A control method for grid-connected system of electro-methanol

Abstract

The present application belongs to the technical field of comprehensive energy, and particularly relates to a control method for an electric methanol grid-connected system. The present application is based on the working characteristics of the electric methanol system, models and analyzes the methanol electrolytic cell, classifies different load disturbance conditions, analyzes the virtual inertia response process of the electric methanol system, and finally introduces the power grid frequency component into the electric methanol system. When different power grid disturbances occur, the electric methanol system can virtually generate greater rotational inertia than the traditional synchronous generator in a short time, and can adjust the power in a short time to provide virtual inertia for the power grid, thereby improving the stability of the power system operation.

Description

Technical Field

[0001] This invention belongs to the field of integrated energy technology, specifically relating to a control method for an electric methanol grid-connected system. Background Technology

[0002] Methanol, a high-energy, clean new energy source, is a liquid at room temperature and pressure, making it easier to store and transport. As an important chemical raw material, methanol is widely used in automobiles, fuel cells, and chemical industries, and has gradually become a globally recognized ideal clean energy source. Therefore, developing electro-methanol production technology is of great significance for achieving low-carbon and sustainable development.

[0003] In the power industry, synchronous generators are widely used in hydropower and thermal power generation. Rich in mechanical inertia, their rotors can be considered energy storage sites. When grid disturbances occur, they release rotor kinetic energy and utilize inherent mechanical inertia to quickly respond to grid disturbances, suppressing grid frequency oscillations. However, many new energy power generation systems lack rotational inertia. When connected to the grid via power electronic converters, this reduces the rotational kinetic energy and energy reserves of the power system, leading to a decrease in its mechanical inertia, which is detrimental to grid stability. Similarly, the electro-methanol production system, being a static absorption unit with no rotational kinetic energy, also reduces the mechanical inertia of the power system when connected to the grid, thus decreasing grid stability. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a control method for a grid-connected methanol electrolysis system. By introducing a grid frequency component, the operating state of the methanol electrolysis system is adjusted under different grid disturbances. Based on the operating status of the methanol electrolyzer and the fluctuations in the grid frequency, power is rapidly regulated, forming a virtual inertia control strategy that achieves stable and efficient methanol electrolysis while maintaining stable grid operation.

[0005] This invention proposes a control method for an electro-methanol grid-connected system. First, it detects disturbances and assesses the frequency variation introduced into the power grid. Then, it switches the operating mode of the electro-methanol system based on the frequency variation. When the frequency variation is less than the allowable deviation, the electro-methanol system operates in a disturbance-free control mode. When the frequency variation exceeds the allowable deviation, the operating status of the methanol electrolyzer is assessed. If the safety factor of the methanol electrolyzer is within the allowable range, the electro-methanol system operates in a disturbance-controlled strategy mode: when the grid frequency variation is greater than 0, the electro-methanol system operates at high power; when the grid frequency variation is less than 0, the electro-methanol system operates at low power; otherwise, the methanol electrolyzer shuts down. This invention, based on the grid frequency variation and the safety factor of the methanol electrolyzer, allows the electro-methanol system to operate in different modes, efficiently producing methanol while providing short-term inertia support for the power system, thus improving the stability of the power grid operation.

[0006] The technical solution of this invention is:

[0007] A control method for an electric methanol grid-connected system, the electric methanol grid-connected system comprising an interconnected grid-connected rectifier, a DC / DC step-down converter, and an electric methanol production system, the electric methanol grid-connected system being connected to a power grid system including wind power generation, a power grid, and AC loads, wherein the power grid is composed of synchronous generators, the control method comprising:

[0008] The system acquires the change in grid frequency, sets the allowable deviation of the change in grid frequency, determines whether the change in AC load causes grid disturbance, and adjusts the input power of the electro-methanol system based on the determination result.

[0009] The specific method for adjusting the input power of the electro-methanol production system is as follows: a safety factor is set for the electro-methanol production system. Within the allowable range of the safety factor, a virtual moment of inertia is set for the electro-methanol production system. The virtual moment of inertia is used to simulate the moment of inertia required by the power generation system. Combined with the relevant parameters of the electro-methanol production system and the generator of the power generation system, the input power of the methanol electrolyzer in the electro-methanol production system is calculated. When the input power exceeds the allowable range of the safety factor, the electro-methanol production system is shut down.

