A Fast-Convergent Modulation Integral Observer for Online Detection of the Fundamental and Harmonics in Grid-Connected Power Electronics Systems

Harmonics detection is a critical element of active power filters. A previous review has shown that the recursive discrete Fourier transform and the instantaneous p-q theory are effective solutions to extracting power harmonics in single-phase and three-phase power systems, respectively. This paper presents the operating principle of a new modulation function integral observer algorithm that offers a fast solution for the extraction of the fundamental current and the total harmonic current when compared with existing methods. The proposed method can be applied to both single- and three-phase systems. The observer-based algorithm has an advantageous feature of being able to be tuned offline for a specific application, having fast convergence, and producing estimated fundamental component with high circularity. It has been tested with both simulations and practical experiments for extracting the total harmonic current in a highly efficient manner. The results have confirmed that the proposed tool offers a new and highly effective alternative for the smart grid industry.