this is referred to as Step B. Step B is a step in which, when changing the current command value from the first current command value to the second current command value and changing the pure water adjustment amount command value from the first pure water adjustment amount command to the second pure water adjustment amount command value, the actual measurement value of the pressure and / or the flow rate is made to reach the second pure water adjustment amount command value from the first pure water adjustment amount command value after the actual measurement value of the current reaches the second current command value from the first current command value.

[0034] As compared to the present embodiment, the second comparative example may have the following problems: the need for electric power to constantly maintain a high pure water adjustment rate; and the electrolytic resistance increases due to supercooling of the electrolytic membrane. As a result, the electrolysis efficiency of the water electrolysis system 100 may decrease (loss may increase).

[0035] FIG. 6 is a flowchart showing the operation process S100 of a first operational example of the current and pure water adjustment amount according to the first embodiment. The process of the flowchart shown in FIG. 6 is implemented in the controller 15 (see FIG. 1). In the description of the process, FIG. 4 will be referred to as appropriate. Starting from a state in which the active power command value has been held since time t0, time is monitored in step S101. If time t is less than time t1 (step S101, No), the process proceeds to step S102. In step S102, the current command value is held at current command value c1 in accordance with the holding of the active power command value, and the process proceeds to step S103. In step S103, the pure water adjustment amount command value is held at pure water adjustment amount command value w1 in accordance with the holding of the active power command value. In step S101, if time t is after time t1 (step S101, Yes), the process proceeds to step S104. In step S104, in order to quickly change the actual measured value of the pure water adjustment amount, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w2, and the process proceeds to step S105. In step S105, the current command value is changed from the current command value c1 to the current command value c2 in accordance with the change in the active power command value, and the process proceeds to step S106. In step S106, the change in the current command value is monitored, and if the current command value has not reached the current command value c2 (step S106, No), the process continues with step S105. In step S106, after confirming that the current command value matches the current command value c2 (step S106, Yes), the process proceeds to step S107. In step S107, the current command value is maintained at the current command value c2, and the series of operations ends.

[0036] 7 and 8, a second operation example of the control method for changing the current and pure water adjustment amount supplied to the electrolytic stack group 11 will be described. Note that the active power command value p1 and the active power command value p2, the current command value c1 and the current command value c2, and the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 will be described in the case where each command value 1 is greater than each command value 2, but this is not limited to this, and a similar operation method is also performed when each command value 1 is smaller than each command value 2.

[0037] Second Embodiment FIG. 7 is a time chart showing a second operation example of the current and the pure water adjustment amount according to the second embodiment. The horizontal and vertical axes in the diagram are the same as those in FIG. 3 , and therefore their explanations are omitted. In FIG. 7 , in order to eliminate the delay in the response speed of the actual measured value of the pure water adjustment amount relative to the response speed of the actual measured value of the current, the pure water adjustment amount command value is immediately changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w3 at time t1, when the active power command value starts to change from active power command value p1 to active power command value p2. At this time, in order to make the response speed of the actual measured value of the pure water adjustment amount faster than in the first operation example, the pure water adjustment amount command value is changed to the pure water adjustment amount command value w3, which is smaller than the pure water adjustment amount command value w2. This allows the actual measured value of the pure water adjustment amount to be changed from time t1, so that it can match the pure water adjustment amount command value w2 by time tB, which is earlier than time t3, when the actual measured value of the current matches the current command value c2. After the actual measurement value of the pure water adjustment amount coincides with the pure water adjustment amount command value w2, the pure water adjustment amount command value w is changed from the pure water adjustment amount command value w3 to the pure water adjustment amount command value w2 at time tC so that the actual measurement value of the pure water adjustment amount coincides with the pure water adjustment amount command value w2. By the above adjustments, the condition near the electrolytic membrane can be maintained in a more appropriate state than in the first comparative example.

[0038] As in the first operation example described above, time t1 may be the time when the change in the active power command value starts, or time t1 may be determined after detecting or receiving a change in the active power command value at a timing prior to time t1.

[0039] FIG. 8 is a flowchart showing the operation process S200 of a second operational example of the current and pure water adjustment amount according to the second embodiment. The process of the flowchart shown in FIG. 8 is implemented in the controller 15 (see FIG. 1). In the description of the process, FIG. 7 will be referred to as appropriate. Starting from a state in which the active power command value has been held since time t0, time is monitored in step S201. If time t is less than time t1 (step S201, No), the process proceeds to step S202. In step S202, the current command value is held at current command value c1 in accordance with the holding of the active power command value, and the process proceeds to step S203. In step S203, the pure water adjustment amount command value is held at pure water adjustment amount command value w1 in accordance with the holding of the active power command value. In step S201, if time t is after time t1 (step S201, Yes), the process proceeds to step S204. In step S204, in order to quickly change the actual measured value of the pure water adjustment amount, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w3, and the process proceeds to step S205. In step S205, the current command value is changed from the current command value c1 to the current command value c2 in accordance with the change in the active power command value, and the process proceeds to step S206. In step S206, the change in the current command value is monitored, and if the current command value c has not reached the current command value c2 (step S206, No), the process continues with step S205. In step S206, after confirming that the current command value matches the current command value c2 (step S106, Yes), the process proceeds to step S207. In step S207, the current command value is maintained at the current command value c2, and the process proceeds to step S208. In step S208, the time is monitored, and if the time t is less than the time tC (step S208, No), the process returns to step S207. In step S208, if time t is after time tC (Yes in step S208), the process proceeds to step S209. In step S209, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w3 to the pure water adjustment amount command value w2 in order to make the actual measurement value of the pure water adjustment amount coincide with the pure water adjustment amount command value w2, and then the series of operations is terminated.

