Active support control method, device and system for wind power plant grid connection through flexible direct current power transmission and storage medium

Abstract

The invention discloses an active support control method, device and system for grid connection of a wind power plant through flexible direct-current power transmission and a storage medium, and belongs to the technical field of active energy frequency modulation of a power grid. The method comprises the following steps: acquiring a frequency modulation control model comprising a wind power plant, a direct-current transmission line and a receiving-end power grid; performing first-layer cooperative control on direct-current voltage in the direct-current power transmission line; second-layer cooperative control is carried out on the active power of each wind turbine generator, and the second-layer cooperative control comprises the steps that the direct current instruction value variable quantity and the direct current voltage variable quantity of the direct current transmission line and the active power of the wind turbine generator are selected to construct macro variables, and the active power of the current wind turbine generator is obtained; and inputting the active power of the current wind turbine generator into a pre-constructed control optimization model to obtain a rapid frequency modulation coefficient of the wind turbine generator so as to control the active power of each wind turbine generator. According to the invention, the grid-connected system provides active energy support by utilizing capacitor energy storage of the direct-current transmission line and active power cooperation of the wind power plant, and the frequency stability of the power grid is optimized.

Description

Technical Field

[0001] The present invention belongs to the technical field of active energy frequency modulation of power grids, and particularly relates to an active support control method, device, system and storage medium for a wind farm connected to the grid through flexible DC transmission. Background Technique

[0002] The reverse distribution of renewable energy and load centers in China makes it a major operation mode for renewable energy bases to transmit power to load centers through flexible DC. Since DC transmission decouples the commutation bus voltage frequency of the converter station on the wind farm side from the frequency of the receiving-end power grid, the wind farm cannot quickly perceive the frequency disturbance of the receiving-end power grid under the condition of no communication or weak communication, and thus cannot use additional fast frequency modulation control to provide active support and frequency response for the receiving-end power grid to improve its frequency dynamic regulation characteristics.

[0003] There are many existing literatures discussing the dynamic characteristics of a wind farm connected to the grid through a flexible DC system to provide inertia support. A few literatures mention the research on a wind farm connected to the grid through an LCC-FHMMC (line-commutated converter - modular multilevel converter hybrid with full-bridge and half-bridge sub-modules) DC transmission line to participate in primary frequency modulation to provide active energy support, but the coordinated control of the wind farm and the DC line is still lacking consideration. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art, and provide an active support control method, device, system and storage medium for a wind farm connected to the grid through flexible DC transmission. By means of the DC voltage droop coefficient and the fast frequency modulation coefficient of the wind turbine generator set, the grid-connected system is enabled to utilize the capacitance energy storage of the DC transmission line and the active power of the wind farm to jointly provide active energy support and optimize the power grid frequency stability problem.

[0005] The present invention provides the following technical solutions:

[0006] In a first aspect, an active support control method for a wind farm connected to the grid through flexible DC transmission is provided, including: obtaining a pre-constructed frequency modulation control model including a wind farm, a DC transmission line and a receiving-end power grid, wherein the wind farm includes a plurality of wind turbine generator sets;

[0007] Based on the frequency modulation control model, a first layer of coordinated control is performed on the DC voltage in the DC transmission line, including: determining the inertial response of the change in the DC voltage in the DC transmission line to the change in the frequency of the receiving-end power grid, and constructing a coordinated control law for the DC voltage droop coefficient according to the inertial response to control the DC voltage in the DC transmission line;

[0008] After controlling the DC voltage in the DC transmission line through the cooperative control law of the DC voltage droop coefficient, the second-layer cooperative control of the active power of each wind turbine is carried out, including: selecting the change amount of the DC current command value, the change amount of the DC voltage of the DC transmission line, and the active power of the wind turbine to construct a macro variable, and obtaining the active power of the current wind turbine;

[0009] Input the active power of the current wind turbine into the pre-constructed control optimization model to obtain the fast frequency modulation coefficient of the wind turbine, so as to control the active power of each wind turbine;

[0010] Among them, the control optimization model includes an objective function and constraint conditions. The objective function takes the minimum change amount of the pitch angle of the wind turbine and the minimum change amount of the frequency of the receiving-end power grid as the optimization objectives, and the constraint conditions include the pitch angle constraint of the wind turbine and the active power constraint of the wind turbine.

[0011] As an optional technical solution of the present invention, the DC transmission line includes a connected receiving-end converter and a sending-end converter; the input end of the receiving-end converter is connected to the wind farm, and is used to control the input active power of the DC transmission line to dynamically track the active power command value, and at the same time keep the current of the DC transmission line at a set value; the output end of the sending-end converter is connected to the receiving-end power grid, and is used to control the output active power of the DC transmission line to dynamically track the input active power of the DC transmission line, and at the same time keep the voltage of the DC transmission line at a set value.

