In this article, a sliding mode control scheme is proposed for a quadrotor in the presence of an exogenous disturbance. A nonlinear sliding mode surface is constructed based on the estimate output of a disturbance observer to reject the effect of the unknown disturbance in the quadrotor. The desired control performance is achieved by bringing the state from unstable state to stable ones. To show the effectiveness of the developed control scheme, simulation results are provided for illustration of the designed controller based on disturbance observer.

In this paper, the flight control of an unmanned aerial vehicle (UAV), quadrotor, in the presence of high-order disturbances is presented. Since during flight, UAV faces enormous, and various kinds of disturbance, the effect of such disturbances becomes vital for consideration during the development of disturbance observer (DO) based tracking control scheme. To obtain the desired tracking performance, standard sliding mode control (SMC) method is utilized while for disturbance estimation, DO based on Simpson's approximation is developed and incorporated with SMC. Furthermore, in this paper, both matched and mismatched disturbances are considered. Hence, a matrix associated with disturbances is invoked in the system model. To show the effective and desired control performance of developed disturbance observer-based control (DOBC) scheme, extensive simulations are conducted, followed by presenting the results in the paper.

In this paper, the robust adaptive control scheme based on backstepping technique is presented that improves the trajectory tracking performance of the quadrotor unmanned aerial vehicles (UAVs), specially tasked for supply, rescue and combat missions. The proposed control scheme is designed to estimate all the system parameters that may posses uncertainties and effectively rejects the completely unknown time varying external disturbances. The adaptive laws, derived through Lyapunov stability theorem are robustified by merging with derivative-integral (DI) term, resulting in rapid and accurate adaptation. In addition, to avoid parametric drift phenomenon, we introduce the projection modification (PM) in the designed DI-adaptive laws that ensures the closed-loop system signals bounded. The trajectory tracking and parameter estimation performance of the UAV in the presence of external disturbances, the payload pick up/drop off effect on altitude and recoil effect on attitude is analyzed by means of numerical simulations. The results validate strict robustness with extended applicability of proposed control scheme.

In recent times, renewable energy demand is rapidly increasing worldwide. Offshore wind energy is one of the alternative solutions to the problems posed by non-renewable energy resources. The kinetic energy of the wind is converted to mechanical energy by using an offshore floating wind turbine (OFWT). The efficiency of the OFWT is dependent upon the vibrational effect induced by the environment. In this paper, for the mitigation of this vibrational effect, a new model of barge-type OFWT is designed by using an active control strategy called translational oscillator with a rotational actuator (TORA). The disturbance observer (DO) based advanced control techniques including robust backstepping sliding mode control (BSMC), backstepping integral sliding mode control (BISMC), backstepping nonsingular terminal sliding mode control (BNTSMC), and a new backstepping integral nonsingular terminal sliding mode control (BINTSMC) technique, are devised for the stabilization of OFWT model. The comparison of these techniques is carried out by using MATLAB/SIMULINK which validates the feasibility and correctness of the proposed OFWT model and control techniques.

A composite disturbance observer based control (CDOBC) technique for a quadrotor attitude is presented in this paper. The structure of CDOBC consists of a robust equivalent controller constructed using adaptive backstepping sliding mode control (ABSSMC), disturbance observer (DO) and an auxiliary gain to combine controller and NDO. In order to construct the DO, it is assumed that the quadrotor attitude model is effected by unknown bounded disturbances. During the development of DO, a state estimator is also constructed to avoid the situation of lack of states availability. Hence, invoking state estimator in estimation criteria followed by combining it with control scheme through an auxiliary gain yields the desired CDOBC based on ABSSMC. To analyze the dynamic and steady state performance of the developed control scheme, a stability proof followed by the simulation study is presented. In addition, before concluding the effectiveness of developed CDOBC, a comparative analysis is conducted by developing CDOBC based on backstepping and adaptive sliding mode control methods.