Synchronised carrier-based SVPWM signal generation scheme for the entire modulation range extending up to six-step mode using the sampled amplitudes of reference phase voltages

The issues in synchronised implementation of space vector-based pulse width modulation (SVPWM) signal generation are addressed on a conventional DSP platform. With the present day digital signal processors (DSPs) with clock over 10 MHz, it is possible to include additional tasks for synchronisation in the interrupt service routine (ISR). Also, the task of the synchronisation can be easily accommodated within the same ISR without disturbing the time critical pulse width modulation (PWM) operation. The authors systematically present the additional software requirements to determine the time period proportional to the half carrier switching time interval that is required for the synchronisation. First, the DSP implementation of the conventional multi-level SVPWM based on the sampled amplitudes of reference voltages is presented and then the additional requirements to maintain the PWM in synchronisation are discussed. The simulation results as well as experimental results are presented for a five-level PWM signal generation. A five-level inverter configuration, using a 1.5 kW open-end winding induction motor drive, is used for experimentally verifying the SVPWM     

Lignin valorization by forming toughened thermally stimulated shape memory copolymeric elastomers: Evaluation of different fractionated industrial lignins

Lignin‐based thermal responsive dual shape memory copolymeric elastomers were prepared with a highly branched prepolymer (HBP, A₂B₃ type) via a simple one‐pot bulk polycondensation reaction. The effect of fractionated lignin type (with good miscibility in the HBP) on copolymer properties was investigated. The thermal and mechanical properties of the copolymers were characterized by DMA, DSC, and TGA. Tensile properties were dominated by HBP <45% lignin content while lignin dominated >45% content. The copolymers glass transition temperature (T_g) increased with lignin content and lignin type did not play a significant role. Thermally stimulated dual shape memory effects (SME) of the copolymers were quantified by cyclic thermomechanical tests. All copolymers had shape fixity rate >95% and >90% shape recovery for all compositions. The copolymer shape memory transition temperature (T_trans) increased with lignin content and T_trans was 20°C higher than T_g. Lignin, a renewable resource, can be used as a netpoint segment in polymer systems with SME behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41389.     

A harmonic elimination and suppression scheme for an open-end winding induction motor drive

In this paper, a harmonic elimination and suppression scheme for a dual-inverter-fed open-end winding induction motor drive is presented. Two isolated dc-link sources with voltage ratio of approximately 1 : 0.366 are required for the present drive. These two isolated do links feeding two inverters to drive the open-end winding induction motor eliminate the triplen harmonic currents from the motor phase. The pulsewidth-modulation scheme proposed enables the cancellation of all the 5th- and 7th-order (6n /spl plusmn/ 1, where n = 1, 3, 5, 7, etc.) harmonic voltages and suppresses the 11th- and 13th-order harmonic voltage amplitudes in the motor phase voltage, in all modulation ranges. The next higher order harmonics present in the motor phase voltages are 23rd, 25th, 35th, 37th etc. (6n /spl plusmn/ 1, n = 4, 6, etc.). By using triangular carrier wave and proper modulating waves for each inverter, the open-end winding induction motor can be operated in the entire modulation range, eliminating all the 6n /spl plusmn/ 1 harmonics (n = 1, 3, 5, 7, etc.) coupled with 11th and 13th harmonic suppression. The proposed scheme also gives a smooth transition to the overmodulation region.     

Lipid composition of five species of Indian prawns

The lipid and fatty acid compositions of five Indian species of prawns, Metapenaeus monoceros, M. dobsoni, M. affinis, Penaeus indicus and Parapenaeopsis stylifera, were examined. Phospholipids constituted 50–70% of the total lipids, with phosphatidyl choline (50%) and phosphatidyl ethanolamine (29%) as their chief components. Unsaponifiable matter comprised 21–40%, chiefly cholesterol: triglycerides only constituted 9–14.5%. In the total lipids (I.V. 90–112), saturated, monoenoic and polyenoic fatty acids averaged 42, 24 and 34%. Palmitic acid is high, oleic low, and 20:5 generally, but not always, higher than 22:6. The only brackish water prawn, M. monoceros, though generally in conformity, was distinctive in several respects.     

