Modeling method and system of electric-hydrogen-ammonia microgrid considering safety and lifespan degradation

Abstract

The present invention discloses an electric-hydrogen-ammonia microgrid modeling method and system that considers safety and life decay, belonging to the technical field of electric-hydrogen-ammonia microgrid modeling, including: constructing a load management model, an operation model, and safety constraints for the electrolyzer, and introducing an electrolyzer life decay model based on the operating status; constructing a hydrogen energy storage operation model and an electric energy storage operation model, quantifying the impact of hydrogen energy storage on the flexibility of the electrolyzer and the life decay of the electric energy storage; constructing an ammonia production model, a power consumption model, and a thermodynamic model for the electric-to-ammonia process, and designing a life decay model for the electric-to-ammonia equipment; establishing an electric-hydrogen-ammonia microgrid operation model, and generating an optimal operation strategy based on equipment constraints with the goal of minimizing total cost. The present invention adds life decay costs and safety constraints to the electric-hydrogen-ammonia microgrid modeling problem, slowing down the life decay of batteries, hydrogen electrolyzers, and ammonia electrolyzers while reducing the system operating costs, and reducing the safety risks of the microgrid.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric-hydrogen-ammonia microgrid modeling, and particularly relates to an electric-hydrogen-ammonia microgrid modeling method and system that takes safety and life attenuation into consideration. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Electric-hydrogen-ammonia microgrids can improve energy efficiency and system flexibility by integrating renewable energy generation, hydrogen storage, and ammonia synthesis technologies. However, existing technologies have the following problems:

[0004] On the one hand, in terms of equipment life degradation, the lifespan of core equipment in electric-hydrogen-ammonia microgrids, such as electrolyzers and batteries, is affected by multiple factors. During electrolyzer operation, rapid current fluctuations, frequent starts and stops, and operation close to open-circuit voltage can cause mechanical wear and chemical degradation of the membrane, accelerating stack degradation, reducing operating efficiency, and reducing the number of cycles. The aging cost of batteries during frequent charge and discharge cycles is related to the battery investment cost, estimated cycle life, battery cycle life coefficient, ambient temperature, and the battery's reference state of charge. However, existing research often focuses solely on economic optimization when conducting system optimization and scheduling, and insufficiently considers these factors that affect equipment life degradation. This makes it difficult to accurately assess equipment life loss in actual operation, increasing the cost of long-term system operation.

[0005] On the other hand, safety is an important issue that cannot be ignored in electric-hydrogen-ammonia microgrids. As a key device in electric-hydrogen-ammonia microgrids, the safety of electrolyzers is crucial to the stable operation of the entire system.

[0006] From the perspective of power variation, if the rate of change of electrolytic cell power is uncontrolled, excessively drastic changes can damage the equipment. Temperature control is equally critical; excessively high or low temperatures can affect equipment performance and even cause safety issues. Existing research on this aspect lacks a robust quantitative model, making it difficult to accurately assess the safe temperature range of the electrolytic cell under different operating conditions and unable to provide a reliable temperature control strategy for system operation.

[0007] In addition, complex thermal effects occur during electrolyzer operation, with heat energy stored and transferred between the internal reaction zone, surrounding walls, and external air. This involves multiple heat sources and heat transfer paths, including external heating provided by renewable energy and enthalpy changes in the power-to-ammonia (P2A) reaction at the electrode / electrolyte interface. However, existing research often oversimplifies these thermal effects and fails to fully consider the interactions between various thermal factors and their impact on the overall temperature distribution and thermal balance of the system. In the optimized operation of the system, there is a lack of models that can comprehensively reflect these thermal effects, making it difficult to effectively ensure the thermal safety of the electrolyzer and limiting improvements in system operating efficiency. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and to provide an electric-hydrogen-ammonia microgrid modeling method and system that takes into account safety and life decay. Life decay costs and safety constraints are added to the electric-hydrogen-ammonia microgrid modeling problem, thereby reducing the system operating costs while slowing down the life decay of batteries, hydrogen electrolyzers and ammonia electrolyzers, and reducing the safety risks of the microgrid.

[0009] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0010] On the one hand, the technical solution of the present invention provides a modeling method for an electric-hydrogen-ammonia microgrid that takes into account safety and lifespan degradation, including:

[0011] Construct the load management model, operation model and safety constraints of the electrolyzer, and introduce the electrolyzer life attenuation model based on the operating status;

[0012] Construct hydrogen and electric energy storage operation models to quantify the impact of hydrogen storage on electrolyzer flexibility and the lifespan degradation of electric energy storage;

[0013] Construct ammonia production models, power consumption models, and thermodynamic models for the power-to-ammonia process, and design a lifespan attenuation model for power-to-ammonia equipment;

[0014] An electric-hydrogen-ammonia microgrid operation model is established, and the optimal operation strategy is generated based on equipment constraints and the goal of minimizing total cost.

[0015] In at least one embodiment, the load management model of the electrolytic cell includes three states: on, standby, and off. At any one time, the electrolytic cell can only be in one state, and it is prohibited to switch directly from the off state to the standby state. The number of times the electrolytic cell is started and stopped is limited to a set range.

[0016] The electrolyzer operation model includes operating status, power management, current and voltage calculation, output calculation, and operating parameter limitations;

[0017] Safety constraints on the electrolyzer include power ramp rate and temperature limits.

[0018] In at least one embodiment, the electrolytic cell life attenuation model based on the operating state includes: dividing the electrolytic cell operating state into four types: standby, start, fluctuating operation and start-stop. The efficiency attenuation is different in different states. The efficiency attenuation coefficient is small in the standby and start states. The greater the fluctuation in fluctuating operation, the greater the efficiency attenuation. Start-stop has the greatest impact on the life of the electrolytic cell.

[0019] In at least one embodiment, the hydrogen energy storage operation model includes hydrogen tank hydrogen balance, storage level, and compressor power consumption.

