Simplification of nonlinear controllers: balancing approaches

This paper extends the work of linear controller reduction to nonlinear affine systems with the help of nonlinear balancing concept and technique. For stable controller, nonlinear model reduction is directly applied to reduce the order. Discussion for unstable controller reduction focuses on H_∞ suboptimal output feedback controller and other controllers with observer-based structures. An unstable controller is reconstructed based on its left (right) coprime factorization such that the above controller reduction technique can be applied. Stability of the closed-loop system with reduced controller is discussed and the upper bound of the closed-loop system performance with respect to L₂-gain is also obtained