[0010] Furthermore, the specific method for determining whether a power grid disturbance is caused by a change in AC load is as follows:

[0011] Define the obtained change in grid frequency as Δf. When Δf is greater than the allowable deviation, record the action value of the frequency change as 1.

[0012] After a set delay time, Δf is collected again. If Δf is greater than the allowable deviation, the action amount of the frequency change is recorded as 1; otherwise, the action amount of the frequency change is recorded as 0.

[0013] Compare the action quantities of the frequency change at two time points. If both action quantities are 1, it is determined that there is a power grid disturbance. In this case, the input power of the electric methanol production system is adjusted. Otherwise, it is determined that there is no disturbance, and the control method remains unchanged.

[0014] Furthermore, when a power grid disturbance is determined to exist, the specific handling method is as follows:

[0015] If Δf > 0, execute:

[0016] First, determine if the safety factor is within the allowable range. If so, the electro-methanol production system will operate at high power. Simultaneously, calculate the input power of the methanol electrolyzer in the electro-methanol production system:

[0017]

[0018]

[0019] Among them, J el Defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of a methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el i el These represent the input voltage and input current of the methanol electrolyzer, respectively, γ CH3OH-0 V is the initial safety factor for the methanol electrolyzer. 额定CH3OH J represents the rated methanol storage capacity of the methanol electrolyzer; g ω e P n E k Let J be the moment of inertia, synchronous angular velocity, number of pole pairs, and rotational kinetic energy of the synchronous generator, respectively. From the above equation, it can be seen that the energy stored in the electro-methanol production system is equivalent to a moment of inertia of J. g The number of pole pairs is P n The rotational kinetic energy stored in the rotor of the synchronous generator; W el P is the power input to the methanol electrolyzer; h is the ratio of the rate of change of the safety factor of the methanol electrolyzer to the rate of change of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; CH3OH The rate at which methanol is produced per unit time; thus, a new control input power is obtained;

[0020] Otherwise, the electro-methanol system will be shut down;

[0021] If Δf≤0, execute:

[0022] First, determine if the safety factor is within the allowable range. If so, the electro-methanol system operates at low power. Simultaneously, calculate the input power of the methanol electrolyzer in the electro-methanol system:

[0023]

[0024]

[0025] Among them, J el Defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of a methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el i el These represent the input voltage and input current of the methanol electrolyzer, respectively, γ CH3OH-0 V is the initial safety factor for the methanol electrolyzer. 额定CH3OH J represents the rated methanol storage capacity of the methanol electrolyzer; g ω e P nE k Let J be the moment of inertia, synchronous angular velocity, number of pole pairs, and rotational kinetic energy of the synchronous generator, respectively. From the above equation, it can be seen that the energy stored in the electro-methanol production system is equivalent to a moment of inertia of J. g The number of pole pairs is P n The rotational kinetic energy stored in the rotor of the synchronous generator; W el P is the power input to the methanol electrolyzer; h is the ratio of the rate of change of the safety factor of the methanol electrolyzer to the rate of change of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; CH3OH The rate at which methanol is produced per unit time; thus, a new control input power is obtained;

[0026] Otherwise, the electro-methanol system will be shut down.

[0027] Furthermore, the specific method for determining whether the safety factor is within the allowable range is as follows:

[0028] Calculate the safety factor γ CH3OH The calculation formula is shown below. If γ CH3OH If the value is less than 0.9, the safety factor is within the acceptable range; otherwise, the safety factor is not within the acceptable range.

[0029]

[0030] In the formula V CH3OH V represents the volume of methanol produced. 额定CH3OH P represents the rated methanol storage capacity of the methanol electrolyzer; CH3OH This represents the rate at which methanol is produced per unit time.

