Electro-hydrogen-ammonia micro-grid modeling method and system considering safety and service life attenuation

Abstract

The invention discloses an electric hydrogen ammonia micro-grid modeling method and system considering safety and life decay, and belongs to the technical field of electric hydrogen ammonia micro-grid modeling, and the method comprises the steps: constructing a load management model, an operation model and safety constraints of an electrolytic cell, and introducing an electrolytic cell life decay model based on an operation state; constructing a hydrogen energy storage operation model and an electric energy storage operation model, and quantifying the influence of hydrogen energy storage on the flexibility of the electrolytic cell and the life attenuation of electric energy storage; constructing an ammonia yield model, a power consumption model and a thermodynamic model in an ammonia conversion process, and designing an ammonia conversion equipment life attenuation model; and establishing an electric hydrogen ammonia micro-grid operation model, and generating an optimal operation strategy by taking the minimum total cost as a target based on equipment constraints. According to the method, the service life attenuation cost and the safety constraint are added into the electric hydrogen ammonia micro-grid modeling problem, the service life attenuation of the storage battery, the hydrogen production electrolytic bath and the ammonia production electrolytic bath is slowed down while the system operation cost is reduced, and the micro-grid safety risk is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric hydrogen ammonia microgrid modeling, and specifically 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 technology. However, existing technologies have the following problems: On the one hand, in terms of equipment life decay, the life of core equipment in the electric hydrogen ammonia microgrid, such as electrolyzers and batteries, is affected by many factors. When the electrolyzer is in operation, rapid current fluctuations, frequent starts and stops, and operation close to the open circuit voltage will cause mechanical wear and chemical degradation of its membrane, which will accelerate stack degradation, reduce operating efficiency and reduce the number of cycles; the aging cost of batteries in frequent charge and discharge cycles is related to the battery investment cost, estimated cycle life, battery cycle life coefficient, ambient temperature and battery reference state of charge. However, existing studies often only focus on economic optimization when performing system optimization and scheduling, and do not consider the factors of these equipment life decay sufficiently, making it difficult to accurately evaluate equipment life loss in actual operation, increasing the cost of long-term system operation.

[0004] On the other hand, safety is an important issue that cannot be ignored in the electric hydrogen ammonia microgrid. As a key device in the electric hydrogen ammonia microgrid, the safety of the electrolyzer is crucial to the stable operation of the entire system.

[0005] From the perspective of power change, if the rate of change of the electrolytic cell power is not controlled, overly drastic changes will cause damage to the equipment. Temperature control of the electrolytic cell is also critical. Too high or too low a temperature will affect the performance of the equipment and even cause safety issues. The quantitative model of existing research in this regard is not perfect, and it is difficult to accurately evaluate the temperature safety range of the electrolytic cell under different working conditions, and it is also impossible to provide a reliable temperature control strategy for system operation.

[0006] In addition, complex thermal effects occur during the operation of the electrolyzer. There is energy storage and transfer of heat among the internal reaction zone, the surrounding walls, and the external air, involving various heat sources and heat transfer paths such as external heating provided by renewable energy and the enthalpy change at the electrode / electrolyte interface during the power-to-ammonia (P2A) reaction. However, existing research often oversimplifies when considering these thermal effects, without comprehensively considering the interactions among various thermal factors and their impacts on the overall temperature distribution and thermal balance of the system. In the optimal operation of the system, the lack of a model that can comprehensively reflect these thermal effects makes it difficult to effectively ensure the thermal safety of the electrolyzer and also limits the improvement of the system operation efficiency. Summary of the Invention

[0007] The object of the present invention is to overcome the deficiencies existing in the above-mentioned prior art, and provide a power-to-hydrogen-to-ammonia microgrid modeling method and system considering safety and life attenuation. The life attenuation cost and safety constraints are added to the power-to-hydrogen-to-ammonia microgrid modeling problem, which reduces the system operation cost while slowing down the life attenuation of the battery, the hydrogen production electrolyzer, and the ammonia production electrolyzer, and reducing the safety risk of the microgrid.

[0008] To achieve the above object, the present invention is realized through the following technical solutions: On the one hand, the technical solution of the present invention provides a power-to-hydrogen-to-ammonia microgrid modeling method considering safety and life attenuation, including: Construct a load management model, an operation model, and safety constraints of the electrolyzer, and introduce an electrolyzer life attenuation model based on the operating state; Construct a hydrogen energy storage operation model and an electrical energy storage operation model to quantify the impact of hydrogen energy storage on the flexibility of the electrolyzer and the life attenuation of electrical energy storage; Construct an ammonia production model, a power consumption model, and a thermodynamic model for the power-to-ammonia process, and design an equipment life attenuation model for the power-to-ammonia equipment; Establish a power-to-hydrogen-to-ammonia microgrid operation model, and generate an optimal operation strategy with the goal of minimizing the total cost based on equipment constraints.

[0009] In at least one embodiment, the load management model of the electrolyzer includes three states: on, standby, and off; at any moment, the electrolyzer can only be in one state, and direct switching from the off state to the standby state is prohibited; the start-stop times of the electrolyzer are limited within a set range; The operation model of the electrolyzer includes the operating state, power management, current and voltage calculation, production calculation, and operating parameter limitations; The safety constraints of the electrolyzer include limitations on the power change rate and temperature.

[0010] In at least one embodiment, the electrolyzer life attenuation model based on the operating state includes: classifying the electrolyzer operating state into four types: standby, startup, fluctuating operation, and startup and shutdown. The efficiency attenuation is different under different states. The efficiency attenuation coefficient is small in the standby and startup states. The greater the fluctuation during fluctuating operation, the greater the efficiency attenuation. Startup and shutdown have the greatest impact on the electrolyzer life.

