IEEE Electrification Magazine - June 2016 - 62

paired are listed in Table 1. There will be some communication between the paired breakers. Gate signals will
be calculated locally at one of the
breakers using the current information from both breakers. One of the
breakers will transmit its current
data continuously to the other breaker while receiving the gate signals.
If a fault happens between the
two paired breakers, both the breakers will remain switched off, even
though the fault is at the input end
for one of them. This is the advantage of this control compared to
local breaker control. More fault
locations can be isolated, and the
conditions where breakers need to be switched on can be
identified. The simulation results for all locations are

summarized in the results section. One limitation with
this control is that the fault at junctions 5 and 9 will be
misconstrued as an example of a
case where a breaker goes off without a fault. This is because at any
given time, either junction 5 or 9
will be at the input end of both the
bidirectional breakers. However,
this limitation can be tolerated if
the breakers at junctions 5 and 9
are located close in space, making
the probability of a fault happening
at those junctions very low. The
communication infrastructure
required for this control is not as
elaborate as for central control,
which makes it easier to implement. It is a compromise
between central control and local control in which absolutely no communication is required.

The only reason
other control
strategies are
considered is to
simplify the
communication
architecture.

TABLe 1. The description of paired devices

for control algorithm.
Paired Devices

Description

Source 1 and
breaker A

Breaker A receives output current
data from source 1.

Source 2 and
breaker B

Breaker B receives output current
data from source 2.

Breakers C and D

Breaker C transmits current data
and receives gate signals.

Breakers J and K

Breaker J transmits current data
and receives gate signals.

Breakers E and F

Breaker E transmits current data
and receives gate signals.

Simulation Results
The notional dc microgrid was simulated using the software PSCAD. For simplicity, the generator, inverter, and
converters are modeled using average-value models.
Table 2 provides a good summary of the results from the
three control strategies discussed in this article. As can
be seen, central control provides the desired result for
all the fault locations, without exception. The only reason other control strategies are considered is to simplify
the communication architecture.
For location 7, the local control turns breaker E back
on. This is because when the control deduces that there
is no fault at the output of breaker E, it will gate the
SCRs. Unlike other breakers, the SCRs in E allow current

TABLe 2. The summary of fault response for all control schemes.

Central Control

Local Control

Fault
Location

Breakers Start
Conducting
Again

Breakers
Are Gated
Again

Breakers Start
Conducting
Again

Breakers
Are Gated
Again

Breakers Start
Conducting
Again

Breakers Should
Start Conducting
Again

None

All except A, B

None

All except A, B

None

C, F, G

None

C, D, E, F

None

E, F, H, I, J

E, F

E, F, H, I

E, F

None

E, F, H, I

E, F, H, I, K

E, F, H, I

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

Paired Control

Ideal Case

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