A Family of Symmetrical Integrated Synchronizations for Grid-Following and Grid-Forming Inverters

Grid-following (GFL) and grid-forming (GFM) inverters are usually synchronized with the phase-locked loop and the power synchronization control respectively, and they exhibit complementary characteristics on the grid strength adaptability. How to make the best of two synchronization approaches and endow the system with superior grid strength adaptivity and transient stability, remains a significant yet unsolved challenge. Based on their structural similarity and duality, this paper proposes a family of novel integrated synchronizations, which are in a symmetric and elegant form. The interaction between the integrated synchronization and other control parts is described by evolving the complex system into a simple single-input-single-output model. On its basis, comprehensive small-signal and transient stability analysis reveals that the proposed synchronization methods can ensure the robust operation of inverters and enhance their tolerance to severe faults.