A power grid frequency prediction method considering the influence of wind power primary frequency regulation starting threshold

Abstract

The application provides a power grid frequency prediction method considering the influence of wind power primary frequency modulation starting threshold, obtains power grid system frequency response model equivalent parameters, obtains key parameters of wind power participating in power grid primary frequency modulation, determines wind power frequency modulation starting threshold value and modulation difference rate, dynamically solves frequency deviation based on the power grid system frequency response model, displays and analyzes expression of the maximum value of frequency dynamic deviation, obtains the maximum frequency deviation of the system based on the obtained expression, and obtains the lowest frequency prediction value, and obtains the steady-state frequency deviation of the system, and obtains the steady-state frequency prediction value. The application can ensure the accuracy of the prediction result.

Description

Technical Field

[0001] This invention belongs to the field of power grid parameter prediction technology, and relates to a power grid frequency prediction method that takes into account the impact of the wind power primary frequency regulation start-up threshold. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] As wind power accounts for an increasingly larger proportion of the energy generation structure, many countries have formulated relevant standards. Taking my country as an example, Chinese standards stipulate that wind farms connected to the grid must meet certain primary frequency regulation capabilities. When a wind farm participates in primary frequency regulation, two parameters need to be set: a start-up threshold and a regulation droop rate. my country's national standard GB / T19963.1-2021, "Technical Regulations for Wind Farm Access to Power Systems," stipulates that the start-up threshold for wind power participation in grid primary frequency regulation is within the range of 0.03 to 0.1 Hz, and the regulation droop rate is within the range of 2% to 10%.

[0004] The existence of a wind power primary frequency regulation initiation threshold directly affects the prediction results of system frequency dynamics after disturbances. Currently, model analysis methods are commonly used to predict grid frequency dynamics, particularly the two key characteristics: the minimum frequency and the steady-state frequency. However, the computational load during prediction is very large. Therefore, some calculation methods ignore the wind power frequency regulation initiation threshold, but this approach directly amplifies the error between the predicted and actual grid frequency response, resulting in inaccurate predictions and consequently affecting the frequency regulation effect. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a grid frequency prediction method that takes into account the impact of the wind power primary frequency regulation start-up threshold. This invention considers the influence of the wind power frequency regulation start-up threshold on the predicted value of the system frequency dynamic characteristics, and fully explicitly analyzes the relationship between the minimum point of frequency dynamics after disturbance and the wind turbine primary frequency regulation start-up threshold. Based on the obtained maximum value of frequency dynamic deviation, frequency dynamic characteristics are predicted to ensure the accuracy of the prediction results.

[0006] According to some embodiments, the present invention adopts the following technical solution:

[0007] A grid frequency prediction method that takes into account the impact of wind power primary frequency regulation start-up threshold includes the following steps:

[0008] Obtain the equivalent parameters of the frequency response model of the power grid system;

[0009] Obtain key parameters for wind power participation in grid primary frequency regulation, and determine the wind power frequency regulation start-up threshold and droop rate;

[0010] The frequency deviation is dynamically solved based on the power grid system frequency response model. The maximum value of the dynamic frequency deviation is expressed analytically. Based on the obtained expression, the maximum frequency deviation of the system is calculated, and the minimum frequency prediction value is obtained.

[0011] The steady-state frequency deviation of the system is calculated to obtain the predicted steady-state frequency value.

[0012] As an alternative implementation method, the specific process of displaying and analyzing the maximum value of frequency dynamic deviation includes: using Taylor expansion to express the relationship between the time when the frequency dynamic deviation reaches the wind power frequency regulation start-up threshold and the size of the start-up threshold.

[0013] The time it takes for the frequency to reach its lowest point is calculated, and then the explicit analytical expression for the maximum value of the frequency dynamic deviation is obtained.

[0014] As a further limitation, the specific process of using Taylor expansion to express the relationship between the time it takes for the frequency dynamic deviation to reach the wind power frequency regulation start-up threshold and the size of the start-up threshold includes:

[0015] Based on system parameters, the dynamic frequency deviation when the primary frequency regulation link of wind power has not yet started is calculated, and then the time when the frequency deviation reaches the wind power start-up threshold is obtained.

