New method for the design of a reduced-order controller

Abstract

The old problem of designing reduced-order controllers has been addressed from many different angles. This paper offers an alternative approach to design reduced-order controllers for S1SO systems (the MIMO case is currently under development). The new design technique lies between the two common design methods. The first obtains the controller based on a reduced-order process model. The second obtains the controller by designing a controller for the full-order process model and by then reducing the order of this controller. Unlike those two ‘open-loop’ methods the method presented in this paper works directly with the closed-loop system during the design, thus ensuring that the reduced-order controller achieves a performance similar to that of a full-order controller. Roughly speaking, the proposed procedure computes the reduced-order controller by approximating an equivalent closed-loop state feedback system and then performing an inverse operation.