[0020] In at least one embodiment, the effect of hydrogen energy storage on electrolyzer flexibility is that hydrogen energy storage affects the flexibility of the electrolyzer stack by affecting the current constraint of a single electrolyzer stack;

[0021] The life decay of electric energy storage is calculated by calculating the battery aging cost caused by charge and discharge cycles.

[0022] In at least one embodiment, the ammonia production model is based on Faraday's law and combines Faraday efficiency to calculate ammonia production. The ammonia production of a single branch is related to multiple parameters. The total ammonia production of the entire electrolyzer module is accumulated by each branch, and the limitations of ammonia production and regulation range are taken into account.

[0023] The power consumption model is specifically the power consumption of the electrolytic cell, which is divided into the power consumption of a single branch and the total power consumption of the entire electrolytic cell. The power consumption of a single branch is related to the reaction enthalpy change and the electrolysis efficiency. The total power consumption of the entire electrolytic cell can be obtained by accumulating the power consumption of each branch.

[0024] The thermodynamic model uses the concepts of thermal resistance and heat capacity and the classical lumped parameter method to process thermal characteristics, providing calculation formulas for the thermal resistance and characteristic length of different parts. Based on Fourier's law, the internal reaction zone and wall heat balance equations and the renewable energy heat supply formula are established to describe their thermal interactions.

[0025] In at least one embodiment, the life decay model of the electric-to-ammonia equipment includes the life decay of the nitrogen generator and the life decay of the electrolyzer; wherein the life decay cost of the nitrogen generator is related to the cost coefficient, the switch status of the electrolyzer branch and the service life of the filter element, and the life decay cost of the electrolyzer is related to the branch cost coefficient, service life, and unit life decay cost at start-up and stop.

[0026] In at least one embodiment, the framework of the electric-hydrogen-ammonia microgrid operation model includes a wind turbine, a photovoltaic generator, a converter, an ammonia-producing electrolyzer, a hydrogen-producing electrolyzer, a boiler, a battery, an ammonia storage tank, a hydrogen storage tank, a pressure swing adsorption device, an electrical load, a thermal load, an ammonia load, a hydrogen load, and is connected to an external power grid.

[0027] In at least one embodiment, the equipment constraints include electrical energy balance constraints, thermal energy balance constraints, power constraints and operating cost constraints; wherein the operating costs include the operation and life degradation costs of hydrogen and ammonia electrolyzers, battery life degradation costs, electricity purchase costs, electricity sales revenue and electrolyzer start-up and shutdown costs.

[0028] On the other hand, the technical solution of the present invention also provides an electric hydrogen ammonia microgrid modeling system that takes safety and life attenuation into consideration, including:

[0029] The electrolyzer modeling module is configured to: construct a load management model and an operation model and safety constraints for the electrolyzer, and introduce an electrolyzer life attenuation model based on the operation status;

[0030] The hydrogen and electric energy storage modeling module is configured to: construct hydrogen and electric energy storage operation models, quantify the impact of hydrogen storage on electrolyzer flexibility and the lifespan degradation of electric energy storage;

[0031] The power-to-ammonia modeling module is configured to: construct an ammonia production model, power consumption model, and thermodynamic model for the power-to-ammonia process, and design a lifespan attenuation model for the power-to-ammonia equipment;

[0032] The microgrid optimization scheduling module is configured to: establish an electric-hydrogen-ammonia microgrid operation model, generate an optimal operation strategy based on equipment constraints and with the goal of minimizing total cost.

[0033] The beneficial effects of the technical solution of the present invention are as follows:

[0034] The present invention incorporates life decay costs and safety constraints into the modeling problem of electric-hydrogen-ammonia microgrids, which reduces the operating costs of the system while slowing down the life decay of batteries, hydrogen electrolyzers, and ammonia electrolyzers, and reduces the safety risks of microgrids. It is expected to further promote the application of electric-hydrogen-ammonia microgrids in the energy field and provide strong support for the further development of renewable energy technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 This is a flow chart of the electric-hydrogen-ammonia microgrid modeling method considering safety and life attenuation disclosed in Example 1 of the present invention;

[0037] Figure 2 It is a schematic diagram of the framework of the electric hydrogen ammonia microgrid operation model in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0039] As introduced in the background technology, the purpose of the present invention is to overcome the shortcomings of the above-mentioned existing technologies and provide an electric-hydrogen-ammonia microgrid modeling method and system that takes into account safety and life decay. Life decay costs and safety constraints are added to the electric-hydrogen-ammonia microgrid modeling problem, which reduces the system operating costs while slowing down the life decay of batteries, hydrogen electrolyzers and ammonia electrolyzers, and reduces the safety risks of the microgrid.

[0040] Example 1

[0041] In a typical embodiment of the present invention, Figure 1 As shown, this embodiment discloses a modeling method for an electric-hydrogen-ammonia microgrid considering safety and life attenuation, comprising the following steps:

[0042] Step 1. Construct the load management model and operation model of the electrolyzer, as well as the safety constraints, and introduce the electrolyzer life attenuation model based on the operation status;

[0043] Step 2. Build hydrogen and electric energy storage operation models to quantify the impact of hydrogen storage on electrolyzer flexibility and the lifespan degradation of electric energy storage.

[0044] Step 3. Construct the ammonia production model, power consumption model, and thermodynamic model of the power-to-ammonia process, and design a lifespan attenuation model for the power-to-ammonia equipment;

[0045] Step 4. Establish an electric-hydrogen-ammonia microgrid operation model and generate the optimal operation strategy based on equipment constraints and the goal of minimizing total cost.

[0046] The above-mentioned electric hydrogen ammonia microgrid modeling method considering safety and life attenuation is described in detail below in conjunction with specific implementation methods.

[0047] Step 1. Construct the load management model, operation model and safety constraints of the electrolyzer, and introduce the electrolyzer life attenuation model based on the operating status.

