电动自行车转矩脉动抑制分析与实现

针对电动自行车生产中如何抑制转矩脉动的问题,结合理论分析,提出采用换相电流闭环控制方法。     

基于滑模变结构的感应电动机直接转矩控制

针对感应电动机常规直接转矩控制中存在磁链、转矩脉动大,低速控制不精确等问题,在建立α-β坐标系感应电动机数学模型的基础上,提出了一种基于滑模变结构的新型直接转矩控制方法。该方法利用转速滑模变结构控制器代替常规直接转矩控制中的PI控制器,可有效减小常规直接转矩控制中的磁链和转矩脉动,增强了系统的稳定性。仿真结果证明了该方法的正确性。     

基于PR控制器的直接转矩控制策略研究

针对传统直接转矩控制中采用开关表控制造成转矩和电流脉动,以及传统调节器不能实现对交流输入信号的无静差控制等问题,基于电机空间电压矢量的转矩和磁链2个分量解耦的控制方式和PR控制器能够在静止坐标系下实现对交流输入信号的无静差控制,将PR控制器用于永磁同步电机的直接转矩控制中,并由此设计出磁链和转矩的双PR控制器。同时,在定子磁链的观测中,采用基于转子位置和定子电流的新型定子磁链估计方法。试验结果证明,将PR控制器对交流输入信号的无静差跟踪特性应用于基于空间电压矢量调制的直接转矩控制中,系统能获得优良的动态和静态响应,取得了显著的应用成效,由此验证了所提方法的正确性和可行性。     

基于尺度解析模拟的HC375液力变矩器的流场分析与特性预测

针对传统的一维束流研究方法无法描述大功率液力变矩器工作腔内复杂的时变瞬态湍流的流动状态,采用多物理场耦合方法构建了一种介质流动与传热的动态耦合数值模型,并给出了液力变矩器瞬态仿真设计方法.通过定性和定量分析液力变矩器内部的流动结构发现,动态混合模型(Dynamic hybrid RANS - LES, DHRL)中的SBES(Stress -blended eddy simulation)方法能够充分识别工作腔内边界层的流动状态,可实现对多流域耦合复杂流动现象的精准捕捉.通过台架实验表明,采用DES模型和     

改进的永磁同步电机双矢量模型预测转矩控制

针对永磁同步电机（PMSM）传统模型预测转矩控制（MPTC）权重系数设置复杂、转矩和磁通脉动大的问题,提出了一种改进的PMSM双矢量MPTC方法。该方法扩展虚拟矢量以增加候选电压矢量,结合电压矢量作用于转矩和磁链的原则,减少选择候选矢量的计算量。同时,针对转矩无差拍和磁通无差拍,运用候选矢量的转矩占空比和磁通占空比构造了优化规则代替传统预测转矩控制中的代价函数,避免权重系数的整定问题。仿真结果表明,所提改进方法不仅提高稳态性能,而且能保持MPTC动态响应迅速的特点。     

Roll force,torque, lever arm coefficient,and strain distribution in edge rolling

Due to the growing importance of width control in strip and plate mills, edge rolling is currently an im-portant process in hot rolling mills. Research in edge rolling has been carried out, and in the present ar-ticle, models for roll force, torque, and lever arm coefficient are derived using the upper bound method. A simple, kinematically admissible deformation zone and velocity field, independent of friction in the roll gap, is proposed, and the energy dissipation rate is derived. The formula for energy dissipation rate has, in practice, no limitation because all edge rolling geometries are safely in the area where the formula is valid. Roll force and torque are derived by means of two independent integrals. Thus, the lever arm coef-ficient is evaluated from the expressions for roll force and torque using conventional rolling theory. Roll-ing trials report good agreement with theory. Measured roll forces are similar to calculated forces. Furthermore, the shape of the dogbone that arises during edge rolling is in fairly good agreement with the calculated dogbone shape. Deviations are due to the deviation from ideally plastic material in the ex-periments. Also, the strain distribution over the dogbone is similar to the proposed deformation zone. Thus, a new formula has been developed to a stage that it can be implemented in width control systems for edge rolling stands in hot strip and plate mills.     

An experimental evaluation of the effects of ripple current generated by the power conditioning stage on a proton exchange membrane fuel cell stack

In this article, an impedance model of the proton exchange membrane fuel cell stack (PEMFCS) is proposed. The proposed study employs an equivalent circuit of the PEMFCS derived by the frequency response analysis technique. An equivalent circuit for the PEMFCS is developed to evaluate the effects of ripple currents generated by the power-conditioning unit. The calculated results are then verified by means of experiments using a commercially available PEMFCS. The relationship between ripple current and fuel cell performance, such as power loss and fuel consumption, is investigated. Experimental results show that the ripple current can contribute up to a 6% reduction in the available output power. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

拧紧力矩和热应力对螺纹插装阀的影响分析

在分析螺纹插装阀整体结构和工作原理的基础上,建立螺纹插装阀阀套与阀芯间隙变化量在拧紧力矩和热应力作用下的理论计算模型,通过理论计算分析其间隙的变化规律,同时结合有限元分析结果对计算模型进行初步验证。结果表明:该计算模型可以用于分析螺纹插装阀在热应力下的使用性能,对螺纹插装阀的设计使用具有一定的指导意义。     

塔式旋转混凝土布料机的工况计算及配重调控分析

塔式旋转混凝土布料机是一种可高效输送混凝土的工程机械,被广泛用于混凝土浇筑。施工过程中,为减小其布料端悬臂力矩、保证其塔架的稳定性,需要随时根据其伸缩桁架的伸缩量来调节其配重块的位置。运用有限元ANSYS软件,分析了布料机在极限工况条件下的结构强度和最大合力矩,计算了19种不同工况下力矩、桁架伸缩量及配重调节距离之间的数值关系。在此基础上,利用MATLAB的拟合优化功能得出三者之间的函数关系并绘制三维曲线。研究结果为塔式旋转混凝土布料机的安全运行提供数据支持,同时为其后续的优化设计提供参考。     

高水头船闸一字闸门水动力特性数值模拟

针对某山区高水头船闸30 m淹没水深下一字闸门的水动力特性进行研究,借助FLUENT软件提供的Realizable k-ε紊流模型对门体启闭过程非恒定流场进行动态模拟,通过建立由二维平面混合网格纵向拉伸成的三维棱柱体网格,结合2.5D重构和弹性光顺动网格法,在降低网格数量、提高计算效率的同时,实现一字闸门启闭全过程三维流场模拟。引入VOF法对自由水面迭代求解,得到一字闸门启闭过程门前后水位差及动水阻力矩变化规律,将计算结果与模型试验进行比较,两者吻合较好。模拟计算发现:门底间隙对闸门运行整个阶段动水阻力矩均有影响,动水阻力矩峰值随门底间隙增大而变小。