Line-interactive UPS system applied to three-phase four-wire systems with universal filtering capabilities

This paper proposes a three-phase line-interactive Uninterruptible Power Supply (UPS) scheme, which is applied to three-phase four-wire systems, allowing harmonic suppression and reactive power compensation of the load, resulting effective power factor correction. The proposed UPS system is composed of two PWM converters, where one of them is placed in parallel with the load and the other one is placed in series between the power source and the load. Both the converters share the same DC-bus, which is composed of a battery bank. The parallel converter is implemented by using a four-leg VSI topology and it is controlled to operate as a sinusoidal voltage source, while the series converter is implemented by means of a three-leg topology and it is controlled to operate as a sinusoidal current source. The proposed scheme allows the voltage level reduction of the DC bus, when compared to the use of two three-leg split-capacitor topologies for performing the series-parallel conditioning. In addition, the number of switches is also reduced when it is compared to the use of two four-leg topologies. Both the UPS voltage and current controllers are implemented in the synchronous rotating reference frame (dq0-axes), and the PWM converters are modulated by using three-dimensional space vector modulation. Simulation results are presented in order to validate the theoretical development and confirm the performance of the UPS system.