Research On Active Disturbance Rejection Sensorless Control Strategy Based On Sliding Mode Observer For Tidal Stream Turbine

The last few decades have witnessed a rapid change in energy consumption and usage of fossil fuels.Growing demands and decreased supply of such fuels have encouraged research into renewable and clean sources of energy.Tidal current energy has shown promise as a source of inexhaustible green energy due to its predictability,high energy density,and availability.Research has been conducted on many advanced control strategies to improve the energy conversion efficiency and stability of the tidal stream turbine generation systems(TSTGS).Among them,most vector-controlled TSTGS need information on rotor position and speed,which requires expensive high-precision mechanical sensors.However,such sensors are damaged easily when operating under harsh marine environments,which can lead to system faults.The study of advanced sensorless control strategies has thus become essential to improve the TSTGS stability.In this thesis,an active disturbance rejection sensorless control strategy based on sliding mode observer(SMO)is in-depth studied to yield stronger anti-interference capabilities and better control performance.The specific research content is described as follows:(1)Considering that various challenges such as swell disturbances,unknown disturbances,or parameter uncertainties may deteriorate the system performance,it is of great significance to study advanced control strategies.An active disturbance rejection control(ADRC)strategy based on optimal tip-speed ratio is proposed to improve the antiinterference ability of the TSTGS.The extended state observer(ESO)is used to estimate the system's lumped disturbance where the nonlinear state error feedback(NLSEF)control rate compensates for the disturbance.In order to conduct in-depth analyses,the gain parameters of the ADRC controller are discussed through a Bode diagram.Performance of the ADRC method is compared to PI,fuzzy,and sliding mode control strategies.A simulation-based comparative study shows the effectiveness and advantages of the ADRC strategy over conventional control methods in terms of convergence speed,overshoot elimination as well as anti-interference ability.(2)An active disturbance rejection sensorless control strategy based on compensated SMO(CSMO)is proposed to eliminate time delay and improve reliability of the TSTGS.This proposed method consists of two parts.The first part proposes a CSMO based on the Smith predictor to conduct real-time delay compensation of the system,which is assessed through the Lyapunov approach analysis to be globally stable.The second part proposes a design for an ADRC controller for the tidal stream turbine that will improve the system's anti-interference ability.The proposed control strategy is verified by simulation,which shows that it is not only able to effectively eliminate the system time delay and suppress the lumped disturbance,but also improve the power extraction capability of the TSTGS.(3)An improved Phase-locked loop(IPLL)sensorless control strategy based on adaptive SMO(ASMO)is proposed to eliminate the chattering phenomenon and improve the control performance of the TSTGS.The proposed method consists of three parts.The first part proposes a design of the ASMO to estimate the back-EMF more accurately.The second part proposes an IPLL based on ESO to estimate the rotor position and speed for the TST system.In the third part,the ADRC controller is used to suppress the lumped disturbance of the TSTGS.Comparative studies show that the proposed method effectively eliminates the chattering phenomenon and improves the disturbance rejection capability.Moreover,the energy conversion efficiency and stability of the TSTGS are enhanced.