Hybrid Cascaded Modular Multilevel Converter With DC Fault Ride-Through Capability for the HVDC Transmission System

DC fault isolation study of bidirectional dual active bridge DC/DC converter for DC transmission grid application

“…This is due to DC fault susceptibility of voltage source converters (VSC) in HVDC transmissions [2]. In the event of DC fault at the converter terminals or along the DC line, the VSC converter functions as uncontrolled rectifier diode, thereby resulting in unacceptable level of fault current flowing through the freewheeling diodes, even when all the IGBTs are switched off.…”

“…But the limiter fault current varies with the condition of the AC grid and the location of the fault along the line [9]. Fault current isolation at VSC level for both two level and modular multilevel (MMC) VSC converters with fault current blocking capability is undergoing extensive research [2,10,11]. [10,11], presented MMC converters with DC reverse blocking capability.…”

“…[10,11], presented MMC converters with DC reverse blocking capability. But with both two level and MMC based VSC converters, a high magnitude inrush current stress is experienced by the switches when the fault is cleared due uncontrolled instant charging of the long DC cables [2]. A hybrid cascaded MMC converter is addressed in [2], that can reduce the extreme inrush currents, provide AC and DC fault ride through, but at significant capital cost and large foot print due to additional AC side cascaded full bridge chain links.…”

Pole-to-Ground Fault Analysis and Fast Protection Scheme for HVDC Based on Overhead Transmission Lines

“…Firstly, overhead lines have a high line fault rate compared with cable lines, which is one of the main causes of DC system outages [9]. Secondly, considering that the DC power grid is a "low inertia" system, the fault current could rise steeply and the entire grid would be affected instantly after a fault [10], so a fast DC line protection scheme is required [11]. Thirdly, to ensure the selectivity and sensitivity of the protection scheme in complex network structures is a great challenge.…”

Full bridge MMC converter optimal design to HVDC operational requirements

“…Several topologies of DC fault tolerant MMC have been reported in the literature [9] - [18], such as the MMC using the clamp double submodules [9], the hybrid cascaded multilevel converter (HCMC) [10], the alternate arm converter [11], a series connected double sub-module [12], the cross-connected half-bridge submodules [13], the hybrid MMC with HB submodules at the DC side and FB submodules at the AC side [14]- [15], the MMC based on unipolar voltage full-bridge SM and three-level cross-connected SM [16], the MMC based on FB (full bridge) submodules [9], [17]- [18] and the MMC with mixed HB submodules and FB submodules [19]- [21]. Among all these DC fault tolerant MMCs, the MMC based on FB submodules (including the mixed submodules MMC) is the only commercially available fault tolerant technology for HVDC application.…”