A new suboptimal control design for cascaded non-linear systems

A new suboptimal control design technique is proposed for a class of cascaded non-linear systems. The design is based on a forward recursive design rather than a backstepping design, and it utilizes a non-linear tracker derived using the state-dependent algebraic Riccati equation approach. The proposed design has two distinct features. First, it provides suboptimal performance with respect to a performance index that is defined in terms of the original state and control variables and thus can be prescribed. Second, the forward recursive procedure eliminates differentiation of fictitious controls (or their functions), which makes the design much simpler in applications. Due to the use of the non-linear tracker, the proposed design has the potential of producing less conservative results than non-linear servo results.