Improved AC-resistance of multiple foil windings by varying foil thickness of successive layers

Purpose: This paper aims to introduce a technique for optimizing conductor dimensions for construction of helical planar inductor windings with reduced ac- and dc-resistance. The loss reduction is evaluated on simulation and experimental level. Design/methodology/approach: Helical planar windings are currently manufactured by forming each conductive and insulating layer individually. The conductive layers are only interconnected later to form the winding. This process allows greater freedom in selecting the optimum conductor dimensions on a per-layer basis. Methods are proposed for sinusoidal and non-sinusoidal current excitation waveforms and shaped windings are introduced for further loss reduction where conductors are in close proximity to air gaps in magnetic cores. Findings: Traditional optimization of the conductor thickness used for foil wound inductors renders one single value used for each of the respective layers in the winding. This is a result of the manufacturing process involved in making traditional "barrel" windings. This optimization technique has simply been applied in planar inductors for the lack of alternatives up to now. It will be shown that large loss reduction may be achieved by manipulating the conductor dimensions of each layer individually. Originality/value: A new approach to optimization problems verified experimentally offers more efficient inductors.