Contribuição ao estudo de técnicas de controle para retificadores ativos em sistemas de média tensão

Abstract

Threephase diode rectifiers results in unidirectional flow of energy, low power factor and high harmonic distortion. The power factor correction is necessary because the more close to unity, less apparent power will be drained by the grid. That means, if the power factor is low a portion of reactive power, which does not perform work, shall be provided by the network. The circulation of harmonic currents in the electrical system is also undesirable because it involves several problems such as losses in the conductors, voltage distortion and electromagnetic interference. Therefore, the level of harmonic distortion is limited by standards, for example, the IEEE5191992 and normative guidelines such as PRODIST and IEC61000. Active Front End Rectifiers appears as an alternative as they have low harmonic distortion, power factor control, bidirectional flow of power, control the voltage level and reduced size of the DC bus capacitor. is work will analyze three control techniques for active front end rectifiers using PWM modulation and one analysis will be performed using selective harmonic elimination. The purpose is to find a compromise between the low switching frequency of the converter, aiming the reduction of the power dissipated in the switches, and the use of larger filters to reduce the THD levels below acceptable limits.