A Blind Spot in the LVRT Current Requirements of Modern Grid Codes for Inverter-Based Resources

Modern grid codes (GCs) require that inverter-based resources (IBRs) inject both positive- and negative-sequence currents during asymmetrical low-voltage ride through (LVRT) conditions. This GC provision prioritizes the reactive currents and also demands maximizing the active positive-sequence current if the IBR has unused current generation capacity when the required reactive current is generated. A variety of inverter control schemes are available to generate positive- and negative-sequence active/reactive currents, and satisfying these GCs seems to be straightforward. However, this paper reveals that the reference current generation methods of existing inverter control schemes fail to fulfil some important requirements of recent GCs. For example, they do not fully utilize the inverter capacity to generate the maximum active and/or reactive current. It is shown that these so-far hidden GC violations can result in a large untapped generation capacity during asymmetrical faults. This paper also develops an algorithm that satisfies recent GCs by deriving the positive- and negative-sequence currents that maximize the IBR's reactive and active currents while the reactive current is prioritized. The simulation of a grid with high IBR penetration verifies that this new algorithm can unlock the full potential of recent GCs by significantly increasing the power generated during LVRT.