[0040] The second operation example according to the second embodiment described above with reference to Figures 7 and 8 differs from the first operation example according to the first embodiment described with reference to Figures 5 and 6 in that the actual measurement value of the pure water adjustment amount is undershot (or overshot). As a result, the second operation example can change the actual measurement value of the pure water adjustment amount more quickly than the first operation example.

[0041] 9 and 10 , a third operation example of the control method for changing the current supplied to the electrolytic stack group 11 and the pure water adjustment amount will be described. Note that the active power command value p1 and the active power command value p2, the current command value c1 and the current command value c2, and the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 will be described in the case where each command value 1 is greater than each command value 2, but this is not limited to this, and a similar operation method is also performed when each command value 1 is smaller than each command value 2.

[0042] The third operation example of the third embodiment described below differs from the first and second operation examples of the first and second embodiments described in Figures 5 to 8 in that the time at which the actual measured value and command value of the pure water adjustment amount change changes from time tD after time t1.

[0043] Third Embodiment FIG. 9 is a time chart showing a third example of the operation of the current and the pure water adjustment amount according to the third embodiment. The horizontal and vertical axes in the diagram are the same as those in FIG. 3 , and therefore their explanations are omitted. In FIG. 9 , in order to eliminate the delay in the response speed of the actual measured value of the pure water adjustment amount relative to the response speed of the actual measured value of the current, the current command value is changed from current command value c1 to current command value c2 at time t1, when the active power command value starts to change from active power command value p1 to active power command value p2. However, at time tD, which is later than time t1, the pure water adjustment amount command value is immediately changed from pure water adjustment amount command value w1 to pure water adjustment amount command value w2. As a result, even when the actual measured value of the pure water adjustment amount is changed after time t1, it can be made to match the pure water adjustment amount command value w2 by time tE, which is earlier than time t3, when the actual measured value of the current matches the current command value c2. This allows the conditions around the electrolytic membrane to be maintained in a more appropriate state than in the first comparative example.

[0044] As in the above-described operation example, time t1 may be the time when the change in the active power command value starts, or time t1 may be determined after detecting or receiving a change in the active power command value at a timing prior to time t1.

[0045] FIG. 10 is a flowchart showing the operation process S300 of a third operational example of the current and pure water adjustment amount according to the third embodiment. The process of the flowchart shown in FIG. 10 is implemented in the controller 15 (see FIG. 1). In the description of the process, FIG. 9 will be referred to as appropriate. Starting from a state in which the active power command value has been held since time t0, time is monitored in step S301. If time t is less than time t1 (step S301, No), the process proceeds to step S302. In step S302, the current command value is held at current command value c1 in accordance with the holding of the active power command value, and the process proceeds to step S303. In step S303, the pure water adjustment amount command value is held at pure water adjustment amount command value w1 in accordance with the holding of the active power command value. If time t is after time t1 in step S301 (step S301, Yes), the process proceeds to step S304. In step S304, the current command value is changed from current command value c1 to current command value c2 in accordance with the change in the active power command value, and the process proceeds to step S305. In step S305, the change in the current command value is monitored. If the current command value has not reached the current command value c2 (step S305, No), the process proceeds to step S306. In step S306, time t is monitored. If time t is less than time tD (step S306, No), the process returns to step S304. In step S306, if time t is after time tD (step S306, Yes), the process proceeds to step S307. In step S307, in order to quickly change the actual measured value of the pure water adjustment amount, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w2, and the process returns to step S304. After performing step S304, in step S305, it is confirmed that the current command value matches the current command value c2 (step S305, Yes), and the process proceeds to step S308. In step S308, the current command value is maintained at the current command value c2, and the series of operations ends.

[0046] 11 and 12 , a fourth operation example of the control method for changing the current and the pure water adjustment amount supplied to the electrolytic stack group 11 will be described. Note that the active power command value p1 and the active power command value p2, the current command value c1 and the current command value c2, and the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 will be described in the case where each command value 1 is greater than each command value 2, but this is not limited to this, and a similar operation method is also performed when each command value 1 is smaller than each command value 2.

[0047] The fourth operation example according to the fourth embodiment described below differs from the first and second operation examples according to the first and second embodiments described in Figures 5 to 8 in that the time at which the actual measurement value and command value of the pure water adjustment amount change starts at time tF after time t1. Also, unlike the third operation example according to the third embodiment described in Figures 9 and 10, the actual measurement value of the pure water adjustment amount is undershoot (or overshoot).

