Method and system for coordinated control of wind power generation through dynamic matching of sending and receiving ends in a flexible direct current transmission system

Abstract

The present application belongs to the technical field of power system transmission control, and particularly relates to a sending-receiving end dynamic matching wind power through flexible transmission sending out system cooperative control method and system. Including measuring the speed of wind turbine generator, calculating the effective frequency modulation energy of the sending end; modeling the frequency modulation energy demand of the receiving end, taking the effective frequency modulation energy as the modeled frequency modulation energy demand, calculating the lower limit of the wind power control dead zone, taking the frequency safety boundary value as the upper limit of the dead zone; considering the frequency modulation cost and frequency modulation effect, introducing the economic coefficient, determining the final wind power frequency modulation control dead zone based on the upper and lower limits of the dead zone; according to whether the measured frequency of the receiving end of the wind power through flexible transmission sending out system is in the wind power frequency modulation control dead zone, the frequency is segmented, and the critical droop coefficient is calculated based on the segmented state space equation of the wind power through flexible transmission sending out system; the calculated wind power frequency modulation control dead zone and critical droop coefficient are input into the controller to realize cooperative control. The present application realizes the dynamic matching control of demand-capacity.

Description

Technical Field

[0001] This invention belongs to the field of power system transmission control technology, and particularly relates to a method and system for coordinated control of wind power transmission via flexible direct current transmission system with dynamic matching between sending and receiving ends. Background Technology

[0002] Existing research primarily focuses on improving the safety of sending-end units or the frequency support level of receiving-end units through methods such as adaptive inertia control and optimization control. However, these studies still have the following shortcomings: (1) Adaptive inertia control ensures the unit speed safety by dynamically adjusting the support power during frequency regulation. However, due to excessive focus on the sending end and lack of analysis of the frequency regulation energy demand of the receiving end and attention to the matching relationship between the two, its support has a certain degree of blindness, and the frequency support effect is difficult to guarantee.

[0003] (2) Optimization control research proposes corresponding control strategies by analyzing the mechanism of maximizing the lowest frequency point of the receiving end system. However, due to the lack of analysis on the effective support capacity of the sending end unit, its utilization of the sending end rotor kinetic energy may be excessive or the support cost may be too high, and the dynamic matching of sending and receiving end demand and capacity is not achieved. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a method and system for coordinated control of wind power transmission via flexible direct current transmission with dynamic matching between the sending and receiving ends. It proposes a coordinated control mode that considers the dynamic matching of demand and sending-end capacity, approximates the effective frequency regulation energy at the sending end as a constant, analyzes the influence mechanism of wind power control dead zone on the frequency regulation energy demand at the receiving end, derives the dead zone upper and lower limit tuning method based on the effective frequency regulation energy at the sending end, and presents a droop coefficient tuning method based on the dynamic state space equation of the segmented system frequency, thereby achieving dynamic matching control of demand and capacity.

[0005] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: The first aspect of the present invention provides a method for coordinated control of a wind power transmission system via flexible direct transmission with dynamic matching at the sending and receiving ends.

[0006] The method for coordinated control of wind power transmission systems via flexible direct current transmission with dynamic matching at both the sending and receiving ends includes the following steps: Measure the wind turbine speed and calculate the effective frequency regulation energy at the sending end; The frequency regulation energy demand at the receiving end is modeled, and the effective frequency regulation energy is used as the modeled frequency regulation energy demand. The lower limit of the wind power control dead zone is calculated, and the frequency safety boundary value is used as the upper limit of the dead zone. Considering frequency regulation costs and effects, an economic coefficient is introduced, and the final wind power frequency regulation control dead zone is determined based on the upper and lower limits of the dead zone. Based on whether the measured frequency at the receiving end of the wind power transmission system is in the dead zone of wind power frequency regulation control, the frequency is segmented, and the critical droop coefficient is calculated based on the segmented state space equation of the wind power transmission system. The calculated dead zone and critical droop coefficient of wind power frequency regulation control are input into the controller to achieve coordinated control of the sending and receiving ends of the wind power transmission system via flexible direct current transmission.

[0007] The second aspect of the present invention provides a collaborative control system for dynamic matching of wind power transmission via flexible direct transmission at the sending and receiving ends.

[0008] The dynamic matching control system for wind power transmission via flexible direct current transmission at both the sending and receiving ends includes: The effective frequency regulation energy calculation module is configured to: measure the wind turbine speed and calculate the effective frequency regulation energy at the sending end; The dead zone upper and lower limit determination module is configured to: model the frequency modulation energy demand at the receiving end, use the effective frequency modulation energy as the modeled frequency modulation energy demand, calculate the lower limit of the wind power control dead zone, and use the frequency safety boundary value as the upper limit of the dead zone. The wind power frequency regulation control dead zone determination module is configured to: consider frequency regulation cost and frequency regulation effect, introduce an economic coefficient, and determine the final wind power frequency regulation control dead zone based on the upper and lower limits of the dead zone; The critical droop coefficient determination module is configured to: segment the frequency based on whether the measured frequency at the receiving end of the wind power transmission system is in the dead zone of wind power frequency regulation control, and calculate the critical droop coefficient based on the segmented state space equation of the wind power transmission system. The collaborative control module is configured to input the calculated wind power frequency regulation control dead zone and critical droop coefficient into the controller to achieve collaborative control of the wind power transmission system at both the sending and receiving ends.

[0009] The above one or more technical solutions have the following beneficial effects: This invention provides a method and system for coordinated control of a wind power transmission system via flexible direct current (FDDC) with dynamic matching between the sending and receiving ends. First, it analyzes the influencing factors of the frequency regulation energy demand at the receiving end and the effective frequency regulation energy at the sending end, clarifying that the effective frequency regulation energy at the sending end can be approximated as constant under specific wind speeds, but the frequency regulation demand at the receiving end varies greatly due to policy influences. Second, to achieve dynamic matching of demand and capacity (i.e., demand < capacity), it analyzes the influence mechanism of the wind power control dead zone on the frequency regulation energy demand at the receiving end, derives a dead zone upper and lower limit tuning method based on the effective frequency regulation energy at the sending end, and presents a droop coefficient tuning method based on the dynamic state space equation of the segmented system frequency. Finally, simulations verify the effectiveness of the proposed dead zone and droop coefficient tuning methods. With the increasing scale of wind power transmission via FDDC, this is of great significance for comprehensively improving the safety of the sending-end units and the frequency security of the receiving end.

[0010] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0011] 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.

[0012] Figure 1 This is a frequency response model diagram of the receiving-end system without sending-end wind power support in Example 1.

