Estimation of synchronization signal using sinusoidal amplitude integrator in synchronous reference frame

Synchronization with the grid voltage is critical in the control of grid-connected converters Under unbalanced grid condition, the conventional synchronous reference frame PLL (SRF-PLL) does not work well due to the effect of the fundamental negative sequence component. This paper proposes a new synchronization method, which incorporates a sinusoidal amplitude integrator (SAI) into the conventional SRF-PLL. The proposed SAI-PLL method not only eradicates the effect of the fundamental negative sequence component, but also accurately and quickly estimates the amplitude and phase angle of the fundamental components in unbalanced and distorted conditions. Moreover, the proposed SAI-PLL successfully eliminates the influence of dc offset in the grid voltage. Simulation and experimental results demonstrate that the proposed PLL method can effectively extract the synchronization signal under unbalanced and distorted conditions.