Back-to-Back H-Bridge Cell Based Modular Solid State Transformer with High-Frequency Link

With the features of control flexibility, multiple functions and compact size, solid state transformer (SST) is considered to be a promising candidate for the energy conversion in applications such as charge station, data center, distribution grid, traction systems and so on. Generally, SST is used to transform medium-voltage AC to low-voltage AC, through the intermediate DC link. Two modular SST topologies based on the back-to-back H-bridge cells with the high-frequency bus as the extra intermediate link are proposed in this paper. Compared with existing modular SST topologies, the two topologies have smaller module counts, thus lower lost and higher efficiency. The working principle of one topology is analyzed as an example, and the corresponding control strategies and design criterion are provided. The feasibility of the proposed topology is verified using the simulation results of a 10kV/380V SST with the capacity of 1MVA.