[0011] In at least one embodiment, the hydrogen energy storage operation model includes hydrogen balance in the hydrogen storage tank, storage level, and compressor power consumption.

[0012] In at least one embodiment, the impact of hydrogen energy storage on the flexibility of the electrolyzer is that hydrogen energy storage acts on the flexibility of the electrolyzer stack by affecting the current constraint conditions of a single electrolyzer stack; The life attenuation of the electrical energy storage is calculated by the battery aging cost caused by charge and discharge cycles.

[0013] In at least one embodiment, the ammonia production model is based on Faraday's law, and combines the Faraday efficiency to calculate the ammonia production. 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 each branch, and the limitations of ammonia production and adjustment range are considered; The power consumption model is specifically the power consumption of the electrolyzer, which is divided into the power consumption of a single branch and the total power consumption of the entire electrolyzer. The power consumption of a single branch is related to the enthalpy change of the reaction and the electrolysis efficiency. The total power consumption of the entire electrolyzer can be obtained by summing the power consumption of each branch; The thermodynamic model uses the concepts of thermal resistance and heat capacity, adopts the classical lumped parameter method to process the thermal characteristics, and gives the calculation formulas for the thermal resistance and characteristic length of different parts; based on Fourier's law, the heat balance equations of the internal reaction zone and the wall surface and the formula for the heat supply of renewable energy are established to describe their thermal interaction.

[0014] In at least one embodiment, the life attenuation model of the electrolysis-to-ammonia equipment includes the life attenuation of the nitrogen generator and the life attenuation of the electrolyzer; among them, the life attenuation cost of the nitrogen generator is related to the cost coefficient, the switch state of the electrolyzer branch, and the service life of the filter element. The life attenuation cost of the electrolyzer is related to the branch cost coefficient, service life, and unit life attenuation cost during startup and shutdown.

[0015] In at least one embodiment, the framework of the electrolysis-hydrogen-ammonia microgrid operation model includes a wind turbine, a photovoltaic generator, an inverter, an ammonia-producing electrolyzer, a hydrogen-producing electrolyzer, a boiler, a storage 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 the external power grid.

[0016] In at least one embodiment, the device constraints include power balance constraints, heat balance constraints, power constraints, and operating cost constraints; wherein, the operating costs include the operating and life attenuation costs of hydrogen production and ammonia production electrolyzers, the life attenuation cost of the battery, as well as the power purchase cost, power selling revenue, and electrolyzer start-stop cost.

[0017] On the other hand, the technical solution of the present invention also provides an electro-hydrogen-ammonia microgrid modeling system considering safety and life attenuation, including: An electrolyzer modeling module, configured to: construct a load management model, an operating model, and safety constraints of the electrolyzer, and introduce an electrolyzer life attenuation model based on the operating state; A hydrogen energy storage and electrical energy storage modeling module, configured to: construct an operating model of hydrogen energy storage and an operating model of electrical energy storage, and quantify the impact of hydrogen energy storage on the flexibility of the electrolyzer and the life attenuation of electrical energy storage; An electrolysis-to-ammonia modeling module, configured to: construct an ammonia production model, a power consumption model, and a thermodynamic model for the electrolysis-to-ammonia process, and design an electrolysis-to-ammonia equipment life attenuation model; A microgrid optimal scheduling module, configured to: establish an electro-hydrogen-ammonia microgrid operating model, and generate an optimal operating strategy with the goal of minimizing the total cost based on device constraints.

[0018] The beneficial effects of the above technical solution of the present invention are as follows: The present invention adds life attenuation costs and safety constraints to the electro-hydrogen-ammonia microgrid modeling problem, slows down the life attenuation of the battery, hydrogen production electrolyzer, and ammonia production electrolyzer while reducing the system operating cost, and reduces the safety risk of the microgrid, which is expected to further promote the application of the electro-hydrogen-ammonia microgrid in the energy field and provide strong support for the further development of renewable energy technologies. Description of the Drawings

[0019] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0020] Figure 1 It is a schematic flowchart of the electro-hydrogen-ammonia microgrid modeling method considering safety and life attenuation disclosed in Embodiment 1 of the present invention; Figure 2 It is a schematic framework diagram of the electro-hydrogen-ammonia microgrid operating model in Embodiment 1 of the present invention. Detailed Description of the Invention

[0021] 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 of ordinary skill in the technical field to which the present invention belongs.

[0022] As introduced in the background art, the object of the present invention is to overcome the deficiencies existing in the above-mentioned prior art, and provide an electro-hydrogen-ammonia microgrid modeling method and system considering safety and life attenuation. The life attenuation cost and safety constraints are added to the electro-hydrogen-ammonia microgrid modeling problem, while reducing the system operation cost, slowing down the life attenuation of the battery, hydrogen production electrolyzer and ammonia production electrolyzer, and reducing the safety risk of the microgrid.

[0023] Embodiment 1 In a typical implementation manner of the present invention, as Figure 1 shown, this embodiment discloses an electro-hydrogen-ammonia microgrid modeling method considering safety and life attenuation, including the following steps: Step 1. Construct a load management model, an operation model and safety constraints of the electrolyzer, and introduce an electrolyzer life attenuation model based on the operating state; Step 2. Construct a hydrogen energy storage operation model and an electrical energy storage operation model, and quantify the impact of hydrogen energy storage on the flexibility of the electrolyzer and the life attenuation of the electrical energy storage; Step 3. Construct an ammonia production model, a power consumption model and a thermodynamic model for the power-to-ammonia process, and design an equipment life attenuation model for the power-to-ammonia; Step 4. Establish an electro-hydrogen-ammonia microgrid operation model, and generate an optimal operation strategy with the minimum total cost based on equipment constraints.

