VM-DPC-Based Impedance Modeling Method, System and Medium for Doubly Fed Wind Turbines

Abstract

The present invention relates to the technical field of wind power, and specifically provides a method, system and medium for impedance modeling of a doubly-fed wind turbine based on VM-DPC, including: constructing a doubly-fed wind turbine system using VM-DPC based on an induction generator, an RSC and a GSC; constructing a small-signal model of the rotor speed by combining mechanical change information and electromagnetic change information; establishing an RSC part impedance model based on the small-signal model of the stator power combined with the disturbance of the rotor voltage control command value and the small-signal model of the stator and rotor voltages; establishing a GSC part impedance model based on the small-signal model of the GSC output power combined with the disturbance of the GSC voltage control command value and the small-signal model of the DC voltage; comprehensively constructing an impedance model of a doubly-fed wind turbine based on VM-DPC under small disturbances by combining the small-signal model of the rotor speed, the RSC part impedance model and the GSC part impedance model. Analyze the stability and efficiency of the doubly-fed wind turbine to enhance the reliability of wind power grid connection.

Description

Technical Field

[0001] The present invention belongs to the technical field of wind power, and particularly relates to a method, system and medium for impedance modeling of a doubly-fed wind turbine based on VM-DPC. Background Art

[0002] A doubly-fed wind turbine is a common wind power generation device. By analyzing the impedance characteristics of the doubly-fed wind turbine, the stability of wind power grid connection can be effectively evaluated. Since the dynamic characteristics of the doubly-fed wind turbine are mainly dominated by its control strategy, different control strategies will significantly affect its impedance characteristics. The commonly used control strategies mainly include voltage-oriented vector control and direct power control.

[0003] The existing impedance modeling and stability analysis technologies of doubly-fed wind turbines mainly focus on voltage-oriented vector control; there is only a small amount of research on impedance analysis of direct power control, mainly for the scenario where direct power control is applied to the converter.

[0004] Therefore, there is currently no detailed impedance model of a doubly-fed wind turbine based on direct power control, and it is impossible to evaluate and analyze the impedance characteristics and small disturbance resistance performance of direct power control. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the present invention provides a method, system and medium for impedance modeling of a doubly-fed wind turbine based on VM-DPC to solve the above technical problems.

[0006] In a first aspect, the present invention provides a method for impedance modeling of a doubly-fed wind turbine based on VM-DPC, including:

[0007] Construct a doubly-fed wind turbine system using VM-DPC based on an induction generator, an RSC, and a GSC, and obtain the electrical parameters, operating state variables, and mechanical parameters of the generator based on the doubly-fed wind turbine system;

[0008] In αβ coordinate system, construct an aerodynamic model based on the mechanical parameters and operating state variables of the generator and obtain the mechanical change information of the mechanical torque under small disturbances, obtain the electromagnetic change information of the electromagnetic torque under small disturbances based on the electrical parameters and operating state variables of the generator, and construct a small-signal model of the rotor speed by combining the mechanical change information and the electromagnetic change information;

[0009] In αβUnder the [coordinate system], the dynamic relationship between the stator power of the generator and the stator voltage and current is obtained based on the electrical parameters and operating state variables of the generator. The small-signal model of the stator power is obtained by linearizing the stator power. The small-signal model of the stator and rotor voltages is constructed by combining the small-signal model of the rotor speed with the stator voltage and the rotor voltage. The partial impedance model of the RSC is established based on the disturbance of the rotor voltage control command value, combined with the small-signal model of the stator power and the small-signal model of the stator and rotor voltages.

[0010] Under the αβ coordinate system, the dynamic relationship between the output power of the GSC and the stator voltage and the GSC current is obtained based on the electrical parameters and operating state variables. The small-signal model of the GSC output power is obtained by linearization. The DC voltage equation is constructed based on the AC voltages and currents of the RSC and the GSC, and the small-signal model of the DC voltage is obtained by linearization. The partial impedance model of the GSC is established based on the disturbance of the GSC voltage control command value, combined with the small-signal model of the GSC output power and the small-signal model of the DC voltage.

[0011] The impedance model of the doubly-fed wind turbine based on VM-DPC under small disturbances is constructed by integrating the small-signal model of the rotor speed, the partial impedance model of the RSC, and the partial impedance model of the GSC.

[0012] In an optional embodiment, the doubly-fed wind turbine system based on VM-DPC includes a mechanical subsystem and an electrical subsystem. The impedance model of the doubly-fed wind turbine based on VM-DPC is specifically:

[0013]

[0014]

[0015] Where The small disturbance of the stator voltage The small disturbance of the grid-connected point current The conjugate of the small disturbance of the stator voltage The conjugate of the small disturbance of the grid-connected point current θ = ω s t + φ s , where φ s is the initial phase angle of the fundamental frequency voltage, is the impedance of the doubly-fed wind turbine based on VM-DPC, , , , , are the sub-impedances generated during the derivation of the doubly-fed wind turbine impedance, expressed as:

[0016]

[0017]

[0018]

[0019]

[0020]

[0021] Among them, is the impedance related to the stator voltage of the RSC, is the impedance related to the rotor speed of the RSC, is the impedance related to the rotor voltage and rotor current, is the impedance related to the rotor voltage and rotor speed, is a part of the mechanical subsystem impedance, is the impedance related to the stator voltage and rotor current, is the impedance related to the RSC and stator current, is another part of the mechanical subsystem impedance, is the impedance related to the rotor voltage and stator current, is the impedance related to the stator voltage and stator current, is the impedance related to the GSC and stator voltage, is the impedance related to the GSC and GSC current, is the impedance related to the GSC and DC voltage, is the impedance related to the DC side and GSC voltage, is the impedance related to the DC side and GSC current, is the impedance related to the DC side and rotor voltage, is the impedance related to the DC side and rotor current, is a two-dimensional unit diagonal matrix, is the impedance related to the power grid.

[0022] In an optional embodiment, the small-signal model of the rotor speed specifically includes:

[0023] Construct an aerodynamic model as follows:

[0024]

[0025] Among them, is the mechanical torque, ρ is the air density, r is the blade length, is the average wind speed, is the torque coefficient,λ = r / represents the tip speed ratio, where is the mechanical angular velocity;

[0026] For the assumption of constant wind speed, a small perturbation analysis is performed on the aerodynamic model to obtain the linear relationship between the small perturbation of mechanical torque and the small perturbation of mechanical angular velocity;

[0027] Calculate the electromagnetic torque based on the stator current and rotor current, obtain the correlation formula between the electromagnetic torque and the stator current and rotor current, and linearize the correlation formula to obtain the electromagnetic change information of the electromagnetic torque under small perturbations;

[0028] Establish a two-mass block motion equation of the drive system for describing the dynamic coupling relationship between the mechanical and electromagnetic parts, and perform small-signal linearization on the motion equation;

[0029] Integrate the linear relationship between the small perturbation of mechanical torque and the small perturbation of mechanical angular velocity, the electromagnetic change information of the electromagnetic torque under small perturbations, and the motion equation after small-signal linearization to obtain the small-signal model of the rotor speed, specifically:

[0030]

[0031] where, is the small perturbation of the rotor speed, is the small perturbation of the stator current, is the conjugate of the small perturbation of the stator current, is the small perturbation of the rotor current, is the conjugate of the small perturbation of the rotor current.

[0032] In an alternative embodiment, before establishing the impedance model of the RSC part, establish the RSC control impedance model based on the rotor voltage control command value perturbation combined with the small-signal model of the stator power, specifically including:

[0033] Linearize the active power loop and reactive power loop of the RSC control respectively to obtain the α axis component and β axis component expressions of the rotor voltage control command value perturbation, and represent the rotor voltage control command value perturbation in the form of a complex vector based on the α axis component and β axis component expressions;

[0034] Based on the doubly-fed wind turbine system, obtain the active power and reactive power of the stator in the αβ coordinate system in combination with electrical parameters and operating state variables, and linearize the active power and reactive power to obtain the small-signal model of the stator power;

[0035] A small-signal model of the rotor voltage control command value disturbance combined with the stator power is used to establish an RSC control impedance model in a two-dimensional complex vector space, which is specifically as follows:

[0036]

[0037] Among them, is a small disturbance of the rotor voltage, is the conjugate of the small disturbance of the rotor voltage, is a small disturbance of the stator voltage, is the conjugate of the small disturbance of the stator voltage, is a small disturbance of the stator current, is the conjugate of the small disturbance of the stator current, is a small disturbance of the rotor speed.

