Two-stage H∞ optimization approach to multirate controller design

A two-stage H∞ optimization methodology is presented for designing multirate controllers achieving comparable H∞ closed-loop performance with that of an optimal fast rate design at a reduced real-time computational load. In the first stage, a fast rate controller is designed by solving an H∞ optimal control problem formulated to address the design specifications; then the fast rate controller is decomposed into low frequency and high frequency parts. In the second stage, the high frequency part of the controller is retained and the low frequency part is redesigned at the slow rate using lifting and H∞ optimization. In the proposed approach, potential problems of aliasing due to the multirate nature of the controller are addressed by taking into consideration closed-loop performance.