Method for controlling water electrolysis system, and water electrolysis system

Abstract

Provided is a method for controlling a water electrolysis system with which operation states of a plurality of electrolysis stacks can be independently regulated highly responsively and highly efficiently. This method is for controlling a water electrolysis system which comprises: electrolysis stacks where water is electrolyzed to produce hydrogen and oxygen; a pure water feeder for feeding pure water to the electrolysis stacks; a first regulation part and a second regulation part, which are disposed between each electrolysis stack and the pure water feeder and are capable of regulating the operation state of the electrolysis stack; and an operation state regulation control unit which regulates the first regulation part and the second regulation part to regulate the operation states of the electrolysis stacks. The operation state regulation control unit, after receiving a command to change the operation state of an electrolysis stack, operates the first regulation part on the basis of the operation state and, when a predetermined requirement has been satisfied, operates the second regulation part simultaneously with the first regulation part on the basis of the operation state.

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, hydrogen has attracted attention as one of the clean energy sources needed to achieve carbon neutrality, and technological development is underway regarding its production, transportation, and use. In particular, because hydrogen can be produced anywhere by electrolyzing water, 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. Plans are underway to introduce such water electrolysis systems on a large scale, primarily 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. The system also includes a device (defined as a pure water conditioning device in this document) that supplies pure water for electrolyzing water in the electrolysis stack and recovers not only the hydrogen and oxygen generated in the electrolysis stack but also the pure water that was not used in the electrolysis. The pure water conditioning device includes a device that adjusts the pressure and flow rate of the pure water supplied to the electrolysis stack. The configuration and operation method of the water electrolysis system described above are disclosed in, for example, Patent Document 1.

[0004] The water electrolysis system disclosed in Patent Document 1 includes multiple electrolysis stacks connected in series to a DC power supply, a water pump that supplies water to all of the multiple series-connected electrolysis stacks, a large cooler that adjusts the temperature of the water supplied to all of the multiple electrolysis stacks, a water flow control valve and a small cooler provided in a water supply pipe between the water pump or the large cooler and the electrolysis stacks, and a controller that controls the water pump, the large cooler, the small cooler, and the water flow control valve. The controller adjusts the amount of water supplied to each electrolysis stack with the water flow control valve and adjusts the temperature of the water supplied to each electrolysis stack with the small cooler.

[0005] WO 2023 / 012944

[0006] Patent Literature 1 discloses a water electrolysis system in which each electrolysis stack is provided with a water flow control valve and a small cooler for adjusting the flow rate and temperature of pure water supplied to the electrolysis stack, and a method for adjusting the water flow control valve and the small cooler to adjust the state of each electrolysis stack. However, Patent Literature 1 only discloses a method for adjusting static characteristics, and does not disclose a method for transiently adjusting the water flow control valve and the small cooler to adjust dynamic characteristics. Failure to appropriately adjust this transient state may result in problems such as flow loss due to adjustment of the water flow control valve, reduced efficiency due to an increased load on the water pump to eliminate the flow rate decrease caused by the increased flow loss, and reduced efficiency and poor responsiveness due to the time required for temperature adjustment by the small cooler.

[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 are capable of independently adjusting the states of multiple electrolysis stacks with high response and high efficiency.

[0008] The above and other objects of the present invention and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0009] A method for controlling a water electrolysis system of the present invention is a method for controlling a water electrolysis system including an electrolysis stack that electrolyzes water to generate hydrogen and oxygen, a pure water supply device that supplies pure water to the electrolysis stack, a first adjustment unit installed between the electrolysis stack and the pure water supply device and capable of adjusting the operating state of the electrolysis stack, a second adjustment unit installed between the electrolysis stack and the pure water supply device and capable of adjusting the operating state of the electrolysis stack, and an operating state adjustment control unit that adjusts the first adjustment unit and the second adjustment unit to adjust the operating state of the electrolysis stack, wherein the operating state adjustment control unit operates the first adjustment unit based on the operating state after receiving a command to change the operating state of the electrolysis stack, and operates the second adjustment unit simultaneously with the first adjustment unit based on the operating state when a predetermined condition is satisfied.

[0010] The water electrolysis system of the present invention includes an electrolysis stack that electrolyzes water to generate hydrogen and oxygen, a pure water supply device that supplies pure water to the electrolysis stack, a first adjustment unit that is installed between the electrolysis stack and the pure water supply device and is capable of adjusting the operating state of the electrolysis stack, a second adjustment unit that is installed between the electrolysis stack and the pure water supply device and is capable of adjusting the operating state of the electrolysis stack, and an operating state adjustment control unit that adjusts the first adjustment unit and the second adjustment unit to adjust the operating state of the electrolysis stack, wherein the operating state adjustment control unit operates the first adjustment unit based on the operating state after receiving a command to change the operating state of the electrolysis stack, and operates the second adjustment unit simultaneously with the first adjustment unit based on the operating state when a predetermined condition is satisfied.

[0011] According to the present invention, the states of a plurality of electrolysis stacks can be independently adjusted with high response and high efficiency, and the states of the plurality of electrolysis stacks can be set to appropriate states.

[0012] Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments.

