Water electrolysis system, control device for electrolyzer stack, and method for controlling electrolyzer stack

Abstract

This water electrolysis system is provided with: an electrolytic characteristics evaluation unit; a current command value determining unit; a DC current source; an electrolyzer stack; a current sensor; and a voltage sensor. The current sensor and the voltage sensor are disposed on wiring that electrically connects the DC current source and the electrolyzer stack. The electrolytic characteristics evaluation unit evaluates characteristics of the electrolyzer stack by applying predetermined current fluctuations to the electrolysis stack. The current command value determining unit, on the basis of data containing results of the evaluation of the electrolyzer stack characteristics, computes an actual current command value. The DC current source supplies power to the electrolyzer stack so that a current matched to the actual current command value flows. The electrolyzer stack carries out electrolysis of water using power supplied from the DC current source to generate hydrogen. This makes it possible to reduce the electrolysis voltage relative to the electrolysis current supplied to the electrolyzer stack, lower the electrolysis power, and reduce the cost of running the water electrolysis system.

Description

Water electrolysis system, electrolysis stack control device, and electrolysis stack control method

[0001] The present disclosure relates to a water electrolysis system, a control device for an electrolysis stack, and a control method for an electrolysis stack.

[0002] In order to realize a low-carbon society, power generation using renewable energy sources such as solar and wind power is becoming more common, replacing thermal power generation that uses fossil fuels. However, because renewable energy electricity fluctuates greatly due to natural phenomena, it cannot be used as a substitute for grid power as is and can also cause grid instability. Therefore, the market for green hydrogen, which uses renewable energy electricity to electrolyze water, generate hydrogen, store it, and use it as fuel (including for power generation), is rapidly expanding.

[0003] Water electrolysis is performed by a water electrolysis system including a water electrolysis stack (hereinafter also simply referred to as "electrolysis stack"), a power supply, auxiliary equipment, etc. Here, from the viewpoint of long-term use, it is important for the water electrolysis performance to efficiently utilize power in the electrolysis stack to generate hydrogen.

[0004] Patent Document 1 discloses a method for operating a water electrolysis device having a water electrolysis cell the interior of which is partitioned into an anode chamber and a cathode chamber by a solid polymer electrolyte membrane, in which a cation concentration, a resistivity, or a pH value is used as a measurement value that is correlated with and serves as an index of water electrolysis performance, and when the measurement value reaches a predetermined value corresponding to a predetermined lower limit of the water electrolysis performance, electrolysis is performed at a predetermined current that is equal to or greater than the rated current, thereby recovering the water electrolysis performance.

[0005] Japanese Patent Application Laid-Open No. 2004-277870

[0006] To reduce the cost of green hydrogen, it is important to reduce the equipment costs and operating costs (electricity charges) of water electrolysis systems. Operating costs become a dominant factor, especially when the system is operated for long periods of time. A water electrolysis system that can produce the same amount of hydrogen with less electricity will have an advantage. The power required for the system is dominated by the power input to the electrolysis stack. The power input to the electrolysis stack is expressed as the product of the electrolysis current, which roughly reflects the amount of hydrogen produced, and the electrolysis voltage required to maintain the current. For this reason, the power required to produce the same amount of hydrogen depends on a reduction in the electrolysis voltage. Therefore, a reduction in the electrolysis voltage leads to a reduction in the operating costs of the system. Therefore, a reduction in the electrolysis voltage is a differentiating factor for water electrolysis systems.

[0007] The operation method of a water electrolysis apparatus described in Patent Document 1 does not indicate that control is performed to avoid a decrease in performance during the period until the measurement value serving as an indicator reaches a predetermined lower limit value of the water electrolysis performance, and from this perspective, there is thought to be room for improvement.

[0008] An object of the present disclosure is to reduce the electrolysis voltage relative to the electrolysis current supplied to the electrolysis stack, thereby reducing the electrolysis power and reducing the operating costs of the water electrolysis system.

