Passivity characterization of grid-forming converters with fault-ride through capability

Due to the increase in the use of renewable energy sources (RES) and a corresponding reduction in the conventional energy generation systems, 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 at evaluating the impact of various control loops of 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 property are identified. A simplified analytical model has been derived in order to propose possible control modifications to enhance system’s passivity at various frequencies of interest and the findings are verified through detailed time-domain simulations and experiments.