A method for suppressing subsynchronous oscillation of direct-drive wind turbine based on improved first-order LADRC

Abstract

The present invention provides a method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC, and relates to the technical field of direct-drive wind turbines. The method obtains the parameters of the direct-drive wind turbine grid-connected system, establishes a mathematical model of the grid-side converter system and a current inner loop control model of the direct-drive wind turbine grid-side converter based on the improved first-order linear anti-disturbance control; at the same time, a phase advance link is introduced on the basis of the traditional LESO to enhance the disturbance observation capability of the system. In addition, a fuzzy controller is introduced to perform online optimization of the parameters of the improved LADRC controller, forming a fuzzy improved LADRC controller, and applying it to the current inner loop of the grid-side converter, thereby realizing precise control of the current inner loop of the grid-side converter of the direct-drive wind turbine; the SPWM modulation wave is obtained through the output of the improved LADRC to drive the main circuit of the grid-side converter to work. The method aims to improve the robustness and steady-state performance of the grid-connected system of the direct-drive wind turbine, and has good subsynchronous oscillation suppression capability.

Description

Technical Field

[0001] The present invention relates to the technical field of direct-drive fans, and in particular to a method for suppressing subsynchronous oscillation of a direct-drive fan based on an improved first-order LADRC. Background Art

[0002] With the transformation of the global energy structure and the increasing demand for renewable energy, the development and utilization of wind energy as a clean new energy has received widespread attention. Direct-drive wind turbines have become one of the mainstream models of wind farms due to their simple structure and easy maintenance. However, with the rapid growth of wind power installed capacity, grid stability problems caused by large-scale wind power grid connection have gradually emerged, especially when direct-drive wind turbines work under weak grid conditions, they are prone to subsynchronous oscillation (SSO), which poses a major challenge to the safe and stable operation of the power grid.

[0003] Among them, subsynchronous oscillation refers to the oscillation phenomenon caused by the dynamic interaction between the grid-side converter and its control system and the weak power grid when the wind turbine is connected to the grid. This phenomenon will cause fluctuations in grid voltage and current, increase equipment stress, and reduce power generation efficiency. In severe cases, it may aggravate the instability of the grid and cause equipment to be disconnected from the grid or regional voltage collapse. Traditional direct-drive wind turbine grid-side converters usually adopt a dual-loop PI control structure that combines a voltage outer loop and a current inner loop. Although it is simple and easy to implement, it is difficult to achieve ideal control effects under complex working conditions with multiple variables, strong coupling, strong nonlinearity, and system parameters that are prone to perturbations.

[0004] At present, in order to solve this problem, Active Disturbance Rejection Control (ADRC) technology has been proposed and applied to the control of wind turbines. ADRC estimates and compensates the total disturbance of the system by introducing an Extended State Observer (ESO), thereby improving the robustness of the system. However, traditional ADRC contains too many parameters, which is difficult to adjust, and has high requirements for the accuracy of parameters in practical applications, which limits its application in engineering practice. On this basis, Linear Active Disturbance Rejection Control (LADRC) technology came into being. LADRC simplifies parameter adjustment, uses the concept of bandwidth to unify the design of observer and controller parameters, reduces the complexity of online calculations, and facilitates frequency domain analysis and engineering applications. Although LADRC has achieved certain results in suppressing subsynchronous oscillations, its anti-interference ability under weak power grid conditions still needs to be improved.

[0005] In view of this, this application is filed. Summary of the invention

[0006] The present invention provides a method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC, which can at least partially improve the above-mentioned problem.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC, comprising:

[0009] Acquire the parameters of the preset direct-drive wind turbine grid-connected system, and construct a grid-side converter mathematical model according to the parameters of the direct-drive wind turbine grid-connected system;

[0010] According to the mathematical model of the grid-side converter and the first-order LADRC system, a current inner loop control model of the grid-side converter of a direct-drive wind turbine is established;

[0011] The traditional linear extended state observer LESO is processed by adding a phase advance module to the traditional linear extended state observer LESO to obtain an improved linear extended state observer;

[0012] A fuzzy controller is introduced and combined with a linear error feedback control rate LSEF to realize online optimization of parameters, and a fuzzy improved LADRC controller is obtained. The fuzzy improved LADRC controller is applied to the current inner loop control model of the direct-drive wind turbine grid-side converter, and a direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC is obtained.

[0013] The direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC is used to calculate the grid-side converter to be controlled, obtain the modulation signal of the grid-side converter, and drive the grid-side converter to work based on the modulation signal.

