Topology Analysis and Validation of Novel Modular DC-DC Auto-Transformer

A modular DC-DC autotransformer (MDCAT) with novel two-port submodules is proposed in this paper. The novel two-port submodule consists of 6 switches and a capacitor and has 3 general working states. Energy is absorbed from the primary port and stored in the capacitor in working state 1. The energy in the capacitor is transferred to secondary port in working state 2. The 2 ports are isolated and there is no energy exchange in working state 3. Submodules in MDCAT are connected in input-series-output-series structure and the general primary port and secondary port are connected in series to form the auto-transformer style. Primary side voltage is the sum of capacitor voltages of all submodules in working states 1 & 2. Secondary side voltage is the sum of capacitor voltages of submodules in working state 2. Submodule capacitor voltages are maintained almost constant and energy is transmitted from primary side to secondary side by changing submodule working states regularly. Different voltage ratios are achieved by arranging different submodule numbers in each working state simultaneously. The modulation of the proposed MDCAT is simple and reliable. The volume is much reduced due to the application of a two-port submodule and the elimination of AC transformers. The proposed MDCAT is verified by experiment results.