[0031] The beneficial effects of this invention are as follows: This invention proposes a control method for an electric methanol-to-grid system. By introducing a frequency signal into the system and classifying different grid disturbances, the electric methanol-to-grid system can generate a virtual moment of inertia larger than that of a synchronous generator in a short time, and perform power regulation in a short time to provide virtual inertia for the grid and improve the stability of the power system operation. Specifically, it has the following advantages: (1) This invention defines the virtual inertia of the electric methanol-to-grid system and proposes a virtual inertia control strategy based on the electric methanol-to-grid system. When the electric methanol-to-grid system with no rotational inertia is connected to the grid, it can generate the rotational inertia required by the power system, suppress grid disturbances, and improve the stability of the power system operation. (2) This invention enables the electric methanol-to-grid system to operate in different operating modes according to the magnitude of the grid frequency change, providing inertial support for the grid while ensuring the high efficiency of the electric methanol-to-grid system. Attached Figure Description

[0032] Figure 1 This is a simulation topology diagram of the electric methanol grid-connected system of the present invention.

[0033] Figure 2 This is a structural diagram of the control system of the electric methanol grid-connected system of the present invention.

[0034] Figure 3 This is a flowchart of the virtual inertia control of the present invention.

[0035] Figure 4 This is a safety factor diagram of the methanol electrolyzer of the present invention.

[0036] Figure 5 This is a schematic diagram of the virtual inertia control principle of the electric methanol grid-connected system of the present invention.

[0037] Figure 6 This is the power grid frequency diagram for operating condition 1 in the preferred embodiment of the specific application of the present invention.

[0038] Figure 7 This is a safety factor diagram of the methanol electrolyzer in the best embodiment of the specific application of the present invention, under condition 1.

[0039] Figure 8 The diagram shows the grid-connected power of the electro-methanol system in the preferred embodiment of the present invention under operating condition 1.

[0040] Figure 9 This is the power grid frequency diagram for operating condition 2 in the preferred embodiment of the specific application of the present invention.

[0041] Figure 10 This is a safety factor diagram of the methanol electrolyzer in the best embodiment of the specific application of the present invention, specifically under condition 2.

[0042] Figure 11 The diagram shows the grid-connected power of the electro-methanol system in the preferred embodiment of the present invention, under operating condition 2.

[0043] Figure 12 This is the power grid frequency diagram for operating condition 3 in the preferred embodiment of the specific application of the present invention.

[0044] Figure 13 This is a safety factor diagram of the methanol electrolyzer in the best embodiment of the specific application of the present invention, specifically under condition 3.

[0045] Figure 14 The diagram shows the grid-connected power of the electro-methanol system in the preferred embodiment of the present invention under operating condition 3.

[0046] Figure 15 This is the power grid frequency diagram for operating condition 4 in the best embodiment of the specific application of the present invention.

[0047] Figure 16 This is a safety factor diagram of the methanol electrolyzer in the best embodiment of the specific application of the present invention, specifically under condition 4.

[0048] Figure 17 The diagram shows the grid-connected power of the electro-methanol system in operating condition 4, which is the preferred embodiment of the present invention. Detailed Implementation

[0049] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0050] This invention proposes a virtual inertia control strategy for an electro-methanol grid-connected system. By introducing a grid frequency component, the operating state of the electro-methanol system is adjusted under different grid disturbances. Based on the operating status of the methanol electrolyzer and the fluctuations in grid frequency, power is rapidly regulated, thus forming a virtual inertia control strategy that achieves stable and efficient electro-methanol production while ensuring stable grid operation.

[0051] The method of the present invention can be described in the following steps:

[0052] Step 1: Collect the frequency change Δf of the power system.

[0053] Step 2: Determine whether the fluctuation is a false disturbance through disturbance detection. If so, proceed to step 10; otherwise, proceed to step 3.

[0054] Step 3: Determine whether the frequency change Δf is greater than 0. If Δf>0, proceed to step 4; otherwise, proceed to step 6.

[0055] Step 4: Determine whether the safety factor of the methanol electrolyzer is within the allowable range. If yes, proceed to step 5; otherwise, proceed to step 9.

[0056] Step 5: The electro-methanol system operates at high power, then proceed to step 8.

[0057] Step 6: Determine whether the safety factor of the methanol electrolyzer is within the allowable range. If yes, proceed to step 7; otherwise, proceed to step 9.

[0058] Step 7: The electro-methanol system operates at low power; proceed to step 8.

