Floating offshore wind turbine individual pitch control method

Abstract

This invention provides an independent pitch control method for floating offshore wind turbines, which increases lifespan and improves spar stability. It reduces structural loads on the floating offshore wind turbine while adjusting generator power. The method employs a controller that combines a low-authority linear quadratic controller with integral control; and an LQ controller with an integral controller. The LQ controller aims to reduce blade 1P vibration, tower fore-and-aft vibration, and platform pitch motion, while the integral action ensures rotor speed convergence to rated speed above the rated wind range. The LQ controller optimizes dynamic characteristics. The controller combines the low-authority LQ controller and the integral controller to determine the pitch angle of each blade. The control input for each blade pitch angle is obtained using the following formula: Θ=θ+Θ l (1) where θ is the uniform pitch angle from the integral controller, Θ l This is the independent pitch angle from the LQ controller.

Description

Technical Field

[0001] This invention relates to the field of wind power technology, specifically to an independent pitch control method for floating offshore wind turbines. Background Technology

[0002] With the increasing demand for renewable energy, offshore wind power will become one of the main sources of renewable energy in the coming years. Because wind turbines are inherently expensive, optimizing their performance to improve energy production and design life is crucial. Offshore wind turbines are subject to the influence of random wind and wave environments, with most structural loads transferred from the blades to the platform. The rotor of a wind turbine is designed to extract the maximum possible mechanical energy from the incoming wind. In this process, the blades actively pitch according to the magnitude of the inflow wind speed to maintain the rotor speed at its rated value even in winds exceeding the rated speed. While the turbine blades are primarily designed to maintain the rated rotor speed, modern wind turbines also utilize active pitch control to reduce their aerodynamic loads.

[0003] Floating offshore wind turbines (FOWTs) present additional challenges for designing suitable controllers, as the stability of the FOWT (platform pitch and yaw) is a crucial factor that must be considered. Independent pitch control proposed in existing studies has failed to improve platform response, and some controllers have even adversely affected platform motion. Therefore, developing control methods that not only increase power generation but also simultaneously reduce the load on the wind turbine and platform is a significant challenge. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an independent pitch control method for floating offshore wind turbines, which simultaneously reduces the variability of rotor speed, thereby increasing power generation and reducing structural loads on the wind turbine and floating platform, thus increasing lifespan and improving spar stability.

[0005] Wind turbine blade pitch actuators are primarily used to maintain rated power production at wind speeds above the rated speed; therefore, control algorithms are typically developed solely to regulate generator power. However, improving power regulation often has adverse effects on the motion of the floating platform. This invention proposes a novel control method to achieve these two competing objectives.

[0006] The proposed controller combines a low-authority linear quadratic (LQ) controller with integral control to reduce the aerodynamic load at 1P (frequency per revolution), while using a uniform pitch controller, traditionally used only for optimizing generator power, to regulate power production. The proposed method is simple, intuitive, and easy to design, and can significantly reduce rotor oscillation, blade vibration, and platform motion, as well as significantly reduce the turbine load at 1P.

[0007] An independent pitch control method for floating offshore wind turbines is characterized by: reducing the structural load on the floating offshore wind turbine while adjusting generator power; employing a controller that combines a low-authority linear quadratic controller with integral control to reduce aerodynamic load per revolution frequency, while using a pitch controller to regulate power production; combining an LQ controller with an integral controller, where the LQ controller aims to reduce blade 1P vibration, tower fore-and-aft vibration, and platform pitch motion, the integral action ensures that the rotor speed converges to the rated speed when above the rated wind range, and the LQ controller optimizes dynamic characteristics; the controller combines the low-authority LQ controller and the integral controller to determine the pitch angle of each blade, and the control input for the pitch angle of each blade is obtained through the following formula:

[0008] Θ=θ+Θ l (1)

[0009] Where θ is the uniform pitch angle from the integral controller, Θ l Independent pitch angle from the LQ controller;

[0010] The measurement signal at the real-time output of the floating offshore wind turbine is filtered through a low-pass filter and directed to the positive input of the reference signal. Then, the output of the reference signal inputs the error signal to the LQ controller, which calculates Θ1 based on the parameters. The output signal of the reference signal is input to the integral controller, which calculates θ based on the parameters.

[0011] Its further feature is that it includes the following reasoning steps:

[0012] The controller combines a low-authority LQ controller and an integral controller to determine the pitch angle of each blade. The control input for each blade pitch angle is obtained using the following formula:

[0013] Θ=θ+Θ l (1)

[0014] Where θ is the uniform pitch angle from the integral controller, and Θ is the independent pitch angle from the LQ controller;

[0015] The downwind components of a wind turbine are subject to most of the aerodynamic loads; therefore, the degrees of freedom chosen for the reduced-order model are...

