This paper provides a solution to estimate synchrophasors with high accuracy at off-nominal frequencies using a nominal frequency clock. The sampling rate is fixed, while the amplitude of the sampled values is altered to generate a sequence of samples whose sampling frequency is synchronized to the power system frequency. The re-computation of the synchronized samples is done by cubic spline interpolation. The algorithm requires knowledge of the fundamental frequency of the power system which

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... estimated based on the phase angle difference between two phasors. The performance of the algorithm has been tested by simulation, through different scenarios, following the test conditions described in the IEEE Standard C37.118.1-2014a. The test cases include: steady-state with off-nominal frequencies, harmonic distortions, amplitude and phase modulations, positive and negative ramps of frequency, and frequency jump. The simulation results show the technique's capability in efficiently dealing with harmonics and off-nominal frequencies under static and dynamic conditions.