Controllability Issues in Nonlinear State-Dependent Riccati Equation Control

In the last few years, algorithmsusing state-dependent Riccati equations(SDREs) havebeen proposed for solving nonlinear control problems. Under state feedback, pointwise solutions of an SDRE must be obtained along the system trajectory. To ensure the control is well de � ned, global controllability and observability of state-dependent system factorizations are commonly assumed. Here connections between controllability of the state-dependent factorizations and true system controllability are rigorously established. It is shown that a local equivalence always holdsfor the class of systems considered, and special cases that imply globalequivalenceare also given. Additionally, a notion of nonlinear stabilizability is introduced, which is a necessary condition for global closed-loop stability. The theory is illustrated by application to a � ve-state nonlinear model of a dual-spin spacecraft. I.