Experimental investigation of a three-phase series-parallel compensated UPS for non-linear load

This paper presents a three-phase series-parallel compensated UPS with universal filtering capabilities, using Synchronous Reference Frame (SRF) based controller. The proposed UPS is based on the combination of two full-bridge VSI converters: one is series with the input and the other in parallel with the load. The series converter is controlled as a sinusoidal current source in phase with the input voltage, eliminating harmonic input current distortion and providing unity controlled power factor. The parallel converter is controlled as a sinusoidal voltage source in phase with the input voltage, providing to the load a normal and sinusoidal voltage with low total harmonic distortion (THD). In case of loss of input power, the UPS can make a seamless transition to backup mode, drawing power from the battery. Compared to conventional double conversion UPS, the size can be reduced significantly. In this paper, a new control scheme using SRF method and the operation principle of the novel UPS are described in detail. Experimental results of a 20 kVA prototype for non-linear load are presented to verify the good performance of the UPS system and the effectiveness of the new control scheme.