This study presents design guidelines for planar induction systems whose winding is considerably farther from its load than in usual arrangements. Optimum efficiency design is paramount for larger distances due to the magnetic field dispersion. To this end, a parameterised finite element model is used to ascertain the system's parameters in this new configuration. This model is used to test variations in frequency, inductor-load distance and inductor diameter. From simulation results, efficiency, output power, power loss volumetric density and near field measurement predictions are obtained. Graphical representation of these results is used to determine the viability of each possible design, choosing one to develop a prototype. Moreover, a study was carried out with Pareto techniques to determine the effect of ferrite coverage and thickness, as well as its distance to the aluminium shielding on efficiency and near field predictions in order to develop a second prototype. The validity of the model is confirmed by experimental tests in small and operating signal regimes.
Multi-stranded litz wires are commonly used in magnetic devices for power electronics applications at medium-high frequency range, from several kHz up to hundreds of kHz. For these applications, litz-wire structure favours the uniformity of driven current in the cross-sectional area of conductors, alleviating ac losses (skin and proximity effects) and improving the global efficiency of the application. These features are achieved by means of a special cable arrangement consisting of many isolated fine copper strands twisted together according to the manufacturing process. Often, the manufacturing process involves several twisting steps where bundles of moderate number of strands are successively twisted resulting in intricate cable structures. We present a mathematical description of the trajectories of copper strands with the purpose of obtaining the cable losses by means of Finite Element Analysis (FEA) simulation tools. Moreover, a nomenclature for this multilevel structures is also proposed. Parameters as the number of twisting steps, number of strands, strand diameter or pitch length, are included in this representation, allowing to compare the performance of different manufacturing solutions.
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