Cross coupling fractional order sliding mode control method for variable pitch system of wind driven generator

Abstract

The invention relates to a cross coupling fractional order sliding mode control method for a variable pitch system of a wind driven generator, and belongs to the technical field of electro-hydraulic control. The method comprises the steps that the current wind speed of the variable-pitch system of the wind driven generator is determined, when the wind speed is larger than the cut-in wind speed and smaller than the rated wind speed, a controller sends a command to the variable-pitch system, the pitch angle is changed from 90 degrees to 0 degree, and the variable-pitch system starts to work; when the wind speed is larger than the rated wind speed and smaller than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, a controller sends a command to a variable pitch system, synchronous closed-loop adjustment is conducted on the pitch angles of the three blades, and meanwhile the controller is compensated based on the synchronous error among the three pitch angles; and when the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90 degrees, and the generator stops working. According to the method, unknown external disturbance and internal uncertainty in the electro-hydraulic variable pitch system of the wind driven generator can be accurately estimated, and meanwhile, the synchronization error between adjacent blades is compensated.

Description

Technical Field

[0001] The invention belongs to the technical field of electro-hydraulic control, and in particular relates to a cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system. Background Art

[0002] Wind power generation is one of the most mature and largest power generation methods in the existing renewable energy field, and has broad application prospects. In the process of wind power generation, wind power is used to drive the windmill blades to rotate, and then the speed of rotation is increased by the speed increaser to promote the generator to generate electricity. Early wind power generation mostly used fixed pitch systems, which had low utilization of wind energy and difficult to control output power. The variable pitch system can adjust the pitch angle of each blade in real time according to the current wind speed and load, further improving the utilization of wind energy. At present, the control methods of the variable pitch system mainly include hydraulic variable pitch and electric variable pitch. Compared with the electric variable pitch system, the hydraulic variable pitch system has a small unit volume, light weight, fast response, and can output a large torque. It is widely used in wind power systems. However, most wind farms have harsh environments, and the variable pitch system will be subject to large unknown disturbances. At the same time, the system has strong nonlinearity and uncertainty. In addition, the sudden change of wind speed and the instability of the tower shadow effect will have a certain impact on the control of the variable pitch system. At the same time, during the operation of the wind turbine, due to the different loads on the three blades, the pitch angle cannot be synchronized during the pitch change, which will cause system imbalance and affect the safe operation of the wind turbine. Therefore, it is necessary to design a new control method that can achieve precise tracking and control of the pitch system under unknown external loads and nonlinear characteristics, and at the same time improve the synchronization control accuracy of the three blade pitch angles. Reference patent CN202311813978.5 proposes a parallel digital valve-controlled hydraulic pitch system and system, which consists of a plurality of parallel digital valves to form a pitch adjustment module to achieve rapid and precise adjustment of the pitch angle. For example, reference patent CN202311592802.1 proposes a wind turbine pitch self-anti-disturbance control controller, which adds dynamic characteristic compensation of the pitch actuator on the basis of the self-anti-disturbance control algorithm, which can improve the hysteresis and control accuracy of the pitch system. Although the prior art can achieve tracking control of the pitch system, it still has some shortcomings and limitations, and further improvements are needed:

[0003] (1) The electro-hydraulic pitch control system of wind turbines has large unknown external load disturbances, nonlinear characteristics, and internal uncertainties, making it difficult to establish a more accurate mathematical model, resulting in poor tracking performance of the pitch angle. At the same time, the influence of external environments such as sudden changes in wind speed and tower shadow effects will further increase the difficulty of controller design and undermine the stability of the system. In addition, the synchronization error between the three blades will also have a certain impact on the efficiency of the wind turbine. As the capacity of wind turbines continues to increase and the structural design becomes more compact and lightweight, the traditional linearization method of nonlinear problems can no longer meet the high performance requirements of the pitch control system.

[0004] (2) Sliding mode variable structure control can effectively deal with unknown disturbances in the system and has good robustness. However, in actual application, when the system state reaches the vicinity of the sliding mode surface, a larger control gain is required to suppress the influence of the disturbance. The traditional sliding mode control strategy will have an inherent jitter phenomenon, resulting in poor tracking performance. The master-slave synchronization control adopted by most multi-axis synchronous controls has hysteresis. If the slave branch is disturbed, the active branch cannot be quickly adjusted and corrected, resulting in low synchronization control accuracy. The cross-coupling synchronization control structure is complex and has great limitations for systems with more than two axes. Therefore, how to weaken the jitter of the sliding mode control and improve the tracking accuracy and synchronization accuracy of the variable pitch system is the key to improving the utilization rate of wind energy. Summary of the invention

[0005] The object of the present invention is to provide a cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system. This method can achieve a good tracking effect for a single blade pitch angle in the presence of external interference and internal uncertainty during the pitch control process, while achieving a higher synchronization accuracy for the three pitch angles, thereby further enhancing the robustness of the system.

