A simple design technique for nonlinear control systems

A gain-phase chart similar to the Nichols chart is presented for the synthesis of nonlinear systems containing a single nonlinear or time-varying element. It uses the well-known circle criterion as a sufficiency condition for absolute stability. A design procedure is given which uses this chart as a tool, and is a straightforward and essentially a paper and pencil method. The technique, being graphical, gives the designer a physical feel for the system. An example is provided to illustrate the application of the chart for the synthesis of nonlinear systems.