ABSTRACT As the penetration rate of renewable energy represented by photovoltaic (PV) power in power systems continues to increase, the synchronisation stability of grid‐connected inverters under weak‐grid conditions faces severe challenges. The double second‐order generalised integrator–based phase‐locked loop (DSOGI‐PLL), a key technology for grid‐connected control in weak grids, exhibits excellent harmonic suppression capability. However, when significant fluctuations occur in grid frequency or voltage, its dynamic response and phase‐tracking accuracy are significantly affected, even threatening the stable operation of the system. Analysis indicates that one of the key issues leading to the performance degradation of the DSOGI‐PLL in weak grids is the lack of a fast and accurate frequency estimation. To address this, after comparing three frequency estimation methods—namely, the output frequency of the PLL itself, the grid‐voltage zero‐crossing detection frequency and the adaptive notch filter frequency—this paper proposes a multisource frequency fusion and adaptive damping DSOGI‐PLL (MSFFAD‐DSOGI‐PLL). By analysing the harmonic content and frequency deviation of the power grid, the proposed method adaptively weight‐fuses the results of the above three frequency estimation approaches and corrects the resonant centre frequency of the DSOGI in real time. On this basis, to balance the dynamic response and steady‐state accuracy of the system under different operating conditions, an adaptive damping adjustment mechanism based on fuzzy logic linearisation is designed to achieve stable operation over a wide voltage/frequency range. Finally, experimental results demonstrate that compared with the traditional DSOGI‐PLL, the proposed method exhibits stronger robustness and higher tracking accuracy under complex grid conditions such as large‐range fluctuations in grid frequency and voltage.
Yu et al. (Thu,) studied this question.