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 in this paper. The first one is based on the discrete Fourier transform 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. This algorithm can be used for microcomputer based tests and diagnostics of inverter drives. The second one is based on the extended Kalman filtering of the instantaneous symmetrical component of the positive sequence and gives on-line unbiased estimates. The harmonic components are rejected because they are treated as measurement errors. The EKF algorithm may lead to the development and implementation of adaptive control techniques. Several results obtained from these algorithms are reported and compared in this paper.