Comparison of Measurement Methods of LV Grid Access Impedance in the Frequency Range Assigned to Nb‑Plc Technologies

Abstract

The paper presents and evaluates three advanced methods for the characterization of the low-voltage (LV) grid access impedance for the frequency range assigned to Narrow Band-Power Line Communications (NB-PLC): 9 kHz to 500 kHz. This study responds to the recent demand from both regulatory bodies and Distribution System Operators about the need for accurate and validated methods for this frequency band, due to the limited knowledge of the impedance values in the electrical grid and their influence on NB-PLC transmission channels. In this paper, the results of a collaborative work to develop different proposals to overcome the challenges for the proper characterization of the frequency and time-varying grid impedance, from different theoretical approaches, are presented. The methods are compared in a controlled and isolated scenario: the impedance characterization of passive filters. Then, the results are validated two-fold: first, against theoretical simulations, based on the schematics provided by the manufacturer, and second, against the measurement results of a precision impedance meter, used as a reference of accuracy. The results demonstrate a high degree of precision of the three proposals to characterize the access impedance of the LV grid.

Characterization of the Potential Effects of EMC Filters for Power Converters on Narrowband Power Line Communications

“…These filters show a wide range of impedance values along the PLC frequency band, mainly due to the resonance effects they cause at specific frequencies. The frequencydependent impedance of these filters, in terms of magnitude and phase, can be found in previous publications from the authors [17,18].…”

“…The LISN model used in the setup, whose characteristic impedance is 2 Ω, is designed according to the definition included in the PRIME specification [10]. Figure 3 shows the spectral variation of the actual characteristic impedance of the LISN, measured by the impedance measurement system described in [18]. Figure 4 shows the complete measurement setup.…”

“…The EMC filters are connected at either Point A, B or C, considering two different configurations-an open-circuit configuration, i.e., when no external load is connected to the filter in L'-N' [17,18], and a loaded configuration, when a passive load composed of a 50 Ω resistor connected in series with a 560 nF capacitor is connected in L'-N'. For the latter configuration, a 50 Ω resistance is observed for the load of the EMC filters in the frequency band of interest.…”

“…With regards to the potential effects of EMC filters on NB-PLC systems, and starting from a reference in which no device under testing is connected to the setup, the FER- Figure 5 shows the impedance measured at the EUT port of the first LISN when the different filters are connected at this same point in the open-circuit configuration. For that purpose, the impedance measurement system described in [18] has been used. Figure 5 shows the impedance measured at the EUT port of the first LISN when the different filters are connected at this same point in the open-circuit configuration.…”

“…Figure 5 shows the impedance measured at the EUT port of the first LISN when the different filters are connected at this same point in the open-circuit configuration. For that purpose, the impedance measurement system described in [18] has been used. Similarly, Figure 6 shows the impedance modulus of each EMC filter when connecting L-N ports to the setup and L'-N' to the load.…”