A coordinated inertia response control method and system for offshore low-frequency wind power systems

Abstract

The present application relates to the field of new energy grid connection technology, especially to a kind of offshore low-frequency wind power system's coordinated inertia response control method and system, comprising: the influence of analyzing system inertia level to frequency response and the dynamic characteristic of onshore converter station DC capacitor, according to the analysis result determines the virtual inertia control strategy of onshore converter station;The power frequency side of onshore converter station M3C is based on the current frequency of land power frequency network, and combined with the virtual inertia control strategy of onshore converter station M3C, inertia response is executed;The low-frequency side of onshore converter station M3C is based on the inertia response result executed by the power frequency side of onshore converter station M3C, through the frequency conversion control strategy of the low-frequency side of onshore converter station M3C, to transfer the frequency change information of land power frequency network to offshore low-frequency wind farm;Offshore low-frequency wind farm according to the frequency change information of land power frequency network obtained, combined with the virtual inertia control strategy of onshore converter station M3C, inertia response is executed, and with onshore converter station M3C jointly provides frequency support for land power frequency network, improves the inertia level of system, improves the stability of system frequency.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection technology, and in particular to a coordinated inertia response control method and system for offshore low-frequency wind power systems. Background Technology

[0002] With the strategic goal of "carbon neutrality and carbon peaking" being proposed, offshore wind power has received widespread attention and is playing an increasingly important role in my country's clean energy system. Large-scale transmission of offshore wind power is a prerequisite for the rapid development of the wind power industry. Compared to current flexible DC transmission systems, offshore low-frequency wind power systems improve transmission efficiency by reducing the transmission frequency. Furthermore, offshore low-frequency wind power systems only require the construction of onshore converter stations to transmit the generated electricity to the onshore power grid, saving construction costs and providing an efficient and feasible solution for grid connection of offshore wind power.

[0003] However, in offshore low-frequency wind power systems, due to the presence of the onshore converter station M3C and the back-to-back converters of the wind turbines, the low-frequency frequency of the offshore low-frequency wind power system is decoupled from the onshore power grid frequency. Under normal rated wind speed, the wind turbines always operate in maximum power point tracking mode. When the grid frequency is disturbed, the offshore low-frequency wind farm cannot actively provide frequency support for the onshore power grid. Furthermore, the overall inertia level of the system is reduced due to the large-scale wind power integration, which seriously affects the stability of the system frequency. Summary of the Invention

[0004] This invention provides a coordinated inertia response control method and system for offshore low-frequency wind power systems, effectively solving the problems in the background art.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a coordinated inertia response control method for offshore low-frequency wind power systems, comprising the following steps:

[0006] Step 1: Based on the frequency response model of the offshore low-frequency wind power system, analyze the influence of the system inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, determine the virtual inertia control strategy of the onshore converter station M3C. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C and the onshore power grid connected in sequence. The onshore converter station M3C is decoupled into the power frequency side and the low-frequency side for separate control.

[0007] Step 2: Detect the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes inertia response based on the current frequency of the onshore power grid and in combination with the virtual inertia control strategy of the onshore converter station M3C.

[0008] Step 3: Based on the inertial response results executed by the power frequency side of the onshore converter station M3C, the low-frequency side of the onshore converter station M3C uses the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C to transmit the frequency change information of the onshore power frequency grid to the offshore low-frequency wind farm.

[0009] Step 4: The offshore low-frequency wind farm executes inertial response based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid.

[0010] Furthermore, the offshore low-frequency wind farm is composed of permanent magnet direct-drive wind turbine units, which include wind turbines, synchronous generators, and back-to-back converters.

[0011] The back-to-back converter is formed by connecting a machine-side converter and a grid-side converter back-to-back. The machine-side converter is connected to the wind turbine, and the wind turbine directly drives the rotor of the synchronous generator through the rotation of the rotor. The electrical energy generated by the synchronous generator is controlled and regulated by the machine-side converter. The machine-side converter controls the rotor speed of the wind turbine to maintain the optimal tip speed ratio for maximum wind energy capture. The grid-side converter is connected to the low-frequency side of the onshore converter station M3C. The grid-side converter realizes the effective power delivery of the permanent magnet direct-drive wind turbine through a constant DC capacitor voltage.

[0012] Furthermore, in step 1, the onshore power frequency grid consists of synchronous generator sets and active and reactive loads, and the synchronous generator sets in the onshore power frequency grid are connected to the power frequency side of the onshore converter station M3C.

[0013] Furthermore, in step 1, the onshore converter station M3C decouples and converts the power frequency side and the low frequency side for separate control, specifically as follows:

[0014] The power frequency side control of the onshore converter station M3C adopts a constant DC capacitor voltage control method. The control objective of the constant DC capacitor voltage control method is to keep the total DC capacitor voltage of the onshore converter station M3C constant and to perform reactive power interaction with the onshore power frequency grid.

[0015] The low-frequency side control of the onshore converter station M3C adopts a VF control mode with constant AC voltage amplitude and frequency. The VF control mode with constant AC voltage amplitude and frequency actively establishes the low-frequency AC power supply for the offshore low-frequency wind farm.

[0016] Furthermore, in step 2, the determination of the virtual inertia control strategy for the onshore converter station M3C is as follows:

[0017] Based on the dynamic characteristic analysis results of the DC capacitor of the onshore converter station M3C, the dynamic characteristics of the DC capacitor of the onshore converter station M3C are compared with the rotor motion equation of the synchronous generator set in the onshore power frequency grid. Based on the comparison results of the rotor motion equation, the virtual inertia control strategy of the onshore converter station M3C is determined.

[0018] Furthermore, in step 2, the power frequency side of the onshore converter station M3C performs an inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C, specifically as follows:

[0019] Based on the virtual inertia control strategy of the onshore converter station M3C, a droop control method for DC capacitor voltage is designed.

[0020] By detecting the current frequency of the onshore power grid, the power frequency side of the onshore converter station M3C performs inertial response based on the current frequency of the onshore power grid, combined with the droop control mode of the DC capacitor voltage, and by utilizing the energy stored in the DC capacitor in the onshore converter station M3C.

[0021] Furthermore, in step 3, the low-frequency side of the onshore converter station M3C, based on the inertial response results executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, specifically:

[0022] Based on the virtual inertia response results of the power frequency side of the onshore converter station M3C, the onshore converter station M3C introduces a droop control mode, and performs frequency conversion control in combination with the frequency conversion control strategy of the low frequency side of the onshore converter station M3C.

[0023] The frequency converter control on the low-frequency side of the onshore converter station M3C is used to adjust the output frequency on the power frequency side, so that the frequency changes of the onshore converter station M3C and the onshore power frequency grid are synchronized, frequency matching is achieved, and the coupling relationship between the low-frequency frequency of the offshore low-frequency wind power system and the power frequency frequency of the onshore power frequency grid is established.

[0024] Furthermore, the power frequency side virtual inertia response result of the onshore converter station M3C includes the current DC voltage amplitude of the onshore converter station M3C;

[0025] The current DC voltage amplitude of the onshore converter station M3C is detected. Based on the current DC voltage amplitude of the onshore converter station M3C and the reference value of the differential element, the voltage deviation of the reference value is determined.

[0026] The required adjustment amount is calculated based on the voltage deviation of the reference value. The low-frequency side of the onshore converter station M3C performs frequency conversion control based on the required adjustment amount and the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, changing the frequency of the low-frequency side of the onshore converter station M3C so that the low-frequency side frequency can directly follow the frequency of the onshore power grid, realizing the transmission of frequency information.

[0027] Furthermore, in step 4, the offshore low-frequency wind farm executes an inertial response based on the frequency change information of the onshore power grid obtained from the onshore power grid, combined with the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid. This includes: the permanent magnet direct-drive wind turbine units in the offshore low-frequency wind farm execute the inertial response of the offshore low-frequency wind farm based on the frequency change information of the onshore power grid obtained from the offshore low-frequency wind farm, through the virtual inertial control strategy of the onshore converter station M3C, so as to jointly provide frequency support for the onshore power grid with the onshore converter station M3C.

