Optimized dispatching method of off-grid wind-solar power generation hydrogen production system considering frequency safety constraint

Abstract

The invention relates to the technical field of green electricity hydrogen production, and discloses an off-grid type wind and light power generation hydrogen production system optimal scheduling method considering frequency safety constraints, which comprises the following steps: establishing a frequency dynamic model of an off-grid type wind and light power generation hydrogen production system, and providing rapid frequency regulation for the system by taking a proton exchange membrane electrolytic cell as a rapid frequency regulation unit; the alkaline electrolytic bath is used as a primary frequency modulation unit to provide primary frequency regulation for the system; different frequency modulation dead zones are arranged to realize coordinated frequency modulation of the mixed electrolytic cell; nonlinear frequency security constraints in the frequency dynamic model are linearized and incorporated into a day-ahead scheduling optimization model of the hydrogen production unit; and solving the day-ahead scheduling optimization model by taking hydrogen production income maximization of the off-grid type wind and light power generation hydrogen production system as an objective function and combining each constraint condition, and generating a scheduling plan meeting the frequency safety requirement. Optimized dispatching of the hydrogen production unit under the frequency safety constraint is achieved, efficient electric hydrogen production is achieved, and meanwhile the frequency fluctuation coping capacity of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of green electricity hydrogen production, and specifically to an optimization scheduling method for an off-grid wind-solar power generation hydrogen production system taking frequency safety constraints into consideration. Background Art

[0002] The use of renewable energy to generate hydrogen is gradually moving from theory to practice, with green electricity hydrogen production projects experiencing a construction boom both domestically and internationally. Driven by domestic and international policies, off-grid hydrogen production using 100% renewable energy has become a future industry trend. Off-grid wind and solar power generation hydrogen production systems have extremely low inertia, and under conventional control, they participate in primary frequency regulation of the system only through grid-connected energy storage or wind turbines combined with energy storage. If the system is improperly configured, with insufficient frequency regulation reserve and inertia, a fault that causes wind turbines or hydrogen production loads to disconnect from the grid can easily cause the system frequency to exceed the limit, triggering the activation of wind turbine and photovoltaic frequency protection, further causing wind turbines or photovoltaics to disconnect from the grid and endangering the smooth operation of the system. Therefore, studying optimal scheduling methods for off-grid wind and solar power generation hydrogen production systems that consider frequency safety constraints is of great significance for their own safe and stable operation.

[0003] Current research has demonstrated that hydrogen production loads, such as alkaline hydrogen production units and PEM (Proton Exchange Membrane) hydrogen production units, possess rapid frequency and inertia response capabilities. In existing research on hydrogen production unit scheduling, Shen Xiaojun et al. proposed a coordinated control strategy for electrolyzer array rotation in wind power hydrogen production systems, based on constraints such as the electrolyzer's thermal and regulation characteristics. Qiu Y et al. also considered the effects of hydrogen production unit temperature and hydrogen impurity accumulation in oxygen, and proposed a variable load control method for hydrogen production clusters to accommodate wind and solar power generation. Li Y et al. proposed an electrolyzer rotation strategy for wind power hydrogen production systems to balance the operating hours of each electrolyzer. Niu Meng et al., based on the reaction mechanism of electrolytic hydrogen production equipment in hydrogen energy storage systems, proposed a modular hydrogen production control strategy to mitigate the impact of renewable energy on hydrogen energy storage systems. Yuan Tiejiang et al., based on the operating state transition relationship of the electrolyzer, proposed a day-ahead output optimization model for hydrogen production systems that considers the start-stop characteristics of the electrolyzer.

