A wind power direct current collection and sending-out system grid frequency active support method

Abstract

The present application relates to the technical field of wind power collection and DC transmission, and discloses a power grid frequency active support method for a wind power DC collection and transmission system, which comprises the following steps: a land converter station maps the frequency of a land AC power grid to the DC side voltage of the land converter station through droop control, so as to transmit the frequency of the land AC power grid to offshore wind turbines through the DC voltage at the input side of a sea booster station; the land converter station and the sea booster station determine the energy release amount of the capacitor of each sub-module according to the frequency of the land AC power grid, so as to provide short-time support for the frequency of the land AC power grid; in the process of short-time support for the frequency of the land AC power grid by the land converter station and the sea booster station, the offshore wind turbines determine the frequency modulation power required by the machine side converter and the DC voltage required by the grid side converter according to the frequency of the land AC power grid and the rotor speed of the offshore wind turbines, so as to provide long-time support for the frequency of the land AC power grid.

Description

Technical Field

[0001] This invention relates to the field of wind power collection and DC transmission technology, and particularly to a method, system, equipment and medium for active grid frequency support in a wind power DC collection and transmission system. Background Technology

[0002] As the global energy transition continues, offshore wind power, with its abundant wind energy resources, high utilization hours, lack of land occupation, and proximity to coastal load centers, has become one of the core directions for renewable energy development and utilization. Wind power DC collection and transmission systems, as a mainstream technical solution adapted to large-scale offshore wind power development, integrate the electrical energy of various offshore wind turbines through a medium-voltage DC collection network, and then transmit it over long distances to the onshore AC power grid via high-voltage DC transmission lines. This effectively avoids the technical bottlenecks of traditional AC collection methods, such as large reactive power losses, high overvoltage risks, and prominent synchronization stability issues. It possesses significant technical and economic advantages in the construction of large-scale offshore wind farms and has extremely broad application prospects.

[0003] Due to the decoupling of multi-stage power electronic equipment between onshore AC power grids and offshore wind turbines, frequency fluctuations in the onshore AC power grid cannot be directly transmitted to offshore wind turbines. The mechanical inertia of offshore wind turbines cannot respond naturally to grid frequency changes like traditional synchronous generators. This results in the wind power DC collection and transmission system lacking natural inertial response capability and being unable to actively participate in the primary frequency regulation of the AC power grid. Furthermore, with the increasing proportion of new energy installed capacity and the gradual retirement of traditional synchronous generators, the overall inertia level of the power grid is continuously declining, significantly increasing the risk of frequency stability. Therefore, researching methods for the wind power DC collection and transmission system to actively support the frequency of the AC power grid is an urgent need to ensure the safe and stable operation of power grids with high wind power penetration, and has significant practical implications for promoting large-scale grid connection of offshore wind power and constructing a new type of power system.

[0004] However, existing solutions mostly design frequency support control strategies for onshore converter stations and offshore wind turbines in isolation, lacking system-wide coordinated control logic. Therefore, it is difficult to fully tap the frequency regulation potential of multiple links in the wind power DC collection and transmission system, and the performance is poor under complex grid conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a method, system, equipment, and medium for active grid frequency support in a wind power DC collection and transmission system, which can solve the problem of poor frequency support performance under complex grid operating conditions.

[0006] To address the aforementioned technical problems, this invention provides a method for actively supporting the grid frequency of a wind power DC collection and transmission system, comprising: Onshore converter stations acquire the frequency of the onshore AC grid in real time and map the frequency to the DC-side voltage of the onshore converter station through droop control; offshore booster stations use the DC-side voltage of the onshore converter station to inversely calculate the frequency of the onshore AC grid and map the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control; offshore wind turbines use the DC voltage of the input side of the offshore booster station to inversely calculate the frequency of the onshore AC grid. The onshore converter station and the offshore booster station determine the energy release of their respective sub-module capacitors based on the real-time frequency of the onshore AC power grid and the corresponding reverse-engineered frequency, so as to provide short-term support for the frequency of the onshore AC power grid. During the short-term frequency support of the onshore AC grid by offshore wind turbines at onshore converter stations and offshore booster stations, the frequency regulation power required by the turbine-side converter and the DC voltage required to be adjusted by the grid-side converter are determined based on the real-time frequency of the onshore AC grid obtained by reverse calculation and the rotor speed of the offshore wind turbine, so as to provide long-term frequency support for the onshore AC grid.

[0007] Furthermore, determining the frequency regulation power required by the turbine-side converter and the DC voltage required to be adjusted by the grid-side converter of the offshore wind turbine, based on the real-time frequency of the onshore AC power grid obtained through reverse calculation and the rotor speed of the offshore wind turbine, includes: When the frequency of the onshore AC grid and the rotor speed of the offshore wind turbine simultaneously meet the preset trigger criteria, the region to which the frequency of the onshore AC grid belongs in the pre-acquired planned frequency trajectory is determined; the planned frequency trajectory includes a safe zone, a monitoring zone, a regulation zone, and a prohibited zone. If the area is a safe zone or a monitored zone, the offshore wind turbines will continue to operate normally; If the area is a regulation zone or a prohibited zone, then determine the frequency regulation power that the turbine-side converter of the offshore wind turbine needs to provide and the DC voltage that the grid-side converter needs to regulate.