[0016] Calculate the time range within which the frequency deviation reaches the wind power start-up threshold after the disturbance, select the median value of the time range within which the wind power frequency regulation start-up threshold is reached as the Taylor expansion point, and perform Taylor expansion.

[0017] Solve for the time to reach the primary frequency regulation start-up threshold of the wind turbine, which is an explicit analytical expression relating only the start-up threshold value and the magnitude of the disturbance.

[0018] As a further limitation, the process of calculating the time when the frequency reaches its lowest point includes: based on the frequency dynamics predicted by the frequency response model beyond the wind power primary frequency regulation start-up threshold, when the frequency deviation is at its maximum, the first derivative of the frequency deviation is zero, the derivative of the frequency dynamics is taken and set to zero, and the time when the frequency reaches its lowest point is calculated.

[0019] As a further limitation, if the frequency dynamic does not exceed the wind power frequency regulation start-up threshold when it reaches the lowest point, then the frequency drop will not trigger the wind turbine frequency regulation process.

[0020] As a further constraint, when the synchronizer parameters are determined, all disturbance frequencies reach their lowest point at the same time.

[0021] As an alternative implementation method, the power grid system frequency response model is to integrate wind power into the system frequency regulation process and convert it according to the installed capacity of wind power during the integration process.

[0022] As an alternative implementation method, the specific process of dynamically solving the frequency deviation based on the power grid system frequency response model includes:

[0023] When the frequency deviation drop has not yet reached the wind power frequency regulation start threshold, wind power does not participate in the primary frequency adjustment of the system. At this time, the model only has the thermal power unit inertial response and the primary frequency regulation link to support the system frequency drop. When the system experiences an active power disturbance, the predictive expression of the system frequency dynamics is obtained based on the frequency response model when wind power has not yet participated in the primary frequency adjustment of the system.

[0024] Based on the frequency response model of the power grid system, the dynamic differential equation of the system frequency is established. Combining the two boundary states at the instant outside the wind power frequency regulation start-up threshold, the dynamic frequency deviation outside the start-up threshold is solved.

[0025] A power grid frequency prediction system that takes into account the impact of wind power primary frequency regulation start-up threshold includes:

[0026] The equivalent parameter acquisition module is configured to obtain the equivalent parameters of the power grid system frequency response model.

[0027] The key parameter acquisition module is configured to obtain key parameters for wind power participation in the primary frequency regulation of the power grid, and to determine the wind power frequency regulation start-up threshold and droop rate.

[0028] The display expression module is configured to solve the frequency deviation dynamically based on the power grid system frequency response model and to display and analyze the maximum value of the dynamic frequency deviation.

[0029] The prediction module is configured to calculate the maximum frequency deviation of the system based on the obtained expression, thereby obtaining the minimum frequency prediction value; and to calculate the steady-state frequency deviation of the system, thereby obtaining the steady-state frequency prediction value.

[0030] A computer-readable storage medium storing a plurality of instructions adapted for loading by a processor of a terminal device and executing steps in the method.

[0031] A terminal device includes a processor and a computer-readable storage medium, the processor being configured to implement instructions; the computer-readable storage medium being configured to store a plurality of instructions adapted to be loaded by the processor and executed in accordance with the steps of the method described therein.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] This invention is based on a frequency response model that considers the wind turbine frequency regulation start-up threshold, implicitly expressing the frequency dynamics. Based on the implicit frequency dynamics, the lowest frequency of the system after an active power disturbance is approximately and explicitly analyzed using the Taylor expansion method. Based on the explicit expression, the system frequency dynamic characteristics considering the wind power frequency regulation start-up threshold are predicted, which can effectively reduce the error between the predicted and actual values, making the prediction results more accurate, and effectively predicting the frequency dynamic characteristics of the system after an active power deficit. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Figure 1 This is an analysis of the primary frequency regulation characteristics of wind power, taking into account the frequency regulation start-up threshold;

[0036] Figure 2 This is a schematic diagram of the frequency response model including the participation of the wind turbine in frequency regulation;

[0037] Figure 3 This is a schematic diagram of the system frequency response model when wind power has no response;

[0038] Figure 4 This is a schematic diagram of the system frequency response model when wind power participates in frequency regulation;

[0039] Figure 5 The impact of the wind turbine frequency regulation start-up threshold on frequency dynamics is shown in (a), where (a) is the relationship between the lowest frequency point and the wind turbine frequency regulation start-up threshold, and (b) is the relationship between the steady-state frequency and the wind turbine frequency regulation start-up threshold.

