Single-Phase Double Fundamental Frequency PLL Based on the Multiplication Stage under DQ-Axis Dual Closed-Loop Control

With the increasing popularity of single-phase grid connection, single-phase phase-locked loops have become one of the hot research topics in the field of phase-locking. In three-phase systems, phase-locked loops using the double fundamental frequency (DFF) concept have already achieved promising results. In this article, for the first time, the DFF concept is introduced into single-phase systems. A quadrature signal generator (QSG) based on the multiplication stage is proposed, which directly generates two-phase orthogonal DFF ac omponents from the single-phase power grid. Based on the proposed multiplication stage, a single-phase DFF phase-locked loop (DFF-PLL) is introduced. To further enhance the system performance, a dual-closed-loop control method based on the
dq
-axis is introduced. The method of the DFF-PLL with added
dq
-axis dual closed-loop control not only enhances system robustness but also capitalizes on the advantages of DFF to improve system speed. Finally, the experimental results are given to demonstrate and verify the effectiveness of the proposed DFF-PLL in terms of dynamic response.