Study On Pitch Control Of Offshore Floating Wind Turbine Based On Prescribed Performance Function

With the proposal of carbon neutralization goal,all kinds of renewable and clean energy have become the focus of attention.Offshore wind energy has become the key goal of energy development because of its rich resources,good power generation quality and large-scale development.As a tool that can effectively use deep-sea wind energy,offshore floating wind turbine has become the main research object.However,compared with the onshore environment,the offshore environment is more complex,and due to the nonlinearity,uncertainty and strong coupling of the wind turbine structure,it is urgent to design advanced control strategies to reduce the power fluctuation and structural load of the floating wind turbine.In this paper,an appropriate pitch control strategy is designed to solve this problem,the effectiveness of the established control method is realized and verified based on FAST simulation platform.The main research work includes the following aspects::Firstly,the principle of wind energy conversion,the factors affecting aerodynamic balance and hydrodynamic characteristics of offshore floating wind turbine are introduced,and the working conditions of offshore floating wind turbine under different wind speeds are briefly introduced.Then,the pitch control method based on gain scheduling proportional integral(GSPI)is introduced,and the simulation test is carried out based on GSPI controller.GSPI controller has certain robustness,but GSPI controller does not consider the performance of dynamic response and structural load of floating wind turbine platform.According to the nonlinear,uncertain and strong coupling characteristics of the structure of offshore floating wind turbine,combined with the prescribed performance function,a collective pitch controller(FTPP-CPC)is designed to reduce the fluctuation of output power of floating wind turbine and improve the stability of output power and power generation quality,By introducing the state feedback of the floating wind turbine platform,the control target is redesigned to reduce the motion and structural load of the platform.The simulation tests are carried out on the designed FTPP-CPC controller and GSPI controller,and the comparison results verify the effectiveness of the design method.Due to the influence of wind shear,tower shadow effect and turbulent wind,the wind speed on the rotor plane changes,resulting in asymmetric or periodic load on the blades of the wind turbine,and the asymmetric load will seriously affect the service life of the wind turbine.In this paper,the independent pitch control(FTPP-IPC)is designed by combining the prescribed performance function and multi-blade coordinate transformation to reduce this impact,it is combined with the FTPP-CPC controller designed based on the prescribed performance function to reduce the output power fluctuation and structural load of the floating wind turbine.The simulation results show that the designed controller can effectively reduce the output power fluctuation and structural load of the floating wind turbine.Finally,the high-order model of the pitch system of the floating wind turbine is established.According to its strong nonlinear and time-varying characteristics,combined with the specified performance function,adaptive control and sliding mode control,the controller(ASMPP)is designed for the tracking control of the input pitch angle.This method can quickly converge the tracking error of the pitch angle and maintain good steady-state performance.Simulation tests are carried out on ASMPP controller and PI controller to verify the effectiveness of the design method.ASMPP controller can effectively reduce power fluctuation,platform motion and structural load of floating wind turbine.