Efficiency comparison of a single-phase grid-interface bidirectional AC/DC converter for DC distribution systems

The focused bidirectional ac/dc converter works as the interface between dc distribution systems (future residential dc system, energy storage system etc.) and the ac utility. The interface converter regulates ac side current and dc side droop voltage. It also limits the current if ac or dc side is short. An design procedure is developed to optimize the efficiency of this interface converter. Different bidirectional 2-level and 3-level topologies with state of the art IGBTs and SiC MOSFETs are compared. The choice of switching frequency, inductor current ripple and passive components are optimized for each candidate. Grid interconnecting standards are used as the design requirements. The result shows the 2-level full-bridge topology with paralleled SiC MOSFETs has the highest efficiency. The 3 level T-type topology with hybrid devices (IGBTs and SiC MOSFETs) has a good trade-off between efficiency and passive volumes.