Wind power transmission system by flexible transmission ideal frequency trajectory analysis method and system

Abstract

The application discloses a wind power through flexible direct transmission system receiving end ideal frequency trajectory analysis method and system, and belongs to the field of power system flexible direct current transmission. The existing wind power frequency modulation optimization control lacks quantitative analysis of frequency modulation energy demand, resulting in poor physical interpretability of the control strategy and great blindness in engineering application. The application establishes frequency response models in two states of no wind turbine support and wind turbine participation support based on receiving end system parameters, subtracts the two models and converts to the time domain to determine the effective frequency modulation energy demand functional expression of the receiving end to the sending end, establishes a minimum frequency modulation energy demand analysis model in combination with frequency safety constraints and solves the model to obtain an ideal frequency trajectory of rapid decline, approximate level and gradual recovery. The application can realize minimum utilization of the sending end wind power frequency modulation energy under the premise of meeting the receiving end frequency safety constraints, and is suitable for frequency support control scenes of new energy through flexible direct transmission systems.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology in power systems, and in particular to a method and system for analyzing the ideal frequency trajectory of wind power transmitted via flexible DC transmission. 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] With the increasing penetration rate of new energy sources such as wind power and photovoltaics, new power systems are facing challenges such as reduced inertia and increased difficulty in frequency control. As an important form of grid connection for new energy bases, wind power transmission via flexible direct current systems is becoming a crucial support direction for the future construction of new power systems, with sending-end wind power participating in receiving-end system frequency regulation.

[0004] Existing wind power frequency regulation strategies can be broadly categorized into two types: analog synchronous machines and synchronous machine-coordinated strategies. Analog synchronous machine strategies mainly include droop control, virtual inertia control, fast frequency response, and analog synchronous machine control. Since wind power needs to return to maximum power point (MPPT) operation after using rotor kinetic energy to provide frequency support, its frequency regulation energy exhibits significant short-term finite characteristics. Therefore, some research has begun to focus on the coordinated support between wind power and synchronous machines, often employing optimization algorithms to improve frequency regulation performance. However, this type of optimization control research to improve frequency control performance still has the following shortcomings: (1) Wind power frequency regulation control strategies are complex and varied, and the system frequency regulation demand is coupled with the control strategy. Existing optimized control strategies do not analyze the factors affecting the size of the demand, and the conclusions derived by pure mathematical proofs are somewhat blind in application.

[0005] (2) Although intelligent algorithms such as particle swarm optimization can obtain the optimal frequency dynamics under a specific target, they lack power system dynamic process analysis, have poor physical interpretability, and are difficult to apply to actual power systems.

[0006] (3) Some studies have analyzed the frequency modulation energy, but most of them are based on proof by contradiction to prove the optimal frequency trajectory, without analyzing the physical process behind it. The practical guiding significance for the power system needs to be improved.

[0007] The root cause of the above problems lies in the lack of a systematic analytical framework for the quantitative relationship between frequency modulation energy demand and system frequency dynamics from an energy perspective, which makes it difficult to balance optimization effect and physical interpretability. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method and system for analyzing the ideal frequency trajectory of wind power transmitted via flexible direct current transmission. By establishing frequency response models under two states—no wind turbine support and wind turbine support—based on the receiving-end system parameters, the difference between the two models is calculated and transformed to the time domain, determining the functional expression of the effective frequency regulation energy demand from the receiving end to the sending end. Then, a minimum frequency regulation energy demand analysis model is established and solved in conjunction with preset frequency safety constraints, yielding the ideal frequency trajectory at the receiving end. This solves the problem that existing optimization control strategies suffer from a lack of quantitative analysis of factors influencing frequency regulation energy demand, leading to highly arbitrary conclusions, poor physical interpretability, and difficulty in guiding actual system control design. This invention achieves the minimization of wind power frequency regulation energy utilization at the sending end while satisfying the receiving-end frequency safety constraints.

[0009] On the one hand, a method for analyzing the ideal frequency trajectory of the receiving end of a wind power transmission system via flexible direct current transmission is provided, including: Based on the inertial time constant, damping coefficient and synchronous speed governor parameters of the receiving-end system, a frequency response model of the receiving-end system without the support of the sending-end fan and a frequency response model of the receiving-end system with the sending-end fan participating in the support are established. The frequency response model of the receiving system without the support of the sending-end fan is subtracted from the frequency response model of the receiving system with the support of the sending-end fan, and then transformed to the time domain based on the inverse Laplace transform to determine the functional expression of the effective frequency modulation energy demand of the receiving end to the sending end. Based on the functional expression of the effective frequency modulation energy demand, and combined with the preset frequency safety constraints, a minimum frequency modulation energy demand analysis model is established. The minimum frequency modulation energy demand analysis model is solved to obtain the ideal frequency trajectory of the receiving end.

