Robust output feedback control for discrete-time systems with ellipsoidal uncertainty

This paper provides a new robust control synthesis method for linear uncertain multivariable discretetime systems subject to the ellipsoidal parametric uncertainty. This type of parametric uncertainty is delivered by classical prediction error identification methods in a full-order model structure. The uncertainty is represented by linear fractional transformation. Fixed-order H₂ and H_∞ control design problems are formulated in terms of solutions to a set of dilated linear matrix inequalities. The control designs build on quadratically parameter-dependent Lyapunov functions. Flexible structures for the auxiliary variables are introduced to improve the performance and reduce the conservatism related to the fixed-order controller synthesis. The employed structures may be updated by a proposed iterative procedure. Numerical examples show the effectiveness of the proposed method.