Active Damping Control of Multi-port DC Power Flow Controller for Suppressing Power Oscillation of MMC-MTDC under Unbalanced Grid

DC power flow controller has become a key device for facilitating power flow in the modular multi-level converter based multi-terminal direct current (MMC-MTDC) transmission system. For extending the control function of multi-port DC power flow controller (M-DCPFC) to help improving the stability of MMC-MTDC transmission system, this paper proposes a novel control approach to calibrate the active damping control into the M-DCPFC. On the basis of achieving the power flow regulation, it can introduce additional virtual damping to the transmission line to suppress the DC-side power oscillations caused by unbalanced AC grid. The influence of unbalanced grid on the operation of MMC-MTDC transmission system is investigated and the damping control principle of M-DCPFC is presented. A four-terminal MMC-MTDC transmission system is developed in the real-time simulation test system based on RT-lab. The simulation results show the effectiveness of the proposed control strategy.