Investigating UU Powder Core Inductor Winding Configurations Influence on DC Bias Inductance

Powder core materials are popularly used in design of line-frequency filter inductors. Designing with toroidal shape cores is well understood and its performance well predictable from datasheet values. Recently the use of “E” and “U” core shapes is gaining popularity for SiC applications. These new core shapes enable the use of flat-wire technology with automated assembly process improving efficiency and cost. But for these new core shapes, the Inductance Factor (AL) value provided by the core manufacturer is accurate only for the reported test condition. Other winding arrangements can result in considerably different AL values. This discrepancy is high for low permeability cores. This paper aims to highlight this discrepancy, provide technical insights on expected performance and design trade-offs. Finite element analysis (FEA) is used to support this, and the results match experimental measurements for the two mock inductors fabricated. When designing with low Perm U -cores the leakage fields effect the resultant inductance at nominal and overload conditions. Leakage field distribution between two common winding (one-leg and two-leg) configurations is also provided. It is shown that additional inductance in one-leg winding is relatively independent of permeability of core.