Accurate Low Access Impedance Measurements With Separated Load Impedance Measurements on the Power-Line Network

The precise knowledge of the access impedance and load impedances on the power-line communication (PLC) medium enables the optimum design of smart grid applications. The impedance of the PLC channel is strongly affected by the unmatched loads and considered as time- and frequency-dependent. This problem is the main reason for reducing the power amplifier output level of PLC modems, the transmitted signals, and the data rate of the PLC channel. This paper presents a description of an accurate access impedance measurement system in the frequency range 30-500 kHz with calibration processes and procedure to measure loads impedances on the power grid. This system provides a cancellation of the main frequency component and enables the analysis of the cyclostationary behavior of the access impedance of the power line. Off-line and online impedance measurements on different power outlets are presented. Very low and time-variant access impedances are found. This impedance behavior on the power line is related to the power supply unit and the electromagnetic interference filter design. The presented impedance measurements are evaluated and can be used to classify loads behavior.