Optimized operation method of grid-connected wind power hydrogen production system considering operation characteristics of electrolytic cell

Abstract

The invention discloses an optimized operation method of a grid-connected wind power hydrogen production system considering operation characteristics of an electrolytic cell. Firstly, whether a wind power plant meets grid-connected fluctuation requirements is obtained and judged; extracting a wind power output power grid-connected component and a fluctuation component from the original wind power which does not meet the requirement by adopting a wavelet packet decomposition method; an electrolytic cell array and other flexible resources are introduced to stabilize wind power fluctuation, and a PEMEL electrolytic cell start-stop operation strategy is formulated; and finally, constructing an operation constraint model of the wind power hydrogen production system, and realizing optimized operation of the wind power hydrogen production system based on the formulated electrolytic cell start-stop operation strategy. Based on the energy efficiency characteristics of the electrolytic cell, the method can effectively improve the hydrogen production efficiency of the electrolytic cell, thereby improving the overall benefit of the system. The adopted electrolytic cell starting and stopping strategy can be suitable for electrolytic cell array hydrogen production in multiple scenes, and under the condition that the requirement for stabilizing wind power fluctuation is met, the system operation hydrogen production income and the system overall hydrogen production efficiency serve as evaluation indexes of strategy effectiveness.

Description

Technical Field

[0001] The present invention belongs to the field of optimizing the operation of electrolyzers in a wind-hydrogen coupling system, and relates to an optimized operation strategy for a proton exchange membrane electrolyzer (PEMEL) considering improving hydrogen production efficiency under large-scale wind power grid connection. Background Art

[0002] Currently, with the high proportion of new energy power generation connected to the grid, new energy power generation represented by wind power has strong random volatility, which will have many impacts on the power system and seriously threaten the safe and stable operation of the power system. At the same time, due to the unpredictable output power of large-scale wind power grid connection, a large amount of clean energy will be wasted. Therefore, it is of great significance to study how to suppress the fluctuating power of wind power, further improve the consumption of new energy, and stabilize the power of wind power grid connection.

[0003] Based on the fact that hydrogen energy is a green zero-carbon energy and has the advantages of high combustion calorific value and large-scale long-cycle storage. The existing grid-connected wind power hydrogen production system mainly uses an electrolytic hydrogen production device to suppress the fluctuating component of wind power and uses flexible equipment for auxiliary operation. Most of the research on wind power grid-connected hydrogen production technology focuses on suppressing wind power fluctuations and equipment power distribution methods, rather than considering the operation level of electrolyzer equipment. In order to ensure the efficient operation of the electrolyzer and a high level of energy utilization rate, under the conventional electrolyzer start-stop mode, the hydrogen production efficiency is low, and the hydrogen production characteristics of the electrolyzer cannot be fully utilized.

[0004] Reference: [1] Liang Danxi, Zong Zheng, Song Jie, etc. Operation optimization of multi-stack electrolytic hydrogen production system considering efficiency and life [J / OL]. Journal of China Coal Society, 1-11 [2025-01-16]. https: / / doi.org / 10.13225 / j.cnki.jccs.2024.0534. Summary of the Invention

[0005] Aiming at the deficiencies in the existing technology, the present invention provides an optimized operation method for a grid-connected wind power hydrogen production system considering the operation characteristics of the electrolyzer. Based on the energy efficiency characteristics of the electrolyzer, this method can effectively improve the hydrogen production efficiency of the electrolyzer, thereby increasing the overall system benefit. The electrolyzer start-stop strategy adopted by the present invention is applicable to hydrogen production by an electrolyzer array in multiple scenarios. Under the requirement of suppressing wind power fluctuations, the system operation hydrogen production benefit and the overall system hydrogen production efficiency are used as evaluation indicators for the effectiveness of the strategy.

[0006] The following problems in the existing electrolyzer array operation strategy need to be solved urgently:

[0007] 1) The existing operation strategies divide the working conditions too simply, insufficiently consider the fluctuating conditions such as low load and overload, and ignore the impact on the performance and lifespan of the electrolyzer.

[0008] 2) The existing operation strategies cannot balance the improvement of hydrogen production efficiency and the stability of the system. That is, when the hydrogen production efficiency is improved, the overall lifespan of the system is not considered; when the overall lifespan of the system is ensured, the high-efficiency performance of the electrolyzer is wasted.

[0009] The strategy of the present invention:

[0010] In order to ensure the safe and stable integration of wind power into the power grid, corresponding wind power grid connection standards have been formulated when the scale of wind farms reaches a certain level, and clear requirements for the fluctuation of wind power are put forward. According to "GB / T 19963.1-2021, Technical Regulations for Wind Farms Connecting to the Power System", the volatility limit of the grid-connected power of wind farms is related to the installed capacity of wind farms. The specific grid connection requirement standards are shown in Table 1:

[0011] Table 1 National Wind Power Fluctuation Grid Connection Requirements

[0012] Wind farm installed capacity / MW 10 - minute maximum fluctuation / MW 1 - minute maximum fluctuation / MW <30 10 3 30～150 Installed capacity / 3 Installed capacity / 10 >150 50 15

[0013] As a signal processing method, the wavelet packet decomposition method can divide the original signal of the wind farm into a series of small signals with different center frequencies but the same bandwidth, so that the high-frequency and low-frequency components of the original signal can be further analyzed and processed. The schematic diagram of the wavelet packet decomposition method is as Figure 3 shown. In the figure, S is the original signal, S n,0 is the decomposed low-frequency signal, and S n,i is the decomposed high-frequency component.