[0040] Figure 6 The impact of the fan droop rate on frequency dynamics is shown in (a) for the relationship between the lowest frequency point and the fan droop rate, and (b) for the relationship between the steady-state frequency and the fan droop rate.

[0041] Figure 7 This relates to the relationship between the frequency regulation start-up time of the fan and the start-up threshold value;

[0042] Figure 8 This is a schematic diagram of the frequency dynamic characteristic prediction process that takes into account the frequency regulation start-up threshold of the wind turbine;

[0043] Figure 9 The comparison is between the explicit and exact solutions of the lowest frequency under different wind power frequency regulation parameters. Among them, (a) is the explicit solution of the lowest frequency when the frequency regulation start threshold is different (δ=0.033), and (b) is the explicit solution of the lowest frequency when the wind power regulation droop rate is different (kd=0.05Hz).

[0044] Figure 10It is a simulation diagram of the frequency dynamic explicit solution. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0048] To facilitate understanding by those skilled in the art, this embodiment introduces the technical solution in the order of solution / derivation:

[0049] I. Dynamic Implicit Solution of Frequency Considering the Wind Power Primary Frequency Regulation Start-up Threshold

[0050] To prevent wind power from frequently participating in primary frequency regulation of the power system, which could lead to mechanical wear and potentially shorten the lifespan of wind turbines, a frequency deviation threshold is set when wind power participates in primary frequency regulation. When the power system experiences a sudden load surge and active power disturbance, the system frequency response process is as follows: Figure 1 As shown.

[0051] In the figure, the system experiences a power deficit at time 0, Δf is the system frequency deviation, and ΔP is the power deficit. wind This represents the increase in active power when wind power participates in the primary frequency regulation of the power grid. As shown in the figure above, when the frequency drop has not yet reached the wind power frequency regulation activation threshold, wind power does not participate in frequency regulation, which corresponds to the area in the figure where wind power has no response; however, when the frequency continues to drop and the frequency deviation continues to expand to the wind power frequency regulation activation threshold, the primary frequency regulation of wind power is activated, and active power is increased according to the size of the system frequency deviation, which corresponds to the other shaded areas in the figure above.

[0052] Therefore, when wind power participates in system frequency regulation, the relationship between the increase in active power generation and the system frequency deviation is shown in the following formula:

[0053]

[0054] As wind power's share in the energy structure continues to increase and its participation in primary frequency regulation of the power system grows, the simplified wind power participation in system frequency regulation needs to be recalculated based on wind power installed capacity when incorporated into traditional frequency response models. Assuming the proportion of wind power installed capacity in the system is α, the model recalculated according to this proportion can be expressed as follows: Figure 2 As shown.

[0055] In the figure, ΔP W ΔP represents the increased power generation after wind power conversion. L This represents the magnitude of the active power disturbance experienced by the system. With the large-scale grid connection of wind power and its participation in the first frequency adjustment, the system's inertial constant H, damping coefficient D, and droop coefficient R of thermal power units will decrease by an equivalent factor of 1-α. R F is the time constant of the reheat steam volume in the intermediate pressure cylinder of a thermal power unit. H This represents the percentage of the steady-state output power of the high-pressure cylinder to the total output power of the thermal power unit. The following calculation uses this model to dynamically solve for the frequency deviation.

[0056] (1) Dynamic frequency solution of the no-response zone of wind power

[0057] When the frequency deviation drop has not yet reached the wind power frequency regulation start-up threshold, wind power does not participate in the primary adjustment of the system frequency. At this time, only the inertial response of thermal power units and the primary frequency regulation stage support the system frequency drop. Figure 2 The block diagram shown can be simplified to Figure 3 As shown, the dynamic frequency deviation of the system can be directly solved using the frequency domain method.