[0012] As an optional technical solution of the present invention, determining the inertial response of the change amount of the DC voltage of the DC transmission line to the change amount of the frequency of the receiving-end power grid includes:

[0013] The inertial response of the change amount of the DC voltage of the DC transmission line to the change amount of the frequency of the receiving-end power grid is expressed as:

[0014] ;

[0015] Among them, represents the change amount of the DC voltage of the DC transmission line, represents the change amount of the frequency of the receiving-end power grid, represents the virtual inertia time constant, represents the DC voltage of the DC transmission line in steady-state operation, represents the DC voltage droop coefficient, represents the change amount of the active power of the wind farm, represents the change amount of the output active power of the DC transmission line, C represents the capacitance of the DC transmission line, and s represents the complex frequency of the transfer function.

[0016] As an optional technical solution of the present invention, constructing the cooperative control law of the DC voltage droop coefficient includes:

[0017] Based on the coordinated control theory, the frequency change of the receiving-end power grid is selected and the virtual inertia time constant to construct the first macro variable , which is expressed as:

[0018] ;

[0019] Among them, represents the weight parameter of the frequency change of the receiving-end power grid when the first macro variable tends to the target position along the manifold;

[0020] Since the macro variable satisfies , the control law of the virtual inertia time constant is obtained, which is expressed as:

[0021] ;

[0022] Among them, T represents the coordinated motion coefficient, represents the frequency change rate of the receiving-end power grid, represents the DC voltage change rate of the DC transmission line;

[0023] Combined with the inertial response of the DC voltage change of the DC transmission line to the frequency change of the receiving-end power grid, the coordinated control law of the DC voltage droop coefficient is obtained, which is expressed as:

[0024] ;

[0025] Among them, represents the coordinated control law of the DC voltage droop coefficient.

[0026] As an alternative technical solution of the present invention, the method for selecting the DC current command value change, the DC voltage change of the DC transmission line, and the active power of the wind farm to construct a macro variable to obtain the active power of the current wind farm includes:

[0027] Select the DC current command value change, the DC voltage change of the DC transmission line, and the active power of the wind farm to construct the second macro variable , which is expressed as:

[0028] ;

[0029] Among them, represents the adjustment weight of the direction displacement change of the DC current command value change of the DC transmission line when the second macro variable tends to the target position along the manifold, Represents the second macro variable DC voltage variation of the HVDC transmission line when approaching the target position along the manifold Adjustment weight of the directional displacement variation, Represents the active power of the wind farm;

[0030] Due to the macro variable Satisfy , the active power of the wind farm is obtained The control law of, expressed as;

[0031] ;

[0032] Wherein, Represents the DC voltage change rate of the HVDC transmission line, Represents the DC current command value change rate of the HVDC transmission line, T represents the cooperative motion coefficient Represents the change rate of the active power of the wind farm;

[0033] According to the active power of the wind farm The control law of obtains the active power of the current wind turbine unit.

[0034] As an alternative technical solution of the present invention, the active power of the current wind turbine unit is input into a pre-constructed control optimization model to obtain the fast frequency modulation coefficient of the wind turbine unit, including:

[0035] The objective function is expressed as:

[0036] ;

[0037] Wherein, Represents finding the minimum value, Represents the weight parameter of the pitch angle change amount of the wind turbine unit, Represents the pitch angle change amount of the wind turbine unit, Represents the weight parameter of the frequency change amount of the receiving-end power grid, f represents the actual frequency of the receiving-end power grid, f ref Represents the frequency reference value of the receiving-end power grid;

[0038] The pitch angle constraint and the active power constraint of the wind turbine unit are respectively expressed as:

[0039] ;

[0040] Wherein, Respectively represent the pitch angle of the wind turbine unit Lower and upper limits of, Respectively represent the lower and upper limits of the active power of the wind turbine unit;

[0041] Based on the objective function and the constraint conditions, control the optimization model to output the fast frequency regulation coefficient of the wind turbine generator set , so as to control the active power output of each wind turbine generator set in an orderly manner.

