Planar Transformer X-Core Magnetic Circuit Air Gap Segmentation
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Solution Overview
Problem
High power resonant DC-DC converters in automotive applications face challenges with planar magnetic circuits due to the difficulty in achieving a low primary choke and high transformation ratio, leading to issues with air gap integration and increased leakage flux, which results in high losses and electromagnetic disturbances.
Innovation Solution
A planar transformer design with a magnetic circuit featuring four lateral branches forming an X shape, a primary winding around the central branch, and multiple secondary windings around the lateral branches, along with a film of low magnetic permeability to guide leakage flux, reducing air gap thickness and leakage flux, and integrating the resonance inductor within the transformer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large air gap is created at the central branch of the planar magnetic circuit to achieve low primary choke, then the primary inductance is reduced, but the height of the planar magnetic circuit increases and leakage flux increases
Solution Approach 1:
The invention divides the single large air gap into multiple smaller air gaps distributed across different branches of the magnetic circuit. Specifically, air gaps are introduced in the central branch and/or in the lateral branches, allowing the total air gap effect to be achieved while maintaining a compact structure and reducing leakage flux compared to a single large air gap.
Solution Approach 2:
The invention applies air gaps selectively in specific locations (central branch and/or lateral branches) rather than uniformly throughout the magnetic circuit. This localized application of air gaps allows optimization of the magnetic circuit in different regions, achieving the desired inductance while minimizing overall height and leakage flux.
2Power
If air gap thickness is increased to reduce primary inductance, then the primary choke is reduced, but eddy current losses and electromagnetic disturbances increase
Solution Approach 1:
The invention segments the total air gap into multiple smaller air gaps distributed in the central branch and/or lateral branches. This segmentation reduces the eddy current losses and electromagnetic disturbances associated with a single large air gap while achieving the same effect on primary inductance, thereby reducing energy losses.
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 design achieves a compact, high-efficiency, low-loss transformer suitable for high power HV/LV applications by reducing air gap thickness, minimizing eddy current losses, and enhancing electromagnetic compatibility.
Implementation Method 1
a film of low magnetic permeability to guide leakage flux, reducing air gap thickness and leakage flux
Implementation Method 2
at least one primary winding; at least one secondary winding arranged around each of the lateral branches
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The planar transformer according to the invention (14) is of the type of those comprising a magnetic circuit (15) exhibiting a predetermined number at least equal to four of lateral branches (16) each linked at each end to a central branch (21) by a first and a second magnetic bridge (28, 29), at least one primary winding (18) and at least one secondary winding (19, 20) which is arranged around each of the lateral branches. In accordance with the invention, the primary winding is arranged around the central branch. According to a particular characteristic, a plurality of air gaps (22, 23) are disposed in the lateral branches and/or the central branch as a function of a predetermined primary inductance. According to another particular characteristic, the primary winding is a flat coil extending substantially perpendicularly to the central branch.