Reduction of Torque Ripple in Induction Motor Drives Using an AdvancedHybrid PWM Technique

A voltage source inverter-fed induction motor produces a pulsating torque due to application of nonsinusoidal voltages. Torque pulsation is strongly influenced by the pulsewidth modulation (PWM) method employed. Conventional space vector PWM (CSVPWM) is known to result in less torque ripple than sine-triangle PWM. This paper aims at further reduction in the pulsating torque by employing advanced bus-clamping switching sequences, which apply an active vector twice in a subcycle. This paper proposes a hybrid PWM technique which employs such advanced bus-clamping sequences in conjunction with a conventional switching sequence. The proposed hybrid PWM technique is shown to reduce the torque ripple considerably over CSVPWM along with a marginal reduction in current ripple

Parameters Influencing the Molecular Weight of 3,6-Carbazole-Based D-pi-A-Type Copolymers

Condensation copolymerization reactions of carbazole 3,6-diboronate with 4,7-bis(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (DTBT) only produce low-molecular-weight donor (D)-pi-acceptor (A) copolymers. High-molecular-weight copolymers for use in optoelectronic devices are necessary for achieving extended pi-conjugation and for controlling the copolymer processibility. To elucidate the cause of the persistently low molecular weight, we synthesized three 3,6-carbazole-based D-A copolymers using copolymerizations of N-9'-heptadecanyl-3,6-carbazole with DTBT, N-9'{2-[2-(2-methoxyethoxy)-ethoxy]-ethyl}-3,-6-carbazole with DTBT, and N-9'-heptadecanyl-3,6-carbazole with alkyl-substituted DTBT. We investigated several parameters for their influence on molecular copolymer weight, including the conformation of the chain during growth, the solubility of the monomers, and the dihedral angles between the donor and acceptor units. Size exclusion chromatography, UV-vis absorption spectroscopy, and computational studies revealed that the low molecular weights of 3,6-carbazole-based D-A copolymers resulted from conjugation breaks and the resulting high coplanarity, which led to strong interactions between polymer chains. These interactions limited formation of high-molecular-weight-copolymers during copolymerization. The strong intermolecular interactions of the 3,6-carbazole moiety were exploited by incorporating 3,6-carbazole units into poly[9',9'-dioctyl-2,7-flourene-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] prepared from 9',9'-dioctyl-2,7-flourene and DTBT. Interestingly, the number average molecular weight increased gradually with increasing 2,7-fluorene monomer content but the number of conjugation breaks was a range of 6-7. The hole mobilities of the copolymers were studied for comparison purposes. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4368-4378, 2011X111314sciescopu

Exploring the Heterogeneous Interfaces in Organic or Ruthenium Dye-Sensitized Liquid- and Solid-State Solar Cells

The interfacial properties were systematically investigated using an organic sensitizer (3-(5'-{4-[(4-tert-butyl-phenyl)-p-tolyl-amino]-phenyl)-[2,2']bithiophenyl-5-yl)-2-cyano-acrylic acid (D)) and inorganic sensitizer (bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bipyridine-4,4'-dicarboxylato) ruthenium(II) (N719)) in a liquid-state and a solid-state dye-sensitized solar cell (DSC). For liquid-DSCs, the faster charge recombination for the surface of D-sensitized TiO2 resulted in shorter diffusion length (L-D) of similar to 3.9 mu m than that of N719 (similar to 7.5 mu m), limiting the solar cell performance at thicker films used in liquid-DSCs. On the other hand, for solid-DSCs using thin TiO2 films 2 pm), D-sensitized device outperforms the N719-sensitized device in an identical fabrication condition, mainly due to less perfect wetting ability of solid hole conductor into the porous TiO2 network, inducing the dye monolayer act as an insulation layer, while liquid electrolyte is able to fully wet the surface of TiO2. Such insulation effect was attributed to the fact that the significant increase in recombination resistance (from 865 to 4,400 Cl/cm(2)) but shorter electron lifetime (from 10.8 to 0.8 ms) when compared to liquid-DSCs. Higher recombination resistance for solid-DSCs induced the electron transport-limited situation, showing poor performance of N719-sensitized device which has shorter electron transport time and similar LD (2.9 mu m) with D-sensitized device (3.0 mu m).X111212sciescopu