AN1714 datasheet(7/46 Pages) STMICROELECTRONICS

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AN1714

Powerline communication

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1.1.1

Impedance of powerlines

A powerline has very variable impedance depending on several factors such as its

configuration (star connection, ring connection) or the number of entities linked.

Extensive data on this subject has been published by Malack and Engstrom of IBM

(Electromagnetic Compatibility Laboratory), who measured the RF impedance of 86

commercial AC power distribution systems in six European countries (see Figure 3).

These measurements show that the impedance of the residential power circuits increases

with frequency and is in the range from about 1.5 to 8

Ω at 100 kHz. It appears that this

impedance is determined by two parameters - the loads connected to the network and the

impedance of the distribution transformer. Recently a third element influences the

impedance of the powerline, in particular in residential networks. It is represented by the

EMI filters mounted in the last generation of home appliances (refrigerators, washing

machines, television sets, stereos). Wiring seems to have a relatively small effect. The

impedance is usually inductive.

For typical resistive loads, signal attenuation is expected to be from 2 to 50 dB at 150 kHz

depending on the distribution transformer used and the size of the loads. Moreover, it may

be possible for capacitive loads to resonate with the inductance of the distribution

transformer and cause the signal attenuation to vary wildly with frequency.

For the compliance tests the normative EN50065 use two artificial mains networks

conforming to sub clause 11.2 of CISPR 16-1:1993. Measurements on real networks have

shown that this artificial network does not truly represent practical network impedance. To

better evaluate the performance of a real signaling system, an adaptive network must be

used in conjunction with the CISPR 16-1 artificial network. The design of the adaptive circuit

is included in the informative annex F of EN50065-1 (revision 2001).

Figure 3.

Aggregate European powerline impedance (by Malack and Engstrom)

1.1.2

Noise

Appliances connected to the same transformer secondary to which the powerline carrier

system is connected cause the principal source of noise. The primary sources of noise are

Triacs used in light dimmers, universal motors, switching power supplies used in small and

portable appliances and fluorescent lamps.

IMPEDANCE MAGNITUDE (OHM)

0.1

1.0

10.0

100.0

1000.0

0.04

0.08

0.10

0.30

0.75

2.10

5.00

15.00

30.00

FREQUENCY (MHz)

MAXIMUM

MEAN

MINIMUM

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