A floating offshore wind turbine safety control method

Abstract

The application provides a floating offshore wind turbine safety control method, steps comprising: constructing a mechanical-electrical coupling model based on a secondary problem description, converting into a control affine system, and studying the relationship between the blade pitch angle and the generator rotor angular velocity; constructing a control Lyapunov function candidate according to the speed reference value under the over-rating operation mode, constructing a control barrier function candidate according to the platform pitch angle threshold, and verifying the rationality; taking the control Lyapunov function and the control barrier function as constraints, constructing a control framework of a nonlinear optimization problem, and solving the blade pitch angle control output. The method can effectively improve the generator speed tracking performance under the over-rating condition on the premise that the platform pitch angle does not exceed the safety boundary, enhance the adaptability of the control strategy to the complex marine environment and model uncertainty, and has good engineering application value and popularization prospect.

Description

Technical Field

[0001] This invention relates to the field of wind turbine coordinated control technology, and more specifically, to a safety control method for floating offshore wind turbines. Background Technology

[0002] Against the backdrop of a global push for green energy transition and a strong advocacy for sustainable development, renewable energy technologies have made significant progress, and my country's energy structure is undergoing a critical stage of deep adjustment and continuous transformation. In this process, wind energy, as a crucial component of clean energy, is playing an increasingly important role in the construction of new power systems due to its abundant resources and wide distribution. Floating offshore wind turbines, with their advantages of adaptability to deep-sea deployment and improved wind energy utilization efficiency, are gradually becoming an important development direction for offshore wind power. Compared to onshore and fixed offshore wind turbines, large floating offshore wind turbines are connected to the seabed through mooring systems and are simultaneously subjected to multiple disturbances from wind, waves, and currents during operation, exhibiting stronger nonlinear, coupled, and time-varying characteristics. Furthermore, there is a significant mechanical-electrical coupling relationship between the turbine's mechanical structure movement and the power generation and grid connection process, making its dynamic behavior more complex. Especially in over-rated operation modes, the larger average wind speed and more severe wind speed fluctuations in deep-sea areas can easily cause the generator speed to deviate from the rated target and induce an increase in the platform pitch angle, thereby threatening the safe operation of the turbine. Therefore, how to balance stable generator speed tracking and platform pitch safety constraints under over-rated operating conditions has become a key issue that urgently needs to be addressed in the field of large floating offshore wind turbine control.

[0003] In existing technologies, on the one hand, most studies model the mechanical and electrical subsystems of floating offshore wind turbines separately, making it difficult to accurately reflect the coupling effects between platform motion, transmission chain dynamics, aerodynamic torque, electromagnetic torque, and current control; on the other hand, existing over-rated operation control methods mostly aim at generator speed tracking and platform pitch suppression, usually treating platform pitch only as a performance optimization indicator, rather than incorporating it into the controller design as a strict safety constraint. Therefore, under complex sea conditions and strong wind disturbances, the safety and engineering applicability of the control strategy are still insufficient.

[0004] Based on this, the present invention proposes a safety-critical speed control method for large floating offshore wind turbines in over-rated operation mode, so as to achieve safe and stable operation of large floating offshore wind turbines under complex wind and wave disturbances. Summary of the Invention

[0005] This invention proposes a safety control method for floating offshore wind turbines. Based on the mechanical-electrical coupling model of large floating offshore wind turbines, the method solves the pitch angle control output by considering the optimization problem with speed tracking and unit safety as constraints. This fully considers the operational safety requirements of the unit and provides a new approach for the design of unit operation and control methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A safety control method for floating offshore wind turbines, characterized by comprising the following steps: A simplified dynamic model of a large floating offshore wind turbine considering the mechanical-electrical coupling mechanism was established. Based on the simplified dynamic model and the dynamic relationship between the generator rotor angular velocity and the platform pitch angle, the system is converted into a form suitable for control design. Candidate control Lyapunov functions are constructed based on the generator speed reference value under over-rated operation mode; Based on the platform pitch angle safety threshold, candidate control obstacle functions are constructed to form unit operation safety constraints; The control Lyapunov function constraints and control barrier function constraints are uniformly incorporated into the nonlinear optimization control framework to construct an optimization problem, and the blade pitch angle control output is solved in real time based on the optimization problem. Safety-critical speed control of large floating offshore wind turbines in over-rated operation mode is achieved based on the blade pitch angle control output.