[0028] Furthermore, the permanent magnet direct-drive wind turbines in offshore low-frequency wind farms, based on the frequency change information of the onshore power grid obtained from the offshore low-frequency wind farm, execute the inertial response of the offshore low-frequency wind farm through the virtual inertial control strategy of the onshore converter station M3C, so as to jointly provide frequency support for the onshore power grid with the onshore converter station M3C. Specifically:

[0029] In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines use phase-locked loop (PLL) technology to detect the current frequency of the low-frequency side of the onshore converter station M3C. By comparing the detected current frequency of the low-frequency side of the onshore converter station M3C with the preset frequency, the low-frequency deviation is obtained.

[0030] Based on the virtual inertia control strategy of the onshore converter station M3C, and by introducing the proportional relationship of the droop control loop, the low-frequency deviation is converted and calculated to obtain the required additional power value.

[0031] Based on the calculated additional power value, the control system of the offshore low-frequency wind farm adjusts the active power output of the permanent magnet direct-drive wind turbine.

[0032] By adjusting the active power output of the permanent magnet direct-drive wind turbine, the turbine releases the rotational kinetic energy stored in the wind turbine blades to provide frequency support for the onshore power grid.

[0033] This invention proposes a coordinated inertia response control system for offshore low-frequency wind power systems, comprising:

[0034] Analysis Module: Based on the frequency response model of the offshore low-frequency wind power system, the influence of the system inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C are analyzed. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, the virtual inertia control strategy of the onshore converter station M3C is determined. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C and the onshore power grid connected in sequence. The onshore converter station M3C is decoupled into a power frequency side and a low-frequency side for separate control.

[0035] Inertia Response Module: Detects the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes the inertia response based on the current frequency of the onshore power grid and in conjunction with the virtual inertia control strategy of the onshore converter station M3C.

[0036] Coupling relationship establishment module: Based on the inertial response results executed by the power frequency side of the onshore converter station M3C, the low-frequency side of the onshore converter station M3C transmits the frequency change information of the onshore power frequency grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C.

[0037] Coordinated Inertia Response Module: The offshore low-frequency wind farm executes inertia response based on the frequency change information of the onshore power grid and the virtual inertia control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid.

[0038] Furthermore, the offshore low-frequency wind farm is composed of permanent magnet direct-drive wind turbine units, which include wind turbines, synchronous generators, and back-to-back converters.

[0039] The back-to-back converter is formed by connecting a machine-side converter and a grid-side converter back-to-back. The machine-side converter is connected to the wind turbine, and the wind turbine directly drives the rotor of the synchronous generator through the rotation of the rotor. The electrical energy generated by the synchronous generator is controlled and regulated by the machine-side converter. The machine-side converter controls the rotor speed of the wind turbine to maintain the optimal tip speed ratio for maximum wind energy capture. The grid-side converter is connected to the low-frequency side of the onshore converter station M3C. The grid-side converter realizes the effective power delivery of the permanent magnet direct-drive wind turbine through a constant DC capacitor voltage.

[0040] Furthermore, the onshore power frequency grid consists of synchronous generator sets and active and reactive loads, and the synchronous generator sets in the onshore power frequency grid are connected to the power frequency side of the onshore converter station M3C.

[0041] Furthermore, the onshore converter station M3C decouples and controls the power frequency side and low frequency side separately, specifically as follows:

[0042] The power frequency side control of the onshore converter station M3C adopts a constant DC capacitor voltage control method. The control objective of the constant DC capacitor voltage control method is to keep the total DC capacitor voltage of the onshore converter station M3C constant and to perform reactive power interaction with the onshore power frequency grid.

[0043] The low-frequency side control of the onshore converter station M3C adopts a VF control mode with constant AC voltage amplitude and frequency. The VF control mode with constant AC voltage amplitude and frequency actively establishes the low-frequency AC power supply for the offshore low-frequency wind farm.

[0044] Furthermore, the process for determining the virtual inertia control strategy of the onshore converter station M3C is as follows:

[0045] Based on the dynamic characteristic analysis results of the DC capacitor of the onshore converter station M3C, the dynamic characteristics of the DC capacitor of the onshore converter station M3C are compared with the rotor motion equation of the synchronous generator set in the onshore power frequency grid. Based on the comparison results of the rotor motion equation, the virtual inertia control strategy of the onshore converter station M3C is determined.

[0046] Furthermore, in step 2, the power frequency side of the onshore converter station M3C performs an inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C, specifically as follows:

[0047] Based on the virtual inertia control strategy of the onshore converter station M3C, a droop control method for DC capacitor voltage is designed.

[0048] By detecting the current frequency of the onshore power grid, the power frequency side of the onshore converter station M3C performs inertial response based on the current frequency of the onshore power grid, combined with the droop control mode of the DC capacitor voltage, and by utilizing the energy stored in the DC capacitor in the onshore converter station M3C.

[0049] Furthermore, in step 3, the low-frequency side of the onshore converter station M3C, based on the inertial response results executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, specifically:

[0050] Based on the virtual inertia response results of the power frequency side of the onshore converter station M3C, the onshore converter station M3C introduces a droop control mode, and performs frequency conversion control in combination with the frequency conversion control strategy of the low frequency side of the onshore converter station M3C.

[0051] The frequency converter control on the low-frequency side of the onshore converter station M3C is used to adjust the output frequency on the power frequency side, so that the frequency changes of the onshore converter station M3C and the onshore power frequency grid are synchronized, frequency matching is achieved, and the coupling relationship between the low-frequency frequency of the offshore low-frequency wind power system and the power frequency frequency of the onshore power frequency grid is established.

[0052] Furthermore, the power frequency side virtual inertia response result of the onshore converter station M3C includes the current DC voltage amplitude of the onshore converter station M3C;

[0053] The current DC voltage amplitude of the onshore converter station M3C is detected. Based on the current DC voltage amplitude of the onshore converter station M3C and the reference value of the differential element, the voltage deviation of the reference value is determined.

[0054] The required adjustment amount is calculated based on the voltage deviation of the reference value. The low-frequency side of the onshore converter station M3C performs frequency conversion control based on the required adjustment amount and the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, changing the frequency of the low-frequency side of the onshore converter station M3C so that the low-frequency side frequency can directly follow the frequency of the onshore power grid, realizing the transmission of frequency information.

[0055] Furthermore, in step 4, the offshore low-frequency wind farm executes an inertial response based on the frequency change information of the onshore power grid obtained from the onshore power grid, combined with the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid. This includes: the permanent magnet direct-drive wind turbine units in the offshore low-frequency wind farm execute the inertial response of the offshore low-frequency wind farm based on the frequency change information of the onshore power grid obtained from the offshore low-frequency wind farm, through the virtual inertial control strategy of the onshore converter station M3C, so as to jointly provide frequency support for the onshore power grid with the onshore converter station M3C.

[0056] Furthermore, the permanent magnet direct-drive wind turbines in offshore low-frequency wind farms, based on the frequency change information of the onshore power grid obtained from the offshore low-frequency wind farm, execute the inertial response of the offshore low-frequency wind farm through the virtual inertial control strategy of the onshore converter station M3C, so as to jointly provide frequency support for the onshore power grid with the onshore converter station M3C. Specifically:

[0057] In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines use phase-locked loop (PLL) technology to detect the current frequency of the low-frequency side of the onshore converter station M3C. By comparing the detected current frequency of the low-frequency side of the onshore converter station M3C with the preset frequency, the low-frequency deviation is obtained.

[0058] Based on the virtual inertia control strategy of the onshore converter station M3C, and by introducing the proportional relationship of the droop control loop, the low-frequency deviation is converted and calculated to obtain the required additional power value.

[0059] Based on the calculated additional power value, the control system of the offshore low-frequency wind farm adjusts the active power output of the permanent magnet direct-drive wind turbine.

[0060] By adjusting the active power output of the permanent magnet direct-drive wind turbine, the turbine releases the rotational kinetic energy stored in the wind turbine blades to provide frequency support for the onshore power grid.

