IEEE Electrification Magazine - June 2016 - 58

By Atif Maqsood and Keith Corzine

DC Microgrid
Protection
Using the coupled-inductor solid-state circuit breaker.

INCE THE GREAT DEBATE BETWEEN
Thomas Edison and Nikola Tesla, our
nation's power system has operated on
alternating current (ac). This was chosen
over direct current (dc) because of the need
to increase voltage with ac transformers to a high value
using transformers for long-distance power transmission.
The system has served its purpose well, but now, many
energy sources, such as solar panels, fuel cells, and batteries, supply dc voltage. Also, dc/dc power converters are
commonly used to transform voltage and to interface
these dc sources with a larger system. Because of this, local
dc power systems (or microgrids) have become popular
topics in research literature. It also turns out that interfacing a wind power generator to a dc system is simpler than
interfacing it to an ac system because ac/dc conversion is
needed for the former and ac/dc/ac conversion is needed
for the latter. Although energy sources and power conversion are readily available for dc power systems, some highperformance applications require fast-acting dc circuit
breakers, which are currently in the experimental phase.
This article discusses options for high-performance dc circuit breakers and specifically details the coupled-inductor
dc breaker. This breaker is demonstrated for fault protection in a notional dc microgrid.

S

DC Circuit Breaker Technologies
Many dc microgrid systems require rapid
reconfiguration for survivability. This has
led to research into advanced dc circuit
breakers. One popular choice is the hybrid
dc breaker, which uses a mechanical switch
in parallel with a path containing semiconductor devices. When the mechanical
switch is opened, the current is diverted to the semiconductor, which is then opened. The current is
ultimately diverted to a metal-oxide varistor,
which clamps the voltage and allows system
inductance to reduce the current. A main
advantage of this type of breaker is its low
on-state power losses. Another type of dc circuit breaker is the fully solid-state version.
There are many types of solid-state breakers. Some
use a resonant circuit to cause the semiconductor current to go to zero, and others divert the current to a freewheeling diode at the breaker output. The main advantage
of solid-state breakers is their extremely rapid operation.
The following section describes a coupled-inductor dc
breaker, which is a variation of a solid-state breaker that
includes automatic fault detection.

The Coupled-Inductor DC Breaker
Digital Object Identifier 10.1109/MELE.2016.2544240
Date of publication: 31 May 2016

58

I E E E E l e c t r i f i cati o n M agaz ine / j un e 2016

The coupled-inductor dc circuit breaker is shown in
Figure 1. The main conduction path consists of
2325-5987/16©2016IEEE



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