Water electrolysis system that manages renewable energy power supply

Abstract

To improve utilization efficiency of a water electrolysis device in a water electrolysis system that manages power supply with renewable energy.SOLUTION: A water electrolysis system manages power supply with renewable energy to a system and an electrolytic tank of a water electrolysis device. The water electrolysis system acquires renewable energy power and operation information for a renewable energy device from a power conversion device connected to the renewable energy device, calculates an estimated value of the renewable energy power on the basis of the renewable energy power and the operation information, calculates an estimated value of residual power at a predetermined timing on the basis of the estimated value of the renewable energy power and sold power, calculates an electrolyte power command value by performing a conversion process based an allowable lamp rate of the electrolysis tank on the estimated value of the residual power before the predetermined timing and the estimated value of the residual power at the predetermined timing, and inputs the electrolyte power command value to the power conversion device of the electrolytic tank.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a water electrolysis system that manages the supply of renewable energy power. [Background technology]

[0002] In order to realize a low-carbon society, power generation using renewable energy sources such as solar and wind power (hereinafter sometimes abbreviated as "renewable energy") is becoming more common, replacing thermal power generation using fossil fuels. However, because the power generated by renewable energy sources fluctuates greatly due to natural phenomena, it cannot be used as a substitute for grid power as is.

[0003] It will be necessary to store the electricity using batteries, or to have the option of converting it into a means of storage other than converting it into electricity (for example, hydrogen). With batteries, the cost of the storage equipment increases in proportion to the amount of electricity to be stored. On the other hand, with hydrogen, once the conversion equipment is in place, it is possible to prepare tanks and transport it, and the cost does not increase as much relative to the amount of storage. For this reason, hydrogen is considered an important energy carrier when utilizing renewable energy.

[0004] However, the cost of producing hydrogen using renewable energy remains high compared to generating electricity using fossil fuels. This is because the electricity generated from renewable energy sources cannot always be kept up with fluctuations, and because the fluctuations in renewable energy are so large that the generated power can sometimes exceed the installed capacity, limiting the operating rate of hydrogen production facilities.

[0005] Figure 1 shows a typical example of a conventional water electrolysis system that obtains electricity from one or more renewable energy devices and produces hydrogen. Renewable energy devices include solar cells (hereinafter sometimes abbreviated as "PV") and wind turbines. These devices are connected to power conversion devices such as DC / AC converters and AC / DC / AC converters, which generate electricity at the optimal operating point of each device (usually the point at which maximum power is generated) and convert it to AC, which is then connected to the grid to supplement fossil fuel electricity. Hydrogen is then produced by inputting part of this electricity into an electrolyzer. Since electrolyzers operate on direct current, the AC power from the grid is converted to direct current by a power conversion device called a dedicated AC / DC converter before being connected to the electrolyzer.

[0006] The amount of electricity used to produce hydrogen from the electricity obtained from renewable energy is the remainder after subtracting the electricity supplied to the grid from the generated electricity. Therefore, in the diagram, the AC / DC is controlled so that only the electricity obtained by subtracting the amount sold from the electricity generated from renewable energy is supplied to the electrolyzer.

[0007] Patent Documents 1 and 2 describe known configurations for supplying renewable energy power to a water electrolysis device for producing hydrogen.

[0008] The technology in Patent Document 1 utilizes the respective advantages of water electrolysis cells and SOECs to efficiently and stably produce hydrogen from surplus electricity generated by renewable energy sources, which are prone to fluctuations. The surplus electricity situation is predicted in advance using weather forecasts, etc., and the surplus electricity actually supplied is separated into stable electricity, which is maintained at a constant level, and unstable electricity.

[0009] In the technology of Patent Document 2, unstable maximum energy power is smoothed using the charging and discharging of a storage battery, and then hydrogen is produced in a water electrolysis device. Any surplus power from the smoothed power during the operation of the electrolysis device is supplied to the grid, and any power shortage is made up for by discharging from the storage battery. Unstable renewable energy power can be stored not only in storage batteries, which require high equipment costs, but also in electrolytic cells, and stable power can be supplied to the grid. Operation can be tailored to the response speed of the water electrolysis device. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2019-173082 [Patent Document 2] Japanese Patent Application Publication No. 2018-85862 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the conventional technology has a problem that there is room for improvement in the utilization efficiency of the water electrolysis device.

