Patent ID: 8717040
Filing Date: 2014-05-06
Classification: G01R

Abstract:
1. A method for determining a distortion rate of an alternating-current main supply for an electric network comprising: receiving, from the electric network, an input signal corresponding to the main supply, wherein a fundamental period of the main supply is unknown; identifying the fundamental period of the main supply by analyzing the input signal, wherein the identification of the fundamental period includes filtering the input signal by removing certain frequencies from the input signal to obtain a filtered signal, wherein the filtering is performed using a first lowpass filter passing frequencies of the input signal below a first cut-out frequency and a second lowpass filter passing frequencies of the input signal below a second cut-out frequency, and the filtering of the input signal further comprises: identifying start and end alternation instants of the filtered signal by detecting when the amplitude of the filtered signal reaches a certain value, generating a sample signal from the input signal, wherein a period of the sample signal corresponds to the fundamental period and the duration of the sample signal is the period, wherein the generation of the sample signal includes applying the identified start and end alternation instants of the filtered signal to determine a start and an end of the sample signal, and calculating a harmonic distortion rate for the main supply using the fundamental period and the sample signal.