Implementation and Stability Analysis of Synthetic Inertia for Inverter-Based Energy Resources

Abstract

Abstract Inverters are being integrated into power systems around the world at a rapid pace due to the shift from traditional energy sources to renewable sources such as wind and solar power. As the number of inverters increases, the inertia in the system with respect to the power level decreases. Since frequency stability in power systems heavily relies on the kinetic energy stored in rotating masses to provide inertia, such as synchronous generators which are now being partly phased out, it may become necessary for inverters to provide synthetic inertia as well. This thesis work includes the implementation of grid following and grid forming inverters together with an external grid of variable strength and an island grid constituted of a hydro power generator. The simulations are carried out in Matlab and Simulink. The implementation is based on the theory of existing methods and includes an important definition of synthetic inertia, namely that it is proportional to the rate of change of frequency. Contrary to fast frequency response which is proportional to frequency deviation. The models were then tested against grid frequency disturbances to analyze how aggressively the system could be tuned while still maintaining stability. The results showed that grid following inverters are highly dependent on the strength of the external grid, mainly because of their need to synchronize their own frequency with the grid. When operating in synthetic inertia mode, the grid following inverter stability region increased linearly between proportional gain and the filtering time constant. When providing active power based on frequency deviation, the stability decreased as the filtering increased. The grid forming inverter was highly dependent on its droop constant to remain stable where as the droop constant increased, the stability decreased.