Z源NPC三电平变换器恒功率并网控制策略研究

Z源中点钳位式(NPC)三电平变换器把逆变和升压两种环节结合在一起,结构简单、工作效率高,但是针对这种结构输出的无功功率研究较少。提出了一种Z源NPC三电平变换器的恒功率并网控制策略。首先对这种变换器的结构及原理进行分析；再把恒功率控制引入到这种变换器的并网控制中,并采用空间矢量脉宽调制(SVPWM)实现了变换器的并网控制。MATLAB/Simulink软件仿真结果证明了这种变换器能够提高电压升压比。该控制策略可使变换器输出的有功功率、无功功率稳定于设定值,且并网电流谐波较低。     

任意铺层复合材料加筋板屈曲/后屈曲行为的解析解

给出了一种求解任意铺层复合材料加筋板屈曲/后屈曲问题的解析方法。首先将加筋板简化为受弹簧约束的层合板,而后通过构造位移函数,并利用伽辽金法得到了加筋板压缩、剪切和压剪载荷下的屈曲/后屈曲解析解。求解中引入了无量纲参数,使得结果更具一般性;在后屈曲行为中考虑了初始缺陷和由耦合刚度引起的前屈曲挠度,使得结果更加准确。通过与有限元结果的比较,讨论了几何参数、弹簧刚度等对解的影响。最后将该方法应用于T形加筋对称铺层复合材料加筋板的屈曲/后屈曲分析中,考虑T形筋对复合材料层板粘结区的刚度增强作用,采用刚度平均化方法引入增强效果,并与两种T形筋刚度简化模型以及有限元结果进行了比较,验证刚度平均化方法对计算加筋板屈曲/后屈曲行为的有效性。     

轴向柱塞泵滑靴副的热结构耦合特性

为了改善轴向柱塞泵滑靴副的耐磨损性能,建立了滑靴与斜盘摩擦副的瞬态热结构耦合模型,分析压力冲击条件下滑靴的表面温度、应力以及变形的变化规律.研究结果表明:某型轴向柱塞泵中滑靴温度随柱塞腔压力呈周期性变化,滑靴温度范围为45.5~49.8℃,且滑靴的最高温度出现在泵的吸排油过渡区.当滑靴处于泵的排油区时,滑靴的最大轴向应力为250MPa,集中在滑靴油腔与密封带之间的边缘区域.滑靴的轴向应力分层显著,引起滑靴的变形分化,其变形量为12.5~15μm,出现在滑靴的边缘.由于滑靴的输入热流密度增强磨粒的剪切力,加剧滑靴表面的微切削和挤压变形,导致滑靴表面出现条状剥落和凹坑磨损,呈现出黏着和磨粒磨损特征.      

一体式挠性接头及其制造技术

针对目前动力调谐陀螺仪中普遍采用的组合式挠性接头的不足之处，给出了一种新型的一体式挠性接头。分析了其结构特点，提出了相应的加工制造技术并进行了样件试制，运用专门研制的角刚度测量仪对加工样件的角刚度进行了测量评定，结果表明提出的制造工艺切实可行。     

基于磁链重构的永磁同步电机分布参数模型

针对基于电感的永磁同步电机(PMSM)线性集中参数模型无法描述电机磁路饱和、反电动势非正弦等非理想特性的问题,提出一种基于磁链重构的PMSM分布参数模型,并进行了仿真和试验验证。首先通过有限元分析(FEA)获取电机不同工作点下的磁链,其次利用傅里叶级数展开和多项式拟合方法对磁链进行重构,再根据重构的磁链建立起PMSM分布参数模型,并进行了仿真和试验验证。仿真和试验结果表明,模型能准确描述PMSM在不同工况下的非线性特性。     