[0061] The present invention also provides an electronic device, the electronic device comprising:

[0062] Processor and memory;

[0063] The processor executes the steps of the coordinated inertia response control method by calling programs or instructions stored in the memory.

[0064] The present invention also provides a computer-readable storage medium storing a program or instructions that are steps of a computer executing the coordinated inertia response control method described above.

[0065] The beneficial effects of this invention are as follows: By coordinating the control of offshore low-frequency wind farms and onshore converter stations M3C, this invention combines the DC capacitor energy of the onshore converter station M3C with the kinetic energy of the wind turbine rotor. By releasing the energy stored in the wind turbine and the onshore converter station M3C to jointly participate in the inertial response process of the system, the onshore converter station M3C actively supports the frequency, improves the inertial level of the system, reduces the risk of frequency instability, and improves the stability of the system frequency. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 This is a structural diagram of the offshore low-frequency wind power system in this invention;

[0068] Figure 2 Diagram of virtual inertia control strategy for M3C at onshore converter station;

[0069] Figure 3 This is a phase control diagram for low-frequency AC power supply.

[0070] Figure 4 This is the frequency control diagram for the low-frequency side of the M3C.

[0071] Figure 5 Virtual inertia control for offshore low-frequency wind farms;

[0072] Figure 6 A coordinated inertia response control scheme for offshore low-frequency wind power systems. Detailed Implementation

[0073] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0074] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0075] Unless otherwise defined, 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. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0076] The coordinated inertia response control method for offshore low-frequency wind power systems in this invention includes the following steps:

[0077] Step 1: Based on the frequency response model of the offshore low-frequency wind power system, analyze the influence of the system's inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, determine the virtual inertia control strategy for the onshore converter station M3C. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C, and the onshore power grid. The offshore low-frequency wind farm is responsible for wind power collection and initial conversion, the onshore power grid is the final power consumption network, and the onshore converter station M3C is the core of the entire system. The M3C, the core device for AC / AC conversion and power transmission, lacks a DC link for direct AC-AC frequency conversion. As a result, the onshore converter station is composed of cascaded H-bridge modules with nine arms. The direct coupling of two different frequencies within the M3C increases control complexity, necessitating decoupling of internal electrical quantities. Furthermore, the M3C is decoupled so that the power frequency side and low-frequency side are controlled separately. Therefore, the M3C can be equivalent to a combination of two voltage source inverters, enabling the use of classic voltage and current dual closed-loop control.

[0078] Specifically, the onshore power grid consists of synchronous generator sets and active and reactive loads. The synchronous generator sets in the onshore power grid are connected to the power frequency side of the onshore converter station M3C. The offshore low-frequency wind farm consists of permanent magnet direct-drive wind turbine sets, which include wind turbines, synchronous generators, and back-to-back converters. The back-to-back converters are formed by connecting the turbine-side converter and the grid-side converter back-to-back. The turbine-side converter is connected to the wind turbine. The wind turbine directly drives the rotor of the synchronous generator to rotate through the rotor rotation. The electrical energy generated by the synchronous generator is controlled and regulated by the turbine-side converter. The turbine-side converter controls the wind turbine rotor speed to maintain the optimal tip speed ratio for maximum wind energy capture. The grid-side converter is connected to the low-frequency side of the onshore converter station M3C. The grid-side converter achieves effective power delivery of the permanent magnet direct-drive wind turbine sets through a constant DC capacitor voltage, ensuring a stable power supply to the grid. By controlling back-to-back converters, reactive power support can be provided, improving grid voltage stability and power quality. For example... Figure 1 As shown, a typical offshore low-frequency wind farm is applied in a grid-connected structure via an onshore converter station M3C: the wind farm's voltage is stepped up by a 690V / 35kV transformer, and then connected to the external 35kV AC grid via a 50km submarine cable through the onshore converter station M3C. The wind farm consists of 50 wind turbines with a rated capacity of 2MW.

[0079] In step 1, the onshore converter station M3C is decoupled and converted into separate control of the power frequency side and the low frequency side. Specifically, the power frequency side of the onshore converter station M3C adopts a constant DC capacitor voltage control mode. The control objective of the constant DC capacitor voltage control mode is to keep the total DC capacitor voltage of the onshore converter station M3C constant and to perform reactive power interaction with the onshore power frequency grid system.

[0080] Offshore low-frequency wind farms are similar to passive networks and require a synchronous power source to transmit power. Therefore, the low-frequency side control of the onshore converter station M3C adopts a VF control mode with constant AC voltage amplitude and frequency. The VF control mode with constant AC voltage amplitude and frequency actively establishes a low-frequency AC power source for the offshore low-frequency wind farm and supplies power to the offshore low-frequency wind farm.

[0081] Through the above control methods, a steady-state operation control scheme for offshore low-frequency wind power systems can be established. That is, the offshore low-frequency wind farm generates low-frequency power through maximum power point tracking, and the onshore converter station M3C converts the low-frequency power into power frequency power through AC / AC conversion and integrates it into the power grid system, thereby achieving efficient and reliable transmission of offshore wind power.

[0082] Step 2: Detect the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes inertia response based on the current frequency of the onshore power grid and in combination with the virtual inertia control strategy of the onshore converter station M3C.

[0083] In step 2, the determination of the virtual inertia control strategy for the onshore converter station M3C is carried out as follows:

[0084] Based on the dynamic characteristic analysis results of the DC capacitor of the onshore converter station M3C, the dynamic characteristics of the DC capacitor of the onshore converter station M3C are compared with the rotor motion equation of the synchronous generator set in the onshore power frequency grid. Based on the comparison results of the rotor motion equation, the virtual inertia control strategy of the onshore converter station M3C is determined.

[0085] In a further proposed scheme, the power frequency side of the onshore converter station M3C performs inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C. Specifically, based on the virtual inertial control strategy of the onshore converter station M3C, a droop control method for the DC capacitor voltage is designed. By detecting the current frequency of the onshore power grid, the power frequency side of the onshore converter station M3C performs inertial response according to the current frequency of the onshore power grid, in conjunction with the droop control method for the DC capacitor voltage, and by utilizing the capacity stored in the DC capacitor in the onshore converter station M3C.

[0086] When the frequency of the power grid changes, the onshore converter station M3C uses a virtual inertia control strategy and a DC capacitor voltage droop control method to utilize the energy stored in the DC capacitor to respond quickly to the frequency change of the onshore power grid, release or absorb energy, and provide necessary inertial support to maintain the stability of the grid and the frequency, improve the grid's adaptability to renewable energy fluctuations, and enhance the overall stability of the grid.

[0087] The specific implementation plan for the virtual inertia control of the M3C converter at the onshore converter station in step 2 is as follows:

[0088] In a power system, inertia can be represented as the ability of various frequency regulation resources to maintain a constant frequency or resist frequency changes when the system experiences active power imbalance, using kinetic, chemical, and electrical energy. The inertia of a traditional power system is mainly provided by the rotor kinetic energy of synchronous generators in onshore power grids. Because the rotor speed of the synchronous generator is directly coupled to the power grid frequency, when a disturbance occurs and the system experiences active power imbalance, the rotor speed changes accordingly, providing inertia to resist changes in the system frequency. For synchronous generators in onshore power grids, the per-unit equation of their rotor motion can be expressed as:

[0089]

[0090] In the formula: H SGP is the inertial time constant of the synchronous machine; f and f0 are the actual frequency and rated frequency of the power frequency system, respectively; m P e These are the mechanical power input to the prime mover and the electromagnetic power output to the generator, respectively; ΔP g This represents the imbalance between mechanical power and electromagnetic power.