[0007] Furthermore, the process of establishing a simplified dynamic model of a large floating offshore wind turbine that considers the mechanical-electrical coupling mechanism includes: A mechanical model is established based on the theory of blade element momentum and the principles of fluid mechanics. The mechanical model includes the calculation of aerodynamic thrust, rotor torque and wind power, as well as the dynamic equations under the platform pitch degree of freedom. The electrical component model is established based on the first-order transmission chain model and the voltage model of the permanent magnet synchronous motor. By combining the mechanical part model and the electrical part model, a control affine system is established with the platform pitch angle, platform pitch angular velocity, generator rotor angular velocity and q-axis current as state variables.

[0008] Furthermore, the mechanical model focuses on the dynamic changes of the floating wind turbine under the pitch degree of freedom:

[0009] in, The moment of inertia refers to the pitch and rotation of a platform about its center of gravity. The linear hydrostatic restoring stiffness coefficient, which is related to buoyancy and hydrodynamic restoring force. The added quality factor refers to the infinite frequency. It is the radiation damping coefficient, used to characterize the wave radiation effect caused by platform motion. The moment of inertia of the rotor, Indicates the angular velocity of the rotor. This indicates the mass of the supporting structure.

[0010] Furthermore, the electrical component model is represented by the following formula:

[0011]

[0012] in, This represents the stator resistance of a permanent magnet synchronous motor. This represents the stator winding inductance of a permanent magnet synchronous motor. This refers to the permanent magnet flux linkage in a permanent magnet synchronous motor. Indicates the number of pole pairs of the motor. Let represent the current and voltage along the d-axis and q-axis of the permanent magnet synchronous motor, respectively. It is a constant.

[0013] The control Lyapunov function constraint and the control barrier function constraint are integrated into the nonlinear optimization control framework.

[0014] Furthermore, the control affine system is shown in the following equation:

[0015] in, State variables, The moment of inertia refers to the pitch and rotation of a platform about its center of gravity. The linear hydrostatic restoring stiffness coefficient, which is related to buoyancy and hydrodynamic restoring force. The added quality factor refers to the infinite frequency. It is the radiation damping coefficient, used to characterize the wave radiation effect caused by platform motion. The moment of inertia of the rotor, Indicates the angular velocity of the rotor. Indicates the mass of the supporting structure. This refers to the permanent magnet flux linkage in a permanent magnet synchronous motor. Indicates the number of pole pairs of the motor. Refers to air density. Refers to the length of the turbine blades. Refers to wind speed. Refers to the height of the tower.

[0016] Furthermore, the Lyapunov function candidates are shown in the following equation:

[0017] in The angular velocity of the generator rotor. This is the reference value for the rated speed.

[0018] Furthermore, the candidate control barrier function is shown in the following equation:

[0019]

[0020] in, The platform's pitch angle, For the platform's pitch angular velocity, The platform pitch angle safety threshold, This is the aiming time.

[0021] Furthermore, the optimization problem is as follows:

[0022]

[0023]

[0024]

[0025] in, It is an optional control set. It is a slack variable. H and p λ is the weighting parameter, and λ is the adjustment parameter.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention takes floating wind turbine generators as the research object. Compared with traditional fixed wind turbines and floating wind turbine modeling that only focuses on the mechanical parts, it improves the model's adaptability to wind and wave fluctuations and higher degrees of freedom by considering the mechanical-electrical coupling mechanism. Furthermore, it reduces the computational cost and improves deployment and operation and maintenance capabilities through simplification.

[0027] This invention considers floating offshore wind turbines as the modeling object, encompassing various floating foundation types such as column-mounted, semi-submersible, tension leg, and barge-type foundations. Furthermore, it can be applied to different operating modes of large floating offshore wind turbines, including under-rated power, maximum wind energy capture, and over-rated power modes, covering a wide range.

[0028] This invention is based on the established mechanical-electrical coupling model of a large floating offshore wind turbine generator set. It takes the blade pitch angle as the control object, considers the generator speed tracking problem outside the rated operating range, and for the first time considers the platform pitch angle constraint as a strict safety requirement, and designs a new control strategy.