[0012] When electricity generated from renewable energy sources is directly used as the power source for hydrogen production, two efficiency problems arise. The first is that the electrolyzer may not be able to keep up with changes in the renewable energy power. While renewable energy power fluctuates in response to changes in solar radiation and wind speed, the power that the electrolyzer can accept is limited by the electrolyzer's cell structure and characteristics, operating temperature, and the operating status of auxiliary equipment such as pumps and compressors. For this reason, electrolysis equipment often specifies variable parameters (such as ramp rates).

[0013] The second problem is that renewable energy power fluctuates widely, making it difficult to make full use of fluctuating power. Increasing the rating of the electrolysis equipment in an attempt to utilize power to the maximum extent of the fluctuation reduces the utilization rate of the electrolysis cell as equipment. On the other hand, reducing the rating of the electrolysis equipment may improve the apparent utilization rate, but the power outside the rating will be wasted, making it difficult to say that renewable energy is being used effectively.

[0014] The technology in Patent Document 1 estimates fluctuations in renewable energy power in advance to utilize the unstable power of renewable energy, but because the estimation is based on weather forecasts, there is a discrepancy between the actual power generation and the estimated value. Furthermore, surplus power is defined as the value obtained by subtracting the amount of demand from the amount of renewable energy power generated. However, there is a possibility that surplus power cannot be transmitted via the grid or may be subject to restrictions, and the amount of renewable energy power generated is not necessarily the maximum power. For this reason, the accuracy of renewable energy predictions is poor, and it is expected that the response speed to changes in renewable energy will be slow.

[0015] In the technology of Patent Document 2, unstable renewable energy power is smoothed using a filter to stabilize it, but if the characteristics (for example, passband) of this filter do not match the response speed of the electrolyzer, the discharge operation of the storage battery will result in the unstable power being supplied to the grid. Complete stabilization requires a large-capacity storage battery.

[0016] The present invention has been made to solve the above problems, and has an object to improve the utilization efficiency of a water electrolysis device in a water electrolysis system that manages the supply of renewable energy power. [Means for solving the problem]

[0017] An example of a water electrolysis system according to the present invention includes: A water electrolysis system that manages a supply of renewable energy to a grid and an electrolytic cell of a water electrolysis device, acquiring renewable energy power and operation information of the renewable energy device from a power conversion device connected to the renewable energy device; calculating an estimated value of the renewable energy power based on the renewable energy power and the operation information; calculating an estimated value of surplus power at a predetermined timing based on the estimated value of the renewable energy power and the power to be sold; calculating an electrolysis power command value by performing a conversion process based on an allowable ramp rate of the electrolytic cell for the estimated value of the surplus power before the predetermined timing and the estimated value of the surplus power at the predetermined timing; The electrolysis power command value is input to a power converter of the electrolytic cell. [Effects of the Invention]

[0018] According to the present invention, it is possible to improve the utilization efficiency of a water electrolysis device in a water electrolysis system that manages the supply of renewable energy power.

[0019] For example, it is possible to reduce the load on the electrolytic cell due to a sudden change in power, and it is also possible to increase the amount of power used for electrolysis in the electrolytic cell, thereby improving the efficiency of electrolysis.

[0020] Therefore, even in situations where renewable energy power fluctuates, that power can be used to produce hydrogen without being overlooked. Furthermore, when renewable energy power output is restricted due to grid constraints, this restriction can be alleviated, allowing that power to be used for hydrogen production. As a result, the capacity utilization rate of electrolyzers increases and hydrogen production costs decrease. [Brief explanation of the drawings]

[0021] [Figure 1] A typical example of a conventional water electrolysis system. [Figure 2] 1 shows the configuration of a water electrolysis system according to a first embodiment of the present invention. [Figure 3A] A moving average type filter. [Figure 3B] Basis for calculating the value of k in Figure 3A. [Figure 4] 10 shows an example of the progress of calculations in the first embodiment. [Figure 5] 1 shows the configuration of a water electrolysis system according to a second embodiment of the present invention. [Figure 6A] 10 shows the configuration of a filter section according to a third embodiment of the present invention. [Figure 6B] 10 shows the configuration of a filter unit and an electrolytic cell according to Example 3. [Figure 7] 1 shows the configuration of a filter section and an electrolytic cell according to Example 4 of the present invention. [Figure 8] 10 is an outline of a process according to a fifth embodiment of the present invention. [Figure 9] 10 shows the configuration of a filter section and an electrolytic cell according to Example 7 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Example 1 2 shows the configuration of a water electrolysis system 100 according to a first embodiment of the present invention. The water electrolysis system 100 is a system that manages the supply of renewable energy power to a grid and an electrolytic cell 101 of a water electrolysis device. The grid refers to a power grid, such as, but not limited to, a commercial power grid.