[0038] In an optional implementation manner, an RSC partial impedance model between the stator voltage and the stator current is obtained based on the RSC control impedance model, which specifically includes:

[0039] Based on the main circuit of the induction generator, the stator voltage equation and the rotor voltage equation are obtained, and after linearizing the stator voltage equation and the rotor voltage equation, a small-signal model of the stator-rotor voltage is constructed;

[0040] Substitute the small-signal model of the rotor speed into the RSC control impedance model, and based on the small-signal model of the stator-rotor voltage, eliminate the rotor voltage and current disturbances to obtain the RSC partial impedance model between the stator voltage and the stator current:

[0041] .

[0042] In an optional implementation manner, before establishing the GSC partial impedance model, a GSC control impedance model of the small-signal model of the GSC voltage control command value disturbance combined with the GSC output power is established, which specifically includes:

[0043] Linearize the active power loop and the reactive power loop controlled by the GSC respectively to obtain the α axis component and β axis component expressions of the GSC voltage control command value disturbance, and represent the GSC voltage control command value disturbance in the form of a complex vector based on the α axis component and β axis component expressions;

[0044] Based on the doubly-fed wind turbine system, combine the electrical parameters and the operating state variables to obtain the αβ GSC output active power and reactive power in the coordinate system, and linearize the active power and the reactive power to obtain a small-signal model of the GSC output power;

[0045] Based on the small-signal model of the GSC voltage control command value perturbation combined with the GSC output power represented in the complex vector form, a GSC control impedance model in the two-dimensional complex vector space is established as follows:

[0046]

[0047] Among them, is the small perturbation of the GSC voltage, is the conjugate of the small perturbation of the GSC voltage, is the small perturbation of the stator voltage, is the conjugate of the small perturbation of the stator voltage, is the small perturbation of the GSC current, is the conjugate of the small perturbation of the GSC current, is the small perturbation of the DC bus voltage.

[0048] In an alternative embodiment, before establishing the GSC partial impedance model with the DC bus connecting the GSC and the RSC, obtaining the frequency-domain model of the DC voltage perturbation is also included, specifically including:

[0049] According to the equality of the instantaneous power on the AC side and the DC side of the converter, the DC bus voltage equation is obtained based on the AC voltage and current of the GSC and the RSC;

[0050] Linearize the DC bus voltage equation at the steady-state operation trajectory to obtain αβ The frequency-domain model of the DC voltage perturbation represented by the complex vector in the coordinate system, specifically including:

[0051] ;

[0052] Based on the frequency-domain model of the DC voltage perturbation, the interaction between the DC side and the AC side is obtained, and the GSC partial impedance model is constructed based on the GSC control impedance model combined with the frequency-domain model of the DC voltage perturbation.

[0053] In an alternative embodiment, based on the GSC control impedance model combined with the frequency-domain model of the DC voltage perturbation, the GSC partial impedance model between the stator voltage and the stator current and the GSC current is obtained, specifically including:

[0054] Based on the filter circuit, the relationship equation between the GSC voltage, the GSC current, and the stator voltage is obtained, and the relationship equation is linearized to obtain the transfer relationship between the GSC voltage perturbation and the stator voltage perturbation in the two-dimensional complex vector space;

[0055] Substitute the transfer relationship and the frequency-domain model of the DC voltage perturbation into the GSC control impedance model to obtain the GSC partial impedance model between the stator voltage and the stator current and the GSC current:

[0056] 。

[0057] In a second aspect, the present invention provides a doubly-fed wind turbine impedance modeling system based on VM-DPC. When the system is implemented, the above-mentioned method for modeling the impedance of a doubly-fed wind turbine based on VM-DPC is executed. The system includes:

[0058] A system construction module constructs a doubly-fed wind turbine system using VM-DPC based on an induction generator, an RSC, and a GSC, and obtains the electrical parameters, operating state variables, and mechanical parameters of the generator based on the doubly-fed wind turbine system;

[0059] A small-signal model construction module for rotor speed constructs an aerodynamic model based on the mechanical parameters and operating state variables of the generator and obtains the mechanical change information of the mechanical torque under small disturbances in the αβ coordinate system. The electromagnetic change information of the electromagnetic torque under small disturbances is obtained based on the electrical parameters and operating state variables of the generator. A small-signal model of the rotor speed is constructed by combining the mechanical change information and the electromagnetic change information;

[0060] An RSC partial impedance model construction module obtains the dynamic relationship between the stator power of the generator and the stator voltage and current based on the electrical parameters and operating state variables of the generator in the αβ coordinate system, linearizes the stator power to obtain a small-signal model of the stator power, and constructs a small-signal model of the stator-rotor voltage by combining the small-signal model of the rotor speed with the stator voltage and the rotor voltage; An RSC partial impedance model is established based on the rotor voltage control command value disturbance, in combination with the small-signal model of the stator power and the small-signal model of the stator-rotor voltage;

[0061] A GSC partial impedance model construction module obtains the dynamic relationship between the output power of the GSC and the stator voltage and the GSC current based on the electrical parameters and operating state variables in the αβ coordinate system, obtains a small-signal model of the GSC output power through linearization, constructs a DC voltage equation based on the AC voltage and current of the RSC and the GSC, and obtains a small-signal model of the DC voltage through linearization; A GSC partial impedance model is established based on the GSC voltage control command value disturbance, in combination with the small-signal model of the GSC output power and the small-signal model of the DC voltage;

[0062] A doubly-fed wind turbine impedance model construction module comprehensively constructs a doubly-fed wind turbine impedance model based on VM-DPC under small disturbances by combining the small-signal model of the rotor speed, the RSC partial impedance model, and the GSC partial impedance model.

[0063] In a third aspect, a computer-readable storage medium is provided. Instructions are stored in the computer-readable storage medium. When it runs on a computer, the computer is made to execute the methods described in the above aspects.

[0064] The beneficial effects of the present invention are as follows. The impedance modeling method, system and medium of the doubly-fed wind turbine based on VM-DPC provided by the present invention start from constructing a doubly-fed wind turbine system using VM-DPC and obtaining relevant parameters, to respectively establishing a small-signal model of the rotor speed, impedance models of the RSC and GSC parts, and finally comprehensively constructing an impedance model of the doubly-fed wind turbine based on VM-DPC, which can accurately describe the dynamic characteristics of the doubly-fed wind turbine under small disturbances, enabling us to have a deeper understanding of the complex internal electrical and mechanical interactions, thereby providing a solid theoretical basis for optimizing the wind turbine control strategy, helping to improve the operation stability and efficiency of the doubly-fed wind turbine, and enhancing the reliability of wind power grid connection.

[0065] In addition, the design principle of the present invention is reliable and the structure is simple, having a very broad application prospect. Brief Description of the Drawings

[0066] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0067] Figure 1 is a schematic flowchart of the impedance modeling method of the doubly-fed wind turbine based on VM-DPC according to an embodiment of the present invention.

[0068] Figure 2 is a structure diagram of the doubly-fed wind turbine based on VM-DPC according to an embodiment of the present invention.

[0069] Figure 3 is the transfer relationship of small disturbances inside the doubly-fed wind turbine based on VM-DPC according to an embodiment of the present invention.

[0070] Figure 4 is the comparison result of four impedance models according to an embodiment of the present invention.

[0071] Figure 5(a) is the VM-DPC control parameter k p,rsc Eigenvalue trajectory when decreasing from 378 to 31.5.

[0072] Figure 5(b) is the VM-DPC control parameter k p,gsc Eigenvalue trajectory when decreasing from 3720 to 310.

[0073] Figure 5(c) is the VM-DPC control parameter ki,rsc Eigenvalue trajectory when increasing from 2900 to 50000.

[0074] Figure 5(d) shows the VM-DPC control parameters of an embodiment of the present invention k i,gsc Eigenvalue trajectory when increasing from 9800 to 117600.

[0075] Figure 6 is the comparison result of the theoretical derivation and frequency sweep measurement of the comprehensive impedance of a doubly-fed wind turbine in an embodiment of the present invention.

[0076] Figure 7(a) shows the change in an embodiment of the present invention k p,rsc Waveform diagram of the simulation result.

[0077] Figure 7(b) shows the change in an embodiment of the present invention k p,rsc FFT of the simulation result.

[0078] Figure 8(a) shows the change in an embodiment of the present invention k i,rsc Waveform diagram of the simulation result.

