Design- and simulation-based comparison of grid-forming converter control concepts

Until now, the textbook example of voltage source behavior along with the provision of inertia is the behavior of the synchronous generator (SG). This can be explained by the historical success of large scale electrification with AC power systems, which is closely linked to the SG. Therefore, previously SG-based electrical power systems face significant challenges due to the shift towards renewable energy sources (RES). Being generally converter-based, these do not provide essential stabilizing properties as SG do. Consequently, beyond a certain share of this kind of generation, interconnected power system stability is at stake. If, on the other hand, the previous paradigm of converter control is changed, then system operation without any SG is possible. To this end, the converters have to exhibit essential voltage source properties as SG do. Such converters are then referred to as grid-forming converters (GFC). However, the dynamic behavior of GFC is not defined by physical properties as in the case of SG. It is defined by the grid-forming control concept only, providing a high degree of freedom for possible implementations. Taking advantage of this freedom, a wide range of different, but partly also similar or even equivalent grid-forming control concepts have been developed in recent years. Therefore, in this paper, ten of today's most discussed control concepts are compared. In this comparison, unique features, similarities and equivalences of the control concepts are shown. The focus is on the instantaneous and stationary behavior of the control concepts, which is analysed by means of a system-theoretical and simulative analysis. The insights gained from this comparison can be helpful for the functional specification, development and improvement of GFC, as the variety of control concepts can be better understood.