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This paper presents a novel analytical framework for the design and understanding of class EF inverters under both optimal and non-optimal load conditions. Unlike conventional approaches that rely heavily on numerical simulations, the proposed method provides a fast, visual, and intuitive tool for analyzing inverter operation. Its effectiveness is demonstrated experimentally on a 15 MHz class EF inverter across three distinct load conditions, showing good agreement with theoretical predictions. To highlight the robustness and broad applicability of the approach, a class Φ2 inverter—a lumped-element analog of the class EF inverter—is also implemented and successfully analyzed. By combining theoretical insight, experimental validation, and generalization to alternative topologies, the proposed framework offers an efficient, accessible, and versatile tool for high-frequency resonant inverter design.

The magnetizing inductance of the medium frequency transformer (MFT) impacts the performance of the isolated dc-dc power converters. The ferrite material is considered for high power transformers but it requires an assembly of type “I” cores resulting in a multi air gap structure of the magnetic core. The authors claim that the multiple air gaps are randomly distributed and that the average air gap length is unpredictable at the industrial design stage. As a consequence, the required effective magnetic permeability and the magnetizing inductance are difficult to achieve within reasonable error margins. This article presents the measurements of the equivalent B(H) and the equivalent magnetic permeability of two three-phase MFT prototypes. The measured equivalent B(H) is used in an FEM simulation and compared against a no load test of a 100 kW isolated dc-dc converter showing a good fit within a 10% error. Further analysis leads to the demonstration that the equivalent magnetic permeability and the average air gap length are nonlinear functions of the number of air gaps. The proposed exponential scaling function enables rapid estimation of the magnetizing inductance based on the ferrite material datasheet only.

Purpose To understand the behavior of the magnetization processes in ferromagnetic materials in function of temperature, a temperature-dependent hysteresis model is necessary. This study aims to investigate how temperature can be accounted for in the energy-based hysteresis model, via an appropriate parameter identification and interpolation procedure. Design/methodology/approach The hysteresis model used for simulating the material response is energy-consistent and relies on thermodynamic principles. The material parameters have been identified by unidirectional alternating measurements, and the model has been tested for both simple and complex excitation waveforms. Measurements and simulations have been performed on a soft ferrite toroidal sample characterized in a wide temperature range. Findings The analysis shows that the model is able to represent accurately arbitrary excitation waveforms in function of temperature. The identification method used to determine the model parameters has proven its robustness: starting from simple excitation waveforms, the complex ones can be simulated precisely. Research limitations/implications As parameters vary depending on temperature, a new parameter variation law in function of temperature has been proposed. Practical implications A complete static hysteresis model able to take the temperature into account is now available. The identification is quite simple and requires very few measurements at different temperatures. Originality/value The results suggest that it is possible to predict magnetization curves within the measured range, starting from a reduced set of measured data.

In the design of such power electronics applications as power converters, lack of precise characterization and diagnosis of losses from components has unacceptable effects on efficiency, reliability, and power consumption. Because passive components, especially magnetic components, are crucially important in power converters, accurate characterization and modeling of magnetic materials is mandatory, to enable realistic prediction of their behavior under variable operating conditions. Temperature is one such condition that induces major changes in a component’s behavior by modifying the material’s magnetic properties. In the work discussed in this paper we investigated the magnetic and thermal behavior of nanocrystalline and powder materials in a DC–DC converter application. Core loss measurements under variable conditions were performed on toroid-shaped samples. Measured results were analyzed for different frequencies, flux densities, and temperatures.

Purpose - The purpose of this paper is to analyze the main assumption of a dynamic flux tube model and to define its rules of use.Design methodology approach - The studied dynamic model lumps together all dynamic effects in the circuit by considering a single dynamic parameter. A physical meaning of this parameter as well as rules of use of the model are elaborated from analyses performed on several samples. A systematic comparison between experimental and calculated results allows to argue the conclusions.Findings - The model gives accurate results when a weak heterogeneity of magnetic data exists, nevertheless, the saturation phenomenon enlarges the validity domain. By considering the losses separation assumption, the model allows to obtain separately an estimation of losses due to classical eddy currents and due to the wall motion effects.Research limitations implications - The estimation of the model's parameter value is still empiric, a work is in progress on this subject.Practical implications - The model's implementation in a flux tubes network allows to simulate the dynamic behaviour of industrial actuators having massive cores.Originality value - A physical interpretation of the parameter associated to the dynamic flux tube model is given. Rules of use of the model are also defined.