[0058] The frequency domain equation of the frequency response model can be expressed as:

[0059]

[0060] Simplifying, we get:

[0061]

[0062] in:

[0063]

[0064] Therefore, by performing an inverse Laplace transform on equation (3), we can obtain the dynamic time-domain expression of the system frequency within the start-up threshold:

[0065]

[0066] in:

[0067]

[0068] Therefore, after a disturbance in the active power of the system, based on the frequency response model, the predicted expression for the system frequency dynamics f1(t) before wind power participates in the first frequency adjustment is as follows:

[0069]

[0070] Where f0 is the initial frequency of the system, f b The system reference frequency is 50Hz in this embodiment.

[0071] (2) Dynamic frequency solution when wind power participates in primary frequency regulation of the power grid

[0072] When solving differential equations using the frequency domain method, the initial system state is assumed to be zero. However, the system state variables at the instant outside the start-up threshold due to frequency deviation are unknown and non-zero, making it impossible to analytically solve the differential equations outside the start-up threshold using the frequency domain method. Therefore, this embodiment solves the expression for Δf(t) outside the start-up threshold from the time domain perspective. Figure 2 The model block diagram considering the wind turbine start-up threshold is shown below. The system frequency dynamic differential equation is established as follows:

[0073]

[0074] When the frequency continues to decrease until it exceeds the start-up threshold, i.e., Δf(t) < -f d hour, Figure 2 It can be equivalently transformed into Figure 4 As shown.

[0075] Substituting equation (1) into equation (8) yields:

[0076]

[0077] Let t be the time when the frequency deviation just reaches the start-up threshold. d Solving for the frequency dynamic deviation outside the start-up threshold is equivalent to solving the second-order differential equation shown above, and its general solution can be expressed as:

[0078]

[0079] Where, Δf T Let F1 and F2 be particular solutions of the differential equation, and let γ1 and γ2 be undetermined constants. Let γ1 and γ2 be the characteristic roots of the corresponding characteristic equation of the differential equation. Their calculation is as follows:

[0080]

[0081] To determine the constants F1 and F2, the two boundary states of the differential equation need to be known. ΔP can be obtained from formula (1). W No mutations will occur, therefore, Both Δf(t) and Δf(t) are continuous at t0. The two boundary states at the instant outside the wind power frequency regulation start-up threshold can be obtained as follows:

[0082]

[0083] Therefore, we get:

[0084]

[0085] Therefore, solving the above equation yields constants F1 and F2:

[0086]

[0087] The frequency dynamics f2(t) beyond the wind power primary frequency regulation start-up threshold predicted based on the frequency response model are:

[0088]

[0089] In the above formula, t d The time when the system frequency deviation just reaches the wind power frequency regulation start-up threshold can be obtained from the following formula:

[0090]

[0091] In summary, when a sudden increase in active power occurs in the system, the complete dynamic prediction expression for system frequency, considering the wind power frequency regulation start-up threshold, based on the system frequency response model, is as follows:

[0092]

[0093] However, since the equation contains both trigonometric and exponential functions, it is a transcendental equation. A transcendental equation is an equation containing transcendental functions, meaning it contains functions that cannot be expressed as a polynomial or square root of the independent variable. Most transcendental equations lack general formulas for solving and are difficult to find explicit analytical solutions. That is, t d It's about f d The implicit function cannot be explicitly parsed as about f. d The expression. Therefore, in other system parameters (H, D, R, F) H T R When α is known, the frequency dynamics outside the starting threshold are essentially about f. d ΔP L and t d The implicit function of wind power primary frequency regulation parameters does not provide a direct visual understanding of their impact on system frequency characteristic prediction. Therefore, this embodiment utilizes sensitivity analysis to study the influence and degree of influence of wind power frequency regulation parameters on the predicted value of Δf(t).

[0094] II. Analysis of the Impact of Wind Power Primary Frequency Regulation Start-up Threshold on Frequency Dynamic Characteristics

[0095] To discuss the primary frequency regulation parameters (f) of wind power d The influence of δ on frequency dynamics, including H, D, R, and F. H T R Both α and β are assigned values, as shown in the table below:

[0096] Table 1 System Parameter Values

[0097]

[0098] Set the magnitude of the active power disturbance ΔP experienced by the system. L =0.05pu. The above analysis process yields the effects of wind power frequency regulation start-up threshold and droop rate on the system frequency minimum point and steady-state frequency, respectively. Figure 5 , Figure 6 As shown.