[0014] An optimized operation method for grid-connected wind power hydrogen production systems considering the operating characteristics of electrolyzers specifically includes the following steps:

[0015] Step 1: Obtain and determine whether the output power of the wind farm meets the requirements of wind power grid connection fluctuations;

[0016] Step 2: Use the wavelet packet decomposition method to extract the grid-connected component and the fluctuation component of the original wind power that does not meet the requirements;

[0017] Step 3: Introduce an electrolyzer array and other flexibility resources to suppress wind power fluctuations;

[0018] Step 4: Establish a polarization characteristic model and a hydrogen production efficiency model of the PEMEL electrolyzer, obtain the energy efficiency curve of the PEMEL electrolyzer, analyze the energy efficiency characteristics of the electrolyzer, and formulate the start-stop operation strategy of the PEMEL electrolyzer;

[0019] Step 5: Use the positive fluctuation high-frequency components obtained from the above Steps 2 and 3 as the electrolysis power source of the wind power hydrogen production system, construct an operation constraint model for the wind power hydrogen production system, and based on the electrolyzer start-stop operation strategy formulated in Step 4, to achieve the optimal operation of the wind power hydrogen production system.

[0020] Furthermore, the specific method of Step 1 is as follows:

[0021] Obtain the 1-minute time-scale output power data P of the wind farm in a day WT That is, the original wind power. Judge whether the output power of the wind farm meets the grid connection fluctuation requirements of 1 minute and 10 minutes. If it meets the requirements, it is directly connected to the grid; if it does not meet the requirements, the original wind power is processed by the wavelet packet decomposition method.

[0022] Furthermore, the specific method of Step 2 is as follows:

[0023] Use the db6 wavelet basis to perform n-layer wavelet packet decomposition on the original wind power. After reconstructing the currently decomposed low-frequency components, judge whether they meet the wind power grid connection requirements. If they meet, the low-frequency components can be used as the grid connection components P O , and the remaining high-frequency components P K Adopt PEMEL electrolyzer and other flexibility resources to absorb and suppress fluctuations, that is: P K = P WT - P O . If it does not meet the requirements, perform n + 1 layer wavelet packet decomposition, and continue to judge after reconstruction until the reconstructed low-frequency components meet the wind power grid connection requirements.

[0024] Furthermore, the specific method of Step 3 is as follows:

[0025] The high-frequency components obtained through wavelet packet decomposition are a quantity that fluctuates around zero, that is, the fluctuation components. Since the electrolyzer can only absorb power, other flexibility resources need to be called for negative power compensation to obtain high-frequency components with only positive fluctuations. At the same time, in order to optimize the operation of the electrolyzer and improve the overall benefit of the system, the corresponding start-stop operation strategy is formulated according to the operation characteristics of the electrolyzer.

[0026] Furthermore, the specific method of Step 4 is as follows:

[0027] The relevant model of the PEMEL electrolyzer is as follows:

[0028] (1) The polarization characteristics of the PEMEL electrolyzer are affected by the reversible voltage, activation overvoltage, ohmic overvoltage, and concentration diffusion voltage. Its polarization characteristic model is as follows:

[0029]

[0030] In the formula: is the electrolysis voltage of the PEMEL electrolyzer; U rev is the reversible voltage, which is the theoretical minimum voltage for water electrolysis; U act is the activation overvoltage; U ohm is the ohmic overvoltage; U diff is the circuit diffusion voltage; T PEMEL is the electrolyzer temperature; R is the ideal gas constant; F is the Faraday constant; are the partial pressures of hydrogen and oxygen; is the activity of water; α an 、α ca are the charge transfer coefficients of the anode and cathode respectively; j is the current density; j 0,an 、j 0,ca are the exchange current densities of the anode and cathode respectively; is the thickness of the electrolyte membrane; σ mem is the conductivity of the membrane; T an 、T ca are the reaction temperatures of the anode and cathode respectively; are the concentrations of oxygen and hydrogen on the anode and cathode electrodes respectively; are the concentrations of oxygen and hydrogen between the membrane and the electrodes respectively.

[0031] (2) PEMEL electrolyzer hydrogen production efficiency model:

[0032]

[0033] In the formula: is the hydrogen production rate of the electrolyzer; η EL is the hydrogen production efficiency of the electrolyzer; I EL is the electrolysis current of the electrolyzer; N c is the number of electrolyzers in series; η F is the Faraday efficiency of the electrolyzer; z is the number of exchanged electrons in the electrolysis reaction, taking 2; F is the Faraday constant; ΔG EL is the Gibbs free energy; P EL is the input power of the electrolyzer.

