Robust adaptive stabilization for time-varying systems with unmodelled dynamics and disturbances

In this paper, robust adaptive stabilization is discussed for time-varying discrete time systems with disturbances and unmodelled dynamics. Both bounded and unbounded stochastic disturbances are considered. It is assumed that the parameters of the nominal model belong to a bounded convex set and that the ‘frozen time’ nominal model is stabilizable for all possible parameter values. Requiring neither external excitation nor stable invertibility of the nominal model, an adaptive regulator is constructed on the basis of the solution to a finite time Riccati equation and a projected gradient estimator. It is shown that the closed-loop system is stable if both the time average of the parameter variations and the model error are sufficiently small.     

Adaptive control of siso plants with unmodelled dynamics

In this paper we pursue a twofold aim. First we want to simplify the complexity of the classical Monopoli's scheme, the so-called ‘Augmented error signal control scheme’. Then we also wish to cope with the realistic situation in which the presence of unmodelled dynamics has to be taken into account. This latter problem has been faced in the literature by suitably modifying the adaptation mechanism in order to avoid undesired phenomena as well as to obtain an attractive stability region for the state trajectories starting from any point in a predefined initial condition set. In our case the necessity of introducing any sort of modification in the adaptation mechanism is completely avoided, but we still obtain asymptotic stability of the output error signal.     

Adaptive prediction in the presence of unmodelled dynamics

This paper considers the prediction problem for a discrete-time stochastic system with unmodelled dynamics. The precisely modelled part of the system is described by an ARMAX model, while unmodelled dynamics is represented by a small constant ζ multiplied by a quantity tending to infinity as the past input, output and noise of the system increase. For the estimation of the unknown predictor parameters, the usual stochastic approximation algorithm is used. Under the standard conditions imposed on the modelled system part, it is shown that the mean-square prediction error converges to a finite limit. This limit depends explicitly on the unmodelled dynamics in such a way that when the unmodelled dynamics decays, the prediction error tends to the minimum possible.     

Stable adaptive control system subject to bounded external disturbances

By means of minimizing a quadratic cost function and employing a modified least squares estimator with a dead zone, a new self-tuning controller is derived. Under simple assumptions the stability of the resulting closed-loop adaptive control system is ensured in the presence of bounded external disturbances even for non-minimum phase systems. The analysis performed also gives the upper bounds of tracking errors and parameter estimates. For the disturbance-free case a modified version of the basic algorithm ensures asymptotic stability, i.e. the output error converges to zero, without any additional assumptions. Simulation results demonstrate the effectiveness of the new controller.     

Synthesis of electric drive systems invariant to parametric and external disturbances by the method of polynomial equations

The possibilities of finding a general solution to a polynomial equation for the synthesis of electric drive systems are considered. It has been shown that regulators with adaptive properties can be designed on their basis, ensuring low system sensitivity to parametric and external disturbances. Examples of the use of such regulators in DC and AC electric drives are presented.     

Oscillator analysis with respect to higher harmonics

Contents The modified harmonic balance method has been worked out to describe the behaviour of oscillators generating output signal not on the first harmonic, as it is usual, but on the higher one. The main assumptions are: All higher harmonics are considered small compared to the first one and there is only one dominant resistive nonlinearity limiting amplitude of oscillations. The approximate solution of a microwave oscillator with Gunn diode is presented as an example. The results are in accordance with experimentally observed phenomena in the oscillator such as discontinuities and power drops in its characterstics.

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Oszillator-Analyse mit höheren Harmonischen

Übersicht Die Methode der modifizierten Harmonischen-Bilanzierung wurde weiterentwickelt, um das Verhalten von Oszillatoren zu beschreiben, die nicht wie üblich Signalleistung auf der Fundamentalen abgeben, sondern auf höheren Harmonischen. Dabei wird als wesentlich angenommen, daß die Amplituden der höheren Harmonischen klein sind, verglichen mit der ersten, und daß nur eine resitive Nichtlinearität dominierend die Schwingamplitude begrenzt.Als Beispiel wird die Näherungslösung eines Mikrowellenoszillators mit Gunn-Element vorgestellt. Die Lösungsergebnisse stimmen mit experimentelll beobachteten Erscheinungen im Oszillatorbetriebsverhalten überein, wie Kurvensprüngen und Leistungseinbrüchen.