[0099] observe Figure 5 It can be observed that the threshold value for wind turbine participation in frequency regulation affects both the system's lowest frequency and steady-state frequency. The higher the threshold setting for wind turbine participation in frequency regulation, the lower the predicted values ​​for both the lowest and steady-state frequencies. Figure 6 It can be observed that the droop rate of wind turbines participating in frequency regulation affects both the system's minimum frequency and steady-state frequency. The higher the droop rate of wind turbines participating in frequency regulation, the lower the predicted values ​​of the system's minimum frequency and steady-state frequency. Therefore, ignoring the existence of the wind power frequency regulation start-up threshold will result in higher predicted system minimum frequency and steady-state frequency, meaning the frequency characteristic prediction results will be more optimistic.

[0100] The above analyses are all qualitative. For a given power system operating state, it is sometimes necessary to analyze how changes in certain variables will cause changes in other variables. This requires sensitivity analysis. Sensitivity is a method that uses the differential relationships of certain variables in a power system to determine the degree to which the dependent variable is sensitive to the independent variable. Based on the sensitivity, guidance can be provided for the input control of the independent variable, thereby achieving the goal of controlling the output of the dependent variable. Therefore, sensitivity analysis is widely used in power systems.

[0101] The sensitivity coefficient e of parameter x is calculated as follows:

[0102]

[0103] Where f represents a frequency dynamic index, which can indicate the lowest frequency point or the steady-state frequency index. z This represents the initial value of the index; e indicates the initial value of parameter x. zWhen the value changes by 5%, the index relative to the initial value f z The percentage change is used to measure the influence of parameter x on index f.

[0104] Based on the above formula, the dynamic frequency response sensitivity index under typical parameters is obtained as follows. Initial parameter settings: ΔP L = -0.05pu, α = 0.3, f d =0.05Hz, δ=0.3.

[0105] Table 2. Sensitivity analysis of fan droop rate to frequency dynamics.

[0106]

[0107]

[0108] Table 3. Sensitivity analysis of fan frequency regulation start-up threshold to frequency dynamics.

[0109]

[0110] Tables 2 and 3 show that although the predicted minimum frequency and steady-state frequency of the system are more sensitive to the droop rate of the wind turbine than to the frequency regulation start-up threshold of the wind turbine, the frequency regulation start-up threshold of the wind turbine cannot be ignored when predicting the frequency dynamic characteristics after the disturbance.

[0111] III. Frequency Characteristic Prediction Method Considering the Wind Power Primary Frequency Regulation Start-up Threshold

[0112] 3.1 Taylor expansion shows the maximum frequency deviation of the analytical system

[0113] The second part of the analysis revealed that the influence of the wind turbine frequency regulation start-up threshold on the predicted value of the system frequency dynamic characteristics is not negligible, but it is based on an implicit expression, making the calculation cumbersome. To fully and explicitly analyze the relationship between the minimum point of frequency dynamics after disturbance and the wind turbine primary frequency regulation start-up threshold, it is first necessary to explicitly express the time t for the frequency dynamic deviation to reach the start-up threshold. d .

[0114] Substituting the data from Table 1 into formula (3), the dynamic frequency deviation before the primary frequency regulation stage of the wind power is started is as follows:

[0115] Δf(t)=-0.522ΔP L e -0.4t cos(0.2236t+1.44)+0.068ΔP L (19)

[0116] Find the time t for the frequency deviation to reach the wind power start-up threshold. dThat is, find the transcendental equations shown below:

[0117]

[0118] If the frequency dynamics do not exceed the wind turbine frequency regulation start-up threshold when reaching the lowest point, then the frequency drop will not trigger the wind turbine frequency regulation process. When the synchronous machine parameters are fixed, the time for the frequency to reach the lowest point is the same for all disturbances, which is t. max = 2.867s, Δf max =0.149ΔP L Therefore, the time range for the frequency deviation after the disturbance to reach the wind power start-up threshold is 0–2.867 s. To illustrate t... d The midpoint of the time range for reaching the wind power frequency regulation start-up threshold is selected as the Taylor expansion point, and the Taylor expansion is performed at this point. The third-order Taylor expansion is approximately as follows:

[0119] Δf(t)=ΔP L [0.0046t 3 -0.0425t 2 +0.136t+0.0024+o((t-1.43) 3 )] (twenty one)

