Measurement and Characterization of Load Impedances in Home Power Line Grids

The measurement and characterization of the load impedances in the home/office power grid is the topic of this paper. This is motivated by the interest of exploiting the home power line grid for data communications. The power line communication (PLC) medium is strongly affected by the presence of unmatched and time-variant loads, so we have carried out a measurement campaign on a representative set of devices that can be found in a house or office. The measurement procedure has allowed the investigation of their behavior both in the time and in the frequency domain, over a time span equal to the mains period and within the frequency range 2-30 MHz that is used by broad band PLC systems. We have found a very limited number of devices with an impedance noticeably time-variant. This is because they include, in the power supply unit, an electromagnetic interference filter that significantly reduces the time-variant behavior of the device impedance in the 2-30 MHz band. Furthermore, the impedance of any device is also affected by the presence of a power cord. Finally, from the experimental results, we propose a behavioral classification of the devices based on certain typical time/frequency characteristics of their impedance.