异步电动机直接转矩控制中的死区效应的仿真研究

逆变器是直接转矩控制系统主电路中的关键部件。逆变器死区的设置虽然防止了逆变器器件的直通,同时也带来了死区效应,特别是对直接转矩控制系统的影响更是明显。本文通过分析异步电动机直接转矩控制系统中死区的生成及死区对电动机和整个系统的影响,定义了偏差电压矢量,并在此基础上,提出了一种死区补偿分析算法。该方法不需附加硬件,只需对原控制软件进行修改。仿真结果显示,在直接转矩控制系统中加入死区补偿,能有效改进电动机定子电流波形,使转矩脉动减小,整个系统的运行性能得到了一定的改善。     

Necessary optimality conditions and regularity results for state and adjoint state of nonlinear control problems

For optimal control problems of nonlinear evolution equations of first order we derive regularity properties for the corresponding adjoint states where the proof is based on the necessary optimal conditions and smoothness properites of the optimal states. These results are used for the characterization of the optimal solution and the corresponding adjoint state of the periodic three-dimensionel NAVIER-STOKES system.     

Flow over rectangular porous block in a fixed width channel: influence of porosity and aspect ratio

Flow over a rectangular porous block placed in a fixed width channel is considered and the influence of block aspect ratio on the heat transfer rate from the block is examined. A non-porous solid block is also accommodated to compare the effect of porosity on the flow field and heat transfer characteristics. Aspect ratio and the porosity of the block are varied in the simulations. A numerical scheme employing a control volume approach is considered when predicting the flow and temperature fields. The Reynolds number is selected to yield the mix convection situation in the flow field. It is found that the aspect ratio significantly influences Nu and Gr numbers, in which case increasing the aspect ratio enhances Nu while lowering Gr. Increasing porosity improves the heat transfer rates from the porous block, provided that at high aspect ratios, this situation ceases due to blockage effect of the body in the channel.     

分级分段印制插头工艺的研发与应用

介绍了一种采用特殊的设计方法制作分级分段印制插头的工艺生产的印制插头完全没有引线残留的踪迹,对分级分段印制插头的品质做到了有效的控制,可靠性实达到品质要求,通过了实际生产应用的验证,建立了工艺规范和品质管制计划,为批量生产奠定了坚实基础。     

How do we know who to include in collaborative research? Toward a method for the identification of experts

Collaborative research, defined as research involving actors participating in the problem situation under study, has an important role in operational research, strategic management and systems thinking. In a recent study, we found that a strong organizational focus incorporated into many soft operational research (OR) approaches is inadequate for studying societal problem situations, which are fragmented and have no clear boundary. Specifically, we failed to find a process of identifying individuals that is capable of representing the perspectives of actors and sufficient for research into societal problem situations. We found no clear terminology accounting for ontological differences between actors, individuals representing them and conceptual representations of acting entities. In response to this gap in the literature, we propose terminology that differentiates among actors (individuals or collective entities in the real world), experts (individuals capable of representing the perspective of an actor) and agents (ideal-typical representations of actors). Based on this terminology, we propose an iterative method to guide the assembly of an expert group to undertake collaborative research into societal problem situations. To demonstrate the application of our method, we present selected insights from our study in an electronic supplement.     

Old Reagent,New Results: Aromatization of Hantzsch 1,4-Dihydropyridines with Supported Bismuth Nitrate under Microwave Irradiation in Solventless System

Hantzsch 1,4-dihydropyriines were rapidly and efficiently oxidized using bismuth nitrate supported onto silica gel under microwave irradiation.     

Solvent Free Synthesis of Coumarins

An efficient synthesis of 3-substituted coumarins under solventless system is described.     

Microwave Thermolysis: A Rapid and Selective Method for the Cleavage of THP Ethers Using CrO 3 Supported onto Zeolite in Solventless System

Oxidative deprotection of tetrahydropyranyl ethers (THP ethers) using chromium trioxide supported onto zeolite under microwave irradiation in solvent free condition is described.