[0059] Step 8: The electro-methanol production system operates in disturbance control mode. During power system frequency changes, the input power of the methanol electrolyzer in the electro-methanol production system is:

[0060]

[0061] In the formula, J el Defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of a methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el i el These represent the input voltage and input current of the methanol electrolyzer, respectively, γCH3OH-0 V is the initial safety factor for the methanol electrolyzer. 额定CH3OH J represents the rated methanol storage capacity of the methanol electrolyzer; g ω e P n E k Let J be the moment of inertia, synchronous angular velocity, number of pole pairs, and rotational kinetic energy of the synchronous generator, respectively. From the above equation, it can be seen that the energy stored in the electro-methanol production system is equivalent to a moment of inertia of J. g The number of pole pairs is P n The rotational kinetic energy stored in the rotor of the synchronous generator; W el P is the power input to the methanol electrolyzer; h is the ratio of the rate of change of the safety factor of the methanol electrolyzer to the rate of change of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; CH3OH The rate at which methanol is produced per unit time; proceed to step 10.

[0062] Step 9: When the safety factor of the methanol electrolyzer reaches the upper limit, the methanol electrolysis system shuts down and stops producing methanol. Proceed to step 10.

[0063] Step 10: End

[0064] In the aforementioned virtual inertia control strategy based on an electric methanol grid-connected system, step 2 involves disturbance detection to determine whether the fluctuation is a frequency-related erroneous disturbance. This process includes the following steps:

[0065] Step 2.1: When the change in grid frequency exceeds the allowable deviation, record the action value of the frequency change as 1.

[0066] Step 2.2: After the set delay time, collect the power grid frequency change again. If the power grid frequency change is greater than the allowable deviation, record the action value of the frequency change as 1; otherwise, record the action value of the frequency change as 0.

[0067] Step 2.3: Compare the action quantities of the frequency change at two time points. If both action quantities are 1, it indicates that there is a power grid disturbance in the power system; otherwise, it is considered that there is no disturbance in the power system.

[0068] In the above control method, step 4 determines whether the safety factor of the methanol electrolyzer is within the allowable range. This process includes the following steps:

[0069] Step 4.1: Calculate the safety factor γ of the methanol electrolyzer. CH3OH ;

[0070] Step 4.2: If γ CH3OH If the value is less than 0.9, the safety factor of the methanol electrolyzer is within the allowable range; otherwise, the safety factor of the methanol electrolyzer is not within the allowable range.

[0071] In the above control method, step 6 determines whether the safety factor of the methanol electrolyzer is within the allowable range. This process includes the following steps:

[0072] Step 6.1: Calculate the safety factor γ of the methanol electrolyzer. CH3OH ;

[0073] Step 6.2: If γ CH3OH If the value is less than 0.9, the safety factor of the methanol electrolyzer is within the allowable range; otherwise, the safety factor of the methanol electrolyzer is not within the allowable range.

[0074] Electric methanol grid-connected system, such as Figure 1 As shown, the system consists of four parts: an electro-methanol production system, wind power generation, a power grid, and an AC load. The simulation mainly verifies the inertial support of the electro-methanol production system to the power grid when the grid is disturbed. Therefore, the wind power generation is simplified, i.e., the average wind speed is set to 10 m / s. The simulation adopts two methods: ① constant power control; ② virtual inertia control. Four operating conditions of the electro-methanol production system are set: (1) Condition 1: the average wind speed of the wind power generation remains unchanged, and the AC load is reduced by 200 kW at 6 s; (2) Condition 2: the average wind speed of the wind power generation remains unchanged, and the AC load is increased by 200 kW at 6 s; (3) Condition 3: the AC load remains unchanged, and the average wind speed of the wind power generation increases to 12 m / s at 6 s; (4) Condition 4: the AC load remains unchanged, and the average wind speed of the wind power generation decreases to 17 m / s at 6 s.

