Control method for electricity-to-methanol grid-connected system

Abstract

The invention belongs to the technical field of comprehensive energy, and particularly relates to a control method for an electricity-to-methanol grid-connected system. Based on the working characteristics of the electrical methanol system, the virtual inertia response process of the electrical methanol system is analyzed by carrying out modeling analysis on a methanol electrolytic cell and classifying different load disturbance conditions, and finally, the power grid frequency component is introduced into the electrical methanol system, so that when different power grid disturbances occur, the virtual inertia response process of the electrical methanol system is analyzed. The electricity-to-methanol system can virtualize rotational inertia larger than that of a traditional synchronous generator in a short time, the power is adjusted in a short time, virtual inertia is provided for a power grid, and therefore the operation stability of an electric power system is improved.

Description

Technical Field

[0001] The present invention belongs to the field of comprehensive energy technology, and in particular relates to a control method for a grid-connected system for producing methanol from electricity. Background Art

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

[0003] In the electric power industry, synchronous generators are widely used in hydropower and thermal power generation. They are rich in mechanical inertia, and their rotors can be regarded as a place to store energy. When the power grid is disturbed, they release the rotor kinetic energy and use the inherent mechanical inertia to quickly respond to the grid disturbance and suppress the frequency oscillation of the grid. However, a large number of new energy power generation systems have no rotational inertia. When they are connected to the grid through power electronic converters, the rotational kinetic energy and energy reserves of the power system will be reduced, resulting in a reduction in its mechanical inertia, which is not conducive to the stable operation of the power grid. The methanol system is a static absorption unit with no rotational kinetic energy. Connecting to the grid will also reduce the mechanical inertia of the power system and reduce the stability of the grid operation. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a control method for a methanol-to-electricity grid-connected system, which introduces the grid frequency component to adjust the working state of the methanol-to-electricity system under different grid disturbance conditions. According to the operating state of the methanol electrolyzer and the fluctuation of the grid frequency, power regulation is performed quickly to form a virtual inertia control strategy that can maintain stable operation of the grid while producing methanol stably and efficiently.

[0005] The present invention proposes a control method for a methanol-to-electricity grid-connected system. First, the introduced grid frequency variation is judged through disturbance detection, and then the operation mode of the methanol-to-electricity system is switched according to the frequency variation. When the frequency variation is less than the allowable deviation, the methanol-to-electricity system operates in a disturbance-free operating condition control mode. When the frequency variation is greater than the allowable deviation, the operating state of the methanol electrolyzer is judged. If the safety factor of the methanol electrolyzer is within the allowable range, the methanol-to-electricity system operates in a disturbance operating condition control strategy mode. When the grid frequency variation is greater than 0, the methanol-to-electricity system operates at high power. When the grid frequency variation is less than 0, the methanol-to-electricity system operates at low power; otherwise, the methanol electrolyzer is shut down. According to the grid frequency variation and the safety factor of the methanol electrolyzer, the methanol-to-electricity system is placed in different operating modes according to the present invention. While efficiently producing methanol, it provides short-term inertia support for the power system and improves the stability of grid operation.

[0006] The technical solution of the present invention is:

[0007] A control method for a methanol-to-electricity grid-connected system, the methanol-to-electricity grid-connected system comprising a grid-connected rectifier, a DC / DC converter and a methanol-to-electricity system connected to each other, the methanol-to-electricity grid-connected system being connected to a power grid system, including wind power generation, a power grid and an AC load, wherein the power grid is composed of a synchronous generator, the control method comprising:

[0008] Obtain the grid frequency change and set the allowable deviation of the grid frequency change to determine whether grid disturbance is caused by the change of AC load, and adjust the input power of the methanol power system according to the determination result;

[0009] The specific method for adjusting the input power of the methanol-to-electricity system is to set a safety factor for the methanol-to-electricity system, and within the allowable range of the safety factor, set a virtual moment of inertia for the methanol-to-electricity system, wherein the virtual moment of inertia is used to virtualize the moment of inertia required for the power generation system, and combine the relevant parameters of the methanol-to-electricity system and the generator of the power generation system to calculate the input power of the methanol electrolyzer in the methanol-to-electricity system, and shut down the methanol-to-electricity system when the input power exceeds the allowable range of the safety factor.

