A Robust AC System Frequency Estimation Method based on Cauchy's Residue Theorem

Abstract

This work presents an innovative frequency estimation algorithm for three-phase ac systems by transforming the time-domain voltages into the complex variable domain and then computing a complex variable line integral. The frequency estimation is obtained by using Cauchy's Residue Theorem, where the closed-loop integral of an analytic complex function vanishes on a closed trajectory. Moreover, the ac phase angle can be derived from the ac estimated frequency. The proposed method outperforms a standard Phase-Locked Loop in terms of its open-loop frequency step response. Furthermore, the estimated frequency and phase generated by the proposed method has been used to successfully control a VSC-HVDC scheme during steady-state and transient operating conditions in a computer simulation environment. In summary, the proposed method presents an efficient mechanism to generate a robust electrical frequency estimation, extendible to phase estimation, with minimal computational effort.