A line-interactive UPS system implementation with series-parallel active power-line conditioning for three-phase, four-wire systems

This paper presents a three-phase line-interactive uninterruptible power supply (UPS) system with active series-parallel power-line conditioning capabilities. Synchronous reference frame (SRF)-based controller is used to harmonic and reactive power compensation generated from any configuration of non-linear load. Under normal line conditions the UPS system works with universal filtering capabilities, such as compensating the input currents and output voltages. Two three-phase pulse width inoculation (PWM) converters, called series and parallel active filters. are used to perform the series and parallel active power-line compensation. The series active power filter works as sinusoidal current source in phase with the input voltage, drawing from utility sinusoidal and balanced input currents with low total harmonic distortion (THD). The parallel active power filter works as sinusoidal voltage source in phase with the input voltage, providing regulated and sinusoidal Output voltages with low THD. Operation of a three-phase phase-locked loop (PLL) structure, used in the proposed line-interactive UPS implementation. is presented and experimentally verified under distorted utility conditions. The performance of the UPS system is evaluated in three-phase. four-wire systems. Digital simulations and experimental results are presented to confirm the theoretical studies. (C) 2004 Elsevier Ltd. All rights reserved.