Universal Modeling and Damping Analysis of Dual-Grid-Forming Control Methods

modular multilevel converter (MMC) based high-voltage direct current (HVDC) transmission systems are critical for integrating large-scale renewable energy into the grid. While ensuring stable grid connection, HVDC systems must also provide frequency and voltage support to the receiving-end grid, necessitating dual-grid-forming control. Currently, dual-grid-forming control methods for HVDC systems are primarily categorized as droop control and energy synchronization control. However, their damping characteristics remain underexplored. This paper develops frequency-domain models for the active power control loops of both methods and qualitatively analyzes their damping characteristics from a small-signal perspective, providing a theoretical foundation for controller design.