Study On Harmonic Detection Of Power System Based On All Phase Spectrum Analysis

With the wide application of various non-linear power electronic devices in the power system, the harmonic pollution in the power grid is becoming serious. Currently, Most of the harmonic detection algorithms are based on Fast Fourier Transform (FFT). In the infinitely long signal truncation process, this method only considers a truncated contained a certain point. It exists fence effect and spectrum leakage as signal processing, which leading to the harmonic detection accuracy is not high. So studying a rapid and accurate harmonic detection algorithm has important theoretical and practical engineering significance.The principle of FFT has been deep studied based on the existing harmonic detection methods. Then analyzing the grid harmonic signals by All Phase spectrum is proposed in this paper. Traditional data truncation only considers one kind of truncated situation contained a certain point, while All Phase method considers all of the truncation and makes data preprocessing. The approximate square of All Phase amplitude spectrum and FFT amplitude spectrum of grid harmonic is proved theoretically. This method can greatly reduce the frequency spectrum leakage. In the non-synchronous sampling conditions, the degree of interference between the spectrums is reduced and it has ’phase invariance’. By simulation compared with the FFT spectrum, it verifies that All Phase method has excellent performance of small energy leakage and clear spectrum, which laid a theoretical foundation for the accurate analysis of the grid harmonic signal.To get more accurate harmonic parameters, an improved spectrum correction method of All Phase time-shifting and phase difference is put forward. This method can eliminate the dependence of the phase value on the sampling midpoint and can directly obtain the initial phase of the signal without correction which required for a shorter sample sequence. The harmonic spectrum correction, frequency, amplitude and phase detection accuracy has greatly improved the feasibility of all phase method in practical applications. Through spectrum correction of network harmonic, the detection accuracy of frequency, amplitude and phase has greatly improved. The feasibility in practical application has been achieved.Make simulation analysis of odd harmonics, even harmonics as well as inter-harmonics of power grid using the improved All Phase time-shifting and phase difference, and the results show that the detection accuracy of the frequency and phase higher3to4orders of magnitude than FFT windowing interpolation. By analyzing the noise immunity of the All Phase method, a strong ability of resisting noise to be obtained. In the high SNR case, phase error can be less than1°that can reflect the superiority of the All Phase method in the harmonic detection application.By doing a large number of simulations and experiments, the accurate detection of the grid harmonic parameters has been achieved, which provides a practical and effective method for building accurate and real-time harmonic detection system.