[0010] Furthermore, the parameters of the synchronous speed controller include the synchronous mechanical power gain, the high-pressure cylinder work ratio, and the reheat time constant.

[0011] Furthermore, the functional expression for the effective frequency-modulated energy demand is: ; in, To meet the effective frequency modulation energy requirements of the receiving end to the sending end. W ( t ) represents the weighting coefficient. t 0 represents the moment when wind power begins to support the system. t s The moment when the wind power support capacity first reaches zero, Δ f ( t )for t The deviation of the system's real-time frequency from the rated frequency after the wind turbine is involved in support, Δ f 0( t )for tThe deviation of the system's real-time frequency from the rated frequency when there is no fan support. Let be the system's inertial time constant.

[0012] Furthermore, the weighting coefficients W ( t The formula for calculating ) is: ; in, D The damping coefficient is... K For the mechanical power gain of the synchronizing machine, The power ratio of the high-pressure cylinder. is the reheat time constant.

[0013] Furthermore, the preset frequency safety constraint is: the absolute value of the frequency deviation of the receiving-end system at any time after the wind turbine participates in the support does not exceed the frequency deviation limit under normal operating conditions.

[0014] Furthermore, the minimum frequency modulation energy demand analysis model is solved to obtain the ideal frequency trajectory at the receiving end. Specifically, based on the fact that the weight coefficients in the effective frequency modulation energy demand functional expression are always greater than zero, the frequency deviation at each moment is set to the minimum feasible value that satisfies the preset frequency safety constraint, thereby obtaining the ideal frequency trajectory at the receiving end.

[0015] Furthermore, the ideal frequency trajectory at the receiving end includes a rapid decline phase, an approximately horizontal phase, and a gradual recovery phase. In the approximately horizontal phase, the sending-end wind power and the receiving-end synchronous machine work together to control the frequency of the receiving-end system to the limit of the preset frequency safety constraint.

[0016] On the other hand, an ideal frequency trajectory analysis system for the receiving end of a wind power transmission system via flexible direct transmission is provided, including: The model building module is configured to: establish the frequency response model of the receiving-end system without the support of the sending-end fan, and the frequency response model of the receiving-end system after the sending-end fan participates in the support, based on the inertial time constant, damping coefficient and synchronous speed governor parameters of the receiving-end system. The energy demand analysis module is configured to: subtract the frequency response model of the receiving system without the support of the sending-end fan from the frequency response model of the receiving system after the sending-end fan is supported, and transform it to the time domain based on the inverse Laplace transform to determine the functional expression of the effective frequency-modulated energy demand of the receiving end to the sending end. The ideal frequency trajectory solving module is configured to: establish a minimum frequency modulation energy demand analysis model based on the effective frequency modulation energy demand functional expression and a preset frequency safety constraint, solve the minimum frequency modulation energy demand analysis model, and obtain the ideal frequency trajectory at the receiving end.

[0017] In another aspect, a computer device is also provided, including a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, wherein when the processor executes the program, it performs the method described in the first aspect.

[0018] In another aspect, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, performs the method described in the first aspect.

[0019] The above technical solution has the following advantages or beneficial effects: To address the challenges of complex and diverse frequency regulation control strategies at the sending end of wind power and the difficulty in uniformly quantifying and assessing the frequency regulation energy demand at the receiving end, this invention establishes frequency response models for the receiving end system under two conditions: no wind turbine support and wind turbine support. By subtracting the two models and transforming them to the time domain, a functional expression for the effective frequency regulation energy demand from the receiving end to the sending end is constructed. This clarifies the key factors affecting the frequency regulation energy demand and overcomes the shortcomings of existing optimization control strategies, which suffer from a lack of analysis of demand influencing factors, leading to highly arbitrary application of conclusions.

[0020] Based on this, a minimum frequency regulation energy demand analysis model was established by combining preset frequency safety constraints. The model was solved point by point based on the mathematical characteristic that the weight coefficient is always greater than zero, and the ideal frequency trajectory of "rapid decline - approximate level - gradual recovery" was obtained. This provides clear physical guidance principles for wind power control response at each stage and solves the shortcomings of existing optimization methods based on intelligent algorithms, such as poor physical interpretability and difficulty in guiding the actual system control design.

