Quantitative Feedback Control of Multiple Input Single Output Systems

Abstract

This paper presents a robust feedback control solution for systems with multiple manipulated inputs and a single measurable output. A structure of parallel controllers achieves robust stability and robust disturbance rejection. Each controller uses the least possible amount of feedback at each frequency. The controller design is carried out in the Quantitative Feedback Theory framework. The method pursues a smart load sharing along the frequency spectrum, where each branch must either collaborate in the control task or be inhibited at each frequency. This reduces useless fatigue and saturation risk of actuators. Different examples illustrate the ability to deal with complex control problems that current MISO methodologies cannot solve. Main control challenges arise due to the uncertainty of plant and disturbance models and when a fast-slow hierarchy of plants cannot be uniquely established.

Frequency Domain Design of a Series Structure of Robust Controllers for Multi-Input Single-Output Systems

“…The counterpart of simpler controllers is a lower flexibility of the structure. Thus, the series structure sets the time sequence of plant intervention, while the controllers could freely allocate it in a parallel structure [16]; furthermore, this can make several plants work in the same frequency band.…”

“…The architectures for MISO control can be grouped in two: the parallel [15,16] and the series disposition of controllers. The latter (see Figure 1) originally appeared in the habituating control by Henson et al [15] and the midranging control by Allison and Isaksson [17].…”

Dual-Control of Autothermal Thermophilic Aerobic Digestion Using Aeration and Solid Retention Time

“…SRT deviated from its bias point whenever any disturbance persisted. The dynamic collaboration between the two inputs was tailored by a proper design of controllers C Qa and C SRT based on a robust methodology in Rico-Azagra et al [24] in the framework of quantitative feedback theory (QFT) with the following main characteristics summarized. Appendix A provides details on the design of the controllers from a more technical point of view for robust control practitioners.…”

“…It follows the method in Rico-Azagra et al [24] for systems that use several manipulated inputs to regulate a single output.…”

“…Figure A2 shows how the shaping of the open-loop functions meet the bounds that represent the robust control specifications. A thorough description of the general methodology can be found in Rico-Azagra et al [24]. The yielded controllers are Equations (3) and (4).…”