Experimental Stability Assessment of Converter-Dominated Electrical Grids

With the increased deployment of renewable energy devices into power systems, more converters controlled by the standard D-Q axis Current Injection (DQCI) theory have been connected to the grid, displacing synchronous generators in the process. Due to the nature of the DQCl strategy, these converters cannot impose a reference voltage and frequency. A study in the simulation environment has been done in [7] where it is shown that, for a certain limit of DQCl converters connected to the grid (or level of penetration of converters), system-wide stability can be compromised. This work presents an experimental equivalent study. It is shown that the main contributor to the system stability and the level of penetration for DQCI-controlled converters is not the active power injected by synchronous generators, but the nominal power of the generators. An alternative converter control strategy which transforms the converter into a real voltage source of energy is tested experimentally on this paper; it is shown that the use of a combination of both algorithms in large electrical grids can provide a robust grid based purely on converters.