[0079] Figure 8(b) shows the change in an embodiment of the present invention k i,rsc FFT of the simulation result.

[0080] Figure 9 is a schematic block diagram of an impedance modeling system for a doubly-fed wind turbine based on VM-DPC in an embodiment of the present invention. Detailed implementation manners

[0081] In order to enable those skilled in the art of the present technology to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0082] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention.

[0083] The following explains the key terms that appear in the present invention.

[0084] Linearization is a mathematical method commonly used in analyzing complex systems. For a non-linear function , near a certain operating point , it is approximately represented as a linear function. Usually, the Taylor series expansion is adopted, and the higher-order infinitesimal terms are ignored to obtain the linearized expression , where is at the derivative.

[0085] The impedance modeling method of the doubly-fed wind turbine based on VM-DPC provided by the embodiment of the present invention is executed by a computer device. Correspondingly, the impedance modeling system of the doubly-fed wind turbine based on VM-DPC runs in the computer device.

[0086] Figure 1 is a schematic flowchart of the impedance modeling method of the doubly-fed wind turbine based on VM-DPC according to an embodiment of the present invention. Among them, Figure 1 The execution subject can be an impedance modeling system of a doubly-fed wind turbine based on VM-DPC. According to different requirements, the order of the steps in this flowchart can be changed, and some can be omitted.

[0087] As Figure 1 shown, the method includes:

[0088] S1, construct a doubly-fed wind turbine system using VM-DPC based on an induction generator, RSC, and GSC, and obtain the electrical parameters, operating state variables, and mechanical parameters of the generator based on the doubly-fed wind turbine system;

[0089] During the system construction process, reasonably configure the connection methods of each component to ensure the smooth interaction of power transmission and control signals. Then, by installing various sensors on the generator, such as voltage sensors, current sensors, speed sensors, torque sensors, etc., to monitor and obtain the electrical parameters of the generator (such as stator voltage, rotor voltage, stator current, rotor current, etc.), operating state variables (such as speed, power factor, power, etc.), and mechanical parameters (such as torque, moment of inertia of the shaft, etc.) in real time.

[0090] The accurately obtained electrical parameters, operating state variables, and mechanical parameters can comprehensively understand the initial state of the doubly-fed wind turbine system, provide the necessary data support for subsequent construction of various models and system performance analysis, and ensure that subsequent analysis and control decisions have a practical physical basis.

[0091] S2, at αβIn the coordinate system, an aerodynamic model is constructed based on the mechanical parameters and operating state variables of the generator to obtain the mechanical change information of the mechanical torque under small disturbances. The electromagnetic change information of the electromagnetic torque under small disturbances is obtained based on the electrical parameters and operating state variables of the generator. A small-signal model of the rotor speed is constructed by combining the mechanical change information and the electromagnetic change information.

[0092] Using the known mechanical parameters and operating state variables, an aerodynamic model is established according to the aerodynamic principle. This model can be a functional relationship between wind speed, rotor radius, pitch angle, etc. and the mechanical torque. By means of experiments or simulations, a small disturbance is applied to the system, and the change of the mechanical torque is observed and calculated to obtain the change information of the mechanical torque under small disturbances. For the electromagnetic torque, using the electrical parameters and operating state variables, according to the electromagnetic principle of the motor, the relationship between the electromagnetic torque and the stator current and rotor current is calculated, and the change information of the electromagnetic torque under small disturbances is obtained. Combining these two parts of information, with the small-signal analysis method, regarding the rotor speed as composed of a steady-state value and a small disturbance component, substituting into the relevant mechanical and electromagnetic torque equations, through linearization processing and the derivation of the system equations, a small-signal model of the rotor speed is finally constructed.

[0093] The constructed small-signal model of the rotor speed can accurately reflect the comprehensive influence of mechanical and electromagnetic factors on the speed, providing an important model basis for subsequent analysis of the stability and control performance of the wind turbine under dynamic conditions.

[0094] S3, in αβ In the coordinate system, the dynamic relationship between the stator power of the generator and the stator voltage and current is obtained based on the electrical parameters and operating state variables of the generator. The small-signal model of the stator power is obtained by linearizing the stator power. A small-signal model of the stator-rotor voltage is constructed by combining the small-signal model of the rotor speed with the stator voltage and the rotor voltage. Based on the disturbance of the rotor voltage control command value, a partial impedance model of the RSC is established by combining the small-signal model of the stator power and the small-signal model of the stator-rotor voltage.

[0095] Starting from the electrical parameters and operating state variables of the generator, based on the basic equations of the motor (such as the power equation), the dynamic relationship expression between the stator power and the stator voltage and current is derived. For the stator power, a linearization method is adopted. Usually, the Taylor series expansion can be used and the high-order terms are ignored, and the stator power is expressed as a combination of the steady-state value and the small-signal component, so as to obtain the small-signal model of the stator power. According to the small-signal model of the rotor speed, combined with the physical relationship and equations of the stator voltage and the rotor voltage, using circuit theory and motor equations, the stator and rotor voltage equations are linearized to obtain the small-signal models of the stator and rotor voltages. Finally, based on the disturbance of the rotor voltage control command value, combined with the small-signal models of the stator power and the stator and rotor voltages, the impedance model of the RSC part is established, and methods such as complex frequency domain analysis can be used to represent it as an impedance in complex form.

[0096] The impedance model of the RSC part can analyze the influence of the RSC on the stator power and the stator and rotor voltages, so as to evaluate the effectiveness of the RSC control strategy and the stability of the system under different operating conditions.

[0097] S4. In αβ coordinate system, based on the electrical parameters and operating state variables, obtain the dynamic relationship between the GSC output power and the stator voltage and the GSC current, and obtain the small-signal model of the GSC output power through linearization. Based on the AC voltages and currents of the RSC and the GSC, construct the DC voltage equation, and obtain the small-signal model of the DC voltage through linearization; based on the disturbance of the GSC voltage control command value, combined with the small-signal model of the GSC output power and the small-signal model of the DC voltage, establish the impedance model of the GSC part;

[0098] According to the electrical parameters and operating state variables, based on the power conversion and control principle of the converter, derive the dynamic relationship between the GSC output power and the stator voltage and the GSC current, and adopt a method similar to the linearization of the stator power for linearization to obtain its small-signal model. Through theoretical analysis and mathematical derivation on the GSC control loop, find the expression of the disturbance of the GSC voltage control command value. According to the principle that the instantaneous power on the AC side and the DC side of the converter is equal, express the DC voltage in terms of the AC voltages and currents of the GSC and the RSC, and obtain the small-signal model of the DC voltage through linearization. Combine the small-signal model of the GSC output power and the small-signal model of the DC voltage with the expression of the disturbance of the GSC voltage control command value, consider the control and circuit characteristics of the converter, and use control theory and circuit analysis methods to establish the impedance model of the GSC part. This model can be obtained through the linearization and frequency domain transformation of the relationship between power, voltage and current.

[0099] The GSC partial impedance model provides an important tool for studying the role of GSC in the system. It can be used to evaluate the impact of GSC control strategies on system stability, especially for the performance evaluation of DC voltage control and grid-side power control, which helps to optimize the control parameters of GSC and ensure the stability of the DC bus voltage and the stable transmission of grid-side power.

[0100] S5. Construct a doubly-fed wind turbine impedance model based on VM-DPC under small disturbances by integrating the small-signal model of rotor speed, the RSC partial impedance model, and the GSC partial impedance model.

[0101] Couple the key variables and equations in each model according to the physical connection and energy transfer relationship of the system. Through appropriate matrix operations, frequency-domain transformation, and solution of system equations, an overall doubly-fed wind turbine impedance model based on VM-DPC is established under the assumption of small disturbances.

[0102] The constructed doubly-fed wind turbine impedance model can comprehensively and systematically describe the electrical characteristics of the doubly-fed wind turbine under small disturbances, providing a unified theoretical model for system analysis, fault diagnosis, stability evaluation, and control strategy optimization of the doubly-fed wind turbine. It helps to study the stability boundary of the wind power system under different operating conditions, provides key theoretical support for improving the grid connection performance of the wind power system, reducing harmonic interference, enhancing the anti-interference ability of the system, and optimizing the overall performance, and promotes the efficient and stable operation of the doubly-fed wind turbine system in practical applications and the efficient utilization of wind power energy.

