Pareto-Optimal Design of Litz-Wire Gapped-Core High-Frequency Transformer for LLC Converters

The optimization of Litz-wire gapped-core high-frequency transformer (LGHT) for LLC converters is a challenging task owing to application requirements and complex relationship between multiple design-objectives and constraints. This necessitates the use of multiobjective optimization-techniques to obtain tradeoff design-solutions; however, these are cumbersome methods that require many iterations and resources. Therefore, this article proposes an improved and efficient Pareto-optimization method for LGHT-design. It combines multiobjective whale-optimization algorithm and analytical core-geometry factor model based core and winding selection method while keeping in consideration the LLC converter requirements. The proposed method utilizes benefits of both method-types; it obtains the best LGHT-design in shortest-time and minimum-iterations with optimized volume and losses, integrated magnetizing-inductance, and satisfied thermal-limit. The method is made resource-efficient by carefully selecting independent and necessary LGHT design-parameters as optimization variables keeping in view interdependency among the parameters and LLC converter performance; these include peak-flux-density, LGHT design-frequency, core-window utilization-factor, core-material, and core-shape. For best design-selection, supplementary decision functions (total-loss and loss-and -volume-product) are used together with the objective functions (core-loss, winding-loss, and total-volume) to enhance the optimal Pareto-solutions' diversity and to assist designers in decision-making. The method is proven via comparison with existing benchmark-methods and validated through performance demonstration of LGHT-prototype in 400 Vdc-to-12 Vdc LLC converter.