Active Damping of VSC-MTDC Grid Equipped With Interline Power Flow Controller

To ensure the secure operation of a multiterminal high-voltage DC (MTDC) grid, power flow controllers (PFCs) are deployed to regulate current distribution among different transmission lines. Besides power flow management, PFCs are envisioned to provide a range of functionalities such as stability enhancement, oscillation damping, and ancillary services to the host MTDC grid. This paper extends the functionality of PFC to provide active damping of MTDC grid current oscillations caused by dc-side resonance. Three simple and effective active compensators integrated with the control scheme of the PFC are proposed. A comprehensive small-signal model of the MTDC grid is developed. Eigenvalue and sensitivity analyses are conducted to evaluate the damping capability of the proposed compensators and assess their dynamic coupling with PFC control loops. Based on a detailed model of a five-terminal high-voltage dc grid, simulation results are provided to evaluate the performance and effectiveness of the proposed active compensators. The results showed the effectiveness of the proposed compensation schemes in increasing the damping of the MTDC grid and enhancing its dynamic response.