JP7518014B2 - Control system, control method, and hydrogen production system - Google Patents

Description

The present invention relates to a hydrogen production system that produces hydrogen using multiple water electrolysis stacks.

In order to popularize hydrogen energy, there is a demand to reduce the price of hydrogen. In order to reduce the price of hydrogen, it is necessary to reduce the cost required to produce hydrogen. Hydrogen is produced, for example, by methods such as the electrolysis of water (hereafter referred to as water electrolysis). The cost of producing hydrogen is broadly divided into capital expenses (CAPEX) and operating expenses (OPEX). OPEX consists of the cost of procuring the electricity used in water electrolysis and the cost of maintaining the system. To reduce CAPEX, the following efforts are necessary.

・Reduction in equipment costs ・Improvement of equipment operating rate (increase in hydrogen production volume)
・Improvement of equipment useful life (reduction of equipment depreciation costs)

In recent years, hydrogen production using renewable energy has been attracting attention, but the amount of electricity generated from renewable energy fluctuates due to wind and weather conditions, making it a challenge to improve the operating rate of hydrogen production facilities. One possible solution is to use storage batteries to level out electricity before producing hydrogen, but the introduction of storage batteries increases the cost of the equipment, making it difficult to reduce CAPEX. Therefore, there is a demand for technology that can reduce CAPEX without using storage batteries.

To improve the service life of a hydrogen production system, it is necessary to suppress the deterioration of the water electrolysis cells, which are one of the components. Water electrolysis methods include alkaline electrolysis, PEM (Proton Exchange Membrane) electrolysis, and AEM (Anion Exchange Membrane) electrolysis. The following describes how to suppress the deterioration of PEM electrolysis cells.

According to Non-Patent Document 1, the deterioration of a water electrolysis cell has the following characteristics:
(a) If high-power operation is maintained for a long period of time (about 1,000 hours), the rate of deterioration is very large (i.e., intermittent operation with reduced power output is desirable);
(b) during intermittent operation, transitions between high and zero power output result in less degradation than transitions between high and intermediate power output;
(c) In the case of intermittent operation, shortening the output cycle (frequent ON/OFF switching) causes rapid deterioration.

There are many technologies for constructing megawatt-class hydrogen production systems using multiple water electrolysis stacks. Patent Document 1 also describes a technology for individually controlling the ON/OFF of water electrolysis stacks. For example, by following the power fluctuations of renewable energy, the number of stacks in operation is increased when power is high. Patent Document 1 also discloses a technology for selecting a stack to operate while monitoring the deterioration state of the stacks in order to prevent a shortened lifespan due to overworking only certain stacks.

JP 2020-084259 A

C. Rakousky et al., J. Power Sources 342, 38 (2017).

Two types of power are assumed to be input to a water electrolysis system: grid power and renewable energy power. If the water electrolysis system is constantly operated at rated power using grid power, there is concern that early degradation will occur due to factor (a) above. On the other hand, renewable energy power is intermittent due to wind conditions and weather conditions, and the output does not drop to zero, and there is a high frequency of intermediate power generation that is smaller than the rated (maximum output). If such power is input to a water electrolysis system, the output will frequently go back and forth between high output and intermediate output, raising concerns about degradation due to factors (b) and (c) above.

When renewable energy power is input to a water electrolysis system, it is possible to turn the water electrolysis stacks on and off individually, as in Patent Document 1. Turning the water electrolysis stacks on and off in response to short-term fluctuations in renewable energy power is not necessarily useful, as the responsiveness of the water electrolysis stacks may be insufficient. In addition, the use of renewable energy power poses the issue of a lower operating rate of the water electrolysis stack, so the operating rate may be increased by limiting the upper limit output of the water electrolysis stack. In such cases, the operating rate of the water electrolysis stacks increases overall, so the number of water electrolysis stacks that can be turned off decreases, and deterioration cannot be sufficiently suppressed by ON/OFF control.

The present invention was made in consideration of the above problems, and aims to provide a technology that can effectively suppress deterioration of water electrolysis stacks in a hydrogen production system that produces hydrogen using multiple water electrolysis stacks.

The hydrogen production system according to the present invention assigns the operation state of the water electrolysis stack to one of the following: operation priority stack, shutdown priority stack, or intermediate operation stack.

The hydrogen production system according to the present invention can effectively suppress deterioration of the water electrolysis stack.

