Synthesis of phase-lead/lag compensators with complete information on gain and phase margins

This work provides a new approach for phase-lead/lag compensators to achieve the desired specifications of gain and phase margins for all-pole stable plants with time-delay. The stabilizing regions of lead/lag compensators are first determined in terms of a graphical stability criterion. These regions are drawn graphically, not to be calculated mathematically. Then, by defining appropriate functions relative to the requirements of gain and phase margins, the curves in the stabilizing regions satisfying the pre-specified gain and phase margins can be drawn, which gives the complete information on gain and phase margins. Illustrative examples are given to show the design procedure and to compare our method with other existing tuning rules.     

Tuning of phase-lead compensators for exact gain and phase margins

In this paper, a simple tuning method for phase-lead compensators with specifications of gain and phase margins is proposed. It can achieve the given margins exactly regardless of the plant order, time delay or damping nature. The solutions are found from the intersections of the curves of two real functions plotted using the frequency response of the plant only. An example is provided for illustration and comparison.     

Characterization of PID and lead/lag compensators satisfying given H/sub /spl infin// specifications

This note deals with the problem of characterizing a class of second-order three-parameter controllers [including proportional-integral-derivative (PID) and lead/lag compensators] satisfying given H/sub /spl infin// closed-loop specifications. Design characterizations of similar form as in the recent work on PID control, are derived for a larger class of compensators using simple geometric considerations. Specifically it is shown that, given the value of one parameter: i) the region of the plane defined by the other two parameters where the considered H/sub /spl infin// constraint is satisfied, consists of the union of disjoint convex sets whose number can be bounded by means of the pancake-cutting formula, and ii) the closed-loop pole distribution can be related to them. An example illustrates how the method can be applied to design a PID controller in the case of bounded sensitivity.     

On the design and properties of multivariable dead time compensators

The design problem of multivariable dead time compensators for MIMO systems with multiple dead times is considered. Analytical design aids which take into account the stability and sensitivity properties of these systems are presented. Conditions for practical stability, estimates on allowable tolerances in process models and methods for determining controller gains are derived. Based upon sufficient conditions, these methods lead to conservative gains. The extent of conservation is related to the amount of computational effort involved in each method and to the available plant information. It is shown that the type of dead time compensator treated here cannot be applied to unstable processes. Diagonal dominance theory is used to derive some of the results. Illustrative examples demonstrate the main results.     

连续挤压收排线机控制系统时滞性研究

DSP1600收排线机是型号TLJ400连续挤压机的配套设备,该型号收排线机的控制系统是由伺服放大器、伺服电机及PLC构成。但由于驱动方式及机械因素等原因导致收排线机在换向时产生时滞性,使收排线机在运行过程中产生不稳定现象。通过东华DH5920动态信号测试仪采集主动轮与从动轮在换向时的频率数据,来分析设备的时滞性。最后采用模糊PID控制方案并且编辑PLC换向程序进行提前补偿,克服间隙影响,消除时滞性和机械设计等环节所造成的非线性因素,从而提高收排线机运行的稳定性及排线精度。     

A generalized relay identification method for time delay and non-minimum phase processes

A generalized relay identification method is proposed in this paper for time delay and non-minimum phase processes. A distinct merit of the proposed method is that the process gain can be uniformly derived from a single run of the relay test, independent of the relay type being unbiased or biased. An analytical relay response expression is derived for assessing the process response under an unbiased or biased relay test. A frequency response algorithm is also derived for estimating the multiple frequency response points of the process. By categorizing cases of the model parameters to be identified, the corresponding identification algorithms are developed using fitting conditions established for the process response at the oscillation frequency. Based on the improved estimation of multiple frequency response points, a recursive least-squares identification algorithm is then proposed for obtaining further enhanced fitting accuracy over a user specified frequency range, e.g., the low frequency range often concerned in practical controller tuning. Illustrative examples from the recent literature are given to demonstrate the effectiveness and merits of the proposed algorithms.     

Analysis of windowing/leakage effects in frequency response function measurements

This paper analyses the errors on the frequency response function measurement of a transfer function due to finite window effects (leakage). First an analysis of the rectangular and the Hanning window is made. It will be shown that the leakage error consists of two components: a transient error due to initial and end condition effects, and an interpolation error due to the combination of neighbouring spectral lines. Starting from these insights an extremely simple expression to calculate the leakage induced bias and variance errors is generated. Eventually, a new ‘default’ window is proposed with slightly better properties. This allows a reduction in measurement time by 25% if the leakage errors dominate the disturbing output noise.     

