Coordinator: Paul Wright

Impedance is a key parameter in power quality (PQ) measurements.  Non-linear loads such as power electronics inject harmonic currents into the grid and the resulting amount of grid voltage distortion is determined by the grid impedance at each harmonic frequency.  In EMC testing, reference impedances called ‘artificial mains networks’ (AMN) are used in the laboratory to test mass market products for CE marking.

By making direct impedance frequency response measurements of the low voltage (LV) network, the suitability of present reference impedance approaches used in IEC standards can be examined and assessed. Frequency dependant grid impedance measurements can be used to specify new AMNs and line impedance stabilisation networks (LISNs) as required.

As appliance emissions are dependent on the source impedance, impedance networks are used to simulate the frequency dependant impedance of the mains when compliance testing electrical appliances in a laboratory.  The reference impedances specified in standards, namely the AMN (2 to 9 kHz) and the LISN (9 to 150 kHz), are not necessarily representative of present-day LV networks that typically supply countless power electronic appliances.  By using LV network measurements to determine the impedance characteristics of a number of typical LV networks, an assessment can be made of whether the normative impedance networks are representative of today’s LV networks.  This information is essential to the future credibility of appliance compliance testing in the range 2‑150 kHz.

Grid impedance measurement systems are developed to measure the in‑phase and quadrature components over the 2-150 kHz frequency range.  This instrument will be tested against lumped impedances in the laboratory and then deployed to measure the impedance at various LV network connection points in order to determine the variation of impedance characteristics between typical grids. The analysis of the results of the impedance characteristics from various LV networks can be used to assess the suitability of the present normative reference impedances.

For more information, see the project webpage >>