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ABSTRACT: In order to overcome the problems such as heavy distortion of winding current, low power factor and high cost of DC inductor met in the traditional rectified permanent magnet (PM) wind generation system, a circuit of cascaded single phase power factor correction (PFC) rectifier pair is proposed and discussed. In the new scheme, proper designed armature inductor of the generator is used as boost inductor, and the winding current is controlled by PWM to approach a sinusoidal waveform aligned with the back EMF in the winding. The DC ports of two such PFC rectifiers linked to a pair of windings placed perpendicularly are then connected in cascade that avoids the voltage ripple at DC link. Simulation and experiments have been performed to validate the new scheme.
Electrical Machines and Systems, 2008. ICEMS 2008. International Conference on; 11/2008
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ABSTRACT: Rhodococcus erythropolis USTB-03 is a promising bacterial strain for the biodesulfurization of dibenzothiophene (DBT) via a sulfur-specific pathway in which DBT is converted to 2-hydroxybiphenyl (2HBP) as an end product. The effects of nicotinamide and riboflavin on the sulfur specific activity (SA) of DBT biodesulfurization by R. erythropolis USTB-03 were investigated. Both nicotinamide and riboflavin were found to enhance the expression of SA, which was not previously reported. When R. erythropolis USTB-03 was grown on a medium containing nicotinamide of 10.0 mmol or riboflavin of 50.0 micromol, SA was raised from 68.0 or so to more than 130 mmol 2HBP/(kg dry cells. x ). When R. erythropolis USTB-03 was grown in the presence of both nicotinamide of 5.0 mmol and riboflavin of 25.0 Cmicrool, SA was further increased to 159.0 mmol 2HBP/(kg dry cells. x ). It is suggested that the biological synthesis of reduced form of flavin mononucleotide (FMNH2), an essential coenzyme for the activities of biodesulfurization enzyme Dsz C and A, might be enhanced by nicotinamide and riboflavin, which was responsible for the increased SA of R. erythropolis USTB-03.
Journal of Environmental Sciences 02/2008; 20(5):613-8. · 1.66 Impact Factor
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ABSTRACT: This paper presents a new topology of a three phase rectifier operating in the discontinuous conduction mode (DCM). It is based on the buck-boost converter and has the step-up and step-down characteristics of output voltage. The rectifier draws sinusoidal ac current from ac line with unity power factor, and needs only one switch and constant duty cycle of PWM control. The dynamic and steady equations of converter are analyzed. The results of the theoretical analysis are verified by digital simulation and the experiment results of laboratory prototype.
Industry Applications Conference, 2004. 39th IAS Annual Meeting. Conference Record of the 2004 IEEE; 11/2004
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ABSTRACT: Current control strategy is a key step in the control of rectifiers. Based on the discrete modeling of current control of rectifier, a novel current controller designed by discrete H∞ optimization is presented in this paper, which can minimize the effect of parameter variation and control period. The simulation and experimental results show that the novel controller operates robustly with parameters variation, and also produces better dynamic performance in various control periods, compared with classic PI controller and cross-coupling controller.
Electric Machines and Drives Conference, 2003. IEMDC'03. IEEE International; 07/2003
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ABSTRACT: To increase the fault tolerance for cascaded H-bridge multilevel inverters, a novel control algorithm is proposed for the inverter operating under faulty conditions. The influence of various faults on space vectors is investigated and the maximum achievable output voltage of the inverter with faulty power cells is derived. Making use of the redundant switching states, the proposed algorithm is able to produce a three-phase balanced line-to-line voltage with minimum harmonic distortion for the inverter with disabled power cells. In addition, the control algorithm is suitable for use in the cascaded H-bridge inverters of any voltage levels. Simulation and experimental results are provided for verification.
Applied Power Electronics Conference and Exposition, 2003. APEC '03. Eighteenth Annual IEEE; 03/2003
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ABSTRACT: Poly(beta-hydroxybutyrate) (PHB) production using a recombinant Escherichia coli VG1 (pTU14) was carried out. PHB granules were gradually biosynthesized in recombinant cells as inclusion bodies and the morphology of cells became linearly inflated with PHB accumulation from 6 h to 36 h of culture. The stability of plasmid pTU14 was inevitably affected by in-cell PHB accumulation. During repeated subcultures under both PHB-accumulating and non-PHB-accumulating conditions, plasmid DNAs of pTU14 were extracted and analyzed after more than 60 generations. The results showed that plasmid pTU14 is structurally stable but segregationally unstable, and that the segregational instability worsened with increasing accumulation of PHB granules. This is due to not only the serious metabolic burden of plasmid replication and gene expression on the host cell, but also the volume effects of PHB granules on the natural random distribution of plasmids during the binary fission of cells.
Journal of Bioscience and Bioengineering 02/2003; 96(2):179-83. · 1.79 Impact Factor
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ABSTRACT: Nitrile hydratase (NHase) is an important industrial enzyme used for acrylamide production from acrylonitrile. The deactivation kinetics of NHases in free resting cells of Rhodococcus sp. was presented based on a bi-steady state assumption. Effects of hydration temperature, product concentration and substrate concentration on NHase deactivation were investigated experimentally and correlated with a first order deactivation kinetics. The results showed that the hydration temperature and product concentration were major factors governing the deactivation of NHases under substrate-feeding conditions. When acrylamide concentration was higher than 250 g·L−1, the deactivation of NHases became serious and the bi-steady state assumption was not applicable. When the hydration temperature was controlled at a relatively higher level such as 28°C, the total deactivation rate constant was about 2.8-fold of that at 20°C.
Chinese Journal of Chemical Engineering.
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ABSTRACT: To obtain a recombinant Rhodococcus or Nocardia with not only higher enzymatic activity but also better operational stability and product-tolerance ability for bioconversion of acrylamide from acrylonitrile, an active and stable expression system of nitrile hydratase (NHase) was tried to construct as the technical platform of genetic manipulations. Two NHase genes, NHBA and NHBAX, from Nocardia YS-2002 were successfully cloned, based on bioinformatics design of PCR primers, and inserted into plasmid pUC18 and pET32a, respectively. Then, two recombinant Escherichia coli strains, JM105 (pUC18-NHBA) and BL21 (DE3) (pET32a-NHBAX) were constructed and their expressions of NHase were focused. The induction results showed that there was either no NHase activity in JM105 (pUC18-NHBA), or as low as 0.04 U (1 U=1 μmol acrylamide min−1 mg−1 dry cell) in BL21 (DE3) (pET32a-NHBAX). SDS-PAGE results showed that the α-subunit of NHBA and NHBAX could not be efficiently expressed in both recombinant E. coli strains. The novel Pichia pastoris system was also applied to express NHase, but the expression level remained quite low (0.5–0.6 U) and the protein was unstable. For solving this problem, a possible genetic strategy, site-directed mutagenesis of the α-subunit of the NHase was carried out. After the successful mutagenesis of the original rare start codon gtg into atg, a new recombinant strain, E. coli XL1-Blue (pUC18-NHBAM), was screened and the NHase activity stably reached as high as 51 U under the same induction conditions.
Enzyme and Microbial Technology.