[0004] The above-mentioned research on the scheduling of hydrogen production units mainly focuses on deterministic optimization based on electricity prices or renewable energy output forecasts in a grid-connected mode. There is still a lack of optimal scheduling strategies for renewable power generation hydrogen production units under system frequency security constraints in an off-grid mode. Summary of the Invention

[0005] In response to the above problems, the purpose of the present invention is to provide an off-grid wind-solar power generation hydrogen production system optimization scheduling method that takes into account the maximum frequency change rate constraint of frequency safety constraints, utilizes the rapid power regulation capability of the hydrogen production load to participate in the frequency regulation of the off-grid wind-solar power generation hydrogen production system, establishes a frequency response model of the renewable power generation hydrogen production system under off-grid operation mode, and incorporates it into the hydrogen production unit day-ahead scheduling optimization model, ultimately achieving the optimal scheduling of the hydrogen production unit under frequency safety constraints, achieving efficient electric hydrogen production while improving the system's ability to cope with frequency fluctuations. The technical solution is as follows:

[0006] An optimization scheduling method for an off-grid wind-solar power generation hydrogen production system considering frequency security constraints includes:

[0007] Establishing a frequency dynamic model of an off-grid wind-solar power generation hydrogen production system, wherein the off-grid wind-solar power generation hydrogen production system includes a grid-type energy storage device, a wind-solar power source, and a water electrolysis hydrogen production unit;

[0008] Based on the power response characteristics of different types of electrolyzers in the water electrolysis hydrogen production unit, the proton exchange membrane electrolyzer is used as a fast frequency regulation unit to provide fast frequency regulation to the system; the alkaline electrolyzer is used as a primary frequency regulation unit to provide primary frequency regulation to the system; and different frequency regulation dead zones are set to achieve coordinated frequency regulation of the hybrid electrolyzer;

[0009] Linearize the nonlinear frequency security constraints in the frequency dynamic model, including the maximum frequency change rate constraint, the quasi-steady-state frequency difference constraint, and the frequency minimum point constraint, and incorporate them into the day-ahead dispatch optimization model of the hydrogen production unit;

[0010] Taking the maximization of hydrogen production revenue of the off-grid wind-solar power generation hydrogen production system as the objective function, combined with the operation constraints of the hydrogen production unit, the energy storage battery, the compressor and hydrogen storage tank, the frequency security constraints and the power balance constraints, the day-ahead scheduling optimization model is solved to generate a scheduling plan that meets the frequency security requirements.

[0011] The beneficial effects of the present invention are:

[0012] 1) The present invention takes into account the power response characteristics of different types of electrolyzers, uses PEM electrolyzers to provide rapid frequency regulation, uses alkaline electrolyzers to provide primary frequency regulation, and realizes the coordinated participation of the hybrid electrolyzer hydrogen production cluster in frequency regulation.

[0013] 2) The present invention establishes a frequency dynamic model of an off-grid wind-solar power generation hydrogen production system, covering the frequency response dynamic models of grid-type energy storage, wind turbines, PEM electrolyzers, and alkaline electrolyzers, and derives nonlinear constraints of large frequency change rate, steady-state frequency difference, and lowest frequency point, and converts them into linear models and incorporates them into the day-ahead optimization scheduling model of the hydrogen production unit; the nonlinear model of frequency constraints is converted into a linear model that can be quickly solved by a commercial solver, effectively avoiding the shortcomings of low timeliness of traditional numerical simulation-based verification of frequency safety constraints.

[0014] 3) The technical method proposed in the present invention for arranging the hydrogen production load to reserve frequency regulation and inertia support standby during the scheduling phase takes into account both the frequency safety and economy of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the overall structure of an off-grid wind-solar hydrogen production system.

[0016] Figure 2 Schematic diagram of the difference in power regulation response between PEM and AWE.

[0017] Figure 3 Schematic diagram of the difference between FFR and PFR responses.

[0018] FIG4( a ) shows the 24-period operating status of each hydrogen production unit in the embodiment considering the frequency constraint (method of the present invention).

[0019] FIG4( b ) shows the 24-period operating status of each hydrogen production unit without considering frequency constraints in the embodiment.

[0020] Figure 5 Schematic diagram of system frequency change in the embodiment.

