| Sumario: | In this work, we present a simple algorithm to calculate automatically the Fourier spectrum
of a Sinusoidal Pulse Width Modulation Signal (SPWM). Modulated voltage signals of this kind are
used in industry by speed drives to vary the speed of alternating current motors while maintaining
a smooth torque. Nevertheless, the SPWM technique produces undesired harmonics, which yield
stator heating and power losses. By monitoring these signals without human interaction, it is possible
to identify the harmonic content of SPWM signals in a fast and continuous manner. The algorithm is
based in the autocorrelation function, commonly used in radar and voice signal processing. Taking
advantage of the symmetry properties of the autocorrelation, the algorithm is capable of estimating
half of the period of the fundamental frequency; thus, allowing one to estimate the necessary number
of samples to produce an accurate Fourier spectrum. To deal with the loss of samples, i.e., the scan
backlog, the algorithm iteratively acquires and trims the discrete sequence of samples until the
required number of samples reaches a stable value. The simulation shows that the algorithm is not
affected by either the magnitude of the switching pulses or the acquisition noise.
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