Nonlinear system-identification of the filling phase of a wet-clutch system

The work presented illustrates how the choice of input perturbation signal and experimental design improves the derived model of a nonlinear system, in particular the dynamics of a wet-clutch system. The relationship between the applied input current signal and resulting output pressure in the filling phase of the clutch is established based on bandlimited periodic signals applied at different current operating points and signals approximating the desired filling current signal. A polynomial nonlinear state space model is estimated and validated over a range of measurements and yields better fits over a linear model, while the performance of either model depends on the perturbation signal used for model estimation.     

全相位OFDM系统的最大自相关帧同步

针对数字地面广播电视（DTMB）系统,提出了一个对载波频偏具有鲁棒性的新的帧同步算法。该算法通过正交频分复用（OFDM）信号的时域复制和对接收信号实行自相关来实施。自相关数值输出的非关联求和的峰值检测是理所当然的帧起始点。理论证明,载波频率偏移（CFO）对全相位自相关帧同步算法没有影响。通过仿真表明,在频率选择性衰落信道中,提出的方法在有频偏存在情况下比传统算法具有很强的优势,对于DTMB系统的PN420模型,系统保持稳定工作的最大CFO在所提方法中要远远大于传统的方法。     

基于Matlab／Simulink的电容组控制系统建模与仿真

无线电射频系统因其成本低廉、可选商品众多成为应用最广泛、性价比最高的EAS系统。该文用Matalb／Simulink仿真无线射频系统中电容随电感变化调整使得电路达到谐振的过程。     

基于GPS/DR的GPS滞后时间自适应检测算法

针对GPS输出信息的随机延迟特性,基于航位推算(DR)系统惯性器件的实时性与短时高精度,提出了航向差和速度自适应GPS滞后时间检测方法,在此基础上,对GPS和DR数据进行数据对准,提出了自适应GPS滞后时间处理算法。在GPS/DR实际系统中的应用结果表明,本算法能够准确检测出GPS的滞后时间,提高车辆的定位精度。     

I/O performance of an RAID-10 style parallel file system

Without any additional cost, all the disks on the nodes of a cluster can be connected together through CEFT-PVFS, an RAID-10 style parallel file system, to provide a multi-GB/s parallel I/O performance.I/O response time is one of the most important measures of quality of service for a client. When multiple clients submit data-intensive jobs at the same time, the response time experienced by the user is an indicator of the power of the cluster. In this paper, a queuing model is used to analyze in detail the average response time when multiple clients access CEFT-PVFS. The results reveal that response time is with a function of several operational parameters. The results show that I/O response time decreases with the increases in I/O buffer hit rate for read requests, write buffer size for write requests and the number of server nodes in the parallel file system, while the higher the I/O requests arrival rate, the longer the I/O response time. On the other hand, the collective power of a large cluster supported by CEFT-PVFS is shown to be able to sustain a steady and stable I/O response time for a relatively large range of the request arrival rate.     

Computation of stabilizing Lag/Lead controller parameters

One of the central problems in control theory relates to the design of controllers for stabilization of systems. The paper deals with the problem of computing all stabilizing values of the parameters of Lag/Lead controllers for linear time-invariant plant stabilization. It is well known that linear controllers of Lag/Lead type are still widely used in many industrial applications. In this paper, an extension of a new approach to feedback stabilization based on the Hermite–Biehler theorem to the Lag/Lead controller structure is given. In addition, the problem of stabilization of uncertain systems defined by an interval plant is studied using the Kharitonov and the Hermite–Biehler theorems. The proposed method is analytical and it can be applied successfully using today’s advanced computer technology. Examples are included to illustrate the method presented.     

Analysis of multi-stage production/inventory system with an acceptable response time

This paper describes a method to decide the inventory levels of semifinished and finished products so as to realize the target service rate by shipping the finished products within a specified time which we call the acceptable response time. We analyze the substitution relation between the acceptable response time and the inventory levels of semifinished and finished products. As a result, inventory levels required according to the length of the acceptable response time under the condition of satisfying the target service rate are obtained. The validity of our method is also demonstrated through simulation experiments with the conditions given by the analysis.     

