Passification by output injection of nonlinear systems

Passivity is an important and useful property for analysis and design of nonlinear control systems. The problem of when a system can be rendered passive by state or output feedback has being very well studied in the last years. For linear time invariant systems it follows by duality that if a system is state feedback passive, then it can also be made passive by output injection. Since such a duality concept is (in general) not true for nonlinear systems, in this paper sufficient conditions for rendering a nonlinear system passive by output injection are given. We concentrate on global conditions for (strict) passivity, but similar results can be obtained along the same lines for local or semiglobal conditions.