Robust control using loop shaping

Abstract

This thesis is concerned with the evaluation of a modern control design method developed by McFarlane & Glover. The method combines modern H-infinity control theory with the older loop shaping approach, and has some intuitive appeal to the designer. Some Matlab functions have also been written for computing the controllers. Case studies are included for a paper machine headbox model and for a distillation column model. - One way to design robust control systems is to employ H-infinity optimization on certain closed loop transfer functions. This approach can, however, be quite complicated and no standard method for selecting appropriate weights has been presented. In 1989 McFarlane & Glover presented a more intuitive approach for robust control systems design. In their loop-shaping method the ideas used for decades to obtain a "good" open loop frequency response are used in design for performance and H-infinity optimization is used to guarantee robust stability. This method is more intuitive than most other methods using H-infinity theory, and easier to use. - The examples considered show that controller design using the McFarlane-Glover loop-shaping method is quite straightforward, and results in robust controllers. Usually all that is needed is some kind of integrating precompensator to amplify the low frequency gain of the open loop system. The simplicity of the use of this design method makes it a promising control system design method.