Digital high-speed calculation of the distorted signal fundamental component

Calculation of current and voltage phasors in power system protection and control is based on correlation of the signals with sine/cosine (or similar) functions, assuming data windows which are constant and usually amount to one period of the fundamental frequency. However this method introduces large errors in transient states, which follow changes of the signal amplitude and/or phase. The transient state lasts as long as the window. The transient errors are eliminated, if the correlation procedure utilises variable data windows which increase until they reach the one full cycle of the fundamental frequency and then become constant. This enables a phasor to be calculated within 1/4 cycle after the input signal changed. The algorithm is very fast, quite accurate and computationally efficient