[0024] The above electro-hydrogen-ammonia microgrid modeling method considering safety and life attenuation will be described in detail below in conjunction with specific implementation manners.

[0025] Step 1. Construct a load management model, an operation model and safety constraints of the electrolyzer, and introduce an electrolyzer life attenuation model based on the operating state.

[0026] In this step, the load management model of the electrolyzer includes three states: on, standby, and off. When the state is on, the electrolyzer consumes power and produces hydrogen within a specific load range, and the power is between the maximum and minimum allowable values; when the renewable energy is insufficient, the electrolyzer will enter the standby or off state. When the state is standby, it consumes a small amount of power to maintain the system temperature and pressure stable, but does not produce hydrogen.

[0027] Specifically, three binary variables are defined for the three states of the electrolyzer being on, standby, and off, which are, and . In the on state, , the electrolyzer operates within a specific load range, as shown in Equation (1): (1); In the formula, is a binary variable representing the electrolyzer at indicates whether it is in the on state at a certain moment. When , the electrolyzer is in the on state; and are the maximum and minimum allowable operating powers of the electrolyzer stack respectively; is the electrolyzer at the actual power consumed at a certain moment.

[0028] When the supply of renewable energy is insufficient, to save costs, the electrolyzer will enter the standby state ( ) or the off state ( ). In the standby mode, the electrolyzer will consume a certain proportion of electricity to maintain the temperature and pressure stability of the system, but no hydrogen is produced. Usually, the standby power consumption is about 1% - 5% of the total load capacity of the electrolyzer.

[0029] To reduce the start-up cost, the electrolyzer can only be in one state at any moment and will not directly switch from the off state to the standby state.

[0030] Specifically, the electrolyzer can only be in one state at any moment, as shown in Equation (2): (2); The start-up and stop states of the electrolyzer are as shown in Equation (3) and Equation (4): (3); (4); In the formula, is a binary variable. When , the electrolyzer starts; is a binary variable. When , the electrolyzer stops.

[0031] The electrolyzer will not switch from the off state to the standby state, thus reducing the start-up cost, which is constrained by Equation (5): (5); To reduce the operating cost of the electrolyzer and extend its service life, the maximum number of start-ups and shut-downs of the electrolyzer is limited within a certain range, as shown in Equation (6) and Equation (7): (6); (7); In the formula, and are the maximum number of start-ups and shut-downs of the electrolyzer respectively.

[0032] Furthermore, the start-up and stop costs of the electrolyzer are shown in Equations (8) and (9) respectively: (8); (9); wherein, is the start-up cost of the electrolyzer at time; is the single start-up cost of the electrolyzer ; is the stop cost of the electrolyzer at time; is the single stop cost of the electrolyzer .

[0033] In this step, the operation model of the electrolyzer includes operation status, power management, current and voltage calculation, production calculation, and operation parameter limits. In terms of power management, the actual power consumption of the electrolyzer consists of rated power and extended power. Range constraints are set for these two types of power respectively, and the continuous use time and cumulative use degree of the extended power are also restricted. The operation model of the electrolyzer gives the calculation methods of stack current, voltage, and hydrogen production. At the same time, upper and lower limits are set for the operation parameters of the electrolyzer stack and single electrolyzer, and the non-linear production characteristics based on current are considered, and the operation conditions under different variable current densities are reflected through different overvoltage segments.

[0034] Larger-scale proton exchange membrane (PEM) electrolyzer stacks have better operation ranges and fast response characteristics, which enable them to be used for extended operation, thereby enhancing their potential to provide support services to the power grid. The extended operation of modular PEM stacks is attributed to their electrochemical properties. Such systems allow a certain degree of overload operation, and this characteristic can be used to absorb excess electrical energy in renewable energy power systems, thus promoting the integrated operation of the system. However, during operation, attention must be paid to avoiding the rebound effect caused by excessive extended operation. In this step, an extended electrochemical stack model applicable to the operation of renewable energy power systems is adopted.

[0035] The actual power consumption of the electrolyzer consists of rated power and extended power. The rated power part reflects the power demand under its normal operation state, while the extended power reflects the additional power that the electrolyzer can consume under specific circumstances (such as coping with the fluctuations of renewable energy) to better adapt to system changes, as shown in Equation (10): (10); wherein, is the actual power consumption of the electrolyzer ; is the electrolyzer Rated power; For the electrolyzer Extended power.

[0036] To ensure the electrolyzer operates under safe and stable conditions and avoid problems such as being unable to work properly due to too low power or equipment damage caused by too high power, the rated power of the electrolyzer is restricted within a certain range, as shown in Equation (11): (11); Wherein, is the minimum stack power; is the rated stack power.

[0037] Furthermore, the extended power range constraint formula is as shown in Equation (12): (12); Wherein, is the rated stack power; is a proportionality coefficient that controls the upper limit of the extended power, prevents the extended power from being too large and causing damage to the equipment, and also provides a constraint basis for the system to reasonably distribute power under different operating conditions.

[0038] The electrolyzer cannot be in the extended power operation state in two consecutive time intervals, and 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 as shown in Equation (13): (13); Wherein, represents t the extended power at time t + 2.

[0039] Furthermore, the cumulative extended power constraint controls the degree of use of the extended power as a whole to ensure that the electrolyzer does not overly rely on the extended power during long-term operation, as shown in Equation (14): (14); Wherein, is the percentage of the total overload within t hours.

