Medium-Frequency Foil Winding Layout to Suppress Circulating Currents
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Solution Overview
Problem
High-frequency transformers face significant challenges in minimizing circulating currents between parallel conductors, leading to increased losses and reduced transformer performance, especially in applications like EV fast charging, PV solar, and battery energy storage systems, due to the inefficiencies of using off-the-shelf litz wire or aluminum foil windings.
Innovation Solution
A method involving a coil configuration where multiple conductive foil strips are stacked with insulating layers and coiled without transpositions, with impedance elements connected between terminals, to reduce circulating currents by creating coil gaps that align with core gaps, thereby minimizing magnetic flux leakage and enhancing magnetic flux confinement within the core material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If parallel conductors (litz wire or foil strips) are used to handle high currents at high frequencies, then current carrying capacity is improved, but circulating currents are induced between parallel conductors which increase losses
Solution Approach 1:
The winding is segmented into multiple discrete turns rather than using continuous parallel conductors. Each turn is electrically isolated from adjacent turns by insulating layers, preventing circulating currents while maintaining high current carrying capacity through proper parallel connection of multiple turns
Solution Approach 2:
Insulating layers are introduced as intermediary elements between adjacent turns of the winding. These insulating layers electrically isolate the turns from each other, blocking the path for circulating currents while allowing the magnetic flux to pass through, thereby reducing losses without compromising current carrying capacity
2Ease of manufacture
If aluminum foil windings are used instead of litz wire, then manufacturing cost and complexity are reduced, but skin- and proximity effects increase winding losses at high frequencies
Solution Approach 1:
The foil winding is segmented into multiple discrete turns with insulating layers between them, preventing the formation of large circulating current loops. This segmentation reduces the impact of skin and proximity effects by limiting the effective area for eddy current formation, thereby reducing losses while maintaining manufacturing simplicity
Solution Approach 2:
The winding geometry is configured with specific dimensional relationships (foil width, height, and length) optimized for high-frequency operation. The insulating layers are positioned at critical locations to disrupt eddy current paths without adding significant manufacturing complexity, achieving low losses through geometric optimization rather than material substitution
3Power
If multiple parallel litz wires are used to increase current capacity above 100-200A, then current carrying capacity is improved, but circulating currents between paralleled wires significantly increase losses
Solution Approach 1:
Multiple litz wires are merged into a single continuous winding structure where the ends of individual wires are connected to form discrete turns. This merging eliminates the parallel connection configuration that causes circulating currents, while maintaining the high current carrying capacity through the combined cross-section of all wires in the winding
Solution Approach 2:
Insulating layers are positioned between adjacent turns formed by the merged litz wires, serving as intermediaries that electrically isolate the turns. This prevents circulating currents from forming between the parallel sections of the merged wires, reducing losses while preserving the high current capacity achieved through merging
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively suppresses circulating currents, reducing transformer losses and maintaining high power ratings while minimizing resource requirements and manufacturing complexity.
Implementation Method 1
wherein an insulating layer is provided between any two adjacent foil strips
Implementation Method 2
coiling up the foil strip stack from the first end... creating coil gaps that align with core gaps, thereby minimizing magnetic flux leakage and enhancing magnetic flux confinement within the core material
Implementation Method 3
enhancing magnetic flux confinement within the core material
Data Source
Figure 1a~1c
Figure 2a~2b
Figure 3
AI summary
A method for producing a coil for a transformer, in particular for a medium frequency transformer for a resonant DC/DC converter or a dual active bridge DC/DC converter, is disclosed which comprises the steps of: providing a plurality of M>1 conductive foil strips, each having a first ending and a second ending; stacking the plurality of conductive foil strips to obtain a foil strip stack having a first ending and a second ending, wherein an insulating layer is provided between any two adjacent foil strips; electrically connecting the first endings of all conductive foil strips to a first terminal; for each of the conductive foil strips providing a connector at the second ending of the foil strip; and coiling up the foil strip stack from the first end.