[0023] The water electrolysis system 100 may further function as a hydrogen production device, an electrolyzer control device for hydrogen production using renewable energy, or a system for aggregating information on renewable energy devices.

[0024] The water electrolysis system 100 may function as a data management platform. For example, the water electrolysis system 100 may operate in cooperation with a renewable energy power generation system, a hydrogen production system that uses low-carbon energy, an electricity price market, and the like.

[0025] One or more renewable energy devices 102 (PV and wind power generation in FIG. 2) are connected to a grid via a power conditioner (PCS) which is a power conversion device 103.

[0026] The electrolytic cell 101 is connected to the wiring to this system via another power conversion device, an AC / DC converter 104. This AC / DC converter 104 may simply convert alternating current to direct current, but may also have current feedback control as shown in the figure and the function of sending a commanded power to the electrolytic cell 101.

[0027] The water electrolysis system 100 includes a control device 110 that controls the entire water electrolysis system 100. Components of the water electrolysis system 100 (e.g., the power conversion device 103 and the AC / DC converter 104) operate under the control of the control device 110. The control device 110 may include, for example, a computer, which may include a calculation means and a storage means. The storage means may store a program. The calculation means may execute the program, causing the control device 110 to cause the water electrolysis system 100 to perform the operations described herein.

[0028] The power conversion apparatus 103 is not simply a DC / AC converter or an AC / DC / AC converter, but has a function of acquiring operation information from the renewable energy device 102 connected thereto.

[0029] The water electrolysis system 100 (for example, but not limited to, the control device 110) acquires power (renewable energy power) output from the power conversion devices 103 connected to each renewable energy device 102. The water electrolysis system 100 also acquires operation information of each renewable energy device 102 from each power conversion device 103. For example, in the case of PV, the amount of solar radiation or PV voltage is acquired as operation information.

[0030] The control device 110 includes an MPP estimation unit 111 that estimates a maximum power point (MPP), and the MPP estimation unit 111 can maximize the power obtained from the renewable energy device 102 and the power conversion device 103 based on the operation information. For example, the MPP estimation unit 111 can output maximum power in accordance with the characteristics of the PV by setting an appropriate DC voltage on the PV side for the amount of solar radiation or PV voltage via the power conversion device 103. In the case of wind power generation, the maximum amount of power can be extracted by obtaining wind conditions (for example, wind speed and wind direction) as operation information and setting an appropriate rotation speed of the wind turbine for the wind conditions via the power conversion device 103.

[0031] In this way, the water electrolysis system 100 acquires renewable energy power and operation information of the renewable energy device 102 from the power conversion device 103 connected to the renewable energy device 102. Then, based on the renewable energy power and the operation information, it calculates an estimated value of the renewable energy power output from the power conversion device 103 (for example, an estimated value corresponding to the case where power is maximized).

[0032] This estimated value may be an estimated value that represents the temporal fluctuation of renewable energy power in the past and / or at the present time, or may be an estimated value that includes a predicted value that represents future renewable energy power. Note that the case where the renewable energy power obtained from the power conversion device 103 is treated as an estimated value as is is not excluded (in this case, the MPP estimation unit 111 may be omitted).

[0033] The control device 110 includes a power sales subtraction unit 112. The power sales subtraction unit 112 calculates an estimated value of surplus power at a predetermined timing based on an estimated value of renewable energy power and power sales (power sent to the grid). For example, the estimated value of surplus power at the current time is calculated by subtracting the power sales from the estimated value of renewable energy power.

[0034] 2 , when the water electrolysis system 100 constitutes a renewable energy site including multiple renewable energy devices 102, the control device 110 may include an aggregation unit 113. When the amount of power sold varies for each renewable energy device 102, multiple power sale subtraction units 112 subtract the corresponding amount of power sold from the corresponding estimated value of renewable energy power. Then, the aggregation unit 113 aggregates the estimated values ​​of surplus power for each renewable energy device 102 to calculate a final estimated value of surplus power.

