Tensões e correntes senoidais em conversores para média tensão industrial

Abstract

This work proposes the use of a passive filter and the selective harmonic elimination in order to synthesize sinusoidal voltages and current with high power and medium voltage static converters. The work presents an investigation of the most important multilevel topologies, the modulation techniques and the alternative harmonic reduction methods for this class of power converters mainly concerned with the synthesis sinusoidal voltages and current with low harmonic content. Following thisinvestigation, the NPC neutral point clamped three-level converter was chosen as the multilevel topology in this study. Its power semiconductor devices work with very low switching frequency, about 200Hz. The harmonic reduction method consists of a third order LCL configuration with resonant branches, added to the main filter so as to improve its low frequency attenuation ratio. In this case, the work proposes and evaluates an optimized design procedure based on the filter total reactive power setup to reduce the cost and size of the filter reactive elements. The work proves that the proposed filter can be useful for both constant and variable fundamental frequency applications. As the modulation technique the selective harmonic elimination was conceived to be able to respond to changes in the system operation conditions within a classical current control loop like all other pulse width modulation techniques in the literature. The work also discusses other theoretical and practical aspects related to the selective harmonic elimination. Simulation and experimental results confirm that it is possible to produce sinusoidal voltage and current with very low switching frequency, and high performance in large converter operation range.