AC-DC-AC power conversion systems for applications as unified power quality conditioners

Abstract

In this work, six single-phase and two three-phase ac-dc-ac configurations that can operate with better levels of harmonic distortion and efficiency than conventional solutions within some application scenarios are analyzed. In this context, this work had the following objectives: i) to propose and analyze ac-dc-ac configurations with multilevel characteristics, that is, that can synthesize multilevel waveforms and lower blocking voltages in semiconductor devices; ii) to propose and analyze single-phase ac-dc-ac configurations, as well as control strategies that improve the performance of the structure in terms of minimum dc-link voltage and series compensation; iii) to propose and analyze three-phase four wire multilevel ac-dc-ac configurations that achieve better performance in terms of minimum dc-link voltage when operating with severely unbalanced loads. The analyzed single-phase and three-phase converters are able to provide a load voltage with constant amplitude and frequency, as well as a sinusoidal grid current with low harmonic content and a high power factor. Furthermore, the studied converters can be used to compensate for harmonics, swells, and sags in the grid voltage, as well as to compensate reactive power and reduce harmonics caused by nonlinear loads. The study methodology for these configurations involves a detailed analysis of the proposed configurations, including the system model, operating principles, PWM modulation strategy, and control strategy. The validation of the studied configurations, to verify their feasibility, was conducted through numerical simulations and experimental results. Additionally, comparative analyses were performed against conventional configurations, demonstrating benefits in terms of harmonic distortion and losses in semiconductor devices, particularly in scenarios of high voltage and low current. The studied configurations can be used as Unified Power Quality Conditioners (UPQC).