High-Frequency Power Conversion for
Machine Drive Applications
Dr Niall Oswald
Electrical Energy Management Group
University of Bristol
niall.oswald@bristol.ac.uk
http://www.bris.ac.uk/engineering/research/em/
Introduction
Presently working on two projects:
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EPSRC ‘Centre for Power Electronics’ components theme
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TSB ‘Power Module Validation’ (PoMoVal)
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Focus is on wound passive components – performance and lifetime
when subjected to high speed switching waveforms.
Development, test and analysis of a high-power, high-frequency
power module for Electric Engine Start functionality.
Safran Power UK, Raytheon Systems Ltd, UoB.
These projects have similar objectives – enabling compact,
efficient power conversion for machine drive applications, using
new device technologies.
Opportunities…
Low per-cycle switching loss of new devices (WBG) allows high
switching frequency operation, in turn enabling:
• High output frequency
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High speed, torque-dense machines (e.g. 10 pole traction machine @
12k rpm – 1 kHz fundamental).
High switching frequency  reduced current waveform distortion.
• Compact, lightweight output filtering
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Sinusoidal output voltage, low harmonic distortion output current
waveform – reduced losses in driven machine.
Possibility of eliminating screened cables – desirable in many
applications, reduces installation cost.
Filter cut-off frequency can be placed outside controller bandwidth.
However…
…and Challenges
Low per-cycle switching loss is largely due to increased
switching speed – dominant DC-AC power conversion
topologies (2L-VSI, 3L-NPC) are hard-switched.
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‘Slow’ IGBT-based drives already require significant
EMC countermeasures to achieve compliance.
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SiC MOSFETs capable of switching at 10s of kV/μs.
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Neither practical nor desirable to have this level of
dv/dt present at inverter output terminals – essentially
mandates use of output filtering!
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Filter components must withstand switching stress
and provide sufficient attenuation of increased highfrequency spectral content.
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Filter topology selection and parasitic circuit elements
important in determining overall performance.
600 V, 10 A
+40 dB above 16 MHz
Oswald, N.; Anthony, P.; McNeill, N.; Stark, B.H., "An Experimental
Investigation of the Tradeoff between Switching Losses and EMI
Generation With Hard-Switched All-Si, Si-SiC, and All-SiC Device
Combinations," IEEE Transactions on Power Electronics, May 2014
Project Plans & Objectives
Key objectives:
• Development of wound component high frequency
electrical behavioural models.
• Investigation of aging effects of high dv/dt on wound
components.
Exemplary application – 40 kVA all-SiC 2L-VSI.
• Consideration of application requirements provides
representative basis for filter design (cut-off frequency,
voltage drop, etc.).
• Based around commercially-available 1200 V, 100 A SiC
MOSFET module (CREE CAS100H12AM1).
• Single phase inductor test-bed circuit under construction.
Project Plans & Objectives
• Test-bed circuit designed to maximise switching
performance (not cost/size optimised!)
• Draws on previous experience (PhD research,
PoMoVal test circuits).
• Loss analysis used to determine capabilities of
CREE all-SiC module.
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100 ARMS @ 40 kHz
50 ARMS @ 100 kHz
30 ARMS @ 200 kHz
• Initial tests will use existing UoBdesigned high-performance inductor.
Potential Outcomes & Exploitation Plans
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Improved understanding of trade-offs between total filter
volume and switching frequency, subject to EMC
limitations.
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Development of improved (compact, low-loss, low-EMI)
output filtering topologies using models developed by this
research.
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Construction of demonstration high-frequency inverter?