Grid-Forming Capability Transfer and Active Power Flow Control in a VSC-HVDC System

Voltage-source-converter-based high-voltage direct current (VSC-HVDC) technology proves to be an efficient solution for renewable energy sources generation and long-distance power transmission. Conventionally, at least one port of VSC in the HVDC systems should operate in grid-following (GFL) mode to maintain system stability. By contrast, this paper investigates a full grid-forming (GFM) control method for both-ports of VSCs in the HVDC system, so that the HVDC system can bidirectionally support the dc line voltage and the ac grid voltage at all ports, i.e., bidirectional grid-forming capability transfer, and meanwhile actively control the active power flow. A full order state-space model is established to assess the small-signal stability of this method. The precision of active power control performance and the bidirectional grid-forming capability transfer are confirmed through several simulation cases.