[0021] Simulation results demonstrate that, under the same minimum frequency constraint, the ideal frequency trajectory derived in this invention significantly reduces the frequency regulation energy consumption of wind power at the sending end compared to traditional droop control schemes. Furthermore, under the same wind power frequency regulation energy consumption, the minimum frequency point corresponding to the ideal frequency trajectory derived in this invention is superior to both fixed-parameter and adaptive-parameter inertia-droop control strategies. Given the continuous growth in the scale of new energy transmission via flexible direct current, this invention can achieve efficient utilization of wind power frequency regulation energy at the sending end while ensuring the frequency security of the receiving-end system, exhibiting both good engineering practical value and promising prospects for widespread application. Attached Figure Description

[0022] 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.

[0023] Figure 1 This is a flowchart of the method in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the frequency response model of the receiving-end system without a supply-end fan support in Embodiment 1 of the present invention; Figure 3 is a schematic diagram of the frequency response model of the receiving-end system when the sending-end wind power participates in the support in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the ideal frequency trajectory for efficient energy utilization at the transmitting end under frequency security constraints in Embodiment 1 of the present invention. Figure 5 is a schematic diagram of the ideal frequency trajectory that takes into account both frequency deviation and frequency change rate in Embodiment 1 of the present invention. Figure 6 is a schematic diagram of the frequency modulation energy demand under different combinations of droop + high-pass control parameters in Embodiment 1 of the present invention. Figure 7 This is a frequency curve diagram under different control methods in Embodiment 1 of the present invention; Figure 8 This is a diagram showing the frequency modulation energy demand under different control methods in Embodiment 1 of the present invention; Figure 9 This diagram illustrates the control effect of different control parameters under the same power consumption for wind power frequency regulation in Embodiment 1 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. Those skilled in the art should understand that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] 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.

[0026] Example 1 This embodiment proposes an ideal frequency trajectory analysis method for the receiving end of a wind power transmission system via flexible direct current. This method derives the functional analysis expression for the receiving end's frequency regulation energy demand from the perspective of wind power energy injection. It establishes a minimum frequency regulation energy demand analysis model under a certain frequency minimum point constraint, combining frequency security constraints. By solving this model, the ideal frequency trajectory for efficiently supporting the receiving end frequency with wind power energy at the sending end is obtained. Its general characteristics are analyzed, and the physical meaning of each stage in the support process is given. Guiding principles for wind power participation in frequency regulation control design are provided, offering certain reference value for practical power systems.

[0027] Figure 1 This is an overall flowchart of the method according to Embodiment 1 of the present invention. The method includes the following steps: S101: Based on the inertial time constant, damping coefficient and synchronous speed governor parameters of the receiving-end system, establish the frequency response model of the receiving-end system without the support of the sending-end fan and the frequency response model of the receiving-end system after the sending-end fan participates in the support. S102: Subtract the frequency response model of the receiving system without the support of the sending-end fan from the frequency response model of the receiving system with the support of the sending-end fan, and transform it to the time domain based on the inverse Laplace transform to determine the functional expression of the effective frequency modulation energy demand of the receiving end to the sending end. S103: Based on the functional expression of effective frequency modulation energy demand and combined with the preset frequency safety constraints, establish a minimum frequency modulation energy demand analysis model, solve the minimum frequency modulation energy demand analysis model, and obtain the ideal frequency trajectory of the receiving end.

[0028] In step S101, the frequency response model of the receiving-end system without the support of the sending-end fan is first established. Figure 2 This is a schematic diagram of the frequency response model of the receiving-end system without a supply-end fan support, where Δ f 0 represents the deviation of the system's real-time frequency from the rated frequency when there is no wind power support at the sending end, Δ P m0 Δ represents the mechanical power adjustment of the synchronous machine when there is no supply fan support. P L This represents the change in load power. H and D These are the system's inertial time constant and damping coefficient, respectively. K For the mechanical power gain of the synchronizing machine, F H The power ratio of the high-pressure cylinder. T R The reheat time constant is s For complex frequency domain variables, t This is a time-domain variable. Accordingly, Figure 2 The system frequency response model can be expressed as: (1); It should be noted that, to distinguish it from the model with fan support, the state variables without a supply-end fan are marked with a subscript 0. The system frequency response model simplifies the boiler-steam process, retaining only the most influential inertial time constant and reheat time constant. This model form is widely used due to its concise expression and accurate calculation, and is particularly suitable for frequency analysis of receiving-end systems with a high proportion of reheat turbine generators.