[0008] Furthermore, determining the frequency regulation power required by the turbine-side converter of the offshore wind turbine and the DC voltage required to be regulated by the grid-side converter includes: Offshore wind turbines obtain the frequency regulation power required by the turbine-side converter based on a proportional controller. Offshore wind turbines obtain the DC voltage that the grid-side converter needs to regulate based on a differential controller.

[0009] Furthermore, the preset triggering criteria for the frequency of the onshore AC power grid and the rotor speed of the offshore wind turbine are as follows: ; In the formula, Δ f For the frequency deviation of the land-based AC power grid,R The rate of change of frequency, F act For frequency deviation action threshold, R act The frequency change rate action threshold; ; In the formula, ω r This refers to the rotor speed of the offshore wind turbine.

[0010] Furthermore, the energy regulation range of the submodule capacitors of the onshore converter station and the offshore booster station is pre-widened by injecting third harmonic voltage into the modulation wave of the onshore converter station and the offshore booster station.

[0011] Furthermore, the onshore converter station and the offshore booster station determine the energy release amount of their respective submodule capacitors based on the real-time frequency of the onshore AC power grid using the following preset energy curves: ; In the formula, This represents the minimum energy value. For energy release margin, t tr1 and t tr2 These are the trigger times for energy release control and energy recovery control, respectively. T rec and k rec These represent the duration of energy recovery control and the slope of the energy recovery curve, respectively. T rel The duration for controlling energy release.

[0012] Furthermore, the offshore booster station uses the DC-side voltage of the onshore converter station to inversely calculate the frequency of the onshore AC grid, and maps the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control. The offshore wind turbine uses the DC voltage of the input side of the offshore booster station to inversely calculate the frequency of the onshore AC grid, including: The offshore booster station acquires the DC voltage on the output side in real time, which is used as the DC voltage on the onshore converter station. The frequency of the onshore AC power grid is then calculated by using the droop control of the onshore converter station. The offshore booster station maps the DC voltage on the output side to the DC voltage on the input side through droop control; Offshore wind turbines acquire their output port voltage in real time, which is then used as the DC voltage input to the offshore substation. This voltage, combined with the droop control of the onshore converter station and the offshore substation, is used to inversely deduce the frequency of the onshore AC power grid.

[0013] Embodiments of the present invention also provide a computer device, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to execute the above-described active grid frequency support method for wind power DC collection and transmission system.

[0014] Embodiments of the present invention also provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described method for actively supporting the grid frequency of a wind power DC collection and transmission system.

[0015] The grid frequency active support method for wind power DC collection and transmission systems provided by this invention has at least the following beneficial effects: This invention constructs a system-wide collaborative control architecture, which enables frequency support for the onshore AC power grid through the coordinated operation of onshore converter stations, offshore booster stations, and offshore wind turbines.

[0016] First, after obtaining the frequency of the onshore AC grid from the onshore converter station, the frequency is transmitted through DC voltage droop mapping, enabling both the offshore booster station and the offshore wind turbines to obtain the frequency of the onshore AC grid in real time. At this point, the equipment distributed in different physical locations in the system shares the system frequency status, fulfilling the prerequisite for coordinated operation at the same time. Then, two different energy sources in the system are utilized and coordinated in the control logic. One is the rotor kinetic energy formed by the frequency regulation power of the offshore wind turbine's generator-side converter and the DC voltage regulation of the grid-side converter. The other is the electrostatic energy of the capacitors in the sub-modules of the onshore converter station and the offshore booster station. Among them, the rotor rotation contains huge mechanical kinetic energy, which can provide long-term primary frequency regulation. The electrostatic energy of the capacitors has an extremely fast release response, which is suitable for providing short-time inertial response at the moment of sudden change in grid frequency, suppressing the peak value of the frequency change rate. The two work together to form frequency support on the entire time scale, thereby realizing the frequency support of the wind power DC collection and transmission system under complex grid conditions. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A flowchart illustrating a method for active grid frequency support in a wind power DC collection and transmission system provided by the present invention; Figure 2 A circuit topology diagram of a wind power DC collection and transmission system provided by the present invention; Figure 3A circuit topology diagram of an onshore converter station provided by the present invention; Figure 4 A circuit topology diagram of an offshore booster station provided by the present invention; Figure 5 This is a schematic diagram of a frequency trajectory region division result provided by the present invention; Figure 6 A control block diagram of an offshore wind turbine provided by the present invention; Figure 7 A control block diagram of an onshore converter station provided by the present invention; Figure 8 This invention provides a control block diagram for an offshore substation. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] The existing methods for actively supporting the frequency of the AC grid in wind power DC collection and transmission systems have the following limitations: (1) Insufficient reliability of communication-dependent solutions: Some studies have proposed transmitting onshore power grid frequency signals to offshore wind turbines through communication links such as optical fibers to achieve frequency response control. However, offshore communication links are susceptible to marine environment and electromagnetic interference, resulting in communication delays and insufficient reliability, which makes it difficult to meet the needs of fast frequency support scenarios such as inertial response.

