Research On Load Mitigation And Control Technology Of Offshore Floating Wind Turbine System

In the past years, with the development of onshore wind energy and fixed-bottom structures offshore wind turbine, many efforts have been made to research deep-sea large floating wind turbines all over the world. Deep sea wind energy exploit will undoubtedly increase the cost of infrastructure installation to a large extent. Obviously, the fixed-bottom foundation cannot meet the economic requirements. Therefore, the floating wind turbine as an effective means to solve this problem has become a hot spot of the world. For the offshore floating wind turbine, due to the impact of the waves, the floating foundation and tower will generate pitch motion, causing structural fatigue and load response. At the same time, the complicated sea conditions will cause a large resonance response between the generator and the nacelle, leading to the output power of the generator with large fluctuations. Based on this, the paper aims to study the load optimization and power control of deep-sea offshore wind turbine, making researches through such perspectives as system dynamics modelling, load mitigation and power tracking control. The main research contents are as follows:(1) System dynamic modelling of offshore wind turbineThe paper summarizes the characteristics of the aerodynamic performance of the variable-speed variable-pitch floating wind turbine. And analysis of the movement of the floating platform is influenced by hydrodynamic load, wind load and response of mooring system. The effect of the floating platform motion on the wind turbine is described and the mooring system dynamics model, hydrodynamic model and generator power conversion model and the whole structure model are established.(2) Active structural control based on TMDThe passive structure control technology and active structure control technology of floating offshore wind turbine are studied in this paper. Based on the model of wind turbine equipped with a TMD. Active structure controller is designed by using the TMD optimal parameter. Full degree of freedom simulations of the system equipped with an active mass damper(AMD) are performed, and the tradeoffs associated with the use of active structural control are highlighted, Active structure control can effectively reduce the pitch angle and displacement of floating platform and the tower top displacement. The active control method greatly improves the stability and the whole performance of the floating wind turbine.(3) Neural adaptive universal power tracking controlAccording to the characteristics of high-order non-affine variable-speed wind turbine(VSWT), this paper proposes adaptive neural universal tracking control method to track the speed of the turbine. Firstly, the nonlinear model of VSWT is built, and the non-affine system model is converted into an affine system by using a novel system transformation method, through which the synthesis is extremely simplified. Secondly a neural network observer is employed to estimate the unavailable states of the system. Then the adaptive neural universal tracking control method is adopted to local controller of the system model. A simulation is carried out and the results verify that the control method proposed in this paper is effective and has desirable control effect.