[0013] Figure 2 The diagram shows the frequency response model of the receiving-end system considering the wind power injection at the sending end in Example 1.

[0014] Figure 3 This is a schematic diagram illustrating the complex and variable frequency regulation requirements at the receiving end under the traditional wind power fixed dead zone strategy in Example 1.

[0015] Figure 4 This is a schematic diagram illustrating the lower limit of the absolute value of the dead zone of wind power frequency regulation to meet arbitrary control requirements < capability, as shown in Example 1.

[0016] Figure 5 The effective frequency modulation end time in Example 1 t s A diagram illustrating the impact of changes on the size of demand.

[0017] Figure 6 This is a schematic diagram of the upper limit of the absolute value of the dead zone of wind power frequency regulation that satisfies the frequency safety constraints in Example 1.

[0018] Figure 7 This is a schematic diagram of dynamic tuning of frequency dead zone considering economic factors in Example 1.

[0019] Figure 8 This is a schematic diagram of the simulation verification model for Example 1.

[0020] Figure 9 This is a frequency dynamic diagram under different dead zones in Example 1.

[0021] Figure 10 The image shows the rotational speed dynamics under different dead zones in Example 1.

[0022] Figure 11 The diagram shows the frequency control results when the actual sagging coefficient is set to the critical sagging coefficient at a wind speed of 8.0 m / s in Example 1.

[0023] Figure 12 The diagram shows the frequency control results when the actual sagging coefficient is set to the critical sagging coefficient at a wind speed of 8.5 m / s in Example 1.

[0024] Figure 13 The diagram shows the frequency control results when the actual sagging coefficient is set to the critical sagging coefficient at a wind speed of 9.0 m / s in Example 1.

[0025] Figure 14 The diagram shows the frequency control results when the actual sagging coefficient is set to the critical sagging coefficient at a wind speed of 9.5 m / s in Example 1.

[0026] Figure 15 This is a frequency dynamic graph for different values ​​of the droop coefficient in an example.

[0027] Figure 16 The following is a dynamic diagram of the rotational speed when the droop coefficient has different values, as shown in the example.

[0028] Figure 17 This is a flowchart of the method in Example 1.

[0029] In the picture: 1. Offshore wind farm; 2. Sending-end converter station; 3. Receiving-end converter station; 4. Receiving-end power grid; 5. Wind turbine; 6. Wind turbine-side converter and grid-side converter; 7. Transformer; 8. 220 kV busbar; 9. +400 kV DC submarine cable; 10. -400 kV DC submarine cable; 11. 500 kV busbar. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration 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.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0032] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0033] Example 1 Wind power transmission via flexible direct transmission systems has become an important form of grid connection for new energy bases. With the advancement of the construction of new power systems, receiving-end systems face problems such as reduced inertia and increased frequency changes after disturbances. Relying solely on the regulating resources of the receiving-end system may not be enough to control the frequency within a safe range. Exploring wind power at the sending end to provide active power support for the receiving-end system can help improve frequency dynamics.

[0034] Existing research largely focuses on "how to achieve support at the sending end," improving frequency support capabilities through additional control of wind turbines, but it pays insufficient attention to "the extent of support." Offshore wind power participating in receiving-end grid frequency regulation via flexible direct current transmission systems cannot be achieved by simply "supporting as much as the sending end can provide" or "supporting as much as the receiving end needs." On the one hand, the receiving end has a clear safety margin for its frequency regulation energy demand from the sending end, given its existing capabilities; insufficient support could threaten frequency security. On the other hand, the available rotor kinetic energy at the sending end is limited by operating conditions; excessive energy utilization would be too costly and could affect unit safety.

[0035] Existing research mainly focuses on methods such as adaptive inertia control and optimization control to improve the safety of the sending-end unit or the frequency support level of the receiving end. However, adaptive inertia control focuses too much on the sending end and lacks analysis of the frequency regulation energy demand of the receiving end and attention to the matching relationship between the two. Its support is somewhat blind and the frequency support effect is difficult to guarantee. Optimization control lacks analysis of the effective support capability of the sending-end unit. Its utilization of the kinetic energy of the sending-end rotor may be excessive or the support cost may be too high, failing to achieve dynamic matching between the demand and capability of the sending and receiving ends.

[0036] Therefore, this embodiment addresses the dynamic matching problem of receiving-end demand and sending-end capacity when offshore wind power is frequency regulated via a flexible direct current transmission system, proposing a collaborative control method for wind power via flexible direct current transmission system with dynamic demand and capacity matching. First, it clarifies that the receiving-end frequency regulation energy demand is significantly affected by the sending-end wind power control strategy, explaining that although the effective frequency regulation energy at the sending end differs under different strategies, it can be conservatively estimated and thus approximated as a constant. Second, it analyzes the impact mechanism of wind power dead zone on frequency regulation demand, then provides methods for setting the upper and lower limits of the dead zone, and derives a method for setting the droop coefficient, forming a dynamic demand-capacity matching principle. Finally, it proposes a specific implementation scheme for the collaborative control strategy of the sending and receiving ends that satisfies the above demand-capacity matching principle.

[0037] To address the challenges of existing research on frequency regulation in offshore wind power transmission systems via flexible direct current transmission, which fails to adequately consider the dynamic matching between receiving-end demand and sending-end capacity, and the difficulty in quantitatively analyzing the demand-capacity relationship due to the complexity and variability of wind power control strategies, a collaborative control method for both the sending and receiving ends that considers the dynamic matching between demand and sending-end capacity is proposed.

[0038] This embodiment discloses a method for coordinated control of a wind power transmission system via flexible direct transmission with dynamic matching at the sending and receiving ends.

[0039] like Figure 17 As shown, the method for coordinated control of wind power transmission via flexible direct current transmission system with dynamic matching at the sending and receiving ends includes the following steps: Measure the wind turbine speed and calculate the effective frequency regulation energy at the sending end; The frequency regulation energy demand at the receiving end is modeled, and the effective frequency regulation energy is used as the modeled frequency regulation energy demand. The lower limit of the wind power control dead zone is calculated, and the frequency safety boundary value is used as the upper limit of the dead zone. Considering frequency regulation costs and effects, an economic coefficient is introduced, and the final wind power frequency regulation control dead zone is determined based on the upper and lower limits of the dead zone. Based on whether the measured frequency at the receiving end of the wind power transmission system is in the dead zone of wind power frequency regulation control, the frequency is segmented, and the critical droop coefficient is calculated based on the segmented state space equation of the wind power transmission system. The calculated dead zone and critical droop coefficient of wind power frequency regulation control are input into the controller to achieve coordinated control of the sending and receiving ends of the wind power transmission system via flexible direct current transmission.