[0091] When the onshore converter station M3C is operating normally, its capacitor voltage remains constant. To achieve active frequency support for the onshore converter station M3C, this invention utilizes the DC capacitor voltage to simulate the change in rotor speed of the synchronous generator to achieve inertial response. The low-frequency side of the onshore converter station M3C is connected to the offshore low-frequency wind farm, and the power frequency side is connected to the onshore power frequency grid. When the active power on both sides is unbalanced, the dynamic equation of the DC capacitor voltage is:

[0092]

[0093] Where: ΔP C The electrostatic energy absorbed or released by a DC capacitor; C eq P is the equivalent capacitance of the onshore converter station M3C; in P represents the active power input to the equivalent capacitance of the low-frequency wind field. out The active power released by the equivalent capacitance; U dc Let be the DC voltage of the equivalent capacitance. Equation 2 describes the dynamic characteristics of the DC capacitor voltage. According to the formula, the energy released or absorbed by the DC capacitor is related to the rate of change of the capacitor voltage, dU. dc / dt related.

[0094] To enable the onshore converter station M3C to have inertial response capability, both sides of Equation 2 are simultaneously divided by the rated power S of the onshore converter station M3C. M3C And cause the unbalanced power ΔP of the DC capacitor to be... C Unbalanced power ΔP with synchronous machine g Equal to this, we can obtain the DC capacitor configuration for the M3C converter station on shore:

[0095]

[0096] In the formula: Let be the inertial response time constant of the onshore converter station M3C.

[0097] Equation 3 establishes the coupling relationship between the DC capacitor voltage of the onshore converter station M3C and the power frequency system frequency. By integrating both sides of Equation 3, the model of the DC capacitor voltage-frequency of the onshore converter station M3C is derived. Since the DC capacitor voltage fluctuation is usually limited to about 15%, the higher-order terms in the integral equation can be ignored, resulting in:

[0098]

[0099] In the formula: U dc0 This is the reference value for the DC capacitor voltage; ΔU dc Δf and Δf represent the deviations of DC voltage and frequency, respectively. According to Equation 5, the virtual inertia control equation for the onshore converter station M3C is:

[0100]

[0101] In the formula: k M3C This represents the droop control coefficient in the virtual inertia control equation. Based on Equation 6, the virtual inertia controller for the onshore converter station M3C is designed. By substituting the values ​​of the onshore converter station M3C's inertia time constant, rated power, and equivalent capacitance into Equation 6, the droop control coefficient for the onshore converter station M3C can be obtained. For example... Figure 2 As shown, when a change in the frequency of the onshore power grid system is detected, the frequency deviation is introduced into the control equation of the onshore converter station M3C to obtain the reference value of the DC capacitor voltage of the onshore converter station M3C. The DC capacitor then releases or absorbs energy to provide virtual inertia for the system to prevent the frequency from changing too quickly.

[0102] This invention uses the DC capacitor energy of the onshore converter station M3C to support frequency by simulating the inertial response of a synchronous generator. When the load suddenly increases and the frequency changes abruptly, the virtual inertial control of the onshore converter station M3C can respond quickly and immediately release the electrostatic energy stored in the DC capacitor, thereby slowing down the rapid frequency drop and effectively reducing the risk of system frequency instability.

[0103] Step 3: Based on the inertial response results executed by the power frequency side of the onshore converter station M3C, the low-frequency side of the onshore converter station M3C transmits the frequency change information of the onshore power frequency grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C.

[0104] In step 3, the low-frequency side of the onshore converter station M3C, based on the inertial response results executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power frequency grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, thereby realizing frequency information transmission. Specifically:

[0105] The M3C at the onshore converter station senses the current frequency of the onshore power grid. Based on the frequency change of the power grid, the DC capacitor of the M3C at the onshore converter station implements a virtual inertial response. The amplitude of the DC capacitor can respond to the frequency change of the onshore power grid, and the DC capacitor contains information about the frequency change of the power grid.

[0106] Based on the virtual inertia response results of the power frequency side of the onshore converter station M3C, droop control is introduced into the onshore converter station M3C. Combined with the frequency conversion control strategy of the low frequency side of the onshore converter station M3C, frequency conversion control is executed.

[0107] By adjusting the output frequency of the power frequency side based on the frequency converter control on the low-frequency side of the onshore converter station M3C, the frequency changes of the onshore converter station M3C and the onshore power frequency grid are synchronized, achieving frequency matching and establishing a coupling relationship between the low-frequency frequency of the offshore low-frequency wind farm and the power frequency frequency of the onshore power frequency grid. This coupling relationship allows the offshore low-frequency wind power system to indirectly respond to the frequency changes of the onshore power frequency grid through the onshore converter station M3C.

[0108] In the preferred embodiment, the virtual inertia response result of the onshore converter station M3C on the power frequency side includes the current DC voltage amplitude of the DC capacitor in the onshore converter station M3C; detecting the current DC voltage amplitude of the onshore converter station M3C, and determining the voltage deviation of the reference value based on the current DC voltage amplitude of the onshore converter station M3C and the reference value of the differential element; deducing the amount to be adjusted based on the voltage deviation of the reference value, and performing frequency conversion control on the low-frequency side of the onshore converter station M3C according to the amount to be adjusted and the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, changing the frequency of the low-frequency side of the onshore converter station M3C so that the low-frequency side frequency can directly follow the frequency of the onshore power grid, realizing the transmission of frequency information. Frequency conversion control refers to matching the offshore wind power frequency with the onshore power grid frequency by adjusting the operating frequency of the power electronic equipment. Frequency conversion control enables the transmission of frequency information between offshore low-frequency wind farms and onshore power grids, allowing wind power systems to adjust their output frequency according to grid demands and thus better integrate into the grid.

[0109] The specific implementation plan for frequency information transmission in step 3 is as follows:

[0110] The offshore low-frequency wind farm is connected to the onshore converter station M3C via an offshore cable. Because the onshore converter station M3C isolates the onshore power grid frequency and decouples it from the low-frequency frequency of the offshore low-frequency wind power system, the offshore low-frequency wind farm cannot know the information on the frequency changes of the onshore power grid, and therefore cannot actively provide frequency support for the onshore power grid.

[0111] Currently, there are two methods for offshore low-frequency wind farms to receive frequency change information from the onshore power grid: remote communication and coordinated control. As offshore wind power continues to expand into the mid-to-far sea, the latency issues associated with remote communication are becoming increasingly severe, and the installation of communication equipment incurs additional costs. Therefore, this paper chooses the coordinated control scheme, utilizing the M3C frequency converter control at the onshore converter station to transmit information about frequency changes from the onshore power grid.

[0112] The onshore converter station M3C is a power electronic device used for AC / AC conversion in offshore low-frequency wind power systems. After decoupling conversion, the low-frequency side and the power frequency side can be controlled separately. The power frequency side uses a constant capacitor voltage control scheme to maintain a constant DC capacitor voltage and ensure stable operation of the onshore converter station M3C. The low-frequency side uses a constant AC voltage amplitude and frequency control scheme to establish an offshore low-frequency AC power supply to power the offshore low-frequency wind farm. When performing active grid connection control on the low-frequency side, its frequency needs to be given. After passing through the integrator controller, the low-frequency power supply phase angle is obtained. The phase angle should be between 0 and 2π; if it exceeds 2π, it is reset to 0 and recalculated. The formula for calculating the low-frequency power supply phase angle is:

[0113] θ l =∫2πf l0 dt (7)

[0114] In the formula: θ l The phase angle of the low-frequency power supply; f l0 For the given low frequency. Figure 3 This is the phase control diagram for the low-frequency AC power supply. As shown in Equation 7, the low-frequency side frequency of the M3C converter station on shore depends on a given value f. l0 To ensure that offshore low-frequency wind farms receive information about frequency changes in the onshore power grid, the low-frequency side frequency needs to be adjusted. As previously mentioned, the onshore converter station M3C utilizes the DC capacitor voltage for inertial response, and this capacitor voltage contains information about frequency changes. Therefore, the rate of change of the DC capacitor voltage is directly detected through a differentiating element, amplified by a proportional gain, and added to the initial given frequency to obtain the reference value of the low-frequency side frequency. The overall control equation is:

[0115]

[0116] In the formula: k l This is the proportional coefficient in frequency converter control. Figure 4 The diagram shows the block diagram of the frequency converter control. To filter out noise interference from the DC capacitor voltage, a first-order transfer function is added to the control loop for filtering. In summary, the above control establishes a connection between the land-based power frequency and the marine low-frequency frequency, realizing the transmission of frequency information.