[0013] 1 is a diagram illustrating the device configuration of a water electrolysis system according to an embodiment of the present invention; FIG. 2 is a diagram illustrating the configuration of a pure water adjusting apparatus according to an embodiment of the present invention; FIG. 3 is a diagram illustrating the device configuration of an electrolysis stack group according to an embodiment of the present invention; FIG. 4 is a control block diagram illustrating an electrolysis stack operation state adjustment control unit implemented in a controller according to an embodiment of the present invention; FIG. 5 is a diagram illustrating a first adjustment unit that adjusts the operation state of the electrolysis stack according to an embodiment of the present invention; FIG. 6 is a diagram illustrating a second adjustment unit that adjusts the operation state of the electrolysis stack according to an embodiment of the present invention; FIG. 7 is a control block diagram of an electrolysis stack operation state adjustment control unit according to a first embodiment; FIG. 8 is a time chart illustrating how the electrolysis stack operation state adjustment control unit adjusts the temperature of the electrolysis stack according to the first embodiment; FIG. 9 is a control block diagram illustrating a case where the electrolysis stack deterioration state adjustment control unit determines a temperature target value of the electrolysis stack for adjusting the deterioration state of the electrolysis stack according to the first embodiment; FIG. 10 is a control block diagram of an electrolysis stack operation state adjustment control unit according to a second embodiment; FIG. 11 is a time chart illustrating how the electrolysis stack operation state adjustment control unit adjusts the voltage of the electrolysis stack according to the second embodiment; FIG. 12 is a control block diagram of an electrolysis stack operation state adjustment control unit according to a third embodiment; FIG. 13 is a time chart illustrating how the electrolysis stack operation state adjustment control unit adjusts the current of the electrolysis stack according to the third embodiment. FIG. 10 is a time chart illustrating how the electrolytic stack operation state adjustment control unit independently controls a plurality of heat exchangers and a plurality of flow rate control valves to independently control the states of a plurality of electrolytic stacks in a fourth embodiment. FIG. 11 is a control block diagram illustrating the configuration of the electrolytic stack operation state adjustment control unit according to an embodiment of the present invention. FIG. 12 is a flowchart illustrating the operation process of the electrolytic stack operation state adjustment control unit according to an embodiment of the present invention. FIG. 13 is a time chart illustrating how the electrolytic stack operation state adjustment control unit according to an embodiment of the present invention adjusts only a heat exchanger. FIG. 14 is a time chart illustrating how the electrolytic stack operation state adjustment control unit according to an embodiment of the present invention adjusts only a flow rate control valve. FIG. 15 is a time chart illustrating how the electrolytic stack operation state adjustment control unit according to an embodiment of the present invention simultaneously operates a flow rate control valve and a device upstream of a heat exchanger.

[0014] 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 contents of the present invention, and the present invention is not limited to these descriptions. Various changes and modifications are possible 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 function are designated by the same reference numerals, and repeated explanations thereof may be omitted.

[0015] <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. Pure water is electrolyzed into hydrogen and oxygen in response to the current applied from the power converter 12 to the electrolysis stack group 11. A pure water preparation device 13 is connected to the electrolysis stack group 11 via three pipes 13a, 13b, and 13c. Pure water is supplied via the pipe 13a. Hydrogen generated in the electrolysis stack group 11 and pure water not used for water electrolysis are recovered via the pipe 13b. Oxygen generated in the electrolysis stack group 11 and pure water not used for water electrolysis are recovered via the pipe 13c. The water electrolysis system 100 also includes a controller 15 (control device). The controller 15 detects and adjusts the operating states of the electrolysis stack group 11, the power converter 12, and the pure water preparation device 13.

[0016] The controller 15 is configured to include, 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.

[0017] The water electrolysis system 100 has a configuration in which a transformer 6 is connected to an AC connection end 12a of a power converter 12, the transformer 6 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.

[0018] 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.

[0019] Furthermore, the controller 15 also has a function of acquiring external information such as the voltages of the water electrolysis system 100 and the grid 4, and determines the operating state of the water electrolysis system 100 based on various pieces of information.

[0020] 2 is a diagram showing the configuration of the pure water preparation device 13 of the water electrolysis system 100. A valve 135 capable of adjusting the flow rate 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 from 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 transports the pure water under pressure is connected downstream of the pure water tank 138. A heat exchanger 1310 that adjusts the temperature of the pure water supplied to the electrolysis stack group 11 and a valve 137 that adjusts the flow rate of the pure water supplied to the electrolysis stack group 11 are connected downstream of the water pump 139, and the pure water is supplied to the electrolysis stack group 11 via the pipe 13a. A pressure adjustment valve 132 is connected to the gas-liquid separator 131, and adjusts the internal pressure of the gas-liquid separator 131 and supplies 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. 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 to a pure water tank 138. A pressure adjustment valve 134 is connected to the gas-liquid separator 133, and 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.

[0021] 3 is a diagram showing the device configuration of the electrolysis stack group 11. In this embodiment, four electrolysis stacks #1, #2, #3, #4 (111, 112, 113, 114) are provided. The electrolysis stack #1 (111) and the electrolysis stack #2 (112) are electrically connected in series, and the electrolysis stack #3 (113) and the electrolysis stack #4 (114) are electrically connected in series. Furthermore, a pair of two electrolysis stacks connected in series is connected in parallel and connected to the DC side connection end 12b of the power converter 12. The four electrolysis stacks 111, 112, 113, 114 are provided with first adjustment units 11a1, 11a2, 11a3, 11a4 and second adjustment units 11b1, 11b2, 11b3, 11b4, respectively, which are connected between the pipe 13a and the electrolysis stacks. The four electrolysis stacks 111, 112, 113, and 114 have two outlets for discharging gases generated therefrom and pure water not used in the water electrolysis reaction, which are connected to pipes 13b and 13c, respectively.

