This paper presents a three-phase line-interactive uninterruptible power supply (UPS) system with series-parallel active power-line conditioning capabilities, using a synchronous-reference-frame (SRF)-based controller, which allows an effective power-factor correction, load harmonic current suppression, and output voltage regulation. The three-phase UPS system is composed of two active power filter topologies. The first one is a series active power filter, which works as a sinusoidal current source in phase with the input voltage. The other is a parallel active power filter, which works as a sinusoidal voltage source in phase with the input voltage, providing to the load a regulated and sinusoidal voltage with low total harmonic distortion. Operation of a three-phase phase-locked loop structure, used in the proposed line-interactive UPS implementation, is presented and experimentally verified under distorted utility conditions. The control algorithm using the SRF method and the active power flow through the UPS system are described and analytically studied. Design procedures, digital simulations, and experimental results for a prototype are presented to verify the good performance of the proposed three-phase line-interactive UPS system.
