of the PLC-Link Power Line Carrier (PLC) Communication for a
Building Control System based on IDC2000 consists of the control messages being transmitted in
the electrical wiring of each of the individual lighting circuits connected to the power distribution
panels of the building (hereinafter referred to as PLC branches for the sake of simplicity). This
concept implemented in the Energy Savings Lighting System (ESLS) enables us to avoid the many
problems inherent in large and centralized PLC control networks (refer to application notes SYANL
404, 405 and 406 for further details). These problems are:
Very low line impedance requires PLC transmitters with heightened power.
A high level of total noise generated by a large number of electrical devices connected in the
same network in which the PLC signals are transmitted;
Very high probability of message collision when two or more messages are transmitted at
the same time and jam one another. This significantly decreases the networks message rate.
Thus, according to the ESLS concept, the electrical network of the building is an indivisible system
regarding the low frequency of the Mains (60Hz or 50Hz) but should be separated on autonomous
branches for frequencies higher than 90 kHz (the working frequencies of our PLC). Such isolation
can be achieved by implementing a low-pass back filter. Hence, this back filter is one of the key
elements in the ESLS.
The present back filter reference design for one, two and three phase circuits with common ground
amply fulfills all requirements given in the chapter below. Special attention was paid to its size (in
order to facilitate the integration in existing panels in retrofit works) and to lower its cost. Although
the back filters in the present application note are over-dimensioned, in order to assure complete
reliability of the communication even in the worst operating conditions, it can be seen that the size is
appropriate and their cost is negligible with respect to the overall installation cost.
The present application note includes guidelines for the design of the back filter differential inductor
using the manufacturers data (tables & curves) and the appropriate equations, and/or using
dedicated software supplied by the core manufacturer.



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The simplified block diagram of a building PLC network is shown in Figure 1


Figure 1
As shown in the above block diagram, back filters are installed on power distribution panels after
line circuit breakers and before the PLC network elements (which were not shown in order to
simplify the diagram). Refer to application note SYANL 404 for a detailed network description.

Technical Requirements for a Back Filter
The back filter shall carry out the following main functions:
To attenuate the PLC signals injected to a PLC branch coming from other branches
connected to the same panel to the targeted level less than 1-2 mV rms in the worst case.
The optimal transmitted PLC signal level is one volt in the ESLS application. Hence, the
filters attenuation shall be from 60 dB to 54 dB.
To attenuate noise in the 95125 kHz frequency band coming from the Mains building
electrical network and conducted into the PLC branches, down to 1-2 mV. As shown in
many studies performed in several regions of the world, the maximal noise level measured in
the building electrical networks in the 70200 kHz frequency band is about 10mV, refer to
SYANL404 section 8. For the purposes of a robust design with a reliability margin, so that
communication in any electrical building configuration installed according to acceptable
standards will be very reliable, a maximum noise level of 50 mV was chosen instead of the
{
Power Distribution Panel 1
Back
Filter 1
Back
Filter 2
Back
Filter N
Power Distribution Panel 2
Back
Filter 1
Back
Filter 2
Back
Filter K
Power Distribution Panel j
Back
Filter 1
Back
Filter 2
Back
Filter L
Power Distribution Panel
i
Back
Filter 1
Back
Filter 2
Back
Filter M
Building Power Line
{
PLC Branches
PLC Branches
{

{

PLC Branches
PLC Branches


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10mV. Hence, the required filters attenuation to attenuate this level of noise to 1 2 mV
shall be 34 dB.
The back filters overall dimensions and cost shall be as low as possible.
Note: The Systel's PLC modem embedded in the IDC2000 transmits the power line carrier signal
with harmonic voltage level of 1 mV rms or less at frequencies over the 200 KHz. Therefore, it
complies with the FCC Part 15 and CENELEC EN 50065 standard requirements and no back-filter
is needed to achieve further harmonics attenuation.

