Characterization of Losses and Inductance in Actively Biased Variable Inductors

Abstract

Previous studies have primarily focused on the magnetic coupling behavior between the main and auxiliary winding under symmetrical bipolar operation conditions. However, practical power electronic systems often operate under combined ac-excitation and superimposed dc-bias currents applied to the main winding. To address these realistic operating conditions, this paper extends established coupling analyses by incorporating dcbias currents in the main winding and evaluating their interaction with the auxiliary control circuit. Furthermore, to generalize the assessment of different auxiliary circuit implementations, a frequency-dependent impedance-based framework is introduced to classify induced feedback effects. The analysis is performed for three dedicated pre-magnetization methods-orthogonal, mixed, and parallel biasing-while simultaneously considering dc-bias conditions in the main current path. The discussion comprises a spectral analysis of the induced auxiliary voltages and a systematic investigation on how high-impedance (HI) versus low-impedance (LI) terminations of the auxiliary circuit influence the effective transient primary-side inductance and the measurable hysteresis losses of the magnetic core. By linking auxiliary circuit impedance, induced magnetic feedback, and primary-side loss behavior, this work establishes a unified framework for evaluating controllable magnetic devices under realistic power electronic operating conditions.