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

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.

An improved fault ride-through strategy for back-to-back MMC-Based VSCs in an inverter-dominated renewable energy system

“…DC energy dissipation devices will be triggered when the DC voltage exceeds its upper limit in case of short circuit fault [13]. Literature [14] proposes an overvoltage suppression strategy in fault transient process by reducing the power transfer at the sending end.…”

“…This configuration makes the VSCs vulnerable to overcurrent conditions, which may trigger tripping events in response to short circuit faults within the AC system. Investigations have been conducted on the suppression of fault current and overvoltage for flexible DC transmission systems [11][12][13][14][15][16]. Within the scope of these studies, particular attentions have been given to the transient fault ride-through capabilities for asymmetrical faults in back-to-back VSCs.…”

“…In order to suppress the negative sequence components in case of unbalanced operation, the negative sequence current reference value is directly established to be zero during short circuit faults [12]. In addition, the methods on addressing the overvoltage issues during low voltage ride-through (LVRT) process have been examined in [13][14].…”

Doubly Fed Induction Generator Low Voltage Ride Through Improvement Through Modular Multilevel Converter

“…An alternative to overcome these drawbacks and avoid hardware-based approaches is the use of multilevel converters for DFIG-based WECS LVRT improvement. Assuredly, multilevel power converters have recently improved robustness to electrical disturbances, lower THD, and fault tolerance [23]. In particular, the half-bridge MMC has reached broad relevance due to its flexible modular structure, easy expandability, and capacity to operate at high power levels, such as HVDC systems, photovoltaic, and WECS [24].…”

A Smart Fault-Tackling Strategy Based on PFTE for AC Three-Phase-to-Ground Faults in the Multi-Terminal HVDC Wind Power Integration System: Further Foundings

“…Modular multilevel converter (MMC)-based high voltage direct current (HVDC) technology can directly connect to weak AC systems and has no transmission distance limit and no risk of commutation failure [4,5]. To achieve further rational integration, distribution, and consumption of onshore wind power, the MMC-based, multi-terminal HVDC (MTDC) wind power integration system has received notable interest [6][7][8].…”