[0034] Based on the establishment of the PEMEL electrolyzer polarization characteristic model and hydrogen production efficiency model, the energy efficiency curve of the PEMEL electrolyzer is obtained. The energy efficiency curve of the PEMEL electrolyzer is a non-linear curve, and there is only one optimal efficiency point. The overall trend shows that the hydrogen production efficiency first increases and then decreases with the increase of the hydrogen production power. At the beginning, the hydrogen production efficiency increases rapidly with the increase of the hydrogen production power. After the hydrogen production efficiency reaches the peak value, the hydrogen production efficiency decreases slowly because the polarization reaction consumes a large amount of electric energy. Therefore, the rate of the rising part of the hydrogen production efficiency is much faster than that of the falling part. According to the characteristics of this energy efficiency curve, the start-stop operation strategy of the PEMEL electrolyzer is formulated.

[0035] Based on the above characteristics, a start-stop operation strategy for PEMEL electrolyzers is developed. This strategy takes into account various operating conditions of the electrolyzers, such as shutdown, low load, high efficiency, non-high efficiency, rated, and overload. Assume that the total number of electrolyzers in the grid-connected wind power-to-hydrogen system is n, and the total input electrolysis power is P in , the rated power of each electrolyzer is P EL,N , the optimal operating power is P EL,G , the minimum operating power is P EL,min , the maximum operating power is P EL,max , and the actual operating power of the i-th electrolyzer is P EL,i .

[0036] 1) When the hydrogen production power P in < P EL,min , all electrolyzers are shut down, that is, P EL,i = 0, and the total input power is too small to be used directly and is wasted.

[0037] 2) When the hydrogen production power P EL,min ≤ P in < P EL,G , let k = [P in / P EL,min , where [] is the rounding symbol. Then the first k electrolyzers operate at the minimum operating point first, and the remaining power is continued to be borne by the first electrolyzer. That is, P EL,1 = P in - (k = 1)P EL,min , (P EL,i = P EL,min , i ∈ [2, k]).

[0038] 3) When the hydrogen production power P EL,G ≤ P in < nP EL,G , let k = [P in / P EL,G , then the first k electrolyzers operate at the optimal power point first, and the remaining power is continued to be borne by the first electrolyzer. That is, P EL,1 = P in - (k - 1)P EL,G , (P EL,i = P EL,G , i ∈ [2, k]).

[0039] 4) When the hydrogen production power nP EL,G ≤ P in < nP EL,N , all n electrolyzers operate at the same power level, that is, the n electrolyzers divide the total input power equally, (P EL,i = P in / n, i ∈ [1, n]).

[0040] 5) When the hydrogen production power nPEL,N ≤P in <nP EL,max When, let k = [(P in -nP EL,N ) / (P EL,max -P EL,N )], then the first k electrolyzers operate at overload power, and the remaining power is borne by k + 1 electrolyzers. The electrolyzers numbered [k + 2, n] operate at rated power. That is, (P EL,i = P EL,max , i ∈ [1, k]), (P EL,i = P EL,N , i ∈ [k + 2, n]), P EL,k+1 = P in -kP EL,max -(n - k - 1)P EL,N .

[0041] Furthermore, the constraint conditions of the wind power to hydrogen production system operation constraint model are as follows:

[0042] (1) PEMEL electrolyzer output constraint:

[0043]

[0044] In the formula: P PEMEL,N is the rated power of the PEMEL electrolyzer; P PEMEL,t is the hydrogen production power of the electrolyzer at time t; P EL,t is the total input power of the electrolyzer array at time t.

[0045] (2) Power balance constraint:

[0046] P PEMEL,t +P o,t +P loss,t = P WT,t

[0047] In the formula: P O,t is the grid connection power at time t; P loss,t is the curtailed power at time t; P WT,t is the wind power output at time t.

[0048] Furthermore, the method further includes Step Six: establishing two index models of the total hydrogen production revenue and the overall hydrogen production efficiency of the wind power to hydrogen production system to form an evaluation index system to evaluate the effect of the electrolyzer start-stop operation strategy.

[0049] The electrolyzer operation evaluation indexes are as follows:

[0050] (1) Hydrogen production revenue:

[0051]

[0052] In the formula: is the hydrogen production revenue; is the unit selling price of hydrogen; is the hydrogen production at time t; T is the system operation period.

[0053] (2) Overall hydrogen production efficiency of the system:

[0054]

[0055] In the formula: η t is the overall hydrogen production efficiency of the system at time t; P PEMEL,t,i is the hydrogen production power of the i-th PEMEL electrolyzer at time t; P EL,t is the total input power of the PEMEL electrolyzer array at time t; η t,i is the hydrogen production efficiency of the i-th electrolyzer at time t; N is the total number of the electrolyzer array.

