The regulation of a disturbed output can be improved when several manipulated inputs are available. A popular choice in these cases is the series control scheme, characterized by (1) a sequential intervention of loops and (2) faster loops being reset by slower loops, to keep their control action around convenient values. This paper tackles the problem from the frequency-domain perspective. First, the working frequencies for each loop are determined and closed-loop specifications are defined. Then, Quantitative Feedback Theory (QFT) bounds are computed for each loop, and a sequential loop-shaping of controllers takes place. The obtained controllers are placed in a new series architecture, which unlike the classical series architecture only requires one controller with integral action. The benefits of the method are greater as the number of control inputs grow. A continuous stirred tank reactor (CSTR) is presented as an application example.
(Hindawi, 2014) Rico Azagra, Javier; Gil Martínez, Montserrat; Elso Torralba, Jorge; Automática y Computación; Automatika eta Konputazioa
This paper presents a robust feedback control solution for systemswithmultiplemanipulated inputs and a singlemeasurable 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.