[0009] The water electrolysis system disclosed herein includes an electrolysis characteristic evaluation unit, a current command value determination unit, a DC current source, an electrolysis stack, a current sensor, and a voltage sensor, wherein the current sensor and the voltage sensor are disposed on wiring electrically connecting the DC current source and the electrolysis stack, the electrolysis characteristic evaluation unit evaluates the characteristics of the electrolysis stack by applying a predetermined current fluctuation to the electrolysis stack, the current command value determination unit calculates an actual current command value based on data including the evaluation results of the characteristics of the electrolysis stack, the DC current source supplies power to the electrolysis stack so as to pass a current corresponding to the actual current command value, and the electrolysis stack performs electrolysis of water using the power supplied from the DC current source to generate hydrogen.

[0010] According to the present disclosure, it is possible to reduce the electrolysis voltage relative to the electrolysis current supplied to the electrolysis stack, thereby reducing the electrolysis power and reducing the operating costs of the water electrolysis system.

[0011] 1 is a schematic diagram illustrating a water electrolysis system according to the present disclosure. FIG. 1 is a schematic cross-sectional view illustrating an electrolysis stack having a proton exchange membrane (PEM). FIG. 2 is a graph illustrating the current-voltage characteristics of an electrolysis cell. FIG. 3 is a partial cross-sectional view illustrating a state near the inlet of the anode-side water channel. FIG. 4 is a partial cross-sectional view illustrating a case where a large amount of bubbles adheres downstream of the anode-side water channel. FIG. 5 is a graph illustrating an example of voltage response characteristics when the current applied to the electrolysis stack is increased in a stepwise manner. FIG. 6 is a graph illustrating an example of voltage response characteristics when the current applied to the electrolysis stack is decreased in a stepwise manner. FIG. 7 is a graph illustrating another example of voltage response characteristics when the current applied to the electrolysis stack is increased in a stepwise manner. FIG. 8 is a graph illustrating an example of voltage response characteristics when the current applied to the electrolysis stack is decreased in a stepwise manner. FIG. 9 is a graph illustrating an example of voltage response characteristics when the current applied to the electrolysis stack is increased in a ramp-like manner. FIG. 10 is a graph illustrating an example of voltage response characteristics when the current applied to the electrolysis stack is decreased in a ramp-like manner. FIG. 11 is a graph illustrating an example of voltage response characteristics when the current applied to the electrolysis stack is increased and decreased in a step-like manner. 1 is a graph showing an example of voltage response characteristics when a current applied to the electrolysis stack is increased in a ramp-like manner and then decreased in a step-like manner; FIG. 2 is a graph showing another example of voltage response characteristics when a current applied to the electrolysis stack is increased in a step-like manner and then decreased in a step-like manner; FIG. 3 is a flowchart showing a characteristic evaluation mode of the electrolysis stack according to the embodiment; FIG. 4 is a flowchart showing an operation mode of the electrolysis stack according to the embodiment;

[0012] First, the problem to be solved by the present disclosure will be specifically described with reference to the drawings.

[0013] FIG. 2A is a schematic cross-sectional view showing an electrolysis stack (water electrolysis device) having a proton exchange membrane (PEM).

[0014] In this figure, a cell is shown as the smallest unit constituting the electrolysis stack 200. The actual electrolysis stack 200 includes a plurality of cells.

[0015] The electrolysis stack 200 has an anode-side catalyst layer 202a and a cathode-side catalyst layer 202b (electrodes) provided on both sides of a proton exchange membrane 201, which are in contact with an anode-side water channel 211 and a cathode-side water channel 212 that supply water via an anode-side diffusion layer 203a and a cathode-side diffusion layer 203b. By applying a voltage to both sides, the anode-side catalyst layer 202a decomposes water into oxygen and hydrogen ions, and the cathode-side catalyst layer 202b generates hydrogen. The amount of hydrogen generated corresponds to the amount of electrons supplied, i.e., the amount of current. The current is supplied from a current source 205.

[0016] FIG. 2B is a graph showing the current-voltage characteristics (IV characteristics) of the electrolysis cell.

[0017] This diagram shows the relationship between how much voltage is generated when a current is passed through a cell, and conversely, how much voltage must be applied to maintain the current.

[0018] The voltage required to maintain a given current value in a cell for electrolysis of water, when no gas is generated, is the sum of the Nernst voltage (Erev), the catalyst activation overpotential (Eact), and the resistance overpotential (Eohm) generated by the resistance component of the PEM. Each curve in this figure shows the voltage value obtained by multiplying each voltage by the sum of the voltages below.