[0040] The stack current is calculated as shown in Equation (15): (15); Wherein, is the stack current of the electrolyzer at time t; is the stack current of the electrolyzer at Instantaneous stack voltage.

[0041] The calculation of the stack voltage is shown in Equation (16): (16); Wherein, is the number of individual electrolytic cells in the electrolytic cell stack; is the voltage of a single electrolytic cell.

[0042] The operating parameter limits of the electrolytic cell stack and a single electrolytic cell are shown in Equation (17): (17); Wherein, are the operating parameters of the electrolytic cell stack and a single electrolytic cell (such as current, voltage, hydrogen production, and equipment capacity, etc.); and respectively represent the maximum and minimum values of these parameters.

[0043] The electrolytic cell model considers the non-linear production characteristics based on current and can be used to construct an accurate operating model of the electrolytic cell in different ranges. It illustrates the operating conditions of the electrolytic cell under different variable current densities, and different variable current densities are reflected in various overvoltage segments of the electrolytic cell, as shown in Equation (18): (18); Wherein, is the operating voltage of the electrolytic cell; is the minimum open-circuit voltage required to produce hydrogen; is the voltage related to the activation of the electrode for proton transfer; is the ohmic voltage caused by resistance and proton exchange; is the mass transfer concentration difference voltage, which plays a key role during operation at a high or variable current density.

[0044] The calculation of the open-circuit voltage is shown in Equation (19): (19); Wherein, is the change in Gibbs free energy; is the Faraday constant; is the temperature of the electrolytic cell; , and are the partial pressures of hydrogen, oxygen, and water, respectively.

[0045] The calculation of the electrode activation voltage is shown in Equation (20): (20) Wherein, and The charge transfer coefficients of the anode and cathode, respectively; is the current density; and are the exchange current densities of the anode and cathode, respectively.

[0046] The calculation of the ohmic voltage is shown in Equation (21): (21); In the formula, is the electrolytic cell resistance.

[0047] The calculation of the mass transfer concentration difference voltage is shown in Equation (22): (22); In the formula, is the limiting current density.

[0048] The calculation formula for the hydrogen production is shown in Equation (23): (23); In the formula, is the hydrogen production of the electrolytic cell; is the Faraday coefficient; is the molar mass of hydrogen; is the Faraday constant.

[0049] In this step, the safety constraints of the electrolytic cell include limitations on the power change rate and temperature. In terms of the power change rate, it is limited within a specific upper and lower limit range to prevent damage to the equipment caused by too drastic power changes; in terms of temperature, the temperature of the electrolytic cell is constrained by relevant formulas to avoid affecting the equipment performance and causing safety problems due to too high or too low temperature.

[0050] Specifically, the limitation on the power change rate of the electrolytic cell is shown in Equation (24): (24); In the formula, is the lower limit value of the power change rate of the electrolytic cell; is the upper limit value of the power change rate of the electrolytic cell.

[0051] The temperature limitation of the electrolytic cell is shown in Equation (25): (25); (26); (27); In the formula, is the electrolytic cell temperature; is the thermal power lost by the electrolytic cell; is the thermal power output outside the system; is the lumped heat capacity of the electrolyzer; is the external temperature of the electrolyzer; is the thermal resistance of the electrolyzer; and are the upper and lower limits of the electrolyzer temperature, respectively.

[0052] For the electrolyzer life decay model, the operating states of the electrolyzer are divided into standby, startup, fluctuating operation, and start-stop. The efficiency decay is different in different states. The efficiency decay coefficients are small in standby and startup states. The greater the fluctuation during fluctuating operation, the greater the efficiency decay. Start-stop has the greatest impact on the electrolyzer life.

[0053] Specifically, the electrolyzer life decay model is shown in Equations (28) to (34): (28); (29); (30); (31); (32); (33); (34); In the equations, , , and are the electrolyzer efficiency decay amounts during standby, startup, fluctuating operation, and start-stop, respectively; , , and are the electrolyzer efficiency decay coefficients during standby, startup, fluctuating operation, and start-stop, respectively; and are the electrolyzer efficiency decay and equivalent life decay, respectively; is the rated operating life of the electrolyzer; and are the rated efficiency and limit efficiency of the electrolyzer, respectively; is the rated efficiency decay coefficient of the electrolyzer.

[0054] In the electrolyzer life decay model, the life loss cost of the electrolyzer is shown in Equation (35): (35); In the equation, is the life loss cost of the electrolyzer; is the configuration cost of the electrolyzer.

[0055] Step 2. Construct a hydrogen energy storage operation model and an electrical energy storage operation model to quantify the impact of hydrogen energy storage on the flexibility of electrolyzers and the life attenuation of electrical energy storage.

[0056] In this step, the hydrogen energy storage operation model includes the hydrogen balance in the hydrogen storage tank, the storage level, and the power consumption of the compressor. The hydrogen balance equation of the hydrogen storage tank shows 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 storage level of the hydrogen storage tank at adjacent times. At the same time, storage level constraint conditions are set to specify the maximum and minimum storage levels. The formula for the power consumption of the hydrogen compressor is used to calculate the power consumption during the operation of the compressor.

[0057] The hydrogen balance equation in the hydrogen storage tank is shown in Equation (36): (36); In the formula, is a single electrolyzer; is the set of electrolyzers; is the amount of hydrogen released from the hydrogen storage tank; is the amount of hydrogen stored in the hydrogen storage tank.

[0058] The storage level equation of the hydrogen storage tank is shown in Equation (37): (37); In the formula, is the storage level of the hydrogen storage tank at time is the storage level of the hydrogen storage tank at time

[0059] The constraint condition of the storage level of the hydrogen storage tank is shown in Equation (38): (38); In the formula, and are the maximum and minimum storage levels of the hydrogen storage tank, respectively.

