A Comparative Study of Single Loop and Multiple Loop Design for Uncertain Single Input Single Output Systems
In this paper, studied are the actual advantages offered by SISO cascade loop structures. In Quantitative Feedback Theory it is emphasized that the use of cascaded loops is primarily for the reduction of bandwidth of the controllers. This in turn helps in considerable reduction of the adverse effects of high frequency noise. The question that arises then is whether or not there are any substantial benefits to be gained by cascade loop design in the low frequencies. This issue is the focus of this paper. It is shown using Quantitative Feedback Theory methodology that there aren’t any advantages gained in the low frequencies with the use of cascaded design for meeting performance specifications. In effect it is concluded that if the design is properly executed a single loop controller closed from the output to the input will be sufficient to meet the typical performance specifications. This is shown using an example where the mold level of a continuous casting process is to be controlled. The plant being used has considerable uncertainty so that features of robust control can be highlighted.