[0056] The beneficial effects of the present invention are as follows:

[0057] The grid-connected wind power hydrogen production system processes the original wind power through the wavelet packet decomposition method. The PEMEL electrolyzer absorbs the high-frequency components that cannot be grid-connected after decomposition and reconstruction, effectively suppressing the volatility of the original wind power. At the same time, it improves the consumption capacity of wind power energy, and can produce higher-quality hydrogen with higher efficiency, improving the overall revenue and energy utilization rate of the system. Brief Description of the Drawings

[0058] Figure 1 is the overall thinking framework diagram of the present invention;

[0059] Figure 2 is the energy efficiency curve diagram of the PEMEL electrolyzer;

[0060] Figure 3 is the schematic diagram of wavelet packet decomposition;

[0061] Figure 4 is the simulation case implementation flowchart;

[0062] Figure 5 is the typical daily output power diagram of the wind farm;

[0063] Figure 6 is the diagram of the original wind power and the wavelet packet decomposition power;

[0064] Figure 7 is the diagram of the wind power grid-connected power and the hydrogen production power of the electrolyzer array;

[0065] Figure 8 is the comparison diagram of the hydrogen production efficiency of the electrolysis hydrogen production array. Detailed Embodiment

[0066] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0067] An optimized operation method for a grid-connected wind power hydrogen production system considering the operation characteristics of an electrolyzer specifically includes the following steps:

[0068] Step 1: Obtain and determine whether the output power of the wind farm meets the requirements of wind power grid connection fluctuations;

[0069] Obtain the 1-minute time-scale output power data P of the wind farm in a day WT That is, the original wind power. Determine whether the output power of the wind farm meets the grid connection fluctuation requirements of 1 minute and 10 minutes. If it meets the requirements, it is directly connected to the grid; if it does not meet the requirements, the wavelet packet decomposition method is used to process the original wind power.

[0070] Step 2: Use the wavelet packet decomposition method to extract the grid-connected component and the fluctuation component of the wind power output from the original wind power that does not meet the requirements;

[0071] Use the db6 wavelet basis to perform n-layer wavelet packet decomposition on the original wind power. After reconstructing the currently decomposed low-frequency component, determine whether it meets the wind power grid connection requirements. If it meets, the low-frequency component can be used as the grid-connected component P O , and the remaining high-frequency component P K Use the PEMEL electrolyzer and other flexibility resources for consumption and suppression, that is: P K =P WT -P O . If it does not meet the requirements, perform n + 1 layer wavelet packet decomposition, and continue to judge after reconstruction until the reconstructed low-frequency component meets the wind power grid connection requirements.

[0072] Step 3: Introduce an electrolyzer array and other flexibility resources to suppress wind power fluctuations;

[0073] The high-frequency component obtained through wavelet packet decomposition is a quantity that fluctuates around zero, that is, the fluctuation component. Since the electrolyzer can only absorb power, other flexibility resources such as small generators and gas turbines need to be called for negative power compensation to obtain a high-frequency component with only positive fluctuations. At the same time, in order to optimize the operation of the electrolyzer and improve the overall benefit of the system, a corresponding start-stop operation strategy is formulated according to the operation characteristics of the electrolyzer.

[0074] Step 4: Establish a polarization characteristic model and a hydrogen production efficiency model of the PEMEL electrolyzer, obtain the energy efficiency curve of the PEMEL electrolyzer, analyze the energy efficiency characteristics of the electrolyzer, and formulate a start-stop operation strategy for the PEMEL electrolyzer;

[0075] The relevant models of the PEMEL electrolyzer are as follows:

[0076] (1) The polarization characteristics of the PEMEL electrolyzer are affected by the reversible voltage, activation overvoltage, ohmic overvoltage, and concentration overvoltage in the circuit. The polarization characteristic model is as follows:

[0077]

[0078] Where: is the electrolysis voltage of the PEMEL electrolyzer; U rev is the reversible voltage, which is the theoretical minimum voltage for water electrolysis; U act is the activation overvoltage; U ohm is the ohmic overvoltage; U diff is the concentration overvoltage in the circuit; T PEMEL is the temperature of the electrolyzer; R is the ideal gas constant, which is 8.3144 J / (mol·K); F is the Faraday constant; are the partial pressures of hydrogen and oxygen; is the activity of water, generally taken as 1; α an , α ca are the charge transfer coefficients of the anode and cathode respectively; j is the current density; j 0,an , j 0,ca are the exchange current densities of the anode and cathode respectively; is the thickness of the electrolyte membrane; σ mem is the conductivity of the membrane; T an , T ca are the reaction temperatures of the anode and cathode respectively; are the concentrations of oxygen and hydrogen at the anode and cathode electrodes respectively; are the concentrations of oxygen and hydrogen between the membrane and the electrodes respectively.

[0079] (2) Hydrogen production efficiency model of the PEMEL electrolyzer:

[0080]

[0081] Where: is the hydrogen production rate of the electrolyzer; η EL is the hydrogen production efficiency of the electrolyzer; I EL is the electrolysis current of the electrolyzer; N c is the number of electrolyzers in series; η F is the Faraday efficiency of the electrolyzer; z is the number of exchanged electrons in the electrolysis reaction, taken as 2; F is the Faraday constant; ΔG EL is the Gibbs free energy; P EL is the input power of the electrolyzer.