[0021] Figure 6 Schematic diagram of the system frequency change rate in the embodiment. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] This invention utilizes the rapid power regulation capability of hydrogen production loads to participate in the frequency regulation of off-grid wind and solar power generation hydrogen production systems, establishes a frequency response model for renewable power generation hydrogen production systems in off-grid operation, and incorporates it into the day-ahead scheduling optimization model for hydrogen production units. Ultimately, this achieves optimized scheduling of hydrogen production units under frequency safety constraints, achieving efficient electric hydrogen production while improving the system's ability to cope with frequency fluctuations. The specific process is as follows:

[0024] 1. Frequency dynamic model of off-grid wind and solar power generation hydrogen production system

[0025] The off-grid wind-solar power generation hydrogen production system consists of wind-solar power, water electrolysis hydrogen production unit and its auxiliary equipment, grid-type energy storage device, etc. The overall structure is as follows: Figure 1 shown.

[0026] 1.1 Frequency response model for renewable power generation and energy storage

[0027] 1) Grid-type energy storage

[0028] Under the grid control based on virtual synchronous machines, the energy storage battery simulates the swing equation of the synchronous generator. When the system has a frequency deviation, it provides the system with primary frequency regulation and grid support power, which is expressed as:

[0029]

[0030] Where: is the primary frequency modulation power of the grid-type energy storage; H b 、D b is the virtual inertia and damping in network control; Δf g (τ) is the system frequency deviation.

[0031] 2) Wind turbines

[0032] Under overspeed and pitch load reduction control, the wind turbine can provide a frequency regulation backup. Assuming the load reduction ratio of the wind turbine is k deload , then the primary frequency modulation power provided by the fan can be expressed as:

[0033]

[0034] Where: is the available power of the fan; P w is the actual output of the fan; R w Reserved for primary frequency regulation of the fan; Δf g (τ) is the system frequency deviation.

[0035] 3) Photovoltaics

[0036] Since the photovoltaic system is under MPPT control in the present invention, it is considered that the backup power provided by photovoltaic is

[0037] 1.2 Frequency response model provided by water electrolysis hydrogen production unit

[0038] The electric hydrogen production unit includes auxiliary equipment such as electrolyzers and hydrogen compressors, which can provide frequency support by adjusting their load size when the system frequency changes. Among them, when the electrolyzer is in the startup state, under the additional virtual inertia and frequency droop control, when the system frequency is disturbed, the change in hydrogen production load power can be expressed as:

[0039]

[0040] Where: The coefficient of virtual inertia control is added. From formula (3), it can be seen that when the frequency drops (Δf>0, df / dt<0), the hydrogen generator reduces its load, and vice versa. It can be seen that the frequency regulation capability of the hydrogen generator is affected by its load regulation energy.

[0041] Since off-grid wind-solar power generation hydrogen production systems usually include alkaline water electrolyzers (AWE) and proton exchange membrane (PEM) electrolyzers, there are differences in their power response in terms of adjustment speed and adjustable capacity. 1) Adjustment speed difference. Due to the obvious double-layer capacitance effect of megawatt-level AWE, its load power response time has a delay t delay , the power response change rate is significantly longer than that of PME, such as Figure 2 shown.

[0042] 2) Difference in regulation capacity. The single-unit capacity of AWE is usually 5MW or even larger, while the PEM electrolyzer is often 1MW due to cost constraints. Therefore, under the same load regulation ratio, the load regulation capacity of AWE is larger. Taking the above two factors into consideration, this paper uses PEM as a fast-response frequency regulation unit to provide fast frequency regulation (FFR) to the system; regards AWE as a large-capacity primary frequency regulation unit to provide primary frequency regulation (PFR) to the system, and distinguishes them by setting different frequency regulation dead zone sizes, such as Figure 3 shown.

[0043] At this point, the frequency support provided by the electrolyzer in the hydrogen production plant to the system is as follows:

[0044]

[0045]

[0046] In addition to the electrolyzer, the compressor and electrolyzer auxiliary equipment in the hydrogen production unit are generally driven by asynchronous motors. Ignoring the change in the grid voltage amplitude, their load size and grid frequency can be modeled as follows:

[0047]

[0048] Where: ΔP a (τ),ΔP c(τ) are the frequency modulation powers of electrolyzer auxiliary equipment and compressor respectively; D a 、D c are the equivalent droop coefficients of the electrolyzer auxiliary equipment and compressor in response to frequency changes, respectively.