1 is a configuration diagram of a hydrogen production system 1 according to a first embodiment. This is an example of the change over time in the amount of electricity generated from renewable energy sources. 13 is an example of an operation rotation formulated by the operation plan formulation unit 141 in the embodiment. 4 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 3 . 4 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 3 . 4 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 3 . 1 is a table showing the results of testing the deterioration rate of a water electrolysis stack. An example of an operation rotation plan for operating six water electrolysis stacks 11 will be shown. 7 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 6 . 7 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 6 . 7 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 6 . 1 is an example showing the change over time in the amount of power generated by solar power generation. 9 shows the change over time in power distributed to an operating water electrolysis stack when the supply power in FIG. 8 is distributed to the stack according to a conventional procedure. 9 is an example of an operation rotation plan when the power supply fluctuates as shown in FIG. 8 . 11 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 10 . 11 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 10 . 11 shows the change over time in the power supplied to each water electrolysis stack 11 when each water electrolysis stack 11 is operated according to the operation rotation plan of FIG. 10 . FIG. 1 is a configuration diagram of a hydrogen production system 1 according to a second embodiment. FIG. 11 is a configuration diagram of a hydrogen production system 1 according to a third embodiment. FIG. 11 is a configuration diagram of a hydrogen production system 1 according to a fourth embodiment. FIG. 11 is a configuration diagram of a hydrogen production system 1 according to a fifth embodiment. 13 shows an operation rotation in a case where the operation states of each water electrolysis stack are assigned according to a conventional procedure in embodiment 5. 13 shows the operation rotation of the hydrogen production system 1 in embodiment 5.

<First embodiment>
1 is a configuration diagram of a hydrogen production system 1 according to a first embodiment of the present invention. The hydrogen production system 1 is a system that produces hydrogen using renewable energy or AC (alternating current) power supplied from a power transmission and distribution system. The hydrogen production system 1 produces hydrogen by operating a water electrolysis stack 11 using the supplied power. The hydrogen production system 1 includes the water electrolysis stack 11, a DC/DC converter 12, an AC/DC rectifier 13, and a power distribution control system 14.

The water electrolysis stack 11 produces hydrogen by electrolyzing water. In FIG. 1, two water electrolysis stacks 11 are connected in series, and three pairs of two water electrolysis stacks 11 are connected in parallel. The hydrogen produced by the water electrolysis stack 11 is output to a transportation facility or a storage facility.

The AC/DC rectifier 13 converts the AC power supplied to the hydrogen production system 1 into DC (direct current) power and outputs it to the DC/DC converter 12. The DC/DC converter 12 supplies power to the water electrolysis stack 11 to control the operating state of the water electrolysis stack 11.

The power distribution control system 14 controls the operating state of the water electrolysis stack 11 via the DC/DC converter 12 by outputting an operating command to the DC/DC converter 12. The power distribution control system 14 includes an operation plan formulation unit 141, a stack operation allocation unit 142, a power distribution command unit 143, a deterioration characteristic data management unit 144, and a deterioration rate estimation unit 145.

The operation plan formulation unit 141 formulates an operation rotation plan for the water electrolysis stack 11. The operation rotation here refers to the order in which each water electrolysis stack 11 is assigned as an operation state of either an operation priority stack, a stop priority stack, or an intermediate operation stack, which will be described later. The stack operation allocation unit 142 determines the operation state of each water electrolysis stack 11 according to the operation rotation plan formulated by the operation plan formulation unit 141. The power distribution command unit 143 gives a current command value to the DC/DC converter 12 so that the water electrolysis stack 11 operates according to its operation state.

The deterioration characteristic data management unit 144 holds deterioration characteristic data that describes the deterioration characteristics of the water electrolysis stack 11. The operation plan formulation unit 141 can formulate an operation rotation plan according to the deterioration characteristics. The deterioration rate estimation unit 145 estimates the deterioration rate of each water electrolysis stack 11 when it is assumed that the water electrolysis stack 11 is operated according to the plan.

Figure 2 is an example of the change over time in the amount of power generated from renewable energy. Here, the amount of power generated by wind power is shown as an example. In conventional operational control, in order to increase the availability of the electrolysis stack, the upper limit output of the electrolysis stack may be limited as shown in Figure 2. This improves the availability, but on the other hand reduces the number of electrolysis stacks that can be shut down. For example, when power is supplied evenly to eight electrolysis stacks as shown in Figure 2, the availability of the electrolysis stacks is 84.8%.

