An IGBT based series power flow controller for multi-terminal HVDC transmission

Increased offshore wind penetration has raised the need of multi-terminal high-voltage direct-current (MTDC) grids. An MTDC system will enable cross-border energy exchange where the excessive energy can be transferred between countries, increasing the functionality and reliability of the network. However, as the number of terminals and branches increases, power flow management becomes a challenge. To improve reliability and efficiency, power flow needs to be rescheduled between terminals. This can be achieved by introducing a power flow controller (PFC). In this paper, an insulated-gate bipolar transistor based series PFC is proposed. A PFC is basically a low power rated controllable voltage source connected in series with a DC line. It enables the regulation of grid power flow via a small series voltage injection. A four-terminal MTDC system is modelled using Simulink/ SimPowerSystems to test the impact of the proposed device. This is analysed under two different control strategies for the voltage source converter-based terminals; namely, master-slave and voltage droop control. Simulation results show that the PFC is capable of enhancing the system performance by suitably redirecting the power flow at the point of connection. Moreover, the results clearly illustrate that the converter control modes effectively affect the power flow in the MTDC grid.