[0082] Based on the established polarization characteristic model and hydrogen production efficiency model of the PEMEL electrolyzer, the energy efficiency curve of the PEMEL electrolyzer is obtained (as shown in Figure 2 ), observe Figure 2From the curve characteristics, it can be seen that the energy efficiency curve of the PEMEL electrolyzer is a non-linear curve, and there is only one optimal efficiency point. The overall trend shows that the hydrogen production efficiency first increases and then decreases with the increase of the hydrogen production power. At the beginning, the hydrogen production efficiency increases rapidly with the increase of the hydrogen production power. After the hydrogen production efficiency reaches the peak value, the hydrogen production efficiency decreases slowly because the polarization reaction consumes a large amount of electric energy. Therefore, the rate of the rising part of the hydrogen production efficiency is much faster than that of the falling part. According to the characteristics of this energy efficiency curve, the start-stop operation strategy of the PEMEL electrolyzer is formulated.

[0083] Based on the above characteristics, the start-stop operation strategy of the PEMEL electrolyzer is formulated. This strategy takes into account various operating conditions of the electrolyzer, such as shutdown, low load, high efficiency, non-high efficiency, rated, overload, etc. Assume that the total number of electrolyzers in the grid-connected wind power hydrogen production system is n, and the total input electrolysis power is P in , and the rated power of each electrolyzer is P EL,N , the optimal operating power is P EL,G , the minimum operating power is P EL,min , the maximum operating power is P EL,max , and the actual operating power of the i-th electrolyzer is P EL,i .

[0084] 1) When the hydrogen production power P in < P EL,min , all electrolyzers are shut down, that is, P EL,i = 0, and the total input power is too small to directly discard the energy.

[0085] 2) When the hydrogen production power P EL,min ≤ P in < P EL,G , let k = [P in / P EL,min , [] is the rounding symbol. Then the first k electrolyzers operate at the minimum operating point first, and the remaining power is continued to be borne by the first electrolyzer. That is, P EL,1 = P in - (k - 1)P EL,min , (P EL,i = P EL,min , i ∈ [2, k]).

[0086] 3) When the hydrogen production power P EL,G ≤ P in < nP EL,G , let k = [P in / P EL,G , then the first k electrolyzers operate at the optimal power point first, and the remaining power is continued to be borne by the first electrolyzer. That is, P EL,1 = P in - (k - 1)P EL,G , (P EL,i = PEL,G , where \(i\in[2,k]\).

[0087] 4) When the hydrogen production power \(nP\) EL,G \(\leq P\) in \(< nP\) EL,N , all \(n\) electrolyzers operate at the same power level, that is, the \(n\) electrolyzers evenly divide the total input power, (\(P\) EL,i \(=P\) in / n, \(i\in[1,n]\)).

[0088] 5) When the hydrogen production power \(nP\) EL,N \(\leq P\) in \(< nP\) EL,max , let \(k = [(P\) in \(-nP\) EL,N ) / (P\) EL,max \(-P\) EL,N )], then the first \(k\) electrolyzers operate at overload power, and the remaining power is borne by \(k + 1\) electrolyzers. The electrolyzers in the range \([k + 2,n]\) operate at rated power. That is, (\(P\) EL,i \(=P\) EL,max , \(i\in[1,k]\)), (\(P\) EL,i \(=P\) EL,N , \(i\in[k + 2,n]\)), \(P\) EL,k+1 \(=P\) in \(-kP\) EL,max \(-(n - k - 1)P\) EL,N .

[0089] Step Five: Use the positive fluctuation high-frequency components obtained from Steps Two and Three as the electrolysis power source of the wind power hydrogen production system, construct an operating constraint model for the wind power hydrogen production system, and based on the electrolyzer start-stop operation strategy formulated in Step Four, to achieve the optimal operation of the wind power hydrogen production system.

[0090] The constraint conditions are as follows:

[0091] (1) PEMEL electrolyzer output constraint:

[0092] The electrolyzer cannot operate for a long time under overload, otherwise it will damage the internal structure of the electrolyzer and reduce the performance of the electrolyzer. Similarly, the electrolyzer cannot operate for a long time under low load, otherwise there is a risk of explosion of the hydrogen-oxygen mixture generated by the reaction. The specific output constraints are as follows:

[0093]

[0094] In the formula: \(P\) PEMEL,N is the rated power of the PEMEL electrolyzer; \(P\) PEMEL,t is the hydrogen production power of the electrolyzer at time \(t\); \(P\) EL,t is the total input power of the electrolyzer array at time \(t\).

[0095] (2) Power balance constraint:

[0096] P PEMEL,t +P o,t +P loss,t =P WT,t

[0097] Where: P O,t is the grid-connected power at time t; P loss,t is the curtailed power at time t; P WT,t is the wind power output at time t.

[0098] Step Six: Establish two index models, namely the total hydrogen production revenue and the overall hydrogen production efficiency of the wind power to hydrogen system, to form an evaluation index system to evaluate the effect of the start-stop operation strategy of the electrolyzer.