[0048] In this step, the electrolyzer's load management model includes three states: on, standby, and off. When in the on state, the electrolyzer consumes power and produces hydrogen within a specific load range, with power between the maximum and minimum allowed values. When renewable energy is insufficient, the electrolyzer enters standby or off state. In the standby state, a small amount of power is consumed to maintain stable system temperature and pressure, but no hydrogen is produced.

[0049] Specifically, three binary variables are defined for the three states of the electrolytic cell: open, standby, and closed. and In the open state, , the electrolyzer operates within a specific load range, as shown in formula (1):

[0050] (1);

[0051] Where, is a binary variable representing the electrolytic cell exist Is it in the open state at all times? When , the electrolytic cell is in the open state; and are the maximum and minimum permissible operating power of the electrolyzer stack, respectively; For electrolytic cell exist The actual power consumed at any moment.

[0052] When renewable energy supply is insufficient, the electrolyzer will enter standby mode to save costs ( ) or closed state ( In standby mode, the electrolyzer consumes a certain percentage of power to maintain stable system temperature and pressure, but does not produce hydrogen. Typically, standby power consumption is approximately 1%-5% of the electrolyzer's total load capacity.

[0053] To reduce startup costs, the electrolyzer can only be in one state at any one time and will not switch directly from the off state to the standby state.

[0054] Specifically, the electrolytic cell can only be in one state at any time, as shown in formula (2):

[0055] (2);

[0056] The start and stop states of the electrolytic cell are shown in Equations (3) and (4):

[0057] (3);

[0058] (4);

[0059] Where, is a binary variable, when When , the electrolyzer starts; is a binary variable, when When , the electrolytic cell stops.

[0060] The electrolyzer will not switch from the shutdown state to the standby state, thereby reducing the startup cost, which is constrained by formula (5):

[0061] (5);

[0062] In order to reduce the operating cost of the electrolytic cell and extend its service life, the maximum number of times the electrolytic cell is started and shut down is limited to a certain range, as shown in Equations (6) and (7):

[0063] (6);

[0064] (7);

[0065] Where, and The maximum number of times the electrolyzer is started and stopped, respectively.

[0066] Furthermore, the start-up and stop costs of the electrolyzer are shown in Equations (8) and (9), respectively:

[0067] (8);

[0068] (9);

[0069] Where, For electrolytic cell exist Startup costs at the moment; For electrolytic cell Single startup cost; For electrolytic cell exist Stopping cost at the moment; For electrolytic cell Single stop cost.

[0070] In this step, the electrolyzer's operating model includes operating status, power management, current and voltage calculations, output calculations, and operating parameter limits. Regarding power management, the electrolyzer's actual power consumption consists of rated power and extended power, with range constraints set for each of these two power levels. It also limits the continuous use time and cumulative usage of the extended power. The electrolyzer's operating model provides calculations for stack current, voltage, and hydrogen output. It also sets upper and lower limits for the operating parameters of the electrolyzer stack and individual electrolyzers. It also takes into account the nonlinear production characteristics of current-based production, and uses different overvoltage segments to reflect the operating conditions under different variable current densities.

[0071] Larger proton exchange membrane (PEM) electrolyzer stacks offer a wider operating range and faster response, enabling them to be used for extended operation, thus increasing their potential to provide grid support services. Extended operation of modular PEM stacks is attributed to their electrochemical properties. These systems allow for a certain degree of overload, a feature that can be used to absorb excess power from renewable energy power systems, thereby facilitating system integration. However, care must be taken to avoid the rebound effect caused by over-extended operation. In this step, a model of an extended electrochemical stack suitable for operation in renewable energy power systems is employed.

[0072] The actual power consumption of the electrolyzer consists of the rated power and the extended power. The rated power reflects the power demand under normal operation, while the extended power reflects the additional power that the electrolyzer can consume under specific circumstances (such as responding to fluctuations in renewable energy) to better adapt to changes in the system, as shown in formula (10):

[0073] (10);

[0074] Where, For electrolytic cell Actual power consumption; For electrolytic cell Rated power; For electrolytic cell of extended power.

[0075] In order to ensure that the electrolyzer operates under safe and stable conditions and avoid problems such as failure to work properly due to too low power or equipment damage caused by too high power, the rated power of the electrolyzer should be set. Restricted to a certain range, as shown in formula (11):

[0076] (11);

[0077] Where, is the minimum stack power; is the rated stack power.

[0078] Furthermore, the extended power range constraint formula is shown in formula (12):

[0079] (12);

[0080] Where, is the rated stack power; It is a proportional coefficient that controls the upper limit of the expansion power to prevent damage to the equipment caused by excessive expansion power. It also provides a constraint basis for the system to reasonably allocate power under different operating conditions.

[0081] The electrolyzer cannot be in the extended power operation state for two consecutive time intervals. It is necessary to limit the continuous use time of the extended power to avoid affecting the equipment life and system stability due to long-term excessive extended operation. The extended power time interval constraint formula is shown in Equation (13):

[0082] (13);

[0083] Where, express t +2 moments of expansion power.

[0084] Furthermore, the cumulative expansion power constraint controls the degree of expansion power usage as a whole, ensuring that the electrolyzer does not rely too much on expansion power during long-term operation, as shown in Equation (14):

[0085] (14);

[0086] Where, for The percentage of total overload in the hour.

[0087] The calculation of stack current is shown in formula (15):

[0088] (15);

[0089] Where, For electrolytic cell exist Time stack current; For electrolytic cell exist Stack voltage at all times.

[0090] The calculation of the stack voltage is shown in formula (16):

[0091] (16);

[0092] Where, is the number of individual electrolyzers in the electrolyzer stack; is the voltage of a single electrolytic cell.

[0093] The operating parameter constraints of the electrolyzer stack and a single electrolyzer are shown in Equation (17):

[0094] (17);

[0095] Where, Operating parameters for electrolyzer stacks and individual electrolyzers (e.g., current, voltage, hydrogen production, and equipment capacity); and represent the maximum and minimum values ​​of these parameters respectively.

