Abstract
In this paper, controller order reduction methods based on model matching of loop transfer function's frequency response are proposed. By these methods, a PID controller can be obtained by reducing a high order controller, which is designed by H∞ control or μ synthesis, etc. Since the controller order reduction is performed such that the frequency response of the loop transfer function matches to a high order controller's loop transfer function in cut-off frequency band, the reduced order controller provides almost the same performance as the high order controller in considerable cases. The methods have very small computation effort because the reduced order controller is derived using the least squares method, and the methods could be applied for multivariable controller design.