Low-Temperature Fine-Grained Alumina–Aluminum Titanate Composites Produced from a Titania-Coated Alumina Precursor

A method for the preparation of alumina–aluminum titanate (AT) composites, which can be sintered to high density with a fine-grained microstructure at <1450°C, is reported. The composite precursor is alumina particles coated by sol–gel-derived titania, which reacts during sintering to form AT in situ at temperature as low as 1300°C. The composite can be sintered at 1350°C to 98% density with 1.5–2.0 μm grain size. Other composites containing 5–50 wt% AT are also investigated.     

Natural rubber–polyurethane block copolymers: Nonlinear structural variations with NCO/OH ratio

A series of segmented block copolymers was prepared by the chain extension of hydroxyl terminated liquid natural rubber (HTNR) with polyurethane oligomers derived from toluene diisocyanate (TDI) and 1,3‐butane diol at varying NCO/OH ratio. The previously reported two‐step method of synthesis was modified to get improved products. This was done by optimizing the formation of polyurethane oligomers in the first step of the synthesis. All the samples were characterized by solubility testing, DSC, tensile testing, etching studies, and SEM. The data obtained were correlated to the structural features of the block copolymers. It was found that NCO/OH ratio played an important role in determining the structural variations in the block copolymers. POLYM. ENG. SCI. 46:1812–1821, 2006. © 2006 Society of Plastics Engineers     

Tuning the crystal structure and optical properties of selective area grown InGaAs nanowires

Catalyst-free InGaAs nanowires grown by selective area epitaxy are promising building blocks for future optoelectronic devices in the infrared spectral region.D...     

Synthesis and properties of lignin-highly branched poly (ester-amine) polymeric systems

Combined characteristics of hydrogen bonded/cross-linked polymer networks based on lignin motifs have been developed. This new type of polymeric material was prepared from an industrial lignin and a highly branched poly(ester-amine) (HBPEA) obtained by melt polycondensation of 1,1,1-triethanolamine (TEA) and adipic acid (AA). The lignin-HBPEA polymers were shown to be insoluble in common organic solvents and were characterized by FTIR and NMR spectroscopies. Thermo-mechanical measurements showed that melt mixing HBPEA with 40% lignin results in a flexible and tough material (T_g; 7.7 °C and E′ 3.5 GPa). The hydrogen bonding recognition was based on various hydroxyl groups in lignin and aliphatic ester groups from HBPEA. The extent of interactions could be controlled by varying the amount of lignin added. These networks were thermally reversible and have highly tunable mechanical properties that were controlled by the extent of interactions. High level of mechanical properties could be achieved through the addition of lignin-poly(ester-amine) covalent cross-links. This study shows that the poly(ester-amine) structure plays an important role in the thermo-mechanical properties. By varying the spacer length between lignin and tertiary amine unit, materials with various thermo-mechanical properties were also obtained from the same parent polymer backbone.     

Chemical bath deposition and characterization of CdSe thin films for optoelectronic applications

Cadmium selenide (CdSe) thin films of high crystalline quality on glass substrate have been prepared by chemical bath deposition technique from an aqueous bath containing tetramine cadmium and sodium selenosulphate. Structural analysis using XRD shows that the film is single phase, crystallized in hexagonal structure with preferred growth in (111) direction. The energy band gap calculated from the absorption spectra of unannealed CdSe thin films shows an optical band gap of 1.8 eV and absorption coefficient near band edge (α)—0.58 × 10⁵ cm⁻¹. The conductivity of CdSe thin films is n-type.     

Compounding of nanocomposites by thermokinetic mixing

Nanocomposites have been prepared by melt mixing poly(propylene) (PP) and different levels of a premixed montmorillonite‐organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high‐speed thermokinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating, and compounding of products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin‐screw extruder. The structure and properties of PP/clay nanocomposites were compared by TEM, X‐ray diffraction, mechanical testing, and rheological analysis. Results indicate that a better dispersion of the clay can be achieved by thermokinetic mixing when compared to extrusion, resulting in better mechanical properties. Calculations, based on simplifying assumptions, showed that the shear rates generated in a Gelimat are at least one order higher than those generally generated in an extruder. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1557–1563, 2005