Effects of Network Parameters on Large-Signal Interaction Between Grid-Forming and Grid-Following Converters

Power electronics converters connected to power grids can exhibit distinct synchronization behavior due to their diverse control methods. This diversity leads to complex interaction between multiple grid-connected converters. Although some recent studies have assessed the synchronization stability of two-converter systems, they primarily focus on the effects of controller parameters and often yield results similar to those observed in single-converter systems. In this paper, we reveal the non-trivial effects of network parameters on the interaction of grid-forming and grid-following converters. Recognizing the power grid as an essential part of interaction, we consider a star network comprising two converters and the grid. We derive two specific models corresponding to scenarios with distinct relative electrical distances. Using these models, we reveal that the grid-following converter can synchronize with the grid-forming converter or the grid. We identify two primary types of sub-synchronous oscillations as a practical effect of the two interaction modes. To elucidate the evolvement of the interaction modes, we analyze the bifurcation behavior of the system as network characteristics vary. The results underline the crucial role of the network in shaping the converter interaction. We validate the findings through numerical trajectories and full-circuit simulation.