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

[0011] The acquired power grid frequency change is defined as Δf. When Δf is greater than the allowable deviation, the action value of the frequency change at this time is recorded as 1.

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

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

[0014] Furthermore, when it is determined that there is a power grid disturbance, the specific processing method is as follows:

[0015] If Δf>0, execute:

[0016] First determine whether the safety factor is within the allowable range. If so, the methanol production system will operate at high power. At the same time, the input power of the methanol electrolyzer in the methanol production system is calculated as:

[0017]

[0018]

[0019] Among them, J el is defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of the methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el 、i el are the input voltage and input current of the methanol electrolyzer, γ CH3OH-0 is the initial safety factor of the methanol electrolyzer, V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; J g ,ω e , P n 、E k They are the moment of inertia, synchronous angular velocity, pole pair number, and rotational kinetic energy of the synchronous generator. From the above formula, we can see that the energy stored in the methanol power generation system is equivalent to the moment of inertia J g , the number of pole pairs is P n The rotational kinetic energy stored in the synchronous generator rotor; W el is the power input to the methanol electrolyzer; h is the ratio of the change rate of the safety factor of the methanol electrolyzer to the change rate of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time; thus, a new control input power is obtained;

[0020] Otherwise, the methanol power generation system is shut down;

[0021] If Δf≤0, execute:

[0022] First determine whether the safety factor is within the allowable range. If so, the methanol power generation system operates at low power. At the same time, the input power of the methanol electrolyzer in the methanol power generation system is calculated as:

[0023]

[0024]

[0025] Among them, J el is defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of the methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el 、i el are the input voltage and input current of the methanol electrolyzer, γ CH3OH-0 is the initial safety factor of the methanol electrolyzer, V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; J g ,ω e , P n、E k They are the moment of inertia, synchronous angular velocity, pole pair number, and rotational kinetic energy of the synchronous generator. From the above formula, we can see that the energy stored in the methanol power generation system is equivalent to the moment of inertia J g , the number of pole pairs is P n The rotational kinetic energy stored in the synchronous generator rotor; W el is the power input to the methanol electrolyzer; h is the ratio of the change rate of the safety factor of the methanol electrolyzer to the change rate of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time; thus, a new control input power is obtained;

[0026] Otherwise, the methanol power generation system is shut down.

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

[0028] Calculate the safety factor γ CH3OH , the calculation formula is as follows: if γ CH3OH <0.9, the safety factor is within the allowable range, otherwise the safety factor is not within the allowable range.

[0029]

[0030] Where V CH3OH is the volume of methanol produced; V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time.

[0031] The beneficial effects of the present invention are as follows: the present invention proposes a control method for a methanol-to-electricity grid-connected system, which introduces a frequency signal into the system and classifies different grid disturbances, so that the methanol-to-electricity system can virtualize a larger moment of inertia than a synchronous generator in a short period of time, perform power regulation in a short period of time, provide virtual inertia for the grid, and improve the stability of the power system operation. Specifically, it has the following advantages: (1) The present invention defines the virtual inertia of the methanol-to-electricity system, and proposes a virtual inertia control strategy based on the methanol-to-electricity grid-connected system, so that when a stationary methanol-to-electricity system with no moment of inertia is connected to the grid, it can virtualize the moment of inertia required by the power system, suppress grid disturbances, and improve the stability of the power system operation. (2) According to the magnitude of the grid frequency change, the present invention enables the methanol-to-electricity system to operate in different operating modes, provides inertia support for the grid, and ensures the high efficiency of methanol-to-electricity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a simulation topology diagram of the grid-connected system for producing methanol from electricity according to the present invention.

[0033] Figure 2 It is a control system structure diagram of the power-to-methanol grid-connected system of the present invention.

[0034] Figure 3 It is the virtual inertia control flow chart of the present invention.

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

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

[0037] Figure 6 It is a grid frequency diagram of working condition 1 in the best embodiment of a specific application of the present invention.

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

[0039] Figure 8 It is the grid-connected power diagram of the methanol production system under working condition 1 in the best embodiment of the specific application of the present invention.

[0040] Fig. 9 It is a grid frequency diagram of working condition 2 in the best embodiment of a specific application of the present invention.