[0014] In summary, the subsynchronous oscillation suppression method of direct-drive wind turbine based on improved first-order LADRC is specially designed for direct-drive wind turbines in weak grid environment to enhance system stability and suppress subsynchronous oscillation. Specifically, a mathematical model of the grid-connected system of direct-drive wind turbines is first established. Based on this model, an improved LADRC control strategy is developed; this strategy significantly improves the disturbance observation capability of the system by introducing a phase advance link in the traditional linear extended state observer. Furthermore, combined with fuzzy control technology, the parameters of the improved LADRC controller are optimized online to form a fuzzy improved LADRC controller. The controller is applied to the current inner loop control of the grid-side converter, which effectively improves the dynamic response and anti-interference ability of the system. Finally, the improved LADRC outputs a modulation wave to drive the main circuit of the grid-side converter to achieve precise control of the grid-connected current of the direct-drive wind turbine. This method not only enhances the robustness of the direct-drive wind turbine under weak grid conditions, but also significantly reduces the impact of subsynchronous oscillations on grid stability, ensuring the efficient and stable operation of the wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of a method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC provided in an embodiment of the present invention;

[0016] Figure 2 is a control structure diagram of a grid-side converter provided by an embodiment of the present invention;

[0017] Figure 3 It is a control structure diagram of a current inner loop control system of a direct-drive wind turbine grid-side converter based on an improved LADRC provided in an embodiment of the present invention;

[0018] Figure 4 is a structural diagram of a traditional first-order LADRC system provided by an embodiment of the present invention;

[0019] Figure 5 is a comparison chart of the disturbance observation capabilities of the traditional LESO and the improved LESO provided by the embodiment of the present invention;

[0020] Figure 6 is a structural block diagram of a fuzzy improved LADRC controller provided by an embodiment of the present invention;

[0021] Figure 7 It is a schematic diagram of Bode diagram analysis of the improved LADRC anti-interference capability provided by an embodiment of the present invention;

[0022] Figure 8 is a current loop structure diagram of an improved LADRC provided by an embodiment of the present invention;

[0023] Fig. 9It is a simulation waveform diagram comparing the A-phase current of PI control, LADRC and improved LADRC grid-connected when the SCR is equal to 2.5 and 2.2 respectively provided by the embodiment of the present invention;

[0024] Fig.10 It is an analysis diagram of the A-phase current spectrum diagram of PI control, LADRC and improved LADRC grid-connected when the SCR is equal to 2.2 provided by an embodiment of the present invention;

[0025] Fig.11 It is a comparison diagram of active power and reactive power simulation waveforms of PI control, LADRC and improved LADRC when the SCR is equal to 2.5 and 2.2 respectively provided by the embodiment of the present invention;

[0026] Fig.12 It is a comparison diagram of active power simulation waveforms of PI control, LADRC and improved LADRC under extremely weak power grid conditions with SCR equal to 1.5 provided by an embodiment of the present invention;

[0027] Fig.13 It is a waveform diagram of the grid-connected current, active power and reactive power experiment of a PI-controlled direct-drive wind turbine connected to a weak power grid when the SCR is equal to 2.2 provided in an embodiment of the present invention;

[0028] Fig.14 It is an experimental waveform diagram of grid-connected current, active power and reactive power when PI control is switched to LADRC when SCR is equal to 2.2 provided by an embodiment of the present invention;

[0029] Fig.15 It is a grid-connected current, active power and reactive power experimental waveform diagram of the PI control switching to the improved LADRC when the SCR is equal to 2.2 provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] refer to Figure 1 , Figure 3 As shown, the first embodiment of the present invention discloses a method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC, which can be executed by a grid-side converter current control device based on an improved first-order LADRC (hereinafter referred to as a control device), and in particular, executed by one or more processors in the control device to implement the following method:

[0032] S1, obtaining parameters of a preset direct-drive wind turbine grid-connected system, and constructing a grid-side converter mathematical model according to the parameters of the direct-drive wind turbine grid-connected system;

[0033] Preferably, the direct-drive wind turbine grid-connected system comprises a wind turbine, a permanent magnet synchronous generator, a machine-side converter, a grid-side converter, and a weak AC power grid.

[0034] Preferably, the mathematical expression of the grid-side converter mathematical model is: ,in, is the filter inductor, is the d-axis component of the grid-connected current, is the d-axis component of the grid-side converter output voltage, t is the time, is the grid synchronization angular velocity, is the q-axis component of the grid-connected current, is the equivalent resistance on the AC side, is the d-axis component of the grid-connected voltage, is the q-axis component of the grid-side converter output voltage, is the q-axis component of the grid-connected voltage, C is the DC side capacitance of the grid-side converter, is the DC bus voltage, The output current provided by the controlled current source simulates the wind turbine output power, is the wind turbine grid-connected current;

[0035] The controlled current source of the mathematical model of the grid-side converter is equivalent to the wind turbine, permanent magnet synchronous generator and machine-side converter in the direct-drive wind farm.