[0096] The electrolytic cell model takes into account the nonlinear production characteristics based on current and can be used to construct an accurate operation model of the electrolytic cell under different ranges. It describes the operation of the electrolytic cell under different variable current densities. Different variable current densities are reflected in various overvoltage sections of the electrolytic cell, as shown in Equation (18):

[0097] (18);

[0098] Where, operating voltage for the electrolyzer; The minimum open circuit voltage required to produce hydrogen; is the voltage associated with electrode activation for proton transfer; The ohmic voltage due to resistance and proton exchange; It is the mass transfer concentration voltage and plays a key role when operating at higher or variable current density.

[0099] The calculation of open circuit voltage is shown in formula (19):

[0100] (19);

[0101] Where, is the Gibbs free energy change; is the Faraday constant; is the electrolytic cell temperature; 、 and are the partial pressures of hydrogen, oxygen, and water, respectively.

[0102] The calculation of the electrode activation voltage is shown in formula (20):

[0103] (20)

[0104] Where, and are the charge transfer coefficients of the anode and cathode, respectively; is the current density; and are the exchange current densities at the anode and cathode, respectively.

[0105] The calculation of ohmic voltage is shown in formula (21):

[0106] (twenty one);

[0107] Where, is the electrolytic cell resistance.

[0108] The calculation of mass transfer concentration voltage is shown in formula (22):

[0109] (twenty two);

[0110] Where, is the limiting current density.

[0111] The calculation formula for hydrogen production is shown in formula (23):

[0112] (twenty three);

[0113] Where, is the hydrogen production of the electrolyzer; is the Faraday coefficient; is the molar mass of hydrogen; is the Faraday constant.

[0114] In this step, the electrolyzer's safety constraints include limits on power change rate and temperature. The power change rate is limited to specific upper and lower limits to prevent drastic power changes from damaging the equipment. Regarding temperature, a formula is used to constrain the electrolyzer's temperature to prevent excessively high or low temperatures from affecting equipment performance and causing safety issues.

[0115] Specifically, the electrolytic cell power change rate limit is shown in formula (24):

[0116] (twenty four);

[0117] Where, is the lower limit of the rate of change of electrolytic cell power; It is the upper limit of the rate of change of electrolytic cell power.

[0118] The temperature limit of the electrolytic cell is shown in formula (25):

[0119] (25);

[0120] (26);

[0121] (27);

[0122] Where, is the electrolytic cell temperature; is the heat power lost by the electrolytic cell; is the heat power output outside the system; is the lumped heat capacity of the electrolytic cell; is the external temperature of the electrolytic cell; is the thermal resistance of the electrolytic cell; and are the upper and lower limits of the electrolytic cell temperature respectively.

[0123] The life attenuation model of the electrolytic cell divides the operating states of the electrolytic cell into four types: standby, start, fluctuating operation, and start-stop. The efficiency attenuation varies in different states. The efficiency attenuation coefficient is small in the standby and start states. The greater the fluctuation in fluctuating operation, the greater the efficiency attenuation. Start-stop has the greatest impact on the life of the electrolytic cell.

[0124] Specifically, the electrolytic cell life attenuation model is shown in Equations (28) to (34):

[0125] (28);

[0126] (29);

[0127] (30);

[0128] (31);

[0129] (32);

[0130] (33);

[0131] (34);

[0132] Where, 、 、 and They are the electrolyzer efficiency attenuation in standby state, on state, fluctuating operation and start-stop; 、 、 and These are the electrolyzer efficiency attenuation coefficients in standby state, on-state, fluctuating operation, and start-stop; and They are electrolyzer efficiency decay and equivalent life decay respectively; is the rated operating life of the electrolyzer; and are the rated efficiency and the limiting efficiency of the electrolyzer respectively; is the rated efficiency attenuation coefficient of the electrolyzer.

[0133] In the electrolytic cell life attenuation model, the life loss cost of the electrolytic cell is shown in formula (35):

[0134] (35);

[0135] Where, The cost of electrolytic cell life loss; is the configuration cost of the electrolyzer.

[0136] Step 2. Construct hydrogen energy storage operation models and electric energy storage operation models to quantify the impact of hydrogen energy storage on electrolyzer flexibility and the life degradation of electric energy storage.

[0137] In this step, the hydrogen energy storage operation model includes the hydrogen balance of the hydrogen storage tank, the storage level, and the compressor power consumption. The hydrogen balance equation for the hydrogen storage tank describes the relationship between the amount of hydrogen flowing into and out of the hydrogen storage tank. The storage level equation reflects the change in the hydrogen storage level of the hydrogen storage tank at adjacent moments. Storage level constraints are also set, specifying the maximum and minimum storage levels. The hydrogen compressor power consumption formula is used to calculate the power consumption of the compressor during operation.

[0138] The balance equation of hydrogen in the hydrogen storage tank is shown in formula (36):

[0139] (36);

[0140] Where, It is a single electrolytic cell; is a collection of electrolytic cells; is the amount of hydrogen released from the hydrogen storage tank; The amount of hydrogen stored in the hydrogen storage tank.

[0141] The storage level equation of the hydrogen storage tank is shown in formula (37):

[0142] (37);

[0143] Where, for The storage level of hydrogen storage tanks at all times; for The storage level of the hydrogen storage tank at all times.

[0144] The constraints on the storage level of the hydrogen storage tank are shown in formula (38):

[0145] (38);

[0146] Where, and are the maximum and minimum storage levels of the hydrogen storage tank, respectively.

[0147] The power consumption of the hydrogen compressor is shown in formula (39):

[0148] (39);

[0149] Where, is the power consumption of the compressor; is a parameter related to hydrogen flow rate; is the gas constant; is the compressor inlet temperature; is the adiabatic index; Compressor efficiency ; is the outlet pressure of the hydrogen storage tank; is the inlet pressure of the hydrogen storage tank.