[0041] Fig.10 It is the safety factor diagram of the methanol electrolyzer in working condition 2 in the best embodiment of the specific application of the present invention.

[0042] Fig.11 It is the grid-connected power diagram of the methanol production system under working condition 2 in the best embodiment of the specific application of the present invention.

[0043] Fig.12 It is a grid frequency diagram of working condition 3 in the best embodiment of a specific application of the present invention.

[0044] Fig.13 It is a safety factor diagram of a methanol electrolyzer in operating condition 3 in the best embodiment of a specific application of the present invention.

[0045] Fig.14 It is the grid-connected power diagram of the methanol production system under operating condition 3 in the best embodiment of the specific application of the present invention.

[0046] Fig.15 It is a grid frequency diagram of working condition 4 in the best embodiment of a specific application of the present invention.

[0047] Fig.16 It is a safety factor diagram of a methanol electrolyzer in operating condition 4 in the best embodiment of a specific application of the present invention.

[0048] Fig.17 It is the grid-connected power diagram of the methanol production system under operating condition 4 in the best embodiment of the specific application of the present invention. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0050] The present invention proposes a virtual inertia control strategy based on the grid-connected system of methanol production from electricity. By introducing the grid frequency component, the working state of the methanol production from electricity system is adjusted under different grid disturbance conditions. According to the operating state of the methanol electrolyzer and the fluctuation of the grid frequency, the power is adjusted quickly, thereby forming a virtual inertia control strategy that can produce methanol from electricity stably and efficiently while meeting the stable operation of the grid.

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

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

[0053] Step 2: Through disturbance detection, determine whether the fluctuation is a false disturbance. If so, go to step 10, otherwise go to step 3.

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

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

[0056] Step 5: The methanol production system is operated at high power, and the process goes to Step 8.

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

[0058] Step 7: The methanol production system is operated at low power, and the process goes to Step 8.

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

[0060]

[0061] In the formula, J el is defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of the methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el 、i el are the input voltage and input current of the methanol electrolyzer, γCH3OH-0 is the initial safety factor of the methanol electrolyzer, V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; J g ,ω e , P n 、E k They are the moment of inertia, synchronous angular velocity, pole pair number, and rotational kinetic energy of the synchronous generator. From the above formula, we can see that the energy stored in the methanol power generation system is equivalent to the moment of inertia J g , the number of pole pairs is P n The rotational kinetic energy stored in the synchronous generator rotor; W el is the power input to the methanol electrolyzer; h is the ratio of the change rate of the safety factor of the methanol electrolyzer to the change rate of the synchronous generator speed; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time; go to step 10.

[0062] Step 9: The safety factor of the methanol electrolyzer reaches the upper limit, the methanol production system shuts down, and no longer produces methanol. Go to step 10.

[0063] Step 10: End

[0064] In the above-mentioned virtual inertia control strategy based on the grid-connected system of methanol produced by electricity, step 2 determines whether the fluctuation is a false frequency disturbance through disturbance detection. This process includes the following steps:

[0065] Step 2.1: When the frequency change of the power grid is greater than the allowable deviation, the action value of the frequency change at this time is recorded as 1;

[0066] Step 2.2: After the delay setting time, collect the grid frequency change again. If the grid frequency change is greater than the allowable deviation, the action amount of the frequency change at this time is recorded as 1, otherwise the action amount of the frequency change is recorded as 0;

[0067] Step 2.3: Compare the action quantities of the frequency changes at two moments. If both action quantities are 1, it means that there is a 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 for the methanol electrolyzer CH3OH ;

[0070] Step 4.2: If γ CH3OH <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 for the methanol electrolyzer CH3OH ;

[0073] Step 6.2: If γ CH3OH <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] Power-to-methanol grid-connected system Figure 1 As shown in the figure, it includes four parts: methanol power generation system, wind power generation, power grid and AC load. The simulation mainly verifies the inertial support of methanol power generation system to the power grid when the power grid is disturbed. Therefore, the wind power generation is simplified, that is, the wind speed is set to an average wind speed of 10m / s. The simulation adopts two methods: ① constant power control; ② virtual inertia control, and four operating conditions of methanol power generation system are set: (1) Condition 1: the average wind speed of wind power generation remains unchanged, and the AC load is reduced by 200kw at 6s; (2) Condition 2: the average wind speed of wind power generation remains unchanged, and the AC load is loaded with 200kw at 6s; (3) Condition 3: the AC load remains unchanged, and the average wind speed of wind power generation increases to 12m / s at 6s; (4) Condition 4: the AC load remains unchanged, and the average wind speed of wind power generation decreases to 17m / s at 6s.

