Projeto e implementação de sistemas de controle distribuído em redes de computadores

Abstract

This work presents the main characteristics of the networked control systems and their particularities compared with the classical control systems. The effects of the delays, caused by the inherent network communication process between the various interconnected elements of the control loop, are analyzed. Tests in a real plant, of first order (an RC circuit), have been carried out and a detailed study of the individual and the combined influence of the delays introduced by the network (sensor/controller and controller/actuator) are considered. The tests have been accomplished in didactic platform, where the network has been replaced by buffers to allow full control of the events in time. For analysis of the closed-loop, a PI-controller, designed by the well-known Direct Synthesis method, has been used and implemented in the form of differences equations, whose coefficients have been derived from the Z and delta transforms. A preliminary control algorithm with explicit compensation of the control signal is implemented. This control algorithm uses an estimation of the plant output to compensate for variations in the control action. The strategy has been implemented in a real system aiming at improving the performance of the system under test. Simulated and experimental results are presented. A control algorithm for NCSs, of which the Internet is part, is presented. This algorithm possesses a synchronization routine between the local and remote units, an estimator for the plant output based on delta transform, an on-line parameters estimator, a remote controller, a local controller and an automatic switching scheme between the remote and local controllers. The proposed algorithm is implemented in a real NCS system, developed for this work, named NCS-CMUF. Initially, the system is used to control an RC circuit (the first order plant) and, later, a real plant: the Interacting Tank System. Some simulated and experimental results obtained using the proposed algorithm, as well as an analysis of stability (under particular conditions), are presented.