This paper proposes a novel reconfigurable LLC resonant converter based on an adjustable turns ratio transformer for output voltage regulation. The converter enables dynamic adjustment of the voltage gain by reconfiguring the effective turns ratio of the transformer through a secondary-side switch. Due to the reconfigurable design, the converter realizes output regulation without frequency modulation and operates at a fixed frequency slightly below the resonant frequency as a DC transformer, which ensures soft-switching with high efficiency. The topology and the operation principles of the proposed converter are analyzed in detail. The design considerations of the converter are illustrated and a 30kW nominal power example that converts 1.5kV input to 500V/1kV output is simulated to verify the design.

Green hydrogen production through water electrolysis is emerging as a key technology in the global energy transition. As electrolyzer capacities scale up, the design of their power supply systems becomes critical to ensure efficiency, reliability, and cost-effectiveness. Traditionally, low-frequency transformer (LFT)-based architectures have been employed for grid connection and galvanic isolation. However, solid-state transformer (SST)-based solutions are gaining attention due to their potential for high efficiency, modularity, and advanced control features. This paper presents a comprehensive comparison between LFT-based and SST-based power supply systems for high-power electrolyzer applications. Both systems are rated at 1.5 MVA and designed to interface with a 10 kV distribution grid. The comparison considers component requirements, power density, and overall system efficiency. Simulation and theoretical results are provided, highlighting the trade-offs between the two architectures. The SST-based solution achieves superior performance, with an efficiency of 98.5% compared to 97% for the LFT-based counterpart, and a significantly reduced volume of 420 dm3versus 1473 dm3.

This paper introduces a novel reconfigurable LLC resonant converter using a center-tapped transformer and an adaptive turns ratio approach for output voltage regulation. The proposed topology achieves dynamic voltage gain adjustment by modifying the transformer turns ratio through a unidirectional secondary-side switch. Operating at a fixed switching frequency slightly below resonance, the converter behaves as a DC transformer, ensuring high efficiency and maintaining soft-switching operation. The topology and its operating principles are described in detail. Analytical voltage gain expressions and the mathematical model are derived. Simulation results are presented to validate the converter’s operation across output voltage levels of 500 V to 1 kV with a fixed input voltage of 1.5 kV, demonstrating the effectiveness and advantages of the proposed configuration without requiring variations in switching frequency.

Newer electric vehicle (EV) architectures require different charging voltages compared to the old systems, and to improve compatibility between chargers, a wide output voltage is desirable. While resonant converters offer high efficiency, the efficiency is typically closely tied to fixed operating conditions, making it difficult to maintain high efficiency across a wide output voltage range. This paper proposes a secondary rectifier architecture that enables wide-range output voltages with minimal complexity. With two switches, the rectifier can generate four discrete output voltages to achieve a wide voltage range without changing the switching frequency. Voltage expressions are derived from the analysis of equivalent circuit models for the four operation modes. To validate the operation of the proposed topology, simulation results are described and discussed for a 1 kW output power converter, with an input voltage of 150 V, and rectifier conversion gains of 1, 1.33, 2, and 4.

The more electric aircraft concept is pushing towards a DC distribution system for the on-board electrical appliances. In the scenario where multiple high-voltage and low-voltage buses are present, a power electronics converter interface is mandatory. In order to implement a resilient distribution system, the power exchange between different buses is envisaged, to ensure that a failure in a supply bus does not impair the rest of the distribution system. In this paper, two power converter structures able to achieve this goal are analyzed and compared in view of their contribution to improve the overall system resiliency. A control structure is investigated to manage the load supply with the desired priority. The variable virtual resistor control allows shifting the load priority on demand and, as a consequence, is found suitable for achieving the desired goals. Theoretical analysis and experiments are reported to prove the performance of the chosen solution, which is based on a QAB controlled with virtual resistors.

The focus of this paper is on power flow control in the asymmetric quad-active-bridge (QAB) converter and its limitations imposed by uneven values of parasitic elements in the isolation transformer. The QAB converter under study is intended for solid-state transformer applications in asymmetric configuration, where one of the ports is placed at the low voltage side and rated for the threefold power of the medium voltage ports. Significant imbalance between leakage inductance could be observed between them. The steady-state analysis of the asymmetric QAB converter and assessment of power losses using numerical simulation are provided. Experimental waveforms were obtained using a prototype rated for cumulative MV dc link of 2400 V and power of 30 kW.

This paper presents a nonisolated multilevel buck+boost dc-dc converter suitable for high voltage and high power application. It is composed by a Buck-type and a Boost-type converters, both multilevel and bidirectional. The main features of proposed converter are: reduced voltage stress across the semiconductors, allowing its use in high voltage; bidirectional power flow; frequency operation of the inductor is a multiple of the switching frequency, reducing the volume of magnetic component. This paper focuses on the five-level structure of the proposed converter, in which the theoretical analysis is carried out and discussed. In order to validate the theoretical analysis, a prototype with 10 kW output power capability, 1 kV to 750 V input-to-output voltage and 20 kHz of switching frequency was constructed and experimented. The results attest the advantages of the new dc-dc topology and it is reported herein.