[0022] The electrolysis stacks 111, 112, 113, and 114 constituting the electrolysis stack group 11 can be broadly divided into alkaline and solid polymer electrolysis stacks. In this embodiment, it is assumed that solid polymer electrolysis stacks are used for the electrolysis stacks 111, 112, 113, and 114. The solid polymer electrolysis stacks have a superior response speed compared to the alkaline electrolysis stacks, and are therefore suitable for a water electrolysis system that follows fluctuations in renewable energy. Furthermore, the size of the solid polymer electrolysis stack can be made smaller than that of the alkaline electrolysis stacks, and therefore the solid polymer electrolysis stacks are suitable for a system that requires space-saving installation, such as offshore installation near an offshore wind power generation system.

[0023] 4 is a control block diagram showing the electrolytic stack operation state adjustment control unit 151 implemented in the controller 15. As shown in FIG. 4 , the electrolytic stack operation state adjustment control unit 151 is implemented in the controller 15. The electrolytic stack operation state adjustment control unit 151 receives target state values ​​of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114) and measured state values ​​of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114). The electrolytic stack operation state adjustment control unit 151 also outputs command values ​​to first adjustment units 11a1, 11a2, 11a3, and 11a4 (heat exchangers 21) and second adjustment units 11b1, 11b2, 11b3, and 11b4 (flow rate adjustment valves 22). The target state values ​​and measured state values ​​of the electrolytic stacks #1, #2, #3, and #4 are target values ​​and measured values ​​of the states (e.g., temperature, voltage, current, etc., described later) of the electrolytic stacks #1, #2, #3, and #4.

[0024] Fig. 5 is a diagram showing first adjustment units 11a1, 11a2, 11a3, and 11a4 that adjust the operating state of the electrolysis stack. Hereinafter, the first adjustment units 11a1, 11a2, 11a3, and 11a4 are configured to include a heat exchanger 21 shown in Fig. 5 that is capable of adjusting temperature, and to adjust the temperature of the pure water supplied to the electrolysis stacks 111, 112, 113, and 114 by this heat exchanger 21.

[0025] 6 is a diagram showing second adjustment units 11b1, 11b2, 11b3, and 11b4 that adjust the operating state of the electrolysis stack. Hereinafter, the second adjustment units 11b1, 11b2, 11b3, and 11b4 are configured to include a flow rate adjustment valve 22 shown in FIG. 6 that is capable of adjusting the flow rate, and the flow rate of pure water supplied to the electrolysis stacks 111, 112, 113, and 114 is adjusted by this flow rate adjustment valve 22.

[0026] Below, specific configurations and methods for adjusting the operating states of multiple electrolysis stacks using heat exchangers and flow control valves are described as several embodiments. Note that it is assumed that the electrolysis stack has a characteristic in which the electrical resistance associated with the water electrolysis reaction changes with temperature, and the electrical resistance during the water electrolysis reaction in the electrolysis stack decreases when the temperature of the electrolysis stack is high.

[0027] <<Adjusting the Temperature State of the Electrolysis Stack (First Embodiment)>> Hereinafter, adjusting the temperature state of the electrolysis stack (first embodiment) will be described with reference to Figs. 7 to 9 . Fig. 7 is a control block diagram of the electrolysis stack operation state adjustment control unit 151 implemented in the controller 15 in the first embodiment. This embodiment is an example of an operation in which the temperature of the electrolysis stack is controlled as the operation state of the electrolysis stack. In this embodiment, sensors (temperature sensors) (not shown) are provided for measuring the temperatures of the electrolysis stacks #1, #2, #3, and #4 (111, 112, 113, and 114) of the electrolysis stack group 11. 7 , target temperature values ​​of the electrolytic stacks #1, #2, #3, #4 (111, 112, 113, 114) and temperature measurement values ​​of the electrolytic stacks #1, #2, #3, #4 (111, 112, 113, 114) measured by sensors (temperature sensors) are input to the electrolytic stack operation state adjustment control unit 151. In addition, the electrolytic stack operation state adjustment control unit 151 outputs command values ​​to first adjustment units 11a1, 11a2, 11a3, 11a4 (heat exchangers 21) and second adjustment units 11b1, 11b2, 11b3, 11b4 (flow rate adjustment valves 22).

[0028] FIG. 8 is a time chart showing how the electrolytic stack operating state adjustment control unit 151 adjusts the temperature of the electrolytic stack #1 (111) in the first embodiment. The horizontal axis represents time, and the vertical axis represents the temperature of the electrolytic stack #1 (111), the state of the heat exchanger 11a1, and the state of the flow control valve 11b1, respectively, from the top to the bottom of the diagram. The top of the diagram represents high temperature, high heat exchanger output, and open flow control valve, respectively. With respect to the state continuing from time t0, after the temperature command value changes to increase the temperature at time t1, the heat exchanger 11a1 increases its output to increase the temperature of the pure water, and the flow control valve 11b1 changes to close the valve to reduce the flow rate of the pure water and increase the temperature. From time t1, as the difference between the measured temperature and the target temperature decreases, the output of the heat exchanger 11a1 gradually decreases, and the flow control valve 11b1 is opened. After that, after time t2 when the difference between the target temperature value and the measured temperature value becomes sufficiently small, the output of heat exchanger 11a1 is set to a medium level in accordance with the target temperature value, but the opening of flow control valve 11b1 is increased to the same open state as at time t0.

