Impedance measurement for improved power quality - Part 1: The measurement technique

This paper introduces an improved power system impedance measurement technique. The technique injects a short duration current spike into the supply, and derives the impedance from the measured current and voltage. The method is shown to work extremely well under most conditions, by experimental evaluation using a 45-kVA laboratory prototype. Degradation is observed when a voltage-source-type power-electronic load is connected directly to the measurement equipment. An alternative signal processing strategy, based upon the Prony method is proposed to improve the estimation under these conditions. This method also reduces the overall transient data capture time, thus allowing a faster, online calculation of the impedance.