Anti-Vibration Control Design For Translational Oscillator With Rotational Actuator Based Offshore Floating Wind Turbine

With increasing energy demand in modern society,as well as greater exploitation and utilization of conventional energy sources,the existence of an energy crisis is becoming more apparent for a few decades.Meanwhile,the environmental pollution caused by these traditional energy sources is aggravating the situation and putting human health at risk.To address these energy crises,individuals are committed to the development and use of renewable energy,particularly pollution-free,clean,and easily accessed wind energy.A land-based wind turbine has remained a pertinent source for obtaining wind energy for the last few decades.However,in recent years,wind turbine technology is shifted towards offshore floating wind turbines(OFWT)due to the smooth,and steady high wind resources.Moreover,the transfer of wind turbines from land to sea has been caused due to the damage to the surrounding ecology,and the geographical and scale restrictions caused by wind farms on land.OFWT has the ability to capture highquality wind resources but suffers from a harsh marine environment which causes a large vibration response.This vibrational effect induces a deep impact on the performance of the OFWT.Structural control techniques are the most cost-effective potential solutions for mitigating such vibrations.This research is focused on the new mathematical model of OFWT and the new control scheme for mitigating unwanted disturbances and uncertainties.The main research contributions of this dissertation are as follows:Offshore floating wind turbine control plays an important role in the dynamic behaviour of the system due to the possible platform damping effect and external disturbances.The control algorithms used for the bottom-fixed wind turbines cannot be directly applied to the floating ones.The dynamics of floating platforms,especially the platform pitch motion,must be taken into consideration.Therefore,a new scheme of a translational oscillator with the rotational actuator(TORA)based on three degrees of freedom(3DOF)barge-type OFWT is proposed in order to decrease the vibration effect of OFWT.TORA can be taken as an active mass structural control strategy for OFWT.In this model,OFWT has been treated as a translational cart and a rotor has been added to the nacelle,which yields a kind of TORA.The mathematical model of the proposed scheme is derived based on the Euler Lagrange equation of motion by selecting the angular positions of the barge platform,tower,and the rotational proof-mass actuator of the nacelle as generalized coordinates.According to the mathematical model,there are three configuration variables corresponding to the three generalized coordinates to be controlled but only the angular position of the rotational proof-mass is actuated which can be controlled by the control input torque directly.Therefore,the TORA based barge-type OFWT is an underactuated mechanical system,which means the unactuated configuration variables have to be controlled via the nonlinear coupling of its dynamics.To realize the anti-vibration control of TORA based barge-type OFWT,the obvious challenges are the nonlinear dynamics of the underactuated system itself and the impact of external disturbances and model uncertainties arising from the harsh marine environments.Hence,by combining the traditional,integral,and non-singular terminal sliding mode surfaces along with the output of the disturbance observer(DO),a new exogenous disturbance observer based integral non-singular terminal sliding mode control(INTSMC)scheme is proposed as a solution to the challenges mentioned earlier and firstly applied to the simple TORA dynamics.Afterward,the proposed control scheme with backstepping is presented to TORA based 3DOF barge-type OFWT.And the comparison is carried out with DO-based backstepping sliding mode control,DO-based backstepping integral sliding mode control,and DO-based backstepping nonsingular terminal sliding mode control.Through theoretical and simulations,the correctness of the proposed OFWT model and control techniques are verified and the simulation results prove the efficiency of the proposed controller as compared to its other counterparts.In order to handle the vibration more adequately and effectively,TORA based 3DOF barge-type OFWT model is further extended to TORA based 5DOF barge-type OFWT by considering the dynamics of multiple mooring lines.The proposed TORA based 5DOF bargetype OFWT model is also derived based on the Euler Lagrange equation of motion by adding two more general coordinates,i.e.,translation positions of the barge platform in a horizontal direction along with the wind and the vertical direction.Following the derived TORA based5 DOF barge-type OFWT,further two challenges in the control design of OFWT are considered here,i.e.,the unavailability of the system states,and to bound the output movements of platform pitch and tower bending angle in a limit.To address these challenges,a high gain observer(HGO)based adaptive integral sliding mode control with a backstepping algorithm based on the barrier Lyapunov function(BLF)for output constraint OFWT is designed.The overall design consists of three steps: by using the backstepping methodology,the mathematical model is transformed into five second-order subsystems in the first step;the second step creates an adaptive vibration suppression gain for backstepping integral sliding mode control by using BLF to stabilize the OFWT with respect to the output constraint,against all the matched unknown bounded perturbations;a high gain observer is designed based on the transformed five secondorder subsystems in the normal form of OFWT in the last step.Afterward,this proposed control method is implemented with a typical 5DOF barge-type OFWT and its comparison is carried out with high gain observer based adaptive integral sliding mode control with the backstepping algorithm.The simulation results show the proposed BLF-based adaptive integral sliding mode control can effectively handle vibrations within a bound as compared to its alternative control law.Furthermore,to deal with the low frequencies of disturbances arising from the marine environments,the high gain observer(HGO)is revised to the extended high gain observer(EHGO)to estimate the low-frequency disturbances effectively.EHGO is employed in conjunction with the proposed backstepping integral non-singular terminal sliding mode control scheme in the presence of unwanted disturbances and uncertainties to realize anti-vibration control of the TORA-based 5DOF barge-type OFWT.The phase portrait,frequency response,and stability of the output feedback closed-loop system have demonstrated the performance of the proposed anti-vibrational control scheme.The simulation results demonstrate the efficacy of the suggested anti-vibration control law.This dissertation has introduced and implemented a new control technique for the vibrational control of the new TORA based OFWT model in a systematic manner.The numerical simulations based on MATLAB/SIMULINK demonstrate the feasibility and effectiveness of the proposed control scheme for TORA based OFWT system.