Error Estimation and Correction of Detected Phase by Real Time DFT

Abstract

Recent progress in microprocessor makes it possible to use real time Discrete Fourier Transform (DFT) with sufficiently short sampling period for the ac voltage phase detection. Though the frequency characteristics of the gain were already discussed by several authors, but the error of detected phase has not been discussed yet. This paper discussed about the phase detection error of DFT, and proposed the error correction scheme using the ac frequency. The required accuracy of the ac frequency for phase correction was presented in the paper. The authors used the phase obtained from DFT to calculate the ac system frequency and assessed the frequency error caused by the detected phase error. The presented system can suitably correct the phase detection error. They were expanded to the positive sequence phase detection of the 3-phase ac system. This paper also evaluates the suitability of the presenting error correction scheme to the 3-phase ac system.