[0016] q={q P q TFA1 q B1F1 q B2F1 q B3F1 q ε} T (2)

[0017] The five degrees of freedom listed are platform pitch, first tower forward and backward bending mode, second tower forward and backward bending mode, first flap bending mode of blade 1, first flap bending mode of blade 2, first flap bending mode of blade 3, and generator speed error.

[0018] The equations of motion are obtained using the Kane method. By neglecting quadratic and higher-order terms, the nonlinear equations of motion can be further linearized. These equations of motion are inherently time-varying; however, due to the relatively small amplitude of the time-varying nature along the wind direction, assuming rotor freezing, the time-varying terms will decrease further. The final linear time-invariant equations can be written in matrix form.

[0019]

[0020] Among them, the aerodynamic load F Aero (v,Θ) is a function of wind speed v and blade pitch angle Θ; hydrodynamic load F Hydro It is the effective wave height H s and peak spectral period T p A function of . M, C, and K are the mass, stiffness, and damping matrices, respectively;

[0021] The second-order equation can then be rewritten in first-order form.

[0022]

[0023] in, It is a state vector; This is the control input. Ideally, the control influence matrix B(Θ) is a function of each pitch angle. However, to simplify controller design, it is assumed that the controller gain matrix is ​​derived around the total pitch angle θ and is applicable to Θ [i.e., B(Θ)≈B(θ)]. The control influence matrix is ​​obtained by a Taylor series expansion of the aerodynamic loads with the total pitch angle as the operating point.

[0024]

[0025] Where O represents higher-order terms. The control effect matrix is ​​obtained from the following equation.

[0026]

[0027] Using the linearized system matrix described above, a steady-state (infinite range) LQ controller is designed, ignoring the external disturbance term in (4). The cost function of the low-authority LQ controller can be expressed as:

[0028]

[0029] Where Q is the state weight matrix used in the penalty control system; R is the input weight matrix of the penalty control input vector. For a steady-state LQ regulator, the control input can be obtained from the solution of the algebraic Ricatti equation.

[0030]

[0031] Its further characteristic is:

[0032] The integral controller's response frequency must be lower than the minimum response frequency and wave loading frequency of the floating offshore wind turbine to prevent the controller from amplifying the turbine's response. Therefore, the integral gain K is selected. I To obtain the controller response natural frequency of 0.2 rad / s, in most sea states, the controller response frequency of 0.2 rad / s is lower than the platform pitch natural frequency and wave loading frequency. Therefore, the controller maintains positive damping, and the final control input is obtained from equation (1).

[0033] Compared with existing methods, the proposed controller is more effective in reducing rotor speed fluctuations, thereby improving the power production of FOWT. In addition, the proposed controller can simultaneously mitigate FOWT structural response and power fluctuations. The controller's simple and intuitive characteristics make it easy to design. By using a reduced-order FOWT model and a linear approximation of the control influence matrix, the controller can be designed without requiring accurate information from a nonlinear wind turbine model. It can significantly reduce blade vibration and platform motion, as excessive blade vibration and platform motion seriously affect the normal operation and lifespan of wind turbines. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the method flow model of the present invention. Detailed Implementation

[0035] Independent pitch control method for floating offshore wind turbines, see Figure 1 This system reduces the structural load on floating offshore wind turbines while regulating generator power. It employs a controller that combines a low-authority linear quadratic controller with integral control to reduce aerodynamic load per revolution. A pitch controller is used to regulate power production. The system combines an LQ controller with an integral controller. The LQ controller aims to mitigate blade 1P vibration, tower fore-and-aft vibration, and platform pitch motion. The integral action ensures that the rotor speed converges to the rated speed when above the rated wind range, while the LQ controller optimizes dynamic characteristics. The controller combines the low-authority LQ controller and the integral controller to determine the pitch angle of each blade. The control input for each blade pitch angle is obtained using the following formula:

[0036] Θ=θ+Θ l (1)

[0037] Where θ is the uniform pitch angle from the integral controller, Θ l Independent pitch angle from the LQ controller;

[0038] The measurement signal at the real-time output of the floating offshore wind turbine is filtered through a low-pass filter and directed to the positive input of the reference signal. Then, the output of the reference signal inputs the error signal to the LQ controller, which calculates Θ1 based on the parameters. The output signal of the reference signal is input to the integral controller, which calculates θ based on the parameters.

