Design of optimal robust fixed-structure controllers using the quantitative feedback theory approach

A simple optimization algorithm is proposed for designing fixed-structure controllers for highly uncertain systems. The method can be used to automate the loop-shaping step of the quantitative feedback theory (QFT) design procedure and guarantees robust stability and performance to the feedback loop for all parameters in the plant's uncertainty set. To avoid over-designing the system, the algorithm can be used to minimize either the asymptotic gain, the open-loop crossover frequency or the 3 dB bandwidth of the closed-loop system (nominal or worst case). The proposed algorithm is illustrated with a design example involving a hydraulic actuator, carried out within a computer aided design (CAD) environment ('StdQFT' toolbox) which has been developed by the authors. Some preliminary results of this work appeared in 2002.