Figure 3 shows an example of an operation rotation formulated by the operation plan formulation unit 141 in this embodiment. Here, an example is shown in which eight water electrolysis stacks 11 are paired in pairs of two and operation states are assigned. The operation plan formulation unit 141 assigns one of the following as the operation state of the water electrolysis stacks 11: (a) operation priority stack, (b) stop priority stack, or (c) intermediate operation stack. Figure 3 shows an example in which the operation states are assigned in the order of operation priority => stop priority => intermediate operation => intermediate operation, and the operation states are rotated so that there is no overlap except for the intermediate operation stack.

The operation priority stack is a stack that is given priority in distributing power compared to the other water electrolysis stacks 11. The stop priority stack is a stack that is given priority in stopping the power supply compared to the other water electrolysis stacks 11. The intermediate operation stack is a stack that receives an intermediate power supply between these. For example, the power received by the hydrogen production system 1 is first allocated in its entirety to the operation priority stack and the stop priority stack, and then any remaining power is allocated to the intermediate operation stack.

Figures 4A to 4C show the change over time in the power supplied to each water electrolysis stack 11 when the stacks are operated according to the operation rotation plan in Figure 3. Power is distributed with the highest priority to the operation-priority stacks, and the top priority is not to supply power to the shutdown-priority stacks. The intermediate operation stacks receive a power supply that is intermediate between these two.

Figure 5 is a table showing the results of testing the deterioration rate of the water electrolysis stack. These are described in Non-Patent Document 1, and show the results of testing the deterioration rate (voltage rise rate) in each of the five modes. First, the characteristics of the water electrolysis stack that can be seen from these test results are explained, and then the results of calculations when similar tests are carried out in this embodiment are shown. However, it should be noted that since this embodiment uses a water electrolysis stack and Non-Patent Document 1 uses a single water electrolysis cell, the absolute values of the numerical values are different from each other.

When the current density is maintained at 2 A/ ^cm2 as in mode B, the deterioration rate is the highest at 194 μV/h. Therefore, it can be seen that the deterioration rate is very large when high-output operation is maintained for a long period of time (about 1000 hours) (i.e., intermittent operation in which the output is reduced midway is desirable).

When the current density is transitioned between 2 A/ ^cm2 and 1 A/ ^cm2 as in mode C, the deterioration rate is 65 μV/h, whereas when the current density is transitioned between 2 A/ ^cm2 and 0 A/ ^cm2 as in mode D, the deterioration rate is 16 μV/h. Therefore, it can be seen that during intermittent operation, transitioning between high output and zero output can suppress deterioration more effectively than transitioning between high output and intermediate output.

In mode E, an output of 2 A/ ^cm2 is continued for 10 minutes, followed by an output of 0 A/ ^cm2 for 10 minutes. Therefore, the output cycle is extremely short compared to other modes (for example, modes C and D are 6 hour + 6 hour cycles). The deterioration rate of mode E is 50 μV/h, and the deterioration rate of mode D is 16 μV/h. Therefore, it can be seen that the shorter the output cycle, the faster the deterioration.

When using conventional operating procedures that distribute power equally to each water electrolysis stack, the water electrolysis stack transitions between high and medium output, resulting in operation equivalent to mode C. If the stack is then frequently switched on and off as in Patent Document 1, operation equivalent to mode E will result. In this case, it is estimated that in conventional operating procedures, in addition to the deterioration rate of mode C (65 μV/h), a deterioration rate equivalent to the difference between modes D and E (50-16=34 μV/h) is superimposed by shortening the mode cycle from 6 hours to 10 minutes. In other words, the deterioration rate in conventional operating procedures is estimated to be approximately 99 μV/h.

The operating priority stack in this embodiment corresponds to mode D in that it operates at high output and then assigns a stop priority stack, so the resulting deterioration is 16 μV/h and continues for 6 hours. The stop priority stack in this embodiment frequently goes back and forth between high output and zero output, so it corresponds to mode E, and the resulting deterioration is 50 μV/h and continues for 6 hours. The intermediate operating stack in this embodiment transitions between high output and intermediate output and also frequently switches ON/OFF, so as described above the deterioration rate is 99 μV/h, which continues for 6 hours x 2. Therefore, the deterioration rate in this embodiment is 66 μV/h when averaged across each operating mode, which is a 33% reduction in deterioration rate compared to the conventional method.

Figure 6 shows an example of an operation rotation plan when operating six water electrolysis stacks 11. Operation states are assigned to each stack pair in the following order: operation priority => stop priority => intermediate operation, so that operation states do not overlap between pairs.

