Variable Magnetic Permeability Coreless Transformers via Anti-Resonant Windings for Wide Input Voltage Range DC–DC Converters

To overcome the drawbacks of conventional coreless transformers (CLTs), where smaller magnetizing inductance results in large reactive power circulating current and switches’ turn-off current, this paper proposes a variable magnetic permeability CLT for wide input voltage range DC-DC converters via anti-resonant winding. Compared with the resonant converter using conventional two-winding CLT, the proposed converter exhibits lower switching loss and conduction loss on the primary side. These advantages come from the fact that the magnetic permeability and magnetizing impedance of CLTs can be greatly increased by adding the LC anti-resonant winding. Besides, compared with the ferrite-core resonant converter, both have the same external characteristics, and crucially, the proposed converter has a lighter weight and smaller volume by multiplexing the leakage inductance into a resonant inductance, while ensuring ZVS and a wide input voltage range. A detailed analysis of the proposed converter, including the variable magnetic permeability, the voltage gain, and the wide voltage range modulation, is presented, and a design method is given. Finally, an experimental prototype with an input voltage range of 250-400V and 72V/1kW output is designed to verify the theoretical analysis.