Grid-Forming Control of Offshore Wind Farms Connected With Diode-Based HVdc Links Based on Remote Active Power Regulation

The connection of offshore wind farms (OWFs) via diode rectifier-based- high-voltage direct current (DR-HVdc) transmission requires the use of wind turbine (WT) converters with grid-forming (GFM) capability. However, active and reactive power coupling and oscillation issues have been revealed in WTs employing reactive power frequency (
Q/f
) droop-based control schemes. This paper proposes a GFM control for OWFs based on remote active power regulation. The proposed scheme remotely regulates the active power of the DR-HVdc link by adjusting the dc voltage of the onshore modular multilevel converter (MMC). As a result, the voltages of offshore point of common coupling and WT converters are freed from being controlled for active power. On this basis, the WT converters can be equipped with classical GFM control schemes that incorporate active power frequency (
P/f
) and reactive power voltage (
Q/V
) droop relationships. The offshore frequency acts as an indication of the OWF active power balance and it is measured and transmitted to the onshore MMC through a communication channel to close the remote active power control. Comparative studies of power coupling characteristics and stability reveal that the proposed control scheme can achieve efficient decoupling control of active and reactive power in WT converters, prevent oscillation risks, and significantly enhance the system's stability. The feasibility and advantages of the proposed control scheme are verified through comparative time-domain simulations.