Abstract
Multilevel voltage source converters(MLVSCs) have been widely applied in the medium voltage drive(MVD) industry. The performance of a MVD system is strongly dependent on the utilized topology. As of today, many interesting topologies have been proposed and evaluated in literature. In addition to proposing new topologies, another important research topic is the MLVSC topology derivation. In this paper, two topology derivation principles, i.e. horizontal conformation principle and vertical conformation principle, are proposed from the standpoint of modularity. In both principles, a MLVSC topology can be considered as a certain combination of one base switching cell and several module switching cells. With the proposed principle, the derived topology will naturally have modularity, which is favorable in practical applications. In addition, voltage level extension based on cascaded H-bridge building blocks(HBBBs) is also introduced. The challenging issues faced by the emerging topologies for MVD applications are also discussed. It is hoped that this paper can provide a new perspective on the MLVSC topology derivation and inspire new topologies in the future.
Highlights
Multilevel voltage source converters(MLVSCs) have been dominating in medium voltage drives (MVDs) due to merits like high quality output, reduced voltage stress on semiconductor devices, reduced switching frequency, and so on[1,2,3,4,5]
As seen from the table, popular topologies that have been commercialized in MVD industry, include cascaded H-bridge(CHB) converter and its modifications (e.g. NPC/H-bridge)[6,7,8], neutral point clamped (NPC) converter[9,10,11,12], neutral point piloted(NPP) converter[13,14,15], modular multilevel converter (MMC)[16,17,18], nested neutral point piloted(NNPP) converter[19,20], flying capacitor converter (FCC)[21,22,23], and five-level active NPC(5L ANPC) converter[24,25,26]
New topologies are coming out aiming at improving overall performances of MVD systems, for example the nested neutral point clamped(NNPC) converter[27], various new or modified 5L ANPC converters[28,29,30,31], dual flying capacitor(DFC) converter[32,33], and so forth
Summary
Multilevel voltage source converters(MLVSCs) have been dominating in medium voltage drives (MVDs) due to merits like high quality output, reduced voltage stress on semiconductor devices, reduced switching frequency, and so on[1,2,3,4,5]. As seen from the table, popular topologies that have been commercialized in MVD industry, include cascaded H-bridge(CHB) converter and its modifications (e.g. NPC/H-bridge)[6,7,8], neutral point clamped (NPC) converter[9,10,11,12], neutral point piloted(NPP) converter ( known as T type NPC converter)[13,14,15], modular multilevel converter (MMC)[16,17,18], nested neutral point piloted(NNPP) converter ( known as stacked multicell converter)[19,20], flying capacitor converter (FCC)[21,22,23], and five-level active NPC(5L ANPC) converter[24,25,26]. In the topologies mentioned above, one type of topologies can be referred as full DC bus topology[42], such as NPC, NPP, NNPP, 5L ANPC, NNPC, etc The topologies of these converters will be illustrated . The operation principle and waveforms of the considered MLVSCs are not presented
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