[0029] Based on this, a frequency response model of the receiving-end system after the sending-end wind turbines participate in the support is further established. It should be noted that due to the complexity and variability of actual wind power frequency regulation control strategies, the characteristics of their supporting power variation over time differ, making it difficult to establish a system frequency response model that can reflect various specific control methods. Therefore, this embodiment takes an energy perspective, focusing not on specific wind power control implementation methods, but only on the wind power frequency regulation energy injection, and analyzes the subsequent frequency regulation energy demand accordingly.

[0030] Figure 3 This is a schematic diagram of the frequency response model of the receiving-end system when wind power is involved in the support at the sending end, where Δ P w To inject power into wind power, Δ f Δ represents the deviation of the system's real-time frequency from the rated frequency after the sending-end wind power is involved in the support. P m This model represents the mechanical power regulation of the synchronous motor after the sending-end wind power participates in supporting the system. It is applicable to various wind power control methods, including feedback and non-feedback types. Combined with... Figure 3 The system frequency response model when wind power at the sending end participates in the support can be expressed as: (2); It should be noted that none of the state variables and system parameters in the above formula are marked with a subscript 0, which is used to characterize the state information after wind power participates in frequency regulation. Among them, the synchronous machine parameters are not affected by wind power support, so there is no need to distinguish them. The system inertial time constant and damping coefficient change relatively little before and after wind power frequency regulation, and in this embodiment, they are approximately assumed to remain unchanged, so no distinction is made.

[0031] In step S102, based on the two models established in step S101, the functional expression of the effective frequency modulation energy demand of the receiving end to the sending end is further derived.

[0032] First, to characterize the system state change brought about by wind power participation in frequency regulation, subtracting the second equation from equation (1) yields: (3); Combining the convolution formula, the frequency domain expression is converted to a time domain expression based on the inverse Laplace transform: (4); Where, Δ P m0 (t) represents the mechanical power adjustment of the synchronous machine without fan support, Δ P m ( t This refers to the mechanical power adjustment of the synchronous machine after the wind turbine participates in the support.

[0033] Subtracting the first expression from equation (1) from equation (2), we get: (5); Transformed into a time-domain expression: (6); Where, Δ f ( t )for t The deviation of the system's real-time frequency from the rated frequency after the wind turbine is involved in support, Δ f 0( t )for t The deviation of the system's real-time frequency from the rated frequency when there is no fan support.

[0034] Substituting equation (4) into equation (6) and rearranging the terms, we get: (7); In the above formula, the first term ( ) represents the inertia term in the wind power support capacity, the second term ( ) represents the damping and synchronous high-pressure cylinder fast channel substitution in the wind power support power, the third item ( The expression () represents the synchronous machine reheat lag channel compensation term in the wind power support power. The above formula shows that when a wind turbine provides system frequency support, it needs to compensate not only for the changes in inertial power and damping power caused by frequency increases, but also for the dynamic changes in synchronous machine output. Specifically, as the frequency deviation decreases, the frequency regulation output of the synchronous machine's high-pressure cylinder channel decreases rapidly, and the frequency regulation output of the reheat channel gradually decreases. The wind turbine needs to provide additional power to compensate for the contributions of these two factors, thereby ensuring the stability of the system frequency and the continuity of the regulation effect. In other words, the frequency regulation support of the wind turbine not only undertakes the role of inertial and damping compensation, but also bears the responsibility of tracking and compensating for the output attenuation of the synchronous machine's fast and slow regulation channels, making the frequency regulation of the entire system smoother and more reliable.

[0035] However, the above time-domain expression alone cannot directly provide a quantitative assessment of energy demand. Therefore, a functional analysis model of the effective frequency-regulated energy demand at the receiving end is needed. The fundamental purpose of using wind power at the sending end to provide frequency-regulated energy support for the receiving end system is to ensure the frequency safety of the receiving end system, i.e., that the maximum frequency deviation does not exceed the safety boundary, and to ensure that the inertia and the kinetic energy released by the synchronous machine rotor at any moment during the primary frequency regulation phase do not exceed its maximum releaseable rotor kinetic energy. (8); In the formula, E f This indicates the actual amount of kinetic energy released by the rotor of the synchronous machine. E limit This indicates the maximum rotor kinetic energy that the synchronous machine can release, Δ. flimit The frequency deviation limit under normal operating conditions. t Let be the inertia and any moment during the first frequency modulation stage. Combining the system rotor motion equations, equation (8) can be further expressed as: (9); Then we have: (10); The above equation shows that, in order to ensure system frequency safety, the cumulative energy supplement of wind power at any given time should not be less than the system energy deficit corresponding to the frequency safety requirement (the difference between the energy consumed by disturbance and the energy supplement of the synchronous machine, the energy supplement of damping, and the maximum releaseable rotor kinetic energy of the synchronous machine). In other words, the receiving end has a clear frequency regulation energy requirement for the wind power support of the sending end. Only when the effective frequency regulation energy of the sending end wind power satisfies equation (10) at any given time can the frequency safety of the receiving end system be ensured.

