Inverter drive signal processing via DFT and EKF

Two algorithms for estimating both the positive sequence fundamental symmetrical component and the frequency of the voltage system at the terminals of an inverter-fed three-phase motor are presented. The first one is based on the discrete Fourier transform (DFT) of the instantaneous symmetrical component of the positive sequence and yields off-line estimates. The accuracy is improved by the application of flat-top windows which reduce leakage and negative interference effects. The second one is based on the extended Kalman filtering of the instantaneous (EKF) symmetrical component of the positive sequence and gives on-line unbiased estimates. The harmonic components are rejected because they are treated as measurement errors. Several results obtained from these algorithms are reported and compared