Supervisor:
Stig Munk-Nielsen

Co-Supervisor:
Hongbo Zhao og Szymon Michal Beczkowski

Assessment Committee:
Pooya Davari(Chair)
Associate Professor Arnaud Videt, University of Lille
Professor Kaiji Wada, Tokyo Metropolitan University

Moderator:
Asger Bjørn Jørgensen

Abstract:

Magnetic components play a key role in power electronic devices, such as the storage or transformation of magnetic field energy. Compared to the ideal models, there are leakage inductance, parasitic capacitance, winding losses, core losses, and magnetic saturation in the practical magnetic components. With wide-bandgap (WBG) semiconductors being matured and widely used, the parasitic capacitances in magnetic components result in the electromagnetic interference (EMI) issues and additional losses in power electronic devices due to the rapidly increased switching frequency. To understand and mitigate its effects, this Ph.D. thesis presents a systematic research of the parasitic capacitance in magnetic components, including its definitions, quantifications, modelling, and trade-off design between AC losses and parasitic capacitances.

Different definitions of parasitic capacitance in magnetic components are categorized based on different criteria, such as elemental and equivalent parasitic capacitance based on physical mechanism, or parallel and series parasitic capacitance based on frequency characteristics. High frequency behaviours and negative values of parasitic capacitances are also discussed for a comprehensive understanding.

Guarding measurement is applied for the accurate and efficient quantifications of parasitic capacitance in magnetic components. Compared to the conventional two-terminal measurement, there are no pre-analyses, redundant tests, data post-processing, and error propagation in guarding measurement. Through the tests of circuits and transformer prototypes, the feasibility of guarding measurement is verified.

The widely used single perfect electric conductor (PEC) assumption for core in state-of-the-art analytical models of parasitic capacitance in magnetic components is extended to the multi-PEC assumption for the magnetic components with the cores insulated by airgaps, based on which the analytical models are revised to include the effects of airgaps. Both multi-PEC assumption and revised analytical model are verified by finite element method (FEM) simulations and inductor prototypes.

The analytical models of AC losses and parasitic capacitance in the trade-off design of magnetic components are updated for generalization. The FEM simulations and inductor prototypes with different interleaved winding structures and gap formats verify the trade-off design.