Classical Frequency-Domain Design Methods

Abstract

The design of feedback control systems in industry is probably accomplished using frequency-response (FR) methods more often than any other. Frequency-response design is popular primarily because it provides good designs in the face of uncertainty in the plant model (G(s) in Fig. 1). For example, for systems with poorly known or changing high-frequency resonances, we can temper the feedback design to alleviate the effects of those uncertainties. Currently, this tempering is carried out more easily using FR design than with any other method. The method is most effective for systems that are stable in open loop; however, it can also be applied to systems with instabilities. This section will introduce the reader to methods of design (i.e., finding D(s) in Fig. 1) using lead and lag compensation. It will also cover the use of FR design to reduce steady-state errors and to improve robustness to uncertainties in high-frequency dynamics.