IEEE Electrification Magazine - June 2016 - 68

TECHNOLOGY LEADERS

iL
VD1
ea
eb
ec

T1

Li

T3

VD3

VD5

T5

VD4
T6

VD6

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iC
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Figure 2. A three-phase ac-dc converter with its dc bus being inadvertently shorted showing
1) an initial fault current loop through discharging of the dc link capacitor and 2) a sustaining
fault current loop through the antiparallel diodes of the converter.

the uncontrollable loop cannot be
renewable power systems, is far
interrupted by turning off the active
too slow.
insulated-gate bipolar transition
The problem of slow protective
(IGBT) switches. In such a case, the
device response can be overcome
consequences of a short circuit fault
with solid-state circuit breakers
without circuit protection is a loss of
(SSCBs). The most common approach
renewable power or a system-wide
is to use normally off IGBT switches
blackout, as well as a
or integrated gatecatastrophic destruccommuted thyristors.
There are many
tion of electric equipUnder normal condichallenges to providing
ment and the risk of
tions, these devices
fault protection in both act as feeders to
fires. Circuit breakers
ac and dc microgrids.
must be used in both
loads within the sysac and dc microgrids
tem or as part of a
at almost every juncradially distributed
tion, as shown in Figure 1. However,
network of switches. Current sensing
conventional mechanical molded
circuitry with minimal latency is
case circuit breakers, although comrequired so that, when a fault occurs,
monly used in traditional ac power
the SSCBs can be commanded to an
systems, exhibit a long reaction
off state and drive the current into
time in the range of tens of millithe fault to zero by diverting it into a
seconds, which, for converter-based
dissipative parallel circuit, such as a

SSCB Responded in Under 1 µs
VDS (200 V/div)
Short Circuit
Current: 100 A /div
VGS Going from
0 to -20 V (10 V/div)
Time Scale: 1 µs/div
(a)

(b)

Figure 3. (a) A 400-V/40-A SiC JFET-based SSCB prototype and (b) its short circuit-switching
waveforms.

68

I E E E E l e c t r i f i c ati o n M agaz ine / J UN E 2016

varistor, surge arrester, or voltageclamping circuitry. In addition to
current sensing, such systems
require fast-acting logic circuitry
and microprocessor controls for
data communication to coordinate
with other parts of the system. Auxiliary power supplies and other support electronic circuitry are also
required. These approaches insert
additional conduction losses into
the system, but, in some cases,
these can be unacceptably high. To
mitigate this problem, hybrid
approaches have been proposed to
bypass all or the bulk of the lossy
elements during normal, connected,
and nonfaulted conditions with
electromechanical contacts. However, this approach slows the fault
commutation process and adds considerable complexity.
Recent advances in and the availability of wide-bandgap (WBG)
power semiconductor devices, such
as silicon carbide (SiC) metal-oxide-
semiconductor field-effect transistors (MOSFETs) and junction
field-effect transistors (JFETs),
remedy the loss issue. For example,
for a voltage rating of 1,200  V, SiC
JFETs and MOSFETs exhibit a typical
specific R DSON of 2-4 mX/cm2, which
is 100× lower than silicon MOSFETs
and 10× lower than silicon IGBTs.
The normally on or depletion-mode
WBG devices, such as JFETs, are
generally undesirable for mainstream power converter designs, but
they fit into SSCB applications very
well, as is demonstrated.

Ultrafast SSCBs
A self-powered, autonomous, ultrafast SSCB design concept was
recently proposed. Figure 3 shows a
400-V/40-A SiC JFET-based SSCB
prototype modeled after this
concept and its short circuit faultswitching waveforms. It has experimentally demonstrated repeated
interruption of fault currents up to
180 A at a dc bus voltage of 400 V
with a response time of 0.8 ns,



Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2016

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