Improved closed loop identification of transfer function model for unstable systems

The method of identifying first order plus time delay transfer function model proposed for unstable systems by Ananth and Chidambaram [Closed loop identification to transfer function model for unstable systems, J. Franklin Inst. 336 (1999) 1055-1061] is modified to avoid the stability problems [Cheres, Parameter estimation of an unstable system with a PID controller in a closed loop configuration, J. Franklin Inst., 2005, accepted for publication] of the method. Two modifications are proposed. In the first modification of the method, the under-determined algebraic equations problem is converted into an optimization problem for calculation of the three parameters of the first order plus time delay (FOPTD) model. A simple method is given for the initial guess values of the model parameters. In the second approach, from the definition of Laplace transform of the output response, a third equation is formulated. The resulted three equations, in terms of the three parameters of the transfer function model, are then numerically solved. Simulation results are given for the second order plus time delay transfer function considered by Cheres 2005 [Parameter estimation of an unstable system with a PID controller in a closed loop configuration, J. Franklin Inst., 2005, accepted for publication]. The responses of the identified models with the same PID controllers are compared with that of the actual system. PID controllers are designed based on the identified models. The closed loop responses of the controllers on the original system are evaluated and compared. The present methods give better control performances.     

Modified Realization Technique for Digital Filters Derived from Analog Counterparts

A simple realization scheme for one-dimensional and two-dimensional recursive digital filters derived from analog reference transfer functions is presented. The method is based on proper predistortion of the analog transfer function to obtain a new Hurwitz polynomial. Analog-to-digital transformations, such as the bilinear transformation, are then applied to the resulting predistorted reference transfer function to obtain the discrete version of the system. It is shown that a proper choice of the predistorting function will yield digital realizations which are free of the delay-free loops and in most cases are near minimal. To illustrate the simplicity and efficiency of the technique, examples of 1-D and 2-D cases are worked out. The proposed scheme can readily be extended to include the multi-dimensional case.     

Exact Model-Matching of 2-D Systems via State Feedback

This paper considers the problem of matching the transfer function matrix of a given two-dimensional (2-D) system to that of a desired 2-D model using state feedback. The approach followed refers to systems having square transfer function matrices and reduces the problem to that of solving a linear system of equations. Furthermore, necessary and sufficient conditions are established for exact matching. An example is included to illustrate the proposed method.     

基于兴趣转移的微博用户动态画像生成

【目的/意义】微博用户画像的精准构建,可有效识别用户的需求,提高个性化推荐的准确率。针对现有微 博用户画像构建方法对用户特征提取不全面、不准确的问题,本文提出了基于兴趣转移的用户画像构建方法。【方 法/过程】首先,依据层次分析法确定不同兴趣行为的权重,并将其用于修订兴趣词权重,获得用户的初始兴趣词 集;然后,依据生命周期理论获得用户兴趣行为周期,构建兴趣转移的时间衰减函数,实现对用户兴趣词集的动态 更新和叠加;最后,将用户的静态属性标签与基于兴趣转移的动态兴趣标签融合构建微博用户画像。【结果/结论】 实验采用从新浪微博爬取的真实数据作为数据集,实验结果显示：与已有微博用户画像构建方法相比,本文提出的 方法在个性化推荐中具有较好的性能。【创新/局限】创新点为：借鉴生命周期理论刻画微博用户兴趣行为周期,构 造兴趣转移的时间衰减函数,实现兴趣标签的动态更新。局限是未对静态属性标签的重要性进行界定,且未对存 在异常波动的兴趣行为曲线进行深入探讨。     

Order Reduction of Linear System Models with a Time-Frequency Domain Method

A mixed method of model-order reduction is introduced, which is based on the linear state-space representation of the original system. The derivation of its transfer function matrix expression uses the Leverrier algorithm and the application of well known partial-fraction expansion techniques together with the concept of dominant eigenvalues on the transfer function of the system. The method is general, relatively simple to apply and yields fairly accurate reduced-order models. As an illustration the method has been applied successfully to a tenth-order two-input two-output time-invariant linear model of a practical power system.     

Feedback factorizing control of 3-D transfer functions via a canonical state-space model

The problem factorizing (separating) the transfer function of a given SISO 3-D discrete system, ie of a system depending on three independent variables, is considered. The 3-D system is assumed to be available in its transfer function representation, which is converted to a canonical state-space model by a simple inspection procedure. Then applying state-feedback to this canonical model we choose the feedback matrix gain (under certain conditions) such that the transfer function of the closed-loop system has the desireed factorized form, ie a product of three 1-D transfer functions each one being dependent on a single variable. The method is illustrated by a nontrivial numerical example.     

Model Reduction Over a Frequency Interval Using the Spectral Function

Two simple methods of model reduction over a frequency interval are proposed. In both of the procedures the reduced model is chosen so that its spectral amplitude function matches with that of the original system in a specified frequency band. In the first method we develop a polynomial approximation to the spectral function of the original system. In the second method we force the spectral function of the reduced order model to coincide with that of the original system at certain chosen frequency points. The frequency responses of the reduced models obtained by both methods match fairly well with that of the original system. The virtue of this method is that it can be applied to systems of which only frequency response data are available and not the transfer function.     

