A simplified strategy used to control the output voltage and the input current of a single-phase line-interactive UPS system

This work deals with a simplified strategy used to generate the voltage and current sinusoidal references of a single-phase uninterruptible power supply (UPS) system. Both the references are obtained by using a phase-locked loop (PLL) combined with a self-tuning filter (STF). The power flow control through the UPS is performed varying the amplitude of the series converter sinusoidal reference current, which is achieved by controlling the UPS dc-bus voltage. As result, the UPS system allows output voltage conditioning, such as voltage harmonic suppression and sag and/or swell voltage compensation. Additionally, the UPS input current is also conditioned, allowing current harmonic suppression and reactive power compensation. In other words, the UPS system works as a true unified power quality conditioner (UPQC), when the utility grid is present. Mathematical analyses and experimental results are presented in order to evaluate the performance of the line interactive UPS system taking into account the utility grid disturbances.