Otimização de reguladores para acionamento controlado de motores de indução alimentados por intermédio de inversor de corrente com comutação natural

Abstract

The present work has as purpose the study and implementation, in laboratory, the control and drive system for three-phase induction motor fed by a thyristorized current inverter with natural commutation. The current and speed regulators were adjusted according to the symmetrical optimization criterion. In the proposed control and drive system, it has been used a three-phase induction motor fed by a six pulses thyristorized rectifier-inverter group configured as current source inverter. The DC link voltage and current levels are obtained through variation of the rectifier trigger angle, whereas the inverter trigger angle is maintained fixed. At the inverter output, a large capacitor is connected in parallel with the induction motor so that together they require a leading power factor current. The main function of the capacitor is to provide an enough reactive power that is required by inverter bridge thyristors commutation and to ensure that levels and waveforms are compatibles with motor functioning and driving. The capacitor is therefore able to ensure that the induction motor remains magnetized and that it can produce generated voltages, which can assist in the switching of a naturally commuted inverter. The motor drive and control are achieved by using an analogical speed and current control and regulation in closed loop configuration. The control and regulation have been obtained using the symmetrical optimization method and the regulators were calculated (designed) and incorporated in the system by operational amplifiers, according this method. vii In this configuration, where the inverter bridge trigger angle is maintained fixed, the voltage and current values present at the motor terminals are referred to DC link, as an inductive/resistive load. This configuration and the symmetrical optimization method usage make the calculation easy and simplify the use of electromechanical equations involved. In order to verify the system performance and regulation, load disturbances were promoted; the speed and current waveforms were recorded through a memory oscilloscope. It allows that the regulation dynamics could be evaluated and proved. The data and calculations, the parameters and the result relatives to the simulation are presented as well.