[0117] This invention directly transmits onshore power grid frequency information through M3C frequency converter control at an onshore converter station. Firstly, the frequency converter control scheme can quickly adjust the frequency to respond, avoiding the communication equipment costs and latency issues associated with remote communication schemes, thus achieving better frequency modulation results. Secondly, in the initial stage of frequency change, the dynamic performance of the entire system's frequency response is dominated by the system's inertial response. When the frequency exceeds the primary frequency modulation threshold, the system will perform a frequency modulation. The additional power of the inertial response is related to the system's frequency change rate. This invention primarily focuses on the initial stage of disturbance, preventing rapid frequency changes and reducing the power grid system's frequency change rate by coordinating the inertial response. Therefore, differential control is used in the frequency control stage to transmit frequency conversion rate information, providing greater inertia to the system at the initial stage of frequency modulation.

[0118] Step 4: The offshore low-frequency wind farm executes inertial response based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid.

[0119] In step 4, the offshore low-frequency wind farm executes an inertial response based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C. Together with the onshore converter station M3C, it provides frequency support for the onshore power grid. This includes: the permanent magnet direct-drive wind turbines in the offshore low-frequency wind farm execute the inertial response of the offshore low-frequency wind farm based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C, so as to provide frequency support for the onshore power grid together with the onshore converter station M3C.

[0120] Since step 2 achieves the information transmission of the onshore power frequency, the low-frequency of the offshore low-frequency wind power system changes with the power frequency system frequency. Therefore, to achieve inertia support for the offshore low-frequency wind farm, the specific steps are as follows: First, the permanent magnet direct-drive wind turbine in the offshore low-frequency wind farm detects the current frequency of the low-frequency side of the onshore converter station M3C through phase-locked loop (PLL) technology. The detected current frequency of the low-frequency side of the onshore converter station M3C is compared with the preset frequency to obtain the low-frequency deviation. According to the virtual inertia control strategy of the onshore converter station M3C and introducing the proportional relationship of the droop control loop, the low-frequency deviation is converted and calculated to obtain the required additional power value. Based on the calculated additional power value, the control system of the offshore low-frequency wind farm adjusts the active power output of the permanent magnet direct-drive wind turbine. By adjusting the active power output of the permanent magnet direct-drive wind turbine, the permanent magnet direct-drive wind turbine releases the rotational kinetic energy stored in the wind turbine blades, providing frequency support for the onshore power grid.

[0121] This invention achieves inertia support for offshore low-frequency wind farms by designing a droop control mechanism. Since the onshore converter station M3C transmits information about the rate of frequency change, the additional power value can be obtained by directly controlling the detected low-frequency deviation through the droop control mechanism. The offshore low-frequency wind farm can then rapidly adjust its active power output and utilize rotor kinetic energy to provide instantaneous power support to the onshore power frequency system. Compared to releasing energy through DC capacitors, offshore low-frequency wind farms can provide greater power, effectively relieving the pressure on onshore synchronous generator units, significantly improving the inertia level of the offshore low-frequency wind power system, and enhancing the system's frequency stability.

[0122] The specific implementation plan for virtual inertia control of offshore low-frequency wind farms in step 4 is as follows:

[0123] The M3C low-frequency side of the onshore converter station transmits frequency information through frequency conversion control. When the power frequency system is disturbed and the frequency changes, the frequency of the M3C low-frequency side of the onshore converter station will also change accordingly.

[0124] Under normal circumstances, wind turbines in offshore low-frequency wind farms achieve maximum power output by capturing maximum wind energy.

[0125] When the grid frequency is disturbed, the onshore converter station M3C correspondingly changes the low-frequency side frequency. In the offshore low-frequency wind farm, the wind turbines detect the low-frequency side frequency f through a phase-locked loop (PLL). l The change in frequency is used to introduce the deviation between the detected frequency value and the reference value into the proportional controller to obtain the reference value of the additional power of the offshore low-frequency wind farm, thereby changing the output of the wind turbines to achieve a frequency response. Taking a single wind turbine in the wind farm as an example, the specific control strategy is as follows:

[0126]

[0127] In the formula: The reference active power for the wind turbine during maximum power point tracking; k wt,i This is the proportional control coefficient; This is the new active power reference value after adding the additional power. By adding the additional power of all wind turbines in the wind farm, the active power for the inertial response of the offshore low-frequency wind farm can be obtained as follows:

[0128]

[0129] As shown in Equation 10, when the active power of the system is no longer balanced due to disturbance, the wind turbines in the wind farm release the rotational kinetic energy stored in the rotor through virtual inertia control to provide inertial response, thereby reducing the frequency regulation burden of onshore synchronous wind turbines and avoiding rapid frequency changes. Compared with the virtual inertia control of the M3C converter station on shore, the permanent magnet direct-drive wind turbines in offshore low-frequency wind farms have a larger inertial time constant, and due to the limitation of DC capacitor voltage fluctuations, the rotor kinetic energy is more suitable as a frequency regulation resource to provide more inertia for the system.

[0130] In summary, the offshore low-frequency wind farm, composed of permanent magnet direct-drive wind turbines, generates low-frequency AC power through maximum power point tracking. This power is then boosted and transmitted to the onshore converter station M3C. The onshore converter station M3C achieves AC-AC conversion through decoupling transformation. At this point, the DC capacitor voltage is kept constant by the power frequency side control, thus enabling the effective transmission of offshore low-frequency wind power. The low-frequency power is converted into power frequency power and integrated into the onshore power frequency grid.

[0131] As offshore wind turbines replace some synchronous generators in the onshore power grid, the presence of onshore converter stations (M3C) and full-power converters for wind turbines causes decoupling between low-frequency and power grid frequencies. This reduces the inertia level of the entire system, leading to the risk of frequency instability and seriously affecting the safe operation of the power system.

[0132] Therefore, this invention proposes a coordinated inertial response control scheme for the aforementioned marine low-frequency system. This cascaded control strategy is as follows: Figure 6 As shown, the specific process is as follows:

[0133] When a sudden increase in load or a generator trip occurs in the onshore power system, the active power in the system is no longer balanced. The rotor speed of the onshore synchronous generator decreases to compensate for the active power deficit in the system by releasing rotor kinetic energy. Since the rotor speed of the synchronous generator is directly coupled with the power grid frequency, the grid frequency drops rapidly.

[0134] When the onshore converter station M3C detects a frequency change in the onshore power grid, based on the coupling relationship between DC capacitor voltage and frequency, the reference value of the DC capacitor voltage will change accordingly through virtual inertia control of the onshore converter station M3C. This releases the electrostatic energy stored in the DC capacitor of the onshore converter station M3C to provide frequency support for the system. Due to the limitations of DC capacitor voltage fluctuations, the energy provided by the DC capacitor is limited, requiring offshore low-frequency wind farms to provide more energy.

[0135] To this end, a frequency converter control loop for the M3C onshore converter station was designed. When the DC capacitor voltage changes, the frequency converter control of the M3C onshore converter station will change the low-frequency side frequency value accordingly, thereby realizing the transmission of frequency information.

[0136] When an offshore low-frequency wind farm detects frequency changes via a phase-locked loop (PLL), it releases the rotational kinetic energy stored in the turbine blades through virtual inertia control. This adjusts the active power output of the offshore wind turbine to provide inertial support to the onshore power grid. This is the entire process of coordinating inertia in the offshore low-frequency wind power system. By combining DC capacitor energy with rotor kinetic energy through a coordinated control strategy, the system's frequency regulation process is improved, providing inertial support and effectively enhancing its inertia level. This avoids frequency instability caused by rapid frequency changes and improves the system's frequency stability.

[0137] The present invention also provides a coordinated inertia response control system for an offshore low-frequency wind power system, comprising:

[0138] Analysis Module: Based on the frequency response model of the offshore low-frequency wind power system, the influence of the system inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C are analyzed. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, the virtual inertia control strategy of the onshore converter station M3C is determined. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C and the onshore power grid connected in sequence. The onshore converter station M3C is decoupled into a power frequency side and a low-frequency side for separate control.