[0048] Fourth Embodiment Fig. 11 is a time chart showing a fourth example of the operation of the current and the pure water adjustment amount according to the fourth embodiment. The horizontal and vertical axes in the diagram are the same as those in Fig. 4, and therefore their explanations are omitted. In Fig. 11, in order to eliminate the delay in the response speed of the actual measured value of the pure water adjustment amount relative to the response speed of the actual measured value of the current, the current command value is changed from current command value c1 to current command value c2 at time t1, when the active power command value starts to change from active power command value p1 to active power command value p2. However, at time tF, which is later than time t1, the pure water adjustment amount command value is immediately changed from pure water adjustment amount command value w1 to pure water adjustment amount command value w3. This allows the actual measured value of the pure water adjustment amount to be changed from time tF, and to coincide with the pure water adjustment amount command value w2 by time tG, which is earlier than time t3, when the actual measured value of the current coincides with the current command value c2. After the actual measurement value of the pure water adjustment amount coincides with the pure water adjustment amount command value w2, the pure water adjustment amount command value w is changed from the pure water adjustment amount command value w3 to the pure water adjustment amount command value w2 at time tH so that the actual measurement value of the pure water adjustment amount coincides with the pure water adjustment amount command value w2. By the above adjustments, the condition near the electrolytic membrane can be maintained in a more appropriate state than in the first comparative example.

[0049] As in the above-described operation example, time t1 may be the time when the change in the active power command value starts, or time t1 may be determined after detecting or receiving a change in the active power command value at a timing prior to time t1.

[0050] FIG. 12 is a flowchart showing the operation process S400 of a fourth operational example of the current and pure water adjustment amount according to the fourth embodiment. The process of the flowchart shown in FIG. 12 is implemented in the controller 15 (see FIG. 1). In the description of the process, FIG. 11 will be referred to as appropriate. Starting from a state in which the active power command value has been held since time t0, time is monitored in step S401. If time t is less than time t1 (No in step S401), the process proceeds to step S402. In step S402, the current command value is held at current command value c1 in accordance with the holding of the active power command value, and the process proceeds to step S403. In step S403, the pure water adjustment amount command value is held at pure water adjustment amount command value w1 in accordance with the holding of the active power command value. If time t is after time t1 in step S401 (Yes in step S401), the process proceeds to step S404. In step S404, the current command value is changed from current command value c1 to current command value c2 in accordance with the change in the active power command value, and the process proceeds to step S405. In step S405, the change in the current command value is monitored. If the current command value has not reached the current command value c2 (step S405, No), the process proceeds to step S406. In step S406, time t is monitored. If time t is less than time tF (step S406, No), the process returns to step S404. In step S406, if time t is after time tF (step S406, Yes), the process proceeds to step S407. In step S407, in order to quickly change the actual measured value of the pure water adjustment amount, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w3, and the process returns to step S404. After performing step S404, in step S405, it is confirmed that the current command value matches the current command value c2 (step S405, Yes), and the process proceeds to step S408. In step S408, the current command value is maintained at the current command value c2, and the process proceeds to step S409. In step S409, time t is monitored, and if time t is less than time tH (step S409, No), the process returns to the step immediately before step S409. In step S409, if time t is after time tH (step S409, Yes), the process proceeds to step S410. In step S410, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w3 to the pure water adjustment amount command value w2, and the series of operations ends.

[0051] 13 to 15 , a fifth operation example of the control method for changing the current and the pure water adjustment amount supplied to the electrolytic stack group 11 will be described. Note that the active power command value p1 and the active power command value p2, the current command value c1 and the current command value c2, and the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 will be described in the case where each command value 1 is greater than each command value 2, but this is not limited to this, and a similar operation method is also performed when each command value 1 is smaller than each command value 2.

[0052] In the four operation examples of the first to fourth embodiments, the current command value and the pure water adjustment amount command value are determined based on the active power command value required of the water electrolysis system 100, and the current and the pure water adjustment amount change according to the command values. In the fifth operation example of the fifth embodiment described below, the external information input to the water electrolysis system 100 is information that enables the user to predict in advance that the active power command value will change.

[0053] An example of external information may be the active power or reactive power that determines the amount of hydrogen produced by the water electrolysis system 100 itself. The external information may be information that is installed in the peripheral equipment 6 and that directly or indirectly operates the water electrolysis system 100, and that sets in advance the time at which the active power or reactive power is to be changed using a touch panel or the like, and that changes the active power or reactive power at the time set by a timer.

[0054] Examples of external information include weather information, wind speed information and solar radiation information that can predict fluctuations in the output of a wind power generation system, a solar power generation system, or the like that supplies power to the water electrolysis system 100. This information may be weather forecast information, or output values ​​from a wind speed sensor or a solar radiation sensor located near the wind power generation system or the solar power generation system or in the area where the power generation system is installed.