[0029] By rapidly increasing the output of the heat exchanger 11a1 between times t1 and t2, the temperature of the electrolysis stack #1 is rapidly increased, but it takes time for the temperature of the pure water to increase. Therefore, by closing the flow control valve 11b1, the flow rate of the pure water is reduced, reducing the amount of heat absorbed by the pure water from the electrolysis stack #1, thereby enabling the temperature of the electrolysis stack #1 to be changed with high responsiveness. Furthermore, by opening the flow control valve 11b1 to the same degree as at time t0 after time t2, the flow rate loss due to the flow control valve 11b1 can be reduced. This eliminates the need to increase the output of the pump 139 upstream of the flow control valve 11b1 to accommodate the flow rate loss, thereby suppressing efficiency degradation. Furthermore, by setting the output of the heat exchanger 11a1 to medium after time t2, the target temperature value of the electrolysis stack #1 and the measured temperature value are matched.

[0030] 9 is a control block diagram showing a case where the electrolytic stack deterioration state adjustment control unit 152 determines the electrolytic stack temperature target values ​​for adjusting the deterioration states of the electrolytic stacks 111, 112, 113, and 114. In this case, the electrolytic stack deterioration state adjustment control unit 152 shown in FIG. 9 determines the temperature target values ​​of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114) to be input to the electrolytic stack operation state adjustment control unit 151. As shown in FIG. 9 , the electrolytic stack deterioration state adjustment control unit 152 receives input of the deterioration level target values ​​of the electrolytic stacks #1, #2, #3, and #4 and the deterioration level estimated values ​​of the electrolytic stacks #1, #2, #3, and #4. The electrolytic stack deterioration state adjustment control unit 152 determines the temperature target values ​​of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114) based on the deterioration level target values ​​or the deterioration level estimated values. For example, if the degradation state of the electrolytic stacks #1, #2, #3, #4 (111, 112, 113, 114) is likely to deviate significantly from the average degradation state of the multiple electrolytic stacks or deviates significantly from the average degradation state of the multiple electrolytic stacks, the target temperature value is set lower than normal to suppress the progression of degradation. Also, for example, if the degradation of the electrolytic stacks #1, #2, #3, #4 (111, 112, 113, 114) is progressing slowly, the target temperature value is set to be increased to accelerate the progression of degradation.

[0031] <<Adjusting the voltage state of the electrolysis stack (second embodiment)>> Hereinafter, a case of adjusting the voltage state of the electrolysis stack (second embodiment) will be described with reference to Figs. 10 and 11 . Fig. 10 is a control block diagram of the electrolysis stack operation state adjustment control unit 151 implemented in the controller 15 in the second embodiment. This embodiment is an example of an operation in which the voltage of the electrolysis stack is controlled as the operation state of the electrolysis stack. In this embodiment, a sensor (voltage sensor, not shown) is provided for each of the electrolysis stacks #1, #2, #3, and #4 (111, 112, 113, and 114) of the electrolysis stack group 11 to measure the voltage of the electrolysis stacks #1, #2, #3, and #4. 10 , target voltage values ​​of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114) and voltage measurement values ​​of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114) measured by sensors (voltage sensors) are input to the electrolytic stack operation state adjustment control unit 151. In addition, the electrolytic stack operation state adjustment control unit 151 outputs command values ​​to first adjustment units 11a1, 11a2, 11a3, and 11a4 (heat exchangers 21) and second adjustment units 11b1, 11b2, 11b3, and 11b4 (flow rate adjustment valves 22).

[0032] FIG. 11 is a time chart showing how the electrolytic stack operation state adjustment control unit 151 adjusts the voltage of the electrolytic stack #1 (111) in the second embodiment. The horizontal axis represents time, and the vertical axis represents the voltage of the electrolytic stack #1 (111), the state of the heat exchanger 11a1, and the state of the flow control valve 11b1, respectively, from the top of the diagram. The top of the diagram represents high voltage, high heat exchanger output, and open flow control valve, respectively. Note that FIG. 11 assumes that the temperature of the pure water supplied to the electrolytic stack 111 is increased to reduce the voltage of the electrolytic stack 111. With respect to the state continuing from time t0, after the voltage command value changes at time t1 to reduce the voltage, the heat exchanger 11a1 increases its output to increase the temperature of the pure water, and the flow control valve 11b1 changes to close the valve to reduce the flow rate of the pure water and increase its temperature. From time t1, as the difference between the measured voltage value and the target voltage value decreases, the output of heat exchanger 11a1 is gradually reduced and flow rate adjustment valve 11b1 is opened. After that, at time t2 when the difference between the target voltage value and the measured voltage value becomes sufficiently small, the output of heat exchanger 11a1 is set to a medium level in accordance with the target voltage value, but the opening of flow rate adjustment valve 11b1 is increased to the same open state as at time t0.

[0033] By rapidly increasing the output of the heat exchanger 11a1 between times t1 and t2, the temperature of the electrolysis stack #1 is rapidly increased, but it takes time for the temperature of the pure water to increase. Therefore, by closing the flow rate control valve 11b1, the flow rate of the pure water is reduced, reducing the amount of heat absorbed by the pure water from the electrolysis stack #1, thereby enabling the temperature of the electrolysis stack #1 to be changed with high responsiveness. Furthermore, by opening the flow rate control valve 11b1 to the same degree as at time t0 after time t2, the flow rate loss due to the flow rate control valve 11b1 can be reduced. This eliminates the need to increase the output of the pump 139 upstream of the flow rate control valve 11b1 to accommodate the flow rate loss, thereby suppressing efficiency degradation. Furthermore, by setting the output of the heat exchanger 11a1 to medium after time t2, the target voltage value and the measured voltage value of the electrolysis stack #1 are matched.

[0034] In this embodiment, when a voltage difference occurs between electrolysis stack #1 (111) and electrolysis stack #2 (112), which are electrically connected in series, for example, the voltage difference is reduced to reduce the efficiency difference between the electrolysis stacks caused by the voltage difference, thereby adjusting the efficiency of the water electrolysis system 100.