[0139] Inertia Response Module: Detects the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes the inertia response based on the current frequency of the onshore power grid and in conjunction with the virtual inertia control strategy of the onshore converter station M3C.

[0140] Coupling relationship establishment module: Based on the inertial response results executed by the power frequency side of the onshore converter station M3C, the low frequency side of the onshore converter station M3C transmits the frequency change information of the onshore power frequency grid to the offshore low frequency wind farm through the frequency conversion control strategy of the low frequency side of the onshore converter station M3C.

[0141] Coordinated Inertia Response Module: The offshore low-frequency wind farm executes inertia response based on the frequency change information of the onshore power grid and the virtual inertia control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid.

[0142] Specifically, offshore low-frequency wind farms consist of permanent magnet direct-drive wind turbine units, which include wind turbines, synchronous generators, and back-to-back converters.

[0143] The back-to-back converter consists of a turbine-side converter and a grid-side converter connected back-to-back. The turbine-side converter is connected to the wind turbine, which directly drives the synchronous generator's rotor through rotor rotation. The electrical energy generated by the synchronous generator is controlled and regulated by the turbine-side converter. The turbine-side converter controls the wind turbine rotor speed to maintain the optimal tip speed ratio for maximum wind energy capture. The grid-side converter is connected to the low-frequency side of the onshore converter station M3C. The grid-side converter achieves effective power delivery of the permanent magnet direct-drive wind turbine through a constant DC capacitor voltage.

[0144] The onshore power frequency grid consists of synchronous generator sets and active and reactive loads. The synchronous generator sets in the onshore power frequency grid are connected to the power frequency side of the onshore converter station M3C.

[0145] In the preferred embodiment, the onshore converter station M3C is decoupled and converted into separate control for the power frequency side and the low frequency side, specifically:

[0146] The power frequency side control of the onshore converter station M3C adopts a constant DC capacitor voltage control method. The control objective of the constant DC capacitor voltage control method is to keep the total DC capacitor voltage of the onshore converter station M3C constant and to perform reactive power interaction with the onshore power frequency grid.

[0147] The low-frequency side control of the onshore converter station M3C adopts a VF control mode with constant AC voltage amplitude and frequency. The VF control mode with constant AC voltage amplitude and frequency actively establishes the low-frequency AC power supply for the offshore low-frequency wind farm.

[0148] The confirmation process for the virtual inertia control strategy of the onshore converter station M3C is as follows:

[0149] Based on the dynamic characteristic analysis results of the DC capacitor of the onshore converter station M3C, the dynamic characteristics of the DC capacitor of the onshore converter station M3C are compared with the rotor motion equation of the synchronous generator set in the onshore power frequency grid. Based on the comparison results of the rotor motion equation, the virtual inertia control strategy of the onshore converter station M3C is determined.

[0150] Furthermore, the power frequency side of the onshore converter station M3C executes inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C, specifically as follows:

[0151] Based on the virtual inertia control strategy of the onshore converter station M3C, a droop control method for DC capacitor voltage is designed.

[0152] By detecting the current frequency of the onshore power grid, the power frequency side of the onshore converter station M3C performs inertial response based on the current frequency of the onshore power grid, combined with the droop control mode of the DC capacitor voltage, and by utilizing the energy stored in the DC capacitor in the onshore converter station M3C.

[0153] To establish the coupling relationship between the low-frequency frequency of offshore wind power and the power frequency of the onshore power grid, the low-frequency side of the onshore converter station M3C, based on the inertial response results executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, thereby realizing frequency information transmission. Specifically:

[0154] Based on the virtual inertia response results of the power frequency side of the onshore converter station M3C, a droop control mode is introduced for the onshore converter station M3C. Combined with the frequency conversion control strategy of the low frequency side of the onshore converter station M3C, frequency conversion control is executed. Based on the frequency conversion control of the low frequency side of the onshore converter station M3C, the output frequency of the power frequency side is adjusted to synchronize the frequency changes of the onshore converter station M3C with the onshore power frequency grid, thereby achieving frequency matching and establishing the coupling relationship between the low frequency frequency of the offshore low frequency wind farm and the power frequency frequency of the onshore power frequency grid. In addition, the virtual inertia response results of the power frequency side of the onshore converter station M3C include the current DC voltage amplitude of the DC capacitor in the onshore converter station M3C; detecting the current DC voltage amplitude of the onshore converter station M3C, determining the voltage deviation of the reference value based on the current DC voltage amplitude of the onshore converter station M3C and the reference value of the differential element; calculating the amount that needs to be adjusted based on the voltage deviation of the reference value; and performing frequency conversion control on the low frequency side of the onshore converter station M3C according to the amount that needs to be adjusted and the frequency conversion control strategy of the low frequency side of the onshore converter station M3C to change the frequency of the low frequency side of the onshore converter station M3C, so that the low frequency side frequency can directly follow the frequency of the onshore power grid and realize the transmission of frequency information.

[0155] In this invention, the offshore low-frequency wind farm, based on the frequency change information of the onshore power grid obtained from the onshore power grid, and in conjunction with the virtual inertia control strategy of the onshore converter station M3C, executes an inertia response, and together with the onshore converter station M3C, provides frequency support for the onshore power grid. This includes: the permanent magnet direct-drive wind turbine units in the offshore low-frequency wind farm, based on the frequency change information of the onshore power grid obtained from the offshore low-frequency wind farm, execute the inertia response of the offshore low-frequency wind farm through the virtual inertia control strategy of the onshore converter station M3C, so as to jointly provide frequency support for the onshore power grid with the onshore converter station M3C. Specifically:

[0156] In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines use phase-locked loop (PLL) technology to detect the current frequency of the low-frequency side of the onshore converter station M3C. The detected current frequency is compared with a preset frequency to obtain the low-frequency deviation. A proportional relationship is introduced into the droop control loop to convert and calculate the low-frequency deviation, yielding the required additional power value. Based on this calculated additional power value, the control system of the offshore low-frequency wind farm adjusts the active power output of the permanent magnet direct-drive wind turbines. By adjusting the active power output, the permanent magnet direct-drive wind turbines release the rotational kinetic energy stored in the turbine blades, providing frequency support for the onshore power grid.

[0157] This system, through coordinated control of the offshore low-frequency wind farm and the onshore converter station M3C, combines the DC capacitor energy of the onshore converter station M3C with the kinetic energy of the wind turbine rotor. By releasing the energy stored in the wind turbine and the onshore converter station M3C, the system participates in the inertial response process, thereby achieving active frequency support from the onshore converter station M3C, improving the system's inertial level, reducing the risk of frequency instability, and enhancing the stability of the system's frequency.

[0158] This invention also provides an electronic device, which includes a processor and a memory. The processor executes steps of a coordinated inertia response control method by calling programs or instructions stored in the memory. These steps include: Step 1: Based on the frequency response model of the offshore low-frequency wind power system, analyzing the influence of the system's inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C, and determining the virtual inertia control strategy for the onshore converter station M3C based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C, and an onshore power grid connected sequentially. The onshore converter station M3C is decoupled into a power frequency side and a low-frequency side, and the control strategies are implemented separately. Control; Step 2: Detect the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes an inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C; Step 3: Based on the inertial response result executed by the power frequency side of the onshore converter station M3C, the low frequency side of the onshore converter station M3C transmits the frequency change information of the onshore power grid to the offshore low frequency wind farm through the frequency conversion control strategy of the low frequency side of the onshore converter station M3C; Step 4: The offshore low frequency wind farm executes an inertial response based on the acquired frequency change information of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid. This invention combines the DC capacitor energy of the onshore converter station M3C with the kinetic energy of the wind turbine rotor through coordinated control of the offshore low-frequency wind farm and the onshore converter station M3C. By releasing the energy stored in the wind turbine and the onshore converter station M3C to participate in the system's inertial response process, the onshore converter station M3C actively supports the frequency, improves the system's inertial level, reduces the risk of frequency instability, and improves the stability of the system's frequency.