[0036] Further analysis reveals that in the early stages of a disturbance or when the disturbance is relatively small, the right side of the inequality in equation (10) is less than or equal to 0, indicating that no energy supplementation from the wind turbine is required. However, when the disturbance is large and the cumulative energy consumed by the disturbance gradually increases, the right side of the inequality may be greater than 0, gradually requiring energy supplementation from the wind turbine. Therefore, the actual moment when the sending-end wind power provides frequency support is not 0, but rather begins from a certain moment, denoted in this embodiment as . t 0.

[0037] When analyzing the frequency regulation energy demand from the receiving end to the sending end, if the frequency regulation energy demand is derived solely based on the system frequency response model (2) after wind power participates in frequency regulation, the expression for the frequency regulation energy demand from the receiving end to the sending end can be obtained as follows: (11); In the formula, E req,r This indicates the frequency modulation energy demand from the receiving end to the sending end. t 0 indicates the moment when wind power begins to support the system; T This represents any moment when wind power participates in the support. According to the above formula, due to the complex and variable frequency control strategies of wind turbine units, the frequency curve after frequency regulation is also complex and variable, which will lead to complex and variable mechanical power support from the synchronous machine. This makes it difficult to analyze the influencing factors of frequency regulation energy demand and explore the ideal frequency response trajectory based on the above formula.

[0038] To analyze the factors influencing the frequency regulation energy demand at the receiving end and to use this information for subsequent ideal frequency response trajectory analysis, this embodiment proposes a frequency regulation energy demand analysis method based on the difference between the models before and after wind power support. By integrating equation (7), the expression for the frequency regulation energy demand from the receiving end to the sending end can be obtained: (12); Simplifying the double integral of the third term in the above equation, we get: (13); Considering that wind power participation involves stages such as support, withdrawal, and recovery, different values ​​of the upper limit of the integral in equation (12) will lead to significant differences in the calculation of frequency regulation capacity requirements when analyzing the frequency regulation energy demand from the receiving end to the sending end. To characterize the maximum energy demand from the receiving end to the sending end, the upper limit of the integral should be taken as the moment when the wind power support power first returns to zero. In this embodiment, it is defined as... t s Clearly, the integration interval is ultimately defined as [ t 0, t s After that, the obtained frequency modulation energy demand will be the maximum effective frequency modulation energy under specific control.

[0039] It should be noted that, in this embodiment, the frequency regulation energy demand is considered to be mainly used to raise the lowest frequency point. Therefore, when the wind power frequency regulation strategy is effective, it is within the effective support range. t 0, t s There must exist a point of lowest frequency within the range; conversely, if the point of lowest frequency is not within the effective support range of wind power, it indicates that there is a problem with the formulation of wind power strategy, which is not within the scope of discussion in this embodiment.

[0040] Equation (13) and the upper limit of integration t s Substituting into equation (12), the final simplified expression for the effective frequency modulation energy requirement from the receiving end to the sending end is: (14); The above equation shows that the effective frequency modulation energy demand from the receiving end to the sending end mainly includes the rotor kinetic energy compensation term at the end of the support ( ), support period damping and high-pressure cylinder fast channel compensation items ( ), and compensation item for reheat lag during support period ( ).in, W ( t The weighting coefficient of the compensation term for the wind turbine generator in response to the reduction in power supplied by the synchronous machine and damping is given by the following formula regarding the frequency increase: (15); It can be seen that the magnitude of the above weighting coefficients is affected by the parameters of the high-pressure cylinder's fast channel and reheat slow channel, and varies with time. t Monotonically decreasing, satisfying: (16); The above analysis reflects the following frequency regulation physical process: when wind turbines participate in frequency regulation, they need to compensate for the reduction in synchronous machine output. Furthermore, due to the existence of the reheat slow channel, the compensation efficiency of wind turbines varies at different stages of frequency support.

