A medium-voltage transformerless ac/dc power conversion system consisting of a diode rectifier and a shunt hybrid filter

This paper proposes a 3.3-kV transformerless ac-to-dc power conversion system consisting of a three-phase six-pulse diode rectifier and a shunt hybrid filter. The hybrid filter is formed by a single tuned LC filter per phase and a small-rated three-phase. active filter, which are directly connected in series without any matching transformer. The required rating of the active filter is much smaller than that of a conventional standalone active filter be. In addition, no additional switching-ripple filter is required for the hybrid filter because the LC filter functions not only as a harmonic filter tuned at the seventh harmonic frequency but also as a switching-ripple filter around 10 kHz. Experimental results obtained from a 200-V 5-kW laboratory system and simulation results of a 3.3-kV 300-kW system confirm the validity and effectiveness of the system.