235 – Reactor Core Stray Loss Analysis

Application Note / Model Data

Overview

When designing a high-frequency reactor which is a key component in a converter, inductance and loss, which are parameters required for voltage conversion, are important factors. Copper loss is dependent on coil resistance and current, and iron loss is classified as eddy current loss or hysteresis loss. Other losses are called stray loss.
Stray loss is a loss caused by eddy currents in the core portions near coil ends and conductive parts near the coils which in turn are caused by mainly leakage flux from the coil ends.
Although the stray loss is not always a large part of the entire loss, heat generation may occur locally sometimes causing operational problems. Although it is difficult to capture stray loss by actual measurement and calculation by hand, it is possible to visualize core surface eddy currents which result in stray loss or leakage flux from the coils to the core by JMAG transient analysis.
In this example, reactor core stray loss is described.

Leakage Flux and Eddy Currents

Fig. 1 shows the flux lines near a gap and a core eddy current distribution.
From the enlarged view of the flux lines, it can be confirmed that fringing occurs in which the magnetic flux bulges due to the magnetic flux cross sectional area becoming larger than the core cross sectional area at the core gap. In addition, in-plane eddy currents are generated on the surface right under the right coil near the gap, and it can be seen that the magnetic flux is generated perpendicularly to the laminating direction.

Reactor Loss

Fig. 2 shows the loss in the reactor.
By performing magnetic field analysis and iron loss computations together, analysis results can be obtained by separating out hysteresis loss, eddy current loss, stray loss, and loss.

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