[0035] <<Adjusting the Current State of the Electrolytic Stack (Third Embodiment)>> Hereinafter, a case of adjusting the current state of the electrolytic stack (third embodiment) will be described with reference to Figs. 12 and 13 . Fig. 12 is a control block diagram of the electrolytic stack operation state adjustment control unit 151 implemented in the controller 15 in the third embodiment. This embodiment is an example of an operation in which the current of the electrolytic stack is controlled as the operation state of the electrolytic stack. In this embodiment, a sensor (current sensor, not shown) is provided for each of the electrolytic stacks #1, #2, #3, and #4 (111, 112, 113, and 114) of the electrolytic stack group 11 to measure the current of the electrolytic stacks #1, #2, #3, and #4. 12 , current target values ​​of the electrolytic stacks #1, #2, #3, #4 (111, 112, 113, 114) and current measurement values ​​of the electrolytic stacks #1, #2, #3, #4 (111, 112, 113, 114) measured by sensors (current sensors) are input to the electrolytic stack operation state adjustment control unit 151. In addition, the electrolytic stack operation state adjustment control unit 151 outputs command values ​​to first adjustment units 11a1, 11a2, 11a3, 11a4 (heat exchangers 21) and second adjustment units 11b1, 11b2, 11b3, 11b4 (flow rate adjustment valves 22).

[0036] Fig. 13 is a time chart showing how the electrolysis stack operation state adjustment control unit 151 adjusts the current of the electrolysis stack #1 (111) in the third embodiment. The horizontal axis represents time, and the vertical axis represents the current of the electrolysis stack #1 (111), the state of the heat exchanger 11a1, and the state of the flow control valve 11b1, respectively, from the top of the diagram. The top of the diagram represents a high current, a high heat exchanger output, and an open flow control valve, respectively. Note that Fig. 13 assumes that, in the electrical connection configuration of the electrolysis stack group 11 shown in Fig. 3 , the temperature of the supplied pure water is increased to reduce the electrical resistance of the electrolysis stack #1 (111) so as to increase the current of the electrolysis stacks #1 (111) and #2 (112) and reduce the current of the electrolysis stacks #3 (113) and #4 (114). In the state continuing from time t0, after the current command value changes to increase the current at time t1, the heat exchanger 11a1 increases its output to raise the temperature of the pure water, and the flow rate control valve 11b1 changes to close its valve to reduce the flow rate of the pure water and raise its temperature. From time t1, as the difference between the measured current value and the target current value decreases, the output of the heat exchanger 11a1 gradually decreases, and the flow rate control valve 11b1 opens. After that, at time t2, when the difference between the target current value and the measured current value becomes sufficiently small, the output of the heat exchanger 11a1 is adjusted to a medium level in accordance with the target current value, but the flow rate control valve 11b1 opens to the same degree of opening as at time t0.

[0037] By rapidly increasing the output of the heat exchanger 11a1 between times t1 and t2, the temperature of the electrolysis stack #1 is rapidly increased, but it takes time for the temperature of the pure water to increase. Therefore, by closing the flow rate control valve 11b1, the flow rate of the pure water is reduced, reducing the amount of heat absorbed by the pure water from the electrolysis stack #1, thereby enabling the temperature of the electrolysis stack #1 to be changed with high responsiveness. Furthermore, by opening the flow rate control valve 11b1 to the same degree as at time t0 after time t2, the flow rate loss due to the flow rate control valve 11b1 can be reduced. This eliminates the need to increase the output of the pump 139 upstream of the flow rate control valve 11b1 to accommodate the flow rate loss, thereby suppressing efficiency degradation. Furthermore, by setting the output of the heat exchanger 11a1 to medium after time t2, the target current value of the electrolysis stack #1 and the measured current value are matched.

[0038] In this embodiment, when a current difference occurs between electrolysis stack #1 (111) and electrolysis stack #3 (113), which are electrically connected in parallel, for example, the current difference is reduced to reduce the efficiency difference between the electrolysis stacks caused by the current difference, thereby adjusting the efficiency of the water electrolysis system 100.

[0039] <<Independent Adjustment of Operational States of Multiple Electrolytic Stacks (Fourth Embodiment)>> In the above-described operation examples (first to third embodiments), specific operations during a transient state of the heat exchangers and flow control valves that adjust the temperature and flow rate of pure water supplied to the electrolytic stacks have been described, focusing on electrolytic stack #1 (111). Hereinafter, a case where the operation states of multiple electrolytic stacks are independently adjusted using multiple heat exchangers and flow control valves (fourth embodiment) will be described with reference to FIG. 14 .

[0040] 14 is a time chart showing how the electrolytic stack operating state adjustment control unit 151 independently controls the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow control valves 11b1, 11b2, 11b3, and 11b4 to independently control the states of the electrolytic stacks 111, 112, 113, and 114. The horizontal axis represents time, and the vertical axis represents the states of the heat exchangers and the flow control valves, respectively, from the top of the figure, with the top representing a high heat exchanger output and the bottom representing an open flow control valve. Note that in this embodiment, similar to the first to third embodiments described above, it is assumed that the temperatures of the electrolytic stacks 111, 112, 113, and 114 are increased. At time t1, a command to increase the temperature from the state maintained from time t0 is input to the electrolytic stack operation state adjustment control unit 151, thereby increasing the outputs of the heat exchangers 11a1, 11a2, 11a3, and 11a4, but the states of the heat exchangers 11a1, 11a2, 11a3, and 11a4 take different values. Similarly, at time t1, the flow rate control valves 11b1, 11b2, 11b3, and 11b4 are closed, but the states (opening degrees) of the flow rate control valves 11b1, 11b2, 11b3, and 11b4 are different. Furthermore, after time t2, it is determined that the difference between the target temperature value and the measured temperature value has become sufficiently small, and the outputs of the heat exchangers 11a1, 11a2, 11a3, and 11a4 are maintained at an output higher than that at time t0, and the flow rate control valves 11b1, 11b2, 11b3, and 11b4 are adjusted to maintain the same open state as at time t0. As a result, even when the target temperature states of the electrolysis stacks 111, 112, 113, and 114 are different, the electrolysis stacks 111, 112, 113, and 114 can be independently adjusted with high response and high efficiency by independently adjusting the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow rate control valves 11b1, 11b2, 11b3, and 11b4.