[0075] Working condition 1: At 6s, the AC load is reduced, such as Figure 6 As shown in the constant power control, the grid frequency increases to 50.39Hz. When virtual inertia control is used, the rising speed of the grid frequency decreases, and the peak value of the grid change decreases from 50.39Hz to 50.28Hz. The grid frequency amplitude change is reduced by 28.21%, and there is no fluctuation during the grid frequency recovery process. Compared with synchronous generators of the same capacity, the virtual inertia control has a faster response speed and a stable adjustment process. According to the working characteristics of the methanol electrolyzer, the methanol system abandons part of the methanol production rate to respond quickly to power. Figure 7 It can be seen that the safety factor of the methanol electrolyzer is reduced during the adjustment time. Figure 8 It can be seen that the grid-connected power of the methanol power generation system rises rapidly and reaches the upper limit of power regulation. When the grid frequency variation is adjusted to the allowable deviation range, the methanol electrolyzer works in the undisturbed operating mode. At this time, the power decreases and the methanol power generation continues to be efficient. Figure 8 It can be seen that when virtual inertia control is adopted, the methanol power system can quickly respond to power and provide short-term inertia support for the power grid by quickly adjusting power in a short time.

[0076] Working condition 2: At 6s, AC load is applied, such as Fig. 9 As shown in the constant power control, the grid frequency dropped to 49.61Hz. When virtual inertia control is used, the grid frequency decreases, and the peak value of the grid change increases from 49.61Hz to 49.7Hz. The grid frequency amplitude change decreases by 23.08%, and there is no fluctuation in the grid frequency recovery process. According to the working characteristics of the methanol electrolyzer, the methanol system abandons part of the methanol production rate to respond quickly to power. Fig.10 It can be seen that the safety factor of the methanol electrolyzer is reduced during the adjustment time. Fig.11 It can be seen that the grid-connected power of the methanol production system drops rapidly and reaches the lower limit of power regulation. When the frequency change of the power grid is adjusted to within the allowable deviation range, the methanol electrolyzer operates in an undisturbed operating mode. At this time, the power increases and methanol production continues to be efficient.

[0077] Working condition 3: At 6s, the average wind speed of wind power generation increases, such as Fig.12 As shown in the constant power control in , the grid frequency rises to 50.19Hz. When virtual inertia control is used, the rising speed of the grid frequency becomes smaller, and the peak value of the grid change drops from 50.19Hz to 50.11Hz, the grid frequency amplitude change decreases by 44.44%, and there is no fluctuation during the grid frequency recovery process. Compared with synchronous generators of the same capacity, the virtual inertia control has a faster response speed, better suppression effect, and a more stable regulation process. According to the working characteristics of the methanol electrolyzer, at this time, the methanol system abandons part of the methanol rate to respond quickly to power. Fig.13 It can be seen that the safety factor of the methanol electrolyzer is reduced during the adjustment time. Fig.14 It can be seen that the grid-connected power of the methanol production system increases rapidly. When the grid frequency change is adjusted to within the allowable deviation range, the methanol electrolyzer operates in an undisturbed operating mode. At this time, the power decreases and methanol continues to be produced efficiently.

[0078] Working condition 4: At 6s, the average wind speed of wind power generation decreases, such as Fig.15 As shown in the constant power control in the figure, the grid frequency drops to 49.7Hz. When virtual inertia control is used, the speed of grid frequency decreases, and the peak value of grid change increases from 49.7Hz to 49.84Hz. The grid frequency amplitude change decreases by 30.43%, and there is no fluctuation in the grid frequency recovery process. According to the working characteristics of the methanol electrolyzer, the methanol system abandons part of the methanol rate to respond quickly. Fig.16 It can be seen that the safety factor of the methanol electrolyzer is reduced during the adjustment time. Fig.17 It can be seen that the grid-connected power of the methanol production system drops rapidly. When the grid frequency change is adjusted to within the allowable deviation range, the methanol electrolyzer operates in an undisturbed operating mode. At this time, the power increases and methanol continues to be produced efficiently.