[0035] Here, the allowable ramp rate of the electrolytic cell 101 will be explained. Generally, from the viewpoint of preventing deterioration of the electrolytic cell 101, it is undesirable for the power value input to the electrolytic cell 101 to fluctuate suddenly. For this reason, an allowable ramp rate is specified for the electrolytic cell 101. The allowable ramp rate represents the maximum allowable rate of change in the power value input to the electrolytic cell 101. For example, the allowable ramp rate is represented by the ratio of the power value that can change within a certain period of time to the rated power. Alternatively, the allowable ramp rate is represented by the time it takes for the electrolytic cell value to reach 100% of the rated value from 0%.

[0036] The allowable ramp rate can be determined so as to prevent deterioration of the electrolytic cell apparatus, taking into consideration the characteristics of the electrolytic cell apparatus (particularly the operating characteristics of the electrodes and auxiliary devices that make up the electrolytic cell 101).

[0037] The estimated value of surplus power calculated as described above by the power sales deductor 112 and the aggregation unit 113 directly reflects fluctuations in renewable energy. These fluctuations may exceed the allowable ramp rate of the electrolytic cell 101, and in this case, the estimated value is not suitable as an input power value to the electrolytic cell 101.

[0038] For this reason, the control device 110 includes a filter unit 114. The filter unit 114 performs conversion processing (filtering processing in this embodiment) on the estimated value of surplus power, calculates an appropriate electrolysis power command value, and transmits this to the AC / DC converter 104.

[0039] The filter unit 114 performs filtering using, for example, a low-pass filter, so that even if the estimated value of surplus power changes suddenly, the electrolysis power command value changes gradually.

[0040] Specific examples of the filter used by the filter unit 114 include a CR type low-pass filter and a moving average filter. In this embodiment, a configuration using a moving average type filter shown in Fig. 3A will be described.

[0041] In Figure 3A, D denotes a delay element. The number of taps in the moving average is k, i.e., k stages of delay elements are provided. The moving average is calculated by summing the outputs from each stage of the delay element and dividing by k.

[0042] The cutoff frequency of this filter is determined according to k, and this cutoff frequency is designed according to the characteristics of the connected electrolytic cell 101. The relationship between the allowable ramp rate of the electrolytic cell 101 and the number of taps k of the moving average filter will be explained below.

[0043] Let T be the allowable ramp rate of the electrolytic cell 101 to be controlled (for example, the shortest allowable time for the electrolysis power to reach 100% of the rated value). Let 1 / fs be the update interval for the electrolysis power command value. In other words, fs is the sampling frequency. In this case, k is a natural number proportional to T and fs. As a more precise example, k is a natural number close to (0.443 / 1.1)*π*fs*T. This fs is a value determined by the configuration of the control system, and T is a value determined by the catalog value of the electrolytic cell to be used. These values ​​can be input by the user to the filter unit 114.

[0044] As shown in FIG. 3A, the filter section 114 may operate based on a gain and an offset (described in more detail below).

[0045] The basis for the value of k in Figure 3A will be explained using Figure 3B. As a specific example, the lamp characteristics of the electrolytic cell 101 are approximated by a CR circuit. In this case, the allowable ramp rate T is T ≈ 2.2CR, where C is the capacitance value and R is the resistance value. The cutoff frequency of the CR circuit is expressed as fc = 1 / (2πCR). Meanwhile, the relationship between the number of taps k of the moving average filter and its cutoff frequency fc is fc ≈ 0.443 * fs / k (where 1 / fs is the time interval of the data). To achieve characteristics approximating those of a CR circuit using a moving average filter, the cutoff frequency fc is eliminated from the above two relationships, resulting in the following equation: k≒(0.443 / 1.1)*π*fs*T

[0046] In this way, using a moving average filter as a low-pass filter facilitates the design of the filter unit 114. Also, other CR filters (for example, a first-order CR filter or a second-order CR filter) can be used as the low-pass filter, and in that case, the design of the filter unit 114 is also easy.

[0047] Figure 4 shows an example of the progress of calculations in this embodiment. Figure 4(a) shows an estimated value 121 of renewable energy power and power to be sold 122 (power selling threshold). Figure 4(b) shows a value obtained by subtracting power to be sold 122 from estimated value 121 of renewable energy power, i.e., estimated value 123 of surplus power. Figure 4(c) shows an enlarged view of part of Figure 4(b) (for example, within dashed line area 124) of the estimated value 123 of surplus power (i.e., input to filter unit 114) and electrolytic power command value 125 (i.e., output from filter unit 114).

