Enhanced Frequency-Locked Loop With a Comb Filter Under Adverse Grid Conditions

To improve the performance of frequency-locked loops (FLLs) under distorted grid conditions, the technique of harmonic decoupling with multiple notch filters was usually employed to remove the harmonic components, which, although offering good filtering abilities, suffers from complexity, high computational burden, and deteriorated dynamics. To alleviate these problems, this letter proposes an enhanced adaptive notch-filter-based FLL, which incorporates a comb filter and improves the filtering abilities by introducing purely imaginary zeros to achieve notch peaks and harmonic cancellation. In comparison with the typical existing solutions of multiple notch-filter-based FLLs for distorted grid systems, the proposed FLL features simple structure and low computational load, and it can completely block the dc component, odd and even harmonics of the input grid voltage without sacrificing the FLL dynamics. Experimental results and comparisons are presented to validate the effectiveness of the proposed FLL.