Figures 7A to 7C show the change over time in the power supplied to each water electrolysis stack 11 when the stacks are operated according to the operation rotation plan in Figure 6. The deterioration rate is estimated to be 55 μV/h in the same manner as in the example (first example) of Figures 3 to 4C, which is a 44% reduction in deterioration rate compared to the conventional example. The reason why the deterioration suppression effect is greater in this example (second example) than in the first example is believed to be because the proportion of operation-priority stacks and shutdown-priority stacks, which have a lower deterioration rate, is relatively high.

However, when comparing the operating rates of the first and second examples, the operating rate of the operating-priority stack in the second example decreases (compare Figure 4A with Figure 7A), while the operating rate of the stop-priority stack increases (compare Figure 4B with Figure 7B). This may result in a decrease in the accuracy of the approximation that assumes the deterioration rate of the operating-priority stack to be equivalent to mode D, for example. In other words, even if they are the same operating-priority stacks, the deterioration rate may be higher in the second example than in the first example. Therefore, it is effective to assess the deterioration rate for each input power data in advance, or to obtain it during operation while formulating the operating rotation.

Specifically, for example, the deterioration rate estimation unit 145 estimates the deterioration rate of each water electrolysis stack 11 under the current operation rotation plan, and the operation plan formulation unit 141 formulates a rotation plan so that the difference in deterioration rate between each water electrolysis stack 11 is as small as possible. It is not necessary to make the deterioration rates of each water electrolysis stack 11 strictly equal, and as long as the difference in deterioration rate between the stacks is at least reduced, a corresponding effect can be achieved to that extent.

Figure 8 is an example showing the change in the amount of electricity generated by solar power generation over time. It can be seen that the amount of electricity generated varies depending on the time of day, and that the amount of electricity generated decreases due to the effects of clouds. Below, we consider the case where this electricity is supplied to the hydrogen production system 1.

Figure 9 shows the change over time in the power distributed to the operating stacks when the supply power in Figure 8 is distributed to the water electrolysis stacks according to the conventional procedure. When the amount of power generated varies greatly depending on the time of day, as in solar power generation, it is difficult to increase the availability of the water electrolysis system by filtering the output using an upper limit value as in Figure 2. Therefore, as an example of conventional control, we first estimated the results of power distribution when the water electrolysis stacks are turned ON/OFF depending on the time of day (amount of power generated), as in Patent Document 1. Here, power was distributed equally to eight water electrolysis stacks. Figure 9 shows the results.

The average operating rate of the operating stacks shown in Figure 9 is low at 58.1%, and frequent switching between high and medium output is observed, raising concerns about early deterioration. Therefore, it is clear that the conventional method of controlling the number of stacks to be turned on and off is difficult to suppress deterioration of the water electrolysis stacks.

Figure 10 is an example of an operation rotation plan when the power supply fluctuates as shown in Figure 8. During periods when the power supplied to the hydrogen production system 1 falls below a threshold, the operation plan formulation unit 141 assigns water electrolysis stacks 11 to be completely turned off (power supply is cut off) instead of the operation rotation described in Figures 3 and 6. This is called a stopped stack. For example, during the period from 0 to 2 h in Figure 10, the power supply is low so only four water electrolysis stacks 11 are operated, and during the period from 8 to 10 h, the power supply is even lower so only two are operated.

Which water electrolysis stacks 11 should be turned off so that the operation rates of the water electrolysis stacks 11 are as uniform as possible. It is sufficient that the operation rates averaged over a certain period of time are as uniform as possible, and it is not necessary that the operation rates are strictly uniform all the time. In addition, it is not necessary to assign a stopped stack for the entire period when the power supply is reduced, and as long as a stopped stack is assigned to at least some of the low-power engines, the effect of suppressing deterioration can be achieved to that extent.

Figures 11A to 11C show the change over time in the power supplied to each water electrolysis stack 11 when the stacks are operated according to the operation rotation plan in Figure 10. The operation-priority stack has an improved operation rate compared to Figure 9, and the frequency of transitions between high output and medium output is reduced, so it is expected that the deterioration rate will be lower than with conventional control.

In the calculation of the conventional control method in Figure 9, the number of water electrolysis stacks that are turned on/off is changed in real time (in seconds) in response to fluctuations in the input power. In contrast, the operation rotation in Figure 10 has the advantage in terms of fluctuation tracking, since it can control the operating state of the water electrolysis stack 11 by "current distribution control by the DC/DC converter 12" in addition to "ON/OFF control every two hours."

As described above, even when renewable energy that fluctuates depending on the time of day, such as solar power generation, is supplied, it is possible to suppress deterioration of the water electrolysis stack 11 by using the control method of this embodiment.

