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In distributed power generation systems a fast and accurate positive-sequence fundamental grid-voltage frequency and magnitude tracking is required to synchronize grid-connected converter-systems with the mains. In this paper state-of-the-art fundamental grid-voltage detection methods based on the extension of the Synchronous Reference-Frame phase-locked loop with either an additional pre-filter for the phase detection or an extended loop-filter are presented and compared to each other. The performance of these methods is studied in the laboratory environment during harmonic voltage-distortions as well as characteristic grid-faults. Furthermore, a new approach using a combined pre- and extended loop-filter technique to improve the harmonic voltage-distortion rejection abilities is presented and thoroughly verified by measurements. The analysis reveals that the optimal choice of the PLL-methods is a trade-off between the dynamic performance requirements and the accuracy of the grid-voltage tracking during highly distorted grid-conditions. Furthermore, the proposed combined filter approach reveals fast voltage tracking performance with good voltage distortion rejection abilities.
Date of Conference: 17-22 Sept. 2011