[0040] The method of this embodiment will now be explained in detail.

[0041] (I) First, conduct a frequency modulation energy demand analysis at the receiving end.

[0042] like Figure 1 The figure shows the frequency response model of the receiving-end system without sending-end wind power support. In the figure, Δ... P L Δ represents the change in load power. f 0( t ) 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 This refers to the mechanical power adjustment of the synchronous motor when there is no wind power support at the sending end. 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 is the reheat time constant; s is the complex frequency variable in the Laplace domain.

[0043] The corresponding expression is: (2) in, This represents the Laplace domain expression of the deviation of the system's real-time frequency from the rated frequency when there is no sending-end wind power support. This represents the expression of the mechanical power regulation of the synchronous machine in the Laplace domain when there is no wind power support at the sending end.

[0044] Figure 2 To consider the frequency response model of the receiving-end system taking into account the wind power energy injection at the sending end. Without considering the specific frequency regulation control method of the wind power, and only focusing on its energy injection, the frequency response model of the receiving-end system is expressed as follows: Figure 2As shown in the figure. Δ f ( t ) represents the deviation of the system's real-time frequency from the rated frequency when the wind power supply is supported at the sending end; Δ P w For the power supported by the sending-end wind power; Δ P m This indicates the mechanical power adjustment of the synchronous machine when the wind turbine is supported at the sending end.

[0045] The corresponding expression is: (3) in, This represents the deviation of the system's real-time frequency from the rated frequency in the Laplace domain when the wind power supply is supported at the sending end. This represents the expression of the mechanical power regulation of the synchronous motor in the Laplace domain when the wind turbine is supported at the sending end. This represents the form in which the wind power support capacity is expressed in the Laplace domain.

[0046] Subtracting equation (2) from equation (1), and converting it into a time-domain expression through rearrangement and convolution, we can obtain the expression for wind power support: (4) in, This represents the time-domain representation of wind power support capacity. This represents the time-domain representation of the deviation of the system's real-time frequency from the rated frequency when the wind power supply is supported at the sending end. This represents the time-domain representation of the deviation of the system's real-time frequency from the rated frequency when there is no wind power support at the sending end. This represents the time-domain expression of the mechanical power regulation of the synchronous motor when the wind turbine is supported at the sending end. This represents the time-domain expression of the mechanical power regulation of the synchronous motor when there is no wind turbine support at the sending end; t0 represents the start time of the wind turbine support, and t represents any moment when the wind turbine support is in place. This indicates the frequency deviation of the system at time τ when the wind power supply is supported at the sending end. This represents the frequency deviation of the system at time τ when there is no wind power support at the sending end; τ represents the integral time variable.

[0047] In formula (3), the first term represents the inertia term in the wind power support power; the second term represents the damping and synchronous high-pressure cylinder fast channel substitution term in the wind power support power; and the third term represents the synchronous reheat lag channel compensation term in the wind power support power.

[0048] The above formula shows that the power support of the wind turbine not only needs to compensate for the inertia and damping terms brought about by the frequency increase, but also needs to compensate for the reduced output of the two channels of the synchronous machine due to the rapid reduction of the output of the high-pressure cylinder of the synchronous machine and the gradual reduction of the output of the reheat channel.

[0049] Integrating equation (3), we can obtain the expression for the frequency modulation energy demand from the receiving end to the sending end: (4) in, This indicates the frequency modulation energy demand from the receiving end to the sending end; t s Indicates the end time of wind power support at the sending end; This indicates the system frequency deviation corresponding to the moment when wind power support ended; This indicates the system frequency deviation at the moment when wind power support ends, corresponding to the time when there is no wind power support.

[0050] Considering that wind power utilizes rotor kinetic energy to provide active power support, which involves support, withdrawal, and recovery phases, analyzing the frequency regulation energy demand of the receiving end for the sending end wind power is only meaningful if the maximum frequency regulation energy demand of the receiving end for the sending end is matched with the sending end's capacity. Therefore, the upper limit of the integral in the above formula should be taken as the end time when the wind turbine provides effective support. 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.

[0051] 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 for wind power, it indicates a problem with the wind power strategy formulation, which is not within the scope of this embodiment.

[0052] After simplifying the double integral of equation (4), the final expression for the frequency modulation energy demand from the receiving end to the sending end can be obtained as follows: (5) in, This indicates the system frequency deviation corresponding to the moment when wind power support ended; This indicates the system frequency deviation at the moment when wind power support ends, corresponding to the time when there is no wind power support.

[0053] In formula (5), the first term represents the rotor kinetic energy compensation term at the end of the support; the second term represents the damping and high-pressure cylinder fast channel compensation term during the support period; and the third term represents the reheat lag channel compensation term during the support period.

[0054] Analyzing the above formula, the frequency regulation energy demand from the receiving end to the sending end is a functional model of the frequency increase. In addition to being related to system parameters, the magnitude of the frequency regulation demand is also related to the frequency increase area before and after the support. The frequency increase area is affected by wind power control strategy and control parameters (dead zone, coefficient, etc.).

[0055] (II) Analysis of effective frequency modulation energy at the sending end.

[0056] When a wind turbine uses its own rotor kinetic energy to provide active power support, its effective frequency regulation energy is the difference between the released rotor kinetic energy and the wind energy capture loss. To evaluate the maximum effective frequency regulation energy at the sending end, without pre-setting the wind power control mode, it can be assumed that the wind turbine's rotor kinetic energy release calculation corresponds to a speed reduction to 0.7, which is relatively easy to calculate. However, when calculating the wind energy capture loss, its magnitude is affected by wind speed and control strategy, making it difficult to generalize. This embodiment, based on extensive simulation data, provides a conservative calculation formula for the effective frequency regulation energy at the sending end: (6) In the above formula, E w,eff Indicates the effective frequency modulation energy at the sending end; This represents the proportion of effective frequency modulation energy to the released rotor kinetic energy. Its value varies depending on wind speed and control strategy, but under common wind speeds and common strategies, a conservative value can be obtained through simulation. In this embodiment, it is taken as 0.7. J w The moment of inertia of the wind turbine; w 0 represents the initial speed of the wind turbine. w min The minimum speed limit for safe operation of the fan is generally 0.7 pu, where pu represents the per-unit value.