[0042] In a second aspect, there is provided an active support control device for a wind farm connected to the grid through flexible DC transmission, including: a model acquisition module, configured to acquire a pre-constructed frequency modulation control model including a wind farm, a DC transmission line, and a receiving-end power grid, where the wind farm includes a plurality of wind turbine generator sets;

[0043] A first control module, configured to perform a first-layer coordinated control on the DC voltage in the DC transmission line based on the frequency modulation control model, including: determining the inertial response of the change in the DC voltage of the DC transmission line to the change in the frequency of the receiving-end power grid, and constructing a coordinated control law for the DC voltage droop coefficient according to the inertial response to control the DC voltage in the DC transmission line;

[0044] A second control module, configured to perform a second-layer coordinated control on the active power of each wind turbine generator set after controlling the DC voltage in the DC transmission line through the coordinated control law of the DC voltage droop coefficient, including: selecting the change in the DC current command value, the change in the DC voltage, and the active power of the wind turbine generator set of the DC transmission line to construct a macro variable, and obtaining the active power of the current wind turbine generator set;

[0045] A model optimization module, configured to input the active power of the current wind turbine generator set into a pre-constructed control optimization model to obtain the fast frequency regulation coefficient of the wind turbine generator set, so as to control the active power of each wind turbine generator set;

[0046] Wherein, the control optimization model includes an objective function and constraint conditions, the objective function takes the minimum change in the pitch angle of the wind turbine generator set and the minimum change in the frequency of the receiving-end power grid as optimization objectives, and the constraint conditions include the pitch angle constraint of the wind turbine generator set and the active power constraint of the wind turbine generator set.

[0047] In a third aspect, there is provided an active support control system for a wind farm connected to the grid through flexible DC transmission, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the active support control method for the wind farm connected to the grid through flexible DC transmission described in the first aspect.

[0048] In a fourth aspect, there is provided a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the active support control method for the wind farm connected to the grid through flexible DC transmission described in the first aspect are implemented.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] An active support control method for a wind farm to be connected to the grid via flexible DC transmission is provided by the present invention. The DC voltage droop coefficient is used to control the stability of the DC voltage in the DC transmission line, and the fast frequency modulation coefficient of the wind turbine is controlled by an optimized control model to control the active power of each wind turbine, so as to realize the coordinated control of the grid-connected system using the capacitance energy storage of the DC transmission line and the active power of the wind farm to provide active energy support and optimize the grid frequency stability problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a flowchart of the active support control method for a wind farm to be connected to the grid via flexible DC transmission according to an embodiment of the present invention;

[0052] Figure 2 is a schematic structural diagram of the frequency modulation control model according to an embodiment of the present invention;

[0053] Figure 3 is a schematic diagram of the frequency modulation principle of a wind turbine according to an embodiment of the present invention;

[0054] Figure 4 is a schematic diagram of the scenario of a wind farm connected to the grid via LCC-FHMMC according to an embodiment of the present invention;

[0055] Figure 5 is a curve graph of the change of the receiving-end grid frequency under different controls according to an embodiment of the present invention;

[0056] Figure 6 is a curve graph of the change of the DC line voltage under different controls according to an embodiment of the present invention;

[0057] Figure 7 is a curve graph of the change of the DC line power under different controls according to an embodiment of the present invention;

[0058] Figure 8 is a curve graph of the change of the active power of the wind turbine under different controls according to an embodiment of the present invention;

[0059] Figure 9 is a curve graph of the change of the pitch angle of the wind turbine under different controls according to an embodiment of the present invention;

[0060] Figure 10 is a curve graph of the change of the fast frequency modulation coefficient of the wind turbine according to an embodiment of the present invention;

[0061] Figure 11 is a comparison graph of the active power of the wind turbine and the active power command value according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the protection scope of the present invention.

[0063] Embodiment 1

[0064] This embodiment provides an active support control method for a wind farm to be interconnected with the grid through flexible DC transmission. The key to realizing the communication-free coordinated inertial response of the wind farm through the flexible DC grid connection system is, firstly, to adaptively adjust the DC voltage droop coefficient to enable the energy provided by the DC capacitor energy storage to vary with the grid frequency deviation, and secondly, to adaptively adjust the fast frequency modulation coefficient of the wind turbine generator sets , so that the reserve capacity provided by the wind farm varies dynamically with the receiving-end grid frequency and the DC capacitor energy storage. Therefore, this embodiment optimizes the two parameters by adopting the cooperative control theory with good robustness. As Figure 1 shown, the specific steps are as follows:

[0065] Step 1: As Figure 2 shown, obtain the pre-constructed frequency modulation control model including the wind farm, DC transmission line, and receiving-end grid, where the wind farm includes a number of wind turbine generator sets.