[0041] <<Specific Example of Electrolytic Stack Operational State Adjustment Control Unit>> Hereinafter, a specific example of the electrolytic stack operation state adjustment control unit 151 implemented in the controller 15 will be described with reference to FIGS. 15 and 16 .

[0042] 15 is a control block diagram showing the configuration of the electrolytic stack operating state adjustment control unit 151. Two proportional-integral control units 1511 and 1512 are provided to control the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow rate control valves 11b1, 11b2, 11b3, and 11b4, which adjust the temperature and flow rate of the pure water supplied to the voltage stacks #1, #2, #3, and #4 (111, 112, 113, and 114), respectively. The proportional-plus-integral control units 1511 and 1512 calculate command values ​​(i.e., heat exchanger output target values ​​and flow rate control valve opening target values) for the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow rate control valves 11b1, 11b2, 11b3, and 11b4 by proportional-plus-integral control based on the difference between the state target values, which are target values ​​for the states (temperature, voltage, current, or deterioration) of the electrolytic stacks #1, #2, #3, and #4, and the state estimate values ​​measured or estimated using sensors.

[0043] 16 is a flowchart showing the operation process S100 of the electrolytic stack operation state adjustment control unit 151. First, in step S101, command values ​​for adjusting the states of the electrolytic stacks 111, 112, 113, and 114 are determined, and the process proceeds to step S102. In step S102, the proportional-plus-integral control unit 1511 is executed to determine output command values ​​for the heat exchangers 11a1, 11a2, 11a3, and 11a4, and the process proceeds to step S103. In step S103, the proportional-plus-integral control unit 1512 is executed to determine opening command values ​​for the flow rate control valves 11b1, 11b2, 11b3, and 11b4, and the series of operations ends.

[0044] <<Example of Operation When Adjustment is Made by Only One of the Adjusting Units>> In the above-described embodiments, an example of operation has been shown in which the adjusting units for both the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow rate adjusting valves 11b1, 11b2, 11b3, and 11b4 operate. In contrast, when proportional-plus-integral control is applied as described above and there are limitations on the command values ​​for each of the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow rate adjusting valves 11b1, 11b2, 11b3, and 11b4, a case may arise in which adjustment is made by only one of the adjusting units. An example of operation in this case will be described below with reference to FIGS. 17 and 18 .

[0045] (Example of Operation for Adjusting Only the Heat Exchanger) FIG. 17 is a time chart showing how the electrolytic stack operation state adjustment control unit 151 adjusts only the heat exchanger 11a1. The horizontal axis represents time, and the vertical axis represents the temperature of the electrolytic stack #1 (111), the state of the heat exchanger 11a1, and the state of the flow control valve 11b1, respectively, from the top of the diagram. The top of the diagram represents high temperature, high heat exchanger output, and open flow control valve. In the following, it is assumed that the temperature of the electrolytic stack #1 is reduced at time t1. If the aperture of the flow control valve 11b1 has already reached its upper limit, the flow control valve 11b1 remains open and the output of the heat exchanger 11a1 is reduced even if a temperature reduction command is issued at time t1. After that, after time t2 when the difference between the target temperature and the measured temperature becomes sufficiently small, the output of the heat exchanger 11a1 is maintained lower than the state at time t0 to lower the temperature of the electrolytic stack #1 below the state at time t0.

[0046] (Example of operation for adjusting only the flow rate control valve) Figure 18 is a time chart showing how the electrolytic stack operation state adjustment control unit 151 adjusts only the flow rate control valve 11b1. The horizontal axis represents time, and the vertical axis represents, from the top of the diagram, the temperature of the electrolytic stack #1 (111), the state of the heat exchanger 11a1, and the state of the flow rate control valve 11b1, with the top representing a high temperature, a high output of the heat exchanger, and an open flow rate control valve. In the following, it is assumed that the temperature of the electrolytic stack #1 is increased at time t1. If the output of the heat exchanger 11a1 has already reached its upper limit, the heat exchanger 11a1 will maintain a high output and close the flow rate control valve 11b1 even if a temperature increase command is issued at time t1. After that, after time t2 when the difference between the target temperature value and the measured temperature value becomes sufficiently small, in order to raise the temperature of electrolytic stack #1 to a value higher than the temperature state of electrolytic stack #1 at time t0, the flow control valve 11b1 is closed more than the state at time t0, the flow rate of pure water is reduced, and the amount of heat transferred from electrolytic stack #1 to the pure water is reduced, thereby raising the temperature of electrolytic stack #1.

[0047] 19 , an example of cooperative operation between the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow rate control valves 11b1, 11b2, 11b3, and 11b4 provided in the electrolysis stack group 11 and the pump 139, heat exchanger 1310, and valve 137 provided in the pure water adjustment device 13 will be described. The pump 139, heat exchanger 1310, and valve 137 provided in the pure water adjustment device 13 correspond to the “upstream adjustment unit” according to the present invention.