     

A method to compute reactive power margins with respect to voltagecollapse

A method of computing the reactive power margin-i.e. the difference between the maximum reactive load and the corresponding base case value-for a given set of load buses of a power system is proposed. This margin is aimed at assessing the system robustness with respect to voltage collapse. The corresponding collapse point is directly obtained as the solution of an optimization problem with the load increase as the objective, the nonoptimized loads as equality constraints, and the generator reactive limits as inequality constraints. The CRIC electrical decoupling yields a voltage-only problem. The latter is solved using the Newton approach and a procedure is given to deal with the inequality constraints efficiently. A simple illustrative example and simulation results obtained on the Belgian 520-bus, 41-generator system are given     

Optimal distribution of primary control participation with respect to voltage stability

In competitive electricity markets the transmission system will at times be heavily loaded. At these occasions prevention of voltage instability is an important objective that the system operator has to meet. In this paper a method for finding the primary control participation that maximizes the margin from an operating point to the saddle-node bifurcation surface is proposed. The arising optimization problem is solved using a steepest descent method. The proposed method can find its applications both in generation planning and in real-time operation of electric power systems.     

Dielectric testing of solid insulation with respect to insulationcoordination of low-voltage equipment

In real insulation systems with solid insulation, partial discharges usually occur far below the breakdown voltage. In the long run, these lead to the destruction of nearly all solid insulating materials. The question, How much time has passed until the partial discharges have destroyed the solid insulation?, is of little relevance in low-voltage equipment since the occurrence of partial discharge during normal use will, in general not allow a sufficient lifetime. Moreover, the results of such lifetime investigations are influenced by many parameters; therefore, statements with general validity cannot be made     

Robustness enhancement of DC drives with a smooth optimalsliding-mode control

A quantitative analysis of the robustness of a DC drive system under sliding-mode control is presented. Analytic solutions in the time domain of the drive transient speed deviation and its maximum value due to a step load application are obtained. The new design approach developed here for the third-order optimal sliding-mode control system effectively enhances the system robustness against external disturbance. The differences in design concept between the new robust design and the classical control approach are highlighted. The fast response speed and robust performance of the drive system are both achievable by the new design method without the necessity of compromise. Digital simulations verify the design and results. Practical system implementation based on a low-cost 16 bit CHMOS microcontroller are briefly addressed     

Development of color density concept with color difference formulas in respect to human vision system

The aims of this study are to develop the color density concept and to propose the color density based color difference formulas. The color density is defined using the metric coefficients that are based on the discrimination ellipses and the locations of the colors in the color space. The ellipse sets are the MacAdam ellipses in the CIE 1931 xy-chromaticity diagram and the chromaticity-discrimination ellipses in the CIELAB space. The latter set was originally used to develop the CIEDE2000 color difference formula. The color difference can be calculated from the color density for the two colors under consideration. As a result, the color density represents the perceived color difference more accurately, and it could be used to characterize a color by a quantity attribute matching better to the perceived color difference from this color. Resulting from this, the color density concept provides simply a correction term for the estimation of the color differences. In the experiments, the line element formula and the CIEDE2000 color difference formula performed better than the color density based difference measures. The reason behind this is in the current modeling of the color density concept. The discrimination ellipses are typically described with three-dimensional data consisting of two axes, the major and the minor, and the inclination angle. The proposed color density is only a one-dimensional corrector for color differences; thus, it cannot capture all the details of the ellipse information. Still, the color density gives clearly more correct estimations to perceived color differences than Euclidean distances using directly the coordinates of the color space.     

Sensitivity studies of the powerline carrier channel with respect to the parameters of the coupling equipment

A theoretical sensitivity analysis of the overall losses in a carrier channel is presented. Some numerical results that would be of importance in the planning, design and selection of power-line carrier equipment are presented.     

家用电器防触电设计常见问题分析

阐述了解决家电产品防触电问题的重要性,具体分析了防触电设计中如一些风险较大的结构、在满足电气间隙、爬电距离和元器件合理选用等方面的常见问题,并给出了相关实例。同时提出了一些较为实际的防触电设计理念,为提高家电产品防触电安全性提供必要的技术依据。     

Absolute quantitation of brain metabolites with respect to heterogeneous tissue compositions in 1H-MR spectroscopic volumes

Object

Referencing metabolite intensities to the tissue water intensity is commonly applied to determine metabolite concentrations from in vivo ¹H-MRS brain data. However, since the water concentration and relaxation properties differ between grey matter, white matter and cerebrospinal fluid (CSF), the volume fractions of these compartments have to be considered in MRS voxels.