<Embodiment 1: Summary>
The hydrogen production system 1 according to the first embodiment assigns the operation states of the water electrolysis stack 11 in the order of operation priority stack => shutdown priority stack => intermediate operation stack. This makes it possible to suppress deterioration of the water electrolysis stack 11, compared to conventional operation control that equalizes the operation rates of the water electrolysis stacks 11 or operation control that frequently repeats ON/OFF.

In the hydrogen production system 1 according to the first embodiment, during periods when the power supply is low, the water electrolysis stack 11 is assigned a stopped stack in addition to the above operation states. This makes it possible to effectively suppress deterioration of the water electrolysis stack 11 even when receiving a power supply that fluctuates greatly over time, such as solar power generation.

<Embodiment 2>
12 is a configuration diagram of a hydrogen production system 1 according to a second embodiment of the present invention. In the second embodiment, in addition to the configuration described in the first embodiment, a power generation amount prediction unit 21 is provided. The power generation amount prediction unit 21 may be configured as a part of the hydrogen production system 1, or may be configured as a functional unit separate from the hydrogen production system 1.

The power generation prediction unit 21 predicts the amount of power generated from renewable energy sources according to a known method. For example, it may (a) predict using meteorological data 22 (data describing meteorological conditions such as weather and wind conditions), (b) obtain data on the amount of power generated from renewable energy power generation facilities in real time, or (c) use a combination of these.

The power distribution control system 14 receives the predicted power generation from the power generation prediction unit 21 and assigns the operating state of each water electrolysis stack 11 accordingly. For example, when the power generation is high, the number of operation priority stacks is increased. If the power generation increases while maintaining the number of stacks, the power distributed to the stop priority stacks increases, and there is a concern that the transition between high output and medium output will increase and deterioration will be accelerated. In addition, as in the case of solar power generation in embodiment 1, when a decrease in power generation is expected depending on the time of day, the water electrolysis stacks 11 may be controlled to be turned on and off as shown in FIG. 10. These controls make it possible to suppress deterioration of the water electrolysis stacks 11 while following fluctuations in the amount of renewable energy power generation.

<Third embodiment>
13 is a configuration diagram of a hydrogen production system 1 according to a third embodiment of the present invention. In the third embodiment, in addition to the configuration described in the first embodiment, a deterioration monitoring unit 3 is provided. The deterioration monitoring unit 3 may be configured as a part of the hydrogen production system 1, or may be configured as a functional unit separate from the hydrogen production system 1.

The degradation monitoring unit 3 receives, for example, the output current and output voltage of the water electrolysis stack 11 from the power distribution control system 14, and uses this to calculate the degradation level (State of Health: SOH) of the water electrolysis stack 11. The power distribution control system 14 assigns the operating state of each water electrolysis stack 11 according to the degradation level.

For example, the power distribution control system 14 assigns the operating state of a water electrolysis stack 11 with a low SOH so that the number of times that the stack is operated with a high deterioration rate (e.g., the number of times that an intermediate operating stack is assigned) is reduced compared to the number of other water electrolysis stacks 11. This makes it possible to avoid a situation in which only a specific stack deteriorates early and requires replacement, thereby reducing the maintenance costs associated with replacement.

<Embodiment 4>

Figure 14 is a configuration diagram of a hydrogen production system 1 according to embodiment 4 of the present invention. In addition to the configuration described in embodiment 1, this embodiment 4 includes a management system 41 and a distributor 42. The management system 41 and the distributor 42 may be configured as part of the hydrogen production system 1, or may be configured as separate functional parts from the hydrogen production system 1.

In this embodiment, the distributor 42 switches between supplying the electricity generated by the renewable energy power generation facility 43 to the water electrolysis stack 11 or selling the electricity to the consumer 44 (i.e., outputting the received electricity to the power transmission and distribution system) in accordance with instructions from the management system 41. The management system 41 instructs the distributor 42, for example, on the distribution ratio between the two.

The management system 41 further collects demand data for various types of energy (electricity, heat, hydrogen, etc.) from consumers 44, and controls energy distribution according to the data. For example, it can predict electricity demand and the spot price of energy that reflects it, and implement controls such as increasing the electricity sales ratio when electricity demand is high and producing hydrogen when electricity demand is low. Data can also be collected on the supply amounts of these energies in a similar manner, and the above control can be implemented according to the balance between supply and demand.

