Synthesis of multiport resistors with piecewise‐linear characteristics: a mixed‐signal architecture

Non‐linear multiport resistors are the main ingredients in the synthesis of non‐linear circuits. Recently, a particular PWL representation has been proposed as a generic design platform (IEEE Trans. Circuits Syst.‐I 2002; 49 :1138–1149). In this paper, we present a mixed‐signal circuit architecture, based on standard modules, that allows the electronic integration of non‐linear multiport resistors using the mentioned PWL structure. The proposed architecture is fully programmable so that the unit can implement any user‐defined non‐linearity. Moreover, it is modular: an increment in the number of input variables can be accommodated through the addition of an equal number of input modules. Copyright © 2005 John Wiley & Sons, Ltd.     

Chua's circuit 10 years later

More than 200 papers, two special issues (Journal of Circuits, Systems, and Computers, Vol.3, Nos. 1 and 2, 1993; IEEE Transactions on Circuits and Systems, Vol. 40 No 10, 1993), an international workshop on ‘Chua's Circuit: Chaotic Phenomena and Applications’ at NOLTA ‘93, and a book (R. N. Madan (ed.), Chua's Circuit: A Paradigm for Chaos, World Scientific, Singapore, 1993) on Chua's circuit have been published since its inception a decade ago. This review paper attempts to present an overview of these timely publications, almost all within the last six months, and to identify four milestones of this very active research area. An important milestone is the recent fabrication of a monolithic Chua circuit. the robustness of this IC chip demonstrates that an array of Chua circuits can also be fabricated into a monolithic chip, thereby opening the floodgate to many unconventional applications in information technology, synergetics and even music. The second milestone is the recent global unfolding of Chua's circuit obtained by adding a linear resistor in series with the inductor to obtain a canonical Chua circuit—now generally referred to as Chua's oscillator. This circuit is most significant because it is structurally the simplest (it contains only six circuit elements) but dynamically the most complex among all non-linear circuits and systems described by a 21-parameter family of continuous odd-symmetric piecewise-linear vector fields. The third milestone is the recent discovery of several important new phenomena in Chua's circuits, e.g. stochastic resonance, chaos-chaos-type intermittency, 1/f noise spectrum, etc. These new phenomena could have far-reaching theoretical and practical significance. The fourth milestone is the theoretical and experimental demonstration that Chua's circuit can be easily controlled from a chaotic regime to a prescribed periodic or constant orbit, or it can be synchronized with two or more identical Chua circuits operating in an oscillatory or chaotic regime. These recent breakthroughs have ushered in a new era where chaos is deliberately created and exploited for unconventional applications e.g. secure communication.     

Preventive and corrective open access system dispatch based on the voltage stability security assessment and diagnosis

The capabilities of the voltage stability security assessment (VSSAD) to assess proximity to and ranking voltage instability by (a) performing a contingency selection of each model determined subsystem and (b) diagnosing where, why, when and what can be done to cure voltage instability for each equipment outage and transaction combination is thoroughly documented in IEEE Trans. Power Syst. 13 (1998) 1423; Division of Engineering Research Technical Report December 1998, Santorini, Greece. This paper reviews these capabilities and how they can be used to implement a contingency selection module and security constrained optimization module for the open access system dispatch (OASYDIS) being proposed as part of the proposed transmission dispatch and congestion management (IEEE Trans. Power Syst. 13 (1998) 1466) in an ISO. The open access system dispatch can be implemented as either a preventive control as given in IEEE Trans. Power Syst. 13 (1998) 1466 or as a corrective control as proposed in this paper. The VSSAD based contingency selection can provide the security constraints for either a preventive or corrective control implementation of OASYDIS. The advantages of corrective control are discussed and the changes in the proposed open access system dispatch (IEEE Trans. Power Syst. 13 (1998) 1466) required to implement a corrective control are discussed.     

Simple and accurate modeling of the output transition time in nanometer CMOS gates

In this paper, a model of the output transition time on nanometer CMOS gates is proposed. The development of this model follows the general approach used by Auvergne in (IEE Electron. Lett. 2002; 38 (4):175–177, IEEE Trans. Circuits Systems—part I 2000; 47 (9):1362–1369, IEEE Proc. ISCAS 2001; 5 :363–366, IEEE Trans. Computer‐Aided Design Integr. Circuits Systems 2002; 21 (11):1352–1363), which separately models the output transition time under fast and slow inputs. The proposed model is based on a combined transient and DC circuit analysis, and requires a few simulations. This approach allows for strongly reducing the number of required parameters and simulations compared with other models proposed in the literature. The analytical model proposed is very simple and has a clear physical meaning, thereby allowing an efficient implementation in CAD tools performing timing analysis, as well as an easy scalability through different processes and technology generations. Spectre simulations on a 65 nm CMOS technology and the 45, 32, 22 nm Berkeley Predictive Technology Models (BPTM) [Berkeley Predictive Technology Model (BPTM). ONLINE@11/25/2008: http://www.eas.asu.edu/～ptm/ ] show that the model accuracy is the same as the state‐of‐the‐art models, with an average error of only 4%. Comparison with currently used table‐based models showed also a significant reduction in the CPU time needed to simulate and characterize CMOS logic gates. Copyright © 2009 John Wiley & Sons, Ltd.     

