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

Abstract

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 sizeselection 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 coreairgap, 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. INDEX TERMS Area-product based core-geometry features estimation (ACGFE) parameters, Litz-wired high-frequency gapped-transformer (LHFGT), LLC resonant converter, optimal area-product model (OAPM), optimal Litz-wire strand-radius selection (LSS) model, optimal transformer-design parameters' models (OTDPMs), optimization.

LLC DC-DC Converter Performances Improvement for Bidirectional Electric Vehicle Charger Application

“…Refs. [21][22][23] highlight an optimized transformer design for LLC converter to reduce core volume and conduction losses in the transformer windings for high power density. In addition to that, it provides the necessary isolation and required voltage-conversion and magnetizing inductance for efficient converter operation.…”

“…However, the proposed optimization strategies in the literature are mostly intended to minimize the cost and weight of the DC-DC LLC converter and guarantee soft-switching property in one operation mode, i.e., G2V mode [11,12,20,[24][25][26]. Moreover, the LLC converter is designed based on a reduced battery voltage (12-48 V) [8,[20][21][22][23][24][25][26] and converter power (20-1000 W) [8,12,[20][21][22][23][24][25][26]. For our best knowledge, no optimization algorithm, which takes into consideration the DC-DC LLC converter behavior in the two operation modes G2V and V2X for a bidirectional charger application, is presented to minimize the cost and increase the soft-switching range for a wide variation of the battery voltage and power.…”

A new detailed loss model and design approach for LLC resonant converter with phase shift control to overall optimization of converter loss at whole battery charging process

“…There are some references that investigate how to design an HF‐transformer to reduce losses 25–28 . In Liu et al 25 a so‐called quarter‐turn planar transformer structure was proposed and implemented in an LLC resonant converter for server power supply applications.…”

“…With proposed design which is examined by FEM analysis, transformer secondary‐side winding loss and core loss have been reduced by reducing the minimum numbers of turns on the primary and secondary sides also core size. In Ahmed and Wang 26 a Litz‐wired high‐frequency gapped transformer has been designed for LLC converter. The main contribution of this work is the design procedure is not iterative, and its design targets are maximizing the efficiency of transformer and its power density but no design procedure has been introduced for other components.…”

“…There are some references that investigate how to design an HF-transformer to reduce losses. [25][26][27][28] In Liu et al 25 a so-called quarter-turn planar transformer structure was proposed and implemented in an LLC resonant converter for server power supply applications. With proposed design which is examined by FEM analysis, transformer secondaryside winding loss and core loss have been reduced by reducing the minimum numbers of turns on the primary and secondary sides also core size.…”