Abstract

In this paper, a chattering free adaptive sliding mode controller (SMC) is proposed for stabilizing a class of multi-input multi-output (MIMO) systems affected by both matched and mismatched types of uncertainties. The proposed controller uses a proportional plus integral sliding surface whose gain is adaptively tuned to prevent overestimation. A vertical take-off and landing (VTOL) aircraft system is simulated to demonstrate the effectiveness of the proposed control scheme.

Introduction

Physical systems suffer from performance degradation and instability due to uncertainties existing in nature which can be broadly classified into matched and mismatched types. Uncertainties acting on the system through the input channel are called matched uncertainties, whereas perturbations in the system parameters are termed as mismatched uncertainties. Classical control techniques like adaptive control [1], optimal control [2], sliding mode control [3] and intelligent control methods like fuzzy logic control [4] have been extensively used in control systems perturbed by matched uncertainty. Among these methods, sliding mode control has received wide acceptance owing to its robustness and simplicity. However, designing sliding mode controllers for systems perturbed by the mismatched type of uncertainty still remains a challenge to the research community. The difficulty lies in the fact that the dynamics of the uncertain system are affected even after reaching the sliding mode.