A three-phase series-parallel compensated line-interactive UPS system with sinusoidal input current and sinusoidal output voltage

This paper deals with a three-phase line-interactive uninterruptible power supply system with active series-parallel power-line conditioning capability, which has sinusoidal output voltage regulation capability and unity power factor. In this system, two active power filter topologies are applied. The first one is a series active power filter which can compensate supply voltage harmonics and voltage unbalances as well. The other is a parallel active power filter which has the following main goals: reactive power compensation; load current harmonics suppression; and battery bank charging during normal power supply conditions. During input power failure, the parallel filter maintains uninterruptible power for critical loads, delivering power from the battery bank without power interruption, ensuring sinusoidal output voltages with constant RMS voltage value and low total harmonic distortion (THD). Therefore the proposed line-interactive UPS has low THD sinusoidal input currents with unity power factor. The control algorithm and mathematical models of the proposed three-phase line-interactive UPS system are described, and digital simulations are presented to verify the good dynamic responses of the versatile scheme.