Off-grid hydrogen production system comprehensive efficiency optimization method based on alternating current frequency modulation

Abstract

The invention provides an off-grid hydrogen production system comprehensive efficiency optimization method based on alternating current frequency modulation, and belongs to the technical field of new energy hydrogen production. Comprising the following steps: establishing an electrolytic cell performance evaluation system; obtaining a performance index weight; dividing a working interval by an improved TOPSIS method; aC frequency information transmission and electrolytic cell power adaptive control are carried out. Compared with the prior art, the system state information is transmitted through the frequency signals, communication does not need to be depended on, and the problem that communication faults affect the system stability is solved. In addition, a hydrogen production power self-adaptive control strategy is designed in combination with the working interval of the electrolytic cell, the influence of the working state of the electrolytic cell is considered, and the method is suitable for various weather conditions.

Description

Technical Field

[0001] This invention relates to the field of new energy hydrogen production, and in particular to a method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation. Background Technology

[0002] Hydrogen production from renewable energy sources is an important means of absorbing renewable energy sources such as wind and solar power. In the architecture of renewable energy hydrogen production systems, off-grid renewable energy hydrogen production systems have advantages over grid-connected systems, such as lower equipment investment costs, flexible site selection, environmental friendliness, no need for grid connection, and policy convenience, and represent the future trend of "green hydrogen" development.

[0003] Chinese invention patent application publication (CN119696013A), published on March 25, 2025, entitled "An Off-Grid New Energy Hydrogen Production System," incorporates an AC / DC converter in the new energy unit and a DC / AC converter in the hydrogen production unit. The new energy unit and the hydrogen production unit are connected via a DC line, enabling local consumption of new energy electricity and ensuring the stable operation of the hydrogen production system. However, the effectiveness of this system highly depends on the real-time transmission of system status information via a communication network.

[0004] Chinese invention patent application publication (CN119602359A), published on March 11, 2025, entitled "Coordinated Control Method, Device, Electronic Equipment and Medium for Off-Grid New Energy Hydrogen Production," sets fluctuation ranges by detecting the fluctuation range of the frequency. Different fluctuation ranges employ corresponding coordinated control to adjust the electrolyzer load to ensure stable system operation and improve the utilization rate of new energy. However, while utilizing the adjustment characteristics of the electrolyzer, this method neglects the working characteristics of the electrolyzer itself as a complex piece of equipment.

[0005] Based on the above literature, existing off-grid hydrogen production systems have the following shortcomings: 1. Long-distance transmission is highly dependent on communication. If communication delays or failures occur, the system may become unstable.

[0006] 2. When utilizing the adjustment characteristics of the electrolytic cell, its working characteristics as a complex device are ignored. Summary of the Invention

[0007] The technical problem to be solved by this invention is a problem existing in the prior art. The aim is to provide a method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation. This method, without requiring dedicated communication lines, considers the operating state of the electrolyzer and utilizes its dynamic adjustment characteristics to achieve adaptive power adjustment and overall energy efficiency improvement of the hydrogen production system, ensuring stable and efficient system operation.

[0008] To solve the technical problem of this invention, the technical solution adopted is as follows: A method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation is disclosed. The off-grid hydrogen production system includes an AC bus, N photovoltaic units, 1 energy storage unit, and M hydrogen production units. The N photovoltaic units, 1 energy storage unit, and M hydrogen production units are all coupled to the AC bus via transformers. Each hydrogen production unit includes multiple electrolyzers, and each energy storage unit includes a battery. Includes the following steps: Step 1: Establish an electrolytic cell performance evaluation system. Specifically, conduct t experiments on any given electrolytic cell and record the different input powers. The corresponding performance metrics, and constitute a performance metric set. h is the experiment number, h=1,2,…,t; j is the performance index number, j=1,2,3; the performance index includes: hydrogen production rate index Efficiency indicators Energy consumption indicators ; Step 2, based on the performance index set obtained in Step 1 Construct the decision matrix i = 1, 2, 3; Decision matrix The element components include data indicator values. Optimal reference value for data indicators Data indicator qualification threshold ; Step 3: Assign weights to the three performance metrics using the Delphi and CRITIC methods; Step 4, based on the decision matrix obtained in Step 2 Based on three performance index weights, the electrolytic cell was divided into four working intervals using the TOPSIS method, and any one of these working intervals was denoted as interval 1. n =1,2,3,4 ; Step 5: Based on the working range defined in Step 4, design the adaptive power adjustment control of the hydrogen production unit. The AC bus frequency f is used to transmit the state of charge (SOC) information of the energy storage unit. The hydrogen production unit obtains the current energy storage state by detecting the AC bus frequency f and adaptively adjusts the hydrogen production power in combination with the working range of the electrolyzer.

