On the assessment of the impact of a conventional HVDC on a test power system

There are several possibilities to improve the first swing transient stability in a power system. One adequate option is to use the high controllability of the HVDC if HVDC is available in the system. This paper presents a control strategy for HVDC to improve the first swing transient. The strategy controls the power through the HVDC to make the system more transient stable during disturbances. The proposed control strategy consists of the PD-controller and feed-forward control, the use of a PD-controller is appropriate since it has the property of fast response. To improve the first swing oscillation even more the feed-forward control is used, since the behavior of system due to the disconnection is known. Two bench mark power systems are subjected to large disturbances to examine the effectiveness of the proposed strategy. Depending on how the power through the HVDC is controlled the transients damp differently. The PD-controller works well and damps the first swing oscillation transient so the system remains stable. When a power step also is applied after the line is disconnected, the transient swing becomes lower and the behaviour of the system is better. There is also a possibility to improve the first swing oscillation even more, by applying a power step through the HVDC which will compensate for the lack of power due to the disconnection of the line caused by the disturbance.