[0150] The impact of hydrogen energy storage on the flexibility of electrolyzer stacks. Hydrogen energy storage affects the flexibility of electrolyzer stacks by affecting the current constraints of a single electrolyzer stack.

[0151] The constraints on the current of a single electrolytic cell stack are shown in Equation (40):

[0152] (40);

[0153] Where, is the Faraday efficiency; is the number of electrolytic cell stacks; is the molar mass of hydrogen.

[0154] The operation model of electric energy storage includes charging and discharging power, state of charge update and state of charge limit.

[0155] The charging and discharging formulas for electric energy storage are shown in Equations (41) and (42):

[0156] (41);

[0157] (42);

[0158] Where, and are the charging power and discharging power of the electric energy storage respectively; It is the maximum charge and discharge power of the energy storage.

[0159] The charge state update formula of the electric energy storage is shown in formula (43):

[0160] (43);

[0161] Where, For electric energy storage State of charge at the moment; For electric energy storage State of charge at the moment; and are the charging efficiency and discharging efficiency of electric energy storage, respectively.

[0162] The limiting formula for the state of charge of the energy storage is shown in formula (44):

[0163] (44);

[0164] Where, and are the minimum and maximum states of charge for the energy storage, respectively.

[0165] The energy storage life attenuation model calculates the battery aging cost caused by charge and discharge cycles. The model believes that the battery aging cost is related to the battery investment cost and estimated cycle life. It is also affected by the battery cycle life coefficient, ambient temperature and battery reference state of charge.

[0166] Specifically, the battery aging cost caused by charge and discharge cycles is shown in formula (45):

[0167] (45);

[0168] Where, The investment cost of the battery; is the estimated cycle life of the battery; 、 、 and is the battery cycle life coefficient; is the ambient temperature; is the reference state of charge of the battery.

[0169] Step 3. Construct the ammonia production model, power consumption model and thermodynamic model of the power-to-ammonia process, and design the life attenuation model of the power-to-ammonia equipment.

[0170] In this step, the ammonia production model specifically refers to the P2A (power-to-ammonia) ammonia synthesis process performed in an electrolyzer with specific electrochemical cells, consisting of multiple electrolytic cells connected in series and parallel to form an electrolyzer module. The ammonia production model calculates ammonia production based on Faraday's law and Faraday efficiency. The ammonia production of a single branch is related to multiple parameters. The total ammonia production of the entire electrolyzer module is the sum of all branches, taking into account the limitations of ammonia production and regulation range.

[0171] P2A refers to the process of synthesizing ammonia in an electrolyzer powered by renewable energy. The overall reaction in aqueous solution is: , which indicates that in this process, water and nitrogen react to produce ammonia and oxygen under specific conditions, which is the core chemical reaction of the entire P2A technology.

[0172] In this step, the Electrochemical cells with mixed conductive electrolytes and Pt / C electrodes have high ammonia production at room temperature and atmospheric pressure, better meeting the needs of research and practical applications. At the anode, water decomposes to produce oxygen, hydrogen ions, and electrons. At the cathode, hydrogen ions are transferred through a Nafion membrane and react with nitrogen to produce ammonia. To ensure sufficient ammonia production, multiple duplicate electrolytic cells are assembled in the center of a large stack. A certain number of electrolytic cells are first connected in series to form a branch, and then these branches are connected in parallel to form the entire electrolyzer module. This structural design helps improve ammonia production efficiency and overall performance.

[0173] According to Faraday's law, under ideal conditions, the yield of ammonia is theoretically roughly proportional to the current density. In actual electrolysis processes, the operating current density, temperature, and pressure will affect parasitic current and cross-permeation. Parasitic current refers to additional current that is not used for the target electrochemical reaction. It consumes energy but does not produce useful products; cross-permeation refers to the undesirable permeation of different substances in the electrode or electrolyte, which will affect the actual yield of ammonia. Therefore, when calculating the ammonia yield of the electrolyzer, one cannot rely solely on Faraday's law, but also needs to consider the Faraday efficiency. In the P2A process, the Faraday efficiency is measured through a large number of electrolysis experiments. In the experiment, known amounts of water and nitrogen react in a stoichiometric ratio to convert into ammonia, and the Faraday efficiency is determined by measuring the current passing through.

[0174] Based on Faraday's law and combined with the efficiency factors in the actual electrolysis process, the ammonia production of a single branch in a specific time period is obtained as shown in formula (46):

[0175] (46);

[0176] Where, For the Time period Ammonia production per branch; is the number of electrolytic cells connected in series; For the Faradaic efficiency for a time period; For the Time period The molar volume of ammonia in each branch; For the Time period The current flowing through each branch; For the The duration of the time period; The number of electrons required to transfer to form one mole of ammonia. The chemical equation for the formation of ammonia from nitrogen gas and hydrogen ions is: It can be seen that 3 moles of electrons need to be transferred to generate 1 mole of ammonia, that is, .

[0177] Under certain conditions, the relationship between the molar volume of a gas and temperature is shown in Equation (47):

[0178] (47);

[0179] Where, For the Time period The molar volume of ammonia in each branch; is the molar volume in different states; For the Temperature during a time period; is the temperature in another state; is a constant.

[0180] The limiting condition of ammonia production in electrolyzer is shown in formula (48):

[0181] (48);

[0182] Where, Maximum ammonia production.

[0183] The ammonia production regulation capability is shown in formula (49):

[0184] (49);

[0185] Where, It is the maximum adjustment range of ammonia production of the electrolyzer branch in adjacent time periods.

[0186] In the The total ammonia production of the entire electrolyzer module in each time period is shown in formula (50):

[0187] (50)

[0188] Where, For the Total ammonia production of the entire electrolyzer module for each time period; is the number of electrolytic cell branches connected in parallel.

[0189] The operating constraints of ammonia storage tanks are similar to those of hydrogen storage tanks.

