Coordinated Operation of Dual-Port Grid-Forming HVDC Unit and E-STATCOM for Damping and Inertia Provision

Dual-port grid-forming control enables simultaneous ac and dc voltage regulation for modular multilevel converters (MMCs) connecting the HVDC transmission line to the ac network. However, its ability to provide damping and inertial power is inherently constrained by the limited internal energy capacity of the converter. To address such limitation, this paper proposes the coordinated operation of a static synchronous compensator with energy storage (E-STATCOM) in parallel with a dual-port grid-forming HVDC-connected offshore wind farm, which enhances converter stability and performance while preserving optimal wind farm operation. Additionally, a new stabilization mechanism is introduced within the MMC's dual-port grid-forming control. This improves the dynamic performance and ensures stable operation even in the absence of additional support. In the numerical example considered, the proposed system enhances the rate of change of frequency after an ac load connection from -0.64 Hz/s to -0.32 Hz/s. It also reduces the standard deviation of the power output fluctuations by 57%, filtering oscillations above 0.5 Hz. Moreover, it decouples dc voltage control from MMC internal energy, ensuring partial firewalling of the dc grid during ac contingencies. Experimental validation demonstrated good agreement with simulations, confirming the potential of coordinated control strategies to enhance stability, inertia provision, and flexibility in future offshore wind power systems.