[0099] The evaluation indexes for the electrolyzer operation are as follows:

[0100] (1) Hydrogen production revenue:

[0101]

[0102] Where: is the hydrogen production revenue; is the unit selling price of hydrogen, taking 60 yuan / kg; is the hydrogen production at time t; T is the system operation period.

[0103] (2) Overall hydrogen production efficiency of the system:

[0104]

[0105] Where: η t is the overall hydrogen production efficiency of the system at time t; P PEMEL,t,i is the hydrogen production power of the i-th PEMEL electrolyzer at time t; P EL,t is the total input power of the PEMEL electrolyzer array at time t; η t,i is the hydrogen production efficiency of the i-th electrolyzer at time t; N is the total number of the electrolyzer array.

[0106] To verify the optimized operation strategy of the grid-connected wind power to hydrogen system considering the improvement of hydrogen production efficiency established by the present invention, a simulation case is carried out for simulation. The specific implementation flowchart is as Figure 4 shown, and the implementation process is as follows:

[0107] 1. Operating scenario;

[0108] Obtain the wind power output of a wind farm in a certain area for one year. To more clearly show the operating effect, the wind power data of one day is obtained through k-means mean clustering as the total input power of the system operation, asFigure 5 As shown in the figure, a PEMEL electrolyzer array with a rated power of 700 kW is used to absorb the fluctuating power of wind power, and the specific parameter information is shown in the table.

[0109] Table 2: Equipment parameters of PEMEL electrolyzer

[0110] Parameter Value Rated power (kW) 700 Operating temperature (°C) 80 Hydrogen production pressure (atm) 3 Oxygen production pressure (atm) 3 <![CDATA[Active area A (cm 2 )]]> 100 Proton exchange membrane water content λ 14

[0111] 2. Operating characteristics of the electrolyzer start-stop strategy;

[0112] It can be analyzed from the combination of the strategy of the present invention and the operating characteristics of the electrolyzer that when the electrolyzer operates at low load or overload, it is necessary to let fewer electrolyzers operate in these two abnormal operating states, which ensures the performance of the electrolyzer device. The inconsistency of the monomer operating power in the electrolyzer array will produce a short-board effect, affecting the overall life and stability of the system. When in a stable working condition, all electrolyzers should operate at the same power level, which can not only improve the hydrogen production efficiency, but also ensure the overall life of the electrolyzer array and stabilize the operation of the system.

[0113] 3. Grid-connected wind power hydrogen production strategy verification test system;

[0114] Based on the 75 MW wind power data in a certain place, the present invention configures 19 electrolyzers with a rated power of 700 kW and a flexibility resource. To verify the operation effect of the strategy proposed by the present invention on the electrolyzer array of the system, two operating scheme strategies are used for comparison.

[0115] Strategy 1: Adopt the traditional start-stop method, that is, the electrolyzer array is started to the rated power in sequence.

[0116] Strategy 2: Adopt the electrolyzer operation strategy in reference [1].

[0117] 4. Simulation operation;

[0118] Build a PEMEL electrolyzer polarization characteristic model and a hydrogen production efficiency model on Matlab, analyze its operating characteristics and energy efficiency characteristics, solve and verify using the evaluation indicators in the evaluation method, and output the corresponding indicator results.

[0119] 5. Simulation results

[0120] The original wind power data of this example is obtained by the wavelet packet decomposition method to obtain the grid-connected power of the wind farm, the input power of the electrolytic hydrogen production array, etc., as Figure 6 、 Figure 7 shown. After verification by the simulation results, it is verified that the strategy of the present invention can further improve the hydrogen production benefit and hydrogen production efficiency compared with the other two scheme strategies. The simulation verification results are as follows:

[0121] Table 3: Hydrogen production benefit

[0122] Hydrogen production revenue This strategy: 129,928 yuan Strategy 1: 123,657 yuan Strategy 2: 125,488 yuan

[0123] As can be seen from the above table, the hydrogen production revenue of the electrolytic water hydrogen production system operating with the strategy of the present invention is 129,928 yuan; the hydrogen production revenue of operating with Strategy 1 is 123,657 yuan; the hydrogen production revenue of operating with Strategy 2 is 125,488 yuan. Therefore, compared with the traditional operating strategy and other improved strategies, this strategy has increased the hydrogen production revenue by 5.07% and 3.54% respectively within one day. Therefore, the simulation results show that the strategy of the present invention can effectively improve the energy utilization rate.

[0124] Comparison of hydrogen production efficiency is as Figure 8 shown. As Figure 8 can be seen, the overall hydrogen production efficiency of the electrolytic water hydrogen production system using this strategy of the present invention is the highest, followed by Strategy 1, and the lowest is Strategy 2. Among them, the average hydrogen production efficiency of the electrolyzer operating with this strategy during operation is 80.84%; the average hydrogen production efficiency of the electrolyzer operating with Strategy 1 during operation is 77.62%; the average hydrogen production efficiency of the electrolyzer operating with Strategy 2 during operation is 72.67%. Although the hydrogen production efficiency of Strategy 1 remains at a relatively high level during operation, the amount of discarded electricity is much higher than that of the strategy of the present invention and Strategy 2. Among them, the total hydrogen production power of the system within one day is 352 MW, the discarded air volumes of this strategy and Strategy 2 are both 19.79 kW, while the discarded air volume of Strategy 1 is 129.22 kW. Therefore, the simulation results show that the strategy of the present invention can effectively improve the hydrogen production efficiency of the electrolytic hydrogen production array and the consumption rate of new energy.

