Using digital methods in active power measurement

Digitized voltage and current waveforms can be used to estimate active power by processing the obtained samples through two methods: Discrete Integration and Spectral Analysis. The former involves computing the average of the sample-by-sample product of the two waveforms, while the latter uses sine fitting algorithms to estimate the amplitude and initial phase of each waveform. Precision expressions for both estimators are derived as a function of the number of samples acquired and the amount of additive random noise present, which is useful for determining the confidence interval for measurements. The two estimators are compared, and it is concluded that the second method, using sine fitting, is sometimes superior.