Regarding the ever-increasing switching frequency of power converters, there is a lack of tools to perform a quick and effective optimization of the high-frequency transformers embedded in isolated power converters. Indeed, at high operating frequency, the geometry of the core and windings deeply impacts the overall transformer performance. Specifically, assessing accurately the current distribution in parallel-connected windings is a challenging and key issue. Winding parallelization, frequently implemented in low-voltage and high-current applications so as to decrease Joule losses, may be an ineffective solution because of skin and proximity effects. They create an unbalanced current distribution in the parallel-connected windings, which greatly impacts the ac resistance and leakage inductance of the transformer. This article proposes an innovative frequency analytical model permitting to simply and accurately compute the current distribution in the transformer windings, the ac resistance, and the leakage inductance. The proposed approach is comprehensively presented, validated using both measurements and two-dimensional finite element analysis and analyzed giving guidelines to engineers designing high-frequency transformers.

This article presents an optimization process applied to the sizing of high power silicon carbide inverters. The case study is the design of an aeronautical converter. A gradient-based optimization method is chosen for its ability to explore a wide solution space with a large amount of constraints, what is the case during the pre-design phase. Many topologies are selected and associated models are developed. Among all these models, active and passive component design, and spectral analysis of voltages and currents, are presented. Optimization results, with the goal of minimizing the global mass of the converter, are provided. The different topologies are compared to find the best one for the selected case study. The relevance of the optimization result is evaluated with the study of the optimality of the solution. Finally, experimental results are compared to the optimization ones, which validates the good accuracy of analytical models.

In this paper, a design by optimization process is used to size a 10-kW three-phase pulse width modulation (PWM) inverter for aeronautic application. The objective function is the converter weight, which has to be minimized. Sizing constraints are the efficiency, alternating current (AC) and direct current (DC) harmonics, and thermal constraints on all devices. A deterministic algorithm is chosen since it allows obtaining quick results and dealing with a large number of variables. All equations are analytical, in order to comply with this gradient-based optimization strategy, which imposes the derivability of the models. Several optimization results using different AC inductor solutions (iron powder and ferrite) are compared. The optimized converters were built and tested experimentally to verify their performances. Semiconductor and inductor losses were measured accurately using calorimetric test benches. The optimality of the solutions was carefully verified by changing parameters.

This paper introduces an optimization method for the design of the filtering inductor of a 3-phase inverter. The inductor model takes into account saturation, copper and iron losses. The optimization method is described, based on a deterministic strategy. Finally, the optimal design of the inductor is given, focusing on the weight minimization and considering a volumetric loss density limitation.

Planar transformer technology provides a serious alternative to wound transformers for improving the efficiency and power density of isolated converters. The flat shape of its coil turns and the interleaving of its windings allow an excellent control of the skin and proximity effects. The major drawback of planar technology is the strong capacitive couplings between the windings. These couplings are detrimental to the increased switching frequency induced by the new wide-bandgap transistors, and to electromagnetic compatibility. Using fundamental equations, material properties, and geometric dimensions, the present work proposes a semianalytical electromagnetic model of planar transformers able to account for capacitive couplings. Compared with current models, it allows rapid estimation of all its sizing parameters: losses, leakage inductance, bandwidth, and interwinding impedance. This novel model was experimentally validated over a wide frequency range (1 kHz up to 100 MHz) using transformers with both series and parallel connected windings.