[0021] (2) Lack of system-level collaborative control scheme: Existing schemes mostly design frequency support control strategies for flexible DC converter stations and offshore wind turbines in isolation, failing to fully explore the frequency regulation potential of multiple links in the wind power DC collection and transmission system, lacking the whole system collaborative control logic, making it difficult to achieve the collaborative support effect of "short-time inertial response + long-time primary frequency regulation", and the overall integrity and robustness of the control strategy are insufficient, making it difficult to adapt to complex power grid conditions.

[0022] (3) Most of the existing frequency support control strategies for offshore wind turbines are based on droop / inertia control. If the control parameters are too small, the compensation effect is insufficient, and the grid frequency index will still have a large deviation, and the risk of triggering relay protection is still high. If the control parameters are too large, the compensation is excessive. Although the grid frequency is safer, the offshore wind turbine will deviate significantly from its optimal operating point, which will not only reduce the operating economy, but may also cause faults such as overcurrent and overheating.

[0023] In summary, existing technologies cannot economically and reliably achieve active frequency support for the AC power grid from wind power DC collection and transmission systems. There is an urgent need for an active frequency support method that is communication-independent, adaptable to all aspects of the system, and balances frequency support effectiveness with frequency regulation economy, in order to overcome the shortcomings of existing technologies and ensure the stability of the power grid frequency.

[0024] The purpose of this invention is to provide a method for actively supporting the grid frequency of a wind power DC collection and transmission system, which can effectively improve the frequency regulation capability of the wind power DC collection and transmission system. It is an effective means to solve the frequency stability problem of new power systems and plays a supporting role in the development of new power systems.

[0025] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] One embodiment of the present invention relates to a method for actively supporting the grid frequency of a wind power DC collection and transmission system. The specific process of the method for actively supporting the grid frequency of a wind power DC collection and transmission system in this embodiment includes: Step 101: The onshore converter station acquires the frequency of the onshore AC grid in real time and maps the frequency to the DC-side voltage of the onshore converter station through droop control; the offshore booster station uses the DC-side voltage of the onshore converter station to inversely calculate the frequency of the onshore AC grid and maps the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control; the offshore wind turbine uses the DC voltage of the input side of the offshore booster station to inversely calculate the frequency of the onshore AC grid. Step 102: The onshore converter station and the offshore booster station determine the energy release of their respective sub-module capacitors based on the real-time frequency of the onshore AC power grid and the corresponding reverse-engineered frequency, so as to provide short-term support for the frequency of the onshore AC power grid. Step 103: During the short-term frequency support of the onshore AC grid by the offshore wind turbine at the onshore converter station and the offshore booster station, the frequency regulation power required by the turbine-side converter and the DC voltage required by the grid-side converter of the offshore wind turbine are determined based on the real-time frequency of the onshore AC grid obtained by back-calculation and the rotor speed of the offshore wind turbine, so as to provide long-term frequency support for the onshore AC grid.

[0027] The following is a detailed description of the implementation details of the grid frequency active support method of the wind power DC collection and transmission system in this embodiment. The following content is only for the convenience of understanding and is not necessary for implementing this solution.

[0028] The active grid frequency support method for the wind power DC collection and transmission system provided in this embodiment specifically includes the following three parts: onshore AC grid frequency information transmission; frequency trajectory planning and control of offshore wind turbines; and capacitor energy optimization control of onshore converter stations and offshore booster stations.

[0029] Firstly, the process of transmitting frequency information in a land-based AC power grid includes the following steps: Step S1.1: The onshore converter station collects the frequency information of the onshore AC power grid in real time, and obtains the frequency change by subtracting it from the rated frequency. The frequency change is then mapped to the DC side voltage adjustment amount through droop control, and the DC side voltage is adjusted based on the adjustment amount. Furthermore, the specific implementation method is as follows: ; Where: Δ U dc This refers to the voltage change on the DC side of the onshore converter station. k 1 represents the droop factor from the grid frequency to the DC-side voltage; Δ f g This represents the frequency variation of the onshore AC power grid.

[0030] Preferably, the sag coefficient k 1. Designed as follows: ; in: This indicates the maximum permissible variation in DC-side voltage; This indicates the maximum permissible variation in the frequency of an onshore AC power grid.