[0066] Specifically, the DC transmission line includes a connected receiving-end converter and a sending-end converter. The input end of the receiving-end converter is connected to the wind farm and adopts constant DC current control to control the input active power of the DC transmission line to dynamically track the active power command value , while keeping the current of the DC transmission line at a set value. The output end of the sending-end converter is connected to the receiving-end grid and adopts constant DC voltage control to control the output active power of the DC transmission line to dynamically track the input active power of the DC transmission line , while keeping the voltage of the DC transmission line at a set value.

[0067] In this embodiment, the receiving-end converter adopts a line commutated converter (LCC), and the sending-end converter adopts a full-half bridge modular multilevel converter (FHMMC).

[0068] Furthermore, when the LCC adopts constant DC current control, according to the control principle of the line commutated converter, the LCC can dynamically adjust the DC current control command value according to the change in the DC line voltage to enable the input active power of the wind farm through the flexible DC grid connection system to dynamically track the active power command value , ignoring the adjustment of the input active power of the LCC on the DC voltage ​ The regulated transient response and the active power loss of the DC line can be considered as the input active power for the DC voltage of the FHMMC is adjusted and remains unchanged. The coordinated operation of the LCC and the FHMMC enables the additional droop control compensation component in the DC voltage control of the FHMMC, which can utilize the DC line capacitance energy storage of the HVDC to provide frequency response for the frequency disturbance of the receiving-end power grid without affecting the output power of the wind farm.

[0069] In this embodiment, the frequency regulation control of the wind farm adopts distributed frequency regulation composed of the fast frequency regulation of wind turbines. As Figure 3 shown, its basic principle is as follows: The hydraulic pitch system in the wind turbine adjusts the pitch angle to capture the wind energy that meets the active power command P corresponding to the optimal torque of the wind turbine tor demand, and regulates the rotor input wind power through pitch angle control, so that the active power P output by the stator of the wind turbine s tracks the active power command P tor while maintaining the generator speed ω r tracking the generator speed reference value ω ref . When a frequency disturbance occurs, the additional frequency regulation inertia control realizes inertia support based on the regulation of the rotor kinetic energy by superimposing the active power command variation ΔP1 to the active power command P tor ; the droop control realizes the pitch backup regulation for driving the pitch angle compensation by superimposing the active power command variation ΔP2 to the active power command P of the substation AGC . Figure 3 Among them, P cmd represents the active power command of the optimal torque, k d and k p respectively represent the additional frequency regulation differential parameter and the proportional parameter, k opt represents the optimal mode gain, T ref represents the rated torque, P ref represents the rated power, f s and f N respectively represent the grid frequency and its rated value, P s represents the output power of the wind turbine, and PI represents the PI controller.

[0070] Step 2: Based on the frequency regulation control model, perform the first-layer coordinated control on the DC voltage in the DC transmission line, including: determining the inertia response of the DC voltage variation of the DC transmission line to the frequency variation of the receiving-end power grid, and constructing a coordinated control law for the DC voltage droop coefficient according to the inertia response to control the DC voltage in the DC transmission line.

[0071] 2.1. The inertia response of the DC voltage variation of the DC transmission line to the frequency variation of the receiving-end power grid is expressed as:

[0072] ;

[0073] Wherein, represents the change in DC voltage of the DC transmission line, represents the change in frequency of the receiving-end power grid, represents the virtual inertia time constant, represents the DC voltage of the DC transmission line under steady-state operation, represents the DC voltage droop coefficient, represents the change in active power of the wind farm, represents the change in the output active power of the DC transmission line. C represents the capacitance of the DC transmission line, and s represents the complex frequency of the transfer function.

[0074] 2.2. To enable the DC capacitor to provide inertia support for the frequency deviation of the receiving-end power grid and cooperate with the self-recovery of the DC voltage, based on the cooperative control theory, the change in frequency of the receiving-end power grid and the virtual inertia time constant are selected to construct the first macro variable , which is expressed as:

[0075] ;

[0076] Wherein, represents the weight parameter of the change in frequency of the receiving-end power grid when the first macro variable tends to the target position along the manifold. The larger is, the larger the proportion of in the manifold. The manifold constraint of the first macro variable will cause the DC capacitor of the FHMMC to release more energy to provide greater virtual inertia support.

[0077] Since the macro variable satisfies , the control law of the virtual inertia time constant is obtained, which is expressed as:

[0078] ;

[0079] Wherein, T represents the cooperative motion coefficient, represents the rate of change of frequency of the receiving-end power grid, represents the rate of change of DC voltage of the DC transmission line. Under the control law of the virtual inertia time constant , the DC capacitor energy storage adapts to the frequency deviation of the receiving-end power grid to participate in the inertia response, and the receiving-end power grid operates from the initial state to the manifold , and operates stably along the manifold to reach the stable state.

