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The discrete Fourier transform (DFT) is still a widely used tool for analyzing and measuring both stationary and transient signals in power system harmonics. However, the misapplications of the DFT can lead to incorrect results caused by some problems such as an aliasing effect, spectral leakage, and picket-fence effect. A strategy of recursive group-harmonic power minimizing algorithm is developed for systemwide harmonic/interharmonic evaluation in power systems. The proposed algorithm can restore the dispersing spectral leakage energy caused by the DFT and regain its harmonic/interharmonic magnitude and respective frequency. Every iteration loop for harmonic/interharmonic evaluation can guarantee to be convergent using the proposed group-harmonic bin power algorithm. Consequently, not only high precision in integer harmonic measurement can be retained but also the interharmonics can be accurately identified, particularly under system frequency drift. The numerical example is presented to verify the proposed algorithm in terms of robust, fast, and precise performance.