[0031] Step S1.2: The offshore booster station detects the change in DC voltage on the output side and maps the change in DC voltage on the high-voltage side to the change in DC voltage on the input side through droop control, which is the voltage change of the offshore medium-voltage DC collection network. Furthermore, the specific implementation method is as follows: ; Where: Δ U dcH The voltage change on the output side of the offshore substation is approximately equal to Δ. U dc ; k 2 represents the droop factor from the output voltage to the input voltage; Δ U dcM This refers to the voltage change on the input side of the offshore substation.

[0032] Preferably, the sag coefficient k 2 is designed as follows: ; in: This indicates the maximum permissible variation in the output voltage of the offshore booster station; This indicates the maximum permissible variation in the input voltage of the offshore substation.

[0033] Step S1.3: The offshore wind turbine detects its own output port voltage and calculates the difference between the output port voltage and the rated voltage to obtain the output port voltage change. Based on the output port voltage change and combined with the droop coefficients of the onshore converter station and the offshore booster station, the frequency change of the onshore AC grid is deduced. This frequency change is called the mirror frequency change. Furthermore, the specific implementation method is as follows: ; Where: Δ U dco The voltage change at the output port of the offshore wind turbine is approximately equal to Δ. U dcM ;Δ f ac This represents the change in the image frequency, and the corresponding image frequency is... f ac = f N + Δ f ac , f N This is the rated frequency for the onshore AC power grid.

[0034] Secondly, the frequency trajectory planning and control of offshore wind turbines includes the following steps: Step S2.1: Determine the frequency trajectory region division parameters, divide the potential occurrence area of ​​the power grid frequency into regions, and obtain the frequency trajectory region division results; Specifically, the frequency trajectory area division parameters include: frequency deviation action threshold, frequency change rate action threshold, frequency deviation planning value, frequency change amount planning value, frequency deviation protection threshold, and frequency change rate protection threshold; the frequency trajectory area division results are: safe zone, monitoring zone, adjustment zone, and prohibited zone.

[0035] Step S2.2: Calculate the critical frequency trajectory curve and the planned frequency trajectory curve to provide a reference for the frequency support control of offshore wind turbines. The specific implementation steps are as follows: Step S2.2.1: Calculate the critical frequency trajectory curve based on the frequency deviation protection threshold and the frequency change rate protection threshold; Specifically, the time-domain expression of the critical frequency trajectory curve is: ; in: f cr (t) represents the trajectory curve at the preset critical frequency; F cr The frequency deviation protection threshold specified in the power grid guidelines; R cr The frequency change rate protection threshold is specified in the power grid guidelines.

[0036] Step S2.2.2: Calculate the planned frequency trajectory curve based on the reserved frequency deviation safety margin and the reserved frequency change rate safety margin; Specifically, the time-domain expression for the planned frequency trajectory curve is: ; in: f tp (t) represents the planned critical frequency trajectory curve; F tp This is the planned value for frequency deviation; R tp The planned value is the frequency change.

[0037] Furthermore, the planned value of frequency deviation F tp The expression is: ; in: F mar This represents the safety margin for frequency deviation.

[0038] Furthermore, the planned value of the rate of change of frequency R tp The expression is: ; in: R mar This represents the safety margin for the rate of change of frequency.

[0039] Step S2.3: Determine whether the frequency index of the mirror frequency and the rotor speed of the offshore wind turbine simultaneously meet the preset trigger criteria. If they do, proceed to step S2.4. Specifically, frequency indicators include frequency deviation and frequency change rate.

[0040] Specifically, the preset trigger criterion for the mirror frequency is: ; in: S 1 is the action flag bit 1 for the frequency trajectory planning and control module; Δ f This represents the deviation of the image frequency; R The rate of change of the image frequency; F act The frequency deviation action threshold is set to 0.1Hz; R act The frequency change rate action threshold is set to 1 Hz / s.

[0041] Specifically, the preset trigger criterion for rotor speed is: ; in: S 2 is the action flag bit 2 of the frequency trajectory planning and control module; ω r This refers to the rotor speed of the offshore wind turbine.

[0042] Step S2.4: Determine the trajectory area where the mirror frequency is located. If the mirror frequency exceeds the monitoring area, proceed to step S2.5. Step S2.5: Set the mirror frequency f ac Planning frequency trajectory with reserved safety margin f tp The frequency trajectory error signal is obtained by subtracting the frequency trajectory error signal; based on the frequency trajectory error signal and the trajectory area where the actual frequency of the power grid is located, the frequency regulation power required by the offshore wind turbine generator-side converter is obtained based on the proportional controller, and the DC voltage required by the offshore wind turbine grid-side converter is obtained based on the differential controller.

[0043] Third, the optimized control of capacitor energy in onshore converter stations and offshore booster stations includes the following steps: Step S3.1: Inject the third harmonic voltage into the modulation wave of the onshore converter station and the offshore booster station to broaden the energy regulation range of the onshore converter station and the offshore booster station. Step S3.2: Calculate the preset energy curves for the onshore converter station and the offshore booster station; Taking an onshore converter station as an example, its preset energy curve is as follows: ; in: An expression for a preset energy curve; This represents the minimum energy required for an onshore converter station. For the energy release margin of onshore converter stations; t tr1 and t tr2 These are the trigger times for energy release control and energy recovery control at the onshore converter station, respectively. T rec and k rec These represent the duration of energy recovery control for onshore converter stations and the slope of the energy recovery curve, respectively. T rel The duration of energy release control for onshore converter stations.