[0079] The virtual inertia control principle of the methanol power grid-connected system is analyzed as follows:

[0080] The rated methanol storage capacity of the power-to-methanol 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] Where V CH3OH is the volume of methanol produced; V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time.

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

[0084]

[0085] Where U el 、i el are the input voltage and input current of the methanol electrolyzer, γ CH3OH-0 is the initial safety factor of the methanol electrolyzer, V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer.

[0086] During the frequency change of the power system, the energy stored in the methanol power generation system can be expressed as:

[0087]

[0088]

[0089] From equations (3-11), we can see that the energy of the methanol production system can be regarded as the number of pole pairs P n The moment of inertia is J g The kinetic energy of the synchronous generator can be controlled by h = (ω e *Δγ CH3OH ) / (γ CH3OH-0 *Δω e ) can make the methanol power system without rotational inertia virtualize a larger rotational inertia than the synchronous generator, provide inertia support for the power grid, and improve the stability of power system operation. el Defined as the virtual inertia of the methanol power generation system.

[0090] The virtual inertia of the methanol power generation system can be further expressed as:

[0091]

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

[0093] like Figure 5 The figure shows the virtual inertia control principle diagram of the methanol production grid-connected system of the present invention. When the system is operating normally, it works in the undisturbed operating mode, and the methanol production system works at the maximum efficiency of methanol production, achieving methanol production at maximum efficiency. When a disturbance occurs in the power system, the change in the grid frequency Δf is collected, and then disturbance detection is performed to determine whether the disturbance occurs. If the disturbance is a false disturbance, it continues to work in the false disturbance operating mode, otherwise it works in the disturbance operating mode. When the existence of a grid disturbance is confirmed, in order to suppress sudden changes in the grid and ensure the safe operation of the methanol production system, the methanol electrolyzer safety factor γ is introduced CH3OH , when γ CH3OH Within the allowable range, the frequency change of the power grid is passed through a low-pass filter, and the working current of the methanol system is controlled by adjusting the ratio of the change rate of the safety factor of the methanol electrolyzer to the change rate of the speed of the synchronous generator, thereby controlling the power of the methanol system, and quickly adjusting the power in a short time to provide inertial support for the power grid; when γ CH3OH It is not within the allowable range. In order to ensure the safety of the methanol production system, the methanol production system is shut down.

[0094] In summary, the present invention proposes a control method for a methanol-to-electricity grid-connected system, which aims at the problem that the methanol-to-electricity grid-connected system leads to a reduction in the mechanical inertia of the power system. In order to improve the stability of the operation of the power system, improve the efficiency of methanol-to-electricity, and ensure the efficient operation of the methanol-to-electricity system. The inertia response is to control the power output through the introduced frequency signal, and respond to the frequency fluctuation like a synchronous unit. The methanol-to-electricity system produces methanol through a methanol electrolyzer, and its efficiency is related to the input power of the electrolyzer. When the grid frequency changes, no response is made. Therefore, the methanol-to-electricity system has no coupling relationship with the grid frequency, and cannot perform inertia response like a conventional synchronous generator, thereby suppressing grid frequency fluctuations. Based on the working characteristics of the methanol-to-electricity system, the present invention models and analyzes the methanol electrolyzer, classifies different load disturbances, analyzes the virtual inertia response process of the methanol-to-electricity system, and finally introduces the grid frequency component into the methanol-to-electricity system. When different grid disturbances occur, the methanol-to-electricity system can virtualize a larger rotational inertia than the synchronous generator in a short time, and adjust the power in a short time to provide virtual inertia for the grid, thereby improving the stability of the power system operation.