[0048] 4(c), the control device 110 calculates an electrolysis power command value by performing a filter process based on the allowable ramp rate of the electrolytic cell 101 on an estimated value of surplus power in the past (i.e., before a predetermined timing) and an estimated value of surplus power at the present time (i.e., at the predetermined timing). The control device 110 then inputs the calculated electrolysis power command value to the AC / DC converter 104. The calculation and input of the electrolysis power command value can be repeated for each predetermined operation cycle.

[0049] As shown in Fig. 4(c), the change in the electrolysis power command value 125 is more gradual than the change in the estimated surplus power value 123, and there is a higher possibility that the ramp rate will be kept below the allowable ramp rate of the electrolytic cell 101. This improves the utilization efficiency while avoiding deterioration of the water electrolysis device.

[0050] In FIG. 4(c), due to the filter characteristics, the change in the electrolysis power command value 125 lags behind the estimated surplus power value 123 at the rising edge, and since the change is small, it can be input to the electrolytic cell 101. On the other hand, at the falling edge, the electrolysis power command value 125 becomes larger than the estimated surplus power value 123. For this reason, the electrolysis power may exceed the surplus power, resulting in a power shortage. In this case, the shortage can be made up for by subtracting it from the power sold (i.e., by reducing the power supplied to the grid), or by adding a gain and an offset to the filter output to minimize the shortage. In this way, by performing filter processing based on the gain and offset, fluctuations in the filter output can be appropriately controlled.

[0051] The gain and offset values ​​can be designed appropriately by those skilled in the art. For example, the gain may be set to 1 / 2 and the offset to 1 / 2. If such values ​​are used, when the internal output of the filter is assumed to be a sine wave of angular velocity ω, i.e., cos(ωt), the final electrolysis power command value will be 0≦(1 / 2)+(1 / 2)·cos(ωt)≦1, so the electrolysis power command value can be made positive more reliably.

[0052] Alternatively, these values ​​can be used as initial values, and after operational data from the renewable energy site has been accumulated, the allowable ramp rate can be calculated from the operational data. For example, the least squares method can be used as shown in Fig. 3A. Note that when the gain is significantly different from 1, the time it takes for the electrolysis power command value to reach 0% to 100% of the rated value of the electrolytic cell 101 also changes in proportion to 1 / gain, so it is preferable to determine the allowable ramp rate to a value that takes the gain into consideration.

[0053] <Example 2> FIG. 5 shows the configuration of a water electrolysis system 100 according to a second embodiment of the present invention. In the second embodiment, a first electrolytic cell 101A and a second electrolytic cell 101B are installed as the multiple electrolytic cells. Furthermore, a first filter unit 114A and a second filter unit 114B are installed as the multiple filter units. Each filter unit calculates an electrolysis power command value for each electrolytic cell, each with different characteristics, based on an estimated value of surplus power. Hereinafter, a description of parts common to the first embodiment may be omitted.

[0054] Here, one renewable energy device 102 (a wind power generator in the example of FIG. 5) is connected to a wiring to a grid through a power conditioner (PCS) serving as a power conversion device 103. Note that, as in the first embodiment, multiple renewable energy devices 102 may be connected to aggregate surplus power.

[0055] In Example 2, there are multiple electrolytic cells, each with a different allowable ramp rate. Generally, there are types of electrolytic cells, such as AEM (Anion Exchange Membrane) electrolysis, which have difficulty in inputting fluctuating power with a large ramp rate but are efficient under stable power conditions, and there are also types such as PEM (Proton Exchange Membrane) electrolysis, which can accept input of fluctuating power with a large ramp rate but do not have as high an electrolysis efficiency as AEM.

[0056] Therefore, multiple filters suited to the respective allowable ramp rates are provided to distribute the fluctuating renewable energy power. That is, the water electrolysis system 100 calculates each electrolysis power command value for each of the multiple electrolytic cells by performing filtering based on the allowable ramp rate of that electrolytic cell.