Cellular wave computer algorithms with spatial semantic embedding for handwritten text recognition

The recognition of cursive handwritten texts is a complex, in some cases unsolvable, task. One problem is that in most cases it is difficult or impossible to identify each letter, even if the words are separated. In our new method, the identification of letters is not needed due to the extensive and iterative use of semantic and morphological information of a given language. We are using a spatial feature code, generated by a cellular nonlinear network (CNN) based cellular wave computer algorithm, and combine it with the linguistic properties of the given language. Most general‐purpose handwriting recognition systems lack the ability to integrate linguistic background knowledge because they use it only for post‐processing recognition results. The high‐level a priori background knowledge is, however, crucial in human reading and similarly it can boost recognition rates dramatically in case of recognition systems. In our new system we do not treat the visual source as the only input: geometric and linguistic information are given equal importance. On the geometric side we use word‐level holistic feature detection without letter segmentation by analogic CNN algorithms designed for cellular wave computers (IEEE Trans. Circuits Syst. 1993; 40 :163–173; Cellular Neural Networks and Visual Computing, Foundations and Applications. Cambridge University Press: Cambridge, U.K., New York, 2002). The linguistic side is based on a morpho‐syntactic linguistic system (Proceedings of COLING‐2002, vol. II, Taipei, Taiwan, 2002; 1263–1267). A novel shape coding method is used to interface them, and their interaction is enhanced via an inverse filtering technique based on features that are global or of a low confidence value. A statistical context selection method is also applied to further reduce the output word lists. Copyright © 2008 John Wiley & Sons, Ltd.     

Bibliography on the application of probability methods in powersystem reliability evaluation

This paper presents a bibliography of papers on the subject of power system reliability evaluation. Papers in such areas as probabilistic load flow, probabilistic production costing, probabilistic transient stability evaluation etc. have not been included except where they specifically address power system reliability evaluation. It includes material which has become available since the publication of the five previous papers. “Bibliography on the Application of Probability Methods in Power System Reliability Evaluation”, IEEE Trans. on Power Apparatus and Systems PAS-91, 1972, pp.649-60; PAS-97, 1978, pp.2235-42; PAS-103, 1984, pp. 275-82; IEEE Trans. on Power Systems, Vol. 3, No. 4, Nov. 1988, pp. 1555-64, and Vol. 9, No. 1, Feb. 1994, pp. 41-9     

Weighted least squares methods for load estimation in distribution networks

This paper investigates two weighted least squares (WLS) approaches to the problem of load estimation (LE) in unbalanced power distribution networks: (1) the WLS load parameter method in is restated more rigorously; and (2) a constrained distribution state estimation (DSE)-based method is introduced to consider operating and loading constraints. Detailed simulation results on 394-bus radial and weakly meshed power distribution systems are evaluated through four error indices proposed by the authors previously (see Proc. IEEE Int. Symp. Circuits Syst., Pheonix, AZ, vol.5, p.697-700, 2002). The results of both methods are compared and discussed. Observability issues are also addressed.     

Output feedback control of discrete-time nonlinear systems with unknown time-delay based on Takagi-Sugeno fuzzy models

In this paper, a new discrete-time fuzzy output feedback control method for nonlinear systems with unknown time-delay is proposed. The method follows on from the analysis and design method for a fuzzy controller and observer proposed by Ma et al. (IEEE T Fuzzy Syst (1998) 6(1):41–51), and the extension of this to nonlinear systems with known time-delay by Cao et al. (IEEE T Fuzzy Syst (2000) 8(2):200–211) For the case of unknown time-delay, we derive the sufficient condition for the asymptotic stability of the equilibrium point by applying Lyapunov-Krasovskii theorem and convert this condition into the famous LMI problem.     

