Planar Transformer Winding Layout for Low-Capacitance CLLC Converters
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Solution Overview
Problem
Existing models for high-frequency isolated resonant converters, such as those used in electric vehicle charging and aircraft power supplies, fail to accurately account for physical constraints like PCB thickness, insulation layers, and air gaps, leading to inefficiencies and increased stray capacitance, which affects power conversion efficiency and noise immunity.
Innovation Solution
A bidirectional resonant asymmetric CLLC converter with a high-frequency planar transformer (HFPT) designed on a multi-layer printed circuit board, featuring a specific winding configuration and magnetic planar core, optimized for minimal magnetic losses and high power density, along with a method for iterative design and 3D finite element analysis to minimize system losses and optimize winding structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a high-frequency planar transformer is designed with conventional winding arrangements, then the power conversion efficiency is improved, but the stray capacitance increases leading to reduced noise immunity
Solution Approach 1:
The patent applies asymmetry by using non-uniform winding arrangements where primary and secondary windings have different configurations. The primary winding uses a multi-layer planar structure while the secondary winding uses a different arrangement, creating asymmetric coupling that reduces stray capacitance while maintaining efficient power transfer. This asymmetric design allows optimization of each winding independently to balance efficiency and noise immunity.
Solution Approach 2:
The patent transitions from conventional two-dimensional winding arrangements to a three-dimensional multi-layer planar structure. By utilizing multiple PCB layers with vertical stacking, the transformer achieves better spatial separation of windings while maintaining compact footprint. This dimensional change allows optimization of winding geometry to reduce stray capacitance without compromising power conversion efficiency.
2Ease of manufacture
If the PCB thickness and insulation layers are not optimized, then the manufacturing is simplified, but the power density and conversion efficiency are reduced
Solution Approach 1:
The patent systematically optimizes PCB parameters including thickness (0.6mm to 1.6mm), copper trace thickness (35μm to 140μm), and insulation layer thickness to achieve optimal power density. By changing these physical parameters within manufacturing constraints, the design achieves high power density (greater than 100W/inch³) while maintaining standard PCB fabrication processes. The optimization involves adjusting conductor geometry and layer spacing to maximize power transfer efficiency.
3Object-affected harmful factors
If the air gaps between windings are increased, then the stray capacitance is reduced, but the magnetic coupling and power transfer efficiency are worsened
Solution Approach 1:
The patent applies local quality by creating non-uniform air gaps between windings. Instead of uniform spacing, the design uses varying gap distances at different locations to optimize the balance between stray capacitance reduction and magnetic coupling maintenance. Critical regions have smaller gaps for strong coupling while less critical regions have larger gaps for capacitance reduction. This localized optimization allows simultaneous achievement of both goals.
4Loss of energy
If the conductor trace thickness is increased, then the winding resistance is reduced, but the PCB complexity and fabrication constraints are increased
Solution Approach 1:
The patent uses partial action by applying thicker conductor traces (up to 140μm) only in specific high-current regions rather than uniformly across all windings. In low-current regions, standard trace thickness is used. This selective thickening reduces winding resistance where it matters most while avoiding unnecessary PCB complexity and fabrication constraints in other areas. The design optimizes copper distribution to match current density requirements.
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
The solution achieves efficient bidirectional power flow with voltage conversion efficiency ranging from 96% to 98.5%, reduced stray capacitance, and enhanced noise immunity, while maintaining high power density and minimizing system volume.
Implementation Method 1
a high frequency planar transformer (HFPT) that electrically couples the primary full or half-bridge and the secondary full or half-bridge
Implementation Method 2
reduces AC resistance through interleaving of primary and secondary windings in successive layers
Implementation Method 3
asymmetry in values of inductance-capacitance (L-C) tank parameters produce voltage conversions
Data Source
AI summary
Adhering to the objective of modelling and selecting the most optimal winding configuration for a high frequency planar transformer (HFPT) for auxiliary charging systems for more electric aircrafts (MEA) this disclosure elucidates numerous fabrication and design-based constraints and correlations to enable parametric modelling of various magnetic components. This disclosure characterizes possible winding configurations for HFPT employed in a bidirectional CUE DC/DC converter. A detailed analytical study is presented for each component and verified using several instances of 3D Finite Element Analysis (FEA) based model to synthesize the effective field and current density distribution in the windings. Several design-based trade-offs are graphically explained with various criteria pertaining to optimal winding selection to study the interdependence of the resultant parameters on hardware specifications, such as the PCB thickness and its fabrication layout, air gaps and conductor thickness.