EFFECT OF STABILITY INDICES ON ROBUSTNESS AND SYSTEM RESPONSE IN COEFFICIENT DIAGRAM METHOD

Surekha Bhusnur

Abstract: In Control systems, designing a robust controller such that a desired system response is obtained despite plant parameter variations is ubiquitous problem. In this context, Coefficient diagram method is an effective method and one of the recent design methods based on the polynomial approach introduced by Shunji Manabe. In CDM, stability indices, stability limits and time constant are the main design parameters. The stability indices and stability limits are indicative of stability and equivalent time constant is indicative of speed of system response. A semi-log diagram known as coefficient diagram is the design tool using which one can analyse the important features of a design such as stability, speed of response and robustness, all in one diagram. The right choice of the stability indices is of paramount importance in the controller design. This paper deals with the effect of variation in the stability indices upon the system response and robustness. A type 2 fourth order plant has been considered as an example to analyse the effects of stability indices. The stability indices are varied one by one relative to the standard Manabe form and in each case response is observed. The transient response of the system is sensitive to lower order indices. Also, robustness in the design is analysed by coefficient diagrams of the perturbed plant.

Keywords: Coefficient Diagram Method (CDM), robustness; Stability Indices, Coefficient Diagram

DOI: https://doi.org/10.15623/ijret.2015.0410049