[0044] Furthermore, the duration of energy release control at onshore converter stations T rel The calculation method is as follows: ; Where: Δ Pacmax This represents the maximum permissible variation in active power on the AC side of the onshore converter station.

[0045] Step S3.3: Set the preset energy curve of the onshore converter station to the reference value of the onshore converter station energy loop, and set the preset energy curve of the offshore booster station to the reference value of the offshore booster station energy loop.

[0046] In one specific embodiment, the circuit topology of the wind power DC collection and transmission system is as follows: Figure 2 As shown, it mainly consists of three parts: an offshore wind farm, an offshore booster station, and an onshore converter station. The offshore wind farm comprises multiple offshore wind turbines connected in parallel; these turbines are DC-type. The onshore converter station is a hybrid modular multilevel converter with a full and half-bridge submodule configuration, capable of unblocked DC short-circuit fault ride-through. Its topology is shown in the diagram. Figure 3 As shown; the offshore booster station adopts a modular multilevel DC / DC converter based on a full-half-bridge submodule, which can also achieve DC short-circuit fault ride-through without blocking. Its topology is as follows. Figure 4 As shown.

[0047] In conjunction with the above embodiments, the active grid frequency support method for the wind power DC collection and transmission system in this embodiment is as follows: Firstly, the process of transmitting frequency information in a land-based AC power grid includes the following steps: Step S1.1: The onshore converter station collects the frequency information of the onshore AC power grid in real time, and obtains the frequency change by subtracting it from the rated frequency. The frequency change is then mapped to the DC side voltage adjustment amount through droop control, and the DC side voltage is adjusted based on the adjustment amount. Furthermore, the specific implementation method is as follows: ; Where: Δ U dc This refers to the voltage change on the DC side of the onshore converter station. k 1 represents the droop factor from the grid frequency to the DC-side voltage; Δ f g This represents the frequency variation of the onshore AC power grid.

[0048] Preferably, the sag coefficient k 1. Designed as follows: ; in: This represents the maximum permissible variation in DC-side voltage, taken as 0.1 pu; This represents the maximum permissible variation in the frequency of the onshore AC power grid, taken as 0.01 pu.

[0049] Step S1.2: The offshore booster station detects the change in DC voltage on the output side and maps the change in DC voltage on the high-voltage side to the change in DC voltage on the input side through droop control, which is the voltage change of the offshore medium-voltage DC collection network. Furthermore, the specific implementation method is as follows: ; Where: Δ U dcH The voltage change on the output side of the offshore substation is approximately equal to Δ. U dc ; k 2 represents the droop factor from the output voltage to the input voltage; Δ U dcM This refers to the voltage change on the input side of the offshore substation.

[0050] Preferably, the sag coefficient k 2 is designed as follows: ; in: This represents the maximum allowable variation in the output voltage of the offshore booster station, taken as 0.1 pu; This represents the maximum allowable variation in the input voltage of the offshore substation, taken as 0.1 pu.

[0051] Step S1.3: The offshore wind turbine detects its own output port voltage and calculates the difference between the output port voltage and the rated voltage to obtain the output port voltage change. Based on the output port voltage change and combined with the droop coefficients of the onshore converter station and the offshore booster station, the frequency change of the onshore AC grid is deduced. This frequency change is called the mirror frequency change. Furthermore, the specific implementation method is as follows: ; Where: Δ U dco The voltage change at the output port of the offshore wind turbine is approximately equal to Δ. U dcM ;Δ f ac This represents the change in the image frequency, and the corresponding image frequency is... f ac = f N + Δ f ac , f N This is the rated frequency for the onshore AC power grid.

[0052] Secondly, the frequency trajectory planning and control of offshore wind turbines includes the following steps: Step S2.1: Determine the frequency trajectory region division parameters, divide the potential occurrence area of ​​the power grid frequency into regions, and obtain the frequency trajectory region division results as follows: Figure 5 As shown; Specifically, the frequency trajectory area division parameters include: frequency deviation action threshold, frequency change rate action threshold, frequency deviation planning value, frequency change amount planning value, frequency deviation protection threshold, and frequency change rate protection threshold; the frequency trajectory area division results are: safe zone, monitoring zone, adjustment zone, and prohibited zone.