Claims

1. A control method for a methanol-to-electricity grid-connected system, the methanol-to-electricity grid-connected system comprising a grid-connected rectifier, a DC / DC converter and a methanol-to-electricity system connected to each other, the methanol-to-electricity grid-connected system being connected to a power grid system, including a wind power generation system, a power grid and an AC load, wherein the power grid is composed of a synchronous generator, the control method comprising: Obtain the grid frequency change and set the allowable deviation of the grid frequency change to determine whether grid disturbance is caused by the change of AC load, and adjust the input power of the methanol power system according to the determination result; The specific method for adjusting the input power of the methanol-to-electricity system is to set a safety factor for the methanol-to-electricity system, and within the allowable range of the safety factor, set a virtual moment of inertia for the methanol-to-electricity system, wherein the virtual moment of inertia is used to virtualize the moment of inertia required for the power generation system, and combine the relevant parameters of the methanol-to-electricity system and the generator of the power generation system to calculate the input power of the methanol electrolyzer in the methanol-to-electricity system, and shut down the methanol-to-electricity system when the input power exceeds the allowable range of the safety factor.

2. A control method for a power-to-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 the AC load is: The acquired power grid frequency change is defined as Δf. When Δf is greater than the allowable deviation, the action value of the frequency change at this time is recorded as 1. After the delay setting time, collect Δf again. If Δf is greater than the allowable deviation, the action amount of the frequency change at this time is recorded as 1, otherwise the action amount of the frequency change is recorded as 0; Compare the action quantities of the frequency changes at two moments. If both action quantities are 1, it is determined that there is a grid disturbance. At this time, the input power of the methanol system is adjusted. Otherwise, it is determined that there is no disturbance and the control method remains unchanged.

3. The control method for a power-to-methanol grid-connected system according to claim 2, characterized in that: When it is determined that there is a power grid disturbance, the specific processing method is as follows: If Δf>0, execute: First determine whether the safety factor is within the allowable range. If so, the methanol production system will operate at high power. At the same time, the input power of the methanol electrolyzer in the methanol production system is calculated as: Among them, J el is defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of the methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el 、i el are the input voltage and input current of the methanol electrolyzer, γ CH3OH-0 is the initial safety factor of the methanol electrolyzer, V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; J g ,ω e , P n 、E k They are the moment of inertia, synchronous angular velocity, pole pair number, and rotational kinetic energy of the synchronous generator. From the above formula, we can see that the energy stored in the methanol power generation system is equivalent to the moment of inertia J g , the number of pole pairs is P n The rotational kinetic energy stored in the synchronous generator rotor; W el is the power input to the methanol electrolyzer; h is the ratio of the change rate of the safety factor of the methanol electrolyzer to the change rate of the speed of the traditional synchronous generator; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time; thus, a new control input power is obtained; Otherwise, the methanol power generation system is shut down; If Δf≤0, execute: First determine whether the safety factor is within the allowable range. If so, the methanol power generation system operates at low power. At the same time, the input power of the methanol electrolyzer in the methanol power generation system is calculated as: Among them, J el is defined as the virtual moment of inertia of the methanol electrolyzer; γ CH3OH Defined as the safety factor of the methanol electrolyzer; Δγ CH3OH Defined as the change in the safety factor of the methanol electrolyzer; U el 、i el are the input voltage and input current of the methanol electrolyzer, γ CH3OH-0 is the initial safety factor of the methanol electrolyzer, V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; J g ,ω e , P n 、E k They are the moment of inertia, synchronous angular velocity, pole pair number, and rotational kinetic energy of the synchronous generator. From the above formula, we can see that the energy stored in the methanol power generation system is equivalent to the moment of inertia J g , the number of pole pairs is P n The rotational kinetic energy stored in the synchronous generator rotor; W el is the power input to the methanol electrolyzer; h is the ratio of the change rate of the safety factor of the methanol electrolyzer to the change rate of the speed of the traditional synchronous generator; k is the ratio of the methanol production rate to the input power of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time; thus, a new control input power is obtained; Otherwise, the methanol power generation system is shut down.

4. The control method for a power-to-methanol grid-connected system according to claim 3, characterized in that: The specific method for judging whether the safety factor is within the allowable range is: Calculate the safety factor γ CH3OH , the calculation formula is as follows: if γ CH3OH <0.9, the safety factor is within the allowable range, otherwise the safety factor is not within the allowable range. Where V CH3OH is the volume of methanol produced; V 额定CH3OH is the rated methanol storage capacity of the methanol electrolyzer; P CH3OH is the rate of methanol production per unit time.

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