Modular Multilevel Converter for Low-Voltage Ride-Through Support in AC Networks

New grid-connected systems have imposed additional requirements regarding reliability, power quality, high levels of power processing capacity, and fault support, where power converters have a crucial role in fulfilling these requirements. Overcoming one of these challenges, this paper proposes a new alternative application to improve the low-voltage ride-through (LVRT) support based on the arm impedance employment of the modular multilevel converter (MMC) by attenuating the fault impacts, avoiding overcurrents and overvoltages. This proposal does not require additional hardware or control loops for LVRT support, only using PI controllers. This paper evaluates symmetrical and asymmetrical grid fault impacts on the converter DC side of four converter topologies: two-level voltage source converter topology (2L-VSC), neutral point clamped (NPC), MMC, and 2L-VSC equipped with a DC-chopper, employing the same control structure for the four topologies, highlighting that the MMC contributed better to LVRT improvement under severe grid conditions.

Automated summary

This paper proposes a new alternative application to improve LVRT support using the arm impedance of MMC, which successfully attenuates fault impacts. The proposal does not require additional hardware or control loops, only PI controllers are needed. Evaluation of four converter topologies shows that MMC contributes better to LVRT improvement under severe grid conditions.