A power flow controller (PFC) may be needed to control the currents and power transmitted in the transmission lines in a highly meshed HVDC system. The paper presents a new and simple topology for series interline PFC for a simple 3 terminal HVDC system. Interline PFCs do not need an external power supply to change the current distribution in the HVDC system. The performance of the proposed PFC during steady state operation and ground faults is analyzed in detail using PLECS software. A protection circuit and its design aspects are also proposed for ground faults on one of the cables.