Voltage Phasor Based Current Limiting for Grid-Forming Converters

In order to ensure reliable power supply and stable grid operation in future, predominantly distributed power grids, a trend to increase the grid-forming capability of distributed converters has been proposed [1]. Besides grid-forming control methods, an appropriate current limiting is required which, on the one hand, protects the converter against undesired over-currents for all present scenarios (e.g. fault ride through (FRT), significant frequency and phase angle fluctuations) and, on the other hand, does not affect normal operation. This paper presents a current limiting method for grid-forming power converters based on limiting the provided voltage phasor of the grid-forming control in a defined area with respect to the measured output voltage phasor. The permissible area is derived from the internal impedance and in addition allows the prioritization of different quantities (e.g. active and reactive power). In a laboratory test setup, the current limiting method is verified for symmetrical LVRT, phase angle jump as well as defined frequency changes.