Materials and methods

The impact of partial volume correction was validated by phantom measurements in voxels containing mixtures of solutions with different NAA and water concentrations as well as by analyzing in vivo ¹H-MRS brain data acquired with various voxel compositions.

Results

Phantom measurements indicated substantial underestimation of NAA concentrations when assuming homogeneously composed voxels, especially for voxels containing solution, which simulated CSF (error: ≤92%). This bias was substantially reduced by taking into account voxel composition (error: ≤10%). In the in vivo study, tissue correction reduced the overall variation of quantified metabolites by up to 35% and revealed the expected metabolic differences between various brain tissues.

Conclusions

Tissue composition affects extraction of metabolite concentrations and may cause misinterpretations when comparing measurements performed with different voxel sizes. This variation can be reduced by considering the different tissue types by means of combined analysis of spectroscopic and imaging data.     

An express method for optimally tuning an analog controller with respect to integral quality criteria

An express method for optimally tuning analog PI and PID controllers is considered. An integral quality criterion with minimizing the control output is proposed for optimizing control systems. The suggested criterion differs from existing ones in that the control output applied to the technological process is taken into account in a correct manner, due to which it becomes possible to maximally reduce the expenditure of material and/or energy resources in performing control of industrial equipment sets. With control organized in such manner, smaller wear and longer service life of control devices are achieved. A unimodal nature of the proposed criterion for optimally tuning a controller is numerically demonstrated using the methods of optimization theory. A functional interrelation between the optimal controller parameters and dynamic properties of a controlled plant is numerically determined for a single-loop control system. The results obtained from simulation of transients in a control system carried out using the proposed and existing functional dependences are compared with each other. The proposed calculation formulas differ from the existing ones by a simple structure and highly accurate search for the optimal controller tuning parameters. The obtained calculation formulas are recommended for being used by specialists in automation for design and optimization of control systems.     

提高LCL型并网逆变器阻抗重塑控制鲁棒性的延时补偿方法

阻抗重塑方法通过增大LCL型并网逆变器的输出阻抗,提高逆变器对电网谐波电压的抗扰能力。但阻抗重塑控制通常采用数字控制方法,存在控制延时,降低了逆变器的稳定性,并在高于1/6采样频率(f_s/6)的频率段减小了逆变器输出阻抗的模值。为此,提出一种LCL型并网逆变器的状态预估延时补偿方法,通过补偿延时环节产生的相位滞后,优化了虚拟阻抗函数。该方法显著增大了逆变器输出阻抗的模值,提高了阻抗重塑控制的鲁棒性,使逆变器在电网含有谐波电压时满足并网电流的谐波标准。以三相LCL型并网逆变器为例进行实验,验证了控制策略的有效性。     

S变换在电能质量扰动分析中的应用综述

结合国内外采用S变换应用于电能质量扰动分析的现状,对基于S变换的电能质量扰动检测、识别以及其他方面的应用进行了分类和总结.分析了S变换结合各种人工智能与数学工具在进行电能质量扰动分析时的优势和不足,介绍了近年来利用广义S变换、改进S变换和双曲S变换等其他形式S变换在电能质量扰动分析中的应用情况.最后对S变换应用于电能质量扰动分析的发展趋势以及值得进一步研究的问题进行了展望.     

Robust control of multi-machine power systems with compensation of disturbances

The paper is devoted to the robust control with compensation of disturbances for power systems under parametric uncertainties. It is shown that problem can be solved when only relative speed of each generator is available for measurement. The proposed control algorithm synchronizes the power system with the required accuracy in the normal mode and under symmetrical 3-phase short circuit faults which occur on transmission lines. Efficiency of the proposed scheme is illustrated by modeling of a power systems consisting of three and fifty generators.     

具有可测干扰非线性系统的前馈/反馈线性化

研究了一类具有可测干扰的非线性系统的线性问题。在基于输出对控制输入的相对阶基础上,应用于输出对于干扰输入的相对阶概念,给出了一个非线性前馈／状态反馈变换律,与系统的结构特性有关,变换律可能是静态的也可能是动态的,从而可以基本消除可测干扰对系统输出的影响,并且在闭环系统中得到了一个线性输入输出的关系,最后给出了计算实例来证明所提变换律的有效性。