[0036] Specifically, in this embodiment, when the direct-drive wind turbine is connected to a weak power grid, it is equivalent to adding an equivalent inductor to the line. , first there will be a subsynchronous current Generated at the grid connection point, this current passes through the PI controller of the current inner loop and forms a sub-synchronous voltage at the output end of the GSC. , the sub-synchronous voltage will generate a new sub-synchronous current on the line. These newly generated sub-synchronous currents will be combined with the original The superposition makes the sub-synchronous current component in the grid-connected system increase continuously. At the same time, the proportional and integral links in the PI control It has an amplifying effect, further increasing the subsynchronous current content in the grid-connected current, and eventually triggering subsynchronous oscillations, leading to system instability.

[0037] When the direct-drive wind power system is connected to a weak power grid, the formula including the subsynchronous disturbance component is: ,in, is the subsynchronous voltage disturbance component output by the grid-side converter under the d-axis, is the subsynchronous voltage disturbance component output by the grid-side converter under the q axis, is the next synchronous voltage of the d-axis at the grid connection point, is the next synchronous voltage of the q-axis at the grid connection point, is the current disturbance component of the d-axis at the grid connection point, is the q-axis current disturbance component at the grid connection point.

[0038] In this embodiment, the influence of the inner loop PI controller of the grid-side converter current is analyzed, and the formula of the subsynchronous disturbance component can be rewritten as follows: ,in, is the proportional coefficient of the current inner loop PI controller, is the integral coefficient of the current inner loop PI controller.

[0039] It can be seen from the above formula that the proportional-integral link of PI control has an amplifying effect on the subsynchronous disturbance component, which will cause the subsynchronous disturbance component in the loop to increase continuously, and eventually cause the system to lose stability. Taking the d-axis as an example, the mathematical expression of the grid-side converter mathematical model including the subsynchronous disturbance component can be written as: . Further, let F1 be the subsynchronous disturbance component, and we get .

[0040] LADRC can estimate the subsynchronous disturbance component in real time through the Linear Extended State Observer (LESO), and compensate the subsynchronous current as a disturbance, blocking the positive feedback generation loop of the subsynchronous component and maintaining the stability of the output current of the grid-side converter, thereby achieving the goal of suppressing SSO. When it is equal to F1, we can get: According to this formula, the grid-side converter output current i od The expression of is consistent with that in the steady state of the system. This shows that when the inner loop of the grid-side converter current adopts LADRC, the grid-connected current will not contain subsynchronous disturbance components, and the direct-drive wind turbine grid-connected system can operate stably without being affected by the weak grid. Therefore, LADRC can effectively suppress the occurrence of SSO by blocking the interaction between GSC and the weak grid through real-time estimation and compensation of disturbances.

[0041] In simple terms, this method accurately obtains the parameters of the grid-connected system of the direct-drive wind turbine, which include the characteristics of the wind turbine, the electrical characteristics of the machine-side converter and the grid-side converter, and the relevant parameters of the weak AC power grid. Using these parameters, a detailed mathematical model of the grid-side converter is constructed, which can accurately describe the dynamic behavior of the direct-drive wind turbine when it is connected to the grid. In addition, since the subsynchronous oscillation phenomenon is mainly caused by the interaction between the grid-side converter and the weak AC power grid, in the process of constructing the mathematical model, special attention is paid to the behavior of the grid-side converter, and the wind turbine, permanent magnet synchronous generator and machine-side converter are equivalent to controlled current sources. The output current of the controlled current source is adjusted to simulate the output power change of the direct-drive wind turbine. The mathematical expression of the mathematical model of the grid-side converter describes in detail the relationship between the filter inductance, the d-axis and q-axis components of the grid-connected current and voltage, the synchronous angular velocity of the grid, the equivalent resistance of the AC side, the output voltage of the grid-side converter, the DC side capacitance of the grid-side converter, and the DC bus voltage. The precise description of these parameters enables the model to accurately simulate the working conditions in the actual power grid.

[0042] The d-axis component i of the grid-connected current in the model od , q-axis component i oq And the equivalent resistance R on the AC side f , and the d-axis component u of the grid voltage od and the q-axis component u oq , are the key factors for the accuracy of the model. The d-axis component u of the grid-side converter output voltage id and the q-axis component u iq , and the corresponding components of the grid voltage, are defined by precise mathematical relationships. The grid-side converter DC link capacitance C and the DC bus voltage u dc , which provides the necessary electrical parameters for the model to ensure its accuracy and practicality.

