Modeling and Minimization of the Parasitic Capacitances of Single-Layer Toroidal Inductors

Abstract

High-frequency power converters need electromagnetic interferences filters using common and differential mode chokes with low parasitic capacitance to comply with the electromagnetic compatibility standards. This paper proposes a modelling method of this capacitance and ways to minimize it. The studied components are ring core inductors with magnetic materials considered as perfect conductors or with high permittivity, such as nano-crystalline material and most Mn-Zn ferrite materials. In comparison to other work in the literature, the proposed approach takes into account the curvature of the turn in addition to the coating of the core and the insulation layer of the wire. The hypotheses, used in this work to simplify the real geometry, are compatible with two dimensional approaches to compute the parasitic inter-turns and turn-core capacitances. These capacitances are evaluated thanks to the 2D finite element method. The obtained model allows accurate evaluation of the effect of turn-core space on the parasitic capacitance, and enables to reduce its value with a limited impact on the volume of the magnetic component.

Winding Optimization for Reducing Parasitic Capacitances of Common-Mode Chokes

“…This result is intuitive because electric coupling is generally expected to decrease with distance between coupled conductors. The apparent contradiction with the conclusions reported in Salomez et al's [14] work, serves to emphasize the key impact that the permittivity of the core has on the capacitive response that inductive components exhibit at high frequencies.…”

“…In this case, the coupling through the core would be determined solely by C tc . This approximation is assumed by works that treat the core as a conductive material when calculating parasitic capacitances of inductors and CMCs [5], [9], [11], [12], [14]. For single-layer windings on high-permittivity materials, the coupling C tc could also be a dominant effect over C tt in determining the total electrical coupling between windings [13], [14].…”

“…Recently, in Li and Wang's [13] work, the impact of the number of turns on the EPC of a single-layer inductor with a high-permittivity ring-core is analyzed, and an interesting method is proposed to reduce the EPC of the inductor by using stacked cores. In Salomez et al's [14] work, a model is proposed to estimate the EPC of single-layer inductors with high-permittivity ring cores. The impact of winding technique is analyzed, and it is concluded that since in this case the EPC is dominated by the electrical coupling of turns to the core, the EPC can be reduced by using tight winding or by increasing the distance between turns and the core.…”

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

“…As introduced in [19], [20], [24], [25], the parasitic capacitance of inductors is contributed by the energy stored inside the winding Eintra, between the winding and core Ewc, and between the two neighbor windings Eww, and therefore could be written as eq. ( 1).…”

“…Both physics-based [19], [20] and behavior-based [21], [22] modeling methods can be used to identify the parasitic capacitance and capacitive couplings in inductors. For reducing the parasitic capacitance in the inductors, besides using advanced dielectric material with lower permittivity, two main solutions have been researched: 1)using spacers to decrease the electric field between the two plates [23], [24], at the cost of the power density. 2)using advanced winding structures to decrease the electric field strength between the two adjacent plates [25], sacrificing manufacturing simplicity.…”