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In many state-of-the-art signal processing techniques, a signal within sliding-window (SW) is assumed stationary for analysing non-stationary signals. Whenever this assumption is violated, inaccuracies increase to the unacceptable levels. A narrow window-width is recommended for limiting the effect of variations within window, however, it results in poor frequency resolution and demands for increased computational resources. This study presents a simple and efficient algorithm to address amplitude-variation in a signal within SW, thus, allowing time resolution of 1-cycle and frequency resolution of 5 Hz (as per IEC Std. 61000-4-7) with improved accuracy and reliability of the fast Fourier transform of the time-varying signal. The proposed algorithm computes and applies necessary corrections to provide accurate estimates of the integer harmonics for the most recent cycle, irrespective of the number of cycles within the SW. The proposed algorithm is computationally efficient and fast, therefore, can be implemented easily either on digital signal processor or field programmable gate arrays hardware platform. The salient features of the proposed algorithm have been validated on variety of simulated and experimental signals, and have been compared with similar existing techniques in practice nowadays.
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