[0060] The power consumption of the hydrogen compressor is shown in Equation (39): (39); In the formula, is the power consumption of the compressor; is a parameter related to the hydrogen flow rate; is the gas constant; is the temperature at the inlet of the compressor; is the adiabatic index; is the compressor efficiency ; is the outlet pressure of the hydrogen storage tank; is the inlet pressure of the hydrogen storage tank.

[0061] The impact of hydrogen energy storage on the flexibility of electrolyzer stacks. Hydrogen energy storage affects the current constraint conditions of individual electrolyzer stacks, thereby acting on the flexibility of electrolyzer stacks.

[0062] The constraint conditions for the current of an individual electrolyzer stack are shown in Equation (40): (40); In the formula, is the Faraday efficiency; is the number of electrolyzer stacks; is the molar mass of hydrogen.

[0063] The operation model of electrical energy storage includes charge-discharge power, state-of-charge update, and state-of-charge limit.

[0064] The charge-discharge formulas of electrical energy storage are shown in Equations (41) and (42): (41); (42); In the formula, and are the charging power and discharging power of electrical energy storage, respectively; is the maximum charge-discharge power of electrical energy storage.

[0065] The state-of-charge update formula of electrical energy storage is shown in Equation (43): (43); In the formula, is the state of charge of electrical energy storage at time; is the state of charge of electrical energy storage at time; and are the charging efficiency and discharging efficiency of electrical energy storage, respectively.

[0066] The state-of-charge limit formula of electrical energy storage is shown in Equation (44): (44); In the formula, and are the minimum and maximum state of charge of electrical energy storage, respectively.

[0067] The electrical energy storage life attenuation model calculates the battery aging cost caused by charge-discharge cycles. This model believes that the battery aging cost is related to the battery investment cost and the estimated cycle life, and is also affected by the battery cycle life coefficient, environmental temperature, and the battery reference state of charge.

[0068] Specifically, the battery aging cost caused by charge-discharge cycles is shown in Equation (45): (45); In the formula, is the investment cost of the battery; is the estimated cycle life of the battery; , , and are the battery cycle life coefficients; is the environmental temperature; is the reference state of charge of the battery.

[0069] Step 3. Construct an ammonia production model, a power consumption model, and a thermodynamic model for the electroammonia process, and design an equipment life attenuation model for electroammonia.

[0070] In this step, the ammonia production model specifically refers to that the P2A (electroammonia) ammonia synthesis process is carried out in the electrolytic cell of a specific electrochemical cell, and the electrolytic cell module is composed of a series-parallel connection of multiple electrolytic cells. The ammonia production model is based on Faraday's law, and the ammonia production is calculated by combining the Faraday efficiency. The ammonia production of a single branch is related to multiple parameters, and the total ammonia production of the entire electrolytic cell module is accumulated by each branch, and the limitations of ammonia production and adjustment range are considered.

[0071] P2A refers to the process of ammonia synthesis. In the electrolytic cell driven by renewable energy, the overall reaction formula in aqueous solution is , which indicates that in this process, water and nitrogen react under specific conditions to produce ammonia and oxygen, which is the core chemical reaction of the entire P2A technology.

[0072] In this step, an electrochemical cell based on mixed-conducting electrolyte and Pt / C electrode is adopted. At room temperature and atmospheric pressure, this kind of cell has a high ammonia production, which can better meet the needs of research and practical applications. At the anode, the water decomposition reaction occurs to generate oxygen, hydrogen ions and electrons; at the cathode, the hydrogen ions are transferred through the Nafion membrane and react with nitrogen to generate ammonia. To ensure sufficient ammonia production, multiple repeated 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 electrolytic cell module. This structural design helps to improve the ammonia production efficiency and overall performance.

[0073] According to Faraday's law, in an ideal situation, the ammonia production is theoretically approximately proportional to the current density. During the actual electrolysis process, the operating current density, temperature, and pressure will affect the parasitic current and cross - penetration. The parasitic current refers to the additional current that is not used for the target electrochemical reaction. It consumes energy but does not produce useful products; cross - penetration refers to the undesirable penetration of different substances in the electrodes or electrolytes, and these will all affect the actual ammonia production. Therefore, when calculating the ammonia production of the electrolyzer, one cannot rely solely on Faraday's law, and the Faraday efficiency also needs to be considered. In the P2A process, the Faraday efficiency is measured through a large number of electrolysis experiments. In the experiment, a known amount of water and nitrogen react in a stoichiometric ratio to be converted into ammonia, and the Faraday efficiency is determined by measuring the current passed through.

[0074] Based on Faraday's law and combined with the efficiency factors in the actual electrolysis process, the ammonia production of a single branch within a specific time period is as shown in Equation (46): (46); where is the ammonia production of the th time period and the th branch; is the number of electrolytic cells connected in series; is the Faraday efficiency of the th time period; is the molar volume of ammonia in the th time period and the th branch; is the current passed through the th time period and the th branch; is the duration of the th time period; is the number of electrons transferred required to generate one mole of ammonia. From the chemical equation for the reaction of nitrogen and hydrogen ions to form ammonia, it can be seen that 3 moles of electrons need to be transferred to generate 1 mole of ammonia, that is, .

[0075] Under specific conditions, the relationship between the molar volume of a gas and temperature is as shown in Equation (47): (47); where is the molar volume of ammonia in the th time period and the th branch; is the molar volume in different states; is the temperature of the th time period; is the temperature in another state; is a constant.

[0076] The limiting conditions for the ammonia production of the electrolyzer are shown in Equation (48): (48); In the formula, The maximum ammonia production.