[0080] Combined with the inertial response of the change in the DC voltage of the DC transmission line to the change in the frequency of the receiving-end power grid, a coordinated control law for the DC voltage droop coefficient is obtained, expressed as:

[0081] ;

[0082] where represents the coordinated control law of the DC voltage droop coefficient.

[0083] It can be seen from observing the above formula that the first part of the numerator of the coordinated control law of the DC voltage droop coefficient is related to and its rate of change, indicating that the DC capacitor can adapt to the changes in the frequency of the receiving-end power grid and its rate of change. At the initial stage of the disturbance of the frequency of the receiving-end power grid, the rate of change of frequency and the rate of change of DC voltage are large, rapidly increases, causing the DC capacitor to quickly release energy to provide greater inertia support. The second part of the numerator of the control law is related to the rate of change of the DC voltage, indicating that the energy storage regulation of the DC capacitor can adapt to the change in the rate of change of the DC voltage. As the DC capacitor quickly releases energy storage for inertia support, the DC voltage decreases rapidly, and the rate of change of the DC capacitor voltage increases, gradually decreases, which helps to provide damping for the component of over-regulation to avoid overshoot of the DC voltage during the inertial response process. At the same time, it can provide a damping component for optimizing the dynamic recovery process and avoiding secondary frequency disturbances caused by active power charging of the capacitor during the process of restoring the DC capacitor voltage after inertia support.

[0084] Step 3: After controlling the DC voltage in the DC transmission line through the coordinated control law of the DC voltage droop coefficient, perform a second-layer coordinated control on the active power of each wind turbine, including: selecting the change in the DC current command value, the change in the DC voltage of the DC transmission line, and the active power of the wind turbine to construct a macro variable to obtain the active power of the current wind turbine.

[0085] The wind farm adaptively adjusts the fast frequency modulation coefficient of the wind turbine based on coordinated control to provide coordinated inertia support, which can damp the change in the DC capacitor energy storage and quickly restore the DC voltage of the system. Based on this, considering the DC voltage constraint of the DC capacitor, select the change in the DC current command value, the change in the DC voltage of the DC transmission line, and the active power of the wind farm to construct a second macro variable

[0086] ;

[0087] where represents the second macro variable Change in DC current command value of DC transmission line when approaching the target position along the manifold Adjustment weight for directional displacement change, Represents the second macro variable DC voltage change of DC transmission line when approaching the target position along the manifold Adjustment weight for directional displacement change, Represents the active power of the wind farm. Selecting a smaller and Can make the active power of the wind farm larger, which is beneficial for the wind turbines to participate in the primary frequency regulation of the system and assist in the DC voltage recovery.

[0088] Since the macro variable Satisfies , the control law of the active power of the wind farm is obtained, expressed as;

[0089] ;

[0090] Wherein, Represents the DC voltage change rate of the DC transmission line, Represents the DC current command value change rate of the DC transmission line, T represents the cooperative motion coefficient, Represents the change rate of the active power of the wind farm.

[0091] Observing the above formula, it can be seen that the control law of the active power of the wind farm is related to , . On the one hand, it shows that the active power provided by the wind farm can adapt to the change of the DC capacitor voltage and its change rate; on the other hand, the wind farm senses the change of the receiving-end grid frequency through the change of the DC voltage. In the initial stage of the receiving-end grid frequency disturbance, the DC capacitor voltage change rate and the DC current change rate are relatively large, which rapidly increases to make the wind farm quickly release the energy reserved by the pitch and provide greater active energy support.

[0092] According to the control law of the active power of the wind farm, the active power of the current wind turbine is obtained.

[0093] Step 4: Input the active power of the current wind turbine into the pre-constructed control optimization model to obtain the fast frequency modulation coefficient of the wind turbine to control the active power of each wind turbine.

[0094] Wherein, the control optimization model includes an objective function and constraint conditions. The objective function takes the minimum change in the pitch angle of the wind turbine and the minimum change in the frequency of the receiving-end grid as the optimization objectives, and the constraint conditions include the pitch angle constraint of the wind turbine and the active power constraint of the wind turbine.

[0095] The objective function is expressed as:

[0096] ;

[0097] wherein, represents minimizing, represents the weight parameter of the pitch angle change of the wind turbine, represents the pitch angle change of the wind turbine, represents the weight parameter of the frequency change of the receiving-end power grid, f represents the actual frequency of the receiving-end power grid, f ref represents the frequency reference value of the receiving-end power grid.

