Controle por escalonamento de ganhos fuzzy PDC-FOPID: Implementação em CLP aplicada em um sistema de rastreamento de nível

Abstract

A continuous improvement of control systems is leading to the development of new controllers. Among these advances, those of the FOPID (fractional order PID) type, once they are an extension of PIDs, have been very promising for improving industry control loops, accumulating advantages of greater robustness and a greater number of project criteria that can be achieved. However, one of the difficulties in transitioning from the state-of-the-art to the state-of-the-use of such controllers concerns their implementation in industrial devices. Aiming to address this issue, this work describes the stages of controller design, simulation, implementation based on a programmable logic controller (PLC) and experimental tests on a level control bench. The work plant was modeled as a first-order plus dead time (FOPDT) around each operating point and present centrifugal pump power saturation. In total, controllers were designed by Fractional Order Pole Placement (FOPP), by Gain Margin and Phase Margin (GMPM) and, for comparison purposes, by Integer Order Pole Placement (IOPP). Each controller was discretized and implemented in the RST structure with anti-windup action. Furthermore, an association of controllers with fuzzy logic by Parallel Distributed Control (PDC) was adopted to improve performance for different operating points. For tracking tests, multiple sequential steps, ascending and descending, were carried out, covering the entire operating region. To evaluate the controllers, metrics based on error and control effort were used. The anti-windup action ensured that there was no excessive overshoot or oscillatory response. The PDC association proved to be effective for the IOPP controllers, and a slight improvement was observed in some error indexes for the GMPM controller. There was no significant performance improvement in the PDC-FOPP controller. Overall, all fractional order controllers proved to be superior to integer order controllers.