A modified homotopy method and H_∞ robust controller design

A novel method of robust controller design with degree constraint is proposed for feedback control systems, where the performance indices are firstly transferred to the sensitivity function problem that will be solved by Nevanlinna-Pick interpolation. A modified homotopy method is presented to solve nonlinear equations induced by the sensitivity function problem. A new controller based on modified homotopy method is designed without using weighting functions, which can also overcome the defect of high order. At last, the 4th order plant is considered and the corresponding H1 robust controller with degree constraint is designed. It is be shown from simulations that the robust controller has not only lower degree than traditional robust controller, but also superior quality obviously.