An Improved Multiport DC Power Flow Controller for VSC-MTDC Grids

As a key device to facilitate power flow in the multi-terminal direct current (MTDC) transmission system, DC power flow controller (DCPFC) can effectively expand the power flow regulation area by implementing its multiport output functionality. In order to solve the coupling issue between the transmission line current and the capacitor voltage of the inter-line multiport DCPFC (M-DCPFC), an improved M-DCPFC with a partial power rated auxiliary DC/DC converter unit is proposed in this paper. It provides the advantages of power flow reversal, high adjustment flexibility and low port-expansion cost. Meanwhile, a generic control strategy is developed for the M-DCPFC with random number of the ports. Moreover, from the perspective of the transmission system, the proposed M-DCPFC is modeled as the equivalent series voltage source. Its power flow adjustment capability and its impact on the local voltage source converter (VSC) stations are investigated in detail in this paper. Lastly, to validate the effectiveness of the proposed M-DCPFC, it is first tested in the simulations of the MATLAB/Simulink and then deployed on an experiment platform. Both simulation and experimental results show that the proposed M-DCPFC can achieve stable power flow control in different conditions.