The synchronization between power grid and distributed power sources is a crucial issue in the concept of smart grids. For tracking the real-time frequency and phase of threephase grids, phase-locked loop (PLL) technology is commonly used. Many existing PLLs with enhanced disturbance/harmonic rejection capabilities, either fail to maintain the fast response or are not adaptive to grid frequency variations or have high computational complexity. This paper therefore proposes a low computational burden Repetitive Controller (RC) assisted PLL (RCA-PLL) that is not only effective on harmonic rejection, but also has remarkable steady-state performance while maintaining fast dynamic. Moreover, the proposed PLL is adaptive to variable frequency conditions and can self-learn the harmonics to be cancelled. The disturbance/harmonic rejection capabilities together with dynamic and steady-state performances of the RCA-PLL have been highlighted in the paper. The proposed approach is also experimentally compared to the synchronous rotation frame PLL (SRF-PLL) and the Steady-State Linear Kalman filter PLL (SSLKF-PLL), considering the effect of harmonics from the grid-connected converters, unbalances, sensor scaling errors, d.c. offsets, grid frequency variations and phase jumps. The computational burden of the RCA-PLL is also minimized, achieving an experimental execution time of only 12 μs.

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Abstract-The paper presents various control strategies for an advanced multilevel-based power converter. A Fuzzy Logic Control, based on power balance constrains and Proportional Reactive Power control based on a more rigorous approach, have been proposed. Two different ways to assign reactive powers have been illustrated for both the control strategies and then compared in Matlab/Simulink environment accounting two active power sets. Finally, advantages and drawbacks of the proposed strategies have been highlighted.

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