[0048] In Figure 19, the horizontal axis represents time, and the vertical axis represents, from the top to the bottom, the operation commands to the devices 137, 139, and 1310, the states of the heat exchangers 11a1, 11a2, 11a3, and 11a4, and the states of the flow control valves 11b1, 11b2, 11b3, and 11b4. The top of the figure represents Command 1 (operation performed), the output of the heat exchangers is high, and the flow control valves are open. Note that Figure 19 assumes that the temperatures of the electrolysis stacks 111, 112, 113, and 114 are increased. The state at time t0 is maintained until time t1. After the operation commands are issued to the devices 137, 139, and 1310 at time t1, the outputs of the heat exchangers 11a1, 11a2, 11a3, and 11a4 are changed to high, and the flow control valves 11b1, 11b2, 11b3, and 11b4 are changed to closed. After time t1, the high output states of the heat exchangers are reduced, and the apertures of the flow control valves are changed to open states. After time t2, when the temperatures of the electrolysis stacks 11, 112, 113, and 114 have sufficiently increased, the outputs of the heat exchangers 11a1, 11a2, 11a3, and 11a4 are maintained at a higher level than that at time t0. Thus, even when the operating load (amount of hydrogen generated) of the water electrolysis system 100 is changed to operate the pure water supply device 13, the heat exchangers 11a1, 11a2, 11a3, and 11a4 in the electrolysis stack group 11 are operated in coordination with the flow control valves 11b1, 11b2, 11b3, and 11b4, thereby enabling the state of the electrolysis stacks 111, 112, 113, and 114 to be changed more responsively and efficiently than when only the pure water supply device 13 is adjusted.

[0049] Although the above-described operational example of the embodiment of the present invention has been described with respect to a method for changing the heat exchanger and the flow control valve, the present invention is not limited to this. Although the example has been described in which the state of the heat exchanger and the state of the flow control valve are changed in a step-like manner to the target values ​​of temperature, voltage, and current, they may be changed in a ramp-like manner or in a fluctuating manner, or any command value that changes over time may be used.

[0050] In the above-described embodiment of the present invention, a heat exchanger is used as the first adjustment unit and a flow rate control valve is used as the second adjustment unit, but this is not limited to this. The second adjustment unit may be another device that has an adjustment function different from the operation state adjustment function of the first adjustment unit. By configuring in this manner, particularly in cases where there is a disadvantage in operating the second adjustment unit despite the second adjustment unit having high response, the disadvantage can be suppressed. Furthermore, the second adjustment unit may be another device that can adjust the operation state by enhancing the operation state adjustment function of the first adjustment unit.

[0051] In the above-described embodiment and operation example, the heat exchangers 11a1, 11a2, 11a3, and 11a4 and the flow control valves 11b1, 11b2, 11b3, and 11b4 are connected in series upstream of each electrolysis stack 111, 112, 113, and 114, and the heat exchangers are arranged upstream of the flow control valves. However, the control method according to the present invention can also be implemented by conversely arranging the flow control valves upstream of the heat exchangers. However, because the flow rate changes as the volume of pure water changes, the operating state of the electrolysis stack can be controlled more accurately by arranging the heat exchangers upstream and adjusting the flow rate after stabilizing the temperature.

[0052] As described in the above embodiments, the method for controlling a water electrolysis system according to the present invention has the following features: (1) A method for controlling a water electrolysis system including an electrolysis stack that electrolyzes water to generate hydrogen and oxygen, a pure water supply device that supplies pure water to the electrolysis stack, a first adjustment unit that is installed between the electrolysis stack and the pure water supply device and that is capable of adjusting the operating state of the electrolysis stack, a second adjustment unit that is installed between the electrolysis stack and the pure water supply device and that is capable of adjusting the operating state of the electrolysis stack, and an operating state adjustment controller that adjusts the first adjustment unit and the second adjustment unit to adjust the operating state of the electrolysis stack, wherein the operating state adjustment controller operates the first adjustment unit based on the operating state after receiving a command to change the operating state of the electrolysis stack, and operates the second adjustment unit simultaneously with the first adjustment unit based on the operating state when a predetermined condition is satisfied (see FIGS. 8 , 11 , and 13 ). This method improves the responsiveness of temperature adjustment of the electrolysis stack and suppresses an increase in loss due to pure water flow rate control, thereby achieving high efficiency and maintaining an appropriate electrolysis state in the electrolysis stack.

[0053] (2) A method for controlling the water electrolysis system of (1), in which a plurality of first adjustment units and a plurality of second adjustment units are independently adjusted (see FIG. 14).

[0054] (3) In the control method for the water electrolysis system of (1), when the adjustment amount of either the first adjustment unit or the second adjustment unit has reached its limit value, only the first adjustment unit or the second adjustment unit is adjusted (see Figures 17 and 18).

[0055] (4) A control method for the water electrolysis system of (1), in which the first adjustment unit and the second adjustment unit are adjusted in conjunction with the operation of an upstream adjustment unit that adjusts one or more of the flow rate, pressure, and temperature of pure water upstream of the first adjustment unit and the second adjustment unit, and both the first adjustment unit and the second adjustment unit are adjusted during a period in which the difference between the state target value and the state measurement value is large, and when the difference between the state target value and the state measurement value has become sufficiently small, only the first adjustment unit is adjusted (see Figure 19).

