Adaptive second order sliding mode control strategies for uncertain systems
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2013
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Abstract
The main objective of this thesis is to develop robust sliding mode control strategies for uncertain systems. More specifically, the aim of this thesis is to develop sliding mode control schemes which are successful in controlling systems affected by both matched and mismatched types of uncertainty. One major drawback suffered by conventional sliding mode controllers is the presence of high frequency oscillations in the control input known as chattering. Because of the discontinuous control action in sliding mode controllers, chattering becomes an inherent undesired phenomenon. Apart from chattering, another disadvantage faced by conventional sliding mode controllers is their design prerequisite of advance knowledge about the upper bound of the system uncertainty. This thesis is an attempt to provide solution for these two main limitations of conventional first order sliding mode controllers. The central focus of this thesis is to improve upon the existing sliding mode control techniques with the prime objective of chattering mitigation. An adaptive gain tuning mechanism which can estimate the uncertainty adaptively is proposed in this thesis. Hence prior knowledge about the upper bound of system uncertainty is no longer a necessary requirement in the proposed adaptive sliding mode controller. The basic idea of the proposed adaptive sliding mode controller is that the discontinuous sign function is made to act on the time derivative of the control input and the actual control signal obtained after integration is continuous and hence chattering is removed. The adaptive gain tuning strategy ensures that the controller gain is not overestimated. Based upon the core idea of adaptive sliding mode, various classes of sliding mode controllers are proposed in this thesis. In order to ensure smooth control action throughout the entire operating range, this thesis proposes an adaptive integral sliding mode controller. The integral sliding mode (ISM) algorithm eliminates the reaching phase. Therefore, invariance towards matched disturbances can be ensured from the very beginning by using this method. The proposed adaptive sliding mode control methodology is used to control nonlinear multiple input multiple output (MIMO) systems which are highly cross-coupled. The proposed con.
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Supervisor: Chitralekha Mahanta
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ELECTRONICS AND ELECTRICAL ENGINEERING