[0057] As a specific example, the first filter unit 114A performs filtering based on the allowable ramp rate of the first electrolytic bath 101A to calculate a first electrolysis power command value (command value A) and inputs it to the first AC / DC converter 104A. Meanwhile, the second filter unit 114B performs filtering based on the allowable ramp rate of the second electrolytic bath 101B to calculate a second electrolysis power command value (command value B) and inputs it to the second AC / DC converter 104B (in Figure 5, the arrow for command value B is interrupted midway to improve visibility).

[0058] It is desirable that the sum of the values ​​from the multiple filter units (i.e., the sum of the power values ​​corresponding to the respective electrolytic power command values) does not exceed the original estimated value of the surplus power. If the sum exceeds the estimated value, i.e., if there is a power shortage, the shortage can be subtracted from the power to be sold (i.e., the power supplied to the grid is reduced), or a gain and offset can be added to the filter output to minimize the shortage. The gain and offset values ​​can be designed appropriately by those skilled in the art.

[0059] Thus, according to the second embodiment, a plurality of electrolytic cells with different characteristics can be efficiently used.

[0060] Example 3 FIG. 6A shows the configuration of a filter unit according to Example 3 of the present invention. In this example, multiple electrolytic cells are provided as in Example 2, and further, filter processing for each electrolytic cell is cascaded. Each filter unit calculates an electrolysis power command value for each electrolytic cell with different characteristics. Hereinafter, explanations of parts common to Example 2 may be omitted.

[0061] Figure 6B shows the configuration of the filter unit and electrolytic cell according to Example 3. First, based on the estimated value of surplus power, the first filter unit 114A calculates a first electrolysis power command value for the first electrolytic cell 101A and inputs it to the first AC / DC converter 104A. Then, the first electrolysis power command value (or the value of the power actually flowing through the first electrolytic cell 101A according to the first electrolysis power command value) is subtracted from the original estimated value of surplus power. Based on the result of this subtraction, the second filter unit 114B calculates a second electrolysis power command value for the second electrolytic cell 101B and inputs it to the second AC / DC converter 104B.

[0062] If any of the electrolysis power command values ​​becomes negative (i.e., if there is a power shortage), the shortage can be made up by subtracting the sold power (i.e., reducing the power supplied to the grid), or by adding a gain and an offset to the filter output to make the shortage as small as possible. The gain and offset values ​​can be designed appropriately by those skilled in the art.

[0063] As described above, according to Example 3, it is possible to efficiently use a plurality of electrolytic cells with different characteristics. In particular, by cascading the filtering processes, the results of the filtering process at the previous stage can be used in the filtering process at the subsequent stage, thereby stabilizing the power supplied to the grid.

[0064] Example 4 7 shows the configuration of a filter unit and an electrolytic cell according to a fourth embodiment of the present invention. In this embodiment, the water electrolysis system further manages the supply of renewable energy power to the storage battery 105. Hereinafter, a description of parts common to the third embodiment may be omitted.

[0065] In the third embodiment, by replacing the electrolytic cell connected to the final-stage power control device (third AC / DC converter 104C in FIG. 7) with a storage battery 105, it is possible to make up for power shortages in electrolysis.

[0066] The water electrolysis system according to the fourth embodiment calculates a storage power command value based on an estimated value of renewable energy power and an electrolysis power command value. First, as in the third embodiment, the first filter unit 114A calculates a first electrolysis power command value and the second filter unit 114B calculates a second electrolysis power command value based on the estimated value of renewable energy power. Then, the first electrolysis power command value and the second electrolysis power command value are subtracted from the original estimated value of surplus power, thereby calculating the storage power command value.

[0067] The water electrolysis system then inputs this storage power command value to the third AC / DC converter 104C, which is a power conversion device for the storage battery. In response to this, the third AC / DC converter 104C controls charging and discharging of the storage battery 105. If the storage power command value is positive, charging occurs. If the storage power command value is negative, discharging occurs, thereby preventing a decrease in power supplied to the grid.

[0068] Thus, according to the fourth embodiment, by using a storage battery whose charging and discharging can be controlled more freely than an electrolytic cell, it is possible to further stabilize the power supplied to the grid.

[0069] In the example of FIG. 7, the filter unit and the electrolytic cell are cascade-connected as in Example 3, but they may be connected in parallel as in Example 2, or the filter unit and the electrolytic cell may each be independent as in Example 1.

