Power Magnetics: Emerging Technologies and Research - ARPA-E

33 Pages·2010·1.89 MB·English

Power Magnetics:
Emerging Technologies and
Research Needs
Charles R. Sullivan
[email protected]
Dartmouth Magnetics and Power
Electronics Research Group
http://power.engineering.dartmouth.edu
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Why Magnetics?
Magnetics (inductors and transformers) are
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required for most power conversion circuits, but
are responsible for much of the
Size (volume and weight)
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Power loss
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Cost
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Difficulty in design (long development cycles)
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Advances depend on magnetics:
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High frequency circuits for miniaturization.
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Resonant circuit designs.
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Directions
not mutually exclusive
Miniaturization:
Very high frequency,
integrated, thin-film, small,
and (eventually) low cost.
Ultra-high efficiency:
Efficiencies in the high
90’s without increasing
size or cost.
High-power
High-frequency,
high-efficiency at
multi-MW scale.
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Minaturization
General idea: for given impedance
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Z = jωL, the inductance needed goes
down with frequency.
Similar scaling for transformers.
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Actual scaling depends on material
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properties (with a magnetic core).
Examine “performance factor” B·f…..
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“Performance factor” for
40 mT
MnZn power ferrites
Curves of B·f
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30 kHz·T
product for
constant power
loss density…
200 mT
No benefit from
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20 kHz·T
f > ~ 1 MHz.
Need different
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materials for
higher
frequency.
plotted for 300 mW/cm3
100 kHz 1 MHz
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Air-core vs. magnetic core
Magnetic
coil coil
Core:
soft
magnetic
material
“Air core” with relative
(cid:132) Magnetic core
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is really any permeability
increases L (inductance)
non-magnetic,
by a factor μ , μ >> 1
r r
dielectric
typ. 4 ~10,000
material.
Allows smaller volume,
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·
fewer turns for same L r 0
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The case for air-core
At very high frequencies
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(e.g. VHF = 30 MHz to 300 MHz), the inductance value is
small and readily achievable without magnetic materials.
Always gets better at higher frequency:
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At constant η (constant Q): Volume proportional to f -3/2
At constant heat flux: Volume proportional to f -1/2
with Q improving as f 1/3
Avoid magnetic material disadvantages:
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Power losses due to hysteresis and eddy currents.
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Frequency limitations: any material gets too lossy above some
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frequency, often only a few MHz.
Not available in standard IC or packaging processes.
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Air-core challenges
Low permeability leads to low flux density, which
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requires substantial volume for sufficient flux.
Requires more turns → more winding loss.
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Flux is not contained by a core; external flux can
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cause EMI problems and eddy-current loss in nearby
conductors.
Requires significant air volume.
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Air-core geometries
Our work
C.P. Yue,
CMU
Toroid Planar spiral
No external flux
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problem.
surroundings.
Field is parallel to
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Field perpendicular to
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conductor: low eddy
conductor: high eddy currents.
currents.
Easy to make.
Harder to make. (cid:132)
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Typical Q:
Q: can be > 100 (cid:132)
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< 10 for 1 GHz
< 4 for 100 MHz
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Air-core performance limits
Field between two
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layers of copper (e.g.
large-footprint toroid)
100
Q

m
u
m
Can do better with
i (cid:132)
x
a multilayer copper
M 100 MHz
300 MHz 30 MHz (in theory):
10
improve by a factor
p
where p is
number of copper
layers.
Requires height for
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flux path!
10 μm 100 μm 1 mm
Packaging layer vs.
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Height on-chip.
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