[0098] The pitch angle constraint of the wind turbine and the active power constraint of the wind turbine are respectively expressed as:

[0099] ;

[0100] wherein, respectively represent the pitch angle lower limit and upper limit of the wind turbine, respectively represent the lower limit and upper limit of the active power of the wind turbine.

[0101] Based on the objective function and the constraint conditions, the control optimization model outputs the fast frequency modulation coefficient of the wind turbine to control the orderly output of active power of each wind turbine. Specifically, the control optimization model performs rolling solution on the output active power for a future period of time, and the solution result of each round is used as the input for the solution of the next round of the control optimization model, so as to realize the orderly release of active power by each wind turbine in the wind farm to support the DC voltage recovery and the frequency disturbance of the receiving-end power grid.

[0102] Embodiment 2

[0103] Based on Embodiment 1, a simulation experiment is carried out by applying the scenario of the wind farm connected to the grid through LCC-FHMMC as shown in Figure 4 .

[0104] In this embodiment, a model including a wind farm connected to the DC grid through LCC-FHMMC as shown in Figure 4 is built in MATLAB / Simulink. In the model, the wind farm is equivalent to a single wind turbine by using the equivalent modeling method of the wind turbine according to the wind speed, and the input wind speed is 12 m / s. It is set that the active power load of the receiving-end power grid increases by 0.4 p.u. at t = 5.0 s, and the receiving-end power grid is compared in the case of no additional control response in the wind farm connected to the grid system through LCC-FHMMC, and only FHMMC adopts additional The response dynamic characteristics under droop control (single - layer coordinated control), the wind farm, and the FHMMC using the control method described in Embodiment 1 (double - layer coordinated control). In the simulation, in the FHMMC coordinated control, T1 = 0.1s, T2 = 0.02s, , , .

[0105] As Figures 5 - 7 shown, the curves of the receiving - end grid frequency, DC line voltage, and DC line transmission power under the action of three control strategies are compared. Without additional control, the DC line transmission power remains unchanged, and the receiving - end grid frequency drops to the lowest point of 49.829Hz, indicating that it cannot sense the change of the receiving - end grid frequency and does not provide active energy support. When using FHMMC control (single - layer coordinated control) and the control method of this Embodiment 1 (double - layer coordinated control), the DC voltage releases energy to provide inertia support, making the lowest point of the receiving - end grid frequency rise to 49.858Hz, indicating that the additional droop control in the FHMMC can make the wind farm sense the receiving - end grid frequency drop through the DC voltage change, thereby effectively improving the inertia support ability of the wind power grid - connected system via LCC - FHMMC. Under the action of the control method of Embodiment 1, the receiving - end grid frequency has a better frequency recovery dynamic process.

[0106] As Figure 8 and Figure 9 shown, the pitch angles of the wind turbines and the active power curves of the doubly - fed induction generator (DFIG) - based wind turbines under no additional control and double - layer coordinated control are compared. Without additional control, the pitch angle of the wind turbine remains unchanged, and the active power reserve capacity cannot be released, and the active power also remains unchanged, indicating that it cannot provide active energy support for the primary frequency regulation of the receiving - end grid. When using double - layer coordinated control, as Figure 10 shown, when the wind turbine senses the frequency change of the receiving - end grid through the fast frequency modulation coefficient , the additional frequency modulation control and pitch angle control of the wind turbine cause the wind turbine to adjust the pitch angle to decrease, release the active power reserve capacity, increase the active power of the wind turbine, and participate in the primary frequency regulation of the power system.

[0107] As Figure 11 shown, by adjusting the fast frequency modulation coefficient , the active power of the wind turbine is approximately the same as the active power command value of the second - layer coordinated control law.

[0108] Embodiment 3

[0109] This embodiment provides an active support control device for a wind farm grid - connected via flexible DC transmission, including:

[0110] A model acquisition module, configured to acquire a pre - constructed frequency modulation control model including a wind farm, a DC transmission line, and a receiving - end grid, wherein the wind farm includes a plurality of wind turbines;

[0111] The first control module is used to perform the first - layer coordinated control on the DC voltage in the HVDC transmission line based on the frequency - modulation control model, including: determining the inertial response of the change in the DC voltage of the HVDC transmission line to the change in the frequency of the receiving - end power grid, and constructing a coordinated control law for the DC voltage droop coefficient according to the inertial response to control the DC voltage in the HVDC transmission line;

[0112] The second control module is used to perform the second - layer coordinated control on the active power of each wind turbine after controlling the DC voltage in the HVDC transmission line through the coordinated control law of the DC voltage droop coefficient, including: selecting the change in the DC current command value, the change in the DC voltage of the HVDC transmission line, and the active power of the wind turbine to construct a macro - variable, and obtaining the active power of the current wind turbine;

[0113] The model optimization module is used to input the active power of the current wind turbine into a pre - constructed control optimization model to obtain the fast frequency - modulation coefficient of the wind turbine, so as to control the active power of each wind turbine;

[0114] Wherein, the control optimization model includes an objective function and constraint conditions. The objective function takes the minimum change in the pitch angle of the wind turbine and the minimum change in the frequency of the receiving - end power grid as the optimization objectives, and the constraint conditions include the pitch - angle constraint of the wind turbine and the active - power constraint of the wind turbine.

