ABSTRACT
This chapter presents the classical and conventional approaches for the design of control law for continuous time control systems (CTCS) are: root locus and frequency domain methods. The root locus method for CTCS can be extended to a discrete time control system (DTCS) with minor changes. This is because the characteristic equations, for both the type of systems, are of the same form. The controller design for a continuous time system using root locus is based on the approximation that the closed loop system has a complex conjugate pole pair, since such a pair would dominate the system behavior. Similarly, for a DTCS, the controller can be designed based on the features of a dominant pole pair. Hither to, the design of the controller for control system was based on the transfer function of the considered dynamic systems/plants/processes; these methods are applicable only for linear time-invariant and initially relaxed systems and to the linearized plants.
