Research on a Three-Phase Phase-Locked Loop Based on Improved SOGI-DDSRF

Under the trend of weak grid in the power system, traditional SRF-PLL can no longer meet the demand. At present, second-order generalized integrators (SOGI) are widely used to filter out harmonic pollution. However, traditional SOGI has no suppression effect on DC bias and its ability to suppress low order harmonics near the fundamental wave is limited according to its characteristics. DDSRF is widely used to extract positive and negative sequence components, but it is greatly affected by harmonics. This article proposes an improved dual synchronous coordinate system decoupling phase-locked loop and an improved second-order generalized integrator (SOGI) structure composite front-end PLL considering unbalanced operating conditions, harmonic pollution, DC bias, etc. Through the construction of a simulation platform, it is verified that the new phase-locked loop can effectively lock the frequency and phase of the fundamental voltage under complex operating conditions.