Sliding mode functional observers for classes of linear and non-linear systems / Navid Nikraz

2008

[Truncated abstract] In many practical situations the physical state of a system cannot be determined by direct observation. The problem of constructing both state and functions of the states is currently one of the leading topics in Control Engineering. Since the reemergence of the state-space methods to form a direct multivariable approach to linear control systems synthesis and design, a host of controllers now exist to meet the qualitative and quantitative criteria including system stability and optimality. Sliding Mode Control (SMC) has been successfully applied to many practical control problems due to its attractive features such as invariance to matched uncertainties. The characteristic feature of the continuous-time SMC system is that sliding mode occurs on a prescribed manifold, where switching control is employed to maintain the state on the surface. When a sliding mode is realised, the system exhibits some superior robustness properties with respect to external matched uncertainties. Systems with sliding modes have proven to be an efficient tool to control complex high-order nonlinear dynamic plants operating under uncertainty conditions, a common problem for many processes that are in modern control. It is acknowledged that the notion of the sliding mode observer is inherently critical to the field of sliding mode control. Sliding mode state observers have been the focus of research in the field of control for the past decade and their applications have extended to most areas in this field. The concept of the Sliding Mode Functional Observers is an area that is untouched by previous research. This thesis introduces the concept of the Sliding Mode Functional Observer and demonstrates its vast potential in the field of control. It is appreciated that sliding mode observers do have a very important place in the field of control, and in particular motor

control. However, it has been discovered that currently one of the major fallbacks of sliding mode

observers is their strict and sometimes unrealistic boundaries and conditions on systems. This has narrowed the scope to which they can effectively be applied to practical cases. The major objective of this thesis is to extend the application of sliding mode observers to incorporate sliding mode functional observers for systems that exhibit somewhat unique properties, that have made the practical applications relatively difficult in the past. In this thesis the Sliding Mode Functional Observer is applied to a number critical areas in control; Neutral-Delay System, Systems with Unknown Inputs, Non- Linear Systems and Descriptor Systems. Firstly the problem of estimating a linear function of the states of a class of linear time-delay systems of the neutral-type using sliding mode functional observers is investigated. Next, conditions for designing a sliding mode functional observer when the system is subjected to unknown inputs are presented, reducing the existence conditions for the Utkin Observer and also reducing the well known Matching and Observability conditions required for the design of the observer...

Thesis (Ph.D.)--University of Western Australia, 2010

http://repository.uwa.edu.au:80/R/-?func=dbin-jump-full&object_id=26585&silo_library=GEN01