[0055] An example of the external information may be electricity market price information that determines the price of electricity received by the water electrolysis system 100. The external information may be information that detects in advance the time when the electricity price will fluctuate and changes the active power in response to the fluctuation in the electricity price.

[0056] An example of the external information may be power information from facilities that supply power and are installed in the vicinity of the water electrolysis system 100. As described above, the external information may be power information output by a wind power generation system or a solar power generation system, or the power information may be determined based on the operating status or maintenance plan of a thermal power plant or a nuclear power plant.

[0057] An example of the external information may be load information on power-consuming equipment installed in the vicinity of the water electrolysis system 100. The external information may be information on power-consuming manufacturing equipment installed in a factory, large air conditioning equipment, electric furnaces, or rotating machines, and may be information based on the operating conditions (load conditions) of these equipment.

[0058] An example of the external information may be operation information of a device for storing electricity (power storage device) installed in the vicinity of the water electrolysis system 100. The operation status of the water electrolysis system 100 may be changed based on information on the transmission and reception of electricity by charging and discharging the power storage device.

[0059] Fifth Embodiment Fig. 13 is a diagram showing the configuration of a water electrolysis system, peripheral devices, and a system according to a fifth embodiment. The system is assumed to include a water electrolysis system 100 connected to a system 4 via a transformer 7 and a switch 3, and peripheral equipment 6 that transmits and receives power to and from the system 4 via a power line 6a. In addition to the power line 6a, the peripheral equipment 6 receives information from the system 4 and transmits information about the peripheral equipment 6 to the system 4 via a communication line 6b between the system 4 and the peripheral equipment 6. The peripheral equipment 6 also transmits information about the peripheral equipment 6 to the water electrolysis system 100 via a communication line 6c. In the fifth operation example, it is assumed that the power transmission and reception status of the peripheral equipment 6 is transmitted in advance to the water electrolysis system 100 via the communication line 6c. This allows the water electrolysis system 100 to determine the power transmission and reception status of the peripheral equipment 6 in advance, thereby enabling the operating state of the water electrolysis system 100 to be changed in advance, at a time prior to changing the active power command value.

[0060] FIG. 14 is a time chart showing a fifth example of operation of the current and the pure water adjustment amount according to the fifth embodiment. The horizontal and vertical axes in the diagram are the same as those in FIG. 4 , and therefore their explanations are omitted. In FIG. 14 , in order to eliminate the delay in the response speed of the actual measured value of the pure water adjustment amount relative to the response speed of the actual measured value of the current, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w2 at time t1 before the active power command value starts to change from the active power command value p1 to the active power command value p2, based on external information transmitted from the peripheral equipment 6. Thereafter, at time t1, the current command value is changed from the current command value c1 to the current command value c2 in response to the change in the active power command value from the active power command value p1 to the active power command value p2. In response to this, the actual measured value of the current starts to change from time t1 and coincides with the current command value c2 by time tL, but by changing the pure water adjustment amount command value from w1 to w2 at time t1, the actual measured value of the pure water adjustment amount starts to change from time t1 and can reach the pure water adjustment amount command value w2 by time tJ. By the above adjustments, the condition near the electrolytic membrane can be maintained in a more appropriate state than in the first comparative example described above.

[0061] FIG. 15 is a flowchart showing the operation process S500 of a fifth operational example of the current and pure water adjustment amount according to the fifth embodiment. The process of the flowchart shown in FIG. 15 is implemented in the controller 15 (see FIG. 1). In the description of the process, FIG. 12 will be referred to as appropriate. Starting from a state in which the active power command value has been held since time t0, time is monitored in step S501. If time t is less than time t1 (step S501, No), the process proceeds to step S502. In step S502, the current command value is held at current command value c1 in accordance with the holding of the active power command value, and the process proceeds to step S503. In step S503, the pure water adjustment amount command value is held at pure water adjustment amount command value w1 in accordance with the holding of the active power command value. In step S501, if time t is after time t1 (step S501, Yes), the process proceeds to step S504. In step S504, the pure water adjustment amount command value is changed from pure water adjustment amount command value w1 to pure water adjustment amount command value w2, and the process proceeds to step S505. In step S505, the time is monitored, and if time t is less than time tI (step S505, No), the process returns to step S504. If it is determined in step S505 that time t is after time tI (step S505, Yes), the process proceeds to step S506. In step S506, the current command value is changed from current command value c1 to current command value c2, and the process proceeds to step S507. In step S507, it is monitored whether the current command value matches the current command value c2. If the current command value does not match the current command value c2 (step S507, No), the process returns to step S506. After it is determined in step S507 that the current command value matches the current command value c2 (step S507, Yes), the process proceeds to step S508. In step S508, the current command value is maintained at the current command value c2, and the series of operations ends.