[0041] Specifically, regarding the effective support range of a particular wind power [ t 0, t s Analysis shows that in the early stage of the interval, the reduction in energy replenishment of the high-pressure cylinder fast channel and reheat channel of the synchronous machine due to the frequency increase is very obvious. Therefore, the wind power frequency regulation energy required to increase the same frequency is relatively larger. However, in the later stage of the interval, the effect of the reduction in energy replenishment of the reheat channel gradually weakens. The wind power mainly replenishes the energy of the high-pressure cylinder fast channel, and the wind power frequency regulation energy required to increase the same frequency is relatively smaller.

[0042] The following analysis examines the start time of frequency support. t The characteristics of changes in frequency modulation energy demand at different times: the larger t0 is, the greater the lag in response, and the more certain the support end time. t s The next support period begins W ( t The smaller the frequency regulation value, the less wind power energy is consumed to increase the frequency. Therefore, if the goal is to efficiently utilize wind power frequency regulation energy, the response should be delayed as much as possible.

[0043] In summary, the effective frequency regulation energy demand at the receiving end is affected not only by system parameters and synchronous machine parameters, but also by the frequency boost area, and is closely related to the start time of wind power frequency support.

[0044] In step S103, based on the effective frequency modulation energy demand functional expression established in step S102, a minimum frequency modulation energy demand analysis model for efficient energy utilization at the sending end under frequency security constraints is further constructed, and the ideal frequency trajectory at the receiving end is obtained by solving the model.

[0045] When using wind power at the sending end to support the receiving end power grid, two core issues need to be considered simultaneously: first, how to ensure the frequency security of the receiving end system after support; and second, when the wind turbine at the sending end uses rotor kinetic energy to provide support, it needs to recover after support. Therefore, it is also necessary to explore efficient utilization methods for limited frequency regulation energy. In summary, the above issues can be summarized as the problem of efficient utilization of wind power energy at the sending end under the goal of frequency security control. Based on the functional expression of effective frequency regulation energy demand derived in step S102, this embodiment abstracts it into a mathematical optimization model, as shown in equation (17): (17); The objective function is to minimize the effective frequency modulation energy demand from the receiving end to the sending end, and the first term ( ) can be understood as the frequency-increase area term, the second term ( ) is the boundary energy term, and the constraint condition is that the frequency at any time is greater than the frequency deviation limit under normal operating conditions, that is, the minimum frequency point must be maintained within the safety boundary.

[0046] When solving the above optimization model, since the frequency-enhanced area term is much larger than the boundary energy term, the frequency-enhanced area term only needs to be analyzed. From equation (16), it can be seen that... W ( t The value is always greater than 0, therefore for every time step... t As long as Δ f (t) achieves a ratio Δ f limit A larger frequency deviation will increase the energy demand for frequency regulation. Therefore, the only feasible way to minimize the objective function, i.e., the integral of energy demand, is to take the minimum feasible value that satisfies the preset frequency safety constraint at each point in time, as shown in equation (18): (18); The physical meaning is that after a disturbance occurs, wind power should delay its participation in frequency regulation until the frequency drops to a given frequency deviation limit before providing support. The minimum frequency regulation energy demand is achieved when the frequency is supported to the limit without additional support. Figure 4 As shown, the red dashed line represents the ideal frequency trajectory corresponding to the minimum effective frequency modulation energy requirement from the receiving end to the sending end.

[0047] It should be noted that if the frequency safety limit mentioned above is taken as the safety limit specified in the national standard, it is easy to result in too low frequency safety margin. Therefore, in practical applications, the safety limit should be appropriately higher than the safety limit specified in the national standard. The specific margin can be determined according to the actual project. This embodiment focuses on providing an ideal frequency trajectory analysis method for efficient utilization of wind power energy at the sending end under frequency safety constraints and giving general conclusions.

[0048] The aforementioned ideal frequency trajectory optimization problem primarily focuses on frequency deviation. If the rate of frequency change is also taken into account, the ideal frequency trajectory should be further improved, as illustrated in the diagram below. Figure 5 As shown by the red dashed line in the image, its trajectory is relatively... Figure 4 Smoother, but with basic features Figure 4 resemblance.

[0049] comprehensive Figure 4 and Figure 5The ideal frequency trajectory shown in this embodiment is characterized by three stages: rapid decline, near-level, and gradual recovery. In the rapid decline stage, the sending-end wind power does not participate in frequency regulation; it is only supported by the receiving-end synchronous generator. The purpose of the rapid frequency decline is to stimulate the regulating potential of the synchronous generator. In the near-level stage, the sending-end wind power and the receiving-end synchronous generator work together to control the frequency within safe limits. In the gradual recovery stage, the receiving-end synchronous generator responds, the sending-end wind power withdraws its support, and the system frequency gradually recovers. These three stages constitute the complete ideal frequency trajectory. The control objectives and physical meanings of each stage are clear, providing clear guiding principles for the design of control strategies for wind power participation in receiving-end system frequency support.

