A Comparative Study on Parasitic Capacitance in Inductors With Series or Parallel Windings

Abstract

In high-power medium-voltage applications, inductors usually have multiple windings on a single core, due to the high inductance value and high current stress. The multiple coils are electronically connected in either series or parallel, with considerations of windings loss and cost. However, the differences in parasitic capacitance of inductors using parallel and series connections are not discussed. Therefore, this paper reveals that compared with using parallel connections, using series connections for windings can significantly reduce the parasitic capacitance in multi-windings inductors without sacrificing the power density and adding manufacturing complexities. Physics-based models of parasitic capacitance in inductors with round-cable and copper-foil are developed for theoretical analysis. According to the theoretical analysis, the equivalent capacitance contributed by the stored electric field energy between two layers can be halved at least. The theoretical analysis is also verified by FEM simulations. Six prototyped inductors are also experimentally compared to validate the theory.

Design of Interleaved Winding for Multilayer Planar Inductor and Its Application in Reducing Current Ringing of LLC Resonant Converter

“…As for the AC impedance, it is primarily influenced by the skin effect and proximity effect. References [19,20] have calculated the AC impedance caused by the skin and proximity effects on copper foil, with the calculation method shown in Equation (13).…”

“…Furthermore, Ref. [13] analyzed the parasitic capacitance in series and parallel windings, and used the method of combining the series and parallel windings to reduce the parasitic capacitance of the inductor. Methods for reducing the parasitic parameters of planar magnetic components were summarized in [14], and it was verified that the parasitic capacitance can be effectively reduced by optimizing the winding design.…”

Hybrid Foil-Litz Windings for Highly Efficient and Compact Medium-Frequency Transformers

“…The price for these advantages is the use of more complex and therefore more expensive conductors and core materials to keep the frequencyinduced losses in an acceptable range. In this respect, the conductor choice is constrained among foil or litz wire, e.g., [11]- [14]: litz wire is disfavored by the reduced filling factor, the limited availability and the elevated cost, whereas foil conductor exhibits additional ohmic losses due to the so-called "current crowding" or edge effect, caused by the deformation of the magnetic field due to the insulation clearance to the core [15]. Foil windings exhibit a uniform voltage distribution in the case of steepfronted PWM voltages [16], which is advantageous for MV SST applications; however, the electric field hotspots at the foil winding corners limit the insulation rating [17].…”