When the amount of electricity supplied to the hydrogen production system 1 is large, the number of stop priority stacks that can be assigned decreases relatively. In such a case, the distributor 42 may increase the ratio of electricity sold to the consumer 44 (in other words, if the amount of electricity generated decreases, the electricity selling ratio is decreased accordingly). This reduces the electricity supplied to the water electrolysis stack 11, and therefore increases the number of stop priority stacks that can be assigned. As a result, deterioration of the water electrolysis stack 11 can be suppressed.

<Fifth embodiment>
15 is a configuration diagram of a hydrogen production system 1 according to a fifth embodiment of the present invention. In this fifth embodiment, the hydrogen production system 1 receives power from a power transmission and distribution system 5. Therefore, unlike the case where the hydrogen production system 1 receives renewable energy power, a constant current load is applied to the water electrolysis stack 11, and deterioration due to this load must be taken into consideration. The other configurations are the same as those of the first to fourth embodiments.

16A shows the operation rotation when the operating state of each water electrolysis stack is assigned according to the conventional procedure. The numerical values are the current densities (A/cm ² ) supplied to the water electrolysis stacks. Power is distributed equally to each stack.

FIG. 16B shows the operation rotation of the hydrogen production system 1 in this embodiment. If the rated current is 2.0 A/ ^cm2 , a stack with a current value of 1.8 A/ ^cm2 generally corresponds to an operation-priority stack, and a stack with a current value of 1.0 A/ ^cm2 generally corresponds to a stop-priority stack. Therefore, by allocating these as the operation states of each stack in FIG. 16B, the same effect as in the first embodiment can be achieved. Alternatively, in consideration of the fact that the power supplied by the power transmission and distribution system 5 does not fluctuate over time, the power supplied to the water electrolysis stack 11 may be fixed at the current value shown in FIG. 16B and supplied to the water electrolysis stack 11 as it is, without increasing or decreasing the power supplied to the water electrolysis stack 11 as in the operation-priority stack and the stop-priority stack. The type of power to be used may be switched depending on the type of power to be supplied.

The deterioration rate in the conventional control of FIG. 16A was estimated to be 78 μV/h by linearly interpolating the deterioration rate in mode B of FIG. 5. The deterioration rate in FIG. 16B was estimated to be 52 μV/h by linearly interpolating the deterioration rate in mode C. Therefore, compared to the conventional control, the deterioration rate can be reduced by 33%. Therefore, even when receiving power with small fluctuations over time such as grid power, deterioration of the water electrolysis stack 11 can be suppressed.

<Modifications of the present invention>
The present invention is not limited to the above-described embodiment, and includes various modified examples. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

In the deterioration test in Non-Patent Document 1, it is stated that a voltage of 1.4 V or more is applied to the water electrolysis cell even when the current density is zero. This is slightly higher than the theoretical voltage for water electrolysis (1.23 V) and is the voltage value near the start of the electrolysis reaction. If the voltage is reduced to 0 V during operation, a reverse current may flow and deteriorate the water electrolysis cell. Therefore, in the present invention, a DC/DC converter 12 is placed at the entrance of the power supply path to the water electrolysis stack 11 so that a voltage near the start of the electrolysis reaction can be applied to the water electrolysis stack 11 even when the current flowing through the water electrolysis stack 11 becomes zero. A similar role can be substituted by a power converter capable of outputting at least two or more voltages. Therefore, such a power converter may be placed instead of the DC/DC converter 12.

The present invention can also be applied to fuel cells, which are the reverse reaction of water electrolysis. In that case, the water electrolysis stack 11 is replaced with a fuel cell stack, the power distribution control system 14 is replaced with a power generation sharing control system, and the flow of electricity and hydrogen is reversed.

In the above embodiment, the power distribution control system 14 and each of its functional units can be configured by hardware such as a circuit device that implements these functions, or by a processor or other computing device that executes software that implements these functions. The same applies to the power generation prediction unit 21, the degradation monitoring unit 3, and the management system 41.

1: Hydrogen production system 11: Water electrolysis stack 12: DC/DC converter 13: AC/DC rectifier 14: Power distribution control system 21: Power generation prediction unit 3: Deterioration monitoring unit 41: Management system

Claims (21)