[0075] Operating condition 1: At 6s, the AC load is unloaded, such as Figure 6 As shown in the constant power control diagram, the grid frequency increases to 50.39Hz. When using virtual inertia control, the rate of increase in grid frequency decreases, and the peak value of the grid frequency change drops from 50.39Hz to 50.28Hz. The magnitude of the grid frequency change decreases by 28.21%, and there are no fluctuations during the grid frequency recovery process. Compared to a synchronous generator of the same capacity, virtual inertia control has a faster response speed and a more stable adjustment process. Based on the operating characteristics of the methanol electrolyzer, the electro-methanol production system at this time abandons a portion of the electro-methanol production rate for rapid power response, and... Figure 7 It can be seen that the safety factor of the methanol electrolyzer decreases somewhat during the adjustment period. (From...) Figure 8 It can be seen that the grid-connected power of the electro-methanol system rises rapidly, reaching the upper limit of power regulation. When the grid frequency variation is adjusted to within the allowable deviation range, the methanol electrolyzer operates in a undisturbed mode, at which point the power decreases, and efficient electro-methanol production continues. From Figure 8 It can be seen that when virtual inertia control is used, the electric methanol production system can quickly respond to power changes and provide short-term inertial support to the power grid by rapidly adjusting power in a short time.

[0076] Operating Condition 2: At 6 seconds, the AC load is applied, such as... Figure 9 As shown in the constant power control diagram, the grid frequency drops to 49.61Hz. When virtual inertia control is used, the rate of decrease in grid frequency decreases, and the peak value of the grid frequency change increases from 49.61Hz to 49.7Hz. The magnitude of the grid frequency change decreases by 23.08%, and there is no fluctuation during the grid frequency recovery process. Based on the operating characteristics of the methanol electrolyzer, the electro-methanol production system abandons a portion of the electro-methanol production rate to quickly respond to power changes. Figure 10 It can be seen that the safety factor of the methanol electrolyzer decreases somewhat during the adjustment period. (From...) Figure 11 It can be seen that the grid-connected power of the electro-methanol system drops rapidly, reaching the lower limit of power regulation. When the change in grid frequency is adjusted to within the allowable deviation range, the methanol electrolyzer operates in a undisturbed mode, at which point the power increases, and methanol is produced efficiently through electro-methanol production.

[0077] Operating condition 3: At 6s, the average wind speed for wind power generation increases, such as Figure 12 As shown in the constant power control diagram, the grid frequency rises to 50.19Hz. When virtual inertia control is used, the rate of increase in grid frequency decreases, and the peak value of the grid frequency change drops from 50.19Hz to 50.11Hz. The magnitude of the grid frequency change decreases by 44.44%, and there are no fluctuations during the grid frequency recovery process. Compared to a synchronous generator of the same capacity, virtual inertia control has a faster response speed, better suppression effect, and a more stable adjustment process. Based on the operating characteristics of the methanol electrolyzer, the electro-methanol production system at this time abandons a portion of the electro-methanol production rate to quickly respond to power, and... Figure 13 It can be seen that the safety factor of the methanol electrolyzer decreases somewhat during the adjustment period. (From...) Figure 14 It can be seen that the grid-connected power of the electro-methanol system rises rapidly. When the change in grid frequency is adjusted to within the allowable deviation range, the methanol electrolyzer operates in a undisturbed mode, at which point the power decreases, and the system continues to efficiently electro-produce methanol.

[0078] Operating condition 4: At 6s, the average wind speed for wind power generation decreases, such as Figure 15 As shown in the constant power control diagram, the grid frequency drops to 49.7Hz. When virtual inertia control is used, the rate of decrease in grid frequency decreases, and the peak value of the grid frequency change increases from 49.7Hz to 49.84Hz. The magnitude of the grid frequency change decreases by 30.43%, and there is no fluctuation during the grid frequency recovery process. Based on the operating characteristics of the methanol electrolyzer, the electro-methanol production system abandons a portion of the electro-methanol production rate to quickly respond to power changes. Figure 16 It can be seen that the safety factor of the methanol electrolyzer decreases somewhat during the adjustment period. (From...) Figure 17 It can be seen that the grid-connected power of the electro-methanol system drops rapidly. When the change in grid frequency is adjusted to within the allowable deviation range, the methanol electrolyzer operates in a undisturbed mode, at which point the power increases, and the system continues to efficiently electro-methanol.