Estimation of synchronous machine parameters using new discrete time-filtering algorithm

This paper presents a new method for estimating synchronous machine parameters from frequency test using a discrete time-dynamic filter based on the least absolute value parameter estimation algorithm (see G.S. Christensen and S.A. Soliman, Automatica. 26 (2) (1990) 389–395). The proposed method uses a digital set of measurements for the direct axis impedance magnitude and phase as a function of the frequency for estimating the d-axis parameters, such as the direct reactance and the different direct axis time constants, as well as the q-axis parameters.A practical example from the literature is used (see F.B. De Mello and L.N. Hannet, IEEE Trans. Power Appar, Syst., PAS-102 (12) (1983) 3810–3815) to test the proposed algorithm, and results are obtained and compared with those obtained using other methods such as the least error squares algorithm (see S.A. Soliman, S.E. Emam and G.S. Christensen, Can. J. Electr. Comput. Eng., 14 (3) (1989) 98–102) and the Kalman filtering algorithm (see M. Mambo, T. Nishiwaki, Syokokawa and Y. Ueki, IEEE Trans Power Appar. Syst., PAS-100 (7) (1981) 3304–3311).     

Cellular neural networks: Theory and circuit design

Cellular neural networks or CNNs are a novel neural network architecture introduced by Chua and Yang which is very general and flexible, has some important properties desirable for design applications and can be efficiently implemented on custom hardware based on analogue VLSI technology. In this paper an abstract normalized definition of cellular neural networks with arbitrary interconnection topology is given. Instead of stability, the property of convergence is found to be of central importance: large classes of convergent CNNs in practice always asymptotically approach some stable equilibrium where each component of the corresponding output is binary-valued. A highly efficient CMOS-compatible CNN circuit architecture is then presented where a basic cell consists of only two fully differential op amps, two capacitors and several MOSFETs, while a variable interconnection weight is realized with only four MOSFETs. Since all these elements are standard components in the current analogue IC technology and since all network functions are implemented directly on the device level, this architecture promises high cell and interconnection densities and extremely high operating speeds.     

Automatic detection and tracking of moving image target with CNN‐UM via target probability fusion of multiple features

A high speed target detection and tracking algorithm for a CNN‐UM chip is presented in this paper. The target confidence value is computed based on the fusion of target existence probabilities of features using products of weighted sums. The target decision is done with such a confidence value and target initiation is done through the temporal accumulation of the confidence. The probability of the target existence for each feature is created in the region of influence depending on the reliability and the strength of the feature. By virtue of the analogic parallel processing structure of the CNN‐UM (Roska T, Chua LO. The CNN universal machine: an analogic array computer. IEEE Trans. Circuits Systems II 1993; CAS‐40 : 163–173), real time tracking can be achieved with presently available technologies with the speed of several kilo‐frames per second. Due to the utilization of multiple features of target, robust target detection is possible via the proposed algorithm. On‐chip experiments of the proposed target‐tracking algorithm have been done and properties of the proposed approach are disclosed through the various experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

Discretization Scheme for the Density-Gradient Equation and Effect of Boundary Conditions

In recent years, the density gradient theory (DG) (M.G. Ancona and H.F. Tiersten 1987, Phys. Rev. B. 35(15): 7959–7965, M.G. Ancona 1990, Phys. Rev. B. 42: 1222) has been established as a viable alternative to the solution of the Schrödinger equation for solving problems such as charge density distribution in MOS inversion layers and MOS tunneling (M.G. Ancona 1998, J. Tech. CAD(11), M.G. Ancona et al. 2000, IEEE Trans. Electron Devices 47: 1449). Primary advantages of the DG method over the Schrödinger method are flexibility in extending to multi-dimension and easiness in incorporating into the conventional drift-diffusion or hydrodynamic solver (C.S. Rafferty et al. 1998, Proc. SISPAD, p. 137, A. Wettstein et al. 2001, IEEE Trans. Elec. Dev. 48: 279). However, the DG term that represents the quantum effects is a singular perturbation term and requires special care for discretization (X. Wang 2001, Master's thesis, University of Massachusetts, Amherst). In this work, we examine the validity of the linear vs. the nonlinear discretization scheme and the effect of boundary conditions on the scheme used.     

A simple variable step size LMS adaptive algorithm

A new LMS based variable step size adaptive algorithm is presented. The step size is incremented or decremented by a small positive value, whenever the instantaneous error is positive or negative, respectively. The algorithm is simple, robust and efficient. It is characterized by fast convergence and low steady state mean squared error. The performance of the algorithm is analysed for a stationary zero‐mean white‐Gaussian input. MC simulations are provided to demonstrate its improved performance over the conventional LMS (Proc. IEEE 1976; 64 :1151–1162) and some other variable step size adaptive algorithms (IEEE Trans. Signal Process. 1992; 40 :1633–1642; IEEE Trans. Signal Process. 1997; 45 :631–639) within a range of statistical environments. For a non‐stationary input, the proposed algorithm behaves similar to these algorithms. A modified version of the algorithm is presented to perform in the presence of abrupt changes. Copyright © 2004 John Wiley & Sons, Ltd.     