[0049] The power response of each participating primary frequency regulation unit is represented by a linear model, and energy storage and PEM are used to provide FFR, while wind turbines and AWE provide PFE. At this point, the frequency response model of the off-grid wind-solar power generation hydrogen production system can be expressed as:

[0050]

[0051] Where: ΔP e PFR,P (τ),ΔP e PFR,A (τ) are the frequency modulation powers of PEM and AWE respectively.

[0052] 2. Linearization of nonlinear frequency safety constraints in the frequency response model of off-grid wind-solar power generation and hydrogen production system.

[0053] During normal operation, the off-grid wind-solar power generation hydrogen production system meets the following power balance:

[0054]

[0055] Where: P w0 、P s0 、P b0 and are the initial powers of wind turbines, photovoltaics, energy storage, and hydrogen production plants, respectively.

[0056] When a power disturbance occurs in the system, the wind turbine, energy storage, and hydrogen production plant respond to power changes, and Equation (8) can be rewritten as

[0057] ΔP w (τ)+ΔP b (τ)+ΔP h (τ)=ΔP dis (9)

[0058] Where: ΔP w (τ),ΔP h (τ) and ΔP dis Especially for wind turbine energy storage and hydrogen production plant response to frequency changes of power.

[0059] Substituting equation (1) into equation (9), we have:

[0060]

[0061] Where, is the equivalent damping coefficient of the system. is the number of electrolytic cells; Nc Number of compressors; D a 、D c Damping coefficient of hydrogen production auxiliary equipment and compressor; P e auxi and P c,t comp They are the power of hydrogen production auxiliary machine and compressor respectively.

[0062] Substituting (7) into (10), the frequency dynamic model of the off-grid wind-solar power generation hydrogen production system in different time periods can be obtained as follows:

[0063]

[0064] make At this time there are:

[0065]

[0066]

[0067] Where: The equivalent inertia provided for AWE and PEM electrolyzer. According to (11)-(13), the mathematical expressions of the maximum frequency change rate, quasi-steady-state frequency difference and the lowest frequency point that characterize frequency safety can be obtained.

[0068] 2.1 Maximum frequency change rate constraint

[0069] Considering a serious offline failure, t DB1 Approaching 0, it is considered that Δf g (t DB1 )≈0. Therefore, the maximum frequency change rate constraint of the off-grid wind-solar power generation hydrogen production system can be expressed as follows according to (11):

[0070]

[0071] Where: is the maximum frequency change rate allowed by the system, ΔP dis Power disturbance magnitude.

[0072] 2.2 Quasi-steady-state frequency difference constraint

[0073] Considering that the primary frequency regulation reserve in the system is sufficient to balance the power disturbance, the quasi-steady-state frequency difference constraint of the system can be expressed as:

[0074]

[0075] Where: Reserved for the system's primary frequency modulation.

[0076] 2.3 Frequency Minimum Point Constraint

[0077] Since the frequency response time of grid-type energy storage and PEM is short, the lowest frequency point may fall at [t DB1 ,t DB2 ] and [t DB1 ,+∞] in any interval. In order to simplify the analysis, set t DB2 -t DB1 ≤t delay , it can be considered that the grid-connected energy storage, wind turbine, PEM, and AWE start frequency modulation at the same time. At this time, (12) and (13) can be combined to express as:

[0078]

[0079] Assume that before the frequency disturbance occurs, Δf g (0) = 0, and using this as the boundary condition to solve the first-order differential equation about frequency in (16), the expression of the frequency changing with time is obtained as follows:

[0080]

[0081] Among them, D s =D b +D l , H s =H b +H e +H w , f DB is the frequency dead zone; D s 、H s 、R s They are the system's damping, inertia and total frequency regulation reserves respectively.