[0009] Preferably, the implementation process of step 3 is as follows: Step 3.1: Determine subjective weights using the Delphi method. Specifically, multiple experts were invited to score the three performance indicators, and after multiple rounds of feedback, a subjective weight vector for each performance indicator was obtained. ,in The subjective weighting of the hydrogen production rate index. Subjective weighting of efficiency indicators As the subjective weight of the energy consumption index, any one of the three subjective weights is denoted as the subjective weight of the j-th index. ; Step 3.2: Determine the objective weights using the CRITIC method. , ,in As an objective weighting for the hydrogen production rate index, As the objective weight of efficiency indicators, As the objective weight of the energy consumption index, any one of these objective weights is denoted as the objective weight of the j-th index. The objective weight of the j-th indicator The specific calculation process is as follows: Calculate the correlation coefficient matrix k is the performance index number, k=1,2,3, and k≠j. The correlation coefficient between the j-th performance index and the k-th performance index is calculated as follows: ; in, , These are the experimental values ​​of the j-th and k-th performance indicators in the h-th experiment, respectively. , These are the average values ​​of the experimental values ​​of the j-th performance index and the k-th performance index, respectively. Calculate the information content of the j-th indicator The calculation formula is: ; in, Standard deviation; The objective weight of the j-th indicator The formula for calculation is: ; Step 3.3, based on the subjective weights obtained in steps 3.1 and 3.2 and objective weight Combine weights The determination of is expressed as: ; in, As the first weighting coefficient, It is the second weighting coefficient, and .

[0010] Preferably, the implementation process of step 4 is as follows: Step 4.1, use the decision matrix obtained in Step 2. Normalization, constructing a weighted normalization matrix ,in, The elements of the weighted normalized matrix are calculated as follows: ; Step 4.2, based on the weighted normalization matrix obtained in Step 4.1 Calculate data indicator values To the optimal reference value of the indicator European distance Data indicator values Reaching the qualified threshold European distance The calculation formula is as follows: ; ; Step 4.3: Based on the two Euclidean distances obtained in Step 4.2, calculate the comprehensive score of the j-th indicator. Its expression is as follows: ; Step 4.4, Select the comprehensive score The operating point corresponding to the highest value is denoted as the optimal operating point, and the power corresponding to the optimal operating point is denoted as the optimal power (OOP). According to the overall score Divide the working area of ​​the electrolytic cell: interval 80 < ≤85; interval 75 < ≤80; interval 70 < ≤75; interval 65≤ ≤70.