A robust fractional-order controller design with gain and phase margin specifications based on delayed Bode’s ideal transfer function

In this study, a robust fractional-order controller design methodology for a type of fractional-order or integer-order model with dead time is proposed using phase and gain margin specifications. The delayed Bode’s ideal transfer function is used as a reference model to design the controller analytically. The delay term in delayed Bode’s ideal transfer function provides the exact determination of these frequency domain specifications when the system owns a dead time. The analytical robust controller design problem is transformed to solving four nonlinear equations with four unknown variables, two of which are the desired specifications; namely, phase and gain margins. The remaining two are the phase and gain cross-over frequencies. Next, some conditions are set based on the desired specifications so that nonlinear equations provide a unique solution. The proposed method is compared with the other existing robust controller methods based on the same frequency domain specifications. The simulation results reveal that the proposed method outperforms the other methods and also gives closer outcomes to the desired specifications.     

预解算法在模式转换中的应用探讨

针对如何求取系统的开环传递函数,提出一种面向系统结构图应用预解算法求取单输入——单输出系统开环传递函数的方法。该方法简单,计算精度高。     

超前进位原理研究和逻辑设计改进

利用直观的图形方法研究了不同于传统超前进位函数的其它传递函数,这些新的传递函数同样能实现超前进位.在此基础上,对现行的超前进位发生器、超前进位加法器的逻辑电路提出改进意见.     

Method for Computing Time Response of Systems Described by Transfer Functions

A simple numerical method for computing the time domain response of linear time invariant systems described by their transfer functions is presented. The method does not require computation of transfer function poles or residues; it is not influenced by the multiplicity of poles or zeroes, nor does it require computation of the matrix exponential. Rather, it is based on a numerical method for inverting Laplace transforms. It is equivalent to very high order, absolutely stable numerical integration. Stiff systems present no problems.     

隐性知识转移的不完全合约激励措施研究——基于经济人假设与互惠性假设条件下的对比性博弈均衡分析

隐性知识转移是知识管理活动中的一项重要行为,是实现知识的资本性功能的有效方式。知识理论中关于隐性知识转移的研究目前仍停留在宏观理论领域,缺乏对微观层面的应用性探讨。隐性知识转移模型与激励理论中的委托—代理模型存在着天然的拟合性,但是,基于理性经济人前提下的完全合约理论对隐性知识转移行为不存在实质性的指导作用。借助于莫里斯—霍姆斯特姆模型的简化形式,通过对互惠性假设下与经济人假设下隐性知识转移行为的博弈均衡的对比分析可知:基于不完全合约的互惠性激励措施在隐性知识转移活动中更具有现实性的实践意义。     

Stability-equation method for sampled-data systems

This paper presents a new transformation by which the stability-equation method can be applied for analysis and design of sampled-data systems. New stability criteria applicable to systems with transfer function having both real and complex coefficients are presented. Several kinds of examples are considered with computer results given.     

On the Input—Output Decoupling of 2-D Systems by State Feedback

The problem of designing a linear state feedback controller for single-input single-output decoupling of linear multivariable 2-D (two-dimensional) systems is discussed. A method is presented for the determination of the decoupling controller matrices which, when applied to the open-loop system, yield a closed-loop system whose transfer function matrix is diagonal and nonsingular. Necessary and sufficient conditions are established for the state feedback decoupling problem to have a solution. Two examples are included to illustrate the proposed decoupling method.     

MATLAB和VC混合编程在时滞混沌系统仿真中的应用

本文结合MATLAB与VC的编程优势,给出了一种将MATLAB中编译的m函数文件生成可脱离MATLAB环境的动态连接库,然后在VC环境中编写应用程序界面并加载调用动态连接库,从而实现了MATLAB的数学函数与VC的无缝连接。以时滞混沌系统仿真为例,实现了MATLAB图形结果在VC中的调用,证实了方法的可行性。     

传递函数灵敏度最小化的数字状态反馈控制系统FWL结构

数字状态反馈控制系统的有限定长结构的优化实现问题,主要考虑了系统的传递函数灵敏性测度,通过分析该测度一个上确界与实现所在坐标系的关系,得到了最小化该测度上确界的结构,仿真例子说明了优化的结果。     

Pole sensitivity in coupling networks

When designing lossless networks, one is faced with the problem of choosing a zero configuration for the reflection coefficient ?(s). Bode showed that if parasitic capacitances are present as well as for power transfer optimization, the best zero configuration is to locate all of them in the left half-plane. Recently, Bode's result was generalized to include parasitic immitances at both ends (source and load) of the quadripole.This work adds a new result to the theory by looking at the overall transfer function poles. It is shown that (a) if the source resistance varies, one should select left half-plane zeros for ?(s); and (b) if the load impedance varies, one should select right half-plane zeros.The pole sensitivity criterion used is the distance between the actual transfer function poles and the poles of the ideal transfer function.     

Disturbance rejection and control system design based on a high-order equivalent-input-disturbance estimator

This paper presents an improved equivalent-input-disturbance (EID) approach to deal with exogenous disturbances. A high-order filter is newly used to construct an improved EID estimator. The parameters of the filter are selected to improve the disturbance-rejection performance without changing the bandwidth of an EID-based control system. The stability and disturbance-rejection mechanism of the system are analyzed using the transfer function from the EID to the output. The high-order filter is designed using the loop-shaping method. Simulation results of a rotational control system demonstrate the validity of the approach and superiority over other methods.     

Direct design of recursive digital filters based on a new stability test

In this paper we present an alternative approach to the direct design of 1-D recursive digital filters satisfying prescribed magnitude specifications with or without constant group delay characteristic. This method uses an iterative method to calculate the coefficients of the filter's transfer function and guarantees the stability of the designed filter using a new stability test reported by Ramachandran and Gargour. To illustrate the usefulness of the technique, examples are given.