[0029] The safety-critical speed control method for unit operating under over-rated conditions proposed in this invention can obtain the dynamic information directly from the unit parameters and the control information directly from the source, without the need to develop a separate dynamic and control system, and is easy to integrate with existing tools and platforms.

[0030] The safety-critical speed control method proposed in this invention has been verified in open-source large floating offshore wind turbines, demonstrating that it can quickly and effectively achieve speed tracking under dynamic operating conditions including platform pitch angle safety constraints, providing a control method reference for the stable operation of the unit.

[0031] In summary, this invention possesses both theoretical innovation and engineering feasibility, as well as industrial application promotion value, making it suitable for demonstration deployment in large floating offshore wind turbine generators operating under complex conditions. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings: Figure 1 This is a schematic diagram of the overall process of the safety control method for floating offshore wind turbines of the present invention; Figure 2 This is a schematic diagram of a simulated random wind and wave condition scenario in an embodiment of the present invention; Figure 3 This is a graph showing the experimental results of the dynamic response of the wind turbine in an embodiment of the present invention. Detailed Implementation

[0033] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0034] This embodiment proposes a safety control method for floating offshore wind turbines, such as... Figure 1 As shown, a simplified dynamic model of a large floating offshore wind turbine considering the mechanical-electrical coupling mechanism is first established. While balancing modeling accuracy and computational efficiency, the dynamic relationship between blade pitch angle, generator rotor angular velocity, and platform pitch angle is characterized. Furthermore, to address the speed tracking requirement under over-rated operation mode, a control Lyapunov function based on generator speed tracking error is constructed. Simultaneously, a control obstacle function is constructed for the platform pitch angle safety threshold, and both are integrated into a nonlinear optimization control framework. Finally, by solving the control input that satisfies the speed convergence requirement and the platform pitch safety constraint in real time, the blade pitch angle control output is obtained, thereby achieving safe and stable operation of the large floating offshore wind turbine under complex wind and wave disturbances. The specific steps include: Step 1. Establish a simplified dynamic model of a large floating offshore wind turbine considering the mechanical-electrical coupling mechanism; Step 2. Based on the established model, analyze the dynamic relationship between the blade pitch angle, the generator rotor angular velocity, and the platform pitch angle, and convert the system into a form suitable for control design; Step 3. Construct candidate Lyapunov control functions based on the generator speed reference value under over-rated operating mode; Step 4. Construct candidate control obstacle functions based on the platform pitch angle safety threshold, and form unit operation safety constraints; Step 5. Integrate the control Lyapunov function constraints and control obstacle function constraints into the nonlinear optimization control framework, and solve the blade pitch angle control output in real time; Step 6. Based on the desired control output, implement safety-critical speed control for large floating offshore wind turbines in over-rated operation mode.

[0035] I. Mechanical-Electrical Coupling Model of Large Floating Offshore Wind Turbine Generator (1) Mechanical part model In large floating offshore wind turbine generators, the mechanical components are primarily affected by wind thrust. According to blade element momentum theory and aerodynamic principles, aerodynamic thrust... Rotor torque and captured wind power It can be represented as:

[0036]

[0037]

[0038] in, Refers to air density. Refers to the length of the turbine blades. This refers to the relative wind speed received by the blades. The pitch angle of the generator platform. Refers to wind speed. Refers to the tower height, This refers to the thrust, torque, and energy coefficient of the wind turbine. Based on this, this embodiment assumes the wind direction is always perpendicular to the rotor orientation, and therefore focuses on the dynamic changes of the floating wind turbine in the pitch degree of freedom:

[0039] in, The moment of inertia refers to the pitch and rotation of a platform about its center of gravity. The linear hydrostatic restoring stiffness coefficient, which is related to buoyancy and hydrodynamic restoring force. The added quality factor refers to the infinite frequency. It is the radiation damping coefficient, used to characterize the wave radiation effect caused by platform motion. The moment of inertia of the rotor, Indicates the angular velocity of the rotor. This indicates the mass of the supporting structure.

[0040] (2) Electrical Part Model Based on the first-order transmission chain model, the dynamic process of rotor speed can be described as follows:

[0041] in, This represents the moment of inertia of the rotor. Indicates the gearbox transmission ratio. This represents the electromagnetic torque of the generator.