[0019] Power, which is an operating cost, is the product of current and voltage. Therefore, from the viewpoint of operating costs, the lower the required voltage is, the better, given the same current value.

[0020] However, in electrolysis cells, gas is generated, and as the electrolysis of water progresses, bubbles form on the surface of the electrode (catalyst) and cover the electrode. The bubbles are removed to some extent by the flow of water being supplied. However, the area on which the bubbles adhere is determined by the balance between the amount of bubbles generated and the amount of bubbles removed by the water flow. Because current does not flow easily in areas where bubbles are attached, the voltage must be further increased to maintain the current flow.

[0021] In this figure, this is shown as the overvoltage of bubbles, which reduces the power efficiency in water electrolysis.

[0022] Next, a state in which the water flow and the generation of bubbles are balanced will be described with reference to FIGS. 3A and 3B.

[0023] FIG. 3A is a partial cross-sectional view showing the state near the inlet of the water channel on the anode side.

[0024] This figure shows the anode catalyst layer 202a, the anode diffusion layer 203a, and the anode water channel 211. Bubbles 301 are generated in the anode catalyst layer 202a, pass through the anode diffusion layer 203a, and are released into the anode water channel 211.

[0025] As shown in the figure, the amount of accumulated bubbles 301 is small near the inlet of the anode-side water channel 211, and the proportion of water is high, so the bubbles 301 are easily removed. Therefore, the amount of bubbles 301 adhering to the electrode is small. As a result, the current density at each position of the electrode shown on the right side of the figure is almost constant.

[0026] On the other hand, near the outlet of the water channel, bubbles may accumulate on the electrode, weakening the water flow near the electrode. In this case, the bubbles become difficult to remove. As a result, bubbles tend to adhere to the electrode.

[0027] FIG. 3B is a partial cross-sectional view showing a case where a large amount of bubbles adheres on the downstream side of the anode-side water channel.

[0028] In this figure, current does not flow easily in the electrode portion where many bubbles 301 are attached, thereby suppressing the generation of bubbles 301. As a result, the current density at each position of the electrode shown on the right side of the figure is higher on the upstream side and lower on the downstream side.

[0029] In the balanced state shown in Figures 3A and 3B, the distribution of bubbles 301 adhering to the electrode is considered to be fixed.

[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0031] FIG. 1 is a schematic diagram showing the configuration of a water electrolysis system according to an embodiment of the present invention.

[0032] In this diagram, the water electrolysis system 100 includes an electrolysis characteristic evaluation unit 101, a current command value determination unit 102, a DC current source 103, and an electrolysis stack 104. A current sensor 105 and a voltage sensor 106 are disposed on wiring electrically connecting the DC current source 103 and the electrolysis stack 104. Note that in this diagram, the water piping system and gas piping system connected to the electrolysis stack 104 are omitted.

[0033] The electrolysis characteristic evaluation unit 101 and the current command value determination unit 102 each have a calculation unit and a storage unit.

[0034] The electrolysis characteristic evaluation unit 101 evaluates the characteristics of the electrolysis stack 104 by applying a predetermined current fluctuation to the electrolysis stack 104 at times other than when hydrogen is being continuously produced in the electrolysis stack 104. Here, the predetermined current fluctuation is applied as a step-like current change, and is accompanied by a voltage change corresponding to this current change, i.e., a step response of the voltage applied to the electrolysis stack 104. The electrolysis characteristic evaluation unit 101 evaluates the voltage change. This evaluation is preferably performed before hydrogen production in the electrolysis stack 104. Of course, it may also be performed after hydrogen production in the electrolysis stack 104 has started. Furthermore, this evaluation may be performed every few days or every month.

[0035] The current command value determination unit 102 receives, from the electrolysis characteristic evaluation unit 101, the evaluation results of the characteristics of the electrolytic stack 104 and policy information regarding the current command value to be given to the DC current source 103, and also receives a current command value from an external source, performs a predetermined calculation to calculate an actual current command value, and transmits the actual current command value to the DC current source 103. Here, the actual current command value refers to a current command value that is actually transmitted to the DC current source 103.

