Detection And Identification Of The Inter-harmonic Sources In Electric Power System

Power quality, just like other commodities, is attracting more and more people from electric company and customers. With the broad application of the frequency conversion device and volatility load, the interharmonic disturbances occur in the modern power grid. In addition to similar hazards as harmonic, the interharmonic could bring flicker and sub-synchronous oscillation in power system. In recent years domestic and foreign scholars start to pay attention to generation mechanism, characteristics and detection methods, and have achieved a lot, while it is noted that previous studies lack the method of the interharmonic source identification and suppression. The common efforts are needed to detect the interharmonic components and identify the location of the interharmonic source, to solve the interharmonic disturbances.On the basis of the introduction of several typical interharmonic sources, the paper gives the analysis of interharmonic generation mechanism and characteristics, and sums up the law of interharmonic sources. After theoretical explanations of existing detection and identification methods, the paper points out the shortcomings of traditional methods, and summarize the theoretical framework of interharmonic source detection and identification. As to deficiencies of the existing methods, the identification method of interharmonic sources based on generalized least squares regression is proposed. The traditional regression methods ignore the influence of the colored noise with large estimation error. The method based on generalized least square could overcome the estimation error caused by the correlation between the variables, and improve the accuracy of parameter estimation. Simulation analysis and practical testing data prove the method effective and feasible.For the distribution network supplied by the single-ended power, the method based on impedance conversion can identify the main interharmonic sources accurately and quantify the responsibility at both sides. Distribution network structure changes when distributed generators are connected to the power grid, then the impedance conversion method may make an incorrect conclusion. To this end, a new method is proposed to deal with the situation of distributed generators. The method corrects the impedance parameters by means of the active and reactive power fed into the grid. Furthermore, the index of interharmonic power is proposed to quantify the responsibility at both sides. Results of calculation example show that the improved method is effective.In addition, the paper develops the detection and identification system of interharmonic sources. In LabVIEW2010development environment, the data acquisition module, spectral analysis module, identification and responsibility quantization module, data storage module and report generation module are programmed, and the software interface is beautified. To complete the development of the hardware circuit, the â…¤-â…  transformer circuit, signal conditioning circuit and data acquisition circuit are designed and tested individually. Finally, the volatility load is selected as the interharmonic source, and the entire system including the hardware and software is debugged. The rationality of the developed system is verified through the Matlab/Simulink simulation and development system test.