Implementação de um sistema de partida e controle de velocidade para máquina síncrona.

Abstract

The aim of this work is to show a start-up and control system to synchronous machines. Using two six thyristors converter bridges, one is operating as rectifier and the other one as inverter with natural commutation, in steady-state. One closed-loop control was used to motor speed regulation and also to limit the current value, for the motor protection. When the motor is working in low speed, there is no voltage enough in motor terminals to allow the natural commutation of the inverter bridge. To work around this situation was developed two circuits to execute a forced commutation, what makes the motor be able to work in low speed, until 150 [RPM]. The first one was implemented using analog e digital components and the second one using a pc-based microcomputer. The microcomputer based circuit to the inverter bridge allows also an automatic motor start-up. So, there is no necessity of use an auxiliary machine. The software created to control the firing pulses of the inverter bridge was developed in C language to be executed in MS-DOS operational system. This one has a graphical user interface, which allows a better interaction between the user and the system. The software allows to the user to start and stop de machine, to visualize the motor speed value (estimated by the motor terminals voltage), to monitor graphically the speed variation and operation mode of the bridge. That can be, forced commutated or natural commutated. The obtained results from the essays in laboratory showed that the overall performance of the system was satisfactory, according to the expectation.