Research On Power System Digital Frequency Measurement Method

With the rapid development of modern electric power system, especially of high-voltage power grid, the system size and power generation capacity increases and the level of automation is higher and structure of the electric power grids and the means of regulation is increasingly complex. At the same time, the national economy depends on the electricity supply stronger and the power users demand more and more on the electric quality. Frequency is a measure of an important indicator of power quality. Power system requires the accurate measurements when in operation control, regulation and measurement.Power system frequency measurement methods are divided into hardware frequency measurement methods and software frequency measurement methods. Due to the software frequency measurement method is flexible; it is used to a wide range of application. Software-based frequency measurement algorithm research has an important practical significance of the project.This paper studies the Phase difference correction method of the frequency measurement algorithm. Using the recursive DFT method dynamic computing spectrum calculations and basing on the phase results compute the frequency of the electric grid changes in reality. The sampling frequency of dynamic adjustment measurement control device achieves the synchronous sampling and proposes the Hanning window recursive DFT algorithm. Using recursive DFT transformation by adding Harming window twice calculates the labor fundamental frequency phase after a cycle of phase variation and reusing the variation gets the variation of corresponding frequency. As a result of the windowed recursive DFT transformation, the impact of spectral leakage is reduced effectively and the phase difference calculation accuracy and speed is enhanced which can improve the frequency accuracy and speed.Based on the windowed interpolation FFT algorithm, this paper proposes a Fast Frequency Measurement Method based on the windowed recursive DFT interpolation algorithm. This method is easy to compute the frequency offset and adopts the recursive DFT method. Therefore the computational amount is reduced effectively. The computational accuracy is improved by using the windowed mode. Comparing to the recursive DFT frequency measurement method, the added windowed can exclude the interference brought by the spectral leakage and harmonic waves and measure the fundamental frequency of the electric power system.