Performance assessment of grid-forming and grid-following converter-interfaced battery energy storage systems on frequency regulation in low-inertia power grids

Power systems with large shares of converter-interfaced renewables may be characterised by low grid inertia due to the lack of frequency containment provided by synchronous generators. Battery energy storage systems (BESSs), which can adjust their power output at much steeper ramping than conventional generation, are promising assets to restore suitable frequency regulation capacity levels. BESSs are typically connected to the grid with a power converter, which can be operated in either grid-forming or grid-following modes. This paper quantitatively assesses the impact of large-scale BESSs on the frequency containment of low inertia power grid and compares the performance of grid-forming and grid-following control modes. Numerical results are provided considering a detailed dynamic model of the IEEE 39-bus system where fully characterized models of stochastic demand and generation are taken into account. In order to assess the performance of the BESS control modes in a practical operative context, daily long simulations are considered where reserve levels for frequency containment and restoration are allocated considering the current practice of a transmission system operator in Europe. Numerical analyses on various metrics applied to grid frequency show that grid-forming outperforms grid-following converter control mode.