‘Circle criteria’ in the parameter plane

The ‘circle criteria’ for giving stability information of linear systems containing one time-varying element are shown to have useful graphical interpretations for design purposes on a parameter-plane diagram. The significance of the parameter-plane approach is that, in a system design, the adjustable parameters of either the time-varying element or the time-invariant subsystem may be selected to satisfy the system stability constraints directly from the diagram. This means that for some design problems the parameterplane approach is more efficient than the application of the well known complex-plane methods.