[0082] when When , the frequency deviation reaches its maximum value, then:

[0083]

[0084] Substituting (18) into (17), we get the expression for the lowest frequency point:

[0085]

[0086] After the disturbance occurs, the lowest frequency point is required to not exceed the maximum allowable frequency difference Δf max , which requires:

[0087]

[0088] If the above inequality holds, then

[0089]

[0090] For the right side of inequality (20), considering -ΔP dis D s <0,D s 2 (Δf max -f DB )>0, the right side of the inequality can be expressed as:

[0091]

[0092] For the left side of inequality (20), let c = ΔP dis (D b +D l,min ), x=H s R s , the left side of inequality (20) is At this time g(x)≤c. So there exists an x * ,make g(x)≤c, so the condition for the inequality in formula (20) to hold can be rewritten as:

[0093]

[0094] At this point, the nonlinear constraint on the lowest frequency point is transformed into a linear constraint, which can be incorporated into the hydrogen production unit's day-ahead scheduling optimization model for a unified solution.

[0095] 3 Optimal scheduling of hydrogen production units considering frequency safety constraints

[0096] 3.1 Operation constraints of hydrogen production units

[0097] A single hydrogen generator can switch between three operating states: startup, standby, and shutdown. In the standby state, only auxiliary equipment is turned on to maintain the temperature and pressure of the electrolyzer, and no hydrogen is produced. Therefore, the state switching model of the hydrogen generator is as follows:

[0098]

[0099] Where: and is a binary variable, and when the value is 1, it means that the electrolyzer is in the startup, standby and shutdown states during period t; is a binary variable, and when the value is 1, it means that the electrolyzer is hot started, cold started, or shut down during the period t; Minimum downtime.

[0100] The power consumption of the hydrogen production unit includes the power of the electrolyzer and auxiliary equipment, and meets a certain power adjustment range, namely:

[0101]

[0102] Where: is the electrolytic cell power, I t is the electrolysis current, is the heat dissipation of the chiller, is the standby power of the hydrogen production unit, is the water pump power.

[0103] Since the heat capacity of the hydrogen production unit is large, a linear model is used to model the temperature dynamics of the hydrogen production unit:

[0104]

[0105] Where: is the heat capacity of the electrolytic cell, T e,t is the electrolysis temperature, is the heat generation and heat dissipation of the electrolytic cell in unit scheduling time, is the cooling coefficient of the chiller.

[0106] After the hydrogen production unit participates in frequency regulation, it must also meet the standby constraints:

[0107]

[0108]

[0109]

[0110] 3.2 Energy Storage Battery Operation Constraints

[0111] The energy storage battery operation constraints are expressed as follows:

[0112]

[0113]

[0114] Where: is the battery charging and discharging power, is the maximum power value, E b,t is the battery level, is the upper and lower limits of battery power, μ b is the self-discharge coefficient. E b,0 is the battery charge at 0; N t is the last scheduling moment; E b,0 =E b,t, t=N t Indicates the balance of battery power within the scheduling cycle.

[0115] 3.3 Compressor and hydrogen storage tank operation constraints

[0116] The hydrogen production rate is less than the maximum allowable flow rate of the compressor, and the storage tank meets the capacity constraint:

[0117]

[0118]

[0119] Where: is the hydrogen flow rate of the compressor and its limitation, Hydrogen storage tank capacity, The upper and lower limits of the hydrogen storage tank capacity.

[0120] 3.4 Frequency Safety Constraints

[0121] The system must meet the maximum frequency change rate constraint (14), the quasi-steady-state frequency difference constraint (15), and the frequency minimum point constraint (23).

[0122] 3.5 Power Balance Constraints

[0123] The off-grid wind and solar power generation hydrogen production system meets the power balance requirement, namely:

[0124]

[0125] Where: It is the predicted value of wind and solar power output.

[0126] 3.6 Objective Function

[0127] Taking the maximization of hydrogen production revenue of the off-grid wind-solar power generation hydrogen production system as the optimization goal, it can be expressed as:

[0128]

[0129] Where: the first part represents the hydrogen production income, is the hydrogen selling price. The second and third parts are the primary frequency regulation and backup costs of PEM and AWE hydrogen production units, and the fourth and fifth parts are the primary frequency regulation and backup costs of energy storage batteries and wind turbines, respectively.