[0077] The ammonia production regulation ability is shown in Equation (49): (49); In the formula, is the maximum regulation range of the ammonia production of the electrolyzer branch in adjacent time periods.

[0078] In the th time period, the total ammonia production of the entire electrolyzer module is shown in Equation (50): (50) In the formula, is the total ammonia production of the entire electrolyzer module in the th time period; is the number of electrolytic cell branches connected in parallel.

[0079] The operating constraints of the ammonia storage tank are similar to those of the hydrogen storage tank.

[0080] In this step, the power consumption model is actually the power consumption of the electrolyzer. The power consumption of the electrolyzer is calculated for a single branch and the entire electrolyzer. The power consumption of a single branch is related to the enthalpy change of the reaction and the electrolysis efficiency. The total power consumption of the entire electrolyzer can be obtained by summing up the power consumption of each branch. In the P2A process, nitrogen is separated from the air by pressure swing adsorption (PSA) technology, and the power consumption is calculated according to the power required to produce a unit volume of nitrogen and the rated gas production. In addition, a mathematical model is constructed by piecewise linear fitting of the relevant efficiency data at different temperatures.

[0081] The power consumption of the electrolyzer in the power-to-ammonia (P2A) process is shown in Equation (51): (51); In the formula, is the power consumption in the th time period and the th branch; is the enthalpy change of the reaction; is the electrolysis efficiency in the th time period.

[0082] The total power consumption of the entire electrolyzer is shown in Equation (52): (52); In the formula, is the The total power consumption of the electrolyzer over a period of time.

[0083] During the P2A process, although liquid water resources are abundant, the nitrogen gas participating in the reaction needs to be separated from the air. Currently, the pressure swing adsorption (PSA) technology has been widely used in nitrogen generators and is considered the preferred method for recovering high-purity nitrogen today. This is because the PSA technology has advantages such as 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 supply-demand matching.

[0084] The power consumption calculation formula of the nitrogen generator is shown in Equation (53): (53); In the formula, is the power consumption of the nitrogen generator in the th time period; is the power required to produce a unit volume of nitrogen; The rated gas production of the nitrogen generator.

[0085] Temperature is an important factor affecting the reaction rate and process of chemical reactions. By performing piecewise linear fitting on the measured and data at different temperatures, a mathematical model as shown in Equation (54) can be obtained.

[0086] (54); In the formula, is the temperature in the th time period; and are the lower limit value and upper limit value of the temperature respectively; and are the segmentation points of the temperature; , and are the slopes of the efficiency change with temperature in three temperature sub-intervals respectively.

[0087] The thermodynamic model of the electrolyzer focuses on the P2A physical electrolysis environment, which is composed of the surrounding wall, the reaction zone, and the external air, and there is heat energy transfer and storage in each part. The model uses the concepts of thermal resistance and heat capacity, and adopts the classical lumped parameter method to deal with the thermal characteristics, and gives the calculation formulas for the thermal resistance and characteristic length of different parts. Based on Fourier's law, the internal reaction zone, wall heat balance equations and the formula for the heat supply of renewable energy are established to describe their thermal interactions.

[0088] The P2A physical electrolysis environment is mainly composed of the surrounding wall, the reaction zone, and the external air. Heat energy is stored and transferred among these parts in different ways. The entire environment is affected by all thermal changes within the region, including external heating provided by renewable energy, enthalpy changes at the cathode / electrolyte and anode / electrolyte interfaces during the P2A reaction, etc. This means that when studying the electrolysis process, it is necessary to comprehensively consider the impacts of these different heat sources and heat transfer paths on the temperature distribution and thermal balance of the entire system.

[0089] To describe the heat storage capacity and heat transfer performance of each part of the electrolyzer, the concepts of thermal resistance and heat capacity are adopted. The classical lumped parameter method is used to deal with the temperature, heat storage, and heat transfer characteristics of the electrolysis region and the surrounding wall. It is assumed that the structure and material properties of the electrolyzer are the same and constant in all directions, so that its thermodynamic parameters can be calculated by spatial averaging along the electrolytic cell.

[0090] Thermal resistance is used to measure the resistance in the heat transfer process. The wall nodes are connected to the internal and external nodes through thermal resistance to represent the external and internal convective / conductive heat transfer. Under laminar flow conditions, the calculation of thermal resistance is related to the Nusselt number, characteristic length, and thermal conductivities of the internal electrolyte, wall, and air.

[0091] The calculation of the thermal resistance between the internal reaction zone and the wall is shown in Equation (55): (55); 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.

[0092] The calculation of the thermal resistance between the wall and the external environment is shown in Equation (56): (56) 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.

[0093] The calculation of the thermal resistance between the wall and the external air is shown in Equation (57): (57); where and are the size parameters related to heat transfer (such as the width and length of the wall), respectively; is the thermal conductivity of the air.

[0094] The calculation of the characteristic length is shown in Equations (58) and (59): (58); (59); In the formula, and are geometric parameters related to the internal electrolyte (such as width and height); and are geometric parameters related to the wall (such as width and height).

[0095] The present invention focuses on the thermodynamics model of the electrolytic cell during the P2A process, and describes the heat interaction between the internal reaction zone, the wall and the external environment based on Fourier's law.

[0096] The heat balance equation of the internal reaction zone is shown in Equation (60): (60); In the formula, is the heat capacity of the internal electrolyte; is the heat from renewable energy; , and are the temperatures of the wall, the internal reaction zone and the external environment, respectively.

[0097] The heat balance equation of the wall is shown in Equation (61): (61); In the formula, is the heat capacity of the wall.

