Introduction

Abstract

Control theory within the 20th century can conveniently be divided into 3 main periods: classical control, optimal control and robust control. In Table 1.1 some of the key results for each period is given. The period 1930–1960 can be classified as the “Classical Control” period. Here famous pioneers, like Bode and Nyquist, developed control design tools which made it possible to meet standard requirements on stability, robustness and performance for scalar (single-input single-output) systems. These are eg Bode and Nyquist plots, Nichols charts and root-locus plots. The chief paradigm for this period was the frequency domain. The results from the classical control period make up the bulk of industrial control practice to this day.