[0057] Based on a large amount of simulation data, this embodiment provides a conservative calculation formula for the effective frequency regulation energy of the transmitting end. The specific simulation method and steps are as follows: First, simulations are performed under common wind speeds and common strategies, and the wind power support power data and rotor speed data are recorded. Data when the rotor speed of the wind turbine just drops to 0.7 pu is selected. Second, the integral of the wind power support power in the selected data when it is greater than 0 is recorded. Then, the integral value of the wind power support power when it is greater than 0 is divided by the corresponding rotor kinetic energy release to obtain the proportional coefficient under this condition. Finally, the proportional coefficients under various wind speeds and various strategies are compared, and the minimum value is taken as the conservative proportional coefficient in the above formula.

[0058] (III) Analysis and adjustment of the impact of wind power frequency regulation dead zone on demand-capacity matching relationship.

[0059] Based on the above analysis, the regulation capability of wind power at the sending end can be approximated as constant under a specific wind speed, while the frequency regulation energy demand at the receiving end varies greatly depending on the different sending end strategy designs. Therefore, the relationship between the receiving end demand and the sending end capability is also complex and variable.

[0060] To achieve dynamic matching of demand and capability, i.e., to make demand less than capability as much as possible, it is necessary to analyze the factors that affect changes in demand and propose targeted design tuning methods.

[0061] It can be understood that the demand mentioned in this embodiment refers to the frequency regulation energy demand of the receiving end to the sending end, and the capacity refers to the effective frequency regulation energy of the wind power at the sending end.

[0062] In traditional wind power frequency regulation strategies, the dead zone is typically fixed at ±0.033Hz or ±0.05Hz. After a control strategy is implemented, the frequency boost area varies significantly depending on the strategy, making it difficult to quantitatively calculate the demand-capacity relationship. This can lead to excessively rapid rotor energy release, triggering speed protection and causing a secondary frequency drop. Conversely, insufficient rotor energy release can result in inadequate frequency support. Therefore, existing strategies generally require complex support exit and recovery strategies to ensure effective frequency support at the receiving end while maintaining safe turbine speed at the sending end.

[0063] like Figure 3 The figure shows a complex and variable frequency curve under the traditional fixed dead zone strategy for wind power. The horizontal axis represents time (seconds), and the vertical axis represents frequency (Hz). The black solid line represents the frequency when only the synchronous motor provides support; the red solid line represents the frequency when the wind power adopts droop control with a smaller parameter; the dark blue solid line represents the frequency when the wind power adopts droop control with a larger parameter; the light blue solid line represents the frequency when the wind power adopts virtual inertial control with a larger parameter; the magenta dashed line represents the frequency when the wind power adopts fast frequency response; and the green dashed line represents the frequency when the wind power adopts virtual inertial control with a smaller parameter.

[0064] However, existing research rarely guides control strategy design from the perspective of dynamically tuning the demand-capacity relationship, and rarely explores whether tuning this relationship can simplify control strategy design. As the foregoing analysis shows, although the complexity and variability of the strategy can lead to differences in the effective frequency modulation energy at the sending end, a conservative assessment of this energy can be achieved by setting a conservative coefficient, which can be considered a constant. Therefore, the key lies in analyzing how to adjust the demand so that demand < capacity, achieving a dynamic match between the two. The following section will discuss the impact mechanism of deadband variation on the demand-capacity relationship and deadband tuning methods to satisfy the demand-capacity matching relationship.

[0065] According to equation (5), the frequency modulation energy at the receiving end is affected by the frequency boost area, and the frequency boost area can be effectively adjusted by dynamically setting the dead zone, thereby limiting the demand. Taking the frequency drop due to a sudden increase in load as an example for analysis. Figure 4 A schematic diagram of the lower limit of the frequency regulation dead zone of wind power to meet arbitrary control requirements < capacity. Figure 4 In the diagram, the horizontal axis represents time in seconds (s), and the vertical axis represents system frequency in hertz (Hz). The solid red line represents the frequency level corresponding to the dead zone, the dashed black line represents the frequency without sending-end wind power support, and the solid blue line represents the frequency after sending-end wind power support. The area enclosed by the solid red line and the dashed black line represents the frequency increase area corresponding to the maximum frequency regulation energy support provided by sending-end wind power under a specific dead zone, and the area enclosed by the solid blue line and the dashed black line represents the frequency increase area after actual control of sending-end wind power under a specific dead zone. Δ f db min Indicates the lower limit of the wind power control dead zone; E req,r = E w,eff This means that when the wind power dead zone is at its minimum, the maximum frequency regulation energy demand at the receiving end is exactly equal to the maximum effective frequency regulation energy at the sending end. E req It represents the actual effective frequency modulation energy demand at the receiving end under specific control.

[0066] like Figure 4 As shown, the larger the dead zone (the more delayed the action), the more limited the frequency boost area becomes, and thus a certain dead zone inevitably exists. When the dead zone is larger than this dead zone, regardless of how the frequency curve changes due to the control strategy, the frequency area enclosed by the frequency curves before and after support will inevitably be smaller than the frequency area corresponding to the sending-end support capacity. Therefore, the lower limit of the frequency dead zone should be calculated based on the sending-end frequency regulation capacity. That is, the effective frequency regulation energy of the sending end calculated by equation (6) can be substituted into the left side of equation (5) as the frequency regulation energy demand to obtain the lower limit of the absolute value of the dead zone. This lower limit will ensure that the demand < capacity is met for any wind power frequency regulation control strategy.

[0067] Further analysis of equation (5) reveals that, in order to calculate the lower limit of the frequency modulation dead zone, the key variable of effective support end time is also needed. t s Calculations are required. Furthermore, the effective support end time varies depending on the specific wind power frequency regulation control strategy. t s It is also complex and ever-changing. Therefore, how to make a reasonable choice is crucial. t s Ensuring that the lower limit of the absolute value of the calculated frequency modulation control dead zone is meaningful will be the focus of the next step of the analysis.

