Research And Application Of Harmonic Detection In The Power System

With the rapid development of the power electronic technology,the widely application of various nonlinear devices in the power system will lead to the appearance of the harmonic pollution,which will do harm to the safe and stable operation of the power grid.Due to the high precision and easily implementation,fast Fourier transform(FFT)has been the most common method of harmonic detection.However,under the circumstance of asynchronized sampling and non-integral period truncation,spectral leakage and fence effect will deteriorate the performance of harmonic detection.Window functions and interpolation algorithms can be used to improve effectively the measurement accuracy of harmonic parameters.Firstly,in terms of definition,source,hazard and analysis indices,harmonic in a power system is introduced systematically in this paper.Then current methods of harmonic detection are explained in detail and the principle and strength and weakness of the FFT algorithm for harmonic detection are elaborated.Based on the analysis of the window functions’ characteristics,evaluation indices to choose the appropriate window function have been proposed.Because of the noise in the actual power system,this paper has proposed an improved triple-spectral-line windowed interpolation FFT algorithm.Meanwhile,considering that the phase difference of any two adjacent spectral lines in a window function’s main lobe is π,the paper deduces a rapid algorithm which obtains the parameter rectification formulas by polynomial curve fit functions.In the simulations,not only has the effectiveness of improved algorithm with different window funcitons been verified when extracting small signals and detecting haromic of complex signals,but also the algorithm performance has been analyzed under the condition of frequency fluctuation and white noise.The results of simulations verify the feasibility of the proposed improved algorithm.In view of the problems in the energy metering of traditional meters,a meter composed of analog-to-digital converter,digital signal processing and RISC-V instruction set architecture has been designed.From the aspects of the overall structure,hardware and software,the design process of a meter is illustrated.Besides,the error in the energy metering system is analyzed thoroughly.Finally,results of the system test prove the feasibility of the designed meter which meets the demand of the A class harmonic measuring instrument in the national standards.