Synthesis of feedback control system by phase-angle loci

THE synthesis of a feedback control system by means of phase-angle loci originates from Evan´s root-locus method1 which enables one to find all possible roots of the characteristic equation of a feedback control system. Once the roots are chosen, the transient response then may be worked out. Thus, it allows the synthesis of feedback control system in time domain. However, the plotting of the root locus requires some sort of guesswork. This is not surprising because the analytical difficulty in extracting the roots of the characteristic equation is imposed on the graphical work, yet help in the effort to solve the problem can be given.