Claims

1. A method for optimizing the operation of a grid-connected wind power hydrogen production system taking into account the operating characteristics of an electrolyzer, characterized in that: The following steps are involved: Step 1: Obtain and determine whether the wind farm output power meets the wind power grid-connected fluctuation requirements; Step 2: Using wavelet packet decomposition method to extract the grid-connected component and fluctuation component of wind power output power from the original wind power that does not meet the requirements; Step 3: Introduce electrolyzer arrays and other flexibility resources to smooth out wind power fluctuations; Step 4: Establish the polarization characteristic model and hydrogen production efficiency model of the PEMEL electrolyzer, obtain the energy efficiency curve of the PEMEL electrolyzer, analyze the energy efficiency characteristics of the electrolyzer, and formulate the start-stop operation strategy of the PEMEL electrolyzer; Step 5: The positive fluctuating high-frequency components obtained in the above steps 2 and 3 are used as the electrolysis power source of the wind power hydrogen production system, and the operation constraint model of the wind power hydrogen production system is constructed. Based on the electrolyzer start-stop operation strategy formulated in step 4, the optimized operation of the wind power hydrogen production system is realized.

2. The method for optimizing operation of a grid-connected wind power hydrogen production system taking into account the operation characteristics of an electrolyzer according to claim 1, characterized in that: Step 1: Obtain the 1-minute output power data P of the wind farm for one day WT That is, the original wind power is used to determine whether the output power of the wind farm meets the grid-connected fluctuation requirements of 1 minute and 10 minutes. If it meets the requirements, it is directly connected to the grid; if it does not meet the requirements, the wavelet packet decomposition method is used to process the original wind power.

3. The method for optimizing operation of a grid-connected wind power hydrogen production system taking into account the operation characteristics of an electrolyzer according to claim 1, characterized in that: The specific method of step 2 is as follows: The original wind power is decomposed into n-layer wavelet packets using the db6 wavelet basis. The low-frequency components currently decomposed are reconstructed to determine whether they meet the requirements for wind power grid connection. If they meet the requirements, the low-frequency components can be used as the grid connection components P. O , the remaining high frequency component P K Use PEMEL electrolyzers and other flexible resources to absorb and stabilize, namely: K =P WT -P O If not, perform n+1 layers of wavelet packet decomposition, reconstruct again and continue to judge until the decomposed low-frequency component meets the wind power grid connection requirements after reconstruction.

4. The method for optimizing operation of a grid-connected wind power hydrogen production system taking into account the operation characteristics of an electrolyzer according to claim 1, characterized in that: Step 3: The high-frequency component obtained by wavelet packet decomposition is a quantity that fluctuates around zero, namely the fluctuating component. The electrolyzer can only absorb power, so it is necessary to call on other flexible resources to compensate for the negative power, so as to obtain a high-frequency component with only positive fluctuations. At the same time, in order to optimize the operation of the electrolyzer and improve the overall benefit of the system, corresponding start-stop operation strategies are formulated according to the operating characteristics of the electrolyzer.