[0011] Preferably, the implementation process of step 5 is as follows: Step 5.1: Design the functional relationship based on the AC frequency f-energy storage state of charge (SOC) mapping. The energy storage side status information is transmitted through the AC frequency f, and its expression is as follows: ; in, For adjustment coefficients, and These are the preset upper and lower limits for the battery's state of charge, respectively. Step 5.2: The hydrogen production unit collects the AC frequency f and adaptively adjusts the hydrogen production power based on the electrolyzer's operating range, as follows: Under sunny conditions: When the AC frequency f is maintained at the rated frequency f of the electrolytic cell n When the hydrogen production power is at its optimal operating power (OOP), the AC frequency f is greater than the rated frequency f of the electrolyzer. n And less than or equal to the clear sky transition frequency f rr At that time, hydrogen production capacity increases, and it operates within the range. When the alternating frequency f is greater than the clear sky transition frequency f rr Furthermore, when the hydrogen production power is less than or equal to the clear-day cutoff frequency f1, the operating range continues to increase. When the AC frequency f continues to increase to the photovoltaic cutoff frequency f2, the output of the photovoltaic unit is limited to the rated power of the electrolytic cell. On rainy or cloudy days: When the AC frequency f is maintained at the rated frequency f of the electrolytic cell n When the hydrogen production power is at its optimal operating power (OOP), the AC frequency f is less than the rated frequency f. n And greater than or equal to the turning frequency f of rainy days rl At that time, hydrogen production capacity decreases, and the system operates within a certain range. When the alternating frequency f is less than the transition frequency f on a cloudy or rainy day rl Furthermore, when the frequency exceeds the standby frequency f3, the hydrogen production power continues to decrease, operating within the range... When the AC frequency f continues to decrease to the standby frequency f3, the electrolytic cell enters the standby state; when the AC frequency f rises to the restart frequency f4, the electrolytic cell enters the working state again.

[0012] Compared with the prior art, the beneficial effects of the present invention include: 1. The system status information is transmitted using frequency signals, eliminating the need for communication and solving the problem of communication failures affecting system stability.

[0013] 2. An adaptive control strategy for hydrogen production power was designed based on the working range of the electrolyzer, taking into account the influence of the working state of the electrolyzer.

[0014] 3. The implementation method is simple and applicable to various weather conditions. Attached Figure Description

[0015] Figure 1 This is a topology diagram of the off-grid hydrogen production system in an embodiment of the present invention.

[0016] Figure 2 This is a flowchart of the division of the working area of ​​the electrolytic cell in this invention.

[0017] Figure 3This is the adaptive power control diagram of the electrolytic cell in this invention.

[0018] Figure 4 This is the power diagram under sunny conditions.

[0019] Figure 5 This is the f-SOC diagram under sunny conditions.

[0020] Figure 6 This is a power diagram under cloudy or rainy weather conditions.

[0021] Figure 7 This is the f-SOC diagram under cloudy or rainy weather conditions.

[0022] Figure 8 This is the control diagram for the energy storage converter. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is a topology diagram of an off-grid hydrogen production system in an embodiment of the present invention. For example... Figure 1 As can be seen, the off-grid hydrogen production system includes an AC bus, N photovoltaic units, 1 energy storage unit, and M hydrogen production units. The N photovoltaic units, 1 energy storage unit, and M hydrogen production units are all coupled to the AC bus via transformers. The hydrogen production unit includes multiple electrolyzers, and the energy storage unit includes batteries.

[0025] Depend on Figure 1 As can be seen, the photovoltaic unit includes photovoltaic panels, a boost converter, an inverter, and a transformer connected in series in sequence; the energy storage unit includes a battery, a bidirectional buck / boost converter, an inverter, and a transformer connected in series in sequence; and the hydrogen production unit includes a transformer, a PWM rectifier, a three-phase interleaved buck converter, and an electrolyzer.

[0026] This invention provides a method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation, comprising the following steps: Step 1: Establish an electrolytic cell performance evaluation system. Specifically, conduct t experiments on any given electrolytic cell and record the different input powers. The corresponding performance metrics, and constitute a performance metric set. h is the experiment number, h=1,2,…,t; j is the performance index number, j=1,2,3; the performance index includes: hydrogen production rate index Efficiency indicators Energy consumption indicators .

[0027] Step 2, based on the performance index set obtained in Step 1 Construct the decision matrix i = 1, 2, 3; Decision matrix The element components include data indicator values. Optimal reference value for data indicators Data indicator qualification threshold .

[0028] Step 3: Assign weights to the three performance metrics using the Delphi and CRITIC methods.

