Dc Network Faults Research Articles

A Novel Converter Station Structure for Improving Multiterminal HVDC System Resiliency Against AC and DC Faults

In an effort to minimize the power disruption between a dc grid and ac grids that host power converters during ac and dc network faults, this paper proposes a novel converter station structure to improve ac and dc fault ride-through performance of the multiterminal HVdc grid. The proposed structure consists of two independent ac and dc interfacing circuits, which are a half-bridge modular multilevel converter and a cascaded H-bridge (CHB) based energy storage system. Taking the advantages of high controllability and flexibility of the independent CHB converter and ease of integrating energy modules, a decoupled power relationship between the ac and dc sides is achieved, which is important for enhancing ac and dc fault performance. Operation of the proposed converter station under normal conditions and during ac and dc faults is explained, with the control system presented. Simulation validation of the proposed structure on a three-terminal HVdc grid confirms the enhanced performance, including the continuous operation during ac and dc faults with negligible power transfer disruption.

Multi‐pole voltage source converter HVDC transmission systems

This study connects several modular multilevel converters to form multi-pole voltage source converter highvoltage dc (VSC-HVDC) links which are suited for bulk power evacuation, with increased resiliency to ac and dc network faults. The proposed arrangements resemble symmetrical and asymmetrical HVDC links that can be used for bulk power transfer over long distances with reduced transmission losses, and for the creation of multi-terminal supergrids currently being promoted for transitional dc grids in Europe. The technical feasibility of the proposed systems is assessed using simulations on symmetrical and asymmetrical tri-pole VSC-HVDC links, including the case of permanent pole-to-ground dc faults.

Impact of HVDC Transmission System Topology on Multiterminal DC Network Faults

This paper compares how a dc fault affects a multiterminal dc (MTdc) network depending on the HVDC transmission system topology. To this end, a six-step methodology is proposed for the selection of the necessary dc fault protection measures. The network consists of four voltage-source converters converters radially connected. The converters natural fault response to a dc fault for the different topologies is studied using dynamic simulation models. For clearing of the dc faults, four different dc breaker technologies are compared based on their fault interruption time, together with a current direction fault detection method. If necessary, the converters are reinforced with limiting reactors to decrease the peak value and rate of rise of the fault currents providing sufficient time for the breakers to isolate the fault without interrupting the MTdc network operation. The study shows that the symmetric monopolar topology is least affected by dc contingencies. Considering bipolar topologies, the bipolar with metallic return exhibits better fault response compared to the one with ground return. Topologies with ground or metallic return require full semiconductor or hybrid breakers with reactors to successfully isolate a dc fault.

Half- and Full-Bridge Modular Multilevel Converter Models for Simulations of Full-Scale HVDC Links and Multiterminal DC Grids

This paper presents an improved electromagnetic transient (EMT) simulation model for the half- and full-bridge modular multilevel converters (MMCs) that can be used for full-scale simulation of multilevel high-voltage dc (HVDC) transmission systems, with hundreds of cells per arm. The presented models employ minimum software overhead within their EMT parts to correctly represent MMCs behavior during dc network faults when converter switching devices are blocked. The validity and scalabilities of the presented models are demonstrated using open-loop simulations of the half- and full-bridge MMCs, and closed-loop simulation of a full-scale HVDC link, with 201 cells per arm that equipped with basic HVDC controllers, including that for suppression of the second harmonic currents in the converter arms. The results obtained from both demonstrations have shown that the presented models are able to accurately simulate the typical behavior of the MMC during normal, and ac and dc network faults.

New emerging voltage source converter for high‐voltage application: hybrid multilevel converter with dc side H‐bridge chain links

Hybrid multilevel converters (HMCs) are more attractive than the traditional multilevel converters, such as modular converters, because they offer all the features needed in a modern voltage source converter-based dc transmission system with reduced size and weight, at a competitive level of semiconductor losses. Therefore this study investigates the viability of a HMC that uses dc side H-bridge chain links, for high-voltage dc and flexible ac transmission systems. In addition, its operating principle, modulation and capacitor voltage balancing, and control are investigated. This study focuses on response of this HMC to ac and dc network faults, with special attention paid to device issues that may arise under extreme network faults. Therefore the HMC with dc side chain links is simulated as one station of point-to-point dc transmission system that operates in an inversion mode, with all the necessary control systems incorporated. The major results and findings of subjecting this version of the hybrid converter to ac and dc networks faults are presented and discussed.

Interoperability of voltage source converters in dc grids

This study examines the possibility of operating different voltage source converter topologies in high-voltage direct current grids. The investigation is motivated by growing concern from the utility companies and transmission system operators regarding the compatibility of these converters, especially the behaviour of resultant multi-vendor dc grids during ac and dc network faults. In an attempt to establish the credibility of the expressed concerns, the transient response of illustrative multi-vendor six-terminal dc grids that consists of four two-level converters, a two-switch modular converter and a H-bridge modular converter are examined during ac and dc network faults. The main results obtained and observations drawn are highlighted and discussed.

Hybrid converter with ac side cascaded H‐bridge cells against H‐bridge alternative arm modular multilevel converter: steady‐state and dynamic performance

This study explorers the operating principles of the hybrid converter with ac side cascaded H-bridge cells and the H-bridge alternative arm modular multilevel converter, where the main objective is to compare their steady-state and transient performance. This comparison focuses on steady-state aspects such as active and reactive power control and semi-conductor losses and the transient performance of these converters during ac and dc network faults. To facilitate this comparison, detailed switch models of both high-voltage direct current (HVDC) converters are developed and simulated in Matlab-Simulink. The major outcomes are discussed and strengths and weakness associated with each converter are highlighted.