Rethinking Basic Assumptions for Modeling Parasitic Capacitance in Inductors

Abstract

This paper rethinks the basic assumptions often used in analytically modeling parasitic capacitance in inductors. These assumptions are classified in two commonly-used physicsbased analysis methods: the lumped capacitor network method and the energy conservation method. The lumped-capacitor network method is not the proper solution for calculating the equivalent parasitic capacitance in inductors at the first resonant frequency, but rather represents the equivalent parasitic capacitance above the last resonant frequency. The energy-conservation based method is shown to be more accurate and a reasonable solution to model the equivalent parasitic capacitance at the first resonant frequency. Multiple case studies of inductors are used for verifying the theory.

Optimal Design of Single-Layer and Multi-Layer Air-Core Inductors Considering Uncertainty Factors

“…Moreover, the lumped-capacitance network method considers the equivalent circuit of the inductor as a purely capacitive network composed of C tt , disregarding the elementary inductance (L tt ) of each turn due to its high impedance compared to C tt . On the other hand, the energy-conservation method takes into account the effect of the elementary inductance and assumes a linear voltage distribution along the coils [11]. Consequently, the total stray capacitance C tot can be calculated by equating the energy of the electric field stored in C tot to the total energy stored between all turns.…”

“…The comparison in [11] shows that the energy-conservation method is more accurate than the lumped-capacitance network method when a toroid inductor with a ferrite core is modeled. However, this conclusion may only apply to inductors with ferrite cores.…”

“…Conversely, the energy-conservation method is preferable for multi-layer inductors and transformers [10]. The accuracies of these two approaches for a single-layer ferrite-core inductor were compared in [11], demonstrating that the energyconservation method is more accurate. However, it is important to note that this conclusion may only be applicable to inductors with magnetic cores, and further validation is necessary for air-core inductors.…”

Parasitic Capacitive Couplings in Medium Voltage Power Electronic Systems: An Overview

“…The two types of capacitive couplings will result in significantly different behaviours in the frequency-domain as each of the two types of capacitive couplings governs a unique LC resonant circuit; a) the parallel capacitive coupling corresponds to a parallel resonance, which acts inductive and turns capacitive after the resonance frequency. The parallel capacitive coupling model is well known from the literature of inductor modelling as the equivalent circuit model up to and around the first resonance frequency [41], [42], and b) the series capacitive coupling corresponds to a series resonance, which acts capacitive and turns inductive after the resonance frequency. The series capacitive coupling model is Hz Fig.…”

“…17(b) and (d), where the two common-mode capacitances can also be analytically calculated by using the improved modelling methods [5]. The physics-based modelling methods can only quantify the equivalent capacitor before the first resonant/antiresonant frequency [42]. In order to quantify the characteristics (or capacitive couplings) after the first resonant frequency/antiresonant frequency, the behavioural-based modelling method can be applied [46], which however, requires manufacturing prototypes first and then measuring the time-domain or frequency-domain response.…”