[0120] Where o represents a higher-order infinitesimal. Solving for the time to reach the primary frequency regulation start-up threshold of the wind turbine is equivalent to solving the analytical solution of the cubic equation:

[0121]

[0122] Following Cardan's method for solving cubic equations, we introduce the variable y and let t = y + 3.0797, thus obtaining:

[0123]

[0124] The discriminant Δ is:

[0125]

[0126] Therefore, the equation has one real root and a pair of conjugate imaginary roots, where the real root is what we are looking for. The expression for solving the real root y is as follows:

[0127]

[0128] Furthermore, we can obtain:

[0129] t d =y+3.0797 (26)

[0130] Among them, t d It is an explicit analytical expression relating only the start threshold value and the size of the perturbation.

[0131] from Figure 7 It can be observed that Taylor expansion can be used to approximately express the relationship between the time when the frequency dynamic deviation reaches the wind power frequency regulation start-up threshold and the size of the start-up threshold. Although there is some error, it is all within 0.1s, which is within an acceptable range.

[0132] When the frequency deviation is at its maximum, the first derivative of the frequency deviation Since it is 0, the derivative is:

[0133]

[0134] get:

[0135]

[0136] Finally, we can obtain the explicit analytical expression for the maximum frequency deviation, which is only about f. d δ and ΔP L Explicit expression:

[0137] Δf min =ΔP L ·g(δ,f d (29)

[0138] In the above formula, g(δ,d) is only about f d Explicit function expressions for k.

[0139] 3.2 Frequency Dynamic Characteristics Prediction Method Considering Wind Power Frequency Regulation Start-up Threshold

[0140] Frequency variations in the power grid reflect the balance of active power in the power system. When the system experiences a sudden load surge, the system frequency drops, triggering the activation of primary frequency regulation equipment such as synchronous generators, thus increasing active power generation. During primary frequency adjustments, operators focus on two key frequency characteristics: the system's minimum frequency and its steady-state frequency. The formulation of frequency protection measures, such as low-frequency load shedding, high-frequency generator tripping, and reserve capacity determination, all require prediction and estimation of the system's dynamic frequency characteristics, making them crucial aspects of system frequency security.

[0141] With the development of new energy sources, the frequency regulation start-up threshold set when wind power participates in the primary frequency regulation of the power grid cannot be ignored in the prediction of frequency dynamic characteristics; otherwise, it will lead to an optimistic estimation of the frequency dynamics after system disturbance. Therefore, based on the maximum value of the displayed frequency dynamic deviation obtained in Section 3.1, the following frequency dynamic characteristic prediction method that takes into account the wind power frequency regulation start-up threshold is proposed, as follows.

[0142] Step 1: Obtain the equivalent parameters of the power grid system frequency response model;

[0143] Step 2: Obtain key parameters for wind power participation in grid primary frequency regulation;

[0144] Step 3: Calculate the maximum frequency deviation of the system to obtain the lowest frequency prediction value;

[0145] Having obtained an explicit expression for the maximum frequency deviation of the system after the disturbance, the lowest frequency after the disturbance can be estimated using the following formula:

[0146] f min =f0+f b Δf min (30)

[0147] Step 4: Calculate the steady-state frequency deviation of the system to obtain the predicted steady-state frequency value.

[0148] According to formula (31), the predicted steady-state frequency of the system when time approaches infinity is:

[0149]

[0150] like Figure 8 As shown, the maximum dynamic deviation of the system frequency, taking into account the frequency regulation starting threshold of the wind turbine, is explicitly and analytically solved when the system experiences an active power disturbance. The method of estimating the lowest system frequency after the disturbance effectively reduces the error between the predicted and actual values, resulting in more accurate predictions.

[0151] IV. Simulation Analysis

[0152] To verify the effectiveness of the prediction method proposed in this embodiment, a frequency response model of a system involving wind power participation in primary frequency regulation was built on the Matlab / Simulink simulation platform. The typical system parameters in the simulation were set as in Part III, with an active power disturbance of 0.05 pu occurring at 0s. The exact solution of the system's lowest frequency was compared with the prediction method proposed in this embodiment when different wind turbine frequency regulation start-up thresholds were set. Figure 9 As shown.

