Since frequency response techniques and root locus diagrams are not applicable to a nonlinear process, there is an important need for a graphical tool to allow nonlinear behaviour to be displayed. This need is filled by the phase plane diagram. The method is applicable to second-order processes without input, although effects equivalent to step or ramp inputs can be obtained by choice of initial conditions.

Inspec keywords: differential equations; nonlinear control systems; step response

Other keywords: step inputs; nonlinear control theory; graphical tool; ramp inputs; phase plane portrait; second order processes

Subjects: Nonlinear control systems