[0043] S2, establishing a current inner loop control model of a direct-drive wind turbine grid-side converter according to the grid-side converter mathematical model and the first-order LADRC system;

[0044] Preferably, the first-order LADRC system consists of a linear extended state observer, a linear error feedback control rate and a total disturbance compensation, and the mathematical expression of the linear error feedback rate of the first-order LADRC system is: , , the mathematical expression of the control signal of the disturbance compensation link of the first-order LADRC system is: , where r is the preset reference input, is the output observation value, is the proportionality coefficient, is the controller bandwidth, u is the control quantity, is the total disturbance observation value, To control the gain.

[0045] Preferably, the mathematical expression of the d-axis current inner loop control of the current inner loop control model of the direct-drive wind turbine grid-side converter is: ,in, is the differential of the output observation, is the differential of the total perturbation observation, is the observer bandwidth, It is the d-axis control current reference input.

[0046] Specifically, in this embodiment, since the dq axis is symmetrical, only the d axis is used as an example for description, and the q axis is not described in detail. Figure 4 It can be seen that the first-order LADRC is composed of the second-order LESO, linear state error feedback (LSEF), total disturbance compensation and linear tracking differentiator (LTD); and because LTD may cause high-frequency oscillation problems in the system, LTD is usually not used in the design; among them, Figure 4 G(s) represents the controlled object and y represents the output.

[0047] It can be seen from step S1 that the grid-side converter control system is a first-order system, and the expression of the controlled object is: , where f is the total disturbance of the system. Assuming f1 is the internal disturbance of the system, the formula of the mathematical model of the grid-side converter including the subsynchronous disturbance component can be summarized as: ,in, , is the error part of the model, b= is the disturbance compensation factor of the system, ; At this time, the total disturbance of the system d axis is defined as ,get .

[0048] Next, let x1=i od , x2=F d , , and the state equation of the system is obtained According to the state equation of the system, the second-order LESO is constructed: ,in, , is the gain matrix of LESO.

[0049] Among them, LSEF is designed based on the results of LESO disturbance estimation, and its control rate is: Furthermore, according to the pole placement method, the gain coefficient of LESO and the proportional control gain of LSEF are parameterized respectively. , , Based on this, LADRC can be simplified to controller bandwidth , observer bandwidth and Three adjustable parameters.

[0050] In simple terms, this method first establishes a current inner loop control model of the direct-drive wind turbine grid-side converter based on the parameters of the direct-drive wind turbine grid-connected system and the mathematical model of the grid-side converter. This model is constructed using a first-order linear active disturbance rejection control (LADRC) system, which consists of three core parts: a linear extended state observer, a linear error feedback control rate, and a total disturbance compensation. This structural design enables the control model to accurately respond to grid changes while effectively suppressing subsynchronous oscillations. Among them, the linear extended state observer is responsible for real-time monitoring of the system state and disturbances, and its core lies in the ability to quickly and accurately estimate the total disturbance of the system. The linear error feedback control rate adjusts the control signal according to the observed state error to achieve precise control of the system. The total disturbance compensation link adjusts the control amount according to the observed disturbance to compensate for the uncertainty and external disturbances in the system.

[0051] S3, adding a phase advance module to the traditional linear extended state observer LESO to obtain an improved linear extended state observer;

[0052] Preferably, the mathematical expression of the improved linear extended state observer is: , the mathematical expression of the disturbance observation transfer function of the improved linear extended state observer is: ,in, is the leading time constant, a is a coefficient greater than 1, s is the Laplace operator, It is the differential of the total disturbance observation value z3 that ultimately acts on the disturbance compensation link.

[0053] Specifically, in this embodiment, according to the disturbance observation transfer function of the traditional second-order LESO It can be seen that the disturbance observation transfer function of LESO It is a second-order system. The second-order system has a contradiction between rapidity and overshoot in the time domain response of the medium and low frequency bands; in the frequency domain, it manifests as significant phase lag and amplitude attenuation, which reflects the limitations of traditional LESO in disturbance observation capabilities. It can enhance the disturbance estimation capability of LESO, but due to the influence of observation noise, it is difficult to increase the disturbance in the actual system. To enhance the disturbance estimation capability of LESO and avoid increasing In order to solve the problem that the system's ability to suppress high-frequency disturbances decreases, based on the concept of series lead correction, an advance link is introduced into the total disturbance branch, and the LESO disturbance transfer function is improved as follows:

[0054] Comparison of the perturbation capabilities of traditional LESO and improved LESO Figure 5 As shown, in Under the same numerical conditions, the disturbance observation capability of the improved LESO is significantly improved. Based on the above formula, the state space equation of the improved LESO can be obtained: , where z3 is the total disturbance observation value that ultimately acts on the disturbance compensation link, and is obtained by connecting z2 in series with the advance correction link.