[0006] To achieve the above object, the technical solution of the present invention is: a cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system, comprising:

[0007] Step S1, determining the current wind speed of the wind turbine pitch system. When the wind speed is greater than the cut-in wind speed and less than the rated wind speed, the controller sends a command to the pitch system, the pitch angle changes from 90° to 0°, and the pitch system starts working;

[0008] Step S2: when the wind speed is greater than the rated wind speed and less than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, and the controller sends a command to the variable pitch system to perform synchronous closed-loop adjustment on the pitch angles of the three blades through three sets of independent variable pitch electro-hydraulic drive devices, and at the same time compensate the controller based on the synchronization error between the three pitch angles;

[0009] Step S3: When the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90° and the wind turbine stops working.

[0010] In one embodiment of the present invention, the specific implementation method of step S2 is:

[0011] Step S21, when the current wind speed reaches the rated wind speed, a mathematical model of an independent pitch control system is established that takes into account the strong dynamic nonlinearity, wind speed mutation, tower shadow effect, and unknown internal and external disturbances of the electro-hydraulic pitch control system;

[0012] Step S22, converting the dynamic model into a control-oriented model, and designing an extended state observer to achieve accurate estimation of the lumped disturbance to each independent pitch system;

[0013] Step S23, designing a fractional-order sliding mode controller, and compensating the controller based on the disturbance value estimated by the extended state observer designed in step S22, so as to suppress the lumped disturbance of the pitch system, weaken the system chattering, and enhance the robustness;

[0014] Step S24: To solve the problem of asynchronous pitch angles of the three blades, a synchronous control method of adjacent cross coupling is adopted, and feedforward compensation is performed considering the error between the expected and actual pitch angles and the synchronization error between two adjacent blades, so as to improve the synchronization control accuracy between the pitch angles of the three blades;

[0015] Step S25, optimizing the parameters of the extended state observer and the fractional-order sliding mode controller, improving the tracking performance and synchronous control performance of the entire variable pitch system, and ensuring the stability of the entire system.

[0016] In one embodiment of the present invention, the implementation method of step S21 is:

[0017] Wind turbines require three independent electro-hydraulic pitch systems. Each system is regarded as a crank slider mechanism, which converts the linear motion of the hydraulic cylinder piston rod into the rotation of the pitch angle. For a single blade, the external disturbance and internal nonlinear characteristics of the pitch system are regarded as lumped disturbances, and a hydraulic model of the pitch system is established. The asymmetric hydraulic cylinder is controlled by a servo proportional valve. The state variables are the displacement and speed of the hydraulic cylinder and the pressure of the rodless and rod chambers. The input is the valve opening, and the output is the displacement of the hydraulic cylinder. The state space equation of the single blade electro-hydraulic pitch system is obtained. The details are as follows:

[0018] The valve port flow equation is:

[0019]

[0020] The continuity equation of hydraulic cylinder flow is:

[0021]

[0022] The force balance equation is:

[0023]

[0024] The asymmetric hydraulic cylinder is controlled by a servo proportional valve, and the state variable is selected as Input is valve core displacement x vi , the output is the hydraulic cylinder displacement x pi , then the system state space equation can be expressed as:

[0025]

[0026] in,

[0027]

[0028] sgn(g) is the sign function:

[0029]

[0030] Where i is the hydraulic cylinder No. i; x p is the displacement of the hydraulic cylinder piston rod; is the speed of the hydraulic cylinder piston rod; is the acceleration of the hydraulic cylinder piston rod; u is the control input, i.e., the displacement of the valve core; m is the mass of the piston rod; A and a are the areas of the rodless cavity and the rod cavity of the hydraulic cylinder, respectively; p1 and p2 are the pressures of the rodless cavity and the rod cavity of the hydraulic cylinder, respectively; are the first-order derivatives of the pressure in the rodless chamber and the rod chamber of the hydraulic cylinder respectively; Q1 is the flow rate flowing into the oil inlet chamber of the hydraulic cylinder; Q2 is the flow rate flowing out of the oil return chamber of the hydraulic cylinder; B p is the viscous damping coefficient; K is the load spring stiffness, β e V is the effective bulk elastic modulus of the oil; 01 、V 02 are the initial volumes of the rodless cavity and the rod cavity respectively; C ip , C ep are the internal and external leakage coefficients respectively; C d is the flow coefficient of the servo proportional valve; W is the area gradient; x v is the valve core displacement; ρ is the oil density; p s is the pump source pressure; d is the lumped disturbance.