[0079] The principle of virtual inertia control in an electric methanol grid-connected system is analyzed as follows:

[0080] The rated methanol storage capacity of the electro-methanol production system is V. 额定CH3OH The methanol production rate per unit time is P. CH3OH Then the safety factor of the methanol electrolyzer at time t is:

[0081]

[0082] In the formula V CH3OH V represents the volume of methanol produced. 额定CH3OH P represents the rated methanol storage capacity of the methanol electrolyzer; CH3OH This represents the rate at which methanol is produced per unit time.

[0083] Therefore, the input power of the methanol electrolyzer can be expressed as:

[0084]

[0085] In the formula, U el i el These represent the input voltage and input current of the methanol electrolyzer, respectively, γ CH3OH-0 V is the initial safety factor for the methanol electrolyzer. 额定CH3OH This is the rated methanol storage capacity of the methanol electrolyzer.

[0086] During the frequency variation of the power system, the energy stored in the electro-methanol production system can be expressed as:

[0087]

[0088]

[0089] From equations (3-11), it can be seen that the energy of the electro-methanol production system can be considered as having a pole pair number of P. n The moment of inertia is J g The kinetic energy possessed by the synchronous generator can be controlled by h=(ω e *Δγ CH3OH ) / (γ CH3OH-0 *Δω e The size of J allows an electrically powered methanol production system with no rotational inertia to virtually generate a larger moment of inertia than a synchronous generator, providing inertia support for the power grid and improving the stability of the power system operation. el Defined as the virtual inertia of the electro-methanol production system.

[0090] The virtual inertia of the electro-methanol production system can be further expressed as:

[0091]

[0092] In the formula, γ CH3OH Defined as the safety factor of a methanol electrolyzer; γ CH3OH-0 Δγ is the initial safety factor for the methanol electrolyzer. CH3OH Defined as the change in the safety factor of the methanol electrolyzer; V 额定CH3OH J represents the rated methanol storage capacity of the methanol electrolyzer; g ω e P n E k These are the moment of inertia, synchronous angular velocity, number of pole pairs, and rotational kinetic energy of a synchronous generator, respectively; W el P is the power input to the methanol electrolyzer; h is the ratio of the rate of change of the safety factor of the methanol electrolyzer to the rate of change of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; CH3OH The rate at which methanol is produced per unit time;

[0093] like Figure 5 The diagram shows the virtual inertia control principle of the electro-methanol grid-connected system of this invention. During normal operation, the system operates in a disturbance-free mode, maximizing the efficiency of the electro-methanol production process. When a disturbance occurs in the power system, the change in grid frequency Δf is collected and detected. If the disturbance is a false disturbance, the system continues to operate in the false disturbance mode; otherwise, it operates in the disturbance mode. When a grid disturbance is confirmed, a safety factor γ for the methanol electrolyzer is introduced to suppress sudden grid changes and ensure the safe operation of the electro-methanol system. CH3OH When γ CH3OH Within acceptable limits, the grid frequency variation is passed through a low-pass filter. By adjusting the ratio of the rate of change of the methanol electrolyzer's safety factor to the rate of change of the synchronous generator's speed, the operating current of the electro-methanol production system is controlled, thereby controlling the power of the electro-methanol production system. This allows for rapid power regulation within a short time, providing inertial support to the grid. When γ... CH3OH If the situation is not within acceptable limits, the electric methanol production system will be shut down to ensure its safety.

[0094] In summary, this invention proposes a control method for an electro-methanol grid-connected system, addressing the problem of reduced mechanical inertia in the power system caused by grid connection of the electro-methanol system. To improve the stability of power system operation, increase the efficiency of electro-methanol production, and ensure efficient operation of the electro-methanol system, the inertia response is achieved by controlling power output through an introduced frequency signal, responding to frequency fluctuations similar to synchronous generators. The electro-methanol system produces methanol through a methanol electrolyzer, and its efficiency is related to the input power of the electrolyzer. When the grid frequency changes, it does not respond, therefore the electro-methanol system is not coupled with the grid frequency and cannot perform an inertia response like a conventional synchronous generator to suppress grid frequency fluctuations. Based on the operating characteristics of the electro-methanol system, this invention models and analyzes the methanol electrolyzer, classifies different load disturbances, and analyzes the virtual inertia response process of the electro-methanol system. Finally, by introducing a grid frequency component into the electro-methanol system, the electro-methanol system can generate a larger virtual moment of inertia than a synchronous generator in a short time when different grid disturbances occur, and adjusts its power to provide virtual inertia to the grid, thereby improving the stability of power system operation.

