微重力落塔落舱释放控制振动信号的小波分析

论述了微重力落塔落舱电磁悬吊、释放、提升控制系统的关键技术,结合电磁释放系统特点,分析了释放时振动信号的特点,介绍了应用小波分析方法进行信号去噪的基本原理.基于阈值小波变换去除振动信号高、低频噪声,然后应用小波包分解方法获取信号的特征量从而进行信号的重构,消除瞬态突变干扰信号,并对系统结构和组成进行了分析.实验结果表明:该方法可以有效地进行信号的消噪,并获取真实的释放振动信号.     

微重力空间下微纳遥感卫星太阳翼构型仿真分析

针对微纳遥感卫星从技术试验阶段到业务化应用的转型发展,如何缓解其能量来源的受限条件,获取更高的太阳能充电效能,对微纳遥感卫星未来星座构建的发展需求有重要作为。通过设计不同构型的微纳卫星太阳翼,构造太阳电池阵列的仿真模型,根据太阳能电池阵列在微重力空间下的工作特性,仿真分析微重力空间下不同构型太阳翼的充电性能和充电效率,并对不同构型的使用性能进行了分析比较,结果表明,选择最优太阳翼构型能够为微纳遥感卫星提供更好的能源和动力支撑,为后续微纳遥感卫星开展更多商业应用提供有效参考。     

空间微重力下植物栽培水分养分控制研究

通过"天宫2号"空间实验室搭载的空间植物栽培装置,研究了微重力下植物栽培水分养分控制技术.针对空间微重力特点,设计了植物栽培水分养分传导结构,并验证了其可行性和合理性.生菜在空间实验室微重力环境下的顺利萌发、生长发育,证明了水分养分传导结构的合理性和可行性,为后续开展更大规模的空间植物栽培奠定了基础.通过实验,了解了空间微重力下水分养分的传导和分布规律,为研究空间植物栽培水分养分供应方法和测试方法提供了依据.     

Optimal tracking performance of MIMO discrete‐time systems with communication constraints

The optimal tracking problem for multiple‐input multiple‐output linear‐time‐invariant discrete‐time systems with communication constraints in the feedback path is studied in this paper. The tracking performance is measured by the energy of the error signal between the output of the plant and the reference signal. The objective is to obtain an optimal tracking performance, attainable by all possible stabilizing compensators. It is shown that the optimal tracking performance consists of two parts, one depends on the nonminimum phase zeros and zero direction of the given plant, as well as the reference input signal direction, and the other depends on the nonminimum phase zeros, unstable poles, and pole direction of the given plant, as well as the bandwidth and additive white Gaussian noise of the communication channel. It is also shown that, if the constraint of the communication channel does not exist, the optimal tracking performance reduces to the existing tracking performance of the control system without communication constraints. A typical example is given to illustrate the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.     

编解码和时延约束下的网络化控制系统最优跟踪性能

本文研究了具有丢包、时延、编解码等通信资源受限下多输入多输出离散时间网络控制系统的最优跟踪性能. 基于频域方法, 采用二元随机过程来模拟数据包丢失, 并假设信道噪声是加性高斯白噪声(AWGN), 推导了在丢包、信道噪声、时延和编解码影响下的跟踪性能极限. 采用单参数补偿器(SDOF), 利用互质分解、Youla参数化等工具得到了编解码和时延约束下的网络控制系统最优跟踪性能的显式表达式. 结果表明, 跟踪性能与对象的固有特性(非最小相位零点与不稳定极点的位置和方向)、时延、丢包率和AWGN 功率谱密度密切相关.     

多变量离散系统随机信号跟踪性能极限

研究线性时不变、多变量、离散系统对随机信号的跟踪性能极限问题, 所考虑的随机参考输入信号为布朗运动序列. 研究结果表明此类系统的跟 踪性能极限完全由被控对象的结构特征和参考输入的统计特征决定, 其中, 结构特征指被控对象的非最小相位零点和不稳定极点的位置和方向. 作为特殊情形, 本文给出了参考输入为一致随机信号以及被控对象仅含有单个非最小相位零点和单个不稳定极点时系统跟踪性能极限问题的解. 最后, 给出了两自由度补偿器跟踪系统对随机信号的跟踪性能极限.     

