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Abstract
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.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
The 3L-modular multilevel converter (MMC) presented the best performance, reducing by approximately 42.85% the overvoltage level and 50% the overcurrent level compared to the 2L-VSC with and without the DC chopper and the 3L-neutral point clamped (NPC); double line-to-ground (DLG) fault: Vbus reached a maximum of 617 V, while ICC reached a maximum of 8 A, representing an increase of 2.83- and 2.28-times the steady-state value, respectively;
This paper presented a new application proposal to improve the low-voltage ridethrough in grid-connected systems based on the modular multilevel converter impedance fault current damping capability
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Unlike the aforementioned state-of-the-art solutions, no additional hardware or control loop modification is required because the MMC arm impedance can use its fault-damping capability, reducing the overcurrents and overvoltages, besides maintaining controllability and protecting the power converter. No additional hardware; no complex control loops; avoids DC bus overvoltages under LVRT; avoids overcurrents under LVRT; expandable modular structure. XMMC arm impedance for overcurrent and overvoltage suppression under LVRT; Xavoids the protection activation; Xsupports the grid connection under LVRT; Xmaintains the controllability of the power converter. This standalone solution disregards the protection and controller response time, acting instantaneously under LVRT. This paper evaluated the performance of fourconverter topologies under symmetrical and asymmetrical faults: 3L-MMC, 2L-VSC, 3LNPC, and 2L-VSC equipped with a DC chopper
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