[0103] Optionally, as an embodiment of the present invention, the detailed topology of a doubly-fed induction generator (DFIG) based on voltage-modulated direct power control (VM-DPC) is as Figure 2 shown. Among them u s and u r are the stator and rotor voltages respectively, i s and i r are the stator and rotor currents respectively, u g and i g are the GSC voltage and current respectively, i t is the total current at the point of common coupling (PCC) of the DFIG, u dc is the DC bus voltage. In this application, bold variables representαβ Complex vectors in the coordinate system, for example, u s = u sα +j u sβ 。

[0104] By applying VM-DPC, the rotor-side converter (RSC) is responsible for modulating the stator power, while the grid-side converter (GSC) controls the DC voltage.

[0105] VM-DPC directly decouples and controls the converter output power based on a predefined voltage modulation variable in the stator αβ coordinate system, and then generates the converter voltage command value. For RSC control, since its control object is the stator power, it is necessary to derive the dynamic relationship between the stator power and the rotor voltage output by the RSC to construct the control equation of the VM-DPC of the RSC.

[0106] Optionally, as an embodiment of the present invention, the stator active P s and reactive Q s in αβ coordinate system can be written as:

[0107]

[0108] (1)

[0109] To eliminate the stator current in the stator power, the stator and rotor voltage equations of the DFIG main circuit are established in the αβ coordinate system, which are expressed as follows:

[0110] (2)

[0111] where ω m is the rotor speed, R s and R r are the stator and rotor resistances respectively. The stator flux linkage ψ s and the rotor flux linkage ψ r can be calculated from the stator and rotor currents as follows:

[0112] (3)

[0113] where Ls and L r are the stator and rotor inductances respectively, L m is the field inductance.

[0114] Therefore, by differentiating the stator power (1) and substituting (2) and (3), the control equation of VM-DPC for the RSC can be finally obtained:

[0115] (4)

[0116] where σ αβ = 1 - L s L r / L m L m is the leakage inductance coefficient of VM-DPC, ω s represents the grid fundamental angular frequency. The relationship between the rotor voltage and current angular frequencies ω r and ω m is ω r = ω s - ω m .

[0117] In the above formula, u rP and u rQ are respectively defined as the active control and reactive control voltage modulation variables of VM-DPC on the RSC side, and they have a non-linear relationship with the stator and rotor voltages. By defining the voltage modulation variables, an approximate linear relationship between them and the stator output power can be established, expressed as:

[0118] (5)

[0119] where k s = -2 σ αβ L m / 3 is the gain of VM-DPC for the RSC. In a large-capacity doubly-fed wind turbine system, R r is usually relatively small and has little impact on the control performance. Therefore, the compensation terms C rP andC rQ Can be ignored.

[0120] Therefore, for a given stator power reference value, by setting the decoupling terms k s ω r Q s and k s ω r P s , and then using PI modulation to control the active and reactive power to generate u rP and u rQ reference values. Finally, according to the definition of the voltage modulation variable in (4), the voltage modulation transformation equation (6) is deduced inversely, and the rotor voltage command value in the αβ coordinate system is calculated. The implementation of the above control principle of VM-DPC on the RSC side is as shown in the left blue box in Figure 1 .

[0121] (6).

[0122] Optionally, as an embodiment of the present invention, the outer control loop of the GSC uses PI modulation to maintain the DC bus voltage constant, while the inner control loop uses VM-DPC to control the converter output power according to the power reference value generated by the DC voltage outer loop. Therefore, the control equation of VM-DPC of the GSC is the dynamic relationship between the output power and the GSC voltage.

[0123] αβ The active power P g and reactive power Q g output by the GSC in the

[0124] (7)

[0125] At the same time, according to the GSC filter circuit, the relationship between the GSC voltage, the GSC current, and the stator voltage can be obtained as:

[0126] (8)

[0127] Wherein, R g and L g are the resistance and inductance of the GSC filter.

[0128] Referring to the derivation process of the RSC-side control equation, taking the differential of (7) and substituting (8) to eliminate the GSC current, the control equation of the VM-DPC of the GSC can be obtained:

[0129] (9).

[0130] Similarly, in (9), u gP and u gQ are the non-linear active power control and reactive power control voltage modulation variables of the VM-DPC on the GSC side, respectively. Moreover, the linear relationship between the GSC output power and the voltage modulation variables is:

[0131] (10)

[0132] where k g = 2 L g / 3 is the VM-DPC gain of the GSC.

[0133] Therefore, for the GSC output power reference value given by the DC voltage control outer loop, the active and reactive power control can also be achieved by using PI modulation. Then, by setting the decoupling terms k g ω s Q g and k g ω s P g generate u gP and u gQ reference values. Finally, according to the GSC-side voltage modulation transformation equation (11), the GSC voltage command value in the αβ coordinate system is calculated. The VM-DPC structure corresponding to the above GSC control principle is as shown in the right blue box in Figure 1 .

[0134] (11).

[0135] Optionally, as an embodiment of the present invention, different from the fact that the system steady state in the dq coordinate system is a constant operating point, αβ the system steady state in the αβ coordinate system is a time-varying periodic trajectory. Therefore, x =X +Δ x , where the capital letters X represent the steady-state value, and Δ x represents the small-signal perturbation. At the same time, the three-phase perturbation is represented as [Δ x , e j2θ Δ x * in the two-dimensional complex vector space, while the single-phase perturbation is represented as e jθ Δ x , 0]. The superscript "*" represents the conjugate. θ = ω s t + φ s , where φ s is the initial phase angle of the fundamental-frequency PCC voltage.

[0136] Considering that the DFIG impedance containing the steady-state operation trajectory is not easy to calculate, the steady-state operating point in the dq coordinate system will be used to replace it during the derivation process. Therefore, the following conversion relationships between the complex vectors and complex transfer functions in the αβ coordinate system and the dq coordinate system will be used:

[0137] (12)

[0138] (13)

[0139] where the left side of the arrow is the time-domain conversion relationship and the right side is the frequency-domain conversion relationship.

[0140] Optionally, as an embodiment of the present invention, in step S2, there is a dynamic coupling between the mechanical subsystem and the electrical subsystem of the DFIG, which is mainly reflected by the rotor speed ω m . Therefore, this subsection mainly considers establishing the ω m small-signal model.

[0141] The aerodynamic model calculates the mechanical torque T tur according to the wind power captured by the impeller:

[0142] (14)

[0143] where, ρ is the air density, r is the blade length, Vw is the average wind speed, C T ( λ , τ ) is the torque coefficient. λ = Ω tur r / V w represents the tip speed ratio, where Ω tur is the mechanical angular velocity. In particular, when using the fixed pitch control, the pitch angle τ is a constant value. Therefore, C T and λ The relationship between them can be quadratic-fitted by the least squares method as:

[0144] (15)

[0145] When analyzing the small-signal characteristics of the doubly-fed wind turbine, it is assumed that the wind speed is constant. Therefore, by performing small perturbation linearization on equation (14), the relationship between Δ T tur and Δ Ω tur can be obtained:

[0146] (16)

[0147] The electromagnetic torque T e related to the stator and rotor currents can be calculated as:

[0148] (17)

[0149] where p is the number of pole pairs of the motor. Therefore, linearizing (17) on the steady-state periodic trajectory can obtain the change information of the electromagnetic torque under small perturbations as:

[0150] (18)

[0151] The mechanical torque and the electromagnetic torque are related through the drive train of the DFIG. Considering the balance between the requirements of stability analysis and the model complexity, a two-mass model is adopted. It is considered that all amplitude changes occur on the high-speed shaft, and the motion equation can be written as:

[0152] (19)

[0153] where, N is the gearbox speed ratio, J t and Jm is the double - mass mechanical inertia, D t and D m is the friction coefficient. The stiffness coefficient K tm and the damping coefficient D tm define the flexible coupling between the two masses. The angular velocity of the generator Ω m and ω m are related as: Ω m = ω m / p . Then, perform small - signal linearization and Laplace transform on (19):

[0154] (20)

[0155] Therefore, by substituting (16) and (18) into (20), the small - signal model of the rotor speed can be derived and written in matrix form as:

[0156] (21)

[0157] (22)

[0158] where, is the small perturbation of the rotor angular velocity, is the small perturbation of the stator current, is the conjugate of the small perturbation of the stator current, is the small perturbation of the rotor current, is the conjugate of the small perturbation of the rotor current, H m is Δ ω m and Δ Ω tur transfer function between:

[0159] (23).

