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Stanford University Power Electronics Research - Laboratory (SUPER-Lab)

3D printed components for high frequency power converters

Jiale Xu, Emily Hernandez, Wei Liang, Juan Rivas jmrivas@stanford.edu

February 1, 2017

Stanford University Power Electronics Research Laboratory (SUPER-Lab) February 1, 2017 1 / 18 Stanford University

Int. Conf vol., no., pp.1,20, 16-18 March 2010. ,-Kolar, J.W.; Biela, J.; Waffler, S.; Friedli, T.; Badstuebner, U., “Performance trends and limitations of power electronic systems, CIPS, 2010 6th

Power density in Converters � Inductors and capacitors

� size ∝ f1 s

� Slow improvements in size and performance � Semiconductors

� Switching loss ∝ fs � Great advances in recent years

� Heatsink: Hard to extract heat from small volumes

” Stanford University Power Electronics Research Laboratory (SUPER-Lab) February 1, 2017 2 / 18 Stanford University

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Why switching at 10s of MHz? PowerDensity

Frequency

~500W/in3

~50W/in3Conventional

Air-Core

~200KHz ~1MHz ~10MHz ~500MHz

The promise of VHF power conversion Reduced energy storage → Smaller passive components & Faster transient response

J. S. Glaser, et al, ”A 900W, 300V to 50V dc-dc power converter with a 30 MHz switching frequency,” In Proc. Twenty-Fourth Annual IEEE Applied Power Electronics Conf. and Exposition APEC 2009, pp. 1121-1128, 2009.

Stanford University Power Electronics Research Laboratory (SUPER-Lab) February 1, 2017 3 / 18 Stanford University

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Very High Frequency Power Electronics

Switching at 10’s of MHz High frequency operation reduces the energy storage requirements of inductors and capacitors. Inductors are small enough to be fabricated with an air-core

Stable over a wide temperature range (No Curie temperature limit) May reduce de-rating requirements (No saturation)

Enable high control bandwidth Reduction of bulk energy storage in high power pulsed applications (i.e radars)

Use PCB to implement inductors Inductances and capacitances can be implemented within the PCB Filters and EMI shielding can also be implemented within the PCB.

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Device Switching Loss

+

−

GateDrive

VIN

L

RLoad

vds(t)id(t)

C

t

vds(t) id(t)

t

ploss(t)+

−

GateDrive

VIN

Lchoke LRCR

RLoadC1vds(t)

DOFFT DONT

3.6VIN

Switching loss (hard switching) V-I overlap during device switching Includes device charge removal at turn off (device recovery) Includes device capacitance discharge at turn on

Energy stored at turn off, discharged at turn on (if not ZVS)

Resonant Zero-Voltage Switching reduces switching loss (e.g., Class E)

V-I overlap loss greatly reduced via capacitive snubbing ZVS turn-on avoids capacitive energy dump Only efficient over a narrow load range Device stresses are high for many topologies

Stanford University Power Electronics Research Laboratory (SUPER-Lab) February 1, 2017 5 / 18 Stanford University

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Air-core inductors for VHF converters

Air-core components not subject to saturation or Curie temperature limitations Toroidal are an improvements over solenoids as the magnetic field is constrained to the torus

Lower stray fields → Lower EMI issues

PCB toroids have better copper coverage and lower loss and very repeatable Better air-core passives are possible with new fabrication techniques: 3D-printing

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3D printed passive components

(a) 3D CAD model (b) 3D printed plastic mold (c) cast silver model

Fig.: Steps in the fabrication of a 3D inductor. (a) shows the OpenJSCAD model, (b) shows a translucent plastic model and (c) shows a sterling silver inductor. The 3D inductor has 10nH inductance and its dimensions are OD=18mm, ID=6mm, N=4. Also notice the rounded cross section.

3D printing can overcome limitations of PCB and wire-wound inductors Overhangs, curved surfaces, texture possible

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Path forward

Replacing solenoids with toroids → Printing passives within inner layers of PCB. Top and bottom layers function as EMI shield and heatsink

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“one turn” inductance

one turn axial direction inductance that can lead to EMI, extra losses on the ground plane Also results in current crowding on the inner ring of the toroid For air core inductors, the “one turn” inductance is comparable in value to the toroidal value

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“one turn” inductance cancellation

We can place two inductors with same dimensions but opposite winding direction vertically stacked to cancel the axial fields.

Stanford University Power Electronics Research Laboratory (SUPER-Lab) February 1, 2017 10 / 18 Stanford University

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Prototype Implementation

0 50 100 150 200−100

0

100

200

300

400

500

Time [nS]

Vol

ts [V

]

Drain Voltage

MeasuredSimulated

0 50 100 150 200 250−250

−200

−150

−100

−50

0

50

100

Time [nS]

Vol

ts [V

]

Anode Voltage

MeasuredSimulated27.12 MHz, 320 W Dc-dc Converter (170 V to

28 V) Inductors and capacitors implemented with PCB traces

Inductors implemented in FR4 Capacitors implemented using ROGERS laminate (4360G2)

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3D printed inductor with optimal cross-sections

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3D Printed Inductors with Optimal Cross Section

Parameter value units

Scaffold 0.46 gWeight

Plated 0.71 gWeight

Inductance 98 nH(modeled)

Inductance 90 nH(measured)

Q (@ 27.12 MHz) 105(modeled)

Q (@ 27.12 MHz) 94(measured)

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3D Printed Prototype

+− vds(t)

+

-vgs(t)+

-

LMR

CMR

LF LS CS

RL vload(t)

+

-

VIN

Q1

CP

3D printed

Φ2 Inverter Three inductors connect to MOSFET’s drain node

Single scaffold for the three inductors → 1.13 g Printed using Form 1+ SLA 3D printer (Formlabs)

High frequency → small inductors Good power density

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3D Printed Prototype

+− dc/rfVIN

MatchingNetwork

Gas propelant flow

PermanentMagnetRf coil

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3D printed inductors

0.5 inch

1.3 inch

Advantage of the 3D printed toroidal inductors Obtaining higher power density than the one with solenoidal inductors Reducing a leakage flux of solenoidal inductors (decreasing inductive heating and EMI)

Electrical characteristics depend on surface finishing and printing quality

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Highly Integrated Modular LED Luminaire Contract# DE-EE-0007629

Exploring methods to incorporate PCB Incorporate high permeability material fabrication techniques to the converters in our 3D printed designs operating at 100’s of kHz

In collaboration with General Electric

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Acknowledgments

This work has been possible through the support of: NSF Award Number: ECCS-1439935 The Precourt Institute for Energy Department of Energy DE-EE-0007629

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