3 - Performance

Abstract

This chapter introduces the commonly used measures of control system performance in time and frequency domains and relates them to one another and to the system's z transform description. The common methods for defining the performance of a control system are described. It demonstrates ways that the system characteristics in the z-domain could be used to predict how well a system would meet a given set of specifications. This information is useful in the early phases of a system design to determine what is necessary to make the system successfully meet its real-world design goals. An obvious and powerful measurement of a control system's performance is how well it follows its command input in the time domain. System step responses are informative and useful in large part because a step input, or a step-like input, is nearly ubiquitous. One very important difference between a system step response and a higher order response is that a step response is bounded, while a higher order response is not. Systems are always affected by external, unintentional, or undesired effects. Control system designers refer to these external influences as “disturbances.”