[0031] In one embodiment of the present invention, the implementation method of step S22 is:

[0032] The extended state observer needs to transform the model into a third-order control-oriented model based on the input-output feedback linearization method, ignoring the viscous damping coefficient B p and load spring stiffness K, the state variables are selected as the displacement, velocity and acceleration of the hydraulic cylinder The model will be converted into an integral series form, the disturbance of the system will be expanded into a new state variable, and the state observer of the expanded system will be established according to the input and output signals of the system to achieve accurate estimation of the displacement, velocity and lumped disturbance of the hydraulic cylinder. The system control guidance model is as follows:

[0033]

[0034] in:

[0035]

[0036] According to the obtained control-oriented model, d i ′ is expanded into a new state variable, let The new control system after expansion is:

[0037]

[0038] Establish a state observer for the above expanded system:

[0039]

[0040] In the formula, represents the observation error of the observer; Represents the observed value of the state; ω 0i is any positive constant.

[0041] In one embodiment of the present invention, the implementation method of step S23 is:

[0042] The fractional-order sliding mode controller aims to converge the system tracking error to 0. The error is defined as the difference between the hydraulic cylinder displacement obtained by the desired pitch angle and the actual displacement. A sliding mode surface with fractional order is designed to obtain the control input of the variable pitch system.

[0043] The fractional-order sliding mode combines the advantages of fractional-order calculus and sliding mode control, and can further weaken the system chattering on the basis of traditional sliding mode, with good robustness. The fractional-order sliding mode surface is constructed as follows:

[0044]

[0045] Where: D is the fractional differential operator, which represents the i Perform a differential operation of order α; λ i is a positive constant; 0<α<2 is the order of the fractional order; e i =x d -x i is the tracking error of the i-th axis; is the first-order derivative of the tracking error of the i-th axis.

[0046] By taking the derivative of formula (11), we can get:

[0047]

[0048] Using the exponential reaching law:

[0049]

[0050] Where: c i , k i are all positive constants; is the first-order differential of the sliding surface; Represents the second-order derivative of the tracking error of the i-th axis.

[0051] Combined with the extended observer, the system disturbance d i The estimated value of ′, the final system control input is as follows:

[0052]

[0053] Where: x d is the hydraulic cylinder displacement required for the current optimal pitch angle; It is the third-order differential of the hydraulic cylinder displacement required for the current optimal pitch angle.

[0054] In one embodiment of the present invention, the implementation method of step S24 is:

[0055] The synchronous control method of adjacent cross-coupling is to consider the variable pitch system as three synchronous subsystems. On the basis of individual control of each blade, the error of the pitch angle between two adjacent blades is considered, so that the blades are coupled with each other, and PI control is adopted to realize accurate and fast compensation of the synchronization error.

[0056] To solve the problem of asynchronous pitch angles of the three blades, an adjacent cross-coupling synchronous control method is adopted. Considering the error between the expected and actual pitch angles and the synchronization error between two adjacent blades, feedforward compensation is performed and the error between two adjacent blades is defined as ε i :

[0057]

[0058] In formula (15), if ε i Finally, they can converge to 0, which satisfies the synchronization requirements between the blades. For multi-axis synchronous control, the i-th axis needs to consider the synchronization error between the i-1th axis and the i+1th axis, that is:

[0059]

[0060] According to formula (16), an adjacent cross-coupled synchronous control structure is constructed, and PI control is adopted to achieve rapid compensation of synchronization error and improve the control performance of the system.

[0061] In one embodiment of the present invention, the implementation method of step S25 is:

[0062] A positive Lyapunov function is designed, and various parameters of the sliding mode controller and adjacent cross-coupled synchronization control are selected. According to the Lyapunov stability theorem, the system can quickly converge to the sliding mode surface, ensuring that both the tracking error and the synchronization error can eventually converge to 0.