[0070] <Example 5> Fig. 8 shows an outline of the process according to the fifth embodiment of the present invention. In this embodiment, the conversion process for calculating the electrolysis power command value from the estimated value of surplus power in the first embodiment is changed to a process other than the filtering process. Hereinafter, the description of the parts common to the first embodiment may be omitted.

[0071] In this embodiment, as shown in FIG. 8( a ), the conversion process for calculating the electrolysis power command value from the estimated value of the surplus power is performed by the ramp rate control unit 115 instead of the filter unit 114 .

[0072] 8(b) shows the input / output characteristics according to this embodiment. The ramp rate control unit 115 converts the estimated value 123 of the surplus power, which changes rapidly, into an electrolysis power command value 125 that changes at a ramp rate (the slope of which is represented by θ) equal to or less than a predetermined allowable ramp rate.

[0073] In the example of Fig. 8(b), the stepwise changing estimated value 123 of surplus power is converted into an electrolysis power command value 125 that changes at a specified ramp rate. In this case, the ramp rate can be determined in advance as a value equal to or less than the allowable ramp rate of the electrolytic cell to which the electrolysis device is connected.

[0074] In this way, in this embodiment, the conversion process for the estimated surplus power is realized as a process of changing a rate exceeding the allowable ramp rate to a rate equal to or lower than the allowable ramp rate, thereby achieving the same effect as in the first embodiment without using filter control.

[0075] The above-described fifth embodiment is a modification of the first embodiment, but the same modifications can be made to any of the second to fourth embodiments.

[0076] Example 6 The water electrolysis system according to this embodiment calculates the gain and offset of the filter unit using the least squares method. Hereinafter, a description of parts common to the first embodiment may be omitted.

[0077] The gain and offset can be determined based on past information about the water electrolysis system (e.g., information from the past year up to the present). As a more specific example, the gain and offset can be calculated using the least squares method based on information from the past year, as shown in FIG. 3A.

[0078] A specific application method for the least squares method can be designed appropriately by a person skilled in the art, but one example will be described below. The model function representing the estimated value of surplus power is assumed to be G+O·cos(ωt), where G is the gain, O is the offset, ω is the angular velocity corresponding to the cutoff frequency of the filter, and t is time. For this model function, the values ​​of G and O that best fit the estimated value of past surplus power are determined using the least squares method.

[0079] According to the sixth embodiment, the gain and offset of the filter unit can be determined to more appropriate values.

[0080] The above-described sixth embodiment is a modification of the first embodiment, but the same modification can be applied to any of the second to fourth embodiments.

[0081] Example 7 Figure 9 shows the configuration of a filter unit and electrolytic cell according to Example 7 of the present invention. In this example, the correspondence between the filter unit (each corresponding to a specific allowable ramp rate) and the electrolytic cell in Example 4 is changed depending on the situation. Hereinafter, explanations of parts common to Example 4 may be omitted.

[0082] First, the water electrolysis system according to this embodiment calculates each electrolysis power command value by performing conversion processing based on different allowable ramp rates for each of the multiple electrolytic cells, as in Example 4. Furthermore, the water electrolysis system according to this embodiment interchanges the allowable ramp rates for the multiple electrolytic cells with each other based on a predetermined criterion.

[0083] 9, the water electrolysis system includes a command value rearrangement block 106. The command value rearrangement block 106 controls the correspondence between the filter units and the AC / DC converters, and switches them depending on the situation.

[0084] A more specific example will be described below. The first filter unit 114A performs filtering based on a first allowable ramp rate to calculate a first electrolysis power command value. The second filter unit 114B performs filtering based on a second allowable ramp rate to calculate a second electrolysis power command value. The command value rearrangement block 106 determines whether to input the first electrolysis power command value to the first AC / DC converter 104A and the second electrolysis power command value to the second AC / DC converter 104B, or conversely, to input the first electrolysis power command value to the second AC / DC converter 104B and the second electrolysis power command value to the first AC / DC converter 104A.

[0085] The magnitude relationship between the allowable ramp rates of the electrolytic cells in the initial stage immediately after the water electrolysis system starts operating may change over the course of operation. Electrolytic cells with high allowable ramp rates in the initial stage will be overworked in a loosely filtered path (i.e., a high ramp rate). In order to extend the life of such electrolytic cells, it is necessary to update the allowable ramp rates. This embodiment achieves this.