[0153] It can be observed that the minimum system frequency is affected by both the wind turbine droop rate and the frequency regulation start-up threshold. The larger the wind turbine frequency regulation start-up threshold, the larger the maximum system frequency deviation and the lower the minimum frequency; the larger the wind turbine droop rate, the smaller the maximum system frequency deviation.

[0154] Compared to the precise value of the lowest frequency of the system after a disturbance, the approximate estimation of the lowest frequency of the system after a disturbance using Taylor expansion has some errors, but the errors are relatively small and will not affect the correlation between the lowest frequency of the system obtained in Chapter 2 and the wind power frequency regulation start-up threshold and droop rate.

[0155] Furthermore, to verify the effectiveness of the frequency characteristic prediction method proposed in this embodiment after disturbance, simulations were performed to compare the exact solution of the system's dynamic frequency response with the explicit predictive analytical solution, as well as the frequency response without considering the wind power frequency regulation start-up threshold. Figure 10 As shown.

[0156] As shown in the figure above, compared to the method of using Taylor expansion to approximate the time it takes for the frequency deviation to reach the threshold value and then explicitly analyzing the system frequency dynamics without considering the wind power frequency regulation start-up threshold, this method can more accurately predict the frequency dynamics of the system after an active power disturbance. Furthermore, the predicted steady-state frequency obtained in this embodiment is consistent with the actual value.

[0157] Furthermore, to verify the effectiveness of the proposed method in predicting the lowest frequency of the system after disturbance under different wind power frequency regulation parameter scenarios, different wind power frequency regulation start-up threshold values ​​and wind power droop rates were set. The results are compared in the table below:

[0158] Table 4. Comparison of Taylor expansion approximation and simulation accuracy values ​​at different frequency regulation start-up thresholds, without considering the wind turbine frequency regulation start-up threshold.

[0159]

[0160] Table 5 Comparison of Taylor expansion approximation and simulation accuracy values ​​for different wind turbine droop rates, without considering the wind turbine frequency regulation start-up threshold.

[0161]

[0162] As shown in Tables 1 and 2, under different wind power frequency regulation parameters, the prediction method proposed in this paper can estimate the lowest frequency after the system experiences a power deficit more accurately than when the wind turbine frequency regulation start-up threshold is not considered. Compared with the accurate value obtained from simulation, the error is smaller.

[0163] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0164] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0165] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0166] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0167] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0168] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A grid frequency prediction method considering the impact of wind power primary frequency regulation start-up threshold, characterized in that, Includes the following steps: Obtain the equivalent parameters of the frequency response model of the power grid system; Obtain key parameters for wind power participation in grid primary frequency regulation, and determine the wind power frequency regulation start-up threshold and droop rate; The frequency deviation is dynamically solved based on the power grid system frequency response model. The maximum value of the dynamic frequency deviation is expressed analytically. Based on the obtained expression, the maximum frequency deviation of the system is calculated, and the minimum frequency prediction value is obtained. Calculate the steady-state frequency deviation of the system to obtain the predicted steady-state frequency; The specific process of dynamically solving the frequency deviation based on the power grid system frequency response model includes: When the frequency deviation drop has not yet reached the wind power frequency regulation start-up threshold, wind power does not participate in the primary frequency adjustment of the system. At this time, the model only supports the system frequency drop with the inertial response of thermal power units and the primary frequency regulation link. When the system experiences an active power disturbance, based on the frequency response model, the predicted expression of the system frequency dynamics when wind power has not yet participated in the primary frequency adjustment of the system is obtained as follows: in, f 0 represents the initial frequency of the system. f b The system reference frequency; As wind power's share in the energy structure continues to increase and its participation in primary frequency regulation of the power system grows, the simplified wind power participation in system frequency regulation needs to be recalculated based on wind power installed capacity when integrated into the traditional frequency response model. Let's assume the proportion of wind power installed capacity in the system is... α , This refers to the increased power generation after wind power conversion. The system's inertial constant is the magnitude of the active power disturbance it experiences, along with the large-scale grid connection of wind power and its participation in the first frequency adjustment. H Damping coefficient droop coefficient of thermal power units It will be reduced to 1- of the original value. α times, Let be the time constant of the reheat steam volume in the intermediate-pressure cylinder of the thermal power unit. This represents the percentage of the steady-state output power of the high-pressure cylinder to the total output power of the thermal power unit. Based on the frequency response model of the power grid system, a dynamic differential equation for the system frequency is established. Combining the two boundary states at the instant outside the wind power frequency regulation start-up threshold, the dynamic frequency deviation outside the start-up threshold is solved. The two boundary states at the instant outside the wind power frequency regulation start-up threshold are as follows: ； This is the threshold value for starting.