[0050] To verify the effectiveness of the method proposed in this embodiment, a real wind power transmission system via flexible direct current was used as a reference. Efficient support schemes were investigated under constraints of a certain minimum frequency point at the receiving end and under a certain amount of available frequency-modulated energy at the sending end. The consistency between the frequency curve and the derived ideal frequency trajectory was observed. System parameters are shown in Table 1.

[0051] Table 1 System parameters.

[0052]

[0053] (1) Comparison of energy consumption of different control methods under the constraint of a certain minimum frequency point at the receiving end. The disturbance is set as a sudden increase of 0.05 pu in load, and the minimum frequency point is set to 49.8 Hz. Three control methods are set: wind power does not participate in frequency regulation, wind power adopts droop and high-pass filter control method, and the droop and high-pass filter parameters corresponding to the minimum energy consumption of wind power are programmed to scan the ideal frequency trajectory response derived according to this embodiment, that is, the response begins when the frequency trajectory falls to the set frequency limit and the frequency is supported near the limit.

[0054] First, the calculated frequency regulation energy demand for wind power using droop + high-pass control is presented for different combinations of control parameters. For example... Figure 6 As shown, when wind power adopts a droop-high-pass control method, different combinations of control parameters can control the lowest frequency point to the set value, but the energy consumption varies greatly. Comparing the parameter combination with other control methods, using the one that minimizes frequency regulation energy demand, enhances the effectiveness of the comparison.

[0055] Figure 7 and Figure 8Frequency curves and frequency modulation energy requirements under different control methods are presented. It can be seen that both the droop control scheme and the proposed ideal frequency response trajectory scheme can control the frequency within the specified safety boundary. However, the proposed scheme in this embodiment has a lower frequency modulation energy requirement, reducing it by 38.45% compared to the droop control scheme with the highest power consumption plus high-pass filter. This fully demonstrates the effectiveness of the derivation conclusions of the embodiment, namely, that the derived ideal frequency response trajectory scheme consumes the least energy while ensuring that the lowest frequency point is not less than a certain given value.

[0056] (2) Comparison of frequency boosting effects with different control parameters under a given available frequency-modulated energy at the sending-end wind power. To further illustrate the effectiveness of the derived ideal frequency trajectory, assuming a certain amount of available frequency-modulated energy at the sending-end wind power, the frequency control effects were compared by setting different combinations of droop and high-pass coefficients to ensure the same wind power energy consumption. The disturbance was set as a sudden load increase of 0.05 pu, the lowest frequency point was set at 49.8 Hz, and the available frequency-modulated energy at the sending-end wind power was set at 350 MJ. The following are the frequency control effects of different combinations of control parameters. The results are as follows: Figure 9 As shown, even if the energy consumption of wind power frequency regulation at the sending end is the same, the frequency regulation effect will vary greatly depending on the control strategy design or control parameters. The scheme with the highest minimum frequency point has the same characteristics as the ideal frequency trajectory derived in this embodiment, namely "rapid decline - approximately horizontal - gradual recovery", which verifies the effectiveness of the proposed ideal frequency trajectory in ensuring the frequency security of the receiving end and improving the energy utilization efficiency of wind power at the sending end.

[0057] Example 2 This embodiment provides an ideal frequency trajectory analysis system for the receiving end of a wind power transmission system via flexible direct current transmission, including: The model building module is configured to: establish the frequency response model of the receiving-end system without the support of the sending-end fan, and the frequency response model of the receiving-end system after the sending-end fan participates in the support, based on the inertial time constant, damping coefficient and synchronous speed governor parameters of the receiving-end system. The energy demand analysis module is configured to: subtract the frequency response model of the receiving system without the support of the sending-end fan from the frequency response model of the receiving system with the support of the sending-end fan, and transform it to the time domain based on the inverse Laplace transform to determine the functional expression of the effective frequency-modulated energy demand of the receiving end to the sending end. The ideal frequency trajectory solving module is configured to: establish a minimum frequency modulation energy demand analysis model based on the functional expression of the effective frequency modulation energy demand and the preset frequency safety constraints, solve the minimum frequency modulation energy demand analysis model, and obtain the ideal frequency trajectory at the receiving end.

[0058] It should be noted that each module in this embodiment corresponds one-to-one with each step in Embodiment 1, and their specific implementation process is the same, so it will not be repeated here.