[0190] In this step, the power consumption model actually represents the electrolyzer's power consumption. This power consumption is calculated for both individual branches and the entire electrolyzer. The power consumption of each branch is related to the reaction enthalpy change and electrolysis efficiency. The total power consumption for the entire electrolyzer is calculated by summing the power consumption of each branch. In the P2A process, nitrogen is separated from air using pressure swing adsorption (PSA) technology. Power consumption is calculated based on the power required to produce a unit volume of nitrogen and the rated gas output. Furthermore, a mathematical model is constructed by piecewise linear fitting of relevant efficiency data at different temperatures.

[0191] The power consumption of the electrolyzer in the power-to-ammonia (P2A) process is shown in Equation (51):

[0192] (51);

[0193] Where, For the Time period Power consumption in each branch; is the enthalpy change of the reaction; For the The electrolysis efficiency in a certain period of time.

[0194] The total power consumption of the entire electrolytic cell is shown in formula (52):

[0195] (52);

[0196] Where, For the The total power consumption of the entire electrolyzer during a certain period of time.

[0197] In the P2A process, although liquid water is abundant, the nitrogen involved in the reaction needs to be separated from the air. Currently, pressure swing adsorption (PSA) technology is widely used in nitrogen generators and is considered the preferred method for recovering high-purity nitrogen today. This is because PSA technology has the advantages of high efficiency, low cost, and long service life. The net cost of producing nitrogen using a nitrogen generator is significantly lower than that of using bottled or liquefied nitrogen. Moreover, the output of the nitrogen generator can usually be adjusted according to the gas consumption of the electrolyzer to achieve a good match between supply and demand.

[0198] The calculation formula for the power consumption of the nitrogen generator is shown in formula (53):

[0199] (53);

[0200] Where, For the Power consumption of nitrogen generator in each time period; The electricity required to produce a unit volume of nitrogen; Rated gas output of the nitrogen generator.

[0201] Temperature is an important factor affecting the rate and process of chemical reactions. and The data are fitted with piecewise linear fitting to obtain the mathematical model shown in Equation (54).

[0202] (54);

[0203] Where, For the Temperature during a time period; and are the lower and upper limits of temperature respectively; and is the temperature segmentation point; 、 and are the slopes of the efficiency changing with temperature in the three temperature sub-ranges.

[0204] The thermodynamic model of the electrolyzer focuses on the P2A physical electrolysis environment, which consists of the surrounding walls, the reaction zone, and the external air. Heat energy is transferred and stored in each of these components. The model leverages the concepts of thermal resistance and heat capacity, employing a classical lumped parameter approach to address thermal characteristics, providing formulas for calculating the thermal resistance and characteristic length of different components. Based on Fourier's law, heat balance equations for the internal reaction zone and walls, as well as a formula for renewable energy heat supply, are established to describe their thermal interactions.

[0205] The P2A physical electrolysis environment primarily consists of the surrounding walls, the reaction zone, and the external air. These components store and transfer heat energy in various ways. This entire environment is affected by all thermal variations within the system, including external heating from renewable energy sources and enthalpy changes in the P2A reaction at the cathode / electrolyte and anode / electrolyte interfaces. This means that when studying the electrolysis process, it is necessary to comprehensively consider the impact of these various heat sources and heat transfer pathways on the overall system temperature distribution and thermal balance.

[0206] To describe the heat storage and heat transfer performance of various parts of the electrolytic cell, the concepts of thermal resistance and heat capacitance are employed. The temperature, heat storage, and heat transfer characteristics of the electrolytic region and surrounding walls are treated using the classic lumped parameter method. The electrolytic cell's structural and material properties are assumed to be uniform and constant in all directions, allowing its thermodynamic parameters to be spatially averaged along the cell.

[0207] Thermal resistance measures the resistance to heat transfer. Wall nodes are connected to interior and exterior nodes via thermal resistances to represent external and internal convective / conductive heat transfer. Under laminar flow conditions, thermal resistance is calculated as a function of the Nusselt number, characteristic length, and the thermal conductivities of the internal electrolyte, wall, and air.

[0208] The thermal resistance between the internal reaction zone and the wall is calculated as shown in Equation (55):

[0209] (55);

[0210] Where, is the characteristic length of the internal electrolyte; is the Nusselt number of the internal electrolyte; is the thermal conductivity of the internal electrolyte.

[0211] The thermal resistance between the wall and the external environment is calculated as shown in formula (56):

[0212] (56)

[0213] Where, is the characteristic length of the internal electrolyte; is the Nusselt number of the internal electrolyte; is the thermal conductivity of the internal electrolyte.

[0214] The thermal resistance between the wall and the outside air is calculated as shown in formula (57):

[0215] (57);

[0216] Where, and are the dimensional parameters related to heat transfer (such as the width and length of the wall); is the thermal conductivity of air.

[0217] The calculation of characteristic length is shown in Equation (58) and Equation (59):

[0218] (58);

[0219] (59);

[0220] Where, and are geometric parameters related to the internal electrolyte (such as width and height); and are geometric parameters associated with the wall (such as width and height).

[0221] The present invention focuses on the thermodynamic model of the electrolytic cell during the P2A process and describes the thermal interactions between the internal reaction zone, the wall and the external environment based on Fourier's law.

[0222] The heat balance equation of the internal reaction zone is shown in Equation (60):

[0223] (60);

[0224] Where, is the heat capacity of the internal electrolyte; for heat from renewable energy sources; 、 and are the temperatures of the wall, internal reaction zone and external environment, respectively.

[0225] The heat balance equation of the wall is shown in Equation (61):

[0226] (61);

[0227] Where, is the heat capacity of the wall.

[0228] The heat provided by renewable energy is shown in formula (62):

[0229] (62);

[0230] Where, is the efficiency coefficient; For the Time period The power of electricity generated by renewable energy in each branch.

