Time‐varying linear systems and input–output stability

One useful strategy for establishing input–output stability is to seek conditions on the system map so that a certain lower‐bound condition is met. We show here that, for a large class of time‐varying linear systems, the lower‐bound condition for stability is in fact necessary. Copyright © 2000 John Wiley & Sons, Ltd.     

下限分析中屈服面的最佳线性逼近问题

目前下限分析中往往采用内接正多边形来逼近屈服面以保证解的下限性质.从数值分析角度来看,采用其它拟合方式也能够从下方逼近极限荷载.本文研究了以下几种屈服面的多边形逼近方式:外切逼近、等面积逼近、最佳平方逼近、最优一致逼近、等周长逼近和内接逼近.计算分析表明:最优一致逼近在保证下限性质和求解精度的同时收敛更快,提高了求解效率,便于工程应用.     

Polynomial chaos‐based macromodeling of multiport systems using an input–output approach

An innovative technique to build stochastic frequency‐domain macromodels of generic linear multiport systems is presented. The proposed method calculates a macromodel of the system transfer function including its statistical properties, making it tailored for variability analysis. The combination of the modeling power of the Vector Fitting algorithm with the Polynomial Chaos expansion applied at an input–output level allows to accurately and efficiently describe the system variability features. Thanks to its versatility and automated order selection, the proposed technique is suitable to be applied to a large range of complex modern electrical systems (e.g., filters and interconnections) and can tackle the case of correlated random variables. The performance in terms of accuracy and computational efficiency of the proposed method is compared with respect to the standard Monte Carlo analysis for two pertinent numerical examples. Copyright © 2014 John Wiley & Sons, Ltd.     

I. W. Sandberg, ‘Linear shift‐invariant input–output maps do not necessarily commute’. International Journal of Circuit Theory and Applications, 2000; 28:513–518.

The original article to which this Erratum refers was published in the International Journal of Circuit Theory and Applications, 2000; 28 :513–518.     

Robust output tracking of uncertain nonlinear systems with completely unknown dead‐zone input: A self‐tuning design approach

The main purpose of this paper is to propose a direct and simple approach, called a self‐tuning design approach, to dealing with any nonsymmetric dead‐zone input nonlinearity where its information is completely unknown. In order to describe the approach, the output tracking problem is considered for a class of uncertain nonlinear systems with any nonsymmetric dead‐zone input. First, a dead‐zone input is represented as a time‐varying input‐dependent function such that the considered dynamical system with dead‐zone