challenges for on-board dc-dc conversion · andrew forsyth school of electrical and electronic...

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

andrew.forsyth@manchester.ac.uk