[0159] This invention also provides a computer-readable storage medium storing a program or instructions that are steps of a computer executing a coordinated inertia response control method. The steps include: Step 1: Based on the frequency response model of the offshore low-frequency wind power system, analyze the influence of the system's inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, determine the virtual inertia control strategy for the onshore converter station M3C. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C, and an onshore power grid connected sequentially. The onshore converter station M3C is decoupled into a power frequency side and a low-frequency side for separate control. Step 2: Detect the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes an inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C. Step 3: The low-frequency side of the onshore converter station M3C, based on the inertial response result executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C. Step 4: The offshore low-frequency wind farm executes an inertial response based on the acquired frequency change information of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid. This invention combines the DC capacitor energy of the onshore converter station M3C with the kinetic energy of the wind turbine rotor through coordinated control of the offshore low-frequency wind farm and the onshore converter station M3C. By releasing the energy stored in the wind turbine and the onshore converter station M3C to participate in the system's inertial response process, the onshore converter station M3C actively supports the frequency, improves the system's inertial level, reduces the risk of frequency instability, and improves the stability of the system's frequency.

[0160] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0161] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0162] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0163] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0164] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0165] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A coordinated inertia response control method for an offshore low-frequency wind power system, characterized in that, Includes the following steps: Step 1: Based on the frequency response model of the offshore low-frequency wind power system, analyze the influence of the system inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, determine the virtual inertia control strategy of the onshore converter station M3C. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C and the onshore power grid connected in sequence. The onshore converter station M3C is decoupled into the power frequency side and the low-frequency side for separate control. Step 2: Detect the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes inertia response based on the current frequency of the onshore power grid and in combination with the virtual inertia control strategy of the onshore converter station M3C. Step 3: Based on the inertial response results executed by the power frequency side of the onshore converter station M3C, the low-frequency side of the onshore converter station M3C uses the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C to transmit the frequency change information of the onshore power frequency grid to the offshore low-frequency wind farm. Step 4: The offshore low-frequency wind farm executes inertial response based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid.

2. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 1, the offshore low-frequency wind farm is composed of permanent magnet direct-drive wind turbine units, which include wind turbines, synchronous generators and back-to-back converters. The back-to-back converter is formed by connecting a machine-side converter and a grid-side converter back-to-back. The machine-side converter is connected to the wind turbine, and the wind turbine directly drives the rotor of the synchronous generator through the rotation of the rotor. The electrical energy generated by the synchronous generator is controlled and regulated by the machine-side converter. The machine-side converter controls the rotor speed of the wind turbine to maintain the optimal tip speed ratio for maximum wind energy capture. The grid-side converter is connected to the low-frequency side of the onshore converter station M3C. The grid-side converter realizes the effective power delivery of the permanent magnet direct-drive wind turbine through a constant DC capacitor voltage.

3. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 1, the onshore power frequency grid consists of synchronous generator sets and active and reactive loads. The synchronous generator sets in the onshore power frequency grid are connected to the power frequency side of the onshore converter station M3C.

4. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 1, the onshore converter station M3C decouples and converts the power frequency side and the low frequency side for separate control, specifically as follows: The power frequency side control of the onshore converter station M3C adopts a constant DC capacitor voltage control method. The control objective of the constant DC capacitor voltage control method is to keep the total DC capacitor voltage of the onshore converter station M3C constant and to perform reactive power interaction with the onshore power frequency grid. The low-frequency side control of the onshore converter station M3C adopts a VF control mode with constant AC voltage amplitude and frequency. The VF control mode with constant AC voltage amplitude and frequency actively establishes the low-frequency AC power supply for the offshore low-frequency wind farm.

5. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 2, the determination of the virtual inertia control strategy for the onshore converter station M3C is as follows: Based on the dynamic characteristic analysis results of the DC capacitor of the onshore converter station M3C, the dynamic characteristics of the DC capacitor of the onshore converter station M3C are compared with the rotor motion equation of the synchronous generator set in the onshore power frequency grid. Based on the comparison results of the rotor motion equation, the virtual inertia control strategy of the onshore converter station M3C is determined.

6. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 2, the power frequency side of the onshore converter station M3C executes an inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C. Specifically: Based on the virtual inertia control strategy of the onshore converter station M3C, a droop control method for DC capacitor voltage is designed. By detecting the current frequency of the onshore power grid, the power frequency side of the onshore converter station M3C performs inertial response based on the current frequency of the onshore power grid, combined with the droop control mode of the DC capacitor voltage, and by utilizing the energy stored in the DC capacitor in the onshore converter station M3C.

7. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 3, the low-frequency side of the onshore converter station M3C, based on the inertial response results executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C. Specifically: Based on the virtual inertia response results of the power frequency side of the onshore converter station M3C, the onshore converter station M3C introduces a droop control mode, and performs frequency conversion control in combination with the frequency conversion control strategy of the low frequency side of the onshore converter station M3C. The frequency converter control on the low-frequency side of the onshore converter station M3C is used to adjust the output frequency on the power frequency side, so that the frequency changes of the onshore converter station M3C and the onshore power frequency grid are synchronized, frequency matching is achieved, and the coupling relationship between the low-frequency frequency of the offshore low-frequency wind farm and the power frequency frequency of the onshore power frequency grid is established.

8. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 1, characterized in that, In step 3, the power frequency side virtual inertia response result of the onshore converter station M3C includes: the current DC voltage amplitude of the DC capacitor in the onshore converter station M3C; The current DC voltage amplitude of the onshore converter station M3C is detected. Based on the current DC voltage amplitude of the onshore converter station M3C and the reference value of the differential element, the voltage deviation of the reference value is determined. The required adjustment amount is calculated based on the voltage deviation of the reference value. The low-frequency side of the onshore converter station M3C performs frequency conversion control based on the required adjustment amount and the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, changing the frequency of the low-frequency side of the onshore converter station M3C so that the low-frequency side frequency can directly follow the frequency of the onshore power grid, realizing the transmission of frequency information.

9. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 8, characterized in that, In step 4, the offshore low-frequency wind farm executes an inertial response based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C. Together with the onshore converter station M3C, it provides frequency support for the onshore power grid. This includes: the permanent magnet direct-drive wind turbines in the offshore low-frequency wind farm execute the inertial response of the offshore low-frequency wind farm based on the frequency change information of the onshore power grid and the virtual inertial control strategy of the onshore converter station M3C, so as to provide frequency support for the onshore power grid together with the onshore converter station M3C.

10. The coordinated inertia response control method for offshore low-frequency wind power systems according to claim 9, characterized in that, In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines, based on frequency change information from the onshore power grid, utilize the virtual inertia control strategy of the onshore converter station M3C to execute the inertia response of the offshore low-frequency wind farm. This, together with the onshore converter station M3C, provides frequency support for the onshore power grid. Specifically: In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines use phase-locked loop (PLL) technology to detect the current frequency of the low-frequency side of the onshore converter station M3C. By comparing the detected current frequency of the low-frequency side of the onshore converter station M3C with the preset frequency, the low-frequency deviation is obtained. Based on the virtual inertia control strategy of the onshore converter station M3C, and by introducing the proportional relationship of the droop control loop, the low-frequency deviation is converted and calculated to obtain the required additional power value. Based on the calculated additional power value, the control system of the offshore low-frequency wind farm adjusts the active power output of the permanent magnet direct-drive wind turbine. By adjusting the active power output of the permanent magnet direct-drive wind turbine, the turbine releases the rotational kinetic energy stored in the wind turbine blades to provide frequency support for the onshore power grid.

