REAL-TIME MEASUREMENT OF POWER SYSTEM FREQUENCY

摘要

Most digital algorithms for measuring frequency have acceptable accuracy if voltage waveforms are not distorted. However, due to non-linear devices, e.g. semiconductor rectifiers, electric arc furnaces, the voltage waveform in a power supply system can include higher harmonics with order of magnitude some percent of the fundamental. This paper presents an algorithm for the rapid and accurate measurement of the line frequency based on digital filtering and dynamic parameter estimation method. First the voltage waveform, taken from a voltage transformer, is filtered using a lowpass IIR filter. Then the line frequency is obtained by comparing the filtered voltage with a mathematical model using an optimization procedure. The model's parameters are varied until an adequate match is obtained with the filtered voltage. The method uses digitized samples of input voltage and requires approximately 1/4 cycle of recorded data.