Dynamic analysis and control of support structures for offshore wind turbines

Offshore wind power is a promising technology and is important from the future energy demand. Energy from the offshore wind can be a potential source of renewable energy which is capable of meeting our needs. Research is still underway for addressing the several challenges associated with this technology and one of them is the unwanted response of support structures for wind turbines. Offshore wind turbines are located in severe environment and experience environmental loads like wind, wave, current and seismic excitations. The support structures when subjected to the loads exhibit the nonlinear response. Owing to the irregular waves, the response will often be chaotic which in turn reduces the overall stability of the turbine. A 5MW NREL wind turbine is considered for the study. The turbine is assumed to be installed on a floating platform with water depths of 320 m. To keep the response in safe operating regime, the controlled response of offshore structure is essential. The focus of this paper is to develop robust control techniques so as to regulate the vibration and synchronization of support structures for an offshore wind turbine. To achieve the same, two methods the sliding mode controller and a control mechanism based on altering the oscillation energy are being proposed. The performance of the algorithms is illustrated in this paper by designing the controllers for controlled response of the structures supporting offshore wind turbines in the chaotic regime. The performances of controllers are compared with general back steeping control methodology based on Lyapunov stability theory. Numerical results and simulations are shown to validate the proposed methodology and to demonstrate its effectiveness.