[0063] The designed positive definite Lyapunov function is:

[0064]

[0065] Combining equations (11), (12), and (14), we can derive equation (17) as follows:

[0066]

[0067] In the formula, is the first-order differential of the Lyapunov function.

[0068] From formula (18), we can get that as long as Based on Lyapunov theory, it can be concluded that the system is asymptotically stable.

[0069] The present invention also provides a cross-coupled fractional-order sliding mode control system for a wind turbine pitch control system, comprising:

[0070] The acquisition module collects the current wind speed of the wind turbine pitch system;

[0071] The controller determines the relationship between the current wind speed of the wind turbine pitch system and the cut-in wind speed, rated wind speed, and cut-out wind speed. When the wind speed is greater than the cut-in wind speed and less than the rated wind speed, the controller sends a command to the pitch system, and the pitch angle changes from 90° to 0°, and the pitch system starts to work; when the wind speed is greater than the rated wind speed and less than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, and the controller sends a command to the pitch system to perform synchronous closed-loop adjustment on the pitch angles of the three blades through three sets of independent pitch electro-hydraulic drive devices, and compensates the controller based on the synchronization error between the three pitch angles; when the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90°, and the wind turbine stops working;

[0072] The execution module performs corresponding actions based on the controller commands.

[0073] The present invention also provides a computer software system, including a memory, a processor, and computer program instructions stored in the memory and capable of being executed by the processor. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0074] The present invention also provides a computer-readable storage medium, on which computer program instructions that can be executed by a processor are stored. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] The present invention proposes a wind turbine pitch control system with adjacent cross-coupling fractional-order sliding mode, which can achieve good tracking effect when the system is subject to unknown external loads, internal uncertainties, and strong nonlinearity, and realize synchronous control between three blades. Its significant advantages include:

[0077] 1) Aiming at the strong nonlinearity and unknown external disturbance characteristics in the electro-hydraulic pitch control system, an extended state observer is designed. The external disturbance and internal unmodeled characteristics are regarded as a lumped disturbance and expanded into a new state. A state observer is established to observe the system state and disturbance. Fractional-order calculus is added to the traditional integer-order sliding mode control. Based on the state observer established above, real-time estimation and compensation of disturbances are realized, which effectively weakens the high-frequency jitter problem of sliding mode control and improves the robustness of the system.

[0078] 2) To solve the problem of synchronization error of the pitch angles of the three blades in the electro-hydraulic pitch control system, based on the adjacent cross-coupling synchronization control method, the state between each blade and its two adjacent blades is considered, and PI control is adopted. The feedback signal of the controlled blade is coupled with the difference between the feedback signals of the adjacent blades and then compensated, so as to achieve fast and accurate compensation of the synchronization error and improve the synchronization control accuracy between independent pitch control systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 is a flow chart of a method implementation of an embodiment of the present invention;

[0080] Figure 2 It is a schematic diagram of the adjacent cross-coupled fractional-order sliding mode synchronization control method in an embodiment of the present invention. DETAILED DESCRIPTION

[0081] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0082] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0083] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0084] like Figure 1As shown, the present invention provides a cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system, comprising the following steps:

[0085] Step S1, determining the current wind speed of the wind turbine pitch system. When the wind speed is greater than the cut-in wind speed and less than the rated wind speed, the controller sends a command to the pitch system, the pitch angle changes from 90° to 0°, and the pitch system starts working;

[0086] Step S2: when the wind speed is greater than the rated wind speed and less than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, and the controller sends a command to the variable pitch system to perform synchronous closed-loop adjustment on the pitch angles of the three blades through three sets of independent variable pitch electro-hydraulic drive devices, and at the same time compensate the controller based on the synchronization error between the three pitch angles;

[0087] Step S3: When the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90° and the wind turbine stops working.

