A bidirectional three‐phase triple‐voltage LLC (T ² ‐LLC) resonant converter for DC/DC stage in solid state transformer and DC transformer applications

Abstract

This paper proposes a novel bidirectional three‐phase triple‐voltage LLC (T2‐LLC) resonant converter, which can be applied as the submodule of DC transformer (DCT) with fixed input and output terminal voltages. A novel series‐connected three‐phase circuit is adopted at medium voltage (MV) side to improve the voltage level of single submodule (SM) and decrease SM number. Therefore, the power density of DCT can be improved. Besides, the proposed converter is open‐loop controlled with fixed switching frequency, and it naturally realizes bidirectional power flow without changing controlling modes according to the power direction. However, the efficiency and voltage conversion ratio of proposed T2‐LLC converter are sensitive to resonant parameters, and consistency of three‐phase resonant parameters should be ensured to achieve three‐phase symmetrical operation. Therefore, design and optimization methods are proposed to realize ZVS turn‐on, reduce power losses and ensure fixed voltage conversion ratio. The operation principle and optimization method are presented and a 1000 V/333.3 V/5 kW platform is used to validate feasibility of the proposed converter.

An Overview on Medium Voltage Grid Integration of Ultra-Fast Charging Stations: Current Status and Future Trends

“…However, this topology suffers from turn-off losses in primary-side active switches, high losses in secondary-side diodes, significant ringing induced by M/HFT leakage inductance, the parasitic capacitance of reverse biased diodes and the output inductor. It has trade-offs between conversion efficiency and voltage overshoot and ringing, as the use of active [155] or passive T 2 -LLC topology [173]. f) 3-ϕ BAD topology.…”

“…Three-phase triple-voltage LLC (T 2 -LLC) is a new bidirectional resonant converter as shown in Fig. 19 (e), is presented in [173]. The proposed converter employs a novel series connection at the input to handle MV and a parallel arrangement at the LVDC side to provide a high current.…”

Multi‐objectives optimization of parameter design for LLC converter based on data‐driven surrogate model

“…In order to adapt to the development trend of smaller size and higher power density of switching power supplies, more and more converter topologies are being studied. LLC resonant converters feature the advantages of zero voltage switching (ZVS), simple structure, high efficiency, and low electromagnetic interference [1,2], which stands out among many topologies. To further improve the performance, it is necessary to optimize the design of LLC resonant converter.…”

“…The disadvantages of the optimal design for the LLC resonant converter in the aforementioned methods are summarized as follows: (1) The optimization objective of the LLC resonant converter is single. (2) The computation complexity is high. (3) The resonant tank parameter is discrete when searching for the optimal candidates of parameter scheme.…”