[0042] In the electrical model, a permanent magnet synchronous motor is considered as the power generation unit of a large floating offshore wind turbine. For a surface-mounted permanent magnet synchronous motor, its voltage model can be written as follows:

[0043]

[0044] in, This represents the stator resistance of a permanent magnet synchronous motor. This represents the stator winding inductance of a permanent magnet synchronous motor. This refers to the permanent magnet flux linkage in a permanent magnet synchronous motor. Indicates the number of pole pairs of the motor. These represent the current and voltage along the d-axis and q-axis, respectively. For surface-mounted permanent magnet synchronous motors (PMSMs), the direct-axis current reference value is typically set to zero to obtain the maximum torque-to-current ratio. Furthermore, for the inner current loop, if the controller performs well, it can achieve control to the reference value in milliseconds; therefore, this embodiment ignores the corresponding control inner loop. Additionally, it is assumed that… The value is constant because, for areas exceeding the rated range, the reference value for the rotor speed of a floating offshore wind turbine is constant.

[0045] (3) Controlling the affine system For thrust coefficient By simplifying the empirical model, a linear representation can be obtained:

[0046] in, These are empirical coefficients for fitting, which are related to the fan model and control mode. In this case, this embodiment combines mechanical and electrical models, setting the state variables as... This allows for the creation of a control affine system for large floating offshore wind turbines:

[0047] In this affine control system, the control vector can be characterized as: .

[0048] II. Key Safety Control Methods for Large Floating Offshore Wind Turbine Generators (1) Control objectives of floating wind turbine generator sets As mentioned earlier, under operating conditions above the rated wind speed, the rotor speed is adjusted via the blade pitch angle, and the speed reference value is fixed. Here, we take the 15MW floating wind turbine published by NREL as an example. Therefore, the goal of the pitch controller is to adjust the rotor speed to its rated value, i.e., 7.55 rpm. In the problem of this embodiment, the goal is to achieve FOWT speed tracking while ensuring the safety constraints of the FOWT design. Therefore, the control requirements can be summarized as follows: Stability requirements:

[0049] Safety requirements:

[0050] in, It is the aiming time, used for adjusting the blade pitch angle.

[0051] (2) Control target constraint transformation Based on stability requirements, candidate control Lyapunov functions are proposed:

[0052] Based on security requirements, it is first broken down into two parts: Safety Requirement 1:

[0053] Safety Requirement 2:

[0054] In this case, we propose corresponding candidate control barrier functions:

[0055] (3) Design of control method framework Based on the aforementioned control objective and the transformed control Lyapunov and control obstacle function candidates, an optimization problem can be constructed to solve for the control output:

[0056]

[0057]

[0058]

[0059] in, It is an optional control set. These are slack variables, their function is to ensure that the optimization problem has a solution. Therefore, this controller can meet safety-critical requirements, and its purpose is to handle the problem of nonlinear optimization that may not converge. When At this point, the original CLF constraint will no longer be strictly satisfied; this is to ensure the feasibility of the CLF. However, as long as the NQP problem without slack variables is feasible, slack variables... This avoids any practical impact. At each time step, the control Lyapunov function constraints and the control barrier function constraints are updated based on the current state value. The nonlinear optimization problem is then solved to obtain the control output. This control output is then applied to the nonlinear dynamic system, and the system state is updated within a very small time step. This ensures the forward invariance of the control barrier function.

[0060] IV. Validation of the proposed safety-critical speed tracking method using an open-source wind turbine model. To verify the effectiveness of the proposed control method, this embodiment builds a model of a large floating offshore wind turbine based on NREL 15MW in the MATLAB platform. The simulated random wind and wave conditions are as follows: Figure 2 As shown in the figure, Indicates wind force parameters, This represents wave parameters. In this scenario, the wind speed is... Wave parameters It is time-varying and random.

[0061] The results of the experiment are as follows Figure 3 As shown in the figure, the stability and safety requirements of the system are both met, as can be seen from the CLF and CBF constraints.

