New Series-Resonant Solid-State DC Transformer Providing Three Self-Stabilized Isolated Medium-Voltage Input Ports

This work analyzes the properties of a new four-port, series-resonant, and bidirectional DC transformer topology in steady-state and transient conditions. The investigated topology evolves from the Integration of Three (3) Series-Resonant Converters (I3SRC), enables the realization of a converter with high efficiency (99.0%) and high power density (7.1 kW/dm
³
), due to the utilization of a three-phase High Frequency (HF) transformer and reduced capacitor currents in the secondary-side DC link, and features the use of a six-pack power module on the secondary side. The analysis is based on the results of detailed circuit simulations of an I3SRC, which takes the couplings between the phases, introduced by the three-phase transformer, into account and considers a DC transformer, i.e., DC-DC converter, with a total rated power of 15 kW, three primary-side DC voltages of 1.1 kV, and a secondary-side DC voltage of 700 V, which is a core part of a scaled demonstrator of a Solid-State Transformer (SST). The obtained findings clarify the self-stabilizing capabilities of the I3SRC for operation with Half-Cycle Discontinuous Conduction Mode (HC-DCM), even if the three isolated DC ports are subject to time-varying and substantially different power levels and different directions of energy transfer.