IEEE Transactions on Automatic Control, Vol.57, No.6, 1532-1537, 2012
LMI Relaxations for Reduced-Order Robust H-infinity Control of Continuous-Time Uncertain Linear Systems
This technical note is concerned with the problem of reduced order robust H-infinity dynamic output feedback control design for uncertain continuous-time linear systems. The uncertain time-invariant parameters belong to a polytopic domain and affect all the system matrices. The search for a reduced-order controller is converted in a problem of static output feedback control design for an augmented system. To solve the problem, a two-stage linear matrix inequality (LMI) procedure is proposed. At the first step, a stabilizing state feedback scheduled controller with polynomial or rational dependence on the parameters is determined. This parameter-dependent state feedback controller is used at the second stage, which synthesizes the robust (parameter-independent) output feedback H-infinity dynamic controller. A homogeneous polynomially parameter-dependent Lyapunov function of arbitrary degree is used to assess closed-loop stability with a prescribed H-infinity attenuation level. As illustrated by numerical examples, the proposed method provides better results than other LMI based conditions from the literature.
Keywords:Continuous-time systems;dynamic output feedback;H-infinity control;linear matrix inequality (LMI) relaxations;polynomial Lyapunov functions;reduced order controllers