[0098] The heat provided by renewable energy is shown in Equation (62): (62); In the formula, is the efficiency coefficient; is the th branch in the

[0099] Furthermore, the life decay model of the electro-ammonia conversion equipment includes the life decay of the nitrogen generator and the electrolytic cell. The life decay cost of the nitrogen generator is related to the cost coefficient, the switching state of the electrolytic cell branch, and the service life of the filter element. The life decay cost of the electrolytic cell is related to the branch cost coefficient, the service life, and the unit life decay cost during startup and shutdown.

[0100] The P2A system usually consists of a nitrogen generator, an electrolyzer, and an ammonia storage tank. Under normal circumstances, the P2A system operates according to the given operating set points throughout the scheduling cycle. However, the daily operation of the system and frequent on-off cycles will significantly reduce its service life and further affect the scheduling performance. The main degradation problems come from the electrolyzer and the nitrogen generator.

[0101] The cost modeling of the life attenuation of the nitrogen generator is shown in Equation (63): (63); In the formula, is the life attenuation cost of the nitrogen generator; is a cost coefficient related to the nitrogen generator; is a binary variable of the electrolyzer branch switch state; is the service life of the filter element.

[0102] Under the influence of rapid current fluctuations, frequent start-stop, and operation near the open-circuit voltage, the life and stack performance of the electrolyzer will degrade faster. Operating at too high / too low or fluctuating current / voltage for a long time will cause mechanical wear and chemical degradation of the electrolyzer membrane. In addition, frequent start-stop of the electrolyzer is more likely to accelerate stack degradation, resulting in reduced operating efficiency and fewer cycle times.

[0103] The cost model of the life attenuation of the electrolyzer is shown in Equation (64): (64); In the formula, is for the cost coefficient related to the th electrolyzer branch; is the service life of the electrolyzer; and

[0104] are the unit life attenuation costs generated when the electrolyzer branch starts and stops, respectively.

[0105] In this step, the framework of the electro-hydrogen-ammonia microgrid model is as Figure 2 shown, including wind turbines, photovoltaic generators, converters, ammonia-producing electrolyzers, hydrogen-producing electrolyzers, boilers, storage batteries, ammonia storage tanks, hydrogen storage tanks, pressure swing adsorption devices, electrical loads, thermal loads, ammonia loads, hydrogen loads and connected to the external power grid. Equipment constraints consider power balance constraints, heat balance constraints, power constraints, and operating cost constraints. Among them, the operating cost includes the operating and life attenuation costs of hydrogen production and ammonia production electrolyzers, the life attenuation cost of storage batteries, as well as the power purchase cost, power sales revenue, and electrolyzer start-stop cost.

[0106] The various multi - energy storages and converters in the power - to - hydrogen - to - ammonia micro - grid provide opportunities to improve the utilization rate of renewable energy and the economic efficiency of system operation by offering a certain degree of energy supply flexibility and synergy.

[0107] The power balance in the power - to - hydrogen - to - ammonia micro - grid is shown in Equation (65): (65); Wherein, is the power of the wind turbine; is the power of the photovoltaic generator; and are the power of purchasing electricity from and selling electricity to the main grid by the micro - grid respectively; is the power consumed for hydrogen production; is the power consumed for ammonia production; is the power consumed by the boiler.

[0108] The power consumed for hydrogen production is shown in Equation (66): (66); Wherein, is the auxiliary power of the electrolyzer.

[0109] The power consumed for ammonia production is shown in Equation (67): (67); The power interaction constraints between the micro - grid and the main grid are shown in Equations (68) to (70): (68); (69); (70); Wherein, and are binary variables, which are equal to 1 when the micro - grid is in the state of purchasing electricity from or selling electricity to the main grid respectively; and are the maximum power of purchasing electricity and selling electricity respectively.

[0110] The power constraint of the boiler is shown in Equation (71): (71); Wherein, and are the minimum and maximum power of the boiler respectively.

[0111] The heat balance in the power - to - hydrogen - to - ammonia micro - grid is shown in Equation (72): (72); Wherein, is the heat generated by the boiler; is the power of the heat load.

[0112] The heat generated by the boiler is shown in Equation (73): (73); In the formula, is the heat generation efficiency of the boiler.

[0113] The operating cost of the electro-hydrogen-ammonia electrolyzer includes the operating costs and life attenuation costs of the hydrogen production electrolyzer and the ammonia production electrolyzer, the life attenuation cost of the battery, the cost of purchasing electricity from the power grid, the revenue from selling electricity, and the start-stop cost of the electrolyzer. The operating cost of the electro-hydrogen-ammonia electrolyzer is shown in Equation (74): (74); In the formula, and are the unit power operating costs of the hydrogen production electrolyzer and the ammonia production electrolyzer respectively; is the electricity purchase and sale price between the microgrid and the large power grid.

[0114] Example 2 In a typical implementation manner of the present invention, this embodiment discloses an electro-hydrogen-ammonia microgrid modeling system considering safety and life attenuation, including: An electrolyzer modeling module, configured to: construct a load management model, an operation model and safety constraints of the electrolyzer, and introduce an electrolyzer life attenuation model based on the operating state; A hydrogen energy storage and electrical energy storage modeling module, configured to: construct a hydrogen energy storage operation model and an electrical energy storage operation model, and quantify the influence of hydrogen energy storage on the flexibility of the electrolyzer and the life attenuation of the electrical energy storage; An electricity-to-ammonia modeling module, configured to: construct an ammonia production model, a power consumption model and a thermodynamic model for the electricity-to-ammonia process, and design an equipment life attenuation model for electricity-to-ammonia; A microgrid optimal scheduling module, configured to: establish an electro-hydrogen-ammonia microgrid operation model, and generate an optimal operation strategy with the minimum total cost based on equipment constraints.