A control system for controlling power distribution to a plurality of water electrolysis stacks by controlling a power converter, comprising:
an operation plan formulation unit that formulates an operation rotation plan for the water electrolysis stack based on a deterioration characteristic that indicates a susceptibility to deterioration of the water electrolysis stack;
a stack operation allocation unit that allocates an operation state of the water electrolysis stack to be supplied with power for a predetermined period in the operation rotation plan;
a power distribution command unit that supplies a current command value to the power converter so that the plurality of water electrolysis stacks operate in accordance with the operating state;
Equipped with
The stack operation allocation unit sets, as an operation state when the water electrolysis stack receives a power supply,
(i) an operation priority stack that receives power supply preferentially over the other water electrolysis stacks during a period in which one of the operation states is assigned ;
(ii) a stop-priority stack that receives a current supply during the period, prioritizes stopping the current supply over the other water electrolysis stacks , and receives a supply of power that changes over time throughout the period ;
A control system comprising: The stack operation allocation unit determines an operation state of the water electrolysis stack that receives the supply of the time-varying power over the period as follows:
and (iii) assigning an intermediate operation stack to receive power obtained by subtracting the power supplied to the operation priority stack and the power supplied to the shutdown priority stack from a sum of the powers supplied to the water electrolysis stacks. the stack operation allocation unit sequentially allocates, in the operation rotation plan, the operation priority stack, the shutdown priority stack, and the intermediate operation stack as operation states of a first stack among the plurality of water electrolysis stacks in a first order;
3. The control system according to claim 2, wherein in the operation rotation plan, the stack operation allocation unit sequentially allocates the operation priority stack, the shutdown priority stack, and the intermediate operation stack as operation states of a second stack, different from the first stack, among the plurality of water electrolysis stacks, in a second order different from the first order. the stack operation allocation unit allocates, in the operation rotation plan, the operation states of the first stack in the following order: the operating priority stack, the stop priority stack, and the intermediate operating stack;
The control system according to claim 3, characterized in that when the stack operation allocation unit assigns the operating priority stack to the first stack, it assigns an operating state other than the operating priority stack to the second stack, and when the stack operation allocation unit assigns the stop priority stack to the first stack, it assigns an operating state other than the stop priority stack to the second stack. a deterioration rate calculation unit that calculates a deterioration rate of the water electrolysis stack when the operation rotation plan is executed in accordance with deterioration characteristics of the water electrolysis stack,
The control system according to claim 1 , wherein the stack operation allocation unit allocates the operation rotation plan so as to reduce a difference in the calculated deterioration rate between each of the water electrolysis stacks. the stack operation assignment unit assigns, as an operation state of the water electrolysis stack, any one of the operation priority stack, the shutdown priority stack, the intermediate operation stack, and a shutdown stack that is shut down for a predetermined period of time;
3. The control system according to claim 2, wherein, when a low-power period occurs in which power supplied to the water electrolysis stack is less than a threshold, the stack operation assignment unit assigns the stopped stack as one of the operation states of each of the water electrolysis stacks during at least a part of the low-power period. The water electrolysis stack receives power from a variable power source whose power value fluctuates over time,
receiving a result of predicting the amount of power generated by the variable power source;
The control system according to claim 1 , further comprising: adjusting a number of the water electrolysis stacks to which the operation priority stack is assigned in accordance with the predicted power generation amount. when the predicted amount of power generation is a first amount of power generation, assigning the operation priority stack to a first number of the water electrolysis stacks;
8. The control system according to claim 7, wherein when the predicted amount of power generation is a second amount of power generation smaller than the first amount of power generation, the operation priority stacks are assigned to a second number of the water electrolysis stacks which is smaller than the first number. acquiring a deterioration state of the water electrolysis stack;
The control system according to claim 2 , further comprising: allocating an operating state of the water electrolysis stack according to the acquired deterioration state. for the water electrolysis stack whose acquired deterioration state is a first deterioration state, limiting the number of times that the intermediate operating stack is assigned within a predetermined period to a first number of times or less;
10. The control system according to claim 9, wherein for the water electrolysis stack whose acquired deterioration state is a second deterioration state that is less deteriorated than the first deterioration state, a number of times that the intermediate operating stack is assigned within a predetermined period is set to be greater than the first number of times. A control system for controlling power distribution to a plurality of water electrolysis stacks by controlling a power converter, comprising:
an operation plan formulation unit that formulates an operation rotation plan for the water electrolysis stack based on a deterioration characteristic that indicates a susceptibility to deterioration of the water electrolysis stack;
a stack operation allocation unit that allocates an operation state of the water electrolysis stack to be supplied with power for a predetermined period in the operation rotation plan;
a power distribution command unit that supplies a current command value to the power converter so that the plurality of water electrolysis stacks operate in accordance with the operating state;
Equipped with
