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Power line Overview

Topology Mapping

Challenges to Reliable PLC

Developing and deploying reliable PLC technology is a notoriously hard problem that Echelon has been able to solve. We’ve overcome the following key challenges to build a superior PLC solution:

High Attenuation

It’s important to understand the causes of high attenuation on power line. For example, when we model a neighborhood’s power line distribution network, we immediately see a series of voltage dividers, plus inductive impedances from line feeds and homes. In this topology, if a transmitted signal is intended for the last house’s meter, the signals are going to be divided by the number of homes the signal passes.

 

For this example, let’s assume:

  • The wiring distance between transmit location and each of the houses is underground and only 100m
  • Only three homes are served by the transformer
  • The run between the feeder and each house is only 11m
  • There are 3 microhenries of home inductance
 low-voltage distribution diagram
   
In this very small and seemingly easy configuration, we can calculate that the signal between the transformer and the last house is attenuated by 44 dB at the service entrance. In most areas of the world the number of customers served by a transformer is many more than three, so we can see that the attenuation is a huge factor to overcome in a smart metering system. And it's not the only one. typical signal attenuation

Noise

Noise is a huge obstacle to successful power line communications. It comes from many sources. Here are a few:

  • Light dimmers. These devices produce large impulses of 100–420 Hz.
  • Switch-mode (AC to DC) power supplies used in electronic devices. Switching power supplies with a fundamental frequency between 20 kHz and 1 MHz will generate harmonic distortion able to knock out power line signals.
  • Power line intercoms. These devices generate signals of between 3V and 7V peak-to-peak in the 150–400 kHz band, and block power line signals in that band.
  • Universal series-wound motors. Examples include vacuum cleaners, kitchen appliances, and drills. These devices produce high repetition-rate impulses that can knockout bits in a packet.

 

Because many of these noise sources are tied to human activity, the amount of noise on the power line will vary by time of day. This time attribute makes full characterization of the environment difficult, and it implies that a power line communication system must be adaptive to changes in the environment.

Channel Distortion

Both signal amplitude and phase response will vary with time and frequency, so any power line communication technology must include compensation for these factors in order to be reliable. The figure illustrates a real-world plot of phase distortion in the 120–140 kHz band.

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