Frequency Support from Grid Forming Inverters: A Power-Domain Impedance Perspective

The modelling and analysis of the frequency and voltage dynamic behaviour of power systems is becoming increasingly challenging due to the complex interactions between the power electronics based sources and the rest of the complex power system. In this paper, a novel modelling framework based on power-domain impedance theory is proposed to facilitate the characterisation of the frequency and voltage dynamic behaviour of a particular node of a complex power system, including the dynamic interaction of power electronic inverters. Furthermore, considering the pivotal role of grid-forming (GFM) inverters in future grids, the power-domain impedance model of a GFM inverter is derived and the proposed framework is used as a tool to explore the possibilities of improving the frequency-dynamic behaviour of the grid using GFM inverters. The framework is shown to indicate the feasibility of a series of frequency support strategies further characterising the cases where such strategies are effective or not. The result of the analysis is used to propose an enhanced GFM frequency support control strategy based on a power-domain impedance shaping perspective. The presented theoretical framework, impedance model and proposed control strategy are validated through a case study and experimental tests.