Analysis and design of high frequency gapped transformers and planar transformers in LLC resonant converters

The LLC resonant converter is particularly applicable for power supplies applications since soft switching is easily achieved. The dual objectives in power supply are higher switching frequencies and higher power densities. The analysis and design of the LLC resonant converter, especially the magnetic components needs further investigation and the related research has enormous practical significance. In this thesis, the design methodology for the LLC resonant converter is proposed based on the circuit analysis and the loss calculations with soft switching conditions and input voltage variations considered. The gapped transformer employed in the resonant converter is deeply investigated. The transformer was treated as the multi-winding inductor and a new design methodology is proposed. The parasitic parameters in the transformer involving high frequency leakage inductance and stray capacitance are studied, and reliable evaluation formulas are presented. With the purpose of introducing the planar transformer in the LLC resonant converter, the detailed modelling of planar transformer including the winding loss calculation, the stray capacitance and the leakage inductance for the integrated planar structure incorporating the low permeability magnetic shunt is carried out. Combing the analytical results of the gapped transformer design method and modelling of the planar transformer, the gapped planar transformer for the LLC resonant converter is designed and fabricated. Comparison with the conventional transformer shows that successful operation is possible with the low profile core.

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University of Galway Theses (PhD Theses)