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3D Printed Air Core Inductors for High Frequency PowerConverters
Wei Liang, Luke Raymond, Juan RivasStanford University Power Electronics Research (SUPER) Lab
AbstractThis paper presents the design, modeling andcharacterization of 3D printed air core inductorsfor high frequency power electronics circuits.1 3D printing and molding techniques addflexibility and functionality in the design. Theyallow manufacturing of components withrounded edges and overhanging structuresdifficult to realize in planar processes.
2 We present several air core inductors designedusing 3D printing and molding techniques.
3 We describe the software and modelingtoolchain used to design, fabricate andcharacterize the electromagnetic performanceof the air core inductors.
4 We implement a 70 W prototype 27.12 MHzresonant inverter that incorporates some ofthe 3D printed components developed for thiswork.
We envision a fully 3D-printed power converterthat obviates the need of printed circuits board.
Air Core Magnetics
•Air-core inductors are not subject to saturationor Curie temperature limitations.
•Toroidal inductors are better than solenoids asthe magnetic field is constrained within thetorus.• Lower stray fields → Lower EMI
•PCB toroidal inductors have better coppercoverage, lower loss but limits in via densityresult in fields leaking from the side of thestructure.
•Better air-core passives are possible with modernfabrication techniques: 3D-printing.
Try it Out! Some of the inductor examples areavailable for order at our i.materialise online shop.
Design and implementation process
3D CAD Model 3D printed plastic mold cast silver model
• 3D CAD model is scripted in OpenJSCAD andOpenSCAD.
•A plaster casting mold is 3D printed for lost-waxcasting.
•The parts are cast, or plated•Here, we got silver cast models from a commercial3D printing service (Shapeways, i.materialise).
3D printed Air Core Inductors
Several examples of air core inductors designed using 3D printing and molding techniques to givean idea of the geometries that are possible to realize.A toroid inductor withsquare cross section. Morefreedom on height selectioncan lead to higher qualityfactors. CAD model inductor photo FEA magnetic field
L@27.12MHz Q@27.12 Q@54.24 Q@81.36nH MHz MHz MHz
sim 84.6 135 187 226meas 81 55 a NA NA
anot expected to be accurate
A toroid inductor withcircular section.
CAD model inductor photo FEA magnetic field
L@27.12MHz Q@27.12 Q@54.24 Q@81.36nH MHz MHz MHz
sim 341 236 313 355meas 345 140 a NA NA
anot expected to be accurate
A toroid with a round crosssection and two parallelwindings. It cancels the“one turn” inductance [1].
CAD model inductor photo FEA magnetic field
L@27.12MHz Q@27.12 Q@54.24 Q@81.36nH MHz MHz MHz
sim 22.2 293 411 501meas 18 65 a NA NA
anot expected to be accurate
A toroid with a round crosssection and four parallelwindings. A structureimpossible for planarprocess. CAD model inductor photo FEA magnetic field
L@27.12MHz Q@27.12 Q@54.24 Q@81.36nH MHz MHz MHz
sim 9.3 232 323 392meas 9 60 a NA NA
anot expected to be accurate
“One turn” inductancecancellation with oppositelywound series toroids.
CAD model inductor photo FEA magnetic field
The two toroidinductors are the sameas the one mentionedabove.
Φ2 Inverter with 3D printed Inductors
+
− vds(t)
+
-vgs(t)+
-
LMR
CMR
LF LS CS
RL vload(t)
+
-
VIN
Q1
CP
-100
0
100
200
300
400
0 20 40 60 80 100 120
Voltage [V]
Time [nS]
Drain Voltage
•A 70 W 27.12 MHz prototype Φ2 inverter was designedand implemented with all inductors 3D printed. Theinverter operates at Vin =170 V and Rload =50 Ω. Theefficiency reaches 80 %.
•Three same inductors were 3D printed manufacturedseparately and soldered together. It is not designed forhighest efficiency but rather the proof of concept.
Ongoing Updates
• toroids with optimal cross section shape are modeled [2].•multi-winding structures are possible. 1:1 transformermay provide good coupling and isolation
Next Steps• Incorporate thermal and mechanical properties into theFEM simulation
•Run FEM of multiple components simultaneously toevaluate interaction
•Evaluate repeatability and variability of components•Look into possible mass-production paths
Acknowledgement
The authors would like to thank Mr. Brian Holman andProf. Charles Sullivan (Dartmouth College) for their help inmodeling and implementing 3D toroids with optimal crosssection.
References
[1] J. Qiu, A.J. Hanson, and C. R. Sullivan. Design of Toroidal Inductors with Multiple ParallelFoil Windings. In Proc. IEEE 14th COMPEL, 2013.[2] C. R. Sullivian, Weidong Li, S. Prabhakaran, and Shanshan Lu. Design and fabrication oflow-loss toroidal air-core inductors. In Proc. IEEE PESC 2007.
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