An Advanced Control Technique for Floating Offshore Wind Turbines Based on More Compact Barge Platforms

Abstract

Hydrodynamic Floating Offshore Wind Turbine (FOWT) platform specifications are typically dominated by seaworthiness and maximum operating platform-pitch angle-related requirements. However, such specifications directly impact the challenge posed by an FOWT in terms of control design. The conventional FOWT systems are typically based on large, heavy floating platforms, which are less likely to suffer from the negative damping effect caused by the excessive coupling between blade-pitch control and platform-pitch motion. An advanced control technique is presented here to increase system stability for barge type platforms. Such a technique mitigates platform-pitch motions and improves the generator speed regulation, while maintaining blade-pitch activity and reducing blade and tower loads. The NREL's 5MW + ITI Energy barge reference model is taken as a basis for this work. Furthermore, the capabilities of the proposed controller for performing with a more compact and less hydrodynamically stable barge platform is analysed, with encouraging results.Several attempts have been done to control and improve FOWT systems-however, not so many for barge mounted systems. This is because of the dilemma presented by this type of platform. When the blade-pitch action tries to regulate the generator speed in the above rated wind speed, a coupling between blade-pitch and platform-pitch motions can happen [10], known as the negative platform damping effect. This phenomenon makes the turbine unstable, potentially damaging mechanical components. One of the first and most complete studies done to tackle this phenomenon was carried out in [11], where three control alternatives were proposed to mitigate the barge platform-pitch motions. The best results were achieved detuning the blade-pitch PI control gains. Great reductions in the platform-pitch motion and in the mechanical component loads were achieved. However, the generator speed regulation quickness was degraded.Several Linear Quadratic Regulator (LQR) based controller designs are compared with the baseline blade-pitch PI controller in [12]. The LQR Gain-Scheduling (GS) and the Linear Parameter-Varying (LPV) GS State-Feedback (SF) control techniques show the best results. The LQR GS control provides the best power regulation, whereas the LPV GS SF provides the best platform-pitch damping. The baseline blade-pitch PI controller used for the comparison is tuned with those blade-pitch PI gains used for onshore wind turbines. Unfortunately, a mechanical load analysis is missing to verify the impact of the proposed controllers on the mechanical components.A comparison between the Individual Pitch Control (IPC) and the Collective Pitch Control (CPC) is presented in [13]. The IPC is based on three modules: the Disturbance Accommodating Control (DAC) aimed at eliminating the wind disturbances, the Model Predictive Control (MPC) to remove the influence of wave disturbances, and the fuzzy control module to combine both these algorithms. Both IPC and CPC techniques improve the power productio...

Using Multiple Fidelity Numerical Models for Floating Offshore Wind Turbine Advanced Control Design

“…This was supported by the PSD and DEL load analysis results, where the tower-base-pitch bending moment was reduced by 3.66%, not presenting any increment in the blade-root flapwise and edgewise bending moments. The results of this study, and the previous one [6], suggest a good APS feasibility for different types of FOWT models, motivating the experimental implementation of this control loop on a real FOWT prototype.…”

“…The overall FOWT performance improvements with the TripleSpar platform are not as spectacular as shown with the barge-type platform in [6]. This is because the APS control loop acts proportionally to the tower-top fore-aft displacement.…”

“…The advanced APS control technique was designed to mitigate the platform-pitch motion of the barge-type FOWT in the above rated wind speed [6]. In this article, the APS control loop has been redesigned to achieve the same functionality than in [6] but for a larger rated power wind turbine and a hydrodynamically more stable platform, i.e. the DTU 10 MW TripleSpar model.…”

“…Although all FOWT models need a control unit for the normal operation performance, low hydrodynamically stable platforms require additional advanced control algorithms to counteract the structural load produced by the incident waves, and, hence, extend the working live period. This is the case of the Aerodynamic Platform Stabiliser (APS) control technique presented in [6], which is designed to work in the ITI Energy barge-type platform concept with the NREL's 5 MW wind turbine. Good generator speed regulation, electric power production, generator torque demand and platform-pitch motion reduction were shown, resulting in large tower-base and blade-root bending moment reductions.…”

A Feedback Control Loop Optimisation Methodology for Floating Offshore Wind Turbines

“…In practice, wind turbine manufacturers often favor simple controllers based on the Proportional and Integral (PI) feedback loops over more complex ones [24]. In previous studies, in combination with the conventional PI controller, the Aerodynamic Platform Stabiliser (APS) [25,26] and Wave Rejection (WR) [27] feedback control loops have been designed for above rated wind speed working region to reduce the platform-pitch motions, while improving the generator speed regulation and reducing the tower-base and blade-root loads of the NREL 5-MW wind turbine mounted on the ITI Energy barge.…”