[0036] The DC current source 103 performs feedback control (FB control) based on the actual current command value from the current command value determination unit 102 and the current value detected by the current sensor 105 (measured value of the current flowing through the electrolytic stack 104), and supplies power to the electrolytic stack 104 so as to flow a current that matches the actual current command value.

[0037] The electrolysis stack 104 electrolyzes water using the power supplied from the DC current source 103 to generate hydrogen.

[0038] The electrolysis characteristic evaluation unit 101 calculates two current values, one higher and one lower than the current command value, generates a current command value for a step-like current change from one of the two current values ​​to the other, and supplies the current to the electrolysis stack 104 via the DC current source 103. In the electrolysis stack 104, a voltage change occurs in accordance with the step-like current change. This voltage change is measured by a voltage sensor 106 and input to the electrolysis characteristic evaluation unit 101.

[0039] Next, the principle of control in this embodiment will be explained.

[0040] When the current in the electrolytic stack changes, the distribution of bubbles also changes accordingly. However, even if the current is changed suddenly, it takes time for the bubble distribution to become balanced. When the current driving the electrolytic stack is changed by current control, the overvoltage caused by bubbles changes with a delay, and becomes constant once the balance and distribution are established. Until this state is reached, the overvoltage caused by bubbles will rise and fall.

[0041] FIG. 4A is a graph showing an example of voltage response characteristics when the current applied to the electrolysis stack is increased stepwise.

[0042] As shown in this figure, when the current is increased in a step-like manner, the voltage may rise with a delay depending on the voltage characteristics of the electrolysis stack. Then, the voltage (the area surrounded by the ellipse in the figure) rises gradually until a steady state is reached. In this way, there is a time period where the voltage is lower than in the steady state, which results in a power reduction effect. In other words, compared to when the voltage increases in a step-like manner in the same way as the current, there is a time period where the voltage is lower and power consumption is less. During this time period, the voltage rises over time. This state is called a "voltage rise."

[0043] FIG. 4B is a graph showing an example of the voltage response characteristics when the current applied to the electrolysis stack is decreased stepwise.

[0044] As shown in this figure, when the current is reduced in a step-like manner, depending on the voltage characteristics of the electrolysis stack, the voltage may initially drop significantly, then rise gradually, and reach a steady state (the area surrounded by an oval in the figure). This is similar to Figure 4A in that a time period occurs in which the voltage is lower than in the steady state, and a power reduction effect is obtained. In other words, compared to when the voltage decreases in a step-like manner similar to the current reduction, a time period is obtained in which the voltage is lower and power consumption is lower. During this time period, the voltage increases over time. This state is also referred to as a "voltage increase."

[0045] FIG. 5A is a graph showing another example of the voltage response characteristics when the current applied to the electrolysis stack is increased stepwise.

[0046] As shown in this figure, when the current is increased in a stepwise manner, depending on the voltage characteristics of the electrolysis stack, the voltage may rise sharply at first, then gradually drop, and reach a steady state (the area enclosed by the ellipse in the figure). When there is a period of time like this where the voltage is higher than in the steady state, no power reduction effect can be obtained. During this period of time, the voltage drops over time. This state is called a "voltage drop."

[0047] FIG. 5B is a graph showing another example of the voltage response characteristics when the current applied to the electrolysis stack is decreased stepwise.

[0048] As shown in this figure, when the current is reduced in a stepwise manner, depending on the voltage characteristics of the electrolysis stack, the voltage may drop gradually and reach a steady state (the area enclosed by the ellipse in the figure). In this case, too, there is a period of time when the voltage is higher than in the steady state, so no power reduction effect is obtained. During this period of time, the voltage drops over time. This state is also called a "voltage drop."

[0049] 6A is a graph showing an example of the voltage response characteristics when the current applied to the electrolysis stack is increased in a ramp-like manner, in which case the current is preferably increased over a period of several tens of seconds to several tens of minutes.

[0050] As shown in this figure, by increasing the current in a ramp-like manner, it is sometimes possible to control the voltage so that it increases gradually and reaches a steady state. It is desirable to increase the current gradually enough to allow this type of control. When it is not desirable to increase the current in a step-like manner, it is possible to prevent power waste by increasing the current in a ramp-like manner with an appropriate slope, as shown in this figure.