[0062] 16 and 17 , a sixth operation example of the control method for changing the current supplied to the electrolytic stack group 11 and the pure water adjustment amount will be described. Note that the active power command value p1 and the active power command value p2, the current command value c1 and the current command value c2, and the pure water adjustment amount command value w1 and the pure water adjustment amount command value w2 will be described in the case where each command value 1 is greater than each command value 2, but this is not limited to this, and a similar operation method is also performed when each command value 1 is smaller than each command value 2.

[0063] In the sixth operation example described below, similarly to the fifth operation example described above, it is assumed that the water electrolysis system 100 receives external information from the peripheral equipment 6 and knows in advance that the active power command value will be changed.

[0064] Furthermore, the sixth operation example differs from the fifth operation example of the fifth embodiment described in Figures 13 to 15 in that the actual measured value of the pure water adjustment amount is undershoot (or overshoot).

[0065] Sixth Embodiment Fig. 16 is a time chart showing a sixth example of operation of the current and the pure water adjustment amount according to the sixth embodiment. The horizontal and vertical axes in the diagram are the same as those in Fig. 4 , and therefore their explanations are omitted. In Fig. 16, in order to eliminate the delay in the response speed of the actual measured value of the pure water adjustment amount relative to the response speed of the actual measured value of the current, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w1 to the pure water adjustment amount command value w3 at time t1 before the active power command value starts to change from the active power command value p1 to the active power command value p2, based on external information transmitted from the peripheral equipment 6. Thereafter, at time tN, the active power command value changes from the active power command value p1 to the active power command value p2. As the change is completed by time tP, the current command value is changed from the current command value c1 to the current command value c2, and the change is completed by time tQ. In response to this, the actual measured value of the current begins to change from time tN and coincides with the current command value c2 by time tQ. However, by changing the pure water adjustment amount command value from w1 to w3 at time t1, the actual measured value of the pure water adjustment amount begins to change from time t1 and can reach w2 by time tM. Furthermore, by changing the pure water adjustment amount command value from w3 to w2 at time tO, the actual measured value of the pure water adjustment amount coincides with w2 after time t3. By these adjustments, the condition near the electrolytic membrane can be maintained more appropriately than in the first comparative example.

[0066] FIG. 17 is a flowchart showing the operation process S600 of a sixth operational example of the current and pure water adjustment amount according to the sixth embodiment. The process of the flowchart shown in FIG. 17 is implemented in the controller 15 (see FIG. 1). In the description of the process, FIG. 16 will be referred to as appropriate. Starting from a state in which the active power command value has been held since time t0, time is monitored in step S601. If time t is less than time t1 (step S601, No), the process proceeds to step S602. In step S602, the current command value is held at current command value c1 in accordance with the holding of the active power command value, and the process proceeds to step S603. In step S603, the pure water adjustment amount command value is held at pure water adjustment amount command value w1 in accordance with the holding of the active power command value. If time t is after time t1 in step S601 (step S601, Yes), the process proceeds to step S604. In step S604, the pure water adjustment amount command value is changed from pure water adjustment amount command value w1 to pure water adjustment amount command value w3, and the process proceeds to step S605. In step S605, the time is monitored, and if time t is less than time tN (step S605, No), the process returns to step S604. If it is determined in step S605 that time t is after time tN (step S605, Yes), the process proceeds to step S606. In step S606, the current command value is changed from current command value c1 toward current command value c2, and the process proceeds to step S607. In step S607, it is monitored whether the current command value matches current command value c2, and if the current command value does not match current command value c2 (step S607, No), the process proceeds to step S608. In step S608, the time is monitored, and if time t is less than time tO (step S608, No), the process returns to step S606. In step S608, if time t is after time tO (step S608, Yes), the process proceeds to step S609. In step S609, the pure water adjustment amount command value is changed from the pure water adjustment amount command value w3 to the pure water adjustment amount command value w2, and the process proceeds to step S606. In step S607, it is confirmed that the current command value matches the current command value c2 (step S607, Yes), and then the process proceeds to step S610. In step S610, the current command value is maintained at the current command value c2, and the series of operations ends.

[0067] <<Operation Mode Switching Operation Example>> Up to this point, the first operation example of the first embodiment to the sixth operation example of the sixth embodiment have been described. It was assumed that the operation mode in Comparative Example 1 and Comparative Example 2 is changed to one of the operation modes in the first to sixth operation examples, and the selected operation mode in one of the first to sixth operation examples is continued. Below, an operation example will be described in which an operation mode including Comparative Example 1 and Comparative Example 2 is selected based on the state of the water electrolysis system 100 and external information, rather than continuing one of the operation modes in the first to sixth operation examples.

[0068] Seventh Embodiment FIG. 18 is a flowchart showing operation processing S700 for an example of an operation mode switching operation according to the seventh embodiment. In step S701, information collection for mode switching is performed. For example, the information may include whether or not an abnormal state exists in a component of the water electrolysis system 100, whether or not maintenance has been performed, whether or not a mode switching command has been issued based on external information, or the direction of change in the active power command value. After performing step S701, in step S702, it is determined whether or not mode switching can be performed. If mode switching is successful, the process proceeds to step S703. If mode switching is not successful, the process proceeds to step S704. In step S703, if the mode switching is successful, one of the first to sixth operation examples of the embodiment is performed, and the series of operations ends. In step S704, the operation of Comparative Example 1 or Comparative Example 2 is performed, and the series of operations ends.

