Continuous Grid-Forming Control with Transient Current Limitation

This paper presents a current-limiting approach for grid-forming converters that does not require the switching to grid-following mode during current limitation, as compared to several other approaches. The control structure and its sub-controls are presented in detail. A time-domain case study with different grid configurations is used to analyse the dynamic behaviour of the control approach during and after disturbances. Especially the angular stability for parallel operation with synchronous generators and condensers and the operation in pure converter scenarios is investigated. Moreover, voltage support and returning to a post fault feedin steady state are considered more closely. It is shown that the proposed control leads to successful limitation of the bridge currents under small harmonic distortion. For the investigated grid and scenarios, an increase of stability reserve can be determined, in contrast to the reference scenarios with conventional synchronous machines. Furthermore, we show that this approach possibly has high potential for serving future fault detection and handling, by varying the current limit during fault.