Research On Improvement Strategy Of-hybrid Harmonic Detection Based On FFT And DWT

In this paper,a large number of literatures at home and abroad are studied,and the existing hybrid harmonic detection strategies based on Fast Fourier Transform(FFT)and Discrete Wavelet Transform(DWT)have some shortcomings.Through MATLAB simulation verification,since the original hybrid strategy uses the FFT algorithm at low frequencies,there are problems of fence effect and spectrum leakage,which affects the accuracy of harmonic detection;The DWT algorithm is used at high frequencies,and multiple harmonics cannot be separated in the divided frequency bands.This paper designs an improved strategy for the above problems.Use DWT to break down the original signal into low frequency parts and high frequency parts.The windowed interpolation FFT processing is performed on the low-frequency part reconstructed after decomposition,so as to improve the original hybrid strategy and simply use the FFT to have the spectrum leakage and the fence effect.The presence of the attenuation signal is determined successively for the high-frequency portion reconstructed after the decomposition,and if there is no attenuation signal,the windowed interpolation FFT is performed.If there is an attenuation signal,the frequency of the attenuation signal is detected.All the stationary harmonic signals are restored using windowed interpolation FFT,and then subtracted from the layer reconstructed signal in turn,and finally the attenuation signal is obtained.In order to solve the problem that the original hybrid strategy cannot separate the steady-state harmonics from the transient harmonics in the high-frequency part.In this paper,the program design of the improved hybrid strategy based on MATLAB is completed,and the harmonic analysis effect of the power signal including complex harmonic components is constructed.According to the national standard GB/T 14549-93 calculation method,the maximum large-scale harmonic detection error of the simulation result is less than 2%,and the small-amplitude harmonic detection error is less than 0.10%,which meets the national standard requirements.Compared steadywith the original strategy,the detection error of the low-frequency-state harmonics is reduced to less than 10%of the original strategy error,and the steady-state harmonics can be separated from the transient harmonics from the high-frequency signal,effectively compensating for the hybrid Insufficient strategy.In addition,this paper completed the software development of the improved hybrid strategy based on C language.The simulation results show that the harmonic detection effect of C language program is consistent with the MATLAB program.In order to detect the actual harmonic detection capability of the C language program,this paper uses the Japanese Yokogawa DL850E oscilloscope recorder to collect the microgrid model data built by the laboratory to verify the improvement strategy.The experimental results show that the improved hybrid strategy harmonic detection capability meets the national standard requirements.