[0069] A specific example of step S703 in the flowchart shown in FIG. 18 will be described below with reference to FIGS.

[0070] 19 is a flowchart showing the operation process S703a of the first operation example of the operation mode switching operation according to the seventh embodiment. In step S703a1, the system monitors whether the active power command value changes (whether the active power command value p1 and the active power command value p2 match). If it is determined that the active power command value changes (i.e., whether the active power command value p1 and the active power command value p2 do not match) (No in step S703a1), the system proceeds to step S703a2. If it is determined that the active power command value does not change (i.e., the active power command value p1 and the active power command value p2 match) (Yes in step S703a1), the system terminates the series of operations. Note that the "first operation example" here relates to switching of the operation mode and is different from the first operation example (first embodiment) of the current and pure water adjustment rate shown in FIG. 5 .

[0071] In step S703a2, the direction of change of the active power command value is monitored, and if the active power command value p1 is greater than the active power command value p2 (step S703a2, Yes), the process proceeds to step S703a3, and if the active power command value p1 is less than the active power command value p2 (step S703a2, No), the process proceeds to step S703a4. In step S703a3, under the conditions that the current command value c1 is set to be greater than the current command value c2 and the pure water adjustment amount command value w1 is set to be greater than the pure water adjustment amount command value w2, one of the first to sixth operation examples described above is executed, and the series of operations ends.

[0072] In step S703a4, one of the first to sixth operation examples is performed under the conditions that the current command value c1 is set to be smaller than the current command value c2 and the pure water adjustment amount command value w1 is set to be smaller than the pure water adjustment amount command value w2, and then the series of operations is terminated. By performing the mode switching shown in Fig. 19 , one of the first to sixth operation examples is selected based on the direction of change in the active power command value, and the condition near the electrolytic membrane of the electrolysis stack group 11 can be adjusted to an appropriate state based on the operating state of the water electrolysis system 100.

[0073] <<Second Operation Example in Operation Mode Switching Operation>> Figure 20 is a flowchart showing the operation process S703b of the second operation example in the operation mode switching operation example according to the seventh embodiment. In step S703b1, whether the active power command value changes (whether the active power command value p1 and the active power command value p2 match) is monitored. If it is determined that the active power command value changes (i.e., whether the active power command value p1 and the active power command value p2 do not match) (No in step S703b1), the process proceeds to step S703b2. If it is determined that the active power command value does not change (i.e., the active power command value p1 and the active power command value p2 match) (Yes in step S703b1), the process ends. Note that this "second operation example" relates to switching of the operation mode and is different from the second operation example (second embodiment) of the current and pure water adjustment amount shown in Figure 7 described above.

[0074] In step S703b2, the direction of change of the active power command value is monitored, and if the active power command value p1 is greater than the active power command value p2 (step S703b2, Yes), the process proceeds to step S703b3, and if the active power command value p1 is less than the active power command value p2 (step S703b2, No), the process proceeds to step S703b4. In step S703b3, under the conditions that the current command value c1 is set to be greater than the current command value c2 and the pure water adjustment amount command value w1 is set to be greater than the pure water adjustment amount command value w2, any one of the first to sixth operation examples described above is executed, and the series of operations ends.

[0075] In step S703b4, the above-described comparative example 1 or comparative example 2 is executed under the conditions that the current command value c1 is set to be smaller than the current command value c2 and the pure water adjustment amount command value w1 is set to be smaller than the pure water adjustment amount command value w2, and the series of operations is terminated. In particular, the second operation example shown in Fig. 20 is characterized in that an embodiment according to the present invention is executed when the active power command value is decreased, and comparative example 1 or comparative example 2 is executed when the active power command value is increased. By executing the mode switching shown in Fig. 20 , one of the first to sixth operation examples and comparative example 1 or comparative example 2 is selected based on the direction of change in the active power command value, and the condition near the electrolytic membrane of the electrolysis stack group 11 can be adjusted to an appropriate state based on the operating state of the water electrolysis system 100.

[0076] Although the methods of changing the active power command value, current command value, and pure water adjustment amount command value have been described for the first to sixth operation examples of the embodiment of the present invention, the present invention is not limited to this. While the examples have been described in which the active power command value, current command value, and pure water adjustment amount command value are changed in a ramp-like manner, they do not have to be linear, and changes with a slope that changes over time may also be used. Furthermore, instead of changing the pure water adjustment amount command value in a step-like manner, the pure water adjustment amount command value may be changed in a ramp-like manner or with a varying slope. Any change method may be used as long as it does not specify the change form of each command value and shortens the difference in response speed between the actual measured value of the pure water adjustment amount and the actual measured value of the current.