[0059] Example 3 This embodiment also provides a computer device, including a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor. When the processor executes the program, it completes the method described in Embodiment 1.

[0060] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0061] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0062] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0063] The method in Embodiment 1 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0064] Those skilled in the art will recognize that the units and algorithm steps described in connection with the various examples of this embodiment can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this invention.

[0065] Example 4 This embodiment also provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, complete the method described in Embodiment 1.

[0066] 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.

Claims

1. A method for analyzing the ideal frequency trajectory at the receiving end of a wind power transmission system via flexible direct current transmission, characterized in that, include: Based on the inertial time constant, damping coefficient and synchronous speed governor parameters of the receiving-end system, a frequency response model of the receiving-end system without the support of the sending-end fan and a frequency response model of the receiving-end system with the sending-end fan participating in the support are established. The frequency response model of the receiving system without the support of the sending-end fan is subtracted from the frequency response model of the receiving system with the support of the sending-end fan, and then transformed to the time domain based on the inverse Laplace transform to determine the functional expression of the effective frequency modulation energy demand of the receiving end to the sending end. Based on the functional expression of the effective frequency modulation energy demand, and combined with the preset frequency safety constraints, a minimum frequency modulation energy demand analysis model is established. The minimum frequency modulation energy demand analysis model is solved to obtain the ideal frequency trajectory of the receiving end.

2. The method according to claim 1, characterized in that, The parameters of the synchronous speed controller include the synchronous mechanical power gain, the high-pressure cylinder work ratio, and the reheat time constant.

3. The method according to claim 1, characterized in that, The functional expression for the effective frequency modulation energy demand is: ; in, To meet the effective frequency modulation energy requirements of the receiving end to the sending end. W ( t ) represents the weighting coefficient. t 0 represents the moment when wind power begins to support the system. t s The moment when the wind power support capacity first reaches zero, Δ f ( t )for t The deviation of the system's real-time frequency from the rated frequency after the wind turbine is involved in support, Δ f 0( t )for t The deviation of the system's real-time frequency from the rated frequency when there is no fan support. Let be the system's inertial time constant.

4. The method according to claim 3, characterized in that, The weighting coefficient W ( t The formula for calculating ) is: ； in, D The damping coefficient is... K For the mechanical power gain of the synchronizing machine, The power ratio of the high-pressure cylinder. is the reheat time constant.

5. The method according to claim 1, characterized in that, The preset frequency safety constraint is: the frequency deviation of the receiving-end system at any time after the wind turbine participates in the support shall not exceed the frequency deviation limit under normal operating conditions.

6. The method according to claim 1, characterized in that, Solving the minimum frequency modulation energy demand analysis model yields the ideal frequency trajectory at the receiving end. Specifically, based on the fact that the weighting coefficients in the effective frequency modulation energy demand functional expression are always greater than zero, the frequency deviation at each moment is set to the minimum feasible value that satisfies the preset frequency safety constraint, thus obtaining the ideal frequency trajectory at the receiving end.

7. The method according to claim 6, characterized in that, The ideal frequency trajectory at the receiving end includes a rapid decline phase, an approximately horizontal phase, and a gradual recovery phase. In the approximately horizontal phase, the sending-end wind power and the receiving-end synchronous machine work together to control the frequency of the receiving-end system within the limits of the preset frequency safety constraint.

8. A wind power transmission system via a flexible direct current transmission system with ideal frequency trajectory analysis at the receiving end, characterized in that: include: The model building module is configured to: establish the frequency response model of the receiving-end system without the support of the sending-end fan, and the frequency response model of the receiving-end system after the sending-end fan participates in the support, based on the inertial time constant, damping coefficient and synchronous speed governor parameters of the receiving-end system. The energy demand analysis module is configured to: subtract the frequency response model of the receiving system without the support of the sending-end fan from the frequency response model of the receiving system after the sending-end fan is supported, and transform it to the time domain based on the inverse Laplace transform to determine the functional expression of the effective frequency-modulated energy demand of the receiving end to the sending end. The ideal frequency trajectory solving module is configured to: establish a minimum frequency modulation energy demand analysis model based on the effective frequency modulation energy demand functional expression and a preset frequency safety constraint, solve the minimum frequency modulation energy demand analysis model, and obtain the ideal frequency trajectory at the receiving end.

9. A computer device comprising a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the ideal frequency trajectory analysis method for the receiving end of the wind power transmission system as described in any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the ideal frequency trajectory analysis method for the receiving end of the wind power transmission system as described in any one of claims 1-7.

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