The Research Of Voltage Flicker Monitoring Method Based On Ensemble Empirical Mode Decomposition

As the development of power electronic technology and new energy technology,the nonlinear loads are increasing in the power grid.As a result,power quality has deteriorated.Voltage fluctuation and flicker problem is one of the most important indexes.Therefore,the research of voltage fluctuation and flicker is of great significance.In this paper,the parameters of voltage fluctuation and flicker are introduced firstly.Then the advantages and disadvantages of common flicker detection methods are discussed,such as square detection method,wavelet decomposition and synchronous detection method and HHT detection method.On this basis,a voltage flicker detection method based on ensemble empirical mode decomposition(EEMD)is proposed for extracting feature information of voltage flicker.First,envelope signal could be extracted by using Hilbert Transform.Then the noises components of envelope signal could be removed by using EEMD.Finally,the denoising envelope signal could be decomposed by using ensemble empirical mode decomposition(EEMD)for getting accurate amplitude modulation wave.The start and end time of voltage flicker also can be obtained.Voltage flicker signals can be simulated by MATLAB.The feature information of flicker signals can be obtained respectively by EEMD detection method and common detection methods.By analyzing the detection data,the experiment results show that this new method is applicable for analyzing voltage flicker signal both in time domain and frequency domain.The accurate time,amplitude and frequency of voltage flicker signal which is mutational and non-stationary can be obtained by using this new method.This method is more accurate than the common detecting methods such as wavelet detection method,HHT detection method and so on.The voltage flicker monitoring system based on virtual instrument technology is designed,including hardware and software.The hardware includes sensors,signal conditioning circuit,data acquisition card and computer.The software of the system is realized by using LabVIEW and MATLAB mixed programming method,including timing sampling program,EEMD denoising program,amplitude modulation wave extraction program,voltage parameters calculation program,the short-term flicker value calculation program,data storage program and so on.The voltage flicker monitoring database can be established by SQL Sever and ADO technology is used by LabVIEW to access database.The storage of real-time data and historical data query can be realized by using ActiveX module of LabVIEWand SQLlanguage.The complex voltage flicker simulation signals and single flicker signals with noisesgenerated by high-accuracy waveform generator can be analyzed by monitoring system.Finally,in the motor drive laboratory of smart grid research center,field voltage signals can be real-time online monitored by the system and the experimental results show that the monitoring system is stable and reliable.