FRACTIONAL ORDER BASED TECHINQUES FOR STABILITY ANALYSIS AND CONTROLLER DESIGN

Abstract

In the present day world of modernisation, the field of control system has become a very upcoming research area. There are three main aspects that have to be taken in to consideration while working in the area of control systems i.e., stability analysis, controller design and application. In the recent control literature, a new control strategy has emerged called the fractional order control systems. This control strategy has been found to be more robust, accurate and precise as compared to the existing control strategies. However, as the fractional order control systems gain popularity, it also creates a need for new techniques for the stability testing and controller design for such systems. Therefore, in this thesis, work has been carried out on the three main aspects of fractional order control systems i.e., stability testing techniques for fractional systems, techniques for design of fractional order controllers and its applications. In the first part of the thesis, Kharitonov theorem based technique has been suggested for the stability testing of fractional order interval systems which is mathematically simpler than the existing techniques and applicable to all classes of fractional order interval systems. It is seen from the literature that the existing fractional order controller design techniques are either applicable to only specific type of systems or are mathematically very complex and lengthy. Therefore, new fractional order controller design techniques have been suggested that are mathematically simpler and give improved results as compared to the existing techniques. Further, fractional order controller design technique has also been suggested for the interval systems. The proposed design techniques are based on the concepts of stability boundary locus, internal model control and Kharitonov's theorem. Finally, the fractional order controllers have been designed for different types of practical applications such as load frequency control, mean arterial blood pressure measurement system, heating furnace systems and also gas turbine plant to investigate its performance. It is seen that the fractional order controllers are more robust and give improved results in comparison to existing methods for all these applications.