5. The method for optimizing operation of a grid-connected wind power hydrogen production system taking into account the operation characteristics of an electrolyzer according to claim 1, characterized in that: Step 4: The specific method is as follows: The relevant models of PEMEL electrolyzer are as follows: (1) The polarization characteristics of the PEMEL electrolyzer are affected by reversible voltage, activation overvoltage, ohmic overvoltage, and circuit diffusion voltage. The polarization characteristics model is as follows: Where: is the electrolysis voltage of the PEMEL electrolyzer; U rev is the reversible voltage, which is the theoretical minimum voltage for water electrolysis; U act is the activation overvoltage; U ohm is the ohmic overvoltage; U diff is the circuit diffusion voltage; T PEMEL is the electrolytic cell temperature; R is the ideal gas constant; F is the Faraday constant; is the partial pressure of hydrogen and oxygen; is the activity of water; α an , α ca are the charge transfer coefficients of the anode and cathode respectively; j is the current density; j 0,an 、j 0,ca are the exchange current densities at the anode and cathode, respectively; is the thickness of the electrolyte membrane; σ mem is the conductivity of the membrane; T an , T ca are the reaction temperatures of the anode and cathode, respectively; are the concentrations of oxygen and hydrogen at the anode and cathode electrodes, respectively; are the oxygen and hydrogen concentrations between the membrane and the electrode, respectively; (2) PEMEL electrolyzer hydrogen production efficiency model: Where: is the hydrogen production rate of the electrolyzer; η EL is the hydrogen production efficiency of the electrolyzer; I EL is the electrolytic current of the electrolytic cell; N c is the number of electrolytic cells connected in series; η F is the Faraday efficiency of the electrolytic cell; z is the number of electrons exchanged in the electrolysis reaction, which is 2; F is the Faraday constant; ΔG EL is Gibbs free energy; P EL input power to the electrolyzer; Based on the establishment of the polarization characteristic model and hydrogen production efficiency model of the PEMEL electrolyzer, the energy efficiency curve of the PEMEL electrolyzer is obtained. The energy efficiency curve of the PEMEL electrolyzer is a nonlinear curve with only one efficiency optimum point. The overall trend shows that the hydrogen production efficiency increases first and then decreases with the increase of hydrogen production power. At the beginning, the hydrogen production efficiency increases rapidly with the increase of hydrogen production power. After the hydrogen production efficiency reaches the peak, the hydrogen production efficiency slowly decreases because the polarization reaction consumes a lot of electricity. Therefore, the rate of the rising part of the hydrogen production efficiency is faster than the rate of the falling part. According to the characteristics of the energy efficiency curve, the start-stop operation strategy of the PEMEL electrolyzer is formulated. Based on the above characteristics, the start-stop operation strategy of the PEMEL electrolyzer is formulated. This strategy takes into account various operating conditions of the electrolyzer, such as shutdown, low load, high efficiency, low efficiency, rated, overload, etc. Assume that the total number of electrolyzers in the grid-connected wind power hydrogen production system is n, and the total input electrolysis power is P in , the rated power of each electrolyzer is P EL,N , the optimal operating power is P EL,G , the minimum operating power is P EL,min , the maximum operating power is P EL,max , the actual operating power of the i-th electrolytic cell is P EL,i ; 1) When the hydrogen production power P in <P EL,min When all electrolytic cells are shut down, that is, P EL,i =0, the total input power is too small and energy is directly discarded; 2) When the hydrogen production power P EL,min ≤P in <P EL,G When k = [P in / P EL,min ], [] is the rounding symbol; then the first k electrolytic cells will run at the minimum operating point, and the remaining power will continue to be borne by the first electrolytic cell; that is, P EL,1 =P in -(k-1)P EL,min , (P EL,i =P EL,min ,i∈[2,k]); 3) When the hydrogen production power P EL,G ≤P in <nP EL,G When k = [P in / P EL,G ], the first k electrolyzers will operate at the optimal power point, and the remaining power will be borne by the first electrolyzer; that is, P EL,1 =P in -(k-1)P EL,G , (P EL,i =P EL,G , i∈[2,k]); 4) When the hydrogen production power nP EL,G ≤P in <nP EL,N When n electrolyzers are operated at the same power level, that is, n electrolyzers share the total input power equally, (P EL,i =P in / n, i∈[1,n]); 5) When the hydrogen production power nP EL,N ≤P in <nP EL,max When k = [(P in -nP EL,N ) / (P EL,max -P EL,N )], the first k electrolytic cells operate at overload power, the remaining power is borne by the k+1 electrolytic cell, and the [k+2,n] electrolytic cells all operate at rated power; that is, (P EL,i =P EL,max , i∈[1,k]),(P EL,i =P EL,N ,i<[k+2,n]),P EL,k+1 =P in -kP EL,max -(nk-1)P EL,N .

6. The method for optimizing operation of a grid-connected wind power hydrogen production system taking into account the operation characteristics of an electrolyzer according to claim 1 or 5, characterized in that: The constraints of the wind power hydrogen production system operation constraint model are as follows: (1) PEMEL electrolyzer output constraints: Where: P PEMEL,N is the rated power of the PEMEL electrolyzer; P PEMEL,t is the hydrogen production power of the electrolyzer at time t; P EL,t is the total input power of the electrolyzer array at time t; (2) Power balance constraints: P PEMEL,t +P o,t +P loss,t =P WT,t Where: P O,t is the grid-connected power at time t; P loss,t is the abandoned power at time t; P WT,t is the wind power output at time t.

7. The method for optimizing operation of a grid-connected wind power hydrogen production system taking into account the operation characteristics of an electrolyzer according to claim 1, characterized in that: It also includes step 6: establishing two index models of total hydrogen production revenue and overall hydrogen production efficiency of the wind power hydrogen production system to form an evaluation index system to evaluate the effect of the start-stop operation strategy of the electrolyzer; The electrolytic cell operation evaluation indicators are as follows: (1) Hydrogen production revenue: Where: For the benefit of hydrogen production; is the unit selling price of hydrogen; is the hydrogen production at time t; T is the system operation cycle; (2) Overall efficiency of hydrogen production of the system: Where: η t is the total hydrogen production efficiency of the system at time t; P PEMEL,t,i is the hydrogen production power of the i-th PEMEL electrolyzer at time t; P EL,t is the total input power of the PEMEL electrolyzer array at time t; η t,i is the hydrogen production efficiency of the i-th electrolyzer at time t; N is the total number of electrolyzer arrays.

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