The stack operation allocation unit sets, as an operation state when the water electrolysis stack receives a power supply,
an operation priority stack that receives power supply preferentially over the other water electrolysis stacks during a period in which one of the operation states is assigned ;
a stop-priority stack that receives a supply of power during the period, is stopped preferentially for a longer period than the other water electrolysis stacks , and receives a supply of power that changes over the period ;
A control system comprising: A control method for controlling power distribution to a plurality of water electrolysis stacks by controlling a power converter, comprising:
formulating an operation rotation plan for the water electrolysis stack based on a deterioration characteristic indicating a susceptibility of the water electrolysis stack to deterioration;
allocating an operating state of the water electrolysis stack to be powered for a predetermined period in the operational rotation plan;
providing a current command value to the power converter so that the plurality of water electrolysis stacks operate according to the operating state;
having
In the step of allocating an operation state of the water electrolysis stack, the operation state when the water electrolysis stack receives power is:
(i) an operation priority stack that receives power supply preferentially over the other water electrolysis stacks during a period in which one of the operation states is assigned ;
(ii) a stop-priority stack that receives a supply of power during the period, while giving priority to stopping the current supply over the other water electrolysis stacks, and receives a supply of power that changes over the period ;
and assigning a control signal to the control unit. as an operating state when the water electrolysis stack is supplied with the time-varying power over the period of time ,
(iii) an intermediate operation stack that receives power obtained by subtracting the power supplied to the operation priority stack and the power supplied to the shutdown priority stack from the sum of the powers supplied to the water electrolysis stacks;
The control method according to claim 12, further comprising the step of: assigning a A hydrogen production system for producing hydrogen by a plurality of water electrolysis stacks,
a power distribution control unit that controls a power converter to control power to be distributed to each of the water electrolysis stacks;
Equipped with
The power distribution control unit includes:
an operation plan formulation unit that formulates an operation rotation plan for the water electrolysis stack based on a deterioration characteristic that indicates a susceptibility to deterioration of the water electrolysis stack;
a stack operation allocation unit that allocates an operation state of the water electrolysis stack to be supplied with power for a predetermined period in the operation rotation plan;
a power distribution command unit that supplies a current command value to the power converter so that the plurality of water electrolysis stacks operate in accordance with the operating state;
Equipped with
The stack operation allocation unit sets, as an operation state when the water electrolysis stack receives a power supply,
(i) an operation priority stack that receives power supply preferentially over the other water electrolysis stacks during a period in which one of the operation states is assigned ;
(ii) a stop-priority stack that receives a supply of power during the period, while giving priority to stopping the current supply over the other water electrolysis stacks , and receives a supply of power that changes over the period ;
A hydrogen production system comprising: The stack operation allocation unit determines, as an operation state of the water electrolysis stack when the water electrolysis stack receives the supply of the time-varying power over the period ,
(iii) allocating an intermediate operation stack to receive power obtained by subtracting the power supplied to the operation priority stack and the power supplied to the shutdown priority stack from a sum of the power supplied to each of the water electrolysis stacks. The water electrolysis stack receives power from a variable power source whose power value fluctuates over time,
receiving a result of predicting the amount of power generated by the variable power source;
The hydrogen production system according to claim 14, wherein the number of the water electrolysis stacks to which the operation priority stack is assigned is adjusted according to the predicted power generation amount. The hydrogen production system further includes a distributor that switches between supplying the power supplied from the variable power source to the water electrolysis stack or outputting the power to a power transmission and distribution system,
The hydrogen production system according to claim 16, further comprising a management system configured to control a ratio at which the distributor distributes the supply power between the water electrolysis stack and the power grid in accordance with a power demand. The power distribution control unit receives a result of predicting the amount of power generated by the variable power source,
the management system controls the distributor to output a first ratio of the supply power to the power transmission and distribution system when the predicted power generation amount is a first power generation amount;
18. The hydrogen production system according to claim 17, wherein when the predicted amount of power generation is a second amount of power generation smaller than the first amount of power generation, the management system controls the distributor so as to output a portion of the supply power at a second ratio smaller than the first ratio to the power transmission and distribution system. the management system controls the distributor to output a first ratio of the supply power to the power transmission and distribution system when the power demand is a first amount of power;
18. The hydrogen production system according to claim 17, wherein when the power demand is a second amount of power smaller than the first amount of power, the management system controls the distributor to output a portion of the supply power at a second ratio smaller than the first ratio to the power transmission and distribution system. 18. The hydrogen production system according to claim 17, wherein the management system controls the ratio according to a heat demand, a heat supply amount supplied for the heat demand, a hydrogen demand, and a hydrogen supply amount supplied by the hydrogen production system. The control system of claim 1 , wherein the water electrolysis stack comprises a PEM electrolysis cell.

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