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Dynamic Modeling and Control for an Offshore Semisubmersible Floating Wind Turbine

Yingjie Gong, Qinmin Yang, Hua Geng, Wenchao Meng, Lin Wang

TL;DR

The work develops a nonlinear 7-DOF model for a semi-submersible floating wind turbine that explicitly includes rotor dynamics and finite platform rotations, enabling accurate capture of wind–wave–structure interactions. Building on this model, it introduces a robust adaptive nonlinear blade-pitch controller based on continuous integral of the sign of the error (RISE) with an online neural-network approximator to learn unknown dynamics and mitigate disturbances. Stability is established via a Lyapunov-based analysis, guaranteeing convergence of rotor-speed error and reduction of platform motion, while maintaining bounded internal signals. Validation against a 44-state FAST model shows good agreement, and control experiments demonstrate substantial reductions in rotor-speed tracking error and platform motions, with favorable load mitigation compared to reference methods.

Abstract

Floating wind turbines (FWTs) hold significant potential for the exploitation of offshore renewable energy resources. Nevertheless, prior to the construction of FWTs, it is imperative to tackle several critical challenges, especially the issue of performance degradation under combined wind and wave loads. This study initiates with the development of a simplified nonlinear dynamical model for a semi-submersible FWT. In particular, both the rotor dynamics and the finite rotations of the platform are considered in presented modeling approach, thereby effectively capturing the complex interplay between the platform, tower, nacelle, and rotor under combined wind and wave loads. Subsequently, based on the developed FWT model, a novel adaptive nonlinear pitch controller is formulated with the goal of striking a trade-off between regulating power generation and reducing platform motion. Notably, the proposed control strategy adopts a continuous control approach, strategically beneficial in circumventing the chattering phenomenon commonly associated with sliding mode control. Furthermore, the controller integrates an online approximator and a robust integral of the sign of the tracking error, facilitating real-time learning of system unknown dynamics while compensating for bounded disturbances. Finally, both the accuracy of the established nonlinear FWT model in predicting key dynamics and the superiority of the presented pitch controller are validated through comprehensive comparative studies.

Dynamic Modeling and Control for an Offshore Semisubmersible Floating Wind Turbine

TL;DR

The work develops a nonlinear 7-DOF model for a semi-submersible floating wind turbine that explicitly includes rotor dynamics and finite platform rotations, enabling accurate capture of wind–wave–structure interactions. Building on this model, it introduces a robust adaptive nonlinear blade-pitch controller based on continuous integral of the sign of the error (RISE) with an online neural-network approximator to learn unknown dynamics and mitigate disturbances. Stability is established via a Lyapunov-based analysis, guaranteeing convergence of rotor-speed error and reduction of platform motion, while maintaining bounded internal signals. Validation against a 44-state FAST model shows good agreement, and control experiments demonstrate substantial reductions in rotor-speed tracking error and platform motions, with favorable load mitigation compared to reference methods.

Abstract

Floating wind turbines (FWTs) hold significant potential for the exploitation of offshore renewable energy resources. Nevertheless, prior to the construction of FWTs, it is imperative to tackle several critical challenges, especially the issue of performance degradation under combined wind and wave loads. This study initiates with the development of a simplified nonlinear dynamical model for a semi-submersible FWT. In particular, both the rotor dynamics and the finite rotations of the platform are considered in presented modeling approach, thereby effectively capturing the complex interplay between the platform, tower, nacelle, and rotor under combined wind and wave loads. Subsequently, based on the developed FWT model, a novel adaptive nonlinear pitch controller is formulated with the goal of striking a trade-off between regulating power generation and reducing platform motion. Notably, the proposed control strategy adopts a continuous control approach, strategically beneficial in circumventing the chattering phenomenon commonly associated with sliding mode control. Furthermore, the controller integrates an online approximator and a robust integral of the sign of the tracking error, facilitating real-time learning of system unknown dynamics while compensating for bounded disturbances. Finally, both the accuracy of the established nonlinear FWT model in predicting key dynamics and the superiority of the presented pitch controller are validated through comprehensive comparative studies.
Paper Structure (17 sections, 2 theorems, 77 equations, 7 figures, 2 tables)

This paper contains 17 sections, 2 theorems, 77 equations, 7 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Modeling of the SSFWT system
  3. System kinematics
  4. External forces
  5. Nonlinear model of SSFWT
  6. Controller design
  7. Model reformulation
  8. Problem formulation
  9. Pitch controller design
  10. Stability analysis
  11. Model validation and control results
  12. Model validation
  13. Pitch controller validation
  14. Conclusion
  15. Added mass matrix.
  16. ...and 2 more sections

Key Result

Lemma 1

yang2015robust Define with $\bar{N}=\tilde{W}^T \phi(Z)$. Then it can be concluded with $H_0\equiv \gamma_d|\xi(0)|-\xi^T(0)(\bar{D}(0)+\bar{N}(0))$.

Figures (7)

  • Figure 1: Schematic diagram of the SSFWT.
  • Figure 2: Submerged length of platform floating member.
  • Figure 3: Overall structure of the proposed controller.
  • Figure 4: Profiles of wind and wave height.
  • Figure 5: The system responses under wind-wave joint loads.
  • ...and 2 more figures

Theorems & Definitions (5)

  • Remark 1
  • Remark 2
  • Remark 3
  • Lemma 1
  • Theorem 1