[0068] Figure 5 Effective frequency modulation end time ts A diagram illustrating the impact of changes on the size of demand. Figure 5 In the diagram, the horizontal axis represents time in seconds (s), and the vertical axis represents system frequency in hertz (Hz). The red solid line represents a type of frequency curve after wind power support (its right intersection with the pre-support frequency curve also intersects the dead zone horizontal line), the green solid line represents a type of frequency curve after wind power support (the horizontal coordinate of its intersection with the dead zone horizontal line is greater than the horizontal coordinate of the pre-support frequency curve's intersection with the dead zone horizontal line), the blue solid line represents a type of frequency curve after wind power support (the horizontal coordinate of its intersection with the dead zone horizontal line is less than the horizontal coordinate of the pre-support frequency curve's intersection with the dead zone horizontal line), the black dashed line represents the frequency without sending-end wind power support, and the red dashed line represents the horizontal frequency corresponding to the dead zone. t s1 The x-coordinate represents the intersection of the blue frequency curve and the dead zone horizontal line. ； t s2 This indicates the right intersection point of the horizontal frequency line corresponding to the dead zone and the frequency curve before support. t s3 The x-coordinate of the intersection point of the green frequency curve and the dead zone horizontal line; E req2 > E req1 This indicates that the frequency modulation energy demand corresponding to the red solid line is greater than the frequency modulation energy demand corresponding to the blue solid line. E req2 > E req3 This indicates that the frequency modulation energy demand corresponding to the red solid line is greater than the frequency modulation energy demand corresponding to the green solid line; f 0 indicates the frequency when there is no wind power support at the sending end.

[0069] like Figure 5 As shown, when the lower limit of the absolute value of the dead zone is set, the effective support end time is... t s It should be ensured that the frequency modulation energy demand under this dead zone is greater than the demand corresponding to other end times, so as to ensure that the lower limit of the absolute value of the dead zone calculated after substituting the sending-end capacity is a conservative value. The intersection point of the dead zone corresponding frequency horizontal line and the frequency curve before support is taken as the right intersection point. t s2 As a dividing point, when the effective support end time is less than t s2 That is, in the diagram t s1 At that time, its effective frequency modulation energy demand is at its maximum, as shown by the blue shaded area in the figure, and its value is definitely less than [a certain value]. t s2 The corresponding frequency modulation energy requirement; when the effective support time is greater than t s2 That is, in the diagramt s3 When calculating the frequency modulation demand according to equation (5), a portion of the energy will inevitably be negative, corresponding to the green part in the figure, which is... t s3 The corresponding frequency modulation energy requirement must be less than t s2 The corresponding frequency modulation energy requirements.

[0070] In summary, under a specific dead zone, when the effective support end time is the right intersection of the dead zone line and the frequency curve before support, the frequency regulation demand corresponds to the maximum value under the current dead zone. Setting the lower limit of the dead zone according to this dead zone can ensure that the actual frequency regulation energy consumption under any control will not exceed the wind power capacity, and can ensure the safe speed of the sending-end unit.

[0071] The following analysis examines the upper limit of the absolute value of the dead zone. Figure 6 A schematic diagram illustrating the upper limit of the absolute value of the dead zone for wind power frequency regulation to meet frequency security constraints. Figure 6 In the diagram, the horizontal axis represents time in seconds (s), and the vertical axis represents the system frequency in hertz (Hz); Δ f db1 Indicates the relatively smallest wind power control dead zone; Δ f db2 This indicates a wind power control dead zone of a relatively moderate size; Δ f db3 The red solid line represents the largest relative wind power control dead zone; the red solid line represents the dead zone Δ. f db3 The corresponding frequency curve; the dark blue solid line represents the dead zone Δ f db2 The corresponding frequency curve; the light blue solid line represents the dead zone Δ f db1 The corresponding frequency curve; the black dashed line represents the frequency curve without sending-end wind power support; Δ f db max This indicates the upper limit of the dead zone.

[0072] Depend on Figure 6 As the dead zone increases, the area for frequency increase becomes increasingly limited. Theoretically, the larger the dead zone, the smaller the demand, and the easier it is to meet the demand and ensure the safe rotation speed of the sending unit. However, considering the frequency safety of the receiving system, the dead zone cannot be infinitely large. In an extremely ideal situation, the upper limit of the dead zone can be taken as the frequency safety boundary value (such as ±0.2Hz).

[0073] After calculating and adjusting the upper and lower limits of the absolute dead zone for frequency regulation using the above method, if the sending-end wind power is supported according to the lower limit of the dead zone, the utilization of the wind turbine rotor kinetic energy will be too high, resulting in high frequency regulation costs. If the support is provided according to the upper limit of the dead zone, the frequency safety margin will be too low. In summary, this embodiment proposes a dynamic dead zone determination method that balances frequency regulation effect and cost, as shown in the following formula: (7) In the formula, Δ f db * This represents the final determined dead zone for wind power frequency regulation control (here, dead zones are integers; smaller values ​​indicate easier triggering, while larger values ​​indicate more difficult triggering); Δ f db min This is the lower limit of the FM dead zone; Δ f db max This is the upper limit of the FM dead zone; k This is the frequency modulation economic coefficient, which ranges from 0 to 1. The closer it is to 1, the better the frequency modulation economy, but the worse the frequency modulation effect. The closer it is to 0, the higher the frequency modulation cost, but the better the frequency modulation effect.

[0074] Figure 7 The diagram shown illustrates the dynamic tuning of the frequency modulation dead zone considering economic efficiency. Figure 7 In the diagram, the horizontal axis represents time in seconds (s), and the vertical axis represents system frequency in hertz (Hz). The black dashed line represents the dead zone level frequency set according to the frequency regulation requirements at the receiving end, the red dashed line represents the dead zone level frequency after comprehensive consideration of economics, and the blue dashed line represents the dead zone level frequency set according to the frequency regulation capability at the sending end. The terms "economics," "capacity," and "demand" refer to the following: capacity refers to the frequency regulation capability of the sending end wind power, demand refers to the frequency regulation energy demand at the receiving end, and economics refers to the determination of the dead zone level by comprehensively considering demand and capacity, which can improve the economics of frequency regulation while meeting demand and not exceeding capacity.

[0075] (iv) A method for adjusting the droop coefficient considering frequency safety.

[0076] The aforementioned dead-zone setting ensures that the rotor kinetic energy of the sending-end wind turbine is not overutilized, avoiding triggering speed protection and secondary frequency drops. Further considering receiving-end frequency safety, a larger droop coefficient provides better frequency support; a smaller coefficient may still result in frequency exceeding limits. Therefore, a critical droop coefficient value needs to be set. As long as the actual droop coefficient is greater than this critical value, frequency safety can be ensured.

[0077] The challenge of this embodiment lies in the fact that the wind power support is zero within the dead zone, and support only begins outside the dead zone. Traditional methods with a relatively small fixed dead zone neglect the difference in system state equations between the inside and outside of the dead zone. However, in this embodiment, because the dynamic dead zone is larger than the traditional dead zone, ignoring this difference can easily lead to an underestimation of the critical droop coefficient. Therefore, this embodiment proposes a method for solving the critical droop coefficient based on the piecewise system frequency dynamic state space equations.