11. A coordinated inertia response control system for an offshore low-frequency wind power system, characterized in that, include: Analysis Module: Based on the frequency response model of the offshore low-frequency wind power system, the influence of the system inertia level on the frequency response and the dynamic characteristics of the DC capacitor of the onshore converter station M3C are analyzed. Based on the analysis results of the influence of the inertia level on the frequency response and the dynamic characteristics of the DC capacitor, the virtual inertia control strategy of the onshore converter station M3C is determined. The offshore low-frequency wind power system includes an offshore low-frequency wind farm, the onshore converter station M3C and the onshore power grid connected in sequence. The onshore converter station M3C is decoupled into a power frequency side and a low-frequency side for separate control. Inertia Response Module: Detects the current frequency of the onshore power grid. The power frequency side of the onshore converter station M3C executes the inertia response based on the current frequency of the onshore power grid and in conjunction with the virtual inertia control strategy of the onshore converter station M3C. Coupling relationship establishment module: Based on the inertial response results executed by the power frequency side of the onshore converter station M3C, the low frequency side of the onshore converter station M3C transmits the frequency change information of the onshore power frequency grid to the offshore low frequency wind farm through the frequency conversion control strategy of the low frequency side of the onshore converter station M3C. Coordinated Inertia Response Module: The offshore low-frequency wind farm executes inertia response based on the frequency change information of the onshore power grid and the virtual inertia control strategy of the onshore converter station M3C, and together with the onshore converter station M3C, provides frequency support for the onshore power grid.

12. The coordinated inertia response control system for offshore low-frequency wind power systems according to claim 11, characterized in that, The offshore low-frequency wind farm consists of permanent magnet direct-drive wind turbine units, which include wind turbines, synchronous generators, and back-to-back converters. The back-to-back converter is formed by connecting a machine-side converter and a grid-side converter back-to-back. The machine-side converter is connected to the wind turbine, and the wind turbine directly drives the rotor of the synchronous generator through the rotation of the rotor. The electrical energy generated by the synchronous generator is controlled and regulated by the machine-side converter. The machine-side converter controls the rotor speed of the wind turbine to maintain the optimal tip speed ratio for maximum wind energy capture. The grid-side converter is connected to the low-frequency side of the onshore converter station M3C. The grid-side converter realizes the effective power delivery of the permanent magnet direct-drive wind turbine through a constant DC capacitor voltage.

13. The coordinated inertia response control system for offshore low-frequency wind power systems according to claim 11, characterized in that, The onshore power frequency grid consists of synchronous generator sets and active and reactive loads. The synchronous generator sets in the onshore power frequency grid are connected to the power frequency side of the onshore converter station M3C.

14. The coordinated inertia response control system for offshore low-frequency wind power systems according to claim 11, characterized in that, The onshore converter station M3C decoupled conversion allows for separate control of the power frequency side and the low frequency side, specifically: The power frequency side control of the onshore converter station M3C adopts a constant DC capacitor voltage control method. The control objective of the constant DC capacitor voltage control method is to keep the total DC capacitor voltage of the onshore converter station M3C constant and to perform reactive power interaction with the onshore power frequency grid. The low-frequency side control of the onshore converter station M3C adopts a VF control mode with constant AC voltage amplitude and frequency. The VF control mode with constant AC voltage amplitude and frequency actively establishes the low-frequency AC power supply for the offshore low-frequency wind farm.

15. The coordinated inertia response control system for an offshore low-frequency wind power system according to claim 11, characterized in that, The process for determining the virtual inertia control strategy of the onshore converter station M3C is as follows: Based on the dynamic characteristic analysis results of the DC capacitor of the onshore converter station M3C, the dynamic characteristics of the DC capacitor of the onshore converter station M3C are compared with the rotor motion equation of the synchronous generator set in the onshore power frequency grid. Based on the comparison results of the rotor motion equation, the virtual inertia control strategy of the onshore converter station M3C is determined.

16. The coordinated inertia response control system for offshore low-frequency wind power systems according to claim 11, characterized in that, The power frequency side of the onshore converter station M3C executes inertial response based on the current frequency of the onshore power grid and in conjunction with the virtual inertial control strategy of the onshore converter station M3C. Specifically: Based on the virtual inertia control strategy of the onshore converter station M3C, a droop control method for DC capacitor voltage is designed. By detecting the current frequency of the onshore power grid, the power frequency side of the onshore converter station M3C performs inertial response based on the current frequency of the onshore power grid, combined with the droop control mode of the DC capacitor voltage, and by utilizing the energy stored in the DC capacitor in the onshore converter station M3C.

17. The coordinated inertia response control system for offshore low-frequency wind power systems according to claim 11, characterized in that, The low-frequency side of the onshore converter station M3C, based on the inertial response results executed by the power frequency side of the onshore converter station M3C, transmits the frequency change information of the onshore power frequency grid to the offshore low-frequency wind farm through the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C. Specifically: Based on the virtual inertia response results of the power frequency side of the onshore converter station M3C, the onshore converter station M3C introduces a droop control mode, and performs frequency conversion control in combination with the frequency conversion control strategy of the low frequency side of the onshore converter station M3C. The frequency converter control on the low-frequency side of the onshore converter station M3C is used to adjust the output frequency on the power frequency side, so that the frequency changes of the onshore converter station M3C and the onshore power frequency grid are synchronized, frequency matching is achieved, and the coupling relationship between the low-frequency frequency of the offshore low-frequency wind farm and the power frequency frequency of the onshore power frequency grid is established.

18. The coordinated inertia response control system for an offshore low-frequency wind power system according to claim 11, characterized in that, The power frequency side virtual inertia response results of the onshore converter station M3C include: the current DC voltage amplitude of the DC capacitor in the onshore converter station M3C; The current DC voltage amplitude of the onshore converter station M3C is detected. Based on the current DC voltage amplitude of the onshore converter station M3C and the reference value of the differential element, the voltage deviation of the reference value is determined. The required adjustment amount is calculated based on the voltage deviation of the reference value. The low-frequency side of the onshore converter station M3C performs frequency conversion control based on the required adjustment amount and the frequency conversion control strategy of the low-frequency side of the onshore converter station M3C, changing the frequency of the low-frequency side of the onshore converter station M3C so that the low-frequency side frequency can directly follow the frequency of the onshore power grid, realizing the transmission of frequency information.

19. The coordinated inertia response control system for an offshore low-frequency wind power system according to claim 18, characterized in that, Offshore low-frequency wind farms, based on the frequency change information of the onshore power grid, and in conjunction with the virtual inertia control strategy of the onshore converter station M3C, execute inertia response and, together with the onshore converter station M3C, provide frequency support for the onshore power grid. This includes: the permanent magnet direct-drive wind turbines in the offshore low-frequency wind farms, based on the frequency change information of the onshore power grid, execute the inertia response of the offshore low-frequency wind farm through the virtual inertia control strategy of the onshore converter station M3C, so as to jointly provide frequency support for the onshore power grid with the onshore converter station M3C.

20. The coordinated inertia response control system for an offshore low-frequency wind power system according to claim 19, characterized in that, In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines, based on frequency change information from the onshore power grid, utilize the virtual inertia control strategy of the onshore converter station M3C to execute the inertia response of the offshore low-frequency wind farm. This, together with the onshore converter station M3C, provides frequency support for the onshore power grid. Specifically: In offshore low-frequency wind farms, permanent magnet direct-drive wind turbines use phase-locked loop (PLL) technology to detect the current frequency of the low-frequency side of the onshore converter station M3C. By comparing the detected current frequency of the low-frequency side of the onshore converter station M3C with the preset frequency, the low-frequency deviation is obtained. Based on the virtual inertia control strategy of the onshore converter station M3C, and by introducing the proportional relationship of the droop control loop, the frequency deviation is converted and calculated to obtain the required additional power value. Based on the calculated additional power value, the control system of the offshore low-frequency wind farm adjusts the active power output of the permanent magnet direct-drive wind turbine. By adjusting the active power output of permanent magnet direct-drive wind turbines, the turbines release the rotational kinetic energy stored in the turbine blades to provide frequency support for the onshore power grid.

21. An electronic device, characterized in that, The electronic device includes: Processor and memory; The processor executes the steps of the coordinated inertia response control method as described in any one of claims 1-10 by calling the program or instructions stored in the memory.

22. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a program or instructions that are steps of a computer performing the coordinated inertia response control method as described in any one of claims 1-10.

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