[0231] Furthermore, the life decay model of the electro-ammonia equipment includes the life decay of the nitrogen generator and the life decay of the electrolyzer. The life decay cost of the nitrogen generator is related to the cost coefficient, the switch status of the electrolyzer branch and the service life of the filter element. The life decay cost of the electrolyzer is related to the branch cost coefficient, service life, and the unit life decay cost at start-up and stop.

[0232] A P2A system typically consists of a nitrogen generator, an electrolyzer, and an ammonia storage tank. Typically, a P2A system operates to a given set point throughout the dispatch cycle. However, the system's daily operation and frequent on-and-off cycles can significantly reduce its service life and further impact dispatch performance. The primary degradation issues arise from the electrolyzer and nitrogen generator.

[0233] The nitrogen generator life attenuation cost modeling is shown in formula (63):

[0234] (63);

[0235] Where, is the life decay cost of the nitrogen generator; is a cost factor associated with the nitrogen generator; is a binary variable indicating the switch status of the electrolytic cell branch; The service life of the filter element.

[0236] Electrolyzer life and stack performance degrade more rapidly under the influence of rapid current fluctuations, frequent starts and stops, and operation near open-circuit voltage. Prolonged operation at excessively high / low or fluctuating currents / voltages can cause mechanical wear and chemical degradation of the electrolyzer membrane. Furthermore, frequent starts and stops of the electrolyzer further accelerate stack degradation, leading to reduced operating efficiency and fewer cycles.

[0237] The electrolytic cell life attenuation cost model is shown in Equation (64):

[0238] (64);

[0239] Where, For the Cost coefficients associated with each electrolyzer branch; is the service life of the electrolytic cell; and are the unit life decay costs incurred when the electrolyzer branches are started and stopped, respectively.

[0240] Step 4. Establish an electric-hydrogen-ammonia microgrid operation model and generate the optimal operation strategy based on equipment constraints and the goal of minimizing total cost.

[0241] In this step, the electric hydrogen ammonia microgrid model framework is as follows Figure 2 As shown, it includes wind turbines, photovoltaic generators, converters, ammonia-producing electrolyzers, hydrogen-producing electrolyzers, boilers, batteries, ammonia storage tanks, hydrogen storage tanks, pressure swing adsorption devices, electrical loads, thermal loads, ammonia loads, hydrogen loads and is connected to the external power grid. The equipment constraints take into account the power balance constraints, thermal balance constraints, power constraints and operating cost constraints. Among them, the operating costs include the operation and life degradation costs of hydrogen production and ammonia production electrolyzers, the battery life degradation costs, the electricity purchase costs and electricity sales income and the electrolyzer start-up and shutdown costs.

[0242] Various multi-energy storage and converters in electric-hydrogen-ammonia microgrids provide opportunities to improve the utilization of renewable energy and the economic efficiency of system operation by providing a certain degree of energy supply flexibility and synergy.

[0243] The power balance in the electric hydrogen ammonia microgrid is shown in formula (65):

[0244] (65);

[0245] Where, is the power of the wind turbine; is the power of the photovoltaic generator; and are the power purchased and sold by the microgrid to the large grid; The power consumed for hydrogen production; Power consumed in producing ammonia; The power consumed by the boiler.

[0246] The power consumed by hydrogen production is shown in formula (66):

[0247] (66);

[0248] Where, is the auxiliary power of the electrolyzer.

[0249] The power consumed in ammonia production is shown in formula (67):

[0250] (67);

[0251] The interactive power constraints between the microgrid and the large grid are shown in Equations (68) to (70):

[0252] (68);

[0253] (69);

[0254] (70);

[0255] Where, and It is a binary variable, which is equal to 1 and indicates that the microgrid is in the state of buying or selling electricity from the large grid; and are the maximum power of electricity purchased and sold respectively.

[0256] The power constraint of the boiler is shown in formula (71):

[0257] (71);

[0258] Where, and are the minimum and maximum boiler power respectively.

[0259] The thermal energy balance in the electric hydrogen ammonia microgrid is shown in Equation (72):

[0260] (72);

[0261] Where, is the heat generated by the boiler; is the power of the heat load.

[0262] The heat generated by the boiler is shown in formula (73):

[0263] (73);

[0264] Where, is the boiler heat production efficiency.

[0265] The operating costs of the hydrogen-ammonia electrolyzer include the operating costs and life-degradation costs of the hydrogen and ammonia electrolyzers, the battery life-degradation costs, the cost of purchasing electricity from the grid, the revenue from selling electricity, and the start-up and shutdown costs of the electrolyzer. The operating costs of the hydrogen-ammonia electrolyzer are shown in Equation (74):

[0266] (74);

[0267] Where, and They are the unit power operating costs of hydrogen production electrolyzer and ammonia production electrolyzer; It is the price at which the microgrid purchases and sells electricity to the main grid.

[0268] Example 2

[0269] In a typical embodiment of the present invention, this embodiment discloses an electric-hydrogen-ammonia microgrid modeling system that takes safety and lifespan degradation into consideration, including:

[0270] The electrolyzer modeling module is configured to: construct a load management model and an operation model and safety constraints for the electrolyzer, and introduce an electrolyzer life attenuation model based on the operation status;

[0271] The hydrogen and electric energy storage modeling module is configured to: construct hydrogen and electric energy storage operation models, quantify the impact of hydrogen storage on electrolyzer flexibility and the lifespan degradation of electric energy storage;

[0272] The power-to-ammonia modeling module is configured to: construct an ammonia production model, power consumption model, and thermodynamic model for the power-to-ammonia process, and design a lifespan attenuation model for the power-to-ammonia equipment;

[0273] The microgrid optimization scheduling module is configured to: establish an electric-hydrogen-ammonia microgrid operation model, generate an optimal operation strategy based on equipment constraints and with the goal of minimizing total cost.