[0078] First, when the measured frequency is within the dead zone, the sending-end wind power does not operate, and the system frequency dynamic equation is: (8) Introduce the reheat state variable x: (9) Where, Δ x ( s ) represents the expression of the reheat state variable increment in the Laplace domain; x(t) represents the expression of the reheat state variable in the time domain.

[0079] but: (10) Δ x ( t ) represents the time-domain representation of the reheat state variable increment.

[0080] Substituting into the rotor motion equation, we get: (11) Summarized as follows: (12) The state-space equation for this stage is: (13) writing: (14) The derivative of the system state variable when the measured frequency is within the dead zone; A 0 represents the system state matrix when the measured frequency is within the dead zone; z 0 represents the system state variable when the measured frequency is within the dead zone; b 0 indicates an external input variable when the measured frequency is within the dead zone.

[0081] Its classic interpretation for: (15) In the formula, z 0,ss This is the steady-state solution when only the synchronous machine is supported.z 0(0) represents the initial state, and by default, all previous state variables are zero. It is an identity matrix.

[0082] Once the frequency deviation exceeds the dead zone, the wind power begins to provide support. Considering dead zone and droop control, the system frequency dynamic equation is: (16) In the formula, the dead zone size is -Δ during a load surge and frequency decrease event. f db * ; This represents the wind turbine droop control coefficient; the state variables are the same as within the dead zone. Therefore, the frequency dynamics can be expressed as: (17) Summarized as follows: (18) The state-space equation for this stage is: (19) writing: (20) This represents the derivative of the system state variables when the frequency deviation exceeds the dead zone. This represents the system state matrix when the frequency deviation exceeds the dead zone. This represents the system state variable when the frequency deviation exceeds the dead zone. This indicates the external input variable when the frequency deviation exceeds the dead zone.

[0083] Its classic interpretation is: (20) In the formula, t 0 indicates the moment when wind power begins to support the system; z ( t 0) represents the initial state at the moment when wind power begins to be supported; z ss This is the steady-state solution after wind power is involved in providing support. This indicates the system state at the moment when wind power begins to support the system, where the measured frequency is within the dead zone.

[0084] As can be seen from the above derivation, the system dynamics are second-order both before and after wind power participation, and can be solved analytically. Wind power participation in frequency regulation mainly affects the system dynamics in two ways: the droop coefficient effectively changes the system damping, and the dead zone setting effectively changes the system disturbance magnitude.

[0085] The moment when the wind power starts to be supported can be obtained by setting the dynamic value of the first two stages of support to the dead zone value. Substituting this value into equation (15) will yield the initial state of the wind power participation support expression (21), which will not be elaborated here.

[0086] By solving the dynamic frequency response of the two stages mentioned above, the lowest frequency point can be obtained using the min function (minimum value function). Setting the lowest point to 49.8Hz allows for the inverse solution of the critical droop coefficient. When the actual droop coefficient is greater than the critical droop coefficient, it can be ensured that the frequency after support is within a safe range.

[0087] The calculated dead zone and critical droop coefficient for wind power frequency regulation are input into the controller to achieve coordinated control of the sending and receiving ends of the wind power transmission system via flexible direct current transmission. Specifically, the receiving-end converter station controller measures the frequency of the onshore AC grid and transmits it to the sending-end wind farm controller via communication. The sending-end wind farm controller collects information from the wind farm and the receiving-end system, and calculates the frequency regulation dead zone and droop coefficient based on the receiving-end frequency regulation requirements and the sending-end capacity. The dead zone is controlled by the sending-end converter station controller, while the droop coefficient is controlled by each wind turbine controller.

[0088] (v) Simulation verification.

[0089] A simulation model was built in MATLAB / Simulink, using a real offshore wind power transmission system as a reference. A schematic diagram is shown below. Figure 8 As shown, it includes an offshore wind farm 1, a sending-end converter station 2, a receiving-end converter station 3, and a receiving-end power grid 4: Offshore wind farm 1 includes: wind turbines 5, turbine-side converters and grid-side converters 6, transformers 7, etc.

[0090] The connection relationships of each component are described as follows: After the offshore wind farm 1 is fed into the 220 kV busbar 8, it is transmitted through the flexible DC transmission system. The sending end and receiving end converter stations are connected by a +400 kV DC submarine cable 9 and a -400 kV DC submarine cable 10. On land, it is connected to the receiving end power grid 4 through a 500 kV busbar 11.

[0091] The flexible direct transmission section includes three wind farms with installed capacities of 400MW, 300MW, and 400MW respectively. The generated electricity from the wind farms is transmitted to the onshore converter station via ±400kV DC submarine cables. Other system parameters are shown in Table 1 below.

[0092] Table 1: System Parameters

[0093] The effectiveness of the dead zone and droop coefficient tuning methods will be explained below.

[0094] (1) Verification of the effectiveness of the dead zone tuning method.

[0095] The disturbance was set as a sudden load increase of 0.05 pu and a wind speed of 8.0 m / s. The lower limit of the absolute value of the dead zone calculated based on the proposed dead zone tuning method was ±0.130 Hz. To compare and illustrate the effectiveness, dead zones of ±0.105 Hz and ±0.145 Hz were set respectively, and the control results were observed as follows. Figure 9 and Figure 10 As shown.

[0096] Figure 9 In the middle, the horizontal axis represents time. t The unit is seconds (s); the vertical axis represents frequency. f The unit is Hertz (Hz); the blue solid line represents the frequency dynamics when there is no supply-end fan support; the green dashed line represents the frequency dynamics when the dead zone is ±0.105Hz (demand > capacity); the red solid line represents the frequency dynamics when the dead zone is ±0.130Hz (demand = capacity); and the orange solid line represents the frequency dynamics when the dead zone is ±0.145Hz (demand < capacity).

[0097] Figure 10 In the diagram, the horizontal axis represents time t, in seconds (s); the vertical axis represents rotational speed. w The unit is pu; the green dashed line represents the speed dynamics when the dead zone is ±0.105Hz (demand > capacity); the red solid line represents the speed dynamics when the dead zone is ±0.130Hz (demand = capacity); the orange solid line represents the speed dynamics when the dead zone is ±0.145Hz (demand < capacity).

[0098] As can be seen, when the dead zone is set according to the method proposed in this embodiment, the rotor kinetic energy utilization will not be excessive. However, when the absolute value of the dead zone is small, it is difficult to fully guarantee the safe utilization of rotor kinetic energy. In particular, when the droop coefficient is large, the frequency may drop twice. This demonstrates the effectiveness of the dead zone setting method proposed in this embodiment.

