10 IEEE Power Electronics Society NEWSLETTER Fourth Quarter 2004

INTRODUCTION

Recent breakthroughs in Silicon Carbide

(SiC) material and fabrication technology

have led to the development of High-

Voltage, High-Frequency (HV-HF) power

devices with 10-kV, 15-kHz power switching

capability. Programs are underway to

demonstrate half-bridge modules with 15-

kV, 110-A, 20-kHz capability in the next few

years. The emergence of HV-HF devices

with such capability is expected to revolu-

tionize utility and military power distribution

and conversion by extending the use of

Pulse Width Modulation (PWM) technology

to high voltage applications.

Wide bandgap semiconductors such as

SiC have long been envisioned as the mate-

rial of choice for next generation power

devices [1]. Although wide bandgap semi-

conductor materials have superior proper-

ties, the realization of power device quality

substrates and fabrication technologies

required overcoming many technical chal-

lenges. The rapid advances in single crystal

SiC over the last decade have ushered in a

new era of wide bandgap power semicon-

ductor devices. In 2004, Dr. Calvin Carter of

Cree Inc. received the US National Medal of

Technology from President George W. Bush

for: “his exceptional contributions to the

development of Silicon Carbide wafers,

leading to new industries in wide bandgap

semiconductors and enabling other new

industries in … more efficient/compact

power supplies, and higher efficiency

power distribution/transmission systems.”

Currently, there are significant efforts

underway to accelerate the development and

application insertion of the new HV-HF SiC

devices needed for commercial and military

power conversion and distribution applica-

tions. The goal of the ongoing Defense

Advanced Research Projects Agency

(DARPA) Wide Bandgap Semiconductor

Technology (WBST) High Power Electronics

(HPE) program directed by Dr. John Zolper

is to develop 15-kV class power semicon-

ductor devices enabling future electric ship,

more electric aircraft, and all electric combat

vehicles. DARPA is particularly interested in

developing the power electronics device

technology deemed necessary to enable 2.7

MVA Solid State Power Substations (SSPS) for

future Navy warships.

The benefits of HV-HF semiconductor

technology have also been identified by the

Electric Power Research Institute (EPRI)

including advanced distribution automation

using solid-state distribution transformers

with significant new functional capabilities

and power quality enhancements. In addi-

tion, HV-HF power devices are an enabling

technology for alternative energy sources

and storage systems. The emergence of HV-

HF power devices presents unique opportu-

nities and challenges to the power electron-

ics industry in specifying the device require-

ments and establishing PWM converter

topologies for high voltage applications.

HIGH VOLTAGE POWER CON-

VERSION APPLICATIONS

Figure 1 shows the application ranges for

the majority of power semiconductor

devices indicating shaded areas where SiC is

likely to have an impact in the near future.

Generally the power device market size

decreases with increasing voltage and cur-

rent requirement. Presently the market size

for the relatively lower voltage and current

Power Supply area is several times larger

than for all other applications combined

with device sales of approximately

$5B/year. For higher voltage applications

such as Motor Control and Traction, the

device current requirements typically

increase as the voltage requirement increas-

es due to the large power requirements in

these applications. An

exception to these trends is

in the power distribution

area where the HV-HF

Power Conversion would

require devices for a wide

range of current ratings and

the market size could be

relatively large. However,

the HV-HF Power

Conversion market has not

yet developed due to the

6.5 kV voltage limit and

slow switching speed of

high voltage Silicon power

devices.

Over the last two

decades, PWM power con-

version technology, with

its superior efficiency and

control capability, has

changed the way power is

converted in almost all low

and medium voltage power conversions

applications from 100 V to 6.6 kV. Due to

fundamental limitations of Silicon devices,

the on-resistance increases and switching

speed decreases as the blocking voltage

requirement is increased. The switching

speeds in low voltage power supplies are as

high as several MHz and decrease to sever-

al kHz for high power traction. The higher

on-resistance and slower switching speed

increase losses and limits applicability of

PWM for high power and utility applica-

tions.

The developments of Silicon IGBTs

over the last decade have enabled high fre-

quency power conversion to be used at

increasingly higher power levels. Recently

SiC power Schottky diode products have

also been introduced that increase switch-

ing speed capability by reducing diode

reverse recovery loss. It is expected that

SiC power devices will continue to aid the

evolution of increasing PWM frequency

and power levels in the Power Supply

and Motor Control areas as SiC Schottky

diode and MOSFET products are intro-

duced with higher voltage and current rat-

ings. Because SiC devices have the capa-

bility to increase the voltage beyond that

of Silicon into the 10 kV through 25 kV

range with much higher switching speed

for a given blocking voltage, they provide

the revolutionary potential to extend high

Emerging Silicon-Carbide Power Devices

Enable Revolutionary Changes in High Voltage

Power Conversion

By: Allen Hefner, Ranbir Singh, Jason Lai

Figure 1. Application ranges for the majority of power semi-

conductor devices indicating shaded areas where SiC is likely

to have an impact in the near future.