[0053] Step S2.2: Calculate the critical frequency trajectory curve and the planned frequency trajectory curve to provide a reference for the frequency support control of offshore wind turbines. The specific implementation steps are as follows: Step S2.2.1: Calculate the critical frequency trajectory curve based on the frequency deviation protection threshold and the frequency change rate protection threshold; Specifically, the time-domain expression of the critical frequency trajectory curve is: ; in: f cr (t) represents the trajectory curve at the preset critical frequency; F cr The frequency deviation protection threshold specified in the power grid guidelines is set to 0.5Hz. R cr The frequency change rate protection threshold specified in the power grid guidelines is taken as 2Hz / s.

[0054] Step S2.2.2: Calculate the planned frequency trajectory curve based on the reserved frequency deviation safety margin and the reserved frequency change rate safety margin; Specifically, the time-domain expression for the planned frequency trajectory curve is: ; in: f tp (t) represents the planned critical frequency trajectory curve; F tp The planned value for frequency deviation is 0.3Hz; R tp The planned value for the frequency change is 1.5 Hz / s.

[0055] Furthermore, the planned value of frequency deviation F tp The expression is: ; in: F mar As a safety margin for frequency deviation, we take 0.2Hz.

[0056] Furthermore, the planned value of the rate of change of frequency R tp The expression is: ; in: R mar As a safety margin for the rate of frequency change, we take 0.5 Hz / s.

[0057] Step S2.3: Determine whether the frequency index of the mirror frequency and the rotor speed of the offshore wind turbine simultaneously meet the preset trigger criteria. If they do, proceed to step S2.4. Specifically, frequency indicators include frequency deviation and frequency change rate.

[0058] Specifically, the preset trigger criterion for the mirror frequency is: ; in: S 1 is the action flag bit 1 for the frequency trajectory planning and control module; Δ f This represents the deviation of the image frequency; R The rate of change of the image frequency; F act The frequency deviation action threshold is set to 0.1Hz; R act The frequency change rate action threshold is set to 1 Hz / s.

[0059] Specifically, the preset trigger criterion for rotor speed is: ; in: S 2 is the action flag bit 2 of the frequency trajectory planning and control module; ω r This refers to the rotor speed of the offshore wind turbine.

[0060] Step S2.4: Determine the trajectory area where the mirror frequency is located. If the mirror frequency exceeds the monitoring area, proceed to step S2.5. Step S2.5: Set the mirror frequency f ac Planning frequency trajectory with reserved safety margin f tp The difference is calculated to obtain the frequency trajectory error signal. Based on the frequency trajectory error signal and the trajectory region where the actual frequency of the grid is located, the required frequency regulation power to be provided by the offshore wind turbine's generator-side converter is obtained using a proportional controller, and the required DC voltage to be regulated by the offshore wind turbine's grid-side converter is obtained using a differential controller. The control block diagram of the offshore wind turbine is shown below. Figure 6As shown, it mainly includes a speed protection module, a frequency deviation / frequency change rate triggering module, a frequency trajectory planning module, a machine-side converter control, and a grid-side converter control.

[0061] Third, the capacitor energy optimization control of the flexible DC converter station includes the following steps: Step S3.1: Inject the third harmonic voltage into the modulation wave of the onshore converter station and the offshore booster station to broaden the energy regulation range of the onshore converter station and the offshore booster station. Taking an onshore converter station as an example, the expressions for the modulation waves of the upper and lower bridge arms after the injection of the third harmonic voltage are as follows: ; ; in: M dc Indicates DC modulation. M ac Indicates the fundamental frequency AC modulation scheme. M ac2 This indicates the second harmonic circulating current control modulation.

[0062] Step S3.2: Calculate the preset energy curves for the onshore converter station and the offshore booster station; Taking an onshore converter station as an example, its preset energy curve is as follows: ; in: An expression for a preset energy curve; This represents the minimum energy required for an onshore converter station. For the energy release margin of onshore converter stations; t tr1 and t tr2 These are the trigger times for energy release control and energy recovery control at the onshore converter station, respectively. T rec and k rec These represent the duration of energy recovery control for onshore converter stations and the slope of the energy recovery curve, respectively. T rel The duration of energy release control for onshore converter stations.

[0063] Furthermore, the duration of energy release control at onshore converter stations T rel The calculation method is as follows: ; Where: Δ P acmax The maximum allowable variation in active power on the AC side of the onshore converter station is taken as 0.2pu.

[0064] Step S3.3: Set the preset energy curve of the onshore converter station to the reference value of the onshore converter station's energy loop, and set the preset energy curve of the offshore booster station to the reference value of the offshore booster station's energy loop. The control block diagrams of the onshore converter station and the offshore booster station are as follows: Figure 7 and Figure 8 As shown.

[0065] Compared with existing technologies, the grid frequency active support method of the wind power DC collection and transmission system of the present invention can achieve coordinated support of the rotor kinetic energy of offshore wind turbine and the electrostatic energy of the capacitor in the system based on local DC voltage measurement, thereby suppressing the peak value of the frequency change rate and improving the frequency deviation. It avoids complex controller parameter design, significantly reduces the degree of secondary frequency drop during the wind turbine speed recovery process, and ensures the economic benefits of wind farms participating in grid frequency support services as much as possible.

