Research On High Precision Frequency Measurement Methods Based On The Recursive DFT Algorithm By Adding Six-Term Window

Frequency is an important parameter of electrical measurement, which has an important role in power quality assessment, determining the normal operation of electrical equipments, as well as the comprehensive measurement of the power system stability, etc. So the measurement and adjustment of the power system frequency is a necessary task in the field of power system monitoring and controlling. With the gradual formation of the modern power grid structure, which is large and complex, the size of the power system is larger and larger, the dispatching automation level is higher and higher, which leads to the requirement of frequency measurement technology and method precision is higher and higher. This paper makes a deep exploration and research on the high precision frequency measurement method based on DFT algorithm, on the basis of the analysis and conclusion of the existing various types of frequency measuring methods.Firstly, this paper introduces the principle of the traditional DFT algorithm in measuring frequency and its inherent limitations, and probes into the methods to solve the problem of limitations. This paper is mainly based on the adding window method, has studied the algorithms which can reduce the error and realize high precision of frequency measurement, mainly including windowed interpolation FFT algorithm, and windowed recursive DFT phase difference algorithm and interpolation algorithm.Windowed interpolation FFT algorithm is a very effective solution for the inherent ills such as frequency spectrum leakage and fence effect of traditional DFT algorithm. On the basis of the introduction of the basic features and frequency spectrum characteristics of all kinds of window functions, according to the principle of the selection of window function, this paper seriously analyzes the excellent side lobe characteristics of the optimized six-term cosine combination window function, which is based on minimum side lobe attenuation speed. Furthermore, this paper derivates the correction formula of frequency measurement with four-term, five-term, six-term cosine window interpolation FFT algorithm respectively, and the effect of frequency measuring method by using four-term, five-term, six-term cosine window interpolation FFT algorithm are compared through actual example, which highlights the advantages of six-term cosine window frequency measurement.In order to solve the problem of large computation cost of DFT algorithm, and improve the speed of frequency tracking, the recursive method is used to realize the rapid measurement of power system frequency in this paper. This paper has separately carried on theoretical research about windowed recursive DFT phase difference algorithm and windowed recursive DFT interpolation algorithm on the basis of the introduction of the basic principle of recursive DFT algorithm, further exploring the feasibility and efficiency of high precision frequency measurement of power system by using methods such as the phase difference algorithm by using the four-term Nuttall(I) window and the six-term cosine combination window, the windowed recursive DFT interpolation method by adding six-term combination cosine window. The results show that the recursive DFT interpolation method by adding six-term cosine combination window has more superiority.