A generalized controller reduction technique using LFT framework

In this paper, the solution to controller reduction problem using the linear fractional transformation (LFT) framework via a double-sided frequency weighted model reduction technique is considered. Firstly, a generalization of the structure of the LFTs is proposed. Based on this structure, a new method for finding low order controllers is presented. This algorithm is based on new frequency weights derived using closed-loop system approximation criterion. The formulas of frequency weights are obtained in terms of the plant, the original controller and a free parameter. By varying the free parameter in the resulting two-sided frequency weighted model reduction problem, frequency weighted error can be significantly reduced to yield more accurate low-order controllers.