Design of Digital Controllers for a Two-Degree-of-Freedom Control System Using an Approximate Model-Matching Method (1st Report, Case of Scalar System)

Abstract

In this paper, we propose a new method of designing a digital controller. We consider the design problem for a two-degree-of-freedom control system with a feedforward controller. First, we design a cascade controller in order to obtain a desirable sensitivity and stability margin. Then, we design a feedforward controller so that the resulting control system may satisfy a specification with respect to the reference command. The proposed method is based on minimizing a frequency-weighted error so that the resulting control system approximates the specified reference model. A square error criterion is introduced as a measure of the approximation. By minimizing the criterion, a linear equation is obtained for parameters of a FIR (finite impulse response) controller. Using the method, we can design a control system by a low-order controller which realizes the desirable accuracy of the approximation without regard to the order of the plant or the reference model.