[0077] As described above, the control method for a water electrolysis system according to this embodiment has the following features: (1) A control method for a water electrolysis system including a power converter 12 capable of converting AC and DC and transmitting and receiving power between an AC connection end 12 a and a DC connection end 12 b, an electrolysis stack (electrolysis stack group 11) that electrolyzes water to generate hydrogen and oxygen, a pure water adjusting device 13 that supplies water to the electrolysis stack and recovers hydrogen, oxygen, and water not used in the electrolysis discharged from the electrolysis stack, and a control device (controller 15) that controls the power converter 12 and the pure water adjusting device 13, in which the control device performs the following steps: determining a current command value to be applied to the electrolysis stack; and determining a pure water adjustment amount command value to adjust the pressure and / or flow rate of water supplied to the electrolysis stack based on the current command value. and transmitting a current command value and a pure water adjustment amount command value to the power converter 12 and the pure water adjusting device 13, wherein when changing the current command value from the first current command value (current command value c1) toward a second current command value (current command value c2) that is a different value and changing the pure water adjustment amount command value from the first pure water adjustment amount command value (pure water adjustment amount command value w1) toward a second pure water adjustment amount command value (pure water adjustment amount command value w2) that is a different value, step A includes changing the actual measured value of the pressure and / or flow rate from the first pure water adjustment amount command value to the second pure water adjustment amount command value before the actual measured value of the current applied to the electrolysis stack from the first current command value reaches the second current command value (see FIGS. 5 and 6). This reduces the difference in response characteristics when adjusting the current of the electrolysis stack and the pressure and / or flow rate of water, thereby making it possible to maintain an appropriate electrolysis state of the electrolysis stack.

[0078] (2) The method for controlling the water electrolysis system according to (1), wherein the actual measured value of the pressure and / or the flow rate changes so as to overshoot or undershoot during a period in which the actual measured value of the current is caused to change from the first current command value to the second current command value (see FIGS. 7 , 8 , 11 , and 12 ).

[0079] (3) A control method for the water electrolysis system of (1), wherein when the current command value is changed from the first current command value to the second current command value and the pure water adjustment amount command value is changed from the first pure water adjustment amount command value to the second pure water adjustment amount command value, the actual measured value of the current changes from the first current command value to the second current command value, and then the actual measured value of the pressure and / or flow rate changes from the first pure water adjustment amount command value to the second pure water adjustment amount command value (see Figures 9, 10, 11, and 12).

[0080] (4) A method for controlling the water electrolysis system according to (1), wherein, when the current command value is changed from the first current command value to the second current command value and the pure water adjustment amount command value is changed from the first pure water adjustment amount command value to the second pure water adjustment amount command value, the actual measured value of the pressure and / or flow rate changes from the first pure water adjustment amount command value to the second pure water adjustment amount command value before the actual measured value of the current changes from the first current command value to the second current command value (see Figures 14 and 15).

[0081] (5) The method for controlling the water electrolysis system according to (4), wherein the control device determines, based on external information input from outside the water electrolysis system, that the actual measured value of the pressure and / or flow rate changes from the first pure water adjustment amount command value to the second pure water adjustment amount command value before the actual measured value of the current changes from the first current command value to the second current command value (see FIGS. 16 and 17 ).

[0082] (6) The method for controlling the water electrolysis system according to (1), further comprising: Step B, when changing the current command value from the first current command value to the second current command value and changing the pure water adjustment amount command value from the first pure water adjustment amount command to the second pure water adjustment amount command value, causing the actual measured value of the pressure and / or flow rate to change from the first pure water adjustment amount command value to the second pure water adjustment amount command value after the actual measured value of the current reaches the second current command value from the first current command value; and Step B, selecting Step A and Step B according to external information and / or the state of the water electrolysis system, and switching between Step A and Step B (see FIGS. 18 , 19 , and 20 ).

[0083] (7) The method for controlling a water electrolysis system according to (6) above, wherein step A is not executed when an abnormality occurs in the water electrolysis system or when maintenance is being performed.

[0084] DESCRIPTION OF SYMBOLS 3 Switch 4 System (AC power system) 5 External device 6 Peripheral equipment 6a Power line 6b, 6c Communication line 7 Transformer 11 Electrolysis stack group (electrolysis stack) 12 Power converter 12a AC side connection end 12b DC side connection end 13 Pure water adjustment device 13a, 13b, 13c Pipe 15 Controller (control device) 100 Water electrolysis system 131, 133 Gas-liquid separator 132, 134 Pressure adjustment valve 135, 136, 137 Valve 138 Pure water tank 139 Water supply pump S100, S200, S300, S400, S500, S600, S700, S700a, S700b Operation process p1 Active power command value p2 Active power command value c1 Current command value (first current command value) c2 Current command value (second current command value) w1 Pure water adjustment amount command value (first pure water adjustment amount command value) w2 Pure water adjustment amount command value (second pure water adjustment amount command value) w3 Pure water adjustment amount command value (third pure water adjustment amount command value)

