Impact of Synchronous Condensers on Small-Signal Stability of Offshore Wind Power Plants

Grid-forming (GFM) converter control technology and synchronous condensers (SCs) have both been reported to improve the overall stability of a power system. GFM technology is being considered for offshore wind power plants (OF WPPs) due to their stabilising effect, and SCs are being integrated into OF WPPs as they increase the short circuit level of the system. This paper investigates the effect of SCs on the small-signal stability of an OF WPP with different converter control strategies, namely grid-following (GFL) and grid-forming (GFM). Primarily, the effect of SCs can be two-fold: (1) overall stability enhancement of the WPP by providing reactive power support, and (2) contribution to the effective short circuit ratio (SCR) of the WPP by fault current support. Therefore, this paper focuses on studies concerning these effects on an aggregated model of a WPP connected to the grid. This paper also tries to compare the stabilising effects of GFM converters and SCs by comparing the small-signal stability of the test system with GFL control and SC and with GFM control. To that end, a state-space model of the test system is developed for small-signal stability assessment and the SC's effect on its stability. In addition, a mathematical explanation of SCR enhancement with an SC is provided and is verified against the fault MVA calculations done on time-domain simulation models.