MS#04.2 Modeling and Control for FOWT Performance Improvement

M. AIT-AHMED¹, M.A. HAMIDA², H. CHAOUI³
¹ Nantes Université|² Ecole Centrale de Nantes|³ Carleton University

Turbine technology and Control

Nowadays, the production of energy by offshore wind turbines is gaining more and more attention due to the growing demand for renewable energy. The interest in this type of production, compared to onshore wind turbines, is mainly due to the quality of the winds, which are more regular at sea, as well as the reduced visual and acoustic impact in maritime areas. The distance of these offshore wind turbines from the shore is accompanied by increasingly significant water depths, which can reach more than 50 m, requiring the use of floating offshore wind turbines (FOWTs). To reduce manufacturing and operating costs, FOWTs must have a powerful generator and a minimum overall weight. As a result, the structure of the FOWT is sensitive to dynamic excitation (wind and wave loads). The structural vibrations and the oscillations of FOWT can affect the conversion of wind energy into electricity and lead to accelerated fatigue of the FOWT structure and the mooring lines.

One of the main challenges for floating wind turbines is the development of specific robust and adaptive control systems. Floating wind turbines are multivariable underactuated systems where the number of degrees of freedom (DOF) exceeds the number of control inputs. Thus, the limited number of actuators makes it difficult to minimise the movements of the structure while ensuring maximum energy extraction without giving conflicting control signals to the actuators or affecting other DOF due to couplings. This special feature of floating wind turbines means that non-trivial solutions have to be found to achieve the best compromise between ensuring the stability of the turbine and maximising the power generated. Against this backdrop, there are very few viable control solutions, i.e. with optimum performance that makes the wind turbine economically viable and structurally sustainable. It should be noted that the problem of controlling floating wind turbines has only been addressed by the automation community for a few years, and mainly using linear approaches. The use of non-linear control approaches under realistic conditions, taking into account the various couplings in the system, is very recent and not yet complete. In fact, if we consider a model that accurately represents the floating wind turbine, it will necessarily be non-linear and uncertain. In this case, the solution is much more complex. Therefore, on the one hand, it is necessary to develop uncertain nonlinear models that faithfully represent the system and can be used for control, and on the other hand, it is necessary to synthesise robust and optimal control techniques for these systems in order to achieve good performance levels in all operating regions.

This mini symposium will focus on the modelling and robust control of FOWTs. The aim is to propose : methods for obtaining simple models that are faithful to the dynamic behaviour of FOWTs, as well as techniques for estimating them; control strategies and robust control laws in region II and/or region III to maximize the power generated and its quality; control strategies and robust control laws for the vibration and oscillation reduction.