Abstract: Frequency is one of the most important parameters in power system operating characteristics assessment. The low precision of traditional frequency measurement method results in frequency leaking which influence harmonic measurement accuracy. An improved frequency measuring algorithm based on DFT （Discrete Fourier Transform） is proposed. Three sets of signal data which are separated by half cycle are used to calculate two modification coefficients, which modify phase angle of two adjacent cycles. The frequency is then measured by the phase angle change. Synchronous sampling is achieved by correcting the sampling frequency in real time in order to analyze harmonic accurately. Four different simulation results show that proposed method has better frequency tracking result and harmonic measurement accuracy.

Key words: power system, frequency measurement, discrete Fourier transform （DFT）