[0099] (2) Validation of the effectiveness of the droop coefficient tuning method The wind speeds were set to 8.0, 8.5, 9.0, and 9.5 m / s respectively, and the frequency control results were observed when the actual droop coefficient was set to the critical droop coefficient under different operating conditions.

[0100] Figure 11 The effect of frequency control when the sagging coefficient is taken as the critical value at a wind speed of 8.0 m / s; Figure 12 The effect of frequency control when the sagging coefficient is taken as the critical value at a wind speed of 8.5 m / s; Figure 13 The effect of frequency control when the sagging coefficient is taken as the critical value at a wind speed of 9.0 m / s; Figure 14 The frequency control effect is shown when the droop coefficient is taken as the critical value at a wind speed of 9.5 m / s.

[0101] Figure 11 In the diagram, the horizontal axis represents time t, in seconds (s); the vertical axis represents frequency f, in hertz (Hz); the blue solid line represents the frequency without the supply fan; the green solid line represents the frequency with the supply fan. Figure 12 In the diagram, the horizontal axis represents time t, in seconds (s); the vertical axis represents frequency f, in hertz (Hz); the red solid line represents the frequency when the supply-end fan is supported; the blue solid line represents the frequency when no supply-end fan is involved in the support. Figure 13 In the diagram, the horizontal axis represents time t, in seconds (s); the vertical axis represents frequency f, in hertz (Hz); the blue solid line represents the frequency without the supply fan; the orange solid line represents the frequency with the supply fan. Figure 14 In the graph, the horizontal axis represents time t, in seconds (s); the vertical axis represents frequency f, in hertz (Hz); the blue solid line represents the frequency without the supply fan; the purple solid line represents the frequency with the supply fan.

[0102] As can be seen, based on the droop coefficient tuning method proposed in this embodiment, the frequency can be controlled at the safe boundary value of 49.8Hz when the droop coefficient is set to the critical value under different wind speeds, which shows the effectiveness of the proposed method.

[0103] Furthermore, Figure 15 and Figure 16 These represent the frequency and rotational dynamics for different values ​​of the droop coefficient, where... Figure 15 This represents the frequency dynamics with different values ​​of the droop coefficient. Figure 16 The rotational speed dynamics are shown for different values ​​of the droop coefficient. Frequency control results are presented for wind speeds of 8.0 m / s when the droop coefficient is greater than, equal to, and less than the critical droop coefficient.

[0104] Figure 15 In the graph, the horizontal axis represents time t, in seconds (s); the vertical axis represents frequency f, in Hertz (Hz); the blue solid line represents the frequency without a supply-end fan support; the green solid line represents the frequency when the droop coefficient is less than the critical droop coefficient; the orange solid line represents the frequency when the droop coefficient is equal to the critical droop coefficient; and the red solid line represents the frequency when the droop coefficient is greater than the critical droop coefficient.

[0105] Figure 16 In the graph, the horizontal axis represents time t, in seconds (s); the vertical axis represents rotational speed w, in pu; the green solid line represents the frequency when the droop coefficient is less than the critical droop coefficient; the orange solid line represents the frequency when the droop coefficient is equal to the critical droop coefficient; and the red solid line represents the frequency when the droop coefficient is greater than the critical droop coefficient.

[0106] As can be seen, when the actual droop coefficient is greater than the critical value, the frequency control effect is better and the speed will not exceed the limit. When the actual droop coefficient is less than the critical value, the frequency will exceed the limit, which further illustrates the effectiveness of the proposed droop coefficient tuning method.

[0107] Example 2 This embodiment discloses a collaborative control system for dynamic matching of wind power transmission via flexible direct transmission at the sending and receiving ends.

[0108] The dynamic matching control system for wind power transmission via flexible direct current transmission at both the sending and receiving ends includes: The effective frequency regulation energy calculation module is configured to: measure the wind turbine speed and calculate the effective frequency regulation energy at the sending end; The dead zone upper and lower limit determination module is configured to: model the frequency modulation energy demand at the receiving end, use the effective frequency modulation energy as the modeled frequency modulation energy demand, calculate the lower limit of the wind power control dead zone, and use the frequency safety boundary value as the upper limit of the dead zone. The wind power frequency regulation control dead zone determination module is configured to: consider frequency regulation cost and frequency regulation effect, introduce an economic coefficient, and determine the final wind power frequency regulation control dead zone based on the upper and lower limits of the dead zone; The critical droop coefficient determination module is configured to: segment the frequency based on whether the measured frequency at the receiving end of the wind power transmission system is in the dead zone of wind power frequency regulation control, and calculate the critical droop coefficient based on the segmented state space equation of the wind power transmission system. The collaborative control module is configured to input the calculated wind power frequency regulation control dead zone and critical droop coefficient into the controller to achieve collaborative control of the wind power transmission system at both the sending and receiving ends.

[0109] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0110] 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 method for coordinated control of a wind power transmission system via flexible direct current transmission with dynamic matching at both the sending and receiving ends, characterized in that: Includes the following steps: The effective frequency regulation energy at the sending end is calculated by measuring the wind turbine's rotational speed. The calculation formula is as follows: ； in, E w,eff Indicates the effective frequency modulation energy at the sending end; This indicates the proportion of effective frequency modulation energy to the released rotor kinetic energy; J w The moment of inertia of the wind turbine; w 0 represents the initial speed of the wind turbine. w min Minimum operating speed limit for safe operation of the wind turbine; The frequency regulation energy demand at the receiving end is modeled, with the effective frequency regulation energy used as the modeled frequency regulation energy demand. The lower limit of the wind power control dead zone is calculated, and the frequency safety boundary value is used as the upper limit of the dead zone. The specific modeling process is as follows: The frequency response model of the receiving-end system without wind power support at the sending end and the frequency response model of the receiving-end system considering wind power energy injection at the sending end are analyzed. The deviation of the system's real-time frequency from the rated frequency and the mechanical power adjustment of the synchronous machine are determined under two scenarios: when there is no wind power support at the sending end and when wind power energy injection at the sending end is considered. The wind power support power is obtained through algebraic processing. The wind power support power is integrated, and the upper limit of the integration is taken as the end time of the effective support provided by the wind turbine. The simplified expression is obtained as the frequency regulation energy demand expression from the receiving end to the sending end. Considering frequency regulation costs and effects, an economic coefficient is introduced, and the final wind power frequency regulation control dead zone is determined based on the upper and lower limits of the dead zone. The calculation formula is as follows: ； Where, Δ f db * This indicates the final determined dead zone for wind power frequency regulation control; Δ f db min This is the lower limit of the FM dead zone; Δ f db max This is the upper limit of the FM dead zone; k Frequency modulation economic coefficient; frequency modulation economic coefficient k The value ranges from 0 to 1. The closer it is to 1, the better the frequency modulation cost, but the worse the frequency modulation effect; the closer it is to 0, the higher the frequency modulation cost, but the better the frequency modulation effect. Based on whether the measured frequency at the receiving end of the wind power transmission system is in the dead zone of wind power frequency regulation control, the frequency is segmented, and the critical droop coefficient is calculated based on the segmented state space equation of the wind power transmission system. The calculated dead zone and critical droop coefficient of wind power frequency regulation control are input into the controller to achieve coordinated control of the sending and receiving ends of the wind power transmission system via flexible direct current transmission.