Best Tracking Performance of Networked Control Systems Based on Communication Constraints

The best tracking problem for a single‐input‐single‐output (SISO) networked control system with communication constraints is studied in this paper. The tracking performance is measured by the energy of the error signal between the output of the plant and the reference signal. The communication constraints under consideration are finite bandwidth and networked induced‐delay. Explicit expressions of the minimal tracking error have been obtained for networked control systems with or without communication constraints. It is shown that the best tracking performance dependents on the nonminimum phase zeros, and unstable poles of the given plant, as well as the bandwidth and networked induced‐delay. It is also shown that, if the constraints of the communication channel do not exist, the best tracking performance reduces to the existing tracking performance of the control system without communication constraints. The result shows how the bandwidth and networked induced‐delay of a communication channel may fundamentally constrain a control system's tracking capability. Some typical examples are given to illustrate the theoretical results.     

超临界二氧化碳与异丁醇二元体系气液相互溶解度模型的研究

采用可变体积可视观察法测量装置,测定CO_2与异丁醇在40℃-80℃温度范围和不同压力下的平衡数据。研究高压状态下CO_2在液相中的溶解度和异丁醇在气相中的溶解度模型,以改进亨利定律和Chrastil半经验溶解度方程,提出适合于高压下CO_2与异丁醇二元体系的相互溶解度模型,其中CO_2在液相中的溶解度可用4次多项式模型关联,其形式为:P_(CO_2)=A+B_1·x~(CO_2)+B_2·x_(CO_2)~2+B_3·x_(CO_2)~3+B_4·x_(CO_2)~4。异丁醇在CO_2中的溶解度可用改进的Chrastil半经验溶解度方程模拟,其形式为C=p~k·exp(α/T)+b。结果:所提出的气相溶解度方程和液相溶解度方程与试验数据非常吻合,拟合相关系数和精度较高。     

Optimal Performance in Tracking Stochastic Signal Under Disturbance Rejection

The analysis method of optimal tracking performance is proposed for multiple‐input multiple‐output (MIMO) linear time‐invariant (LTI) systems under disturbance rejection. An H₂ criterion of the error signal between the output of the plant and the reference signal is used as a measure for the tracking performance. Spectral factorization is applied to obtain the optimal solution of the system tracking error. The explicit expressions are derived for this minimal tracking error with respect to random reference signals under disturbance rejection. It is shown that the nonminimum phase zeros, the zero direction, the unstable poles, the pole direction of a given plant, statistical characteristics of the reference input signal, and disturbance signal have a negative effect on a feedback system's ability to reduce the system error with disturbance rejection. The results show that the optimal tracking performance will further be damaged because of disturbance rejection. Some typical examples are given to illustrate the theoretical results.     

热传导反问题中相变界面的实时跟踪

针对固体融化过程中液体与固体之间相变界面的实时跟踪问题,建立了由固定边界上得到的温度和热流到其相变界面轨迹的辨识及跟踪算法。由于在实际过程中无法在液体边测量其温度和热流,因此,该类问题无法通过直接Stefan问题的求解来得到相变界面的实时跟踪。将其归结为一类不适定反Stefan问题的求解,给出了基于Tikhonov正则化方法的滑动区间优化算法。     

Modified performance of MIMO wireless networked time‐delay systems over fading channels

In this paper, the modified performance limitation of multi‐input multi‐output (MIMO) wireless networked time‐delay systems over fading channels is investigated, where the characteristic of the fading channels is assumed to be a random process. The modified tracking performance limitation is considered based on frequency domain representation. The display expressions of performance limitation are achieved by using the co‐prime factorization and the spectral decomposition techniques. The obtained results show that the modified performance limitation of the wireless networked time‐delay systems is related to the inherent characteristics of the given plant, including the non‐minimum phase zeroes, the unstable poles, the encoding‐decoding, the fading channels, the bandwidth and the modified factor. Finally, some numerical examples are provided to demonstrate the efficiency of the proposed design method.     

An Optimal Tracking Performance of MIMO NCS with Quantization and Bandwidth Constraints

This paper presents an optimal tracking performance of multiple‐input multiple‐output (MIMO) networked control systems (NCSs) with quantization and bandwidth constraints. In this study, we simultaneously consider the encoding‐decoding, quantization and bandwidth of communication channel. The optimal tracking performance of NCSs is obtained by spectral factorization technique and partial fraction. The obtained results demonstrate that the optimal tracking performance is influenced by the nonminimum phase zeros and unstable poles as well as their directions for a given plant. In addition, it is shown that characteristics of reference signal, encoding‐decoding, quantization, and bandwidth of communication channel are also closely related to tracking performance. Finally, the efficiency of proposed tracking performance is verified by typical examples.     