[0029] In this embodiment, step 3 is implemented as follows: Step 3.1: Determine subjective weights using the Delphi method. Specifically, multiple experts were invited to score the three performance indicators, and after multiple rounds of feedback, a subjective weight vector for each performance indicator was obtained. ,in The subjective weighting of the hydrogen production rate index. Subjective weighting of efficiency indicators As the subjective weight of the energy consumption index, any one of the three subjective weights is denoted as the subjective weight of the j-th index. .

[0030] Step 3.2: Determine the objective weights using the CRITIC method. , ,in As an objective weighting for the hydrogen production rate index, As the objective weight of efficiency indicators, As the objective weight of the energy consumption index, any one of these objective weights is denoted as the objective weight of the j-th index. The objective weight of the j-th indicator The specific calculation process is as follows: Calculate the correlation coefficient matrix k is the performance index number, k=1,2,3, and k≠j. The correlation coefficient between the j-th performance index and the k-th performance index is calculated as follows: ; in, , These are the experimental values ​​of the j-th and k-th performance indicators in the h-th experiment, respectively. , These are the average values ​​of the experimental values ​​of the j-th performance index and the k-th performance index, respectively. Calculate the information content of the j-th indicator The calculation formula is: ; in, Standard deviation; The objective weight of the j-th indicator The formula for calculation is: ; Step 3.3, based on the subjective weights obtained in steps 3.1 and 3.2 and objective weight Combine weights The determination of is expressed as: ; in, As the first weighting coefficient, It is the second weighting coefficient, and .

[0031] Step 4, based on the decision matrix obtained in Step 2 Based on three performance index weights, the electrolytic cell was divided into four working intervals using the TOPSIS method, and any one of these working intervals was denoted as interval 1. n =1,2,3,4 .

[0032] In this embodiment, step 4 is implemented as follows: Step 4.1, use the decision matrix obtained in Step 2. Normalization, constructing a weighted normalization matrix ,in, The elements of the weighted normalized matrix are calculated as follows: ; Step 4.2, based on the weighted normalization matrix obtained in Step 4.1 Calculate data indicator values To the optimal reference value of the indicator European distance Data indicator values Reaching the qualified threshold European distance The calculation formula is as follows: ; ; Step 4.3: Based on the two Euclidean distances obtained in Step 4.2, calculate the comprehensive score of the j-th indicator. Its expression is as follows: ; Step 4.4, Select the comprehensive score The operating point corresponding to the highest value is denoted as the optimal operating point, and the power corresponding to the optimal operating point is denoted as the optimal power (OOP). According to the overall score Divide the working area of ​​the electrolytic cell: interval 80 < ≤85; interval 75 < ≤80; interval 70 < ≤75; interval 65≤ ≤70.

[0033] Figure 2 This is a flowchart illustrating the division of the working area of ​​the electrolytic cell in this invention. Figure 2 In this study, the optimal operating point of the electrolyzer was determined and the operating range was divided using the improved TOPSIS method, laying the foundation for the subsequent design of adaptive power control for the electrolyzer.

[0034] Step 5: Based on the working range defined in Step 4, design the adaptive power adjustment control of the hydrogen production unit. The AC bus frequency f is used to transmit the state of charge (SOC) information of the energy storage unit. The hydrogen production unit obtains the current energy storage state by detecting the AC bus frequency f and adaptively adjusts the hydrogen production power in combination with the working range of the electrolyzer.

[0035] In this embodiment, step 5 is implemented as follows: Step 5.1: Design the functional relationship based on the AC frequency f-energy storage state of charge (SOC) mapping. The energy storage side status information is transmitted through the AC frequency f, and its expression is as follows: ; in, For adjustment coefficients, and These are the preset upper and lower limits for the state of charge of the battery, respectively.