[0160] Optionally, as an embodiment of the present invention, in step S3, considering the small - signal characteristics of the rotor speed, linearize the stator - rotor voltage equation (2) of the generator main circuit. Thus, a small - signal frequency - domain model of the stator - rotor voltage equation is constructed in the two - dimensional complex vector space:

[0161] (24)

[0162] (25)

[0163] (26)

[0164] (27)

[0165] According to the VM-DPC control principle of the RSC, the stator power decoupling term contains ω r . Since ω r = ω s - ω m , then when ω s is constant, there is Δ ω r = -Δ ω m . Therefore, the impedance modeling of the RSC control also needs to consider the small-signal characteristics of the rotor speed. By linearizing the active and reactive power loops of the RSC control respectively, the α d-axis component and β q-axis component of the rotor voltage command perturbation are obtained and combined into a complex vector form:

[0166] (28)

[0167] where G rsc (s) = k p,rsc + k i,rsc / s is the PI transfer function of the VM-DPC on the RSC side. The small-signal model of the stator power can be obtained by linearizing (1) at the steady-state time-varying trajectory:

[0168] (29)

[0169] Further, take the conjugate of (28) and multiply both sides of the equation by e j2θ on the left simultaneously. At the same time, combine with (28) to establish the RSC control impedance model in the two-dimensional complex vector space:

[0170] (30)

[0171] (31)

[0172] Optionally, as an embodiment of the present invention, substitute (21) into (30), and eliminate the rotor voltage and current perturbations according to (24) and (26), the RSC partial impedance model between the stator voltage and the stator current can be obtained:

[0173] (32)

[0174] (33)

[0175] Optionally, as an embodiment of the present invention, according to Figure 1 the VM-DPC structure of the GSC shown, the α axis component and β axis component expressions of the GSC voltage command value perturbation are respectively derived. Then the GSC voltage command value perturbation is written in the complex vector form:

[0176] (34)

[0177] where G gsc (s)= k p,gsc + k i,gsc / s is the PI transfer function of the VM-DPC on the GSC side. G u (s)= k p,u + k i,u / s is the PI transfer function of the DC voltage control on the GSC side. The small-signal model of the GSC output power can be obtained by linearizing (7):

[0178] (35)

[0179] Similarly, take the conjugate of (34) and multiply both sides of the equation on the left by e j2θ . Then combine (34) to establish the GSC control impedance model in the two-dimensional complex vector space:

[0180] (36)

[0181] (37)

[0182] It can be seen from (36) that the GSC control impedance model contains DC voltage perturbation. This is because the control outer loop of the GSC needs to measure the DC voltage to control it to a given value, resulting in the DC voltage perturbation entering the GSC control. The DC bus connects the GSC and the RSC. According to the equality of the instantaneous power on the AC side and the DC side of the converter, the DC bus voltage equation can be expressed by the AC voltage and current of the GSC and the RSC as:

[0183] (38)

[0184] wherein C dc is the DC bus capacitor. By linearizing the above formula at the steady-state operating trajectory, a frequency-domain model of the DC voltage disturbance represented by complex vectors in the αβ coordinate system can be established:

[0185] (39)

[0186] (40)

[0187] Further linearize (8) to obtain the transfer relationship between the GSC voltage disturbance and the stator voltage disturbance in the two-dimensional complex vector space:

[0188] (41)

[0189] (42)

[0190] Therefore, substitute (39) and (41) into (36). At the same time, combining (24) and (26), the GSC partial impedance relationship between the stator voltage and the stator current and the GSC current can be obtained:

[0191] (43) (44)

[0192] wherein E is a two-dimensional unit diagonal matrix. It should be noted that substituting (24) and (26) in the derivation process is to eliminate the rotor voltage and current disturbances introduced by the DC voltage disturbance. However, this substitution will introduce rotor speed disturbances. Therefore, the rotor speed dynamics will indirectly affect the impedance characteristics of the GSC part through the DC voltage.

[0193] Optionally, as an embodiment of the present invention, step S5 specifically includes: referring to Figure 3 , establish the transfer relationship of small disturbances inside the DFIG. The transfer signals in the figure are actually small-signal disturbances in the two-dimensional complex vector space. However, for the simplicity of the figure, only one-dimensional complex vector disturbances are marked as a schematic when drawing. The figure reveals the dynamic coupling characteristics between the mechanical subsystem, the motor, the RSC, and the GSC, and further illustrates that each part cannot be ignored during impedance modeling. Combining (32) and (43), and noting that Δ i t =Δ i s -Δ i g , finally obtain the complex vector comprehensive impedance model of the DFIG based on VM-DPC in the αβ coordinate system:

[0194] (45)

[0195] wherein

[0196] (46)

[0197] wherein, small disturbance of stator voltage and small disturbance of grid connection point current conjugate of small disturbance of stator voltage and conjugate of small disturbance of grid connection point current θ = ω s t + φ s , wherein φ s is the initial phase angle of fundamental frequency voltage, is the impedance of the doubly-fed wind turbine based on VM-DPC, 、 、 、 、 are the sub-impedances generated in the derivation process of the doubly-fed wind turbine impedance, is the impedance related to the RSC and stator voltage, is the impedance related to the RSC and rotor speed, is the impedance related to rotor voltage and rotor current, is the impedance related to rotor voltage and rotor speed, is a part of the mechanical subsystem impedance, is the impedance related to stator voltage and rotor current, is the impedance related to the RSC and stator current, is another part of the mechanical subsystem impedance, is the impedance related to rotor voltage and stator current, is the impedance related to stator voltage and stator current, is the impedance related to the GSC and stator voltage, is the impedance related to the GSC and GSC current, is the impedance related to the GSC and DC voltage, is the impedance related to the DC side and GSC voltage, is the impedance related to the DC side and GSC current, is the impedance related to the DC side and rotor voltage, is the impedance related to the DC side and rotor current, is a two-dimensional unit diagonal matrix, is the impedance related to the power grid.

[0198] Z DPC The non - zero elements on the non - main diagonal indicate the existence of frequency coupling in the DFIG. For a perturbation with a frequency of ω p , in addition to generating a response with a frequency of ω p , a coupling response with a frequency of 2 ω s - ω p will also be generated. Since the VM - DPC structure is symmetric and there is no PLL, the frequency coupling in the DFIG impedance based on VM - DPC is mainly caused by the single - phase mechanical subsystem, the asymmetric DC voltage control outer loop, and the non - linear power calculation and voltage modulation transformation. At the same time, since VM - DPC does not need to be synchronized with the grid voltage through a phase - locked loop (PLL), when modeling the impedance of DFIG based on VM - DPC, there is no need to consider the angular perturbation of the control system dq coordinate system caused by the PLL dynamics. This is the most significant difference between the impedance modeling of DFIG based on VM - DPC and that of DFIG based on voltage - oriented vector control.

[0199] Optionally, as an embodiment of the present invention, to analyze the influence of each part of the DFIG on the impedance characteristics, the proposed comprehensive impedance is compared with various simplified DFIG impedances. When analyzing the impedance characteristics of the DFIG, the influence of the grid impedance is not considered temporarily, and it is assumed that Figure 1 the DFIG shown is directly connected to an ideal grid. The basic parameters of the DFIG are shown in Table 1. The wind speed V w is 12 m / s, and the total active power P t and total reactive power Q t output by the DFIG are 1.5 MW and 0 Mvar respectively.

[0200] Table 1 DFIG parameters

[0201]

[0202] Simplified impedance 1 ignores the mechanical dynamics by setting Z DPC in Z ωm1 and Z ωm2is obtained from the zero matrix. The simplified impedance 2 assumes a constant DC bus voltage, ignores the GSC dynamics, and is directly derived from (32). The simplified model 3 only considers the GSC dynamics, equivalentizes the RSC and the motor as a constant power source, and is derived from (43) after setting Z dc,ir and Z dc,ur as zero matrices.

