Harmonic Detection Based On Improved All-phase Fft With Phase Difference Correction

With the rapid development of social economy and science and technology,electric energy has become one of the important energy sources for human survival,and electric power quality has gradually attracted people’s attention.At present,the widespread use of a large number of non-linear power electronic equipment has caused a lot of interference to the power system.These interferences will cause harmonic problems of power quality,affect the normal and stable operation of the power system,and even endanger the safety of users’ electricity,causing huge economic losses.Therefore,it is necessary to find suitable harmonic detection methods to detect harmonic parameters in real time and improve power quality.This article first introduces the basic definition of harmonics in power quality and grid harmonic standards,and analyzes the current research status and common methods of power quality analysis methods,including Fourier transform method,Kalman filter method,Hilbert Transform method,spatial spectrum estimation method,wavelet transform method and Plani method.Then the theory of Fourier transform is introduced,the defects of FFT in signal detection are analyzed,and three common spectrum correction methods are analyzed.The idea of all-phase Fourier transform is introduced in detail,and the performance of traditional FFT and all-phase FFT is analyzed and compared.The amplitude of all-phase FFT is the square of traditional FFT,and the phase of all-phase FFT satisfies the invariant characteristics.The effects of the three window functions of rectangular window,Hanning window and Blackman window on the all-phase Fourier transform are analyzed.The simulation shows that Hanning window is more suitable for the all-phase Fourier algorithm when detecting harmonics of the power grid.Aiming at the problem that the all-phase phase difference algorithm handles the interference between harmonics and the anti-noise is insufficient,the paper gives a power quality detection algorithm based on the improved all-phase FFT phase difference correction.The signal is weighted so thatthe spectrum lines on both sides of the main spectrum line decay faster to reduce interference between harmonics.The paper gives the principle and specific steps of the improved all-phase phase difference algorithm.The improved algorithm proposed in the paper is compared with the traditional phase difference and interpolation method.The simulation results show that the parameter error of the harmonic signal estimated by the improved all-phase FFT phase difference algorithm proposed in this paper is smaller than that of the other two algorithms.The proposed algorithm also has higher accuracy and has good anti-noise performance in detection of dynamic harmonics with higher frequency.