Qudrat Khan

A Comparative Experimental Study of Robust Sliding Mode Control Strategies for Underactuated Systems

This paper presents a comprehensive comparative study for the tracking control of a class of underactuated nonlinear uncertain systems. A given nonlinear model of the underactuated system is, at first stage, transformed into an input output form and the driving applied control input of the transformed system is then designed via four sliding mode control strategies, i.e., conventional first order sliding mode control, second order sliding mode, fast terminal sliding mode, and integral sliding mode. At second stage, a ball and beam system is considered and the aforementioned four control design strategies are experimentally implemented. A comprehensive comparative study of the simulation and experimental results is then conducted which take into account the tracking performance, i.e., settling time, overshoots, robustness enhancement, chattering reduction, sliding mode convergences, and control efforts.

Neuro-adaptive dynamic integral sliding mode control design with output differentiation observer for uncertain higher order MIMO nonlinear systems

This paper proposes a practical design method for the robust control of a class of MIMO nonlinear plants operating under model uncertainties and matched disturbances where the only available information for feedback are the outputs of the plant. A neural networks based dynamic integral sliding mode control (NNDISMC) with output differentiator observer is developed for the considered class. This NNDISMC approach utilizes the robust output differentiation observer for the higher derivative estimation and neural networks to estimate the nonlinear functions which are assumed unknown. Having estimated the unknown derivatives and uncertain functions, an integral manifold based on the estimated states is designed and a control law is proposed which confirms the sliding mode enforcement across the designed integral manifold from the very start of the process. The overall robustness of the controller is guaranteed by using the neural networks, differentiator observer and dynamic integral control law in a closed loop. The closed loop stability analysis is presented in detail, and the asymptotic convergence of the system states to the equilibrium is confirmed. The proposed method is very practical and plays a very significant role in the robust control of electromechanical systems, such as robotic manipulators, unmanned air vehicles and underwater vehicles. The simulation results on a robotic manipulator are presented to demonstrate the effectiveness of the proposed method.

Constructive mechanism of Lead/Lag design for a class of linear systems

A generalized algorithm of compensator (Lead/Lag) design, using Root Locus, is proposed for a class of linear systems. The proposed algorithm (set of rules and equations) does not need explicitly drawing the root locus of the plant under consideration and can be a good software tool. The algorithm, takes the performance specifications and plants data, uses the well known angle and magnitude conditions of the Root Locus technique, decides whether Lead or Lag compensator is needed. The steady state error requirements has also been incorporated (in case of Lag compensator). In addition, the dominance of desired pole pair is guaranteed. The proposed algorithm is verified by numerical examples.

Robust stabilization of underactuated systems via fast terminal sliding mode

This paper presents a fast terminal sliding mode control strategy for a class of underactuated systems. Strategically, this development encompasses those electro mechanical underactuated systems which can be transformed into the so-called regular form. The novelty of this article lies in the hierarchical development of a fast terminal sliding manifold design for the considered class. Having established sliding mode against the designed manifold, the close loop dynamics becomes finite time stable which results in high precession. In addition, the adverse effects of chattering phenomenon are eliminated and the robustness of the system against uncertainties is confirmed theoretically in a couple of theorems. A comprehensive numerical example of the cart pendulum is presented to verify the claims for the considered class.