[0066] The steps of the various methods described above are only for clarity. In practice, they can be combined into one step or some steps can be split into multiple steps. As long as they include the same logical relationship, they are all within the protection scope of this invention. Adding insignificant modifications or introducing insignificant designs to the algorithm or process, without changing the core design of the algorithm and process, are also within the protection scope of this invention.

[0067] Another embodiment of the present invention relates to a grid frequency active support system for a wind power DC collection and transmission system. The grid frequency active support system for the wind power DC collection and transmission system of this embodiment includes: The onshore converter station is used to acquire the frequency of the onshore AC power grid in real time and map the frequency to the DC side voltage of the onshore converter station through droop control. Offshore booster stations are used to inversely calculate the frequency of the onshore AC grid based on the DC-side voltage of the onshore converter station, and to map the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control. Offshore wind turbines are used to inversely calculate the frequency of the onshore AC power grid based on the DC voltage input to the offshore substation. The onshore converter station and the offshore booster station are also used to determine the energy release of their respective sub-module capacitors based on the frequency of the onshore AC power grid acquired in real time and the frequency obtained by reverse calculation, so as to provide short-term support for the frequency of the onshore AC power grid. Offshore wind turbines are also used to provide short-term support for the frequency of the onshore AC grid during the process of onshore converter stations and offshore booster stations. Based on the real-time frequency of the onshore AC grid obtained by back-calculation and the rotor speed of the offshore wind turbine, the frequency regulation power that the turbine-side converter of the offshore wind turbine needs to provide and the DC voltage that the grid-side converter needs to adjust are determined in order to provide long-term support for the frequency of the onshore AC grid.

[0068] It is not difficult to see that this embodiment is a system embodiment corresponding to the above method embodiments, and this embodiment can be implemented in conjunction with the above method embodiments. The relevant technical details and technical effects mentioned in the above embodiments are still valid in this embodiment, and will not be repeated here to reduce repetition. Accordingly, the relevant technical details mentioned in this embodiment can also be applied to the above embodiments.

[0069] It is worth mentioning that all modules involved in this embodiment are logical modules. In practical applications, a logical unit can be a physical unit, a part of a physical unit, or a combination of multiple physical units. Furthermore, to highlight the innovative aspects of this invention, this embodiment does not introduce units that are not closely related to solving the technical problem proposed by this invention; however, this does not mean that other units are absent from this embodiment.

[0070] Another embodiment of the present invention relates to a computer device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the grid frequency active support method for the wind power DC collection and transmission system in the above embodiments.

[0071] The memory and processor are connected via a bus, which can include any number of interconnecting buses and bridges, connecting various circuits of one or more processors and memories. The bus can also connect various other circuits, such as peripheral devices, voltage regulators, and power management circuits, which are well known in the art and will not be described further herein. The bus interface provides an interface between the bus and the transceiver. The transceiver can be a single element or multiple elements, such as multiple receivers and transmitters, providing a unit for communicating with various other devices over a transmission medium. Data processed by the processor is transmitted over the wireless medium via an antenna, which further receives data and transmits it to the processor.

[0072] The processor manages the bus and general processing, and also provides various functions, including timing, peripheral interfaces, voltage regulation, power management, and other control functions. Memory is used to store data used by the processor during operation.

[0073] Another embodiment of the present invention relates to a computer-readable storage medium storing a computer program. When executed by a processor, the computer program implements the method embodiments described above.

[0074] That is, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a device (which may be a microcontroller, chip, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0075] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A method for actively supporting the grid frequency of a wind power DC collection and transmission system, characterized in that, The method includes: Onshore converter stations acquire the frequency of the onshore AC grid in real time and map the frequency to the DC-side voltage of the onshore converter station through droop control; offshore booster stations use the DC-side voltage of the onshore converter station to inversely calculate the frequency of the onshore AC grid and map the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control; offshore wind turbines use the DC voltage of the input side of the offshore booster station to inversely calculate the frequency of the onshore AC grid. The onshore converter station and the offshore booster station determine the energy release of their respective sub-module capacitors based on the real-time frequency of the onshore AC power grid and the corresponding reverse-engineered frequency, so as to provide short-term support for the frequency of the onshore AC power grid. During the short-term frequency support of the onshore AC grid by offshore wind turbines at onshore converter stations and offshore booster stations, the frequency regulation power required by the turbine-side converter and the DC voltage required to be adjusted by the grid-side converter are determined based on the real-time frequency of the onshore AC grid obtained by reverse calculation and the rotor speed of the offshore wind turbine, so as to provide long-term frequency support for the onshore AC grid.

