DC Fault Management Strategy for Continuous Operation of HVDC Grids Based on Customized Hybrid MMC

Abstract

Successful deployment of High-Voltage Direct Current (HVDC) grids necessitates effective DC fault handling strategies, which can minimize the severe consequences caused by DC faults on the AC and DC side of the HVDC grids. Therefore, this paper investigates the enhanced DC fault performance of the Customized Hybrid Modular Multilevel Converter (CH-MMC), in which a limited number of full-bridge sub-modules (FB-SMs) is added into the arms of the conventional MMC in an effort to significantly extend the timespan between fault inception and fault clearance, thus allowing the use of relatively slow and cheaper DC circuit breakers. Based on this converter, a dedicated DC fault handling strategy for CH-MMC based HVDC grids is proposed, which aims to improve the fault resiliency and security of HVDC grids for pole-to-pole faults. Moreover, the proposed DC fault management strategy guarantees the continuous operation of the grid during pole-to-ground DC faults, including full reactive power provision from the converter stations. The performance of the strategy is demonstrated using comprehensive electromagnetic transient (EMT) simulation studies conducted on an illustrative four-terminal meshed HVDC grid, which consider a range of scenarios with different fault current limiting inductors and DC circuit breaker operation times.

An Auxiliary Circuit Enhancing DC Fault Clearing Capability of Hybrid MMCs With Low Proportion of FB-SMs

“…η can be chosen according to the mean value of umax. According to (1), ( 5), (7), the expected η is in (11). If the modulation index is 0.85, the expected η will be 35%, which is lower than the traditional value (50%).…”

“…At the same time, large ac inductors should be used at the converter valve-side to limit arm currents during the fault clearing period. In [11], the proportion of FB-SMs is reduced at the expense of increased FB-SM capacitor voltage and dc fault clearing time, which may threaten the security of the converter. In [12], thyristors and metal oxide varistors (MOVs) are employed to adjust the converter terminal dc current decreasing rate.…”

Semi‐hot redundant control method for modular multilevel converter‐based high‐voltage direct current systems under submodules fault

“…Considering the DC‐side short‐circuit fault self‐clearing ability, MMC systems with novel SM topologies or hybrid SM topologies have attracted considerable research attention [35–39]. Considering the system cost and control complexity, this study focuses on a hybrid MMC with HBSMs and SDSMs.…”

“…Considering the DC-side short-circuit fault self-clearing ability, MMC systems with novel SM topologies or hybrid SM topologies have attracted considerable research attention [35][36][37][38][39].…”

Multi‐vendor interoperability in HVDC grid protection: State‐of‐the‐art and challenges ahead

“…High‐speed DCCBs are likely to require smaller limiting inductances while ensure continuous operation of the HVDC grid during DC faults [96, 98]. Recent work focuses on (i) optimizing DCCB parameters coordinating with converter DC fault‐ride‐through requirements (DC‐FRT) [97, 98], (ii) coordinating fault clearing with pole voltage rebalancing in symmetrical monopolar systems [26, 27], (iii) novel DCCB technology, such as unidirectional DCCBs [100] and (vi) using the current control capability of hybrid MMCs to reduce the required speed, breaking capability and/or energy dissipation capability [55, 101, 102].…”