Experimental stability assessment of converter-dominated electrical grids

With the inclusion of renewable generation into the electrical grid, traditional fossil-fueled plants based on synchronous generators have been gradually replaced by converterbased systems, controlled using the standard vectorial current control (DQCI). From the grid point of view, this control strategy makes converter behave as current sources that inject power to the grid but have limited magnitude or angle voltage regulation. The shortage of this task implies a detriment of the stability of key parameters for a stable grid, exposing the system to huge diversions of frequency and voltage. Ultimately, this can make generators to disconnect, compromising with it the stability of the whole system thanks to a cascade failure. However, as it will be seen in this paper, it is possible to transform the converter into a real regulating voltage source changing just the control algorithm. Thanks to this change, same converters can create now reference nodes (also called grid building nodes) in the grid which DQCI converters can follow. This scheme would allow the possibility to a robust system based completely on converters. This scenario is object of test in this paper where a power quality and stability assessment is conducted in the lab.