MMC-Based High Gain Solid-State Transformers for Energy Storage Applications

This paper examines modular high-gain isolated DC/DC converter topologies for energy storage systems (ESS). The structure and operation of the topologies discussed resemble modular multilevel converter (MMC) and dual-active-bridge (DAB), in that regulated bidirectional power flow is realized with traditional circuit building blocks by applying classic phase shift control. The operation of two topologies is presented. Both can realize a high voltage step-down ratio from a medium-voltage (MV) bus to a medium frequency (MF) transformer primary winding so that reduced winding insulation is achieved to shrink the transformer size. These two topologies are compared in terms of their step-down ratios, frequency multiplication factors, switching and conduction losses, submodule (SM) capacitance, and transformer area products. Preliminary experimental results are presented to verify the key features of both topologies using 3.3-kV silicon carbide (SiC) devices (Generation-2 engineering samples from GeneSiC).