Frequency instability and additive noise effects on digital power measurements under non-sinusoidal conditions

This work deals with the effects of frequency instability and additive noise on the quality of power measurements performed by digital techniques. Frequency instability of voltage and current waveforms is modeled as a random variable ranging within a given frequency interval. Additive noise acting on both voltage and current waveforms is also taken into account. Propagation of both the uncertainty sources through the whole measurement process based on analog-to-digital conversion and discrete Fourier transform is investigated. Analytical expressions for the bias and the standard deviation of the measured power are derived and validated numerically.