Graphical method for finding the closed-loop frequency response of nonlinear-feedback control systems

The paper presents a graphical method for determining the closed-loop frequency response of nonlinear-feedback control systems. The necessary gain and phase conditions round the loop for possible harmonic oscillations are examined, and a universal chart is developed. The nonlinear element is represented by its describing function. The use of the universal chart for determining the frequency response of unity-feedback systems having one single-valued nonlinearity is illustrated by suitable examples.