[0055] Specifically, this method innovatively improves the traditional linear extended state observer (LESO) by adding a phase advance module to obtain an improved linear extended state observer. This improvement significantly improves the system's observation capability and response speed to disturbances, thereby enhancing the overall performance of the control system. In practical applications, the introduction of this improved LESO effectively suppresses the subsynchronous oscillation of direct-drive wind turbines under weak grid conditions. Due to the phase advance characteristics of the improved LESO, the system can respond to potential disturbances in advance, reduce the phase lag of the system, and improve the stability and dynamic response speed of the control system. This improvement not only improves the power generation efficiency of wind turbines, but also reduces the mechanical stress and equipment loss caused by subsynchronous oscillations, and extends the service life of the equipment. In addition, the introduction of the improved LESO also improves the robustness of the system, enabling wind turbines to operate stably under a wider range of grid conditions, including fluctuations in grid voltage and frequency. This improvement in robustness enables wind turbines to maintain efficient power output when facing complex grid environments, thereby improving the overall economic benefits of wind farms.

[0056] S4, introducing a fuzzy controller and combining it with a linear error feedback control rate LSEF to achieve online optimization of parameters, obtain a fuzzy improved LADRC controller, and apply the fuzzy improved LADRC controller to the direct-drive wind turbine grid-side converter current inner loop control model to obtain a direct-drive wind turbine grid-side converter current inner loop control system based on improved LADRC;

[0057] Specifically, step S4 includes: using the deviation e between the reference current and the actual current and the rate of change of the deviation As the input signal, the actual current deviation e and the rate of change of the deviation , get the change in the output proportional coefficient ;

[0058] The input and output of the fuzzy set of the fuzzy controller are set to seven levels, namely negative large NB, negative medium NM, negative small NS, zero ZE, positive small PS, positive medium PM, positive large PB, where the membership functions of the input and output are both triangular;

[0059] The amount of change based on the output scale factor , proportionality coefficient , and the levels of input and output, and obtain the tuned controller parameters , generate the fuzzy improved LADRC controller.

[0060] According to the three parts of fuzzy adaptive LSEF, improved LESO, and total disturbance compensation, an improved LADRC control system is established;

[0061] The improved LADRC control system is optimized based on the grid-side converter mathematical model to obtain the direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC, and its mathematical expression is: .

[0062] Specifically, in this embodiment, the performance of the controller is enhanced by introducing fuzzy control technology. The proportional gain coefficient of LSEF is dynamically adjusted by fuzzy reasoning to achieve adaptive parameter setting, thereby achieving the optimal control effect and forming a fuzzy improved LADRC controller. The fuzzy controller uses the deviation e between the reference current and the actual current and the rate of change of the deviation e c As input signals, according to e and e c The change in the output proportional coefficient In addition, the input and output of the fuzzy set are set to seven levels; based on the existing professional knowledge and engineering experience, a fuzzy control rule table that meets the operating conditions of the wind power system is obtained, as shown in Table 1.

[0063] Table 1 Fuzzy control rule table

[0064]

[0065] Furthermore, according to the mathematical expression of the current inner loop control system of the direct-drive wind turbine grid-side converter based on the improved LADRC, the structural block diagram of the improved LADRC combined with the fuzzy adaptive LSEF is obtained, as shown in Figure 6 As shown. Among them, the tracking error can be expressed as e1=z1-y, e2=z3-f. Based on the above formula, its specific expression is obtained: .

[0066] Since the observation error of the improved LADRC is related to the input and output of the controlled object, in order to make the analysis more representative, it is assumed that both the input and output are unit step functions. At this time, the steady-state error can be expressed as: It can be seen that the improved LESO has good convergence and can achieve unbiased estimation of z1 and z3.

[0067] The system input and disturbance closed-loop function of traditional LADRC is: ; The system input and disturbance closed-loop function of the improved LADRC is: ,in, , , .

[0068] The Bode plots of the disturbance term transfer functions of the traditional LADRC and the improved LADRC are compared, as shown in Figure 7 As shown. It can be seen that when When it is equal to 0, it is the traditional LADRC. As the interference resistance of LADRC increases, the anti-interference ability of LADRC continues to improve. In the low and medium frequency bands, the disturbance gain of the improved LADRC is always lower than that of the traditional LADRC, indicating that it has a stronger disturbance suppression ability in the low and medium frequency bands and can more effectively suppress the SSO phenomenon. Ignoring the control inertia of SPWM and the sampling delay of current, the current inner loop control structure diagram of the improved LADRC can be obtained according to the above formula as follows: Figure 8 As shown. The closed-loop transfer function of the system current loop is: , , , , , ; Currently known , , L f and R f The parameters are all positive, so we know that m i The values ​​are all greater than zero, i = 0, 1, 2, 3, 4. According to the Leonard-Chippert stability criterion, the necessary and sufficient condition for the stability of the system is that the odd-order Hurwitz determinant is positive, and we get , By bringing in numerical calculations, we can see that the first-order and third-order Hurwitz determinants are both greater than zero, so the improved LADRC current inner loop control system is stable.