[0088] In the embodiment of the present invention, the specific implementation method of step S2 is:

[0089] Step S21, when the current wind speed reaches the rated wind speed, a mathematical model of an independent pitch control system is established that takes into account the strong dynamic nonlinearity, wind speed mutation, tower shadow effect, and unknown internal and external disturbances of the electro-hydraulic pitch control system;

[0090] Step S22, converting the dynamic model into a control-oriented model, and designing an extended state observer to achieve accurate estimation of the lumped disturbance to each independent pitch system;

[0091] Step S23, designing a fractional-order sliding mode controller, and compensating the controller based on the disturbance value estimated by the extended state observer designed in step S22, so as to suppress the lumped disturbance of the pitch system, weaken the system chattering, and enhance the robustness;

[0092] Step S24: To solve the problem of asynchronous pitch angles of the three blades, a synchronous control method of adjacent cross coupling is adopted, and feedforward compensation is performed considering the error between the expected and actual pitch angles and the synchronization error between two adjacent blades, so as to improve the synchronization control accuracy between the pitch angles of the three blades;

[0093] Step S25, optimizing the parameters of the extended state observer and the fractional-order sliding mode controller, improving the tracking performance and synchronous control performance of the entire variable pitch system, and ensuring the stability of the entire system.

[0094] The following is a further detailed explanation of the relevant contents involved in this method.

[0095] In step S21, the wind turbine generator set requires three independent electro-hydraulic pitch systems, each of which can be regarded as a crank slider mechanism, which converts the linear motion of the hydraulic cylinder piston rod into the rotation of the pitch angle. For a single blade, the external disturbance and internal nonlinear characteristics of the pitch system are regarded as lumped disturbances, and a hydraulic model of the pitch system is established.

[0096] The valve port flow equation is:

[0097]

[0098] The continuity equation of hydraulic cylinder flow is:

[0099]

[0100] The force balance equation is:

[0101]

[0102] The asymmetric hydraulic cylinder is controlled by a servo proportional valve, and the state variable is selected as Input is valve core displacement x vi , the output is the hydraulic cylinder displacement x pi , then the system state space equation can be expressed as:

[0103]

[0104] in,

[0105]

[0106] sgn(g) is the sign function:

[0107]

[0108] Where i is the hydraulic cylinder No. i; x p is the displacement of the hydraulic cylinder piston rod; is the speed of the hydraulic cylinder piston rod; is the acceleration of the hydraulic cylinder piston rod; u is the control input, i.e., the displacement of the valve core; m is the mass of the piston rod; A and a are the areas of the rodless cavity and the rod cavity of the hydraulic cylinder, respectively; p1 and p2 are the pressures of the rodless cavity and the rod cavity of the hydraulic cylinder, respectively; are the first-order derivatives of the pressure in the rodless chamber and the rod chamber of the hydraulic cylinder respectively; Q1 is the flow rate flowing into the oil inlet chamber of the hydraulic cylinder; Q2 is the flow rate flowing out of the oil return chamber of the hydraulic cylinder; B p is the viscous damping coefficient; K is the load spring stiffness, β e V is the effective bulk elastic modulus of the oil; 01 、V 02 are the initial volumes of the rodless cavity and the rod cavity respectively; C ip , C epare the internal and external leakage coefficients respectively; C d is the flow coefficient of the servo proportional valve; W is the area gradient; x v is the valve core displacement; ρ is the oil density; p s is the pump source pressure; d is the lumped disturbance.

[0109] like Figure 2 As shown, in step S22, the extended state observer needs to transform the model into a third-order control-oriented model based on the input-output feedback linearization method, ignoring the viscous damping coefficient B p and load spring stiffness K, the state variables are selected as the displacement, velocity and acceleration of the hydraulic cylinder The model will be converted into an integral series form, the disturbance of the system will be expanded into a new state variable, and the state observer of the expanded system will be established according to the input and output signals of the system to achieve accurate estimation of the displacement, velocity and lumped disturbance of the hydraulic cylinder. The system control guidance model is as follows:

[0110]

[0111] in:

[0112]

[0113] According to the obtained control-oriented model, d i ′ is expanded into a new state variable, let The new control system after expansion is:

[0114]

[0115] In the formula, h i (t) is bounded.

[0116] Establish a state observer for the above expanded system:

[0117]

[0118] In the formula, represents the observation error of the observer; Represents the observed value of the state; ω 0i is any positive constant.

[0119] In step S23, the fractional order sliding mode combines the advantages of fractional order calculus and sliding mode control, can further weaken the chattering of the system on the basis of traditional sliding mode, and has good robustness. The fractional order sliding mode surface is constructed as follows:

[0120]

[0121] Where: D is the fractional differential operator, which represents the i Perform a differential operation of order α; λ i is a positive constant; 0<α<2 is the order of the fractional order; e i =x d -x i is the tracking error of the i-th axis; is the first-order derivative of the tracking error of the i-th axis.