The Back Filter Structure for Different Building Wiring Topologies
Back Filter for Single Phase Branch
The simplest solution that complies with the above requirements is the LC low-pass filter
implementation shown in Figure 2 below. There are two L-shaped second order LC filters in each
branch. These two filters connected together comprise the third order T-shaped LC filter with two
connected in parallel capacitors. The loads of this filter in both directions are the PLC branchs
impedances. It is known that the slope of its Bode diagram is 60 dB/dec, i.e. it is rather easy to
achieve the required attenuation (60 dB) on 100kHz, if the filters cut off frequency will be about
25 kHz. The most suitable filter structure for the Single Phase Branch is a differential one
(Figure 2), because it allows implementation of one core only for two coils in Phase and Neutral
circuits.
The Back Filter Parameters
Figure 2 depicts two single phase PLC branches with back filters (CL
1
L
2
) connected to the power
bus inside the Power Distribution Panel (PDP)

1
2
3
4
*
*
C
Z branch
L2
L1
Mains
Branch 2
1
23
4
*
*
C
Z branch
L2
L1
Branch 1

Figure 2


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The frequency response of these back filters in branch to branch direction is shown in Figure 3

The filter parameters are:
Z
branch
= 20
L
1
= L
2
= 30 µH;
C
T
= 2C = 20µF
Note: C
T
is a sum of capacitors of all filters connected together (two in our case)
As follows from Figure 3 the present filter meets the first parameter requirement above. Each back
filter can have a capacitor of 2 µF (or less), and then ten branches connected together will give the
required 20 µF. If the number of branches in one Power Distribution Panel (PDP) will be less than
ten, an additional capacitor will be needed. It is also possible to use one 20 µF capacitor in the PDP
and a 0.5 µF capacitor in each back filter which will decrease its overall dimension (see Figure 4).
Figure 3


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The frequency response versus branch impedance (Z
b
) of back filter for a noise inducing to branch
from Mains is shown in Figure 5. Here the branch impedance varies from 10 up to 50 .

Figure 5
A BC
N GND
Branch 1
Branch 2
Branch 3
Branch n
BF3
BF2
BFn
BF1
B 1-2
BRCU 1
B 1-1
B 2-2
B 3-2
B n-2
B 2-1
B 3-1
B n-1
BRCU 1
BRCU 1
BRCU n

Figure 4


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The attenuation on the 100 kHz frequency varies from 42dB to 44 dB which is better than required
(34 dB).
The frequency response of the filter in direction from branch to Mains is shown in Figure 6. The
back filter attenuation on the 100 kHz frequency is 53 dB.

As was mentioned above, the filter attenuation in this direction is not so critical in our case. Thus,
additional improvement of network characteristics is achieved.


Table 1
Direction
Attenuation on 100 kHz (dB)
Branch Branch
62
Branch Mains
53
Mains Branch
42


Figure 6


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Back Filter for Two and Three Phase Circuits with Common Neutral.
The above design considerations based on a single phase branch are basically the same for the case
of two and three phase circuits with common neutral.
For three phase branches with common neutral as shown in Figure 7 the considerations for
designing a proper back filter are almost the same. The only difference is that each phase and the
common neutral have their own inductors.

A BC
N
BF1-1
BF3-1
BF4-1
C1-1
C2-1
C3-1
GND
BF2-1
BF1-1
BF3-1
BF4-1
C1-1
C2-1
C3-1
BF2-1
A
1
B
1
C
1
N
1
Branch1
GND
BC-1
BB-1
BA-1
BB-2
BA-2
BRCU
A
BRCU
B
BRCU
A
BC-2
A
1
B
1
C
1
N
1
Branch1
GND
BC-1
BB-1
BA-1
BB-2
BA-2
BRCU
A
BRCU
B
BRCU
A
BC-2
B n-k the network elements: ballasts, LCU, MNS, etc.

Figure 7


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For standardization purposes, the same inductor dimensioned for the same current as for the single
phase can be used but with the difference that its two coils are connected in series and the additional
inductor needs to be connected in Neutral. The result is that total number of turns is kept for the
required inductance. Moreover, the total filters inductance increases due to additional inductor in
Neutral circuit. As a result, the filters cutoff frequency will decrease. This will give the additional
attenuation up to10 dB (see Figure 8).


A simil