challenges for on-board dc-dc conversion · andrew forsyth school of electrical and electronic...
TRANSCRIPT
Challenges for On-Board
DC-DC Conversion Andrew Forsyth
School of Electrical and Electronic Engineering
The University of Manchester
Overview • DC-DC conversion requirements
• Typical performance and challenges
• Interleaved topologies
• Zero voltage switching
• Magnetic component analysis and optimisation
• Silicon carbide (SiC) device technology
DC-DC Conversion Requirements • 50 kW or higher: 250 – 600 V
Prototype performance • 50 kW, 600 V, around 96% efficient
• Conduction cooled to baseplate
• 1200 V, 600 A Si IGBTs (heavily over rated), 25 kHz
• 5.8 litres. 9 kW/litre
Challenges • Reduce losses and size
• Reduce magnetic component requirements
• Increase operating frequency
• Improve thermal management
IGBT Switching Waveforms • Reduce magnetic component size with higher frequency
• Frequency limited by switching losses Turn on Turn off
VCE
VCE
ICE
ICE
EON EOFF
50 ns/div 200 ns/div
Principle of Interleaving • Reduced input and output current ripple and increased
ripple frequency
Principle of Interleaving • Use of interphase transformer (IPT) to reduce magnetic
weight
Principle of Interleaving • Use of IPT to reduce magnetic weight
Duty-ratio = 0.5
Principle of Interleaving • Use of IPT to reduce magnetic weight
Duty-ratio < 0.5
Principle of Interleaving • Use of IPT to reduce magnetic weight
Duty-ratio < 0.5
Zero Voltage Switching • Increase differential current such that the total IPT
current reverses
• IGBT voltage and current with similar power throughput
Zero voltage switching 25 A/div, 100 V/div, 5 µs/div
Hard switching 50 A/div, 100 V/div, 5 µs/div
VCE VCE
ICE ICE
Zero Voltage Switching
Zero Voltage Switching
Zero Voltage Switching
Zero Voltage Switching
Zero Voltage Switching
Zero Voltage Switching • Eliminate diode recovery and turn on losses
• Reduce turn off losses with lossless snubber capacitors
• Total switching losses reduced by 40%
• Increased peak currents
• More complicated IPT design
• Efficiency increased to 97%. Small frequency increase
Magnetic Component Design • FEA electromagnetic and thermal analysis to examine
losses and predict temperatures
Aluminium can
Copper foil windings Gapped nanocrystalline core
Potting compound
Finite element thermal model assembly
Potted inductor with embedded thermal sensors
Simulated temperature profile in the core
Gap Loss Distribution
Use of SiC Devices • More rapid switching with virtually no diode reverse
recovery and no transistor tail current at turn off
Si IGBT turn on SiC BJT turn on
VCE
VCE
ICE
ICE
EON EOFF
EON
ICE
VCE
50 ns/div 50 ns/div
Use of SiC Devices • More rapid switching with virtually no diode reverse
recovery and no transistor tail current at turn off
Si IGBT turn off SiC BJT turn off
VCE
ICE
EOFF
VCE
ICE
EOFF 200 ns/div 200 ns/div
Use of SiC Devices • Operating frequency increased to 75 kHz in 50 kW BJT
converter. 98% efficiency. 2.9 litre volume. 17.3 kW/litre
• Power modules developed by Raytheon
Use of SiC Devices • Operating frequency increased to 75 kHz in 60 kW
MOSFET converter. 98% efficiency. 3 litres. 20 kW/litre
• Cree MOSFET modules
Demonstration Multi-port Converter • TSB project led by Prodrive,
partners: Raytheon, IST, Tata & SCISYS
• Integrated battery / super-capacitor converter: 100 V – 220 V – 600 V
• 12 litre volume
Conclusion • Magnetic components can account for up to 50% of
converter weight
• Increasing frequency is one route to size reduction
• Emerging SiC technology shown to be effective in increasing frequency and efficiency, and reducing size
• Further advances in topologies, magnetic components, thermal management and packaging required for optimum use of SiC technology