[0036] Step 5.2: The hydrogen production unit collects the AC frequency f and adaptively adjusts the hydrogen production power based on the electrolyzer's operating range, as follows: Under sunny conditions: When the AC frequency f is maintained at the rated frequency f of the electrolytic cell n When the hydrogen production power is at its optimal operating power (OOP), the AC frequency f is greater than the rated frequency f of the electrolyzer. n And less than or equal to the clear sky transition frequency f rr At that time, hydrogen production capacity increases, and it operates within the range. When the alternating frequency f is greater than the clear sky transition frequency f rr Furthermore, when the hydrogen production power is less than or equal to the clear-day cutoff frequency f1, the operating range continues to increase. When the AC frequency f continues to increase to the photovoltaic cutoff frequency f2, the output of the photovoltaic unit is limited to the rated power of the electrolytic cell. On rainy or cloudy days: When the AC frequency f is maintained at the rated frequency f of the electrolytic cell n When the hydrogen production power is at its optimal operating power (OOP), the AC frequency f is less than the rated frequency f. n And greater than or equal to the turning frequency f of rainy days rl At that time, hydrogen production capacity decreases, and the system operates within a certain range. When the alternating frequency f is less than the transition frequency f on a cloudy or rainy day rl Furthermore, when the frequency exceeds the standby frequency f3, the hydrogen production power continues to decrease, operating within the range... When the AC frequency f continues to decrease to the standby frequency f3, the electrolytic cell enters the standby state; when the AC frequency f rises to the restart frequency f4, the electrolytic cell enters the working state again.

[0037] In this embodiment, the bidirectional buck-boost converter and inverter in the energy storage unit constitute an energy storage converter. The energy storage converter adopts VF control and collects SOC information and superimposes it onto the frequency signal for transmission. Figure 8 This is the topology diagram of the energy storage converter, where L and R are the filter inductor and filter resistor, respectively. After acquiring the SOC signal, it is processed through... The function superimposes SOC information onto the rated frequency f. n Above, a frequency reference value f is formed. ref The frequency reference value f ref With voltage reference value V ref A PWM modulation signal is generated in a VF constant voltage and constant frequency controller to drive the switching transistor.

[0038] Figure 3 This is the adaptive power control diagram of the electrolytic cell in this invention. Figure 3 In the middle, P el To improve hydrogen production efficiency, adaptive power control is designed based on the collected AC bus frequency information and the power range of the electrolyzer.

[0039] In this example, the following settings are made: , , , , , , f n =50Hz, f rr=50.08Hz, f1=50.1Hz, f2=50.15Hz, f rl =49.92Hz, f3=49.9Hz, f4=49.95Hz. The rated power of the electrolytic cell is 21kW, and the optimal operating point (OOP) is 14.7kW.

[0040] To demonstrate the beneficial effects of the present invention, simulations were performed.

[0041] Figure 4 This is the power diagram under sunny conditions. Figure 5 This is the f-SOC diagram under sunny conditions. Figure 4 In the middle, P pv For photovoltaic power, P el For hydrogen production power, P bat This refers to the battery power. From 0-3 seconds, the photovoltaic power output is approximately 22kW. The State of Charge (SOC) is rising but has not reached the upper limit of 80%, so the SOC function is ineffective, and the system frequency remains at f. n The electrolytic cell operates at OOP (Out of Operation), and the surplus photovoltaic power is absorbed and charged by the battery. At 3 seconds, the SOC (State of Charge) rises to 80%, the SOC function is activated, and the frequency changes from f... n It begins to rise, the electrolytic cell adaptively changes its power consumption and operates at... The surplus photovoltaic power continues to be absorbed and charged by the battery. At 5 seconds, the light intensity increases, the photovoltaic output rises to 28kW, the battery charging power increases, the rate of increase of SOC and f accelerates, and the electrolytic cell power changes more rapidly, but f does not reach f_min. rr Still running When f continues to increase to f rr At that time, the electrolytic cell adjusted the power and operated at As the power regulation range increases, the surplus photovoltaic power is absorbed and charged by the battery. At 7 seconds, f reaches f1, at which point the electrolytic cell has reached its rated power and can no longer consume more power; all surplus power is absorbed by the energy storage. When the frequency reaches f2, the photovoltaic power output is limited to the electrolytic cell's rated power of 21kW, and the battery stops absorbing power.