[0130] 4. Example Analysis

[0131] In this example, an off-grid hydrogen production system with a wind power configuration of 3×6.25MW, a photovoltaic configuration of 5MW, a hydrogen production unit AWE: 3×5MW, a PEM: 5×1MW, and a grid-connected energy storage configuration of 3.6MW / MWh is selected. The maximum frequency difference limit is set to 1Hz, the maximum frequency change rate limit is set to 0.5Hz / s, the steady-state frequency difference limit is set to 0.5Hz, and the scheduling step is set to 1 hour.

[0132] This example builds an electrolyzer optimization scheduling model based on the Wolfram Mathematica platform and uses the Gurobi solver to solve it.

[0133] In this example, the operating status of each hydrogen production unit in 24 periods is shown in Figure 4 (a) and Figure 4 (b); the frequency and frequency change rate at each moment in this example are shown in Figure 4 (a) and Figure 4 (b). Figure 5 and Figure 6 shown.

[0134] It can be seen that the optimization scheduling method proposed in the present invention that can take frequency constraints into consideration can utilize the hydrogen production unit to provide frequency regulation backup and frequency support. The lowest frequency point and frequency change rate of the system under off-grid operation meet the operating requirements, effectively realizing the safe and stable operation of the off-grid wind and solar power generation hydrogen production system.

Claims

1. An optimization scheduling method for an off-grid wind-solar power generation hydrogen production system considering frequency safety constraints, characterized in that: include: Establishing a frequency dynamic model of an off-grid wind-solar power generation hydrogen production system, wherein the off-grid wind-solar power generation hydrogen production system includes a grid-type energy storage device, a wind-solar power source, and a water electrolysis hydrogen production unit; Based on the power response characteristics of different types of electrolyzers in the water electrolysis hydrogen production unit, the proton exchange membrane electrolyzer is used as a fast frequency regulation unit to provide fast frequency regulation to the system; the alkaline electrolyzer is used as a primary frequency regulation unit to provide primary frequency regulation to the system; and different frequency regulation dead zones are set to achieve coordinated frequency regulation of the hybrid electrolyzer; Linearize the nonlinear frequency security constraints in the frequency dynamic model, including the maximum frequency change rate constraint, the quasi-steady-state frequency difference constraint, and the frequency minimum point constraint, and incorporate them into the day-ahead dispatch optimization model of the hydrogen production unit; Taking the maximization of hydrogen production revenue of the off-grid wind-solar power generation hydrogen production system as the objective function, combined with the operation constraints of the hydrogen production unit, the energy storage battery, the compressor and hydrogen storage tank, the frequency security constraints and the power balance constraints, the day-ahead scheduling optimization model is solved to generate a scheduling plan that meets the frequency security requirements.

2. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 1 is characterized in that: The frequency dynamic model includes frequency response models of renewable power generation and energy storage. In the grid-type energy storage, under the grid control based on the virtual synchronous machine, the energy storage battery simulates the swing equation of the synchronous generator. When the system has a frequency deviation, it provides primary frequency regulation and grid support power to the system, which is expressed as: Where: is the primary frequency modulation power of the grid-type energy storage; H b and D b It is the virtual inertia and damping in network control; Δf g (τ) is the system frequency deviation; ΔP b (τ) and are the total power change of the energy storage battery and the grid power provided by the energy storage; τ is the time variable; Under overspeed and pitch-shift load reduction control, the wind turbine provides primary frequency regulation backup. The primary frequency regulation power provided is expressed as: Where: is the available power of the fan; P w is the actual output of the fan; R w Primary frequency regulation reserve for fans; k deload is the load reduction ratio of the fan.

3. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 2 is characterized in that: The frequency dynamic model also includes a frequency response model provided by the water electrolysis hydrogen production unit; wherein, when the electrolyzer is in the startup state, under the additional virtual inertia and frequency droop control, when the system frequency is disturbed, the hydrogen production load power changes Expressed as: Where: Additional virtual inertia control coefficient; ΔP e PFR (τ) and ΔP e IR (τ) is the primary frequency modulation power and virtual inertia power provided by the electrolyzer.

4. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 3 is characterized in that: In the hybrid electrolyzer coordinated frequency regulation, the frequency support provided by the electrolyzer in the electric hydrogen production plant to the off-grid wind and solar power generation hydrogen production system is as follows: Where: Frequency modulation power for hydrogen production stations; t DB1 and t DB2 are the time when the frequency change reaches the FM dead zone limit 1 and the FM dead zone limit 2, respectively, where t DB1 <t DB2 ;ΔP e PEM (τ) and FM power provided to PEM and alkaline electrolyzer respectively; and The inertia size provided for PEM and alkaline electrolyzer respectively; The load size of the electrolyzer auxiliary equipment and compressor in the hydrogen production unit and the grid frequency are modeled as follows: Where: ΔP a (τ),ΔP c (τ) are the frequency modulation powers of electrolyzer auxiliary equipment and compressor respectively; D a and D c are the equivalent droop coefficients of the electrolyzer auxiliary equipment and the compressor in response to frequency changes; P auxi and P comp are the power of electrolyzer auxiliary equipment and compressor respectively; the frequency response model of off-grid wind-solar power generation hydrogen production system is expressed as: Where: ΔP e PFR,P (τ) and ΔP e PFR,A (τ) are the frequency modulation powers of the proton exchange membrane and alkaline electrolyzer, respectively; These are the power reserve sizes of PEM, alkaline electrolyzer, battery and fan frequency regulation respectively; t b , t w These are the response times of the primary frequency modulation of PEM, alkaline electrolyzer, battery, and fan, respectively; The primary frequency modulation power of the fan.

5. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 4 is characterized in that: When a power disturbance occurs in the system, the frequency dynamic model of the off-grid wind-solar power generation hydrogen production system at different time periods is as follows: Where: D l is the equivalent damping coefficient of the system; ΔP dis is the power disturbance magnitude; make At this time there are: Where: Equivalent inertia provided for alkaline electrolyzers and proton exchange membrane electrolyzers; Binary variable, when the value is 1, it means that the electrolytic cell is in the startup state during the period t; The inertia size provided for the PEM; A indicates the set to which the alkaline electrolyzer belongs.

6. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 5 is characterized in that: The maximum frequency change rate constraint is expressed according to formula (8): Where: is the maximum frequency change rate allowed by the system; The quasi-steady-state frequency difference constraint is expressed as: Where: Reserved for the primary frequency modulation of the system; The frequency minimum point constraint is as follows: Set t DB2 -t DB1 ≤t delay , t delay is the delay of PEM response to frequency modulation power, it is considered that the grid-type energy storage, wind turbine, proton exchange membrane, and alkaline electrolyzer start frequency modulation at the same time. At this time, (9) and (10) are combined to express as: Where: H w The amount of inertia provided to the fan; The expression of the lowest frequency point is: Where: Δf nadir is the lowest frequency point; D s 、H s 、R s They are the system's damping, inertia and total frequency regulation reserve respectively; After the disturbance occurs, the following inequality is satisfied: Where: Δf max is the maximum frequency difference; f DB It is the FM dead zone; For the right side of inequality (15), considering -ΔP dis D s <0,D s 2 (Δf max -f DB )>0, then the inequality (15) can be expressed as: Where: ΔP dis and D l,min are the power disturbance magnitude and the minimum damping magnitude provided by the system respectively; For the left side of inequality (15), let the intermediate quantity c = ΔP dis (D b +D l,min ), intermediate quantity x=H s R s , the left side of inequality (15) is expressed as a function At this time g(x)≤c; So there is an auxiliary variable x * ;make g(x)≤c, so the condition for inequality (15) to hold is rewritten as: Where: P is the set to which the PEM belongs; X e 、Y e , M are auxiliary variables; At this point, the nonlinear constraint about the lowest frequency point is transformed into a linear constraint.

7. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 6 is characterized in that: The operation constraints of the hydrogen production unit, the operation constraints of the energy storage battery, the operation constraints of the compressor and the hydrogen storage tank, the frequency safety constraints and the power balance constraints are as follows: 1) Operation constraints of hydrogen production units The state switching model of the hydrogen production unit is as follows: Where: and is a binary variable, and when the value is 1, it means that the electrolyzer is in the startup, standby and shutdown states during period t; is a binary variable, and when the value is 1, it means that the electrolyzer is hot started, cold started, or shut down during the period t; is the minimum downtime; E is the set to which all electrolytic cells belong; The power consumption of the hydrogen production unit includes the power of the electrolyzer and auxiliary equipment, and meets the specific power regulation range, namely: Where: is the electrolytic cell power, I and T are the electrolytic current and electrolytic cell temperature respectively; I t is the electrolysis current at time t, T e,t is the temperature of the electrolytic cell at time t; is the heat dissipation of the chiller, is the standby power of the hydrogen production unit, is the water pump power; P e,t 、 are electrolyzer power and auxiliary power respectively; is the fitting coefficient; is the chiller efficiency; is the standby power of the electrolytic cell; I, are the upper and lower limits of electrolysis current respectively; Model the temperature dynamics of the hydrogen production unit using a linear model: Where: is the heat capacity of the electrolytic cell, and The heat generation and heat dissipation of the electrolytic cell in unit scheduling time; is the cooling coefficient of the chiller; Δt is the scheduling time step; n c is the number of electrolysis chambers; is the neutral voltage; is the chiller conversion coefficient; T cool is the chiller temperature; T and are the upper and lower limits of the electrolytic cell temperature respectively; After participating in frequency regulation, the hydrogen production unit must also meet the reserve constraints: Where: and To serve as standby for the increase and decrease of hydrogen production units; Provide frequency regulation and standby for hydrogen production units; is the virtual inertia parameter; is the electrolysis current climbing limit; 2) Energy storage battery operation constraints The energy storage battery operation constraints are expressed as follows: Where: and are the battery charge and discharge power, is the maximum power value, E b,t is the battery capacity at time t, and is the upper and lower limits of battery power, μ b is the self-discharge coefficient; and is a binary variable; and is the battery charge and discharge efficiency; E b,0 is the battery charge at 0; N t is the last scheduling moment; and They are battery frequency regulation backup, network construction backup and up-regulation backup; 3) Operation constraints of compressors and hydrogen storage tanks The hydrogen production rate is less than the maximum allowable flow rate of the compressor, and the storage tank meets the capacity constraint: Where: and are the hydrogen production flow rate of the electrolyzer and the hydrogen flow rate limit allowed by the compressor, is the hydrogen storage tank capacity, and The upper and lower limits of the hydrogen storage tank capacity; and is the hydrogen flow rate of injection and release; is the storage capacity of the tank at 0; C is the set to which the compressor belongs; 4) Frequency safety constraints The off-grid wind-solar power generation hydrogen production system meets the maximum frequency change rate constraint of formula (11), the quasi-steady-state frequency difference constraint of formula (12), and the frequency minimum point constraint of formula (13); 5) Power balance constraints The off-grid wind and solar power generation hydrogen production system meets the power balance requirement, namely: Where: and It is the predicted value of wind and solar power output.

8. The off-grid wind-solar power generation hydrogen production system optimization scheduling method considering frequency safety constraints according to claim 7 is characterized in that: The objective function is: Where: the first part represents the hydrogen production income, is the selling price of hydrogen; q e,t is the hydrogen flow rate; They are hot start time, cold start time and shutdown time; and They are the standby cost and standby status parameters respectively; the second part is the primary frequency regulation and standby cost of the proton exchange membrane hydrogen production unit, and The third part is the primary frequency regulation and standby cost of the alkaline electrolyzer hydrogen production unit. The fourth part is the primary frequency regulation and backup cost of the energy storage battery. They are PEM frequency regulation, up-regulation, and down-regulation reserve costs respectively; the fifth part is the primary frequency regulation and reserve cost of wind turbines; is the fan standby cost.

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