IEEE Electrification Magazine - June 2016 - 72

TECHNOLOGY LEADERS

Ultrafast Solid-State
Circuit Breakers
Protecting converter-based ac and dc microgrids
against short circuit faults.
By Z. John Shen
E N E WA B L E P O W E R
sources and other distributed energy resources
(DERs), such as photovoltaics, wind,
and battery storage, feed electricity
to the utility grid and/or local loads
through interfacing power electronic
converters. The safe and uninterrupted operation of these microgrids
against fault conditions is an important system requirement. Although
alternating current (ac) is still the
dominant form of electricity, direct
current (dc) has been gaining traction
in data centers and office buildings
because it offers higher system efficiency, lower capital and operating
expenses, and easier integration of
renewable resources and DERs.
Figure 1 conceptually illustrates
ac and dc microgrids with renewable sources and battery storage
feeding both local loads, such as
plug-in electric vehicles and residences. The power networks are
susceptible to short circuit faults
when one of the many load branches or the common power bus is
inadvertently shorted, resulting in a
fault current that is much higher
than the nominal current.
A traditional ac power distribution
system is well protected from short

R

Digital Object Identifier 10.1109/MELE.2016.2544058
Date of publication: 31 May 2016

72

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

Fault Currents

ac Bus

Overheated
Power
Electronic
Converters

Circuit
Breaker

Normal
Load Branches

Fault
Load Branch
(a)
Fault Currents

dc Bus

Overheated
Power
Electronic
Converters

Circuit
Breaker

Fault
Load Branch

Normal
Load Branches

(b)
Figure 1. The roles of circuit breakers in (a) ac and (b) dc microgrids with renewable power sources
feeding both local loads and the utility grid.

circuit faults because its power
source-comprising large synchronous generators and bulky transformers-can sustain a very high
fault current (e.g., 20-30× the nominal current) for a time period of several hundreds of milliseconds. This

allows enough time for a slowresponding mechanical circuit breaker in the faulty branch to activate
and isolate the fault, leaving the rest
of the power system unaffected.
(continued on page 67)



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

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