[0203] Optionally, as a comparison result of the above four impedance models in an embodiment of the present invention, as shown in Figure 4 , by comparing the proposed comprehensive impedance with the simplified impedance 1, it can be seen that the mechanical dynamics will significantly affect the frequency characteristics of the DFIG impedance near 50 Hz, while having less impact in other frequency ranges. This is mainly because the mechanical dynamic time scale of the DFIG is slower, thus affecting the low-frequency characteristics of the rotor speed disturbance. However, when deriving the DFIG complex vector impedance in the αβ coordinate system, the single-phase rotor speed disturbance needs to be multiplied by e jθ , which is equivalent to performing a 50 Hz frequency shift. Therefore, the influence of mechanical dynamics on the DFIG impedance in the αβ coordinate system is finally reflected in the sub / super-synchronous frequency band. This conclusion indicates that it is necessary to consider mechanical dynamics to obtain more accurate analysis results when studying the sub / super-synchronous oscillation or low-frequency power oscillation of DFIG grid connection. Further comparing the proposed impedance with the simplified impedance 2, it can be found that whether considering the GSC dynamics has little impact on the main diagonal elements of the DFIG impedance, and the main difference is also near 50 Hz. However, ignoring the GSC dynamics will significantly affect the accuracy of the non-main diagonal elements of the DFIG impedance, reducing their amplitudes. This shows that the GSC dynamics is one of the main factors causing frequency coupling in DFIG. This can also be proven from the fact that the amplitudes of the non-main diagonal elements of the simplified impedance 3 are much larger than those of the non-main diagonal elements of the simplified impedance 2. This conclusion indicates that even though the impedance characteristics of DFIG are mainly determined by the RSC and the motor, the GSC dynamics cannot be ignored during the modeling process.

[0204] It should be noted that the comprehensive impedance of the DFIG based on VM-DPC has irregular amplitude spikes and strongly nonlinear phase angle variations near 50 Hz. Based on the frequency characteristics of the four impedances in this frequency band, this phenomenon is the result of the combined action of the dynamics of each part of the DFIG, rather than simply being caused by a single factor such as mechanical dynamics or GSC dynamics. Therefore, in order to obtain more accurate impedance characteristics, especially in the sub / super-synchronous frequency band, it is necessary to consider mechanical and GSC dynamics to establish a comprehensive impedance model of the DFIG based on VM-DPC.

[0205] Optionally, as an embodiment of the present invention, the influence of grid impedance on the stability of the DFIG grid-connected system based on the proposed comprehensive impedance analysis VM-DPC is considered. The grid side adopts an RL equivalent circuit, and its αβ coordinate system impedance can be expressed as Z grid . The aggregate impedance Z = Z DPC + Z grid The determinant zeros of are equivalent to the eigenvalues of the DFIG grid-connected system. Therefore, by calculating whether all the determinant zeros of Z are located in the left half s plane, the small-signal stability of the DFIG grid-connected system can be evaluated. αβ The k pair of determinant zeros of the aggregate impedance in the coordinate system have the same real part and the imaginary part is symmetric about ω s and can be denoted as λ 2k-1 = σ k + j ω k and λ 2k = σ k + j(2 ω s- ω k ). The imaginary part ω k and 2 ω s- ω k also represent the oscillation frequencies of the oscillation modes corresponding to this pair of zeros in the αβ coordinate system, reflecting the frequency coupling.

[0206] The basic parameters of the DFIG adopting VM-DPC still refer to Table 1. The numerical setting of the grid impedance makes the short-circuit ratio 2, corresponding to the weak grid condition. The wind speed is 12 m / s, and the total active power and total reactive power of the DFIG are 1.5 MW and 0 Mvar respectively. By changing k p,rsc , k p,gsc , k i,rsc and k i,gsc values in turn, the determinant zeros of the aggregate impedance are calculated successively based on the proposed DFIG comprehensive impedance. Furthermore, the variation of the system eigenvalues with the VM-DPC control parameters is analyzed. According to the distance of the eigenvalues from the imaginary axis, λ1,2 , λ 3,4 , λ 5 is the dominant eigenvalue of the system. Figures 5(a), 5(b), 5(c) and 5(d) respectively show the trajectories of the dominant eigenvalues when the VM-DPC control parameters change. It can be seen from Figures 5(b) and 5(d) that as the PI parameters on the GSC side change, the dominant eigenvalue of the system remains basically unchanged. This indicates that the control parameters of VM-DPC on the GSC side have little effect on the stability of the DFIG grid-connected system. Therefore, this application mainly analyzes the influence of the control parameters of VM-DPC on the RSC side on the system stability.

[0207] According to Figure 5(a) and 5(c) it is known that as k p,rsc decreases, the eigenvalue λ 1,2 will gradually move to the right and finally cross the imaginary axis to reach the right half plane. At k p,rsc = 31.5, there are λ 1 = 2.92 + j282.32, λ 2 = 2.92 + j346. The real part of the eigenvalue λ 3,4 will decrease as k p,rsc decreases, but the change range is much smaller than λ 1,2 , and it always remains in the left half s plane. And the eigenvalue λ 5 is basically not affected. Therefore, near the stability boundary, as the k p,rsc on the RSC side increases, the system stability gradually increases. For Figure 5(c), as k i,rsc increases, the eigenvalue λ 5 also changes little, and the real part only decreases slightly. But the eigenvalues λ 1,2 and λ 3,4 will both move to the right, and the real part gradually increases. Among them, the change range of the eigenvalue λ 1,2 is the largest, and it will finally cross the imaginary axis to reach the right half plane. At k i,rsc = 48000, there are λ 1 = 1.11 + j216.85, λ 2 = 1.11 + j411.47. Therefore, near the stability boundary, the k i,rscAn increase will weaken the system stability until instability occurs.

[0208] Optionally, as an embodiment of the present invention, the correctness of the comprehensive impedance of the proposed VM-DPC-based DFIG is verified by the frequency scanning method. At the same time, the influence of the VM-DPC parameters on the grid connection stability of the DFIG is verified by simulation. These simulation verifications are all based on the DFIG simulation model built in MATLAB / Simulink. The basic parameters of the DFIG refer to Table 1. The wind speed is 12 m / s, and the total active power and total reactive power output by the DFIG are 1.5 MW and 0 Mvar respectively.

[0209] Based on MATLAB / Simulink, build the simulation model of the above-mentioned VM-DPC-based DFIG to Z DPC carry out frequency scanning measurement. For αβ the complex vector impedance in the coordinate system, its value at the disturbance frequency ω p needs to be obtained by injecting two disturbances. The steady state of the DFIG corresponding to these two disturbance injections needs to be kept consistent, and the corresponding disturbance frequencies are ω p and ω p -2 ω s . The form of the disturbance is selected as αβ the sinusoidal voltage disturbance in the coordinate system. The amplitude of the disturbance is set to 0.01 pu, which is small enough to maintain system stability and large enough for impedance identification. The grid connection point voltage and current responses during the injection of the two disturbances are measured in the αβ coordinate system to calculate the DFIG impedance value at the corresponding disturbance frequency. The comparison between the results of the frequency scanning measurement and the theoretically deduced comprehensive impedance of the DFIG is as Figure 6 shown. There is good consistency between the two, which proves the correctness of the comprehensive impedance of the VM-DPC-based DFIG proposed by the present invention.

[0210] Verify the analysis results of the influence of the above-mentioned VM-DPC control parameters on the grid connection stability of the DFIG through simulation. The value of the grid impedance is set so that the short-circuit ratio is 2, corresponding to the weak grid condition. The control parameters at the initial state of the simulation are set according to Table 1. According to Figures 5(a), 5(b), 5(c) and 5(d), it can be seen that the system operates stably. First, verify k p,rsc the influence of k p,rsc is reduced to 94.5 at the 11th second and continues to decrease to 31.5 at the 15th second. The simulation results are as Figure 7(a) and 7(b) shown. Then change ki,rsc Re - conduct the simulation. k i,rsc It increases to 45000 at the 11th second and continues to increase to 48000 at the 15th second. The simulation results are as Figure 8(a) and 8(b) shown. It can be seen from the result graphs of these two simulations that as k p,rsc decreases or k i,rsc increases, the system stability will gradually weaken and finally become unstable. This is consistent with the system dominant eigenvalue trajectories shown in Figures 5(a), 5(b), 5(c) and 5(d). Also, through the FFT analysis of the voltage, it can be known that the oscillation frequencies of the two instabilities are both consistent with the results of the dominant eigenvalue calculation. The simulation proves that too small k p,rsc and too large k i,rsc will indeed make the DFIG grid - connected system more prone to instability.

[0211] In some embodiments, the VM - DPC - based double - fed wind turbine impedance modeling system may include multiple functional modules composed of computer program segments. The computer programs of each program segment in the VM - DPC - based double - fed wind turbine impedance modeling system can be stored in the memory of a computer device and executed by at least one processor to perform the functions of VM - DPC - based double - fed wind turbine impedance modeling (see details in Figure 1 description).

