Patent ID: 8129980

Claim:
An AC electric quantity measuring device comprising: voltage/current measurement means for measuring time-series data on the voltage/current of a system; frequency calculation means for calculating a realtime frequency by determining the amplitude, the chord length, and the rotation phase angle of a voltage rotation vector by performing integral computation on the time-series data obtained by the voltage/current measurement means and determining the rate of change in frequency per step; and estimated instantaneous phase-component voltage/current time-series data calculation means for calculating estimated instantaneous sinusoidal voltage/current time-series data for each phase component in accordance with the least-squares method by using the realtime frequency and the instantaneous voltage/current time-series data for the phase component, wherein the sampling increments in which the instantaneous voltage/current time-series data are measured are set to a fixed frequency, and the sampling increments in which the instantaneous voltage/current time-series data for each phase component are estimated are set to a measured frequency.