Power Loss and Temperature Distribution in Coil of PFC Inductor with Air Gap for Multimode Operation

TL;DR

This paper analyzes how different conduction modes in a PFC inductor with an air gap affect power loss and temperature distribution, highlighting the increased losses in DCM mode and proposing coil construction optimizations.

Contribution

It investigates the impact of conduction modes on power loss mechanisms and temperature distribution in PFC inductors with air gaps, and proposes coil design improvements.

Findings

DCM mode increases power dissipation due to higher fringing flux.

Eddy-current losses are significant and can be reduced by coil optimization.

Air gap influences magnetic flux and power loss mechanisms.

Abstract

Power converters inherently display non-linear load characteristics, resulting in a high level of mains harmonics, and hence the necessity of implementing Power Factor Correction (PFC). Active PFC circuitry typically comprises an inductor and a power switch to control and alter the input current so that it matches, in shape and phase, the input voltage. This modelling of the waveforms can be performed by means of distinct conduction modes of the PFC inductor. The digital controller implemented in the constructed and investigated boost-type PFC converter can be programmed to operate in discontinuous conduction mode (DCM), continuous conduction mode (CCM), or a combination of the two. The individual modes of operation, via distinct PFC inductor current waveforms, impact the overall efficiency of power conversion and, by extension, temperature distribution in the magnetic component. This paper investigates how the examined conduction modes bear on distinct power-loss mechanisms present in the PFC inductor, including high-frequency eddy-current-generating phenomena, and the fringing effect in particular. As demonstrated herein, the DCM operation, for the set output power level, exhibits exacerbated power dissipation in the winding of the inductor due to the somewhat increased RSM value of the current and the intensified fringing magnetic flux at an air gap. The latter assertion will undergo further, more quantitatively focused research. Finally, the construction of the coil was optimised to reduce power loss by diminishing eddy-current mechanisms.