Stationary-Frame Grid-Forming Inverter Control Architectures for Unbalanced Fault-Current Limiting

Abstract

Grid-forming (GFM) control offers promising performance features for inverter-based resources (IBRs) across scales. However, design, analysis, and benchmarking of GFM IBRs during unbalanced faults remains largely unexplored. In this paper, we outline a stationary-reference-frame nested-loop control architecture for GFM IBRs and integrate the same with novel current-limiting strategies. The architecture improves on virtual-impedance and current-reference-saturation limiting as well as state-of-the-art methods for control of voltage-source inverters. Electromagnetic-transient simulations for a modified IEEE 14-bus network validate salient features of the proposed control architectures. The proposed virtual-impedance limiter is shown to provide better voltage support during faults than the current-reference-saturation limiter (quantified via sequence voltages). On the other hand, the current-reference-saturation limiter offers better (and more accurate) fault-current contribution.

Improving voltage imbalance in inverter‐based islanded microgrids during line‐to‐line short circuits

“…In addition, the impedance seen at the output of each inverter is usually different, so the output current of the inverters will be also different. To avoid this behaviour, an adaptive control based on a variable resistance R adapt ,i (t ) is adopted in [26][27][28][29]:…”

“…In this case, the voltage control loop is responsible for enforcing the virtual impedance-based current limitation. Finally, the last control schemes are made up of techniques that combine solutions belonging to the first two control approaches [26][27][28][29]. From an implementation point of view, some of the above techniques are written in natural reference frame (abc) [18], in synchronous reference frame (dq) [19-21, 23, 24] or in stationary reference frame (αβ) [22,[25][26][27][28][29].…”

“…Finally, the last control schemes are made up of techniques that combine solutions belonging to the first two control approaches [26][27][28][29]. From an implementation point of view, some of the above techniques are written in natural reference frame (abc) [18], in synchronous reference frame (dq) [19-21, 23, 24] or in stationary reference frame (αβ) [22,[25][26][27][28][29]. All these controls make it possible to adequately limit the output current of grid-forming inverters in case of overcurrent.…”

“…All these controls make it possible to adequately limit the output current of grid-forming inverters in case of overcurrent. This work focuses on current limiting algorithms in the αβ frame due to their excellent dynamics in different scenarios, which is characterized by being fast and accurate [28,29].…”

Control of Grid-Forming VSCs: A Perspective of Adaptive Fast/Slow Internal Voltage Source

“…On top of the small-signal stability, control of GFM-VSC under large grid disturbances, including voltage sags, phaseangle jumps, high rate of change of frequency (RoCoF), and the combination thereof, is also of concern. Except for current limitation [8]- [10], GFM-VSCs should also remain synchronism with the grid (i.e., transient stability) during and H. Wu is with the AAU Energy, Aalborg University, 9220 Aalborg, Denmark (e-mail:, hew@energy.aau.dk).…”