[0051] 6B is a graph showing an example of the voltage response characteristics when the current applied to the electrolysis stack is decreased in a ramp-like manner, in which case the current is preferably decreased over a period of several tens of seconds to several tens of minutes.

[0052] As shown in this figure, by reducing the current in a ramp-like manner, it is sometimes possible to control the voltage so that it decreases gradually and reaches a steady state. It is desirable to reduce the current slowly enough to allow this type of control. When it is not desirable to reduce the current in a step-like manner, it is possible to prevent power waste by reducing the current in a ramp-like manner with an appropriate slope, as shown in this figure.

[0053] The gradient of the current that increases or decreases like a ramp does not necessarily have to be constant, and may be changed in accordance with conditions such as the characteristics of the electrolytic stack.

[0054] FIG. 7 is a graph showing an example of the voltage response characteristics when the current applied to the electrolysis stack is increased stepwise and then decreased stepwise.

[0055] The control shown in this figure becomes possible when the results shown in FIGS. 4A and 4B are obtained in the evaluation of the characteristics of the electrolytic stack, and the power reduction effect can be obtained in the two areas surrounded by ellipses in the figures.

[0056] FIG. 8 is a graph showing an example of the voltage response characteristics when the current applied to the electrolysis stack is increased in a ramp-like manner and then decreased in a step-like manner.

[0057] The control shown in this figure is possible when the results shown in Figure 4B are obtained in the evaluation of the characteristics of the electrolytic stack, and the power reduction effect is obtained in the area surrounded by the ellipse in the figure. That is, from the viewpoint of power reduction, in the control of the electrolytic stack, it is possible to reduce the current in a stepwise manner, but increasing the current in a stepwise manner does not produce any effect.

[0058] FIG. 9 is a graph showing another example of the voltage response characteristics when the current applied to the electrolytic stack is increased stepwise and then decreased stepwise.

[0059] The control shown in this figure is possible when the results shown in Figure 4A are obtained in the evaluation of the characteristics of the electrolytic stack, and a power reduction effect is obtained in the area surrounded by an ellipse in the figure. That is, when the current is increased in a stepwise manner in the control of the electrolytic stack, a power reduction effect is obtained. On the other hand, when the current is decreased in a stepwise manner in the control of the electrolytic stack, the voltage also decreases in a stepwise manner accordingly, so there is no power waste, but no power reduction effect is obtained.

[0060] In summary, the electrolysis current is increased or decreased in a stepwise manner, and the change in the voltage of the electrolysis stack during this process is recorded. During operation of the electrolysis stack for hydrogen production, the actual current command value is varied in a stepwise or rampwise manner around the external current command value in accordance with the evaluated dynamic characteristics of the electrolysis stack (the direction of voltage change).

[0061] Table 1 shows the relationship between the pattern of the electrolysis stack characteristic evaluation mode and the control policy of the operation mode.

[0062] This table summarizes the four cases and their respective effects. The voltage rise in the characteristic evaluation mode indicates that the voltage rises because the voltage is low until it reaches a steady state (constant value). Therefore, the voltage rise indicates that a power reduction effect is obtained. In contrast, the voltage drop or step in the characteristic evaluation mode indicates that the voltage drops because the voltage is high until it reaches a steady state (constant value).

[0063] Even if the current command value in the operation mode is constant, the current is changed in a step-like manner before and after that in the characteristics evaluation mode. However, since the current may be increased and then decreased, the selection of a step-like or ramp-like change for both the current increase and current decrease in the operation mode is determined in advance from the results of the characteristics evaluation mode.

[0064] In Case 1, the voltage rises when the current rises and falls in the characteristic evaluation mode. The waveforms for this case are shown in Figure 7. Therefore, the power reduction effect is obtained both when the current rises and falls in the operating mode.

[0065] Case 2 corresponds to Fig. 8. Therefore, the effect of power reduction can be obtained only when the current drops in the operation mode.

[0066] Case 3 corresponds to Fig. 9. Therefore, the effect of power reduction can be obtained only when the current rises in the operation mode.

[0067] In case 4, the voltage drops both when the current rises and when the current falls in the operation mode, so the effect of reducing power consumption cannot be obtained.