基于空间机械臂的柔顺抓捕技术研究综述

空间机械臂是广泛应用于空间探索与实验的重要机电设备,柔顺抓捕技术为其执行主要任务的基础。空间机械臂柔顺抓捕技术主要分为结构设计与控制方法两个方面。首先介绍了目前已成功应用的空间机械臂末端执行器系统,分析了其结构与抓捕原理特点,说明了相应优势与不足,并给出结构优化的合理建议。然后介绍柔顺抓捕的控制方法在空间任务以及部分非空间任务中的成功应用,比较了其特性与优劣,归纳出优化的空间机械臂柔顺抓捕控制策略。本研究期望为空间机械臂柔顺抓捕技术的研究提供思路。     

基于声振主要传播路径的汽车风噪简化模型评估

以某款实车为研究对象建立了统计能量分析（Statistical Energy Analysis，SEA）模型，通过传播特性分析对其主要传播路径进行分类，并进行简化模型近似性分析。通过对SEA模型中主要和次要子系统选取，建立了2种简化模型，对其车内噪声和传播路径的计算表明:模型子系统特性改变，能量的传播路径和大小特性随之变化、甚至子系统对外界流体脉动和声场的接受能力也发生变化，导致得到的车内噪声计算结果发生改变。简化模型的使用还需进一步研究。     

SINS在小型无人机测控方面的应用

为了满足小型无人机航姿系统设计需要,本文对捷联式惯导系统特点及其在小型无人机导航制导领域的应用进行了讨论,特别是对捷联惯导系统通过优化算法及由全球定位系统和捷联惯导系统组建的组合式导航系统进行了分析.讨论结果表明,捷联式惯导系统(包括以捷联式惯导系统为基础组建的组合式导航系统)能够满足无人机导航要求,在小型无人机领域具有很好的应用前景.     

Performance analysis of PPP ambiguity resolution with UPD products estimated from different scales of reference station networks

Integer ambiguity fixing with uncalibrated phase delay (UPD) products can significantly shorten the initialization time and improve the accuracy of precise point positioning (PPP). Since the tracking arcs of satellites and the behavior of atmospheric biases can be very different for the reference networks with different scales, the qualities of corresponding UPD products may be also various. The purpose of this paper is to comparatively investigate the influence of different scales of reference station networks on UPD estimation and user ambiguity resolution. Three reference station networks with global, wide-area and local scales are used to compute the UPD products and analyze their impact on the PPP-AR. The time-to-first-fix, the unfix rate and the incorrect fix rate of PPP-AR are analyzed. Moreover, in order to further shorten the convergence time for obtaining precise positioning, a modified partial ambiguity resolution (PAR) and corresponding validation strategy are presented. In this PAR method, the ambiguity subset is determined by removing the ambiguity one by one in the order of ascending elevations. Besides, for static positioning mode, a coordinate validation strategy is employed to enhance the reliability of the fixed coordinate. The experiment results show that UPD products computed by smaller station network are more accurate and lead to a better coordinate solution; the PAR method used in this paper can shorten the convergence time and the coordinate validation strategy can improve the availability of high precision positioning.     

Impact of the thermal effect on the load-carrying capacity of a slipper pair for an aviation axial-piston pump

A thermal hydraulic model based on the lumped parameter method is presented to analyze the load-carrying capacity of a slipper pair in an aviation axial-piston pump under specified operating conditions. Both theoretical and experimental results are presented to demonstrate the validity of the thermal hydraulic model. The results illustrate that the squeezing force and thermal wedge bearing force are the main factors that affect the film thickness and load-carrying capacity. At high oil temperature and high load pressure, the film thickness decreases with increasing clamping force due to a combined action of the squeezing bearing force and the thermal wedge bearing force, but the load-carrying capacity will increase. An increase of the film thickness is proven to be beneficial under high shaft rotational speed but especially dangerous as it strongly increases the ripple amplitude of the film thickness, which leads to decreasing the load-carrying capacity. The structural parameters of the slipper can be optimized to achieve desired performance, such as the slipper radius ratio and orifice length diameter ratio. To satisfy the requirement of the load-carrying capacity, the slipper radius ratio should be selected from 1.4 to 1.8, and the orifice length diameter ratio should be selected from 4 to 5.