TOYOTA Research Institute of North America
Planar type inductors provide an opportunity to meet the size requirement, but improving efficiency, especially at elevated frequency, still needs great research efforts. Since AC winding loss (caused by proximity effect and skin effect) takes a significant portion in high frequency inductor loss, Litz wire structure windings are being investigated. In 2005, PCB type Litz wire windings for planar inductors was proposed, in which the analysis was focused on single board structure. However, inductors in automotive applications require multiple winding layers, but so far there is no published work addressing planar Litz wire stacking and its effect to Litz wire performance. This paper will discuss the multiple winding layers stacking effect, i.e. proximity effect between layers, and how it affects the optimization of the Litz wire strand width and pitch. The analysis is based on FEM with periodic boundary condition in order to model stacking configuration with available computational resources.