Claims

1. A method for controlling a water electrolysis system including a power converter capable of converting AC and DC and transmitting and receiving power between an AC side connection end and a DC side connection end, an electrolysis stack that electrolyzes water to generate hydrogen and oxygen, a pure water conditioning device that supplies water to the electrolysis stack and recovers the hydrogen, the oxygen, and the water not used in the electrolysis discharged from the electrolysis stack, and a control device that controls the power converter and the pure water conditioning device, wherein the control device has the steps of: determining a current command value to be applied to the electrolysis stack; determining a pure water adjustment amount command value that adjusts the pressure and / or flow rate of the water supplied to the electrolysis stack based on the current command value; and transmitting the current command value and the pure water adjustment amount command value to the power converter and the pure water conditioning device, wherein when the control device changes the current command value from a first current command value to a second current command value that is a different value and when the control device changes the pure water adjustment amount command value from the first pure water adjustment amount command value to the second pure water adjustment amount command value that is a different value, a step A of causing an actual measurement value of the pressure or / and the flow rate to reach the second pure water adjustment amount command value from the first pure water adjustment amount command value before an actual measurement value of a current applied from the power converter to the electrolysis stack reaches the second current command value from the first current command value.

2. A method for controlling a water electrolysis system as claimed in claim 1, characterized in that the actual measured value of the pressure and / or the flow rate changes so as to overshoot or undershoot during a period in which the actual measured value of the current reaches the second current command value from the first current command value.

3. A method for controlling a water electrolysis system as described in claim 1, characterized in that when changing the current command value from the first current command value toward the second current command value and changing the pure water adjustment amount command value from the first pure water adjustment amount command value toward the second pure water adjustment amount command value, after the actual measured value of the current changes from the first current command value toward the second current command value, the actual measured value of the pressure and / or the flow rate changes from the first pure water adjustment amount command value toward the second pure water adjustment amount command value.

4. A method for controlling a water electrolysis system as described in claim 1, characterized in that when changing the current command value from the first current command value toward the second current command value and changing the pure water adjustment amount command value from the first pure water adjustment amount command value toward the second pure water adjustment amount command value, the actual measured value of the pressure and / or the flow rate changes from the first pure water adjustment amount command value toward the second pure water adjustment amount command value before the actual measured value of the current changes from the first current command value toward the second current command value.

5. A method for controlling a water electrolysis system as described in claim 4, characterized in that it is determined based on external information input to the control device from outside the water electrolysis system that the actual value of the pressure and / or the flow rate will change from the first pure water adjustment amount command value to the second pure water adjustment amount command value before the actual value of the current changes from the first current command value to the second current command value.

6. A method for controlling a water electrolysis system according to claim 5, characterized in that the external information is active power and / or reactive power required by the water electrolysis system.

7. A method for controlling a water electrolysis system according to claim 5, characterized in that the external information is weather information.

8. The method for controlling a water electrolysis system according to claim 5, wherein the external information is electricity market information.

9. A method for controlling a water electrolysis system according to claim 5, characterized in that the external information is power information from equipment that supplies power and is installed in the vicinity of the water electrolysis system.

10. A method for controlling a water electrolysis system according to claim 5, characterized in that the external information is load information of equipment that consumes electricity and is installed in the vicinity of the water electrolysis system.

11. A method for controlling a water electrolysis system as described in claim 5, characterized in that the external information is power information transmitted and received by equipment for storing power installed in the vicinity of the water electrolysis system.

12. A method for controlling a water electrolysis system as described in claim 1, comprising: when changing the current command value from the first current command value toward the second current command value and changing the pure water adjustment amount command value from the first pure water adjustment amount command value toward the second pure water adjustment amount command value, a step B of changing the actual measurement value of the pressure and / or the flow rate from the first pure water adjustment amount command value to the second pure water adjustment amount command value after the actual measurement value of the current reaches the second current command value from the first current command value; a step of selecting between step A and step B according to external information and / or a state of the water electrolysis system; and a step of switching between step A and step B.

13. A method for controlling a water electrolysis system according to claim 12, characterized in that step A is not executed when an abnormality occurs or when maintenance is being performed on the water electrolysis system.

14. A water electrolysis system comprising: a power converter capable of converting between AC and DC and transmitting and receiving power between an AC side connection end and a DC side connection end; an electrolysis stack that electrolyzes water to generate hydrogen and oxygen; a pure water conditioning device that supplies water to the electrolysis stack and recovers the hydrogen, the oxygen, and the water not used in the electrolysis discharged from the electrolysis stack; and a control device that controls the power converter and the pure water conditioning device, wherein the control device determines a current command value to be applied to the electrolysis stack, determines a pure water adjustment amount command value that adjusts the pressure and / or flow rate of the water supplied to the electrolysis stack based on the current command value, and transmits the current command value and the pure water adjustment amount command value to the power converter and the pure water conditioning device, a step A of causing an actual measurement value of the pressure or / and the flow rate to reach the second pure water adjustment amount command value from the first pure water adjustment amount command value before an actual measurement value of a current applied from the power converter to the electrolysis stack reaches the second current command value from the first current command value.

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