Análise e implementação de uma ups on-line monofásica utilizando estruturas baseadas nos conversores Cuk e SEPIC.

Abstract

This work proposes new topologies for rectifier and inverter converters for application in Uninterruptible Power Supplies (UPS), aiming to improve the power quality of an electrical system. Compared to conventional back-to-back converters used in this application, the proposed structu- res have the advantage of performing both step-down and step-up voltage conversion, allowing the UPS to operate with a reduced DC bus voltage. As a result, the system can operate with fewer batteries compared to traditional systems, enabling a smaller volume and lower cost. The proposed system is a single-phase on-line double-conversion UPS, employing two converters: a rectifier responsible for drawing a sinusoidal current from the grid and charging the batteries, and an inverter responsible for supplying the load. Throughout the work, mathematical and dynamic analyses of the circuits were carried out in order to design the passive components and obtain the corresponding frequency responses needed for the control structure design. The rectifier topology uses a classical Proportional-Integral (PI) controller to control a sinusoidal current with defined amplitude and frequency from the grid, as well as to charge the batteries and maintain an appropriate voltage level on the DC bus. The inverter employs a control structure that combines a PI controller with a multi-resonant structure to control the voltage delivered to the UPS load, ensuring a regulated voltage with low harmonic content. Simulation results using the MATLAB/Simulink® software tool are presented, demonstrating the system's potential to improve power quality by mitigating issues such as grid harmonic distortion, voltage sags, overvoltage, grid intermittencies, or even complete grid outages. Additionally, the simulation presents the waveforms across the circuit elements to validate the previous analyses. Finally, the operation of the UPS system and the proposed converters was validated through experimental results, which showed that the system was capable of operating as an online UPS, drawing a controlled sinusoidal current from the grid and delivering a sinusoidal voltage to the load.