[0056] In the method for controlling a water electrolysis system according to the present invention, the first adjustment unit can be a device capable of changing (increasing and / or decreasing) the temperature of the pure water, such as a heat exchanger, a heater, or a cooler. By using a device capable of changing the temperature of the pure water, such as a heat exchanger, a heater, or a cooler, as the first adjustment unit, it is possible to change the temperature of the pure water supplied to the electrolysis stack and thereby change the operating state of the electrolysis stack.

[0057] In the method for controlling a water electrolysis system according to the present invention, the second adjustment unit may be, for example, a flow control valve that adjusts the flow rate of pure water. By using the flow control valve as the second adjustment unit, the amount of pure water supplied to the electrolysis stack can be adjusted, thereby adjusting the operating state of the electrolysis stack.

[0058] In the method for adjusting a water electrolysis system according to the present invention, the predetermined condition is, for example, a period immediately after the operating state is changed, in which there is a large difference between the target value of the operating state and the measured value of the operating state.

[0059] In the method for adjusting a water electrolysis system according to the present invention, the command to change the operating state of the electrolysis stack is a command received by the electrolysis stack operating state adjustment control unit to change the operating state of the electrolysis stack. Specifically, this command corresponds to the temperature command value, voltage command value, current command value, etc. in the above-described embodiments.

[0060] It should be noted that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0061] 3 Switch, 4 System (AC power system), 5 External device, 6 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 pump, 1310 Heat exchanger, 151 Electrolysis stack operation state adjustment control unit, 152 Electrolysis stack deterioration state adjustment control unit, 1511, 1512 Proportional and integral control unit, S100 Operation processing

Claims

1. A method for controlling a water electrolysis system comprising: an electrolysis stack that electrolyzes water to generate hydrogen and oxygen; a pure water supply device that supplies pure water to the electrolysis stack; a first adjustment unit installed between the electrolysis stack and the pure water supply device and capable of adjusting the operating state of the electrolysis stack; a second adjustment unit installed between the electrolysis stack and the pure water supply device and capable of adjusting the operating state of the electrolysis stack; and an operating state adjustment control unit that adjusts the first adjustment unit and the second adjustment unit to adjust the operating state of the electrolysis stack, wherein the operating state adjustment control unit operates the first adjustment unit based on the operating state after receiving a command to change the operating state of the electrolysis stack, and operates the second adjustment unit simultaneously with the first adjustment unit based on the operating state when a predetermined condition is satisfied.

2. The water electrolysis system control method according to claim 1, characterized in that the water electrolysis system comprises a plurality of sets of the electrolysis stack, the first adjustment unit, and the second adjustment unit, and the operating state adjustment control unit independently adjusts the first adjustment unit and the second adjustment unit of each of the plurality of sets.

3. A method for controlling a water electrolysis system as described in claim 1, characterized in that the second adjustment unit has an adjustment function different from the adjustment function of the operating state that the first adjustment unit has, and the adjustment function of the second adjustment unit adjusts the operating state by enhancing the adjustment function of the first adjustment unit.

4. The method for controlling a water electrolysis system according to claim 1, wherein the first adjusting unit is any one of a heat exchanger, a heater, and a cooler that adjusts the temperature of the pure water.

5. The method for controlling a water electrolysis system according to claim 1, wherein the second adjusting unit is a flow rate adjusting valve that adjusts the flow rate of the pure water.

6. The method for controlling a water electrolysis system according to claim 1, characterized in that the predetermined condition is a period immediately after the operating state is changed, in which there is a large difference between the target value of the operating state and the measured value of the operating state.

7. The method for controlling a water electrolysis system according to claim 1, wherein the operating condition is the temperature of the electrolysis stack.

8. The method for controlling a water electrolysis system according to claim 1, wherein the operating state is a deterioration state of the electrolysis stack.

9. The method for controlling a water electrolysis system according to claim 1, wherein the operating condition is the voltage of the electrolysis stack.

10. The method for controlling a water electrolysis system according to claim 1, wherein the operating condition is the current of the electrolysis stack.

11. The method for controlling a water electrolysis system according to claim 1, characterized in that the water electrolysis system further comprises an upstream adjustment unit that supplies pure water to the first adjustment unit and the second adjustment unit and adjusts one or more of the flow rate, pressure, and temperature of the pure water, and operates either or both of the first adjustment unit and the second adjustment unit in conjunction with the operation of the upstream adjustment unit.

12. A water electrolysis system comprising: an electrolysis stack that electrolyzes water to generate hydrogen and oxygen; a pure water supply device that supplies pure water to the electrolysis stack; a first adjustment unit installed between the electrolysis stack and the pure water supply device and capable of adjusting the operating state of the electrolysis stack; a second adjustment unit installed between the electrolysis stack and the pure water supply device and capable of adjusting the operating state of the electrolysis stack; and an operating state adjustment control unit that adjusts the first adjustment unit and the second adjustment unit to adjust the operating state of the electrolysis stack, wherein the operating state adjustment control unit operates the first adjustment unit based on the operating state after receiving a command to change the operating state of the electrolysis stack, and operates the second adjustment unit simultaneously with the first adjustment unit based on the operating state when a predetermined condition is satisfied.

13. The water electrolysis system according to claim 12, characterized in that the water electrolysis system comprises a plurality of sets of the electrolysis stack, the first adjustment unit, and the second adjustment unit, and the operating state adjustment control unit independently adjusts the first adjustment unit and the second adjustment unit of each of the plurality of sets.

14. The water electrolysis system according to claim 12, further comprising an upstream adjustment unit that supplies pure water to the first adjustment unit and the second adjustment unit and adjusts one or more of the flow rate, pressure, and temperature of the pure water, and operates either or both of the first adjustment unit and the second adjustment unit in conjunction with the operation of the upstream adjustment unit.

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