Claims

1. A control method for an electric methanol grid-connected system, the electric methanol grid-connected system comprising an interconnected grid-connected rectifier, a DC / DC step-down converter, and an electric methanol production system, the electric methanol grid-connected system being connected to a power grid system, including wind power generation, a power grid, and AC loads, wherein the power grid is composed of synchronous generators, the control method comprising: The system acquires the change in grid frequency, sets the allowable deviation of the change in grid frequency, determines whether the change in AC load causes grid disturbance, and adjusts the input power of the electro-methanol system based on the determination result. The specific method for adjusting the input power of the electro-methanol system is as follows: a safety factor is set for the electro-methanol system. Within the allowable range of the safety factor, a virtual moment of inertia is set for the electro-methanol system. The virtual moment of inertia is used to simulate the moment of inertia required by the power generation system. Combined with the relevant parameters of the electro-methanol system and the generator of the power generation system, the input power of the methanol electrolyzer in the electro-methanol system is calculated. When the input power exceeds the allowable range of the safety factor, the electro-methanol system is shut down. When a power grid disturbance is determined to exist, the specific handling method is as follows: If Δf > 0, execute: First, determine if the safety factor is within the allowable range. If so, the electro-methanol production system will operate at high power. Simultaneously, calculate the input power of the methanol electrolyzer in the electro-methanol production system: ， ， ， ， ， Among them, J el Defined as the virtual moment of inertia of the methanol electrolyzer; Defined as the safety factor of a methanol electrolyzer; Defined as the change in the safety factor of the methanol electrolyzer; U el i el These represent the input voltage and input current of the methanol electrolyzer, respectively. V is the initial safety factor for the methanol electrolyzer. 额定CH3OH J represents the rated methanol storage capacity of the methanol electrolyzer; g , P n E k Let J be the moment of inertia, synchronous angular velocity, number of pole pairs, and rotational kinetic energy of the synchronous generator, respectively. From the above equation, it can be seen that the energy stored in the electro-methanol production system is equivalent to a moment of inertia of J. g The number of pole pairs is P n The rotational kinetic energy stored in the rotor of the synchronous generator; W el denoted as , where is the power input to the methanol electrolyzer; h is the ratio of the rate of change of the safety factor of the methanol electrolyzer to the rate of change of the rotational speed of the conventional synchronous generator; and k is the ratio of the methanol production rate to the input power of the methanol electrolyzer. The ratio of P; CH3OH The rate at which methanol is produced per unit time; thus, a new control input power is obtained; Otherwise, the electro-methanol system will be shut down; If Δf ≤ 0, execute: First, determine if the safety factor is within the allowable range. If so, the electric methanol production system will operate at low power; otherwise, the electric methanol production system will be shut down.

2. The control method for an electro-methanol grid-connected system according to claim 1, characterized in that, The specific method for determining whether a power grid disturbance is caused by a change in AC load is as follows: Define the obtained change in grid frequency as Δf. When Δf is greater than the allowable deviation, record the action value of the frequency change as 1. After a set delay time, Δf is collected again. If Δf is greater than the allowable deviation, the action amount of the frequency change is recorded as 1; otherwise, the action amount of the frequency change is recorded as 0. Compare the action quantities of the frequency change at two time points. If both action quantities are 1, it is determined that there is a power grid disturbance. In this case, the input power of the electric methanol production system is adjusted. Otherwise, it is determined that there is no disturbance, and the control method remains unchanged.

3. The control method for an electro-methanol grid-connected system according to claim 2, characterized in that, The specific method for determining whether the safety factor is within the allowable range is as follows: Calculate the safety factor The calculation formula is shown in the following equation: If If the safety factor is within acceptable limits, then the safety factor is within acceptable limits; otherwise, the safety factor is outside acceptable limits. ， In the formula V CH3OH V represents the volume of methanol produced. 额定CH3OH P represents the rated methanol storage capacity of the methanol electrolyzer; CH3OH This represents the rate at which methanol is produced per unit time.

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