Research On Voltage Flicker Detection Methods And It's Development Based On Virtual Instrument

Voltage fluctuation aroused by fluctuating loads impacts on the operation of electric equipment. The flicker, which is related to voltage fluctuation, is an important parameter of power quality, as well as a criterion for selecting compensating methods, devices and technical measures. Research of flick measuring methods and development of measuring equipments has theoretical and practical value.This paper analyzes the previous research on voltage fluctuation and flickermeter, and discusses the method of flicker measurement recommended by International Electrotechnical Commission standard IEC-61000-4-15. Based on IEC standards, the methods of designing square demodulator, bandpass-weighted filter, and smoothing filter are presented. Besides, the signal conditioning circuits and online statistical analysis methods of instantaneous flicker value are given. MATLAB SIMULINK is also used to simulate the measuring process of voltage fluctuation and flcker.Based on virtual instrument technology, the flicker meter's hardware and software is designed, generic PCI bus data acquisition cards and graphical programming language LabVIEW is used. The structure and performance of program are optimized as well. With friendly interface, the flickermeter is function rich, reliable, and precise; it meets the IEC standards. Just as common Virtual instrument, the flickermeter is software based, structure modularized, convenient for upgrade and easy to maintain.As IEC flickering measurement method can only be applyed to analyze stable flickering signals, this paper applies Hilbert-Huang transform, the latest time-frequency analyzing method, to deal with the non-stationary flickering signals. The transform uses the scale of the signal to decompose and make self-adapting frequency band partition of the input signals. Therefore the amplitude value and the modulating frequency of the flickering signal can be obtained. With the instantaneous frequency in this method, the present study also analyzes the signal in terms of both time and frequency, and thus gets the time at which the flickering signal occurs and terminates. Actually, the detecting effect is proved to be good.