Precise simulation models for weak grids

Energynautics starts converter modelling project for EirGrid

At the end of 2020, Energynautics, together with AFRY, Avasition and HickoryLedge, was commissioned by the Irish transmission system operator Eirgrid to develop generic, dynamic simulation models for PLLs (Phase Locked Loop) and grid forming converters.

At present, the Irish grid is already operated temporarily with very high share of converters – especially wind. Yet, the maximum share of converters in the current generation is limited to 65% (System Non-Synchronous Penetration, SNSP). However, this upper limit shall be increased gradually in the foreseeable future as the expansion of renewable energies increases. Extensive studies with realistic simulation models are necessary in order to guarantee secure grid operation even with such high converter penetration.

In the case of highly inverter-dominated grids, larger voltage fluctuations and a higher harmonics content can be expected. Conventional root mean square (RMS) models of wind turbines, for example, may not be suitable for representing these effects and their impact with sufficient accuracy. In particular, the behavior of the PLL, which provides the grid frequency for converter control, may be affected by low or distorted voltages.

In addition, in the power system of the future, with fewer synchronous generators, new control modes will be needed for converters to provide frequency and voltage to the grid. These grid forming converters and their behavior under the given grid conditions must also be modelled accurately.

In the current project, Energynautics and the project partners develop the required generic simulation models of a PLL and grid forming converters and validate them with measurement data. These simulation models, which behave realistically even under difficult grid conditions, will subsequently be used by Eirgrid in grid studies in combination with various generation plants. The software DSATools is used for all models and simulations.