2. The grid frequency prediction method considering the impact of wind power primary frequency regulation start-up threshold as described in claim 1, characterized in that, The specific process of displaying and analyzing the maximum value of frequency dynamic deviation includes: using Taylor expansion to express the relationship between the time when the frequency dynamic deviation reaches the wind power frequency regulation start-up threshold and the size of the start-up threshold; The time it takes for the frequency to reach its lowest point is calculated, and then the explicit analytical expression for the maximum value of the frequency dynamic deviation is obtained.

3. The grid frequency prediction method considering the impact of wind power primary frequency regulation start-up threshold as described in claim 2, characterized in that, The specific process of using Taylor expansion to express the relationship between the time it takes for the frequency dynamic deviation to reach the wind power frequency regulation start-up threshold and the size of the start-up threshold includes: Based on system parameters, the dynamic frequency deviation when the primary frequency regulation link of wind power has not yet started is calculated, and then the time when the frequency deviation reaches the wind power start-up threshold is obtained. Calculate the time range within which the frequency deviation reaches the wind power start-up threshold after the disturbance, select the median value of the time range within which the wind power frequency regulation start-up threshold is reached as the Taylor expansion point, and perform Taylor expansion. Solve for the time to reach the primary frequency regulation start-up threshold of the wind turbine, which is an explicit analytical expression relating only the start-up threshold value and the magnitude of the disturbance.

4. The power grid frequency prediction method considering the impact of wind power primary frequency regulation start-up threshold as described in claim 2, characterized in that, The process of calculating the time when the frequency reaches its lowest point includes: based on the frequency dynamics predicted by the frequency response model beyond the primary frequency regulation threshold value of wind power, when the frequency deviation is at its maximum, the first derivative of the frequency deviation is zero, the derivative of the frequency dynamics is taken and set to zero, and the time when the frequency reaches its lowest point is calculated.

5. The grid frequency prediction method considering the impact of wind power primary frequency regulation start-up threshold as described in claim 1, characterized in that, If the frequency dynamic does not exceed the wind power frequency regulation start threshold when it reaches the lowest point, then the frequency drop will not trigger the wind turbine frequency regulation process. When the parameters of the synchronizer are determined, all disturbances reach their lowest point at the same time.

6. The power grid frequency prediction method considering the impact of wind power primary frequency regulation start-up threshold as described in claim 1, characterized in that, The frequency response model of the power grid system is to integrate wind power into the system frequency regulation process and convert it according to the installed capacity of wind power during the integration process.

7. A power grid frequency prediction system that takes into account the impact of wind power primary frequency regulation start-up threshold. The method described in claim 1, characterized in that it comprises: The equivalent parameter acquisition module is configured to obtain the equivalent parameters of the power grid system frequency response model. The key parameter acquisition module is configured to obtain key parameters for wind power participation in the primary frequency regulation of the power grid, and to determine the wind power frequency regulation start-up threshold and droop rate. The display expression module is configured to solve the frequency deviation dynamically based on the power grid system frequency response model and to display and analyze the maximum value of the dynamic frequency deviation. The prediction module is configured to calculate the maximum frequency deviation of the system based on the obtained expression, thereby obtaining the minimum frequency prediction value; and to calculate the steady-state frequency deviation of the system, thereby obtaining the steady-state frequency prediction value.

8. A computer-readable storage medium, characterized in that, It stores multiple instructions adapted for loading by the processor of a terminal device and executing the steps of the method according to any one of claims 1-6.

9. A terminal device, characterized in that, It includes a processor and a computer-readable storage medium, the processor being used to implement various instructions; the computer-readable storage medium being used to store a plurality of instructions adapted to be loaded by the processor and executed in the steps of the method of any one of claims 1-6.

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