[0115] Embodiment 4

[0116] This embodiment provides an active - support control system for a wind farm connected to the grid through flexible HVDC transmission, including a processor and a storage medium; the storage medium is used to store instructions;

[0117] The processor is used to operate according to the instructions to execute the steps of the active - support control method for a wind farm connected to the grid through flexible HVDC transmission described in Embodiment 1.

[0118] Embodiment 5

[0119] This embodiment provides a computer - readable storage medium, on which a computer program is stored. When the program is executed by a processor, it implements the steps of the active - support control method for a wind farm connected to the grid through flexible HVDC transmission described in Embodiment 1.

[0120] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present 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 memories, CD - ROMs, optical memories, etc.) containing computer - usable program codes.

[0121] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0122] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0123] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0124] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An active support control method for a wind farm to be connected to the grid via flexible DC transmission, characterized in that, including: Obtain a pre - constructed frequency - modulation control model including a wind farm, a DC transmission line, and a receiving - end power grid, where the wind farm includes a number of wind turbines; Based on the frequency - modulation control model, perform the first - layer collaborative control on the DC voltage in the DC transmission line, including: determining the inertial response of the change in DC voltage of the DC transmission line to the change in frequency of the receiving - end power grid, and constructing a collaborative control law for the DC voltage droop coefficient according to the inertial response to control the DC voltage in the DC transmission line; After controlling the DC voltage in the DC transmission line through the collaborative control law of the DC voltage droop coefficient, perform the second - layer collaborative control on the active power of each wind turbine, including: selecting the change in the DC current command value, the change in DC voltage of the DC transmission line, and the active power of the wind farm to construct a macro - variable, and obtaining the active power of the current wind turbine; Input the active power of the current wind turbine into a pre - constructed control optimization model to obtain the fast frequency - modulation coefficient of the wind turbine, so as to control the active power of each wind turbine; Wherein, the control optimization model includes an objective function and constraint conditions. The objective function takes the minimum change in the pitch angle of the wind turbine and the minimum change in the frequency of the receiving - end power grid as optimization objectives, and the constraint conditions include the pitch - angle constraint of the wind turbine and the active - power constraint of the wind turbine.

2. The active support control method for a wind farm to be connected to the grid via flexible DC transmission according to claim 1, characterized in that: The DC transmission line includes a receiving - end converter and a sending - end converter connected in series; The input end of the receiving - end converter is connected to the wind farm, and is used to control the input active power of the DC transmission line to dynamically track the active - power command value, while keeping the current of the DC transmission line at a set value; The output end of the sending - end converter is connected to the receiving - end power grid, and is used to control the output active power of the DC transmission line to dynamically track the input active power of the DC transmission line, while keeping the voltage of the DC transmission line at a set value.

3. The active support control method for a wind farm to be connected to the grid through flexible DC transmission according to claim 1, characterized in that: Determining the inertial response of the change in DC voltage of the DC transmission line to the change in frequency of the receiving - end power grid includes: The inertial response of the change in DC voltage of the DC transmission line to the change in frequency of the receiving - end power grid is expressed as: ； Among them, represents the change in DC voltage of the DC transmission line, represents the change in frequency of the receiving-end power grid, represents the virtual inertia time constant, represents the DC voltage of the DC transmission line under steady-state operation, represents the DC voltage droop coefficient, represents the change in active power of the wind farm, represents the change in the output active power of the DC transmission line, C represents the capacitance of the DC transmission line, and s represents the complex frequency of the transfer function.

