DC Voltage Control of Multi-terminal MMC-HVDC Based on Virtual Synchronous Generator

With large-scale of renewable energy and power electronic devices connected to the grid, modular multilevel converter based high voltage DC (MMC-HVDC) systems exhibit low inertia and low damping characteristics. The virtual synchronous generator (VSG) control provides virtual inertia to the system and simultaneously improves its capability to damp oscillations by mimicking the mechanical characteristics of a synchronous generator (SG). To achieve stable control of DC voltage while providing AC frequency support, a DC voltage control method of multi-terminal MMC-HVDC based on VSG is proposed. The active power reference is provided to the active power-frequency regulator of VSG through an external DC voltage control loop, which greatly improves DC voltage stability and power-balancing performance of the system. The methods of PQ control and VSG control with and without DC voltage controller are applied to a four-terminal MMC-HVDC system respectively for simulation and the control performances are compared. Results show that the proposed DC voltage control method based on VSG can effectively balance the AC and DC side performances of the system.