[0122] By taking the derivative of formula (11), we can get:

[0123]

[0124] Using the exponential reaching law:

[0125]

[0126] Where: c i , k i are all positive constants; is the first-order differential of the sliding surface; Represents the second-order derivative of the tracking error of the i-th axis.

[0127] Combined with the extended observer, the system disturbance d i The estimated value of ′, the final system control input is as follows:

[0128]

[0129] Where: x d is the hydraulic cylinder displacement required for the current optimal pitch angle; It is the third-order differential of the hydraulic cylinder displacement required for the current optimal pitch angle.

[0130] In step S24, in order to solve the problem of asynchronous pitch angles of the three blades, an adjacent cross-coupled synchronous control method is adopted. Considering the error between the expected and actual pitch angles and the synchronization error between two adjacent blades, feedforward compensation is performed. The error between two adjacent blades is defined as ε i :

[0131]

[0132] In formula (15), if ε i Finally, they can converge to 0, which satisfies the synchronization requirements between the blades. For multi-axis synchronous control, the i-th axis needs to consider the synchronization error between the i-1th axis and the i+1th axis, that is:

[0133]

[0134] According to formula (16), an adjacent cross-coupled synchronous control structure is constructed, and PI control is adopted to achieve rapid compensation of synchronization error and improve the control performance of the system.

[0135] In step S25, a positive Lyapunov function is designed, and various parameters of the sliding mode controller and adjacent cross-coupled synchronization control are selected. According to the Lyapunov stability theorem, the system can quickly converge to the sliding mode surface, ensuring that the tracking error and the synchronization error can eventually converge to 0.

[0136] The designed positive definite Lyapunov function is:

[0137]

[0138] Combining equations (11), (12), and (14), we can derive equation (17) as follows:

[0139]

[0140] In the formula, is the first-order differential of the Lyapunov function.

[0141] From formula (18), we can get that as long as Based on Lyapunov theory, it can be concluded that the system is asymptotically stable.

[0142] The present invention also provides a cross-coupled fractional-order sliding mode control system for a wind turbine pitch control system, comprising:

[0143] The acquisition module collects the current wind speed of the wind turbine pitch system;

[0144] The controller determines the relationship between the current wind speed of the wind turbine pitch system and the cut-in wind speed, rated wind speed, and cut-out wind speed. When the wind speed is greater than the cut-in wind speed and less than the rated wind speed, the controller sends a command to the pitch system, and the pitch angle changes from 90° to 0°, and the pitch system starts to work; when the wind speed is greater than the rated wind speed and less than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, and the controller sends a command to the pitch system to perform synchronous closed-loop adjustment on the pitch angles of the three blades through three sets of independent pitch electro-hydraulic drive devices, and compensates the controller based on the synchronization error between the three pitch angles; when the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90°, and the wind turbine stops working;

[0145] The execution module performs corresponding actions based on the controller commands.

[0146] The present invention also provides a computer software system, including a memory, a processor, and computer program instructions stored in the memory and capable of being executed by the processor. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0147] The present invention also provides a computer-readable storage medium, on which computer program instructions that can be executed by a processor are stored. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0148] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0149] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0150] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0151] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1The steps for the functions specified in one or more boxes.

[0152] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system, characterized in that: include: Step S1, determining the current wind speed of the wind turbine pitch system. When the wind speed is greater than the cut-in wind speed and less than the rated wind speed, the controller sends a command to the pitch system, the pitch angle changes from 90° to 0°, and the pitch system starts working; Step S2: when the wind speed is greater than the rated wind speed and less than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, and the controller sends a command to the variable pitch system to perform synchronous closed-loop adjustment on the pitch angles of the three blades through three sets of independent variable pitch electro-hydraulic drive devices, and at the same time compensate the controller based on the synchronization error between the three pitch angles; Step S3: When the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90° and the wind turbine stops working.

2. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system according to claim 1, characterized in that: The specific implementation method of step S2 is: Step S21, when the current wind speed reaches the rated wind speed, a mathematical model of an independent pitch control system is established that takes into account the strong dynamic nonlinearity, wind speed mutation, tower shadow effect, and unknown internal and external disturbances of the electro-hydraulic pitch control system; Step S22, converting the dynamic model into a control-oriented model, and designing an extended state observer to achieve accurate estimation of the lumped disturbance to each independent pitch system; Step S23, designing a fractional-order sliding mode controller, and compensating the controller based on the disturbance value estimated by the extended state observer designed in step S22, so as to suppress the lumped disturbance of the pitch system, weaken the system chattering, and enhance the robustness; Step S24: To solve the problem of asynchronous pitch angles of the three blades, a synchronous control method of adjacent cross coupling is adopted, and feedforward compensation is performed considering the error between the expected and actual pitch angles and the synchronization error between two adjacent blades, so as to improve the synchronization control accuracy between the pitch angles of the three blades; Step S25, optimizing the parameters of the extended state observer and the fractional-order sliding mode controller, improving the tracking performance and synchronous control performance of the entire variable pitch system, and ensuring the stability of the entire system.

3. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system according to claim 2, characterized in that: The implementation method of step S21 is: Wind turbines require three independent electro-hydraulic pitch systems. Each system is regarded as a crank slider mechanism, which converts the linear motion of the hydraulic cylinder piston rod into the rotation of the pitch angle. For a single blade, the external disturbance and internal nonlinear characteristics of the pitch system are regarded as lumped disturbances, and a hydraulic model of the pitch system is established. The asymmetric hydraulic cylinder is controlled by a servo proportional valve. The state variables are selected as the displacement and speed of the hydraulic cylinder and the pressure of the rodless cavity and the rod cavity. The input is the valve opening, and the output is the displacement of the hydraulic cylinder. The state space equation of the single blade electro-hydraulic pitch system is obtained.

4. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system according to claim 2, characterized in that: The implementation method of step S22 is: The expanded state observer needs to transform the model into a third-order control-oriented model. Based on the input-output feedback linearization method, the viscous damping coefficient and the load spring stiffness are ignored, and the state variables are selected as the displacement, velocity and acceleration of the hydraulic cylinder. The model will be transformed into an integral series form, and the system disturbance will be expanded into a new state variable. The state observer of the expanded system is established according to the input and output signals of the system to achieve accurate estimation of the displacement, velocity and lumped disturbance of the hydraulic cylinder.

5. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system according to claim 2, characterized in that: The implementation method of step S23 is: The fractional-order sliding mode controller aims to converge the system tracking error to 0. The error is defined as the difference between the hydraulic cylinder displacement obtained by the desired pitch angle and the actual displacement. A sliding mode surface with fractional order is designed to obtain the control input of the variable pitch system.

6. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system according to claim 2, characterized in that: The implementation method of step S24 is: The synchronous control method of adjacent cross-coupling is to consider the variable pitch system as three synchronous subsystems. On the basis of individual control of each blade, the error of the pitch angle between two adjacent blades is considered, so that the blades are coupled with each other, and PI control is adopted to realize accurate and fast compensation of the synchronization error.

7. A cross-coupled fractional-order sliding mode control method for a wind turbine pitch control system according to claim 2, characterized in that: The implementation method of step S25 is: A positive Lyapunov function is designed, and various parameters of the sliding mode controller and adjacent cross-coupled synchronization control are selected. According to the Lyapunov stability theorem, the system can quickly converge to the sliding mode surface, ensuring that both the tracking error and the synchronization error can eventually converge to 0.

8. A cross-coupled fractional-order sliding mode control system for a wind turbine pitch control system, characterized in that: include: The acquisition module collects the current wind speed of the wind turbine pitch system; The controller determines the relationship between the current wind speed of the wind turbine pitch system and the cut-in wind speed, rated wind speed, and cut-out wind speed. When the wind speed is greater than the cut-in wind speed and less than the rated wind speed, the controller sends a command to the pitch system, and the pitch angle changes from 90° to 0°, and the pitch system starts to work; when the wind speed is greater than the rated wind speed and less than the cut-out wind speed, the optimal pitch angle is obtained according to the current wind speed, and the controller sends a command to the pitch system to perform synchronous closed-loop adjustment on the pitch angles of the three blades through three sets of independent pitch electro-hydraulic drive devices, and compensates the controller based on the synchronization error between the three pitch angles; when the wind speed is greater than the cut-out wind speed, the pitch angle is adjusted to 90°, and the wind turbine stops working; The execution module performs corresponding actions based on the controller commands.

9. A computer software system, characterized in that: The method comprises a memory, a processor, and computer program instructions stored in the memory and executable by the processor. When the processor executes the computer program instructions, the method steps as claimed in any one of claims 1 to 7 can be implemented.

10. A computer-readable storage medium storing computer program instructions that can be executed by a processor, wherein when the processor executes the computer program instructions, the method steps according to any one of claims 1 to 7 can be implemented.

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