Comparison of the Whole Benifits in a MIMO Control System with Large Parameter Variations

The quantitative feedback technique (QFT) is successful in synthesis of control system with large parameter variations. Several QFT design methods are developed with different advantages. In this paper, the whole benifits of QFT which is according to both the design cost (the complexity of designing procedure) and the bandwidth cost (how much overdesign in bandwidth causing the noise amplification) are discussed. For a MISO (multiple-input single output) single loop system, the ICQFT (improved conventional QFT) possesses best bandwidth cost, but its design cost is too high. On the other hand, the EDA (equivalent disturbance attenuation) method can simplify the design complexity, but the resulted bandwidth is too conservative. For a MIMO (multiple-inut multiple-output) system, a n × n system can be decomposed to n² MISO system with n different loops, by using the Schauder´s fixed point theory. Each single loop can be designing by a suitable method, so a combination of various methods to n loops may be a wiser choice. The whole benifits concept can, in this paper, not only evaluate the design result, but also provide the designer a good judgement of choosing QFT method.