5.1.  INTRODUCTION

In the early days of control-system theory, engineers were generally less rigid in defining performance criteria. They were more apt to look on the feedback control system rather qualitatively and center attention primarily on stability and static accuracy. However, modern complex control systems have demanded the development of accurate criteria of performance.

The performance of a feedback control system is generally described in terms of stability, sensitivity, accuracy, transient response, and residual noise jitter. The exact specifications are usually dictated by the required system performance. Certain characteristics are more important in some systems than in others.

The great amount of literature that has appeared on the subject in recent years is evidence of the increasing importance that performance criteria have been given in feedback control-system design. In order to keep pace with the requirements of modern feedback control systems, several new criteria of performance have been developed [1]. It is the purpose of this chapter to review and study several classical performance criteria together with more recent and sophisticated approaches. The control literature abounds with various criteria of performance. Most significant are several performance criteria that have been postulated that are functions of time and error. After examining the literature, we find that the integral of time multiplied by the absolute value of error (ITAE) criterion for ...

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