[0042] Figure 6 This is a power graph under cloudy or rainy weather conditions. Figure 7 This is the f-SOC diagram under cloudy or rainy weather conditions. Initially, the photovoltaic power output is approximately 2.5kW, the electrolyzer is operating at OOP (Out of Operation), and the photovoltaic system and battery work together to power the electrolyzer. The SOC continues to decrease, but has not reached the lower limit of 20%, the SOC function is not activated, and the system frequency remains at f. n When the SOC reaches the lower limit of 20%, the SOC function is activated, and the system frequency f... n The temperature begins to drop, and the electrolytic cell adaptively reduces power consumption. The electrolytic cell operates at... The photovoltaic system and the battery work together to power the electrolyzer. When f decreases to f rl The power adjustment range of the electrolytic cell is increased, and it operates at... To reduce the pressure on energy storage more quickly, the photovoltaic system and battery continue to work together to power the electrolyzer. When the frequency drops to f3, reaching standby conditions, the electrolyzer enters standby mode and stops absorbing power. The photovoltaic output power remains at 2.5kW, fully charging the battery, and the SOC and f are increasing. When the frequency rises to f4, the electrolyzer exits standby mode and resumes operation at the minimum power of 6.3kW, with the photovoltaic system and battery working together to power the electrolyzer. At 14 seconds, the light intensity increases, the photovoltaic output power increases to 7.2kW, the electrolyzer maintains operation at 6.3kW, and the battery transitions from discharging to charging.

[0043] Depend on Figure 4-7 It can be seen that by using frequency signals for information transmission, the power adaptive adjustment and overall energy efficiency improvement of the hydrogen production system can be achieved, ensuring the stable and efficient operation of the system.

Claims

1. A method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation, wherein the off-grid hydrogen production system includes an AC bus, N photovoltaic units, 1 energy storage unit, and M hydrogen production units, wherein the N photovoltaic units, 1 energy storage unit, and M hydrogen production units are all coupled to the AC bus via transformers; each hydrogen production unit includes multiple electrolyzers, and each energy storage unit includes a battery; Its features are, Includes the following steps: Step 1: Establish an electrolytic cell performance evaluation system. Specifically, conduct t experiments on any given electrolytic cell and record the different input powers. The corresponding performance metrics, and constitute a performance metric set. h is the experiment number, h=1,2,…,t; j is the performance index number, j=1,2,3; the performance index includes: hydrogen production rate index Efficiency indicators Energy consumption indicators ; Step 2, based on the performance index set obtained in Step 1 Construct the decision matrix i = 1, 2, 3; Decision matrix The element components, including data indicator values. Optimal reference value for data indicators Data indicator qualification threshold ; Step 3: Assign weights to the three performance metrics using the Delphi and CRITIC methods; Step 4: Based on the decision matrix obtained in Step 2 Based on three performance index weights, the electrolytic cell was divided into four working intervals using the TOPSIS method, and any one of these working intervals was denoted as interval 1. n =1,2,3,4 ; Step 5: Based on the working range defined in Step 4, design the adaptive power adjustment control of the hydrogen production unit. The AC bus frequency f is used to transmit the state of charge (SOC) information of the energy storage unit. The hydrogen production unit obtains the current energy storage state by detecting the AC bus frequency f and adaptively adjusts the hydrogen production power in combination with the working range of the electrolyzer.