4. The active support control method for a wind farm to be interconnected to the grid through flexible DC transmission according to claim 3, characterized in that: Constructing the collaborative control law of the DC voltage droop coefficient includes: Based on the coordinated control theory, the frequency change of the receiving-end power grid is selected and the virtual inertia time constant to construct the first macro variable , which is expressed as: ； Among them, represents the first macro variable The frequency change of the receiving-end power grid when approaching the target position along the manifold is the weight parameter; Due to the macro variable satisfies , the control law of the virtual inertia time constant is obtained and expressed as: ； Among them, T represents the coefficient of coordinated motion, represents the rate of change of the frequency of the receiving-end power grid, represents the rate of change of the DC voltage of the DC transmission line; Combining the inertial response of the change in DC voltage of the DC transmission line to the change in frequency of the receiving - end power grid, and obtaining the collaborative control law of the DC voltage droop coefficient, which is expressed as: ； Among them, represents the cooperative control law of the DC voltage droop coefficient.

5. The active support control method for a wind farm to be connected to the grid via flexible DC transmission according to claim 1, wherein: Selecting the change in the DC current command value, the change in DC voltage of the DC transmission line, and the active power of the wind farm to construct a macro - variable and obtaining the active power of the current wind farm includes: Select the change in the DC current command value of the DC transmission line, the change in the DC voltage, and the active power of the wind farm to construct a second macro variable , expressed as: ； Among them, represents the second macro variable The variation of the DC current command value of the HVDC transmission line when approaching the target position along the manifold The adjustment weight for the change in the directional displacement represents the second macro variable The change in the DC voltage of the HVDC transmission line when approaching the target position along the manifold The adjustment weight for the change in the directional displacement represents the active power of the wind farm; Due to the macro variable satisfies , the control law of the active power of the wind farm is obtained and expressed as; ； Among them, represents the rate of change of the DC voltage of the DC transmission line, represents the rate of change of the DC current command value of the DC transmission line, T represents the cooperative motion coefficient, represents the rate of change of the active power of the wind farm; According to the active power of the wind farm the active power of the current wind turbine is obtained according to the control law 6. The active support control method for a wind farm to be connected to the grid via flexible DC transmission according to claim 1, characterized in that: Inputting the active power of the current wind turbine into a pre - constructed control optimization model to obtain the fast frequency - modulation coefficient of the wind turbine includes: The objective function is expressed as: ； Among them, represents obtaining the minimum value, represents the weight parameter of the pitch angle change of the wind turbine, represents the pitch angle change of the wind turbine, represents the weight parameter of the frequency change of the receiving-end power grid, f represents the actual frequency of the receiving-end power grid, f ref represents the frequency reference value of the receiving-end power grid; The pitch - angle constraint of the wind turbine and the active - power constraint of the wind turbine are respectively expressed as: ； Among them, respectively represent the lower and upper limits of the pitch angle of the wind turbine,[ and the lower and upper limits of the active power of the wind turbine; respectively represent the lower and upper limits of the active power of the wind turbine. Based on the objective function and constraint conditions, control the optimization model to output the fast frequency modulation coefficient of the wind turbine generator set , so as to control the orderly output of active power of each wind turbine generator set.

7. An active support control device for a wind farm to be connected to the grid through flexible DC transmission, characterized in that, including: A model acquisition module, configured to obtain a pre - constructed frequency - modulation control model including a wind farm, a DC transmission line, and a receiving - end power grid, where the wind farm includes a number of wind turbines; The first control module is used to perform the first-layer coordinated control on the DC voltage in the DC transmission line based on the frequency modulation control model, including: determining the inertial response of the change in the DC voltage of the DC transmission line to the change in the frequency of the receiving-end power grid, and constructing a coordinated control law for the DC voltage droop coefficient according to the inertial response to control the DC voltage in the DC transmission line; The second control module is used to perform the second-layer coordinated control on the active power of each wind turbine after controlling the DC voltage in the DC transmission line by the coordinated control law of the DC voltage droop coefficient, including: selecting the change in the DC current command value, the change in the DC voltage of the DC transmission line, and the active power of the wind turbine to construct a macro variable, and obtaining the active power of the current wind turbine; The model optimization module is used to input the active power of the current wind turbine into a pre-constructed control optimization model to obtain the fast frequency modulation coefficient of the wind turbine to control the active power of each wind turbine; Wherein, the control optimization model includes an objective function and constraint conditions. The objective function takes the minimum change in the pitch angle of the wind turbine and the minimum change in the frequency of the receiving-end power grid as optimization objectives, and the constraint conditions include the pitch angle constraint of the wind turbine and the active power constraint of the wind turbine.

8. An active support control system for a wind farm to be connected to the grid via flexible DC transmission, characterized in that It includes a processor and a storage medium; the storage medium is used to store instructions; The processor is used to operate according to the instructions to execute the steps of the active support control method for the grid connection of the wind farm through flexible DC transmission according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, the steps of the active support control method for the grid connection of the wind farm through flexible DC transmission according to any one of claims 1 to 6 are realized.

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