Optimal Area-Product Model (OAPM) Based Non-Iterative Analytical Design Methodology for Litz-Wired High-Frequency Gapped- Transformer (LHFGT) in LLC Converters

In dc-dc LLC resonant converters, the Litz-wired high-frequency gapped-transformer (LHFGT) plays an important role, as it provides the necessary isolation, the required voltage-conversion, and the desired magnetizing inductance (L-m) for efficient converter operation. Since the LHFGT makes a significant contribution to the overall converter weight and size, so the converter designers must rely on complicated and advanced optimization techniques, with a large number of iterations, for its design. This dependence is due to the shortcomings in the conventional analytical modeling techniques for optimal size-selection of the core and winding in the LHFGT. Hence, this manuscript proposes an optimal area-product (A(prod)) model (OAPM)-based non-iterative LHFGT design methodology that maximizes the efficiency and power density, minimizes the losses and volume, integrates the L-m, and maintains the temperature-rise within limits. The method takes into consideration the LLC circuit parameters, the Litz-wire strand-radius (r(s)), the core material and geometrical parameters, the excitation-waveform shape, the stored energy due to core-airgap, and the peak flux-density (B-pk) inside the core. The accuracy improvement is attained through the proposal of accurate A(prod)-based core-geometry features estimation (ACGFE) models and by keeping in view the interdependency between the transformer-design parameters (TDPs). The optimized design is obtained in a single iteration, based on the proposed OAPM, the proposed optimal r(s) selection model, and the proposed optimal TDPs' models. The proposed design routine is validated through the analytical and experimental results of a prototype LHFGT for a 200W-110kHz-400VDC/12VDC LLC resonant converter.