The calculation of power factor considering the harmonic order based on DFT

In order to solve the problems in measurement of power factor that the hardware is complex, the accuracy of measurement is low and measuring time is slow. In this paper, the collected voltage and current parameters are analyzed in the frequency domain by DFT, and proposes a fast and accurate method of calculating the power factor, which is applied for microcomputer protection and smart switch. The voltage and current are sampled with method of AC sampling, and the DFT is used for the analysis and calculation of the collected data. Determine the number of signal acquisition in one cycle which s represented by N and the harmonic order to be considered which s represented by n with the method of matching parameters. Finally, AC sampling transmitter calibration device is used for verifying the accuracy of the fast algorithm which is used in this paper. This algorithm can calculate the power factor within 20ms ~ 30ms, with accuracy being 0.1%. It is ideal for a variety of relay protection equipment.