[0069] In this embodiment, this method introduces a fuzzy controller for online optimization processing based on the improved linear extended state observer (LESO) to obtain a fuzzy improved LADRC controller. The introduction of this controller is intended to further improve the accuracy and adaptability of the current inner loop control of the grid-side converter of the direct-drive wind turbine. Through the reasoning mechanism of fuzzy logic, the controller parameters can be dynamically adjusted according to the specific values ​​of the actual current deviation and its rate of change to generate a fuzzy improved LADRC controller. This controller not only takes into account the dynamic characteristics of the system, but also improves the adaptability of the control system to various complex working conditions through the flexibility of fuzzy logic. Further, the fuzzy improved LADRC controller is applied to the current inner loop of the grid-side converter. This system can not only estimate and compensate for disturbances in the system in real time, but also dynamically adjust the control strategy according to the real-time feedback of the system to achieve precise control of the current inner loop of the grid-side converter of the direct-drive wind turbine.

[0070] Based on the mathematical model of the grid-side converter, we optimized the improved LADRC control system and obtained the current inner loop control system of the grid-side converter of the direct-drive wind turbine based on the improved LADRC. The mathematical expression of this system combines the dynamic adjustment capability of the fuzzy improved LADRC controller, the precise feedback mechanism of the linear feedback control rate and the effectiveness of the total disturbance compensation, thus realizing the efficient control of the current inner loop of the grid-side converter of the direct-drive wind turbine.

[0071] S5, using the direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC to calculate the grid-side converter to be controlled, obtain the modulation signal of the grid-side converter, and drive the grid-side converter to work based on the modulation signal.

[0072] Specifically, step S5 includes: obtaining current current data of the grid-side converter to be controlled;

[0073] The direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC is used to calculate the current current data, and output a modulation wave corresponding to the current current data of the grid-side converter;

[0074] The modulation wave is modulated by adopting sinusoidal pulse width modulation to obtain a modulation signal of the grid-side converter, and the main circuit of the grid-side converter is driven to operate based on the modulation signal.

[0075] Specifically, in this embodiment, the current current data of the grid-side converter is first obtained, and these data are the basis for the control system to make precise adjustments. Subsequently, the current current data are quickly calculated using the current inner loop control system of the direct-drive wind turbine grid-side converter based on the improved LADRC. This calculation process takes into account the dynamic characteristics and real-time changes of the system, and outputs a modulation wave corresponding to the current current data of the grid-side converter. This modulation wave is the key for the control system to make precise adjustments to the grid-side converter. Next, the modulation wave is modulated using sinusoidal pulse width modulation (SPWM) technology. Among them, SPWM technology is an effective modulation method that can convert the modulation wave into a modulation signal suitable for the operation of the grid-side converter. This modulation signal contains all the information required to control the output voltage and frequency of the grid-side converter, and is the core instruction for driving the main circuit of the grid-side converter.

[0076] Finally, based on the obtained modulation signal, we drive the main circuit of the grid-side converter to work, and realize the precise control of the current of the grid-side converter of the direct-drive wind turbine. This control method not only improves the response speed and regulation accuracy of the system, but also enhances the stability and reliability of the system.

[0077] In this embodiment, this control method not only improves the accuracy and stability of the current inner loop control of the grid-side converter of the direct-drive wind turbine, but also enhances the system's resistance to grid disturbances. The implementation of this control strategy enables the direct-drive wind turbine to operate stably under weak grid conditions, effectively suppresses subsynchronous oscillations, and improves the power generation efficiency of the wind turbine and the power quality of the grid. In addition, the adaptive characteristics of the fuzzy improved LADRC controller enable the system to maintain efficient power output and good stability in the face of complex and changeable grid environments, which is of great significance for improving the overall economic benefits of wind farms and the reliability of the grid.

[0078] Specifically, in this embodiment, in order to illustrate the effectiveness of this method, according to Figure 2 The structure shown in the figure is used to build the grid-connected system simulation model of the direct-drive wind turbine using PI control, traditional LADRC and improved LADRC in the grid-side converter current inner loop in MATLAB / Simulink software. The weak grid system is constructed by adjusting the equivalent inductance of the transmission line. In a specific application scenario, the wind speed v=9m / s is set. When the system is in a stable state, when t=1s, it is connected to the weak AC grid, and the SCR is set to 2.5 and 2.2 respectively. The comparison of the three-phase current of the grid is shown in the figure below. Fig. 9 When connected to a weak grid with an SCR of 2.2, the spectrum analysis of the grid-connected A phase current under three control modes is performed. The results are shown in Fig.10 shown.

