IEEE PEDS 2017, Honolulu, USA 12 – 15 December 2017 Highly Efficient Power Inductors for High-Frequency Wide-Bandgap Power Converters Arne Hendrik Wienhausen, Alexander Sewergin, Stefan P. Engel, Rik W. De Doncker Institute for Power Electronics and Electrical Drives RWTH Aachen University, Aachen, Germany Email: post@isea.rwth-aachen.de Abstract—Highly efficient power inductors for high switching frequencies are required to take full advantage of modern wide- bandgap (WBG) semiconductors in terms of power density and efficiency. However, appropriate inductors are usually not available from stock. In this paper a new design approach for high-frequency power inductors is presented using planar cores, 3D printed spiral bobbins and copper foil in vertical orientation. Even though the presented approach is based on low- cost copper foil instead of expensive litz wire, it does not suffer the typical drawbacks at high-frequency operation. It reduces the required amount of copper significantly and shows excellent copper utilization. The new design approach is presented in detail, key design parameters are discussed and simulation as well as measurement results are shown and analyzed. I. I NTRODUCTION Modern WBG power transistors based on silicon carbide (SiC) and gallium nitride (GaN) gain more and more popular- ity in power electronics. Their superior switching characteris- tics and low conduction losses result in high power densities of power electronic systems that cannot be covered by classic sili- con (Si) power semiconductors. To fully utilize the outstanding characteristics of SiC and GaN power transistors suitable inductive components for high-frequency operation are needed since classic approaches limit the switching frequency due to high losses [1], [2], [3]. The design approach for highly efficient power inductors presented in this paper is based on low-cost copper foil instead of expensive litz wire. Nevertheless, it exhibits excellent high- frequency characteristics. A vertical copper foil orientation is used for an improved copper utilization. The copper thickness of the used copper foil is a crucial design parameter and needs to be chosen according to the applied switching frequency. Fig. 1 shows rendered images of the proposed inductor design. While Fig. 1(a) shows the completely assembled inductor, the internal structure of the proposed inductor design is depicted in Fig. 1(b). A 3D printed spiral bobbin serves as spatial separator for each turn of the copper foil winding, ensuring a low parasitic capacitance and providing insulation between each turn of the winding. A low parasitic capacitance is mandatory for high-frequency operation as it directly affects the resonant frequency of the inductor which should be much higher than the switching frequency. Uninsulated copper foil can be used if spacing is sufficient. The used copper foil is very thin and can easily be cut and be placed inside the spiral. (a) Completely assembled inductor (b) Internal inductor structure Fig. 1. Rendered images of the proposed inductor design Iteration steps during the prototyping and optimization pro- cess can rapidly be applied and fabrication tolerances can be kept very small using high-precision 3D printers. The needed plastic parts for the design can be printed within a few hours on a modern 3D printer. Different laboratory prototypes have been built and characterized in the lab. The key aspects of the new approach and measurement 978-1-5090-2364-6/17/$31.00 c 2017 IEEE 442