[0062] Throughout the time series, the CBF constraint remains greater than 0, indicating that the FOWT's pitch angle is consistently below the safety threshold. Furthermore, the CLF constraint is greater than 0 in the initial phase, meaning the slack variable is greater than 0 at the initial moment, and the controller is in a safety-critical state. Therefore, within the operating range above rated wind speed, this method can adjust the FOWT's rotor angular velocity to its reference value while ensuring platform pitch safety.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A safety control method for a floating offshore wind turbine, characterized in that, Includes the following steps: A simplified dynamic model of a large floating offshore wind turbine considering the mechanical-electrical coupling mechanism was established. Based on the simplified dynamic model and the dynamic relationship between the generator rotor angular velocity and the platform pitch angle, the system is converted into a form suitable for control design. Candidate control Lyapunov functions are constructed based on the generator speed reference value under over-rated operation mode; Based on the platform pitch angle safety threshold, candidate control obstacle functions are constructed to form unit operation safety constraints; The control Lyapunov function constraints and control barrier function constraints are uniformly incorporated into the nonlinear optimization control framework to construct an optimization problem, and the blade pitch angle control output is solved in real time based on the optimization problem. Safety-critical speed control of large floating offshore wind turbines in over-rated operation mode is achieved based on the blade pitch angle control output.

2. The method according to claim 1, characterized in that, The process of establishing a simplified dynamic model of a large floating offshore wind turbine that takes into account the mechanical-electrical coupling mechanism includes: A mechanical model is established based on the theory of blade element momentum and the principles of fluid mechanics. The mechanical model includes the calculation of aerodynamic thrust, rotor torque and wind power, as well as the dynamic equations under the platform pitch degree of freedom. The electrical component model is established based on the first-order transmission chain model and the voltage model of the permanent magnet synchronous motor. By combining the mechanical part model and the electrical part model, a control affine system is established with the platform pitch angle, platform pitch angular velocity, generator rotor angular velocity and q-axis current as state variables.

3. The method according to claim 1, characterized in that, The mechanical part model focuses on the dynamic changes of the floating wind turbine under the pitch degree of freedom: ， in, The moment of inertia refers to the pitch and rotation of a platform about its center of gravity. The linear hydrostatic restoring stiffness coefficient, which is related to buoyancy and hydrodynamic restoring force. The added quality factor refers to the infinite frequency. It is the radiation damping coefficient, used to characterize the wave radiation effect caused by platform motion. The moment of inertia of the rotor, Indicates the angular velocity of the rotor. This indicates the mass of the supporting structure.

4. The method according to claim 1, characterized in that, The electrical component model is represented by the following formula: ， ， in, This represents the stator resistance of a permanent magnet synchronous motor. This represents the stator winding inductance of a permanent magnet synchronous motor. This refers to the permanent magnet flux linkage in a permanent magnet synchronous motor. Indicates the number of pole pairs of the motor. Let represent the current and voltage along the d-axis and q-axis of the permanent magnet synchronous motor, respectively. It is a constant; The control Lyapunov function constraint and the control barrier function constraint are integrated into the nonlinear optimization control framework.

5. The method according to claim 2, characterized in that, The control affine system is shown in the following equation: ， in, State variables, The moment of inertia refers to the pitch and rotation of a platform about its center of gravity. The linear hydrostatic restoring stiffness coefficient, which is related to buoyancy and hydrodynamic restoring force. The added quality factor refers to the infinite frequency. It is the radiation damping coefficient, used to characterize the wave radiation effect caused by platform motion. The moment of inertia of the rotor, Indicates the angular velocity of the rotor. Indicates the mass of the supporting structure. This refers to the permanent magnet flux linkage in a permanent magnet synchronous motor. Indicates the number of pole pairs of the motor. Refers to air density. Refers to the length of the turbine blades. Refers to wind speed. Refers to the height of the tower.

6. The method according to claim 1, characterized in that, The Lyapunov function candidates are shown in the following equation: ， in The angular velocity of the generator rotor. This is the reference value for the rated speed.

7. The method according to claim 1, characterized in that, The candidate control barrier function is shown in the following equation: ， ， in, The platform's pitch angle, For the platform's pitch angular velocity, The platform pitch angle safety threshold, This is the aiming time.

8. The method according to claim 1, characterized in that, The optimization problem is shown in the following equation: ， ， ， ， in, It is an optional control set. It is a slack variable. H and p λ is the weighting parameter, and λ is the adjustment parameter.

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