Impact of Grid Characteristics on the Damping of Converter-Driven Subsynchronous Oscillation Modes

This paper studies whether and how grid strength and grid impedance characteristics affect the damping of a critical oscillation mode caused by a large-scale wind farm. Damping can be regarded as one of the most significant grid properties, in terms of power system stability. It is well known that grid strength has a significant impact on the slow converter-driven stability. However, to the best of our knowledge, it is not well documented if grid strength and grid impedance characteristics affect the damping of converter-driven oscillatory modes. The topic is studied using a PSCAD model of a wind farm consisting of average model of grid-following (GFL) Type-4 wind turbines. The main findings provide insight into the impact a wind farm operation point and grid characteristics has on the damping of a converter-driven SSO (subsynchronous oscillation) mode, especially in weak grid conditions. The findings indicate that in weak grid conditions a small change in SCR could result in a rather large change in the damping of critical oscillation mode. This behaviour may cause challenges with power system operation regarding weaker grids with high penetration of IBRs. The findings also suggests that despite the grid impedance characteristics, the wind farm model is more exposed to low-damped SSO events when operated at high capacity. On the contrary, results show that the wind farm is able to operate in really weak grid conditions with decreased capacity while retaining a sufficient damping level.