[0068] 10A is a flowchart showing a characteristic evaluation mode of the electrolytic stack according to the embodiment. The characteristic evaluation mode is performed in the electrolysis characteristic evaluation unit 101 in FIG.

[0069] 10A, the current is reduced by ΔI from the current current command value (step S1010), and then a certain time (T) is waited (step S1020). T may be less than 1 second, but it is preferable to set it to several seconds (e.g., 3 to 8 seconds).

[0070] Next, the current is increased by 2ΔI in a stepwise manner from the current current command value (step S1030). While waiting for a certain time (T), the voltage is measured sequentially and recorded as a voltage change (step S1040). After that, the current is decreased by 2ΔI in a stepwise manner from the current current command value (step S1050). While waiting for a certain time (T), the voltage is measured sequentially and recorded as a voltage change (step S1060).

[0071] Next, an appropriate current command pattern for the operation mode is determined from the step responses of the electrolysis stack voltage in steps S1030 and S1050 (step S1070). Specifically, for control in the operation mode, a pattern is determined in which either or both of the current increase and decrease are changed in a step or ramp manner.

[0072] Then, an operation policy table is created (step S1080). The operation policy table is determined to obtain the effect of power reduction in the operation mode of the electrolysis stack.

[0073] 10B is a flowchart showing an operation mode of the electrolysis stack according to the embodiment. The operation mode is performed by the current command value determination unit 102 in FIG.

[0074] 10B, first, a current command value is received from an external device (step S1110), which is a determination as to whether the driver (user) intends to reduce power consumption.

[0075] Thereafter, it is determined whether to reduce the power (step S1120). If the result is Yes, it is determined whether the power can be reduced (step S1130). If the result is Yes, it is determined whether it is time to change the current (for example, after 100 seconds have passed) (step S1140). If the result is Yes, the current command value is changed by ΔI according to the result of the evaluation mode, and the change method is instructed to the DC current source 103 (FIG. 1) (step S1150). Then, the current command value is transmitted to the DC current source 103 (FIG. 1) (step S1160).

[0076] If the answer is No in any of steps S1120 to S1140, the process proceeds to step S1160.

[0077] 10B is initiated at regular intervals. This is because the current only needs to be changed at specific times. The initiation interval is, for example, one second, and the timing of the change is every 10 seconds.

[0078] When the current is changed in a stepwise manner, it is sufficient to detect the current and voltage every few to 10 seconds, but when the current is changed in a ramp manner, it is desirable to detect the current and voltage every second or at intervals of less than one second.

[0079] Furthermore, a part of the water electrolysis system that does not include a DC current source, an electrolysis stack, etc., i.e., a control device that includes an electrolysis characteristic evaluation unit and a current command value determination unit, can be referred to as an "electrolysis stack control device." Furthermore, a control method executed by this control device can be referred to as an "electrolysis stack control method."

[0080] In the above embodiment, the current command value is step-like, but the present disclosure is not limited to this and may be a ramp-like value having a certain time width (for example, several seconds). The value (variation width) of ΔI may be several percent to 10% of the current command value. It is desirable to provide a user interface to input these numerical values ​​and other conditions into the current command value determination unit 102. The user interface may be a personal computer (PC) or a mobile terminal such as a smartphone.

[0081] When the current supplied to the electrolysis stack is increased or decreased stepwise, the voltage may increase, resulting in increased power consumption. However, current fluctuations can also be advantageous in that they disrupt the balance of the distribution of bubbles adhering to the electrodes of the electrolysis stack. Current fluctuations can actively change the distribution of bubbles adhering to the electrodes of the electrolysis stack, thereby changing the range of catalyst on partially overworked electrodes. This is expected to have the effect of mitigating deterioration of the electrolysis stack. Therefore, to achieve this effect, for example, Case 4, which is considered ineffective in Table 1, can be applied to the operating mode to remove or move bubbles. This can also have the effect of reducing the electrolysis voltage, even if only temporarily.

[0082] Another method is to change the current fluctuation in multiple steps (in stages) while monitoring the voltage. For example, if the final fluctuation range of the current is 10% of the rated value, the steps may be changed by 1 to 3% each time.

