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Enabling foil windings of medium-frequency transformers for high currents

机译：使中频变压器的箔绕组实现大电流

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In foil windings of medium-frequency transformers rated for several hundred Ampères and operating at ten or several tens of kHz, parallel connection of foils is necessary to provide sufficient conductor cross-section. In this case, careful winding design is required to keep circulating currents among the foils under control. Such currents were investigated by means of an analytical model, a 2-d finite-element model, and measurements on a reduced-scale transformer for the case of two parallel connected foils. Simulations and measurements yield a consistent picture and show the potential of high extra losses in foil windings with unmitigated circulating currents. In particular, spiral windings of many turns may incur a circulating current that exceeds the useful net current by far if the inductance of the foil connections is small. Practically, it can be expected that the inductance of the foil connections leads to a noticeable reduction of the circulating current. This reduction, however, is not sufficient to bring the AC losses down to acceptable levels, such that it is recommended to transpose the foils between series-connected winding portions. Transposition largely cancels out the axial magnetic flux in the radial gaps between the parallel connected foils. The effectiveness of transposition in balancing the foil currents at frequencies up to 40 kHz is shown both theoretically and experimentally for aluminum foils of 0.2 mm thickness. With proper transposition, the extra AC losses due to circulating currents between foils can be reduced to practically negligible levels.
机译：在额定频率为数百安培且工作频率为十或几十kHz的中频变压器的箔绕组中，必须并联箔的连接以提供足够的导体横截面。在这种情况下，需要仔细的绕组设计，以使箔片之间的循环电流保持受控状态。通过分析模型，二维有限元模型以及在两个平行连接箔的情况下在缩小比例变压器上进行的测量研究了此类电流。仿真和测量得出一致的图像，并显示了在箔绕组中具有无缓和循环电流的高额外损耗的可能性。特别地，如果箔片连接的电感很小，则许多匝的螺旋绕组可能会产生循环电流，该循环电流远远超过有用的净电流。实际上，可以预期的是，箔片连接的电感导致循环电流的显着降低。但是，这种减小不足以使交流损耗降低到可接受的水平，因此建议将箔片放在串联连接的绕组部分之间。换位在很大程度上抵消了平行连接的箔片之间的径向间隙中的轴向磁通量。理论上和实验上，对于厚度为0.2 mm的铝箔，都证明了换位可有效平衡频率高达40 kHz的箔电流。通过适当的换位，可以将由于箔片之间的循环电流引起的额外AC损耗降低到几乎可以忽略的水平。

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