Controle ressonante macro-micro para conversores de tensão CC-CA multinível

Abstract

Power inverters convert direct current electricity into alternate current. Also called dcac converters, these devices generate discrete alternate waveforms. Therefore, they need inductive-capacitive (LC) low-pass filters connected to its output terminals in order to smooth the ac output waveform. The balance between total harmonic distortion (THD) filtering and the limitation of the switching frequency leads to bulky LC filters. Consequently, it increases the physical size of the system and its costs. This work proposes an alternative for THD attenuation in inverters by combining different stages. The main stage, the macro, comprises of a Neutral-Point-Clamped multilevel inverter operating in high voltage and low switching frequency. This converter is connected to a two-level three-phase inverter, called the micro actuator. The micro is faster and more accurate than the macro actuator due to its higher frequency and limited voltages and currents. In this macro-micro approach, the opposite characteristics of the converters lead the micro actuator to correct the distortions of the main stage, which works in open-loop with its switching signals generated by optimized pulse patterns. For correct THD filtering, feedforward and resonant control systems are designed in order to operate the auxiliary three-phase inverter. The control structure was evaluated through a set of simulations, using numerical models of the electric circuits of the studied converters. The simulation results demonstrate that the proposed control structure reduces THD on the load voltage waveforms.