Sistemas monofásicos de conversão de energia elétrica baseados em conversores estáticos multiníveis CA-CC-CA e CC-CA.

Abstract

This work proposes new topologies of AC-DC-AC and DC-AC single-phase multilevel converters to be applied in electrical energy conversion and compensation systems. The proposed AC-DC-AC confgurations are obtained from the cascaded connection of threeleg (3L) and H-bridge (HB) converters, mainly using low- and high-frequency transformers and DC links with foating capacitors. The studied AC-DC-AC converters provide load voltage with fxed amplitude and frequency and with low harmonic distortion, and maintain the grid current sinusoidal with low harmonic content and high grid power factor. They can be used to mitigate voltage sags and swells and compensate for reactive power and harmonics caused by non-linear loads. In this category, two groups of converters are studied: 1) AC-DC-AC topologies without low-frequency transformers for applications in which the nominal load voltage is higher than the nominal grid voltage; and 2) AC-DC-AC topologies based on low-frequency transformers for applications in which the nominal load voltage can be higher than, lower than, or equal to the nominal grid voltage. These topologies are analyzed in diferent voltage and power scenarios compared to conventional converters. The advantages achieved include lower harmonic distortions and lower stress and losses on the semiconductor devices, especially in applications in which the voltage is high and the current is low. The studied DC-AC confgurations are based on the connection of converters with two dc links and cascaded transformers. Compared to conventional converters, the proposed DC-AC topologies have lower harmonic distortions, a smaller number of components, lower switching stresses, and reduced semiconductor losses. Simulation and experimental results are implemented to validate the operation of the proposed systems, and the PWM techniques and control strategies developed.