Analysis and prototyping of multicellular ac-dc converter for future dc distribution system

A multicellular ac-dc converter is proposed to realize highly efficient dc distribution system in data centers. The proposed converter consists of the singe-phase full-bridge ac-dc cell converters using ultralow loss GaN (Gallium Nitride) transistors and the non-regulated highly efficient isolated dc-dc cell converters. These cell converters are connected in ISOP (Input Series and Output Parallel)-IPOS (Input Parallel and Output Series) to interface various voltage classes in the distribution system. The analysis of the multicellular converter is conducted based on the state-space averaging method, and the control strategy of the ac-dc cell converter is derived from the analysis for the stable operation, taking the behavior of the non-regulated dc-dc cell converter into account. A small-scale prototype is also developed and the potential to achieve the total efficiency over 96% (98% in the ac-dc conversion stage and 98% in the dc-dc conversion stage) was verified. The proposed multicellular ac-dc converter achieves the energy saving not only in the ICT (Information and Communication Technology) distribution system but also in the power grids which have different voltage classes. The proposed topology enables the widespread use of standardized power electronics converters and contributes to realizing highly electrified low-carbon society.