ABSTRACT
This chapter explains the fundamentals of the root-locus technique and describes how the root-locus method may be used to select controller gain. It presents guidelines for sketching the root loci of simple systems and also describes, with the aid of simple root loci, the effect of velocity feedback and proportional plus derivative control. The frequency response results obtained there can easily be reinterpreted in terms of so-called root loci on the s-plane. The presence of the zero in the closed-loop transfer function can be advantageous in some circumstances, by providing greater initial control action and speeding up the response in comparison with velocity feedback. The root locus of the position control system can be derived in a similar way. It shows the complete root locus for position control system, together with the closed-loop pole positions for various values of gain. There is an alternative method, requiring only a knowledge of the open-loop pole-zero configuration.
