Operational improvement of weak HVDC system with unified power flow controller

The paper presents an investigation of HVDC system behavior under variety of AC system conditions. The Effective Short Circuit Ratio (ESCR) of both converter terminals has been varied and faults introduced to understand the behaviour of HVDC system. It has been observed that the converter behavior deteriorates with low ESCR and power transfer may not take place as desired due to operational instability. However, under such scenario introduction of Unified Power Flow Controller (UPFC) as supplementary controller in the adjacent AC network certainly improves converter operation. The tuning of UPFC control parameters plays a predominant role for recovery after the faults in weak AC system conditions. Such studies, if conducted on regular basis in AC/DC network, may help the system operator for effective network operational planning with adequate control strategy. The effectiveness of UPFC in HVDC network has been critically examined from stabilization view point.