Universal Grid-forming Method for Future Power Systems

Abstract

Power system inertia typically refers to the energy stored in large rotating synchronous generators. Dynamics and stability of the traditional power system is closely linked to the natural inertia of these synchronous generators. In recent years, increasing amount of synchronous generators have been replaced by high amount of different type of inverter-based generating units connected at different voltage levels of the power system. Therefore, the dynamics and stability of future low-inertia power systems will be increasingly dominated by the control and synchronization of these inverter-based resources. One essential issue is that the typical grid-following control with phase-locked-loop (PLL) -based synchronization of inverter-based generation is not enough to guarantee frequency stability in future low-inertia power systems. Therefore, different grid-forming inverter control and synchronization methods have been proposed and developed. Currently there does not exist any universal grid-forming control and synchronization method. Therefore, this paper tries to propose a new universal frequency-locked-loop (U-FLL) -based synchronization method which is grid-forming for inverter-based generating units and grid-supporting for inverter-based loads. Advantageous operation of the new U-FLL synchronization and control strategy is confirmed by multiple simulations with different shares of inverter-based resources and synchronous generators in MV and HV hybrid power systems as well as with 100 % inverter-based LV, MV and HV networks.