Estrutura com realimentação por relé para processos sujeitos a perturbações - aplicações e análise.

Abstract

In this work, we present contributions in the area of ​​identification of systems using relay feedback. With the aim of obtaining a limit cycle insensitive to disturbance, a relay feedback structure is proposed composed of a block o to remove static disturbances and/or drift, followed by a relay. this block consists of a high-pass filter followed by by a relay and an integrator. Several simulated and experimental studies are carried out in order to verify the applicability of the proposed relay structure. Through such studies, it appears that the proposed structure is able to generate the symmetrical switching of the relay under disturbance at the process input, while the other structures present in the literature may not even produce a sustained oscillation for some disturbances. Regarding the analysis of the proposed relay structure, the descriptive function method is initially used. From this analysis, it is observed that the proposed structure has characteristics similar to standard relay feedback. Then, the analysis based on the Poincaré map and a representation in state space is performed. As In order to simplify the analysis of the structure of the relay under study, a structure is obtained equivalent. For this LTI framework and systems with and without delay, the necessary and sufficient conditions for the existence of the limit cycle. The local stability of the limit cycle is investigated using the Jacobian corresponding to the Poincaré map. In addition, the analysis of the existence and stability of the Limit cycle is performed from the original relay structure. In this case, the analysis is limited to systems without delay. At the identification context of FOPTD (First Order Plus Time Delay) models, it is presented a technique which uses the proposed open-loop relay structure, with and without integrating element fed back into the loop. In addition, point information of frequency are used as equality constraints to obtain the parameters of the models. To estimate the delay, a Taylor series approximation is used. second order and an iterative procedure. Finally, based on two models identified, a methodology for the phase adjustment of FOPTD models is proposed.