VSG-Based Active Support Strategy for Grid-Forming VSC-HVDC

As renewable generation and power-electronic interfaces account for a growing share of power systems, reduced system inertia and weakened voltage support place greater demands on the stable operation of weak and passive networks. This paper proposes a virtual synchronous generator (VSG)-based active support strategy for grid-forming voltage source converter-based high-voltage direct-current (VSC-HVDC) systems. First, the power-balance relationship between the converter station and the synchronous generator is analyzed to establish the basis for VSG control. For active-power–frequency regulation, a virtual zero-error frequency regulation (VZFR) strategy is proposed by introducing an additional power compensation term into the conventional VSG control, improving frequency recovery while retaining virtual inertia and damping. For voltage–reactive-power regulation, the transient voltage support mechanism is analyzed in two stages: the controlled voltage-source characteristic and virtual impedance provide initial voltage support, while the reactive-power–voltage loop subsequently regulates the internal voltage and reactive power output. PSCAD/EMTDC simulations under active load disturbances and different grid voltage sags show that the proposed strategy enhances both frequency regulation and voltage support provided by the VSC-HVDC system.