Using quadratic indexes in the synthesis of harmonic disturbance attenuation compensators

The paper addresses the synthesis of fixed-structure compensators to attenuate an harmonic disturbance whose frequency is unknown but belongs to a given interval. Besides jointly employing the sensitivity function and Lienard-Chipard criterion to give guaranteed stability margins, the main novelty of the proposed method lies in using (integral) quadratic indexes of unit step tracking error to shape time-domain performances. In such a way the compensator synthesis is converted into a new minimax optimization problem for which an approximate solution is attainable through known numerical algorithms. The method is applied to a problem arising in the control of wood contouring machines