Study On Interharmonic Detection Methods And Influences On Power System

With the wide application of power electronic devices such as non-linear, varying load,the interharmonics caused by which impact on power system more and more seriously, inaddition to the typical problems such as overheating and life reducing of electricalequipment, also would bring some of the subsynchronous oscillations, voltage fluctuationsand flicker. So, it has great significance to study on interharmonic detection methods andinfluences on power system.A comparative analysis of the existing interharmonics detection methods are carried outfor the small content, non-linear and volatility of characteristic. Based on HHT transformtheory, a new interharmonics detection method based EEMD is presented by combining ofthe empirical mode decomposition and the ensemble empirical mode decompositionalgorithm. The signal is decomposed into a single-component signal by EEMD, and thenthe frequency and amplitude of each component is accurately calculate through HHTtransform, and the accuracy of this method is verified through simulation and measurement.Compared with the EMD algorithm, the proposed method can eliminate the falsecomponents and mode mixing and be suitable for the detection of inter-harmonic signal.To meet the rapid and accurate requirements of inter-harmonic detection, theinter-harmonic detection device is designed by the use of DSP chips and the applicationinterharmonic detection method proposed in this paper. Its accuracy is verified byexperiment signal detection.In order analyze the inter-harmonic affections on voltage fluctuations and flickers, therelationship between the inter-harmonics and voltage fluctuations analysis are carried out.In order to be able to accurately determine the level of inter-harmonics to make the electriclight flicker, interharmonic-flicker limit curve drawing method based on the voltage flickerconstraints is established. The interharmonic-flicker experimental platform is built byanalog tester flicker and inter-harmonic detection device，and the limit curve can be drawnthrough the experimental data. The2kinds of harmonic-flicker limit curves for the220V,50Hz fluorescent lamp are drawn by the2methods separately, and the analysis results show that the accuracy of the results obtained by the two methods, the level ofinterharmonics whether lead to fluorescent flicker can be determined by the curves. Themethods have the small amount of calculation, and are practical and easy to implement.In order to analyze the effects of interharmonics on sub-synchronous oscillation, themechanism of sub-synchronous oscillation caused by interharmonics is researched by d-qtransform theory. An engineering example concerning HVDC exciting SSO is enumeratedand analyzed，and the mechanism of interharmonics and SSO caused by HVDC areanalyzed based on the modulation theory; An engineering example concerning SVCinterharmonic exciting SSO is enumerated and analyzed，and the mechanism of SVCgenerating interharmonics and exciting SSO are analyzed according to on-off cycle controlprinciple. At the same time, the reasons of frequency conversion device generatinginterharmonics and the possibility of SSO caused by its interharmonics are analyzed. Toanalyze the degree of severity of the SSO fault in power system, the contingency screeningis carried out for filtering severe contingencies by directly calculating the integrated valuesof the performance indexes. The proposed method has high severe fault capture rate isverified through simulation.