[0212] In this embodiment, according to the functions it performs, the VM - DPC - based double - fed wind turbine impedance modeling system can be divided into multiple functional modules, as Figure 9 shown. The functional modules of the system may include: a system construction module, a small - signal model construction module for rotor speed, an impedance model construction module for the RSC part, an impedance model construction module for the GSC part, and a double - fed wind turbine impedance model construction module. The module referred to in the present invention means a series of computer program segments that can be executed by at least one processor and can complete fixed functions, and are stored in the memory. In this embodiment, the functions of each module will be detailed in subsequent embodiments. The system includes:

[0213] A system construction module, which constructs a double - fed wind turbine system using VM - DPC based on an induction generator, an RSC, and a GSC, and obtains the electrical parameters, operating state variables, and mechanical parameters of the generator based on the double - fed wind turbine system;

[0214] A small - signal model construction module for rotor speed, at αβUnder the coordinate system, an aerodynamic model is constructed based on the mechanical parameters and operating state variables of the generator, and the mechanical change information of the mechanical torque under small disturbances is obtained. The electromagnetic change information of the electromagnetic torque under small disturbances is obtained based on the electrical parameters and operating state variables of the generator. A small-signal model of the rotor speed is constructed by combining the mechanical change information and the electromagnetic change information.

[0215] RSC partial impedance model construction module, in αβ Under the coordinate system, the dynamic relationship between the stator power of the generator and the stator voltage and current is obtained based on the electrical parameters and operating state variables of the generator. The small-signal model of the stator power is obtained by linearizing the stator power. The small-signal model of the stator-rotor voltage is constructed by combining the small-signal model of the rotor speed with the stator voltage and the rotor voltage. Based on the disturbance of the rotor voltage control command value, the RSC partial impedance model is established by combining the small-signal model of the stator power and the small-signal model of the stator-rotor voltage.

[0216] GSC partial impedance model construction module, in αβ Under the coordinate system, the dynamic relationship between the GSC output power and the stator voltage and GSC current is obtained based on the electrical parameters and operating state variables. The small-signal model of the GSC output power is obtained by linearization. The DC voltage equation is constructed based on the AC voltage and current of the RSC and GSC, and the small-signal model of the DC voltage is obtained by linearization. Based on the disturbance of the GSC voltage control command value, the GSC partial impedance model is established by combining the small-signal model of the GSC output power and the small-signal model of the DC voltage.

[0217] Doubly-fed wind turbine impedance model construction module, comprehensively constructs the impedance model of the doubly-fed wind turbine based on VM-DPC under small disturbances by integrating the small-signal model of the rotor speed, the RSC partial impedance model, and the GSC partial impedance model.

[0218] Starting from constructing a doubly-fed wind turbine system using VM-DPC and obtaining relevant parameters, to separately establishing the small-signal model of the rotor speed, the RSC and GSC partial impedance models, and finally comprehensively constructing the impedance model of the doubly-fed wind turbine based on VM-DPC, it brings many significant benefits to the research and application of doubly-fed wind turbines. It can accurately describe the dynamic characteristics of the doubly-fed wind turbine under small disturbances, enabling us to have a deeper understanding of the complex internal electrical and mechanical interactions, thus providing a solid theoretical basis for optimizing the wind turbine control strategy, helping to improve the operating stability and efficiency of the doubly-fed wind turbine, and enhancing the reliability of wind power grid connection.

[0219] The present invention also provides a computer-readable storage medium. The computer storage medium can store a program, and when the program is executed, it can include some or all of the steps in the various embodiments provided by the present invention. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), a random access memory (RAM), or the like.

[0220] Therefore, the technical effects achievable by this embodiment can be referred to the descriptions above, and will not be elaborated here.

[0221] Those skilled in the art can clearly understand that the technologies in the embodiments of the present invention can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solutions in the embodiments of the present invention, in essence, or the parts that contribute to the prior art, can be embodied in the form of a software product. The computer software product is stored in a storage medium such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, etc., which can store program codes, and includes several instructions to enable a computer terminal (which can be a personal computer, a server, or a second terminal, a network terminal, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.

[0222] For the same or similar parts among the various embodiments in this specification, reference can be made to each other. In particular, for the terminal embodiments, since they are basically similar to the method embodiments, the descriptions are relatively simple, and the relevant parts can be referred to the descriptions in the method embodiments.

[0223] In several embodiments provided by the present invention, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For example, the division of the modules is only a logical function division. In actual implementation, there can be other division methods. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of the systems or modules can be in electrical, mechanical, or other forms.

[0224] The module described as a separation component may or may not be physically separated. The component shown as a module may or may not be a physical module, that is, it may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0225] In addition, in each embodiment of the present invention, each functional module may be integrated into one processing module, or each module may exist physically alone, or two or more modules may be integrated into one module.

[0226] Although the present invention has been described in detail by referring to the drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A double-fed wind turbine impedance modeling method based on VM-DPC, characterized in that, It includes the following steps: Build a doubly-fed wind turbine system with VM-DPC based on an induction generator, RSC, and GSC, and obtain the electrical parameters, operating state variables, and mechanical parameters of the generator based on the doubly-fed wind turbine system; In αβ the coordinate system, an aerodynamic model is constructed based on the mechanical parameters and operating state variables of the generator to obtain the mechanical change information of the mechanical torque under small disturbances, the electromagnetic change information of the electromagnetic torque under small disturbances is obtained based on the electrical parameters and operating state variables of the generator, and a small-signal model of the rotor speed is constructed by combining the mechanical change information and the electromagnetic change information; In αβ the coordinate system, the dynamic relationship between the stator power of the generator and the stator voltage and current is obtained based on the electrical parameters and operating state variables of the generator. The small-signal model of the stator power is obtained by linearizing the stator power, and the small-signal model of the stator and rotor voltages is constructed by combining the small-signal model of the rotor speed with the stator voltage and the rotor voltage. The partial impedance model of the RSC is established based on the perturbation of the rotor voltage control command value, combined with the small-signal model of the stator power and the small-signal model of the stator and rotor voltages. In αβ the coordinate system, the dynamic relationship between the GSC output power and the stator voltage and GSC current is obtained based on electrical parameters and operating state variables. The small-signal model of the GSC output power is obtained through linearization. The DC voltage equation is constructed based on the AC voltages and currents of the RSC and GSC, and the small-signal model of the DC voltage is obtained through linearization. The GSC partial impedance model is established based on the perturbation of the GSC voltage control command value in combination with the small-signal models of the GSC output power and the DC voltage; Build an impedance model of the doubly-fed wind turbine based on VM-DPC under small disturbances by integrating the small-signal model of rotor speed, the partial impedance model of RSC, and the partial impedance model of GSC.

2. The impedance modeling method of the doubly-fed fan based on VM-DPC according to claim 1, wherein The doubly-fed wind turbine system based on VM-DPC includes a mechanical subsystem and an electrical subsystem. The impedance model of the doubly-fed wind turbine based on VM-DPC is specifically: Among them, small disturbance of stator voltage and small disturbance of grid connection point current conjugate of small disturbance of stator voltage and conjugate of small disturbance of grid connection point current θ = ω s t + φ s , where φ s is the initial phase angle of fundamental frequency voltage, is the impedance of the doubly-fed wind turbine based on VM-DPC, , , , , are sub-impedances generated in the derivation process of the doubly-fed wind turbine impedance, expressed as: Among them, is the impedance related to the RSC and the stator voltage, is the impedance related to the RSC and the rotor speed, is the impedance related to the rotor voltage and the rotor current, is the impedance related to the rotor voltage and the rotor speed, is a part of the mechanical subsystem impedance, is the impedance related to the stator voltage and the rotor current, is the impedance related to the RSC and the stator current, is another part of the mechanical subsystem impedance, is the impedance related to the rotor voltage and the stator current, is the impedance related to the stator voltage and the stator current, is the impedance related to the GSC and the stator voltage, is the impedance related to the GSC and the GSC current, is the impedance related to the GSC and the DC voltage, is the impedance related to the DC side and the GSC voltage, is the impedance related to the DC side and the GSC current, is the impedance related to the DC side and the rotor voltage, is the impedance related to the DC side and the rotor current, is a two-dimensional unit diagonal matrix, is the impedance related to the power grid.