[0274] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A modeling method for an electric hydrogen ammonia microgrid considering safety and life attenuation, characterized by: include: Construct the load management model, operation model and safety constraints of the electrolyzer, and introduce the electrolyzer life attenuation model based on the operating status; Construct hydrogen and electric energy storage operation models to quantify the impact of hydrogen storage on electrolyzer flexibility and the lifespan degradation of electric energy storage; Construct ammonia production models, power consumption models, and thermodynamic models for the power-to-ammonia process, and design a lifespan attenuation model for power-to-ammonia equipment; Establish an electric-hydrogen-ammonia microgrid operation model and generate an optimal operation strategy based on equipment constraints and the goal of minimizing total cost; Among them, the electrolytic cell life attenuation model is specifically expressed as: ； ； ； ； ； ； ； Where, 、 、 and They are the electrolyzer efficiency attenuation in standby state, on state, fluctuating operation and start-stop; 、 、 and These are the electrolyzer efficiency attenuation coefficients in standby state, on-state, fluctuating operation, and start-stop; and They are electrolyzer efficiency decay and equivalent life decay respectively; is the rated operating life of the electrolyzer; and are the rated efficiency and the limiting efficiency of the electrolyzer respectively; is the rated efficiency attenuation coefficient of the electrolyzer.

2. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The load management model of the electrolyzer includes three states: on, standby, and off. At any given moment, the electrolyzer can only be in one state, and it is prohibited to switch directly from the off state to the standby state. The number of times the electrolyzer is started and stopped is limited to a set range. The electrolyzer operation model includes operating status, power management, current and voltage calculation, output calculation, and operating parameter limitations; Safety constraints on the electrolyzer include power ramp rate and temperature limits.

3. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The electrolytic cell life attenuation model based on operating status includes: dividing the electrolytic cell operating status into four types: standby, start, fluctuating operation and start-stop. The efficiency attenuation is different in different states. The efficiency attenuation coefficient is small in standby and start states. The greater the fluctuation in fluctuating operation, the greater the efficiency attenuation. Start-stop has the greatest impact on the life of the electrolytic cell.

4. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The hydrogen energy storage operation model includes hydrogen tank hydrogen balance, storage level and compressor power consumption.

5. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The impact of hydrogen energy storage on electrolyzer flexibility is that hydrogen energy storage affects the flexibility of electrolyzer stacks by affecting the current constraints of individual electrolyzer stacks; The life decay of electric energy storage is calculated by calculating the battery aging cost caused by charge and discharge cycles.

6. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The ammonia production model is based on Faraday's law and combines it with Faraday efficiency to calculate ammonia production. The ammonia production of a single branch is related to multiple parameters. The total ammonia production of the entire electrolyzer module is accumulated by each branch, and the limitations of ammonia production and regulation range are taken into account. The power consumption model is specifically the power consumption of the electrolytic cell, which is divided into the power consumption of a single branch and the total power consumption of the entire electrolytic cell. The power consumption of a single branch is related to the reaction enthalpy change and the electrolysis efficiency. The total power consumption of the entire electrolytic cell can be obtained by accumulating the power consumption of each branch. The thermodynamic model uses the concepts of thermal resistance and heat capacity and the classical lumped parameter method to process thermal characteristics, providing calculation formulas for the thermal resistance and characteristic length of different parts. Based on Fourier's law, the internal reaction zone and wall heat balance equations and the renewable energy heat supply formula are established to describe their thermal interactions.

7. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The life decay model of the electric-to-ammonia equipment includes the life decay of the nitrogen generator and the life decay of the electrolyzer. The life decay cost of the nitrogen generator is related to the cost coefficient, the switch status of the electrolyzer branch, and the service life of the filter element. The life decay cost of the electrolyzer is related to the branch cost coefficient, service life, and the unit life decay cost during startup and shutdown.

8. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The framework of the electric-hydrogen-ammonia microgrid operation model includes a wind turbine, a photovoltaic generator, a converter, an ammonia-producing electrolyzer, a hydrogen-producing electrolyzer, a boiler, a battery, an ammonia storage tank, a hydrogen storage tank, a pressure swing adsorption device, an electrical load, a thermal load, an ammonia load, a hydrogen load, and is connected to an external power grid.

9. The electric hydrogen ammonia microgrid modeling method considering safety and life attenuation according to claim 1 is characterized in that: The equipment constraints include electric energy balance constraints, thermal energy balance constraints, power constraints and operating cost constraints; among them, the operating costs include the operation and life degradation costs of hydrogen and ammonia production electrolyzers, battery life degradation costs, electricity purchase costs, electricity sales revenue and electrolyzer start-up and shutdown costs.

10. The electric hydrogen ammonia microgrid modeling system considering safety and life attenuation is characterized by: include: The electrolyzer modeling module is configured to: construct a load management model and an operation model and safety constraints for the electrolyzer, and introduce an electrolyzer life attenuation model based on the operation status; The hydrogen and electric energy storage modeling module is configured to: construct hydrogen and electric energy storage operation models, quantify the impact of hydrogen storage on electrolyzer flexibility and the lifespan degradation of electric energy storage; The power-to-ammonia modeling module is configured to: construct an ammonia production model, power consumption model, and thermodynamic model for the power-to-ammonia process, and design a lifespan attenuation model for the power-to-ammonia equipment; The microgrid optimization scheduling module is configured to: establish an electric-hydrogen-ammonia microgrid operation model, generate an optimal operation strategy based on equipment constraints and with the goal of minimizing total cost; Among them, the electrolytic cell life attenuation model is specifically expressed as: ； ； ； ； ； ； ； Where, 、 、 and They are the electrolyzer efficiency attenuation in standby state, on state, fluctuating operation and start-stop; 、 、 and These are the electrolyzer efficiency attenuation coefficients in standby state, on-state, fluctuating operation, and start-stop; and They are electrolyzer efficiency decay and equivalent life decay respectively; is the rated operating life of the electrolyzer; and are the rated efficiency and the limiting efficiency of the electrolyzer respectively; is the rated efficiency attenuation coefficient of the electrolyzer.

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