[0083] Furthermore, the flow rate of water supplied to the electrolysis stack may be changed in accordance with changes in current. The direction of the water flow may also be changed. In this case, the electrodes to which the control for changing the water flow rate or direction is applied may be not only the cathode-side water channel where hydrogen is generated, but also the anode-side water channel where oxygen is generated. This can also have the effect of lowering the electrolysis voltage, even if only temporarily.

[0084] The effects of the present disclosure will be summarized below.

[0085] According to the present disclosure, the response of the electrolysis stack to the input is detected and the result of the response is used for control, without adding any additional hardware to the water electrolysis system, thereby achieving the effect of reducing power consumption. In this case, the electrolysis stack can be controlled using only electrical signals without detecting the actual state of the distribution of bubbles in the electrolysis stack.

[0086] Furthermore, according to the present disclosure, adhesion of bubbles to the electrodes of the electrolysis stack can be suppressed, and the power used for electrolysis of water can be reduced.

[0087] Furthermore, according to the present disclosure, the electrolysis stack can be controlled regardless of the configuration of the electrolysis stack.

[0088] 100: water electrolysis system, 101: electrolysis characteristic evaluation unit, 102: current command value determination unit, 103: DC current source, 104: electrolysis stack, 105: current sensor, 106: voltage sensor, 200: electrolysis stack, 201: proton exchange membrane, 202a: anode side catalyst layer, 202b: cathode side catalyst layer, 203a: anode side diffusion layer, 203b: cathode side diffusion layer, 211: anode side water channel, 212: cathode side water channel, 301: bubbles.

Claims

1. A water electrolysis system comprising: an electrolysis characteristic evaluation unit; a current command value determination unit; a DC current source; an electrolytic stack; a current sensor; and a voltage sensor, wherein the current sensor and the voltage sensor are disposed on wiring electrically connecting the DC current source and the electrolytic stack, the electrolysis characteristic evaluation unit evaluates characteristics of the electrolytic stack by applying a predetermined current fluctuation to the electrolytic stack, the current command value determination unit calculates an actual current command value based on data including evaluation results of the characteristics of the electrolytic stack, the DC current source supplies power to the electrolytic stack so as to flow a current corresponding to the actual current command value, and the electrolytic stack performs electrolysis of water using the power supplied from the DC current source to generate hydrogen.

2. The water electrolysis system according to claim 1, wherein the current command value determination unit determines a current command pattern in an operation mode of the electrolysis stack, and the DC current source varies the actual current command value based on the current command pattern.

3. The water electrolysis system according to claim 2, wherein the current command pattern is a step pattern or a ramp pattern.

4. The water electrolysis system according to claim 1, wherein the predetermined current fluctuation is a step-like fluctuation.

5. A control device for an electrolytic stack, comprising: an electrolysis characteristic evaluation unit; and a current command value determination unit, capable of transmitting and receiving signals between a DC current source and an electrolytic stack, and controlling the electrolytic stack using a current sensor and a voltage sensor arranged on wiring electrically connecting the DC current source and the electrolytic stack, wherein the electrolytic stack performs electrolysis of water using power supplied from the DC current source to generate hydrogen, the electrolysis characteristic evaluation unit evaluates characteristics of the electrolytic stack by applying a predetermined current fluctuation to the electrolytic stack, and the current command value determination unit calculates an actual current command value based on data including evaluation results of the characteristics of the electrolytic stack, transmits the actual current command value to the DC current source, and controls the DC current source so that the DC current source passes a current corresponding to the actual current command value through the electrolytic stack.

6. A method for controlling an electrolytic stack using a current sensor and a voltage sensor arranged on wiring that transmits and receives signals between a DC current source and an electrolytic stack and electrically connects the DC current source and the electrolytic stack, wherein the electrolytic stack electrolyzes water using power supplied from the DC current source to generate hydrogen, an electrolysis characteristic evaluation unit evaluates characteristics of the electrolytic stack by applying a predetermined current fluctuation to the electrolytic stack, and a current command value determination unit calculates an actual current command value based on data including evaluation results of the characteristics of the electrolytic stack, transmits the actual current command value to the DC current source, and controls the DC current source so that the DC current source passes a current corresponding to the actual current command value through the electrolytic stack.

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