[0039] It includes the following reasoning steps:

[0040] The controller combines a low-authority LQ controller and an integral controller to determine the pitch angle of each blade. The control input for each blade pitch angle is obtained using the following formula:

[0041] Θ=θ+Θ l (1)

[0042] Where θ is the uniform pitch angle from the integral controller, and Θ is the independent pitch angle from the LQ controller;

[0043] The downwind components of a wind turbine are subject to most of the aerodynamic loads; therefore, the degrees of freedom chosen for the reduced-order model are...

[0044] q={q P q TFA1 q B1F1 q B2F1 q B3F1 q ε} T (2)

[0045] The five degrees of freedom listed are platform pitch, first tower forward and backward bending mode, second tower forward and backward bending mode, first flap bending mode of blade 1, first flap bending mode of blade 2, first flap bending mode of blade 3, and generator speed error.

[0046] The equations of motion are obtained using the Kane method. By neglecting quadratic and higher-order terms, the nonlinear equations of motion can be further linearized. These equations of motion are inherently time-varying; however, due to the relatively small amplitude of the time-varying nature along the wind direction, assuming rotor freezing, the time-varying terms will decrease further. The final linear time-invariant equations can be written in matrix form.

[0047]

[0048] Among them, the aerodynamic load F Aero (v,Θ) is a function of wind speed v and blade pitch angle Θ; hydrodynamic load F HydroIt is the effective wave height H s and peak spectral period T p A function of . M, C, and K are the mass, stiffness, and damping matrices, respectively;

[0049] The second-order equation can then be rewritten in first-order form.

[0050]

[0051] in, It is a state vector; This is the control input. Ideally, the control influence matrix B(Θ) is a function of each pitch angle. However, to simplify controller design, it is assumed that the controller gain matrix is ​​derived around the total pitch angle θ and is applicable to Θ [i.e., B(Θ)≈B(θ)]. The control influence matrix is ​​obtained by a Taylor series expansion of the aerodynamic loads with the total pitch angle as the operating point.

[0052]

[0053] Where O represents higher-order terms. The control effect matrix is ​​obtained from the following equation.

[0054]

[0055] Using the linearized system matrix described above, a steady-state (infinite range) LQ controller is designed, ignoring the external disturbance term in (4). The cost function of the low-authority LQ controller can be expressed as:

[0056]

[0057] Where Q is the state weight matrix used in the penalty control system; R is the input weight matrix of the penalty control input vector. For a steady-state LQ regulator, the control input can be obtained from the solution of the algebraic Ricatti equation.

[0058]

[0059] In practical implementation, the integral controller's response frequency must be lower than the minimum response frequency and wave loading frequency of the floating offshore wind turbine to prevent the controller from amplifying the floating offshore wind turbine's response. Therefore, the integral gain K is selected. I To obtain the controller response natural frequency of 0.2 rad / s, in most sea states, the controller response frequency of 0.2 rad / s is lower than the platform pitch natural frequency and wave loading frequency. Therefore, the controller maintains positive damping, and the final control input is obtained from Equation (1).

[0060] Compared with existing methods, the proposed controller is more effective in reducing rotor speed fluctuations, thereby improving the power production of FOWT. In addition, the proposed controller can simultaneously mitigate FOWT structural response and power fluctuations. The controller's simple and intuitive characteristics make it easy to design. By using a reduced-order FOWT model and a linear approximation of the control influence matrix, the controller can be designed without requiring accurate information from a nonlinear wind turbine model. It can significantly reduce blade vibration and platform motion, which are serious factors that affect the normal operation and lifespan of wind turbines.

[0061] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An independent pitch control method for floating offshore wind turbines, characterized in that: While regulating generator power, it reduces the structural load on floating offshore wind turbines. It employs a controller that combines a low-authority linear quadratic controller with integral control to reduce aerodynamic load per revolution, while using a pitch controller to regulate power production. The LQ controller is combined with an integral controller; the LQ controller aims to mitigate blade 1P vibration, tower fore-and-aft vibration, and platform pitch motion, while the integral action ensures rotor speed convergence to rated speed above rated wind speeds. The LQ controller optimizes dynamic characteristics. The controller combines the low-authority LQ controller and integral controller to determine the pitch angle Θ of each blade. The control input for the pitch angle Θ of each blade is obtained using the following formula: （1）； Where θ is the uniform pitch angle from the integral controller, Θ l Independent pitch angle from the LQ controller; The measurement signal at the real-time output of the floating offshore wind turbine is filtered through a low-pass filter and redirected to the positive input of the reference signal. Then, the output of the reference signal inputs the error signal to the LQ regulator, which calculates Θ based on the parameters. l The output signal of the reference signal is input to the integrator controller, which calculates θ based on the parameters.

Images