Practical output tracking of switched nonlinear systems in p-normal form with unstable subsystems

This paper studies practical output tracking of switched nonlinear systems in p-normal form. No solvability of the practical output tracking problem for subsystems is required. A constructive scheme to solve the problem for a switched nonlinear system is set up by exploiting the single Lyapunov function method and the tool of adding a power integrator. Also, we design a proper switching law and construct state-feedback controllers of subsystems. A two inverted pendulums as a practical example, which cannot be handled by the existing approaches, illustrates our theoretical result.     

微型测控应答机再生测距码跟踪精度研究

微小卫星的星载测控应答机由于功率和天线增益受限,测距误差较大.而再生伪码测距能显著减少下行链路的噪声,从而提高伪码跟踪精度.针对最新的再生测距码,利用线性分析的方法,对伪码跟踪环的理论均方定时误差进行了推导,并对这些测距码的跟踪性能进行了仿真和比较.与理论值不同的是,环路的实际跟踪性能由于VCO相位噪声的存在,不是环路带宽的单调函数.因此,需要根据信噪比条件设置相应的最佳带宽,以得到最佳的跟踪性能.与理论情况相比,各测距码实际环路跟踪性能的差异有所减小.     

提高液体中石英晶体传感器频率稳定度的方法

石英晶体传感器的动态阻抗显著增大,品质因数下降是液体阻尼负载作用的主要效果。本文从分析液体中石英晶体谐振器的相位平衡条件出发,研究了影响传感器频率稳定度的因素;由石英晶体谐振器的能量局部化效应,分析了传感器液体测头设计中的问题,并由此设计出在液体中工作的石英晶体传感器。实验结果表明,此传感器在液体中具有较高的频率稳定度。     

高动态下直扩接收机关键模块的设计与仿真*

高动态给扩频信号带来较高的多普勒频移,使伪随机码产生较大的动态时延,很容易造成载波跟踪环和码跟踪环的失锁。为了提高跟踪环路的动态应力,防止跟踪环路失锁,在分析了捕获与跟踪原理的基础上,提出了一种捕获与跟踪的设计方案。该方案捕获采用基于FFT的并行快速捕获算法,载波环采用2阶锁频环FLL(frequency locked loop)辅助3阶锁相环PLL(phase locked loop),码环采用2阶延迟锁定环DLL(delay lockedloop)。MATLAB仿真结果表明,在高达65 g的视距动态应力条件下该设计也能够表现出其精确、稳定的性能。     

应用电导探针技术识别气液两相流流型方法及电导波动信号噪声的辨识

针对垂直上升管的气液两相流流型的识别,提出了一种多电导探针测量系统,该测量系统由3个电导探头组成电导传感器,在此基础上利用INV306型数据采集卡实现了电导波动信号的数据采集。由于各种生产过程的参数进行测量时不可避免地信号中存在噪声信息,通过对信号的小波分解和自相关函数的分析发现电导波动信号为低频信号,且其频率一般不会超过128Hz。又通过对信号进行了小波去噪和傅立叶变换去噪之后发现利用小波分析进行信号的消噪可以很好的保存原信号中的有用部分,其有着傅立叶分析不可比拟的优点。     

锁相环技术在频率跟踪中的应用研究

本文介绍锁相环及其频率跟踪的基本原理,给出二阶锁相环和四阶锁相环的设计依据。在此基础上,对四阶锁相环实现频率跟踪的转换时间进行了仿真,就如何减小频率跟踪的转换时间提供了可行方法。通过对锁相环的分析和仿真,达到优化设计频率跟踪方案的目的。     

分子模拟在反相液相色谱分离机理研究中的应用

分子模拟技术是近些年发展起来的一门新兴计算化学技术。本文简要介绍了四种常用的分子模拟方法在反相液相色谱分离机理研究中的应用。详细阐述了采用分子动力学模拟法研究固定相的烷基链构象变化、流动相中溶剂分子与溶质分子间相互作用等与溶质的色谱保留过程的关系。