Quantitative Feedback Theory

Abstract

Designing reliable and high-performance control systems is an essential priority of every control engineering project. In many practical situations, the presence of model uncertainty challenges the design. A robust control approach for these cases, deeply rooted in the classical frequency domain, is the Quantitative Feedback Theory (QFT). As an intrinsically multi-objective methodology, QFT is able to design control solutions that guarantee the achievement of a multi-objective set of performance specifications for every plant within the model uncertainty. It gives the control engineer a physical understanding of the trade-offs, limitations, and possibilities of the control system at every step of the design process, balancing also the trade-off between the simplicity of the controller structure and the minimization of the control activity at each frequency of interest. Control solutions designed by the QFT methodology reach from simple P, PI, or PID (proportional, integral, derivative) structures to much more complex high order and multi-block/multivariable structures. QFT has a proven track record of success in an extensive variety of real-world control problems, including linear and nonlinear plants, stable and unstable systems, multi-input multi-output processes, minimum and non-minimum phase plants, containing time-delay, lumped and distributed parameters, and advanced control topologies. Recent developments on computer-aided design tools facilitate the use of QFT to the control engineer.