[0086] The criteria for determining the replacement can be designed as appropriate by those skilled in the art, but can be, for example, based on elapsed time. As a more specific example, the allowable ramp rates can be replaced every time a predetermined time has elapsed. Furthermore, if the allowable ramp rate for each electrolytic cell can be measured, the measured allowable ramp rate can be used as the basis, and replacement can be performed by assigning a filter unit corresponding to a larger allowable ramp rate to an electrolytic cell with a larger measured allowable ramp rate.

[0087] In the case of a single electrolytic cell as in Example 1, this can be addressed by changing the configuration of the filter unit in accordance with the update of the allowable ramp rate, but in the case of multiple filter units and multiple electrolytic cells, it is preferable to appropriately change the correspondence between these.

[0088] The above-described seventh embodiment is a modification of the fourth embodiment, but the same modification can be applied to any of the second, third, fifth and sixth embodiments.

[0089] Furthermore, in each of the above-described embodiments, the power conversion device of the electrolytic cell is an AC / DC converter, but as a modification, it is also possible to use a DC / DC converter connected to the system via an inverter. [Explanation of symbols]

[0090] 100...Water electrolysis system 101...Electrolytic cell 101A…1st electrolytic cell 101B…Second electrolytic cell 102...Renewable energy devices 103...Power conversion device (power conversion device connected to renewable energy device) 104...AC / DC converter (electrolyzer power conversion device) 104A...First AC / DC converter (power conversion device for electrolyzer) 104B...Second AC / DC converter (electrolyzer power conversion device) 104C...Third AC / DC converter 105...storage battery 106...Command value rearrangement block 110...Control device 111...MPP estimation section 112...Electricity sales deduction section 113...Concentration section 114...Filter section 114A...First filter section 114B...Second filter section 115...Ramp rate control unit 121...Estimated renewable energy electricity 122...Electricity sold 123…Estimated surplus electricity 124...Dotted line area 125...Electrolysis power command value

Claims

1. A water electrolysis system that manages a supply of renewable energy to a grid and an electrolytic cell of a water electrolysis device, acquiring renewable energy power and operation information of the renewable energy device from a power conversion device connected to the renewable energy device; calculating an estimated value of the renewable energy power based on the renewable energy power and the operation information; calculating an estimated value of surplus power at a predetermined timing based on the estimated value of the renewable energy power and the power to be sold; calculating an electrolysis power command value by performing a conversion process based on an allowable ramp rate of the electrolytic cell for the estimated value of the surplus power before the predetermined timing and the estimated value of the surplus power at the predetermined timing; inputting the electrolysis power command value to a power conversion device of the electrolytic cell; A water electrolysis system comprising:

2. 2. The water electrolysis system according to claim 1, wherein the conversion process is performed using a low-pass filter.

3. 3. The water electrolysis system according to claim 2, wherein the low-pass filter is a moving average filter.

4. 3. The water electrolysis system according to claim 2, wherein the low-pass filter is a CR filter.

5. The water electrolysis system according to claim 1, the electrolytic cell is a plurality of electrolytic cells, a plurality of said electrolytic cells having different allowable ramp rates; the water electrolysis system calculates the electrolysis power command value by performing a conversion process based on the allowable ramp rate of each of the plurality of electrolytic cells. A water electrolysis system comprising:

6. 6. The water electrolysis system according to claim 5, wherein the conversion processes of the electrolytic cells are cascade-connected.

7. The water electrolysis system according to claim 1, the water electrolysis system further manages the supply of renewable energy to the storage battery; the water electrolysis system calculates a storage power command value based on the estimated value of renewable energy power and the electrolysis power command value; The storage power command value is input to a power conversion device of the storage battery. A water electrolysis system comprising:

8. 2. The water electrolysis system according to claim 1, wherein the conversion process is a process of changing a rate of change exceeding the allowable ramp rate to a rate of change equal to or less than the allowable ramp rate.

9. 3. The water electrolysis system according to claim 2, wherein the conversion process is performed based on a gain and an offset.

10. 10. The water electrolysis system according to claim 9, wherein the gain and the offset are calculated using a least squares method.

11. The water electrolysis system according to claim 1, the electrolytic cell is a plurality of electrolytic cells, the water electrolysis system calculates the electrolysis power command value by performing a conversion process based on a different allowable ramp rate for each of the plurality of electrolytic cells; the water electrolysis system interchanges the allowable ramp rates of the plurality of electrolytic cells based on a predetermined criterion; A water electrolysis system comprising:

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