A novel three-phase line-interactive UPS system with parallel-series active power-line conditioning capabilities using AC line reactor

In this paper a novel three-phase line-interactive UPS system with parallel-series active power-line conditioning capability using AC line reactor and two four-leg voltage source converter (VSC) is proposed. The four-leg VSC can use the DC-link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by 15% in comparison to that of the conventional line-interactive UPS system. The parallel inverter operating as a shunt active filter is a controlled voltage source and controls the three-phase line voltage independently in order to control the source current. It eliminates the neutral line current and the active ripple power of the source side using the dqo transformation so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series inverter operating as dynamic voltage restorer (DVR) compensates the load voltage and allows it to be balanced and harmonic-free. Both of the series and shunt inverters always act as independently controllable voltage sources, so that the three-phase output voltage can show a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through experimental results.