3. The impedance modeling method of the doubly-fed wind turbine based on VM-DPC according to claim 2, characterized in that, The small-signal model of rotor speed specifically includes: Build an aerodynamic model as follows: Among them, is the mechanical torque, ρ is the air density, r is the blade length, is the average wind speed, is the torque coefficient, λ = r / represents the tip speed ratio, where is the mechanical angular velocity; Under the assumption of constant wind speed, perform small-disturbance analysis on the aerodynamic model to obtain the linear relationship between the small disturbance of mechanical torque and the small disturbance of mechanical angular velocity; Calculate the electromagnetic torque based on the stator current and rotor current, obtain the correlation formula between the electromagnetic torque and the stator current and rotor current, and linearize the correlation formula to obtain the electromagnetic change information of the electromagnetic torque under small disturbances; Establish a two-mass block motion equation of the drive system for describing the dynamic coupling relationship between the mechanical and electromagnetic parts, and perform small-signal linearization processing on the motion equation; Integrate the linear relationship between the small disturbance of mechanical torque and the small disturbance of mechanical angular velocity, the electromagnetic change information of the electromagnetic torque under small disturbances, and the motion equation after small-signal linearization processing to obtain the small-signal model of rotor speed, specifically: Among them, is a small perturbation of the rotor speed, is a small perturbation of the stator current, is the conjugate of the small perturbation of the stator current, is a small perturbation of the rotor current, is the conjugate of the small perturbation of the rotor current.

4. The impedance modeling method of the doubly-fed wind turbine based on VM-DPC according to claim 3, characterized in that, Before establishing the partial impedance model of RSC, establish an RSC control impedance model based on the perturbation of the rotor voltage control command value combined with the small-signal model of stator power, specifically including: Linearize the active power loop and the reactive power loop controlled by RSC respectively to obtain the α axis component and β the expression of the axis component. Based on α axis component and β the expression of the axis component, represent the disturbance of the rotor voltage control command value in the form of a complex vector; Obtain the active power and reactive power of the stator in the coordinate system based on the doubly-fed wind turbine system by combining electrical parameters and operating state variables, and linearize the active power and reactive power to obtain the small-signal model of the stator power; αβ ​ Establish an RSC control impedance model in the two-dimensional complex vector space based on the perturbation of the rotor voltage control command value represented in complex vector form combined with the small-signal model of stator power, as follows: wherein, is a small perturbation of the rotor voltage, is the conjugate of the small perturbation of the rotor voltage, is a small perturbation of the stator voltage, is the conjugate of the small perturbation of the stator voltage, is a small perturbation of the stator current, is the conjugate of the small perturbation of the stator current, is a small perturbation of the rotor speed.

5. The impedance modeling method of the doubly-fed fan based on VM-DPC according to claim 4, characterized in that Based on the RSC control impedance model, obtain the partial impedance model of RSC between the stator voltage and stator current, specifically including: Based on the main circuit of the induction generator, obtain the stator voltage equation and rotor voltage equation, and linearize the stator voltage equation and rotor voltage equation to construct a small-signal model of the stator and rotor voltages; Substitute the small-signal model of rotor speed into the RSC control impedance model, and eliminate the rotor voltage and current perturbations based on the small-signal model of the stator and rotor voltages to obtain the partial impedance model of RSC between the stator voltage and stator current: 。 6. The impedance modeling method of the doubly-fed fan based on VM-DPC according to claim 5, wherein, Before establishing the partial impedance model of GSC, establish a GSC control impedance model based on the perturbation of the GSC voltage control command value combined with the small-signal model of GSC output power, specifically including: Linearize the active power loop and the reactive power loop controlled by the GSC respectively to obtain the α axis component and β the expression of the axis component. Based on α axis component and β the expression of the axis component represents the disturbance of the GSC voltage control command value in the form of a complex vector; Obtain the active power and reactive power output of the GSC in the coordinate system based on the doubly-fed wind turbine system by combining electrical parameters and operating state variables, and linearize the active power and reactive power to obtain the small-signal model of the GSC output power; αβ ​ Establish a GSC control impedance model in the two-dimensional complex vector space based on the perturbation of the GSC voltage control command value represented in complex vector form combined with the small-signal model of GSC output power, as follows: wherein, is a small disturbance of the GSC voltage, is the conjugate of the small disturbance of the GSC voltage, is a small disturbance of the stator voltage, is the conjugate of the small disturbance of the stator voltage, is a small disturbance of the GSC current, is the conjugate of the small disturbance of the GSC current, is a small disturbance of the DC bus voltage.

7. The impedance modeling method of the doubly-fed fan based on VM-DPC according to claim 6, characterized in that, The DC bus connects GSC and RSC. Before establishing the partial impedance model of GSC, it also includes obtaining the frequency-domain model of the DC voltage perturbation, specifically including: According to the equality of the instantaneous power on the AC side and DC side of the converter, obtain the DC bus voltage equation based on the AC voltages and currents of GSC and RSC; Linearize the DC bus voltage equation at the steady-state operating trajectory to obtain αβ the frequency-domain model of the DC voltage disturbance represented by the complex vector in the ； The frequency-domain model based on DC voltage disturbance obtains the interaction between the DC side and the AC side, and constructs the partial impedance model of the GSC based on the GSC control impedance model combined with the frequency-domain model of DC voltage disturbance.

8. The impedance modeling method of the doubly-fed fan based on VM-DPC according to claim 7, characterized in that Based on the GSC control impedance model combined with the frequency-domain model of DC voltage disturbance, the partial impedance model of the GSC between the stator voltage, the stator current, and the GSC current is obtained, specifically including: Based on the filter circuit, the relationship equation between the GSC voltage, the GSC current, and the stator voltage is obtained, and the relationship equation is linearized to obtain the transfer relationship between the GSC voltage disturbance and the stator voltage disturbance in the two-dimensional complex vector space; Substitute the transfer relationship and the frequency-domain model of DC voltage disturbance into the GSC control impedance model to obtain the partial impedance model of the GSC between the stator voltage, the stator current, and the GSC current: 。 9. A double-fed wind turbine impedance modeling system based on VM-DPC, characterized in that, When the system is implemented, the impedance modeling method of the doubly-fed wind turbine based on VM-DPC described in any one of claims 1-8 is executed. The system includes: A system construction module constructs a doubly-fed wind turbine system using VM-DPC based on an induction generator, an RSC, and a GSC, and obtains the electrical parameters, operating state variables, and mechanical parameters of the generator based on the doubly-fed wind turbine system; The small-signal model construction module of the rotor speed constructs, in αβ the coordinate system, an aerodynamic model based on the mechanical parameters and operating state variables of the generator and obtains the mechanical change information of the mechanical torque under small disturbances, obtains the electromagnetic change information of the electromagnetic torque under small disturbances based on the electrical parameters and operating state variables of the generator, and constructs a small-signal model of the rotor speed by combining the mechanical change information and the electromagnetic change information; RSC partial impedance model construction module, in αβ the coordinate system, obtain the dynamic relationship between the generator stator power and the stator voltage and current based on the electrical parameters and operating state variables of the generator, linearize the stator power to obtain the small-signal model of the stator power, and combine the small-signal model of the rotor speed with the stator voltage and rotor voltage to construct the small-signal model of the stator-rotor voltage; establish the RSC partial impedance model based on the disturbance of the rotor voltage control command value, combined with the small-signal model of the stator power and the small-signal model of the stator-rotor voltage; GSC partial impedance model construction module, in αβ the coordinate system, based on electrical parameters and operating state variables, obtains the dynamic relationship between the GSC output power and the stator voltage and GSC current, obtains the small-signal model of the GSC output power through linearization, constructs the DC voltage equation based on the AC voltage and current of the RSC and GSC, and obtains the small-signal model of the DC voltage through linearization; based on the GSC voltage control command value perturbation, combines the small-signal model of the GSC output power and the small-signal model of the DC voltage to establish the GSC partial impedance model; A doubly-fed wind turbine impedance model construction module constructs a doubly-fed wind turbine impedance model based on VM-DPC under small disturbances by integrating the rotor speed small-signal model, the partial impedance model of the RSC, and the partial impedance model of the GSC.

10. A computer-readable storage medium, characterized in that, The readable storage medium stores a doubly-fed wind turbine impedance modeling program based on VM-DPC. When the doubly-fed wind turbine impedance modeling program based on VM-DPC is executed by a processor, the steps of the impedance modeling method of the doubly-fed wind turbine based on VM-DPC described in any one of claims 1-8 are implemented.

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