Automatic Loop Shaping in QFT Using CRONE Structures

This work focuses on the problem of automatic loop shaping in quantitative feedback theory (QFT), where the search for an optimum design (a non-convex and nonlinear optimization problem) is traditionally simplified by linearizing and/or convexifying the problem. In this work, the authors propose a suboptimal solution using a fixed structure in the compensator. In relation to previous work, the main idea consists in the study of the use of fractional compensators, which give singular properties to automatically shape the open loop gain function by using a minimum set of parameters. CRONE controllers, in particular CRONE 2 and CRONE 3, are considered as possible candidate structures, being original structures modified for a better approach to the QFT theoretical optimum. CRONE 3 non-minimum-phase zeros are avoided by constraints on the structure parameters.