Output feedback disturbance decoupling in nonlinear systems

The problem of disturbance decoupling by means of output feedback is addressed. The notion of conditioned invariance is reconsidered in a linear algebraic framework. Using this geometric notion, a necessary and sufficient condition (respectively, necessary condition) is obtained for solving the disturbance decoupling problem by quasi-static output feedback (respectively, the disturbance decoupling problem by dynamic output feedback (DDDPO)). The necessary conditions for DDDPO which are derived are weaker than the existing ones, a sufficient condition for the disturbance decoupling problem by static output feedback is given as well.