Modular DC‐DC auto‐transformer: Topology, operation, and system design

Abstract

Here, a modular DC-DC auto-transformer is proposed with a developed scheme of two-port submodules. The proposed two-port submodule is composed of six switches and single capacitor, and it is featured with three general working states. In the proposed DC-DC auto-transformer, all two-port submodules are connected in the input-series-output-series structure. Then the general primary and secondary ports of the submodules of the proposed DC-DC auto-transformer are connected in series to achieve the auto-transformer operation capability. All submodule capacitors are actively connected in the transformer to form the primary and secondary side voltages. The capacitor utilization is increased therefore. Different voltage ratios can be achieved by arranging different submodule numbers in each working state simultaneously. The volume is reduced due to the developed two-port submodule which eliminates of AC transformers. Detailed topology, working principles, modulation method, and control strategy are provided in the paper. Voltage and current fluctuations are analysed, and the system parameter design method is proposed in detail. Both a simulation system with 40 submodules and a down-scaled experimental system with three submodules were set up and verified the proposed approach.