Research On Speed Sensorless Control Of Direct-drive Wave Power Generation System

Wave energy has high energy density and wide distribution,and has good development potential and broad application prospects.The sustainable development and utilization of wave energy is also a booster for my country to achieve the goals of " peak carbon dioxide emissions" and "carbon neutrality".The environment hinders the practical application of wave power generation systems.This thesis takes the direct-drive wave power generation system as the research object,and explores the application and power optimization strategy of the speed sensorless control technology in the wave power generation system.By analyzing the motion characteristics of the direct-drive wave system,a mathematical model of the hydrodynamic-permanent magnet linear generator is established.According to the principle of maximum power capture,the optimal power capture conditions of the system under resonance conditions are derived.In view of the harsh installation environment of the wave power generation system,the complex structure of traditional mechanical sensors,the difficulty in installation and maintenance,and the corrosion of seawater,an Extended Kalman Filter(EKF)algorithm and a Model Reference Adaptive System(MRAS)scheme are introduced to achieve sensorless control.EKF linearizes the nonlinear system with the help of Taylor series expansion.Based on the two steps of prediction and state update,the motor information is used to estimate the speed and position;MRAS adjusts parameters based on the output difference between the reference model and the actual model,and designs the control law from the perspective of system stability to realize the motor speed identification.The simulation results show that the EKF and MRAS can accurately estimate the velocity and position information,with high precision,small estimation error and certain robustness.By analyzing the equation of motion of the system,the optimal electromagnetic force is obtained according to the principle of maximum power transmission,and the optimal reference currents of d and q axis are obtained by vector control.The wave power generation system is a complex nonlinear system,the wave motion is disordered,and the speed estimation will produce errors.Therefore,a sliding mode control scheme is introduced to design the controller to achieve fast and accurate tracking of the d and q axis reference currents,thereby achieving power optimization.The simulation results show that the sliding mode controller can quickly and accurately track the reference current,has high wave energy capture efficiency,strong robustness and good dynamic performance.