水/N-甲基吡咯啉酮/聚砜铸膜体系热力学相平衡的数值模拟

基于Flory-Huggins理论,考虑组分间的二元相互作用参数而忽略三元相互作用参数的影响,推导了水／N-甲基吡咯啉酮／聚砜铸膜体系的热力学模型。采用Lagrange乘子法将该模型转化为无约束非线性优化问题,通过单纯形法对该类无约束非线性优化问题进行了求解。计算并得到了水／N-甲基吡咯啉酮／聚砜体系在常压及23℃下的连结线和双结点曲线。结果表明,联合Lagrange乘子法和单纯形算法能较好地用于聚合物铸膜体系的热力学模型研究,及对有约束非线性优化问题的求解,本文的研究结果为该类体系相平衡研究以及有关非对称膜制备的理论研究提供了基础依据。     

Implementation and testing of an advanced relay auto-tuner

In this paper, an advanced relay feedback auto-tuner for single-loop controllers is presented. The tuner combines an improved relay feedback process frequency response identification method and a multiple-point frequency response fitting controller design method. In process identification, multiple accurate points on the frequency response curve of a process are obtained in one single relay feedback test. A controller is then designed based on these estimated points using frequency response fitting methodology. The auto-tuner was implemented on a personal computer with AD/DA card. The software was developed on a commercial real-time control platform. The algorithms were written in C++ and compiled as a Dynamic Link Library. The auto-tuner has been tested on a dual-process simulator which can be easily configured as various typical processes, and on pilot coupled-tank and heat exchanger. The testing results show that the tuner gives significant performance improvement over the standard relay auto-tuner.     

超空泡射弹尾拍运动流固耦合动力学响应研究

基于ANSYS软件和CFX软件的双向隐式交错迭代法对超空泡射弹尾拍运动过程中的流固耦合响应进行了研究,结构响应仿真采用有限元法、流场仿真采用分相流模型和SST湍流模型,重点比较分析了流固耦合作用对射弹运动姿态和流体动力的影响,给出了尾拍过程中弹体应力的变化规律.     

Simultaneous determination of lead and cadmium at a glassy carbon electrode modified with Langmuir–Blodgett film of p-tert-butylthiacalix[4]arene

A glassy carbon electrode (GCE) modified with a Langmuir–Blodgett (LB) film of p-tert-butylthiacalix[4]arene (TCA) has been investigated as a disposable sensor for measuring the trace levels of lead and cadmium. The possibility of determining lead and cadmium at trace levels was examined with differential pulse stripping voltammetry in the measurement step. The electrochemical response was characterized with respect to supporting electrolyte, pH of solution, accumulation time, accumulation potential, layers of the LB films, and possible interferences. Calibration plots were found to be linear in the range 2 × 10⁻⁷ to 5 × 10⁻⁵ mol l⁻¹ (Cd²⁺) and 1 × 10⁻⁷ to 2.5 × 10⁻⁵ mol l⁻¹ (Pb²⁺); the detection limits were 2 × 10⁻⁸ mol l⁻¹ (Cd²⁺) and 8 × 10⁻⁹ mol l⁻¹ (Pb²⁺). Possible recognition mechanism was also discussed. From the analysis of real samples (river, lake and tap water) it can be concluded that the method is sensitive and reproducible in determining of these elements and can be used in the analysis of natural water samples.     

基于并串转换DDS技术的任意波形发生器采样率研究

DDS（直接频率合成）技术的基本原理是基于取样技术和计算技术,因其频率分辨率高、输出频率切换速度快等优点,被广泛应用于任意波形发生器的设计。但现有的波形存储器（RAM芯片）读写速度不高,因而大大限制了基于DDS技术的任意波形发生器直接输出频率的范围。针对这一现状,本文提出了并串转换的方法来改进DDS技术,克服RAM读取速度低的问题,从而提高了任意波形发生器的采样率。     

应力型微悬臂梁生化传感器响应机理研究进展

针对静态微悬臂梁表面特异性结合产生表面应力信号的响应机制问题,介绍了微悬臂梁生化传感器的工作原理,阐述了应力响应机制的简化模型,从纵向界面上和横向分子间2个方面对特异性吸附引起的悬臂梁表面应力的变化进行了剖析,讨论了界面能变化、位阻作用、静电力、氢键作用等与表面应力大小及方向之间的关系,总结了应力型微悬臂梁生化传感器的响应机理的研究。