This paper proposes a novel 49-level stacked inverter topology for drives. The 49 levels are achieved by stacking three 17-level inverters. Each of the 17-level inverter is developed by cascading a ...flying capacitor (FC) inverter with three capacitor-fed H-bridges. The device count can be reduced by making the FC and the three cascaded H-bridges common to the dc link in each phase using selector switches in between them. The selector switches need to operate at fundamental frequency only. Also, the devices need to block very low voltages. Hence, MOSFETs can be used. This topology requires three dc sources, each of Vdc/6 only, which can be replaced with stacked batteries for electric vehicle applications. The reduction in the dc voltage requirement is achieved by using a normal symmetric six-phase induction motor with parallel connection of the opposite phase windings. All the floating capacitors in the topology can be balanced irrespective of any modulation index or load power factor. Due to the high number of voltage levels, nearest level control can be used instead of pulse width modulation, which reduces the switching losses. The dv/dt during the inverter operation is also less. Detailed experimental results at different speeds of operation and during transients ensure that the novel topology can be a viable option for high-power adjustable speed drives.
Large N = 4 holography Gaberdiel, Matthias R; Gopakumar, Rajesh
The journal of high energy physics,
09/2013, Letnik:
2013, Številka:
9
Journal Article
Recenzirano
Odprti dostop
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The class of 2d minimal model CFTs with higher spin AdS^sub 3^ duals is extended to theories with large ... = 4 ...superconformal symmetry. We construct a higher spin theory based on the global D(2, 1|alpha) superalgebra, and propose a large N family of cosets as a dual CFT description. We also indicate how a non-abelian version of this Vasiliev higher spin theory might give an alternative description of IIB string theory on an AdS^sub 3^ × S^sup 3^ × S^sup 3^ × S^sup 1^ background.
Traditional cotton gauze derived from cellulose has many limitations in the processes of wound healing. To overcome these hassles, we used cellulose nanofibers (CNF) incorporated with curcumin for ...the fabrication of wound healing 3D porous aerogel. Cellulose nanofibers synthesized from plant waste are promising sustainable nanomaterials due to their biocompatibility and biodegradability. Ionic cross linking with sodium alginate was performed to maintain the mechanical strength. SEM results revealed highly porous architecture that effectively promoted wound healing, as a result of macro- and micro-porous architecture and curcumin. In-vitro drug release studies showed a slow and steady release pattern. The 3D porous nano bio aerogel with curcumin significantly promoted the migration of fibroblast cells and had excellent antimicrobial activity against pathogenic microorganisms. In-vivo studies showed angiogenesis without rejection or inflammation of the scaffold. From the observations, we can conclude that this novel 3D porous aerogel can be used to treat chronic wounds.
Cellulose nanofibers synthesized from agro waste is a promising sustainable nanomaterial due to its biocompatibility and biodegradability. Here in we used cellulose nanofibers (CNF) incorporated with curcumin for the fabrication of wound healing 3D porous aerogel. Ionic cross linking with sodium alginate was performed to maintain the mechanical strength. SEM results revealed highly porous architecture which effectively promoted wound healing, as a result of macro- and micro-porous architecture and curcumin. In-vitro drug release studies showed a slow and steady release pattern. 3D porous nano bio aerogel with curcumin significantly promoted the migration of fibroblast cells and had excellent antimicrobial activity against pathogenic microorganisms. In-vivo studies showed angiogenesis without rejection or inflammation of the scaffold. From the observations we can conclude that this novel 3D porous aerogel can be used to treat chronic wounds. Display omitted
One of the major concerns faced by the iron and steel industry, other than the abundant emission of carbon dioxide into the atmosphere, is the huge quantity of slag that is generated during the ...manufacturing of iron and steel. A comprehensive understanding of the iron and steel slag properties has diverted them away from stockpiling or landfilling to useful engineering applications. The similarity of these slags to natural minerals used in geologic carbon dioxide sequestration has made them sustainable alternative for industrial-scale carbon capture and storage. Further, they possess properties that are conducive for remediation of soil and groundwater contaminated with heavy metals and other toxic chemicals. This paper reviews the iron and steel slag characteristics suitable for engineering applications, describes several engineering application examples, and discusses challenges and opportunities to develop practical applications using iron and steel slags. This paper also discusses the on-going research which explores the use of steel slag along with the biochar-amended soil to develop a biogeochemical landfill cover to sequester fugitive gas emissions such as CH
4
, CO
2
and H
2
S from MSW landfills and attain zero-emissions landfill.
This paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor ...inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n-level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme.
This paper proposes a novel method for instantaneous balancing of neutral-point (NP) voltages with stacked multilevel inverters (MLIs) for variable-speed drives. The stacked MLI uses series-connected ...dc sources and NPs (connecting points of dc sources) to obtain the desired levels. The balancing of NP voltages are obtained by using a low-voltage-capacitor-fed cascaded H-bridge (CHB) per phase of a symmetrical six-phase induction machine (IM), which ensures zero current drawn from NPs (at any given instant). Since no current is drawn from NPs, the single dc-link operation with stacked capacitors is also possible. The scheme is suitable for applications, where low-voltage dc sources and batteries are stacked to form a dc link. A variable-speed operation is done using a seven-level inverter scheme for a symmetrical six-phase IM, which is formed by three dc-link stacked capacitors cascaded with two low-voltage-capacitor-fed CHBs per phase. Furthermore, the method is extended for an open-end IM to obtain a seven-level common-mode eliminated space vector structure using a single dc link. The generalization of this method for any stacked n-level inverter without NP voltage deviation is also presented in this paper. The experimental results and analysis are included to validate the proposed method.
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