[0079] from Fig.10It can be seen that after the system is connected to the weak power grid, when PI control is adopted, the sub / super synchronous frequency components generated by the A phase current are mainly at 22Hz and 78Hz, of which the sub-synchronous component of 22Hz is 43.6% of the fundamental amplitude, and the super-synchronous component of 78HZ is 34.9% of the fundamental amplitude, and the grid-connected current THD is 37.37%. Fig.10 b) and Fig.10 Figure c) is the spectrum diagram of LADRC and improved LADRC. The grid-connected A-phase current only contains a common frequency component of 50 Hz, and no large-amplitude disturbance components of other frequencies appear; this shows that both controls can block the generation of subsynchronous components and effectively suppress the SSO phenomenon.

[0080] When the current inner loop uses LADRC, the THD of the grid-connected current is 2.8% due to the insufficient observation accuracy of the controller; when the improved LADRC is used, the THD of the grid-connected current is reduced to 1.34%. Set the wind speed v=9m / s, when the system is in a stable state, when t=1s, the SCR connected to the weak AC grid is set to 2.5 and 2.2. Comparison of the three control methods of active power and reactive power Fig.11 As shown. Figure 8 and Fig.10 It can be seen that after the grid inductance is connected, the grid-connected current and power under PI control oscillate rapidly, and SSO occurs. And as the SCR decreases, the amplitude of the oscillation increases. When LADRC is used in the inner loop control, SSO can be effectively suppressed. However, due to the insufficient observation performance of LESO, the active power and reactive power fluctuate greatly after entering the steady state, and the grid-connected current waveform is distorted. The control proposed by this method can quickly suppress SSO in both SCR conditions, and the power fluctuation is reduced compared with the traditional LADRC, with better anti-interference ability. By comparing the current waveform, it can be seen that the waveform using the improved LADRC is relatively smooth, with almost no distortion, and the grid-connected output power quality is higher.

[0081] To verify the adaptability of the method, the wind speed is set to 9m / s and the system is connected to an extremely weak grid with SCR=1.5. The active power simulation results are as follows: Fig.12 When PI control is used, the active power output of the direct-drive wind power plant oscillates and the oscillation amplitude further increases; the traditional LADRC can suppress SSO, but the suppression effect is poor under extremely weak power grids, and the active power enters a steady state after fluctuating for a period of time; while the improved LADRC can still quickly suppress SSO and make the direct-drive wind turbine output stable, proving that the improved LADRC has good adaptability.

[0082] In order to further verify the effectiveness of the improved LADRC in suppressing subsynchronous oscillation, a prototype was built using an experimental platform consisting of MT6020HIL and MT1050RCP for verification. Fig.13 , Fig.14 and Fig.15 The following is a comparison of the current, active power and reactive power of the wind turbine prototype under three different control conditions in an environment with SCR=2.2. Fig.14 and Fig.15 It can be seen that the grid-connected current waveform is smoother and the current distortion rate is smaller when the current inner loop adopts the improved LADRC; the fluctuation range of active power and reactive power after entering the steady state is smaller, which is consistent with the theoretical analysis and simulation results. The direct-drive wind turbine grid-connected system controlled by the improved LADRC can operate stably under weak power grids, has good anti-interference ability, can suppress the subsynchronous oscillation problem caused by wind turbine access to the grid, and the system tracking error is smaller than that of the traditional LADRC.

[0083] In summary, the subsynchronous oscillation suppression method of direct-drive wind turbine based on improved first-order LADRC is improved on the basis of traditional LADRC. By analyzing the frequency domain of the improved LADRC, it can be seen that the improved LADRC has good convergence and anti-interference ability, and the disturbance gain in the medium and low frequency bands is lower, which can suppress the subsynchronous disturbance component more effectively than the traditional LADRC. Compared with the traditional LADRC, the improved LADRC can more effectively suppress the subsynchronous oscillation phenomenon. After the system enters the steady state, the fluctuation range of active power and reactive power is smaller, and the current waveform is smoother, which improves the robustness and steady-state performance of the direct-drive wind turbine grid-connected system. Under the working conditions of extremely weak power grids, the direct-drive wind turbine grid-connected system using the improved LADRC can still quickly and stably enter the steady state, and has the advantage of strong adaptability.

