Series Chain-Link Modular Multilevel AC–DC Converter (SCC) for HVDC Applications

Abstract

Introduction of the Modular Multilevel Converter (MMC) has enabled the exploitation of Voltage Source Converters (VSCs) in an increasing number of High Voltage Direct Current (HVDC) applications. Subsequently, some new topologies and solutions have been presented to tailor the MMC concept to specific uses. Particular attention has been paid to reduction of the converter footprint for applications where plant size is a critical economic aspect, for example, in off-shore installations.This paper introduces a new series connected modular multilevel ac/dc converter, the Series Chain-link Converter (SCC), which gives a significant reduction in the required number of submodules (SMs) and a more compact distribution of the energy storage, compared to an MMC. In the paper, the operating principle of the converter and its design are discussed in detail; the sub-module count and energy storage requirement are also given. The basic control loops required for the practical operation of the converter are presented and designed. The SCC concept has been experimentally validated on a small-scale 450V dc, 415V ac, 4.5kVA laboratory prototype, confirming the practical viability of the topology.

Enhanced Modular Multilevel Converter for HVdc Applications: Assessments of Dynamic and Transient Responses to AC and DC Faults

“…Synthesis of the output ac voltage, currents, common-mode and circulating currents in the EMMC are similar to that in the conventional MMC [20]. Fundamentally, maintaining balanced or constant cell capacitor voltages necessitates zero energy exchange with the ac or dc sides as described in (19) and (20).…”

“…The second group of hybrid converters mixes the basic building blocks of MMC such as the HB and FB chain-links or whole MMC power circuits with so called director switches (which are formed by series connected thyristors or IGBT) [14], [15]. Although the latter group compromises system modularity compared to the former, they offer a range of advantages, from nearly doubling the power extraction compared to that of the MMC, to bipolar dc voltage operation with semiconductor losses similar to that of the HB-MMC [16]- [19].…”

A Hybrid Chain-Link Push-Pull Series Connected (H-CL-P2SC) M2C with DC Fault Blocking Capability

“…The purpose of the inter-phase balancing is to ensure that the power balance between three phases is achieved. A method to balance power between the three series connected phases in [17] is used in this paper. When the power between two phases is balanced, the third phase is automatically balanced as the dc voltage correction terms generated by these controllers u k dc corr sum up to zero as shown in Fig.…”

Novel Multirate Modulator for High-Bandwidth Multicell Converters

“…This wide range of end-uses imply in different requirements for each deployment of the technology. Thus, numerous converter configurations exist [8]- [13], as the wellknown neutral point clamped (NPC) [14], the flying capacitor (FC) [15] and the cascaded H-bridge [16] topologies and others as the clamp-double [17] and double-zero [18] converters, each with its particularities.…”