2. The method for coordinated control of a wind power transmission system via flexible direct current transmission with dynamic matching at both the sending and receiving ends as described in claim 1, characterized in that, When determining the calculation formula for the effective frequency modulation energy at the sending end: The difference between the released rotor kinetic energy and the wind energy capture loss is used as the effective frequency modulation energy; Without pre-setting the wind power control mode, it is assumed that the wind speed drops to 0.7 when the rotor kinetic energy is released; and the magnitude of wind energy capture loss is affected by wind speed and control strategy. Based on simulation data, a conservative calculation formula for the effective frequency modulation energy at the sending end is obtained.

3. The method for coordinated control of a wind power transmission system via flexible direct current transmission with dynamic matching at both the sending and receiving ends as described in claim 1, characterized in that, The expression for the frequency modulation energy demand from the receiving end to the sending end is: ； in, This indicates the system frequency deviation corresponding to the time when wind power support ended; This indicates the system frequency deviation at the moment when wind power support ends, corresponding to the time without wind power support. 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 Here, t represents the reheat time constant; t0 represents the start time of wind turbine support, and t represents any time during wind turbine support. t s Indicates the end time of effective support; This represents the time-domain representation of the deviation of the system's real-time frequency from the rated frequency when the wind power supply is supported at the sending end. This represents the time-domain representation of the deviation of the system's real-time frequency from the rated frequency when there is no wind power support at the sending end.

4. The method for coordinated control of a wind power transmission system via flexible direct current transmission with dynamic matching at both the sending and receiving ends as described in claim 1, characterized in that, Also includes: When setting the lower limit of the dead zone, the effective support end time needs to ensure that the frequency modulation energy demand corresponding to the current end time is greater than the frequency modulation energy demand corresponding to other end times under this dead zone. Under a specific dead zone, when the effective support end time is the right intersection of the dead zone line and the frequency curve before support, the frequency regulation demand corresponds to the maximum value under the current dead zone. Setting the lower limit of the dead zone according to this dead zone can ensure that the actual frequency regulation energy consumption under any control will not exceed the wind power capacity.

5. The method for coordinated control of a wind power transmission system via flexible direct current transmission with dynamic matching at both the sending and receiving ends as described in claim 1, characterized in that, The critical droop coefficient is calculated based on the piecewise state-space equations of the wind power transmission system via flexible direct transmission, specifically including: When the measured frequency is within the dead zone, it is considered the first stage. At this time, the sending-end wind power does not operate. The system frequency dynamic equation is determined, and the reheat state variable is introduced for correction to obtain the state space equation of the first stage. When the frequency deviation exceeds the dead zone, it is considered the second stage. Wind power begins to provide support. Taking dead zone and droop control into account, the system frequency dynamic equation is determined, and the state space equation of the second stage is obtained. Solve the frequency response dynamics of the first and second stages described above to find the lowest frequency point; Let the lowest frequency be 49.8 Hz, and then solve for the critical droop coefficient.

6. The method for coordinated control of a wind power transmission system via flexible direct current transmission with dynamic matching at both the sending and receiving ends as described in claim 1, characterized in that, Control the actual sag coefficient to be greater than the critical sag coefficient to ensure that the frequency is within a safe range after support.

7. A dynamic matching control system for wind power transmission via flexible direct current transmission at both the sending and receiving ends, characterized in that: include: The effective frequency regulation energy calculation module is configured to measure the wind turbine speed and calculate the effective frequency regulation energy at the sending end. The calculation formula is as follows: ； in, E w,eff Indicates the effective frequency modulation energy at the sending end; This indicates the proportion of effective frequency modulation energy to the released rotor kinetic energy; J w The moment of inertia of the wind turbine; w 0 represents the initial speed of the wind turbine. w min Minimum operating speed limit for safe operation of the wind turbine; The dead zone upper and lower limit determination module is configured to: model the frequency modulation energy demand at the receiving end, use the effective frequency modulation energy as the modeled frequency modulation energy demand, calculate the lower limit of the wind power control dead zone, and use the frequency safety boundary value as the upper limit of the dead zone. The specific modeling process is as follows: The frequency response model of the receiving-end system without wind power support at the sending end and the frequency response model of the receiving-end system considering wind power energy injection at the sending end are analyzed. The deviation of the system's real-time frequency from the rated frequency and the mechanical power adjustment of the synchronous machine are determined under two scenarios: when there is no wind power support at the sending end and when wind power energy injection at the sending end is considered. The wind power support power is obtained through algebraic processing. The wind power support power is integrated, and the upper limit of the integration is taken as the end time of the effective support provided by the wind turbine. The simplified expression is obtained as the frequency regulation energy demand expression from the receiving end to the sending end. The wind power frequency regulation control dead zone determination module is configured to: consider frequency regulation costs and effects, introduce an economic coefficient, and determine the final wind power frequency regulation control dead zone based on the upper and lower limits of the dead zone. The calculation formula is as follows: ； Where, Δ f db * This indicates the final determined dead zone for wind power frequency regulation control; Δ f db min This is the lower limit of the FM dead zone; Δ f db max This is the upper limit of the FM dead zone; k Frequency modulation economic coefficient; frequency modulation economic coefficient k The value ranges from 0 to 1. The closer it is to 1, the better the frequency modulation cost, but the worse the frequency modulation effect; the closer it is to 0, the higher the frequency modulation cost, but the better the frequency modulation effect. The critical droop coefficient determination module is configured to: segment the frequency based on whether the measured frequency at the receiving end of the wind power transmission system is in the dead zone of wind power frequency regulation control, and calculate the critical droop coefficient based on the segmented state space equation of the wind power transmission system. The collaborative control module is configured to input the calculated wind power frequency regulation control dead zone and critical droop coefficient into the controller to achieve collaborative control of the wind power transmission system at both the sending and receiving ends.

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