Grid-forming (GFM) converters are a promising solution to enable large scale integration of renewable energy sources into the power system. However, due to the intrinsic voltage-source behaviour of GFM converters, current limitation during large grid disturbances is challenging. This paper presents a novel limitation strategy that preserves the GFM properties of the converter and at the same time effectively limits the converter current to the desired value. Through the limitation of the converter's internal voltage, stable operation even during faults and in case of large frequency disturbances in the grid is achieved. Experimental results show the effectiveness of the proposed current limitation strategy in case of various grid disturbances.

The aim of this paper is to present a grid-forming (GFM) control strategy with a novel active-power loop (APL) structure facilitating limitation of active power while providing maximum available inertial support. This is achieved by decoupling the synchronization duties of the APL from the inertial support. The latter is provided by calculating the active-power reference through a dedicated inertia-emulation loop (IEL), which is connected in cascade with the APL. The effectiveness of the proposed method is demonstrated through laboratory experiments including frequency transients of varying size and unbalanced operating conditions.

Due to the increasing integration of renewable energy sources (RES) and a corresponding reduction of conventional generating units, there is nowadays a demand from the power-electronic converters to provide grid-forming properties through proper control of the converter systems. This paper aims to evaluate the impact of various control loops in a grid-forming control strategy equipped with a fault-ride through capability on the passivity properties of the converter system. Through the analysis of the frequency-dependent input admittance of the converter, the main factors affecting the passivity properties are identified. A simplified analytical model is derived in order to propose possible control modifications to enhance the system’s passivity at various frequencies of interest and the findings are validated through detailed time-domain simulations and experimental tests.