[0115] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modeling method for an electric-hydrogen-ammonia microgrid considering safety and life attenuation, characterized in that, Including: Construct a load management model, an operation model and safety constraints of the electrolyzer, and introduce an electrolyzer life attenuation model based on the operating state; Construct a hydrogen energy storage operation model and an electrical energy storage operation model to quantify the impact of hydrogen energy storage on the flexibility of the electrolyzer and the life attenuation of electrical energy storage; Construct an ammonia production model, a power consumption model and a thermodynamic model for the power-to-ammonia process, and design a life attenuation model for power-to-ammonia equipment; Establish a power-hydrogen-ammonia microgrid operation model, and generate an optimal operation strategy based on equipment constraints with the goal of minimizing the total cost.

2. The method for modeling an electric-hydrogen-ammonia microgrid considering safety and life attenuation according to claim 1, wherein The load management model of the electrolyzer includes three states: on, standby, and off; at any moment, the electrolyzer can only be in one state, and it is prohibited to directly switch from the off state to the standby state; the start-stop times of the electrolyzer are limited within a set range; The operation model of the electrolyzer includes the operating state, power management, current-voltage calculation, production calculation, and operating parameter limits; The safety constraints of the electrolyzer include the limits of the power change rate and temperature.

3. The method for modeling an electric-hydrogen-ammonia microgrid considering safety and life attenuation as claimed in claim 1, wherein The electrolyzer life attenuation model based on the operating state includes: dividing the electrolyzer operating state into standby, on, fluctuating operation, and start-stop. The efficiency attenuation is different in different states. The efficiency attenuation coefficients are small in the standby and on states. The greater the fluctuation during fluctuating operation, the greater the efficiency attenuation. Start-stop has the greatest impact on the life of the electrolyzer.

4. The method for modeling an electric-hydrogen-ammonia microgrid considering safety and life attenuation as described in claim 1, wherein, The hydrogen energy storage operation model includes the hydrogen balance in the hydrogen storage tank, the storage level, and the compressor power consumption.

5. The method for modeling an electro-hydrogen-ammonia microgrid considering safety and life attenuation according to claim 1, characterized in that, The impact of hydrogen energy storage on the flexibility of the electrolyzer is that hydrogen energy storage affects the stack current constraint conditions of a single electrolyzer stack, thereby acting on the flexibility of the electrolyzer stack; The life attenuation of electrical energy storage is calculated by calculating the battery aging cost caused by charge and discharge cycles.

6. The method for modeling an electric-hydrogen-ammonia microgrid considering safety and life attenuation as described in claim 1, wherein The ammonia production model is based on Faraday's law, and combines the Faraday efficiency to calculate the ammonia production. 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 each branch, and the limits of ammonia production and adjustment range are considered; The power consumption model is specifically the power consumption of the electrolyzer, which is divided into the power consumption of a single branch and the total power consumption of the entire electrolyzer. The power consumption of a single branch is related to the reaction enthalpy change and electrolysis efficiency. The total power consumption of the entire electrolyzer can be obtained by summing the power consumption of each branch; The thermodynamic model uses the concepts of thermal resistance and heat capacity, adopts the classical lumped parameter method to process the thermal characteristics, and gives the calculation formulas for the thermal resistance and characteristic length of different parts; based on Fourier's law, establish the heat balance equations of the internal reaction zone and the wall surface and the formula for the heat supply of renewable energy to describe their thermal interactions.

7. The method for modeling an electric-hydrogen-ammonia microgrid considering safety and life attenuation according to claim 1, characterized in that, The life attenuation model of the power-to-ammonia equipment includes the life attenuation of the nitrogen generator and the life attenuation of the electrolyzer; among them, the life attenuation cost of the nitrogen generator is related to the cost coefficient, the switch state of the electrolyzer branch, and the service life of the filter element. The life attenuation cost of the electrolyzer is related to the branch cost coefficient, the service life, and the unit life attenuation cost during start-up and shutdown.

8. The method for modeling an electro-hydrogen-ammonia microgrid considering safety and life attenuation as described in claim 1, wherein, The framework of the power-hydrogen-ammonia microgrid operation model includes a wind turbine, a photovoltaic generator, an inverter, 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 the external power grid.

9. The method for modeling an electro-hydrogen-ammonia microgrid considering safety and life attenuation as described in claim 1, wherein, The device constraints include power balance constraints, heat balance constraints, power constraints, and operating cost constraints; among them, the operating costs include the operating and life decay costs of hydrogen production and ammonia production electrolyzers, the life decay cost of the battery, as well as the power purchase cost, power sales revenue, and electrolyzer start-stop cost.

10. An electro-hydrogen-ammonia microgrid modeling system considering safety and life attenuation, characterized in that, including: An electrolyzer modeling module, configured to: construct a load management model, an operating model, and safety constraints of the electrolyzer, and introduce an electrolyzer life decay model based on the operating state; A hydrogen energy storage and electrical energy storage modeling module, configured to: construct an operating model of hydrogen energy storage and an operating model of electrical energy storage, and quantify the impact of hydrogen energy storage on the flexibility of the electrolyzer and the life decay of electrical energy storage; An electrolysis-to-ammonia modeling module, configured to: construct an ammonia production model, a power consumption model, and a thermodynamic model for the electrolysis-to-ammonia process, and design an electrolysis-to-ammonia equipment life decay model; A microgrid optimal scheduling module, configured to: establish an operating model of the electric-hydrogen-ammonia microgrid, and generate an optimal operating strategy with the minimum total cost based on the device constraints.

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