A low order controller design method

Proposes a design method for controller order reduction, using the /spl mu/ framework. The design method accounts for the perturbations to the controller, arising from the order reduction, constructs the weighting functions, representing the maximal size of perturbation to the controller at each frequency for the guaranteed robust performance, and then iterates between searching for optimal controller with respect to the weighs, and computing the optimal weights with respect to the designed controller, thus generates controller which is more susceptible for the post-design controller order reduction. Finally the reduced order controller is obtained through solving frequency weighted balanced truncation in the normalized coprime factorization form.