Extremum Co-Energy Principle for Analyzing AC Current Distribution in Parallel-Connected Wires of High-Frequency Power Inductors

Abstract

Inductor winding is often comprised of parallel-connected wires to suppress copper loss. However, in high-frequency inductors, the proximity effect can cause concentrated AC current distribution, hindering the suppression of the copper loss. Therefore, optimization of the physical inductor structure requires predicting the AC current distribution caused by the proximity effect. Certainly, simulators have been commonly employed for predicting the AC current distribution. However, simple analytical methods are also required for efficient design or invention of inductor structures that have more uniform AC current distribution among the parallel-connected wires. The paper proposes a novel simple analysis method for AC current distribution in parallel-connected wires of high-frequency inductors. The proposed method is based on a novel insight that AC current is distributed to give an extremum of the magnetic co-energy contributed by the AC flux under the given total AC current. Analysis of basic inductor structures revealed that the proposed method can derive the AC current distribution by straightforward calculation. In addition, experiments supported the analysis results. Consequently, the proposed method is suggested to be promising for developing inductor structures with less copper loss.