[0084] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC, characterized in that: include: Acquire the parameters of the preset direct-drive wind turbine grid-connected system, and construct a grid-side converter mathematical model according to the parameters of the direct-drive wind turbine grid-connected system; According to the mathematical model of the grid-side converter and the first-order LADRC system, a current inner loop control model of the grid-side converter of a direct-drive wind turbine is established; The traditional linear extended state observer LESO is processed by adding a phase advance module to the traditional linear extended state observer LESO to obtain an improved linear extended state observer; A fuzzy controller is introduced and combined with a linear error feedback control rate LSEF to realize online optimization of parameters, and a fuzzy improved LADRC controller is obtained. The fuzzy improved LADRC controller is applied to the current inner loop control model of the direct-drive wind turbine grid-side converter, and a direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC is obtained. Using the improved LADRC-based direct-drive wind turbine grid-side converter current inner loop control system to calculate the grid-side converter to be controlled, obtain a modulation signal of the grid-side converter, and drive the grid-side converter to work based on the modulation signal; The first-order LADRC system consists of a linear extended state observer, a linear error feedback control rate and a total disturbance compensation. The mathematical expression of the linear error feedback rate of the first-order LADRC system is: , , the mathematical expression of the control signal of the disturbance compensation link of the first-order LADRC system is: , where r is the preset reference input, is the output observation value, is the proportionality coefficient, is the controller bandwidth, u is the control quantity, is the total disturbance observation value, To control the gain; The mathematical expression of the d-axis current inner loop control of the direct-drive wind turbine grid-side converter current inner loop control model is: ,in, is the differential of the output observation, is the differential of the total perturbation observation, is the observer bandwidth, It is the d-axis control current reference input; The mathematical expression of the improved linear extended state observer is: , the mathematical expression of the disturbance observation transfer function of the improved linear extended state observer is: ,in, is the leading time constant, a is a coefficient greater than 1, s is the Laplace operator, is the differential of the total disturbance observation value z3 that ultimately acts on the disturbance compensation link; The fuzzy controller is introduced and combined with the linear error feedback control rate LSEF to realize the online optimization of parameters and obtain the fuzzy improved LADRC controller, which is as follows: The deviation e between the reference current and the actual current and the rate of change of the deviation As the input signal, the actual current deviation e and the rate of change of the deviation , get the change in the output proportional coefficient ; The input and output of the fuzzy set of the fuzzy controller are set to seven levels, namely negative large NB, negative medium NM, negative small NS, zero ZE, positive small PS, positive medium PM, positive large PB, where the membership functions of the input and output are both triangular; The amount of change based on the output scale factor , proportionality coefficient , and the levels of input and output, and obtain the tuned controller parameters , generate fuzzy improved LADRC controller; in, is the filter inductor, is the d-axis component of the grid-connected current, is the d-axis component of the grid-side converter output voltage.

2. The method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC according to claim 1 is characterized in that: The direct-drive wind turbine grid-connected system comprises a wind turbine, a permanent magnet synchronous generator, a machine-side converter, a grid-side converter, and a weak AC power grid.

3. The method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC according to claim 1 is characterized in that: The mathematical expression of the grid-side converter mathematical model is: , where t is time, is the grid synchronization angular velocity, is the q-axis component of the grid-connected current, is the equivalent resistance on the AC side, is the d-axis component of the grid-connected voltage, is the q-axis component of the grid-side converter output voltage, is the q-axis component of the grid-connected voltage, C is the DC side capacitance of the grid-side converter, is the DC bus voltage, The output current provided by the controlled current source simulates the wind turbine output power, is the wind turbine grid-connected current; The controlled current source of the mathematical model of the grid-side converter is equivalent to the wind turbine, permanent magnet synchronous generator and machine-side converter in the direct-drive wind farm.

4. The method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC according to claim 1 is characterized in that: The fuzzy improved LADRC controller is applied to the current inner loop control model of the direct-drive wind turbine grid-side converter to obtain the direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC, which is specifically: An improved LADRC control system is established based on the three parts of the fuzzy adaptive linear error feedback control rate, the improved linear extended state observer, and the total disturbance compensation; The improved LADRC control system is optimized based on the grid-side converter mathematical model to obtain the direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC, and its mathematical expression is: 。 5. The method for suppressing subsynchronous oscillation of a direct-drive wind turbine based on an improved first-order LADRC according to claim 1 is characterized in that: The direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC is used to calculate the grid-side converter to be controlled, obtain the modulation signal of the grid-side converter, and drive the grid-side converter to work based on the modulation signal, specifically: Acquire current data of the grid-side converter to be controlled; The direct-drive wind turbine grid-side converter current inner loop control system based on the improved LADRC is used to calculate the current current data, and output a modulation wave corresponding to the current current data of the grid-side converter; The modulation wave is modulated by adopting sinusoidal pulse width modulation to obtain a modulation signal of the grid-side converter, and the main circuit of the grid-side converter is driven to operate based on the modulation signal.

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