Bidirectional AC-DC modular multilevel converter based on the three-state switching cell

This paper presents a novel bidirectional ac-dc topology based on modular multilevel converter and employing the interleaving concept suitable for solid-state transformer applications. The main features of this topology are derived from the interleaving technique and the cascaded converters concepts, as reduced conduction losses, passive elements operating with effective high frequency, reduced weight and volume, and reduced high-frequency output current ripple. The basic operation of the proposed topology as well as a pulse-width modulation scheme and proper control strategy are described. Simulation results of the proposed converter operating with switching frequency of 50 kHz, rated output power of 3.3 kW, output voltage of 48 V and supplied by a 127 V/ 60 Hz ac grid are presented.