Harmonic and Interharmonic Estimation Using Time-Domain Quasi-Synchronous Sampling Technique and Comb FIR Filter

A triple-stage signal processing technique is developed for harmonic and interharmonic estimations in power systems. Firstly, the fundamental period is evaluated accurately by the multi-rate narrow bandpass finite impulse response (FIR) filter and the zero-crossing method. The actual sampling sequence can then be reconstructed to a quasi-synchronous sampling one. Consequently, a comb FIR filter can be applied to separate harmonics and interharmonics. Secondly, interharmonics are evaluated by the windowed and interpolated fast Fourier transform method, of which, harmonic interference is eliminated from interharmonics by the comb FIR filter. Thirdly, harmonic parameters are determined directly from the discrete Fourier transform results after quasi-synchronization. Simulation results show that the present method has a high accuracy of measurement for harmonic and interharmonic estimations under the circumstances of noise interference. Finally, experimental results on a self-developed power quality analyzer have demonstrated the validity of both the algorithm and the simulation. Copyright (C) 2011 Praise Worthy Prize S.r.l. - All rights reserved.