Study On Harmonic Measurement In Power System Based On Time-domain Interpolation And Windows Interpolation Fft Algorithms

Power system harmonic issue is a threat to the power system's safety running, it can greatly effects to the electrical environment. The power system harmonics issue is very extensive, the harmonics measure is an important branch of harmonic issue, it is also the starting point and the main basis for the harmonic issue studying. Owing to the inherent non-linearity, randomness, distributing, non-stationarity and complexity of influencing factor on power system harmonics, many conventional detection techniques can't acquire accurate harmonic identification, so it is excellent valuable in theory and practice to investigate new detection and suppression methods. In all kinds of harmonic measurement, The Fast Fourier Transform(FFT)is a common measurement method, many literatures also discuss about it. However the problem of asynchronous sampling always affects the precision, so it causes great error. In order to realize the high precision measurement, this paper do research in algorithm from time domain and frequency domain, then propose new algorithm in harmonics measurement.First, the synchronization formula based on two points Hermite interpolation is derived by use of re-location sampling in time domain. This method interpolates the data sequences sampled in fixed frequency by Hermite, so the synchronization formula based on Hermite interpolation is derived and the synchronous sampled data sequences is obtains, the harmonics measurement is carried out by FFT. This method needs only one cycle when sampling, so it has fast calculation speed, it is easy to realize in algorithm. It also has good results when the power frequency fluctuates greatly.Second, Windows and interpolation FFT algorithms is adopted. An interpolation FFT algorithms based on three-term cosine window is proposed. This paper discusses the frequency response of the exact-Blackman window, the formula of interpolation FFT algorithms based on exact Blackman window is derived in detail, so this new interpolation FFT algorithms can improve the precision of harmonics measurement effectively.Under the new algorithm, it takes advantage of the platform of MATLAB to develop a computer program for Simulation. Simulation results show that this new algorithms has high precision with less calculations. It also has good results when the power frequency fluctuates greatly.