2. The method for actively supporting grid frequency in a wind power DC collection and transmission system according to claim 1, characterized in that, The process of determining the required frequency regulation power of the offshore wind turbine's generator-side converter and the required DC voltage regulation of the grid-side converter, based on the real-time frequency of the onshore AC power grid obtained through reverse calculation and the rotor speed of the offshore wind turbine, includes: When the frequency of the onshore AC grid and the rotor speed of the offshore wind turbine simultaneously meet the preset trigger criteria, the region to which the frequency of the onshore AC grid belongs in the pre-acquired planned frequency trajectory is determined; the planned frequency trajectory includes a safe zone, a monitoring zone, a regulation zone, and a prohibited zone. If the area is a safe zone or a monitored zone, the offshore wind turbines will continue to operate normally; If the area is a regulation zone or a prohibited zone, then determine the frequency regulation power that the turbine-side converter of the offshore wind turbine needs to provide and the DC voltage that the grid-side converter needs to regulate.

3. The method for actively supporting grid frequency in a wind power DC collection and transmission system according to claim 2, characterized in that, The determination of the required frequency regulation power provided by the turbine-side converter and the required DC voltage regulation by the grid-side converter for the offshore wind turbine includes: Offshore wind turbines obtain the frequency regulation power required by the turbine-side converter based on a proportional controller. Offshore wind turbines obtain the DC voltage that the grid-side converter needs to regulate based on a differential controller.

4. The method for active grid frequency support in a wind power DC collection and transmission system according to claim 2, characterized in that, The preset trigger criteria for the frequency of the onshore AC power grid and the rotor speed of the offshore wind turbine are as follows: ； In the formula, Δ f For the frequency deviation of the land-based AC power grid, R The rate of change of frequency, F act For frequency deviation action threshold, R act The frequency change rate action threshold; ； In the formula, ω r This refers to the rotor speed of the offshore wind turbine.

5. The method for actively supporting grid frequency in a wind power DC collection and transmission system according to claim 1, characterized in that, The energy regulation range of the capacitors in the submodules of the onshore converter station and the offshore booster station is pre-widened by injecting third harmonic voltage into the modulation wave of the onshore converter station and the offshore booster station.

6. The method for actively supporting grid frequency in a wind power DC collection and transmission system according to claim 1, characterized in that, The onshore converter station and the offshore booster station determine the energy release of their respective submodule capacitors based on the real-time frequency of the onshore AC power grid using the following preset energy curves: ； In the formula, This represents the minimum energy value. For energy release margin, t tr1 and t tr2 These are the trigger times for energy release control and energy recovery control, respectively. T rec and k rec These represent the duration of energy recovery control and the slope of the energy recovery curve, respectively. T rel The duration for controlling energy release.

7. The method for active grid frequency support of a wind power DC collection and transmission system according to claim 1, characterized in that, The offshore booster station uses the DC-side voltage of the onshore converter station to inversely calculate the frequency of the onshore AC grid, and maps the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control. The offshore wind turbine uses the DC voltage of the input side of the offshore booster station to inversely calculate the frequency of the onshore AC grid, including: The offshore booster station acquires the DC voltage on the output side in real time, which is used as the DC voltage on the onshore converter station. The frequency of the onshore AC power grid is then calculated by using the droop control of the onshore converter station. The offshore booster station maps the DC voltage on the output side to the DC voltage on the input side through droop control; Offshore wind turbines acquire their output port voltage in real time, which is then used as the DC voltage input to the offshore substation. This voltage, combined with the droop control of the onshore converter station and the offshore substation, is used to inversely deduce the frequency of the onshore AC power grid.

8. A grid frequency active support system for a wind power DC collection and transmission system, characterized in that, The system includes: The onshore converter station is used to acquire the frequency of the onshore AC power grid in real time and map the frequency to the DC side voltage of the onshore converter station through droop control. Offshore booster stations are used to inversely calculate the frequency of the onshore AC grid based on the DC-side voltage of the onshore converter station, and to map the DC-side voltage of the onshore converter station to the DC voltage of the input side through droop control. Offshore wind turbines are used to inversely calculate the frequency of the onshore AC power grid based on the DC voltage input to the offshore substation. The onshore converter station and the offshore booster station are also used to determine the energy release of their respective sub-module capacitors based on the frequency of the onshore AC power grid acquired in real time and the frequency obtained by reverse calculation, so as to provide short-term support for the frequency of the onshore AC power grid. Offshore wind turbines are also used to provide short-term support for the frequency of the onshore AC grid during the process of onshore converter stations and offshore booster stations. Based on the real-time frequency of the onshore AC grid obtained by back-calculation and the rotor speed of the offshore wind turbine, the frequency regulation power that the turbine-side converter of the offshore wind turbine needs to provide and the DC voltage that the grid-side converter needs to adjust are determined in order to provide long-term support for the frequency of the onshore AC grid.

9. A computer device, characterized in that, include: At least one processor; And a memory communicatively connected to at least one processor; wherein the memory stores instructions executable by at least one processor, the instructions being executed by at least one processor to enable at least one processor to perform the grid frequency active support method for the wind power DC collection and transmission system as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the active grid frequency support method for the wind power DC collection and transmission system as described in any one of claims 1 to 7.

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