A synchronization scheme for single-phase grid-tied inverters under harmonic distortion and grid disturbances

Synchronization is a crucial aspect in grid-tied systems, including single-phase photovoltaic inverters, and it can affect the overall performance of the system. Among prior-art synchronization schemes, the Multi Harmonic Decoupling Cell Phase-Locked Loop (MHDC-PLL) presents a fast response under grid disturbances and high accuracy under harmonic distortions. However, major drawbacks of the MHDC-PLL include increased complexity and inaccurate response under non-nominal frequencies, which may occur in practical applications. Thus, this paper proposes strategies to address these issues. At first, a novel re-formulation of an equivalent decoupling cell is proposed for reducing the implementation complexity, and then a frequency adaptive quadrature signal generator for the MHDC-PLL is proposed to enable an accurate response even under non-nominal frequencies. Simulation and experimental results are provided, which show that the proposed synchronization (i.e., the frequency adaptive MHDC-PLL) can achieve a fast and accurate response under any grid disturbance and/or severe harmonic conditions.