2. The method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation according to claim 1, characterized in that, The implementation process of step 3 is as follows: Step 3.1: Determine subjective weights using the Delphi method. Specifically, multiple experts were invited to score the three performance indicators, and after multiple rounds of feedback, a subjective weight vector for each performance indicator was obtained. ,in The subjective weighting of the hydrogen production rate index. Subjective weighting of efficiency indicators As the subjective weight of the energy consumption index, any one of the three subjective weights is denoted as the subjective weight of the j-th index. ; Step 3.2: Determine the objective weights using the CRITIC method. , ,in As an objective weighting for the hydrogen production rate index, As the objective weight of efficiency indicators, As the objective weight of the energy consumption index, any one of these objective weights is denoted as the objective weight of the j-th index. The objective weight of the j-th indicator The specific calculation process is as follows: Calculate the correlation coefficient matrix k is the performance index number, k=1,2,3, and k≠j. The correlation coefficient between the j-th performance index and the k-th performance index is calculated as follows: in, , These are the experimental values ​​of the j-th and k-th performance indicators in the h-th experiment, respectively. , These are the average values ​​of the experimental values ​​of the j-th performance index and the k-th performance index, respectively. Calculate the information content of the j-th indicator The calculation formula is: in, Standard deviation; The objective weight of the j-th indicator The formula for calculation is: Step 3.3, based on the subjective weights obtained in steps 3.1 and 3.2 and objective weight Combine weights The determination of is expressed as: in, As the first weighting coefficient, It is the second weighting coefficient, and .

3. The method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation according to claim 2, characterized in that, The implementation process of step 4 is as follows: Step 4.1, use the decision matrix obtained in Step 2. Normalization, constructing a weighted normalization matrix ,in, The elements of the weighted normalized matrix are calculated as follows: Step 4.2, based on the weighted normalization matrix obtained in Step 4.1 Calculate data indicator values To the optimal reference value of the indicator European distance Data indicator values Reaching the qualified threshold European distance The calculation formula is as follows: Step 4.3: Based on the two Euclidean distances obtained in Step 4.2, calculate the comprehensive score of the j-th indicator. Its expression is as follows: Step 4.4, Select the comprehensive score The operating point corresponding to the highest value is denoted as the optimal operating point, and the power corresponding to the optimal operating point is denoted as the optimal power (OOP). According to the overall score Divide the working area of ​​the electrolytic cell: interval 80 < ≤85; interval 75 < ≤80; interval 70 < ≤75; interval 65≤ ≤70.

4. The method for optimizing the overall efficiency of an off-grid hydrogen production system based on AC frequency modulation according to claim 3, characterized in that, The implementation process of step 5 is as follows: Step 5.1: Design the functional relationship based on the AC frequency f-energy storage state of charge (SOC) mapping. The energy storage side status information is transmitted through the AC frequency f, and its expression is as follows: in, For adjustment coefficients, and These are the preset upper and lower limits for the battery's state of charge, respectively. Step 5.2: The hydrogen production unit collects the AC frequency f and adaptively adjusts the hydrogen production power based on the electrolyzer's operating range, as follows: Under sunny conditions: When the AC frequency f is maintained at the rated frequency f of the electrolytic cell n When the hydrogen production power is at its optimal operating power (OOP), the AC frequency f is greater than the rated frequency f of the electrolyzer. n And less than or equal to the clear sky transition frequency f rr At that time, hydrogen production capacity increases, and it operates within the range. When the alternating frequency f is greater than the clear sky transition frequency f rr Furthermore, when the hydrogen production power is less than or equal to the clear-day cutoff frequency f1, the operating range continues to increase. When the AC frequency f continues to increase to the photovoltaic cutoff frequency f2, the output of the photovoltaic unit is limited to the rated power of the electrolytic cell. On rainy or cloudy days: When the AC frequency f is maintained at the rated frequency f of the electrolytic cell n When the hydrogen production power is at its optimal operating power (OOP), the AC frequency f is less than the rated frequency f. n And greater than or equal to the turning frequency f of rainy days rl At that time, hydrogen production capacity decreases, and the system operates within a certain range. When the alternating frequency f is less than the transition frequency f on a cloudy or rainy day rl Furthermore, when the frequency exceeds the standby frequency f3, the hydrogen production power continues to decrease, operating within the range... When the AC frequency f continues to decrease to the standby frequency f3, the electrolytic cell enters the standby state; when the AC frequency f rises to the restart frequency f4, the electrolytic cell enters the working state again.

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