Modelling and control of a seven level NPC voltage source inverter. Application to high power induction machine drive
作者:H. Gheraia、E. M. Berkouk、G. Manesse
DOI:10.1051/epjap:2001172
日期:2001.8
In this paper, we study a new kind of continuous-alternating converters: a seven-level neutral point clamping (NPC) voltage source inverter (VSI). We propose this inverter for applications in high voltage and high power fields. In the first part, we develop the knowledge and the control models of this inverter using the connections functions of the semi-conductors. After that, we present two pulse width modulation (PWM) algorithms to control this converter using its control model. We propose these algorithms for digital implementation. This multilevel inverter is associated to the induction machine. The performances obtained are full of promise to use it in the high voltage and high power fields of electrical traction.
Ketone Methylenation Using the Tebbe and Wittig Reagents - A Comparison
作者:Stanley H. Pine、Gregory S. Shen、Huan Hoang
DOI:10.1055/s-1991-26406
日期:——
Ketone methylenation has been accomplished using the Tebbe and the Wittig reagents. Comparison of the two reagents for a variety of ketones shows that the Tebbe reagent gives better product yields than the Wittig reagent. This is particularly important when the ketone substrate is hindered. It is also noted that the Tebbe reaction accomplishes methylenation in a non-basic medium, thus racemization does not take place on substrates with enolizable chiral centers.
Non-stabilized and semi-stabilized phosphonium diylids of the type (C6H5)2P(CHR)(CHLiR) (5) show a greater nucleophilic reactivity toward carbonyl compounds than the corresponding monoylids (C6H5)2P(CHR)(CH2R) (8). Thus diylid 5a reacts readily at room temperature with sterically hindered ketones such as fenchone or di-t-butylketone. However, the residual negative charge in the intermediate adduct
(C 6 H 5)2 P(CHR)(CHLiR)(5)类型的非稳定化和半稳定化的磷鎓二碘化物对羰基化合物的亲核反应性高于相应的单酰基(C 6 H 5)2 P( CHR)(CH 2 R)(8)。因此,二碘化物5a在室温下容易与空间受阻的酮例如fenchone或二叔丁基酮反应。然而,中间加合物13中残留的负电荷减慢了向维蒂希产物的分解,并且可能是造成E中观察到的变化(通常增强)的原因。在非稳定的和半稳定的脂质的情况下的-选择性。
The stereochemical course of 2-methylisoborneol biosynthesis
作者:Binbin Gu、Anwei Hou、Jeroen S Dickschat
DOI:10.3762/bjoc.18.82
日期:——
Both enantiomers of 2-methyllinalyl diphosphate (2-Me-LPP) were synthesized enantioselectively using Sharpless epoxidation as a key step and purification of enantiomerically enriched intermediates through HPLC separation on a chiral stationary phase. Their enzymatic conversion with 2-methylisoborneol synthase (2MIBS) demonstrates that (R)-2-Me-LPP is the on-pathway intermediate, while a minor formation
使用 Sharpless 环氧化作为关键步骤,并通过手性固定相上的 HPLC 分离纯化对映体富集的中间体,对映体选择性地合成了 2-甲基芳樟基二磷酸 (2-Me-LPP) 的两种对映体。它们与 2-甲基异冰片合酶 (2MIBS) 的酶促转化表明 ( R )-2-Me-LPP 是通路中间体,而从 ( S )-2-Me-LPP形成少量 2-甲基异冰片可以解释异构化为 2-Me-GPP,然后异构化为 ( R )-2-Me-LPP。