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A novel algorithm for fundamental frequency and harmonic components detection is presented in this paper. The technique is based on a real-time implementation of discrete Fourier transform and it allows fast and accurate estimation of fundamental frequency and harmonic amplitudes and phases of a distorted and noisy signal with fluctuating fundamental frequency. It is suitable for active shunt filter applications, when fast and accurate tracking of the reference signal is required in order to achieve a good control performance. The main application for the proposed algorithm is for aircraft AC power systems, where the fundamental frequency is 400 Hz and its actual value can fluctuate around the nominal value, hence a real-time estimation of fundamental frequency is essential for accurate active filter control. The proposed algorithm has been first implemented in Matlab/Simulink environment for computer simulation, and then the simulation results have been validated by means of experimental tests on a three-phase system, where a voltage signal generated by a programmable power supply has been analyzed and processed by means of a digital implementation on a microprocessor.