Instantaneous line-frequency measurement under nonstationary situations

A virtual instrument for the measurement of instantaneous power-system-frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is further developed that diminishes the variance of the estimation. The procedure is applied to the case of single and three-phase networks and relative errors in the frequency estimation are obtained. Low cost hardware, consisting of compatible PC, standard data acquisition card and signal conditioning module, has been used in conjunction with a software application developed with LABVIEW™. Finally, measurements using single and three-phase signals, simulating severe conditions of signal quality, were performed. A variation of the frequency throughout the measurement time has been assumed, according to a sinusoidal signal of 5 Hz, within a ±1 Hz margin. The developed tool has been proven, with worst case data and relative errors of 0.1% and 0.025% having been obtained for single and three-phase signals, respectively.