On-line voltage stability assessment using radial basis function network model with reduced input features

In recent years, voltage instability has become a major threat for the operation of many power systems. This paper presents an artificial neural network (ANN)-based approach for on-line voltage security assessment. The proposed approach uses radial basis function (RBF) networks to estimate the voltage stability level of the system under contingency state. Maximum L-index of the load buses in the system is taken as the indicator of voltage stability. Pre-contingency state power flows are taken as the input to the neural network. The key feature of the proposed method is the use of dimensionality reduction techniques to improve the performance of the developed network. Mutual information based technique for feature selection is proposed to enhance overall design of neural network. The effectiveness of the proposed approach is demonstrated through voltage security assessment in IEEE 30-bus system and Indian practical 76 bus system under various operating conditions considering single and double line contingencies and is found to predict voltage stability index more accurate than feedforward neural networks trained by back propagation algorithm and AC load flow. Experimental results show that the proposed method reduces the training time and improves the generalization capability of the network than the multilayer perceptron networks.     

Audio source separation: solutions and problems

The problem of separating out a number of audio sources observed from an array of microphones in a real room environment has received a great deal of attention in the past decade. While there are now a number of workable methods that can even deal with relatively high reverberation (IEEE Trans Audio Speech Process, 2003; 11 :489–497), a number of interesting problems still remain. In this paper, the authors review the methods based around independent component analysis, discussing the various choices available in algorithm design. We then explore the issue of sensitivity to speaker movement which appears to impose fundamental limitations on BSS performance. Copyright © 2004 John Wiley & Sons, Ltd.     

A study on the condition of reverse control action of tap changer in a single on-load tap changer power system

This paper investigates the voltage stability in a single OLTC (On-Load Tap Changer) system, which consists of a single OLTC and multiple generators as well as loads. It is shown that the sensitivity of the load voltage to tap position dV/dn = (I₁ = exact value) plays an important role, independently of the existence of the equilibrium of the tap position. That is, when the equilibrium exists, the region where I₁ > O is in the stability region; if the equilibrium disappears, the stability region also disappears but the voltage is still recovering in the region where I₁ > O. Based on these results, the region of reverse control action of OLTC is defined as the region where I₁ > O. It is proved that another sensitivity I₂, which is defined as dV/dn when constant power characteristics are assumed for loads, can be used to estimate the region of reverse control action when the exact load characteristics are not available.     

Infinite networks of positive operators

Infinite resistive networks have recently been analyzed by H. Flanders. The present work is an extension of Flanders results in three directions:

• (1) It analyzes the more general case where the resistances in the network are positive bounded linear operators on a Hilbert space H and the currents and voltages are members of H.
• (2) An infinite number of sources is now allowed.
• (3) The network is permitted to have finite loops of doubly infinite paths consisting entirely of short circuits.

Conditions are developed under which existence and uniqueness theorems for the set of branch currents can be stated. These conditions include the requirement that all branch resistances be either zero or invertible. The situation where some or all of the resistances have nontrivial null spaces is also considered. In those cases where the branch currents need not be unique for a given set of sources, the difference between two possible current distributions can be characterized as a current distribution that produces zero voltage drops in all branches. An application to time-varying resistive networks containing switches is also given.     

A sufficient condition of controllability of RLCM active networks over F(z)

This paper defines the separability of an RLCM active network and finds a sufficient condition that the active network is controllable and observable over F(z) if its passive network is controllable and observable over F(z). So the controllability (observability) criteria in (Proc. IEEE ISCAS, 2005) can be used to analyse and design active networks. Copyright © 2006 John Wiley & Sons, Ltd.     

分布式电源接入配网对其静态电压稳定性影响多角度研究

分布式电源(Distributed Generation, DG)接入配网后,将对配网静态电压稳定性造成影响。基于IEEE33节点配电网络和Matlab仿真测试软件平台,考虑分布式电源的接入数量、接入位置、接入容量和功率因数4个影响因素。应用电压稳定性判定指标L,对比单个DG接入单分支线路和多个DG接入多条分支线路两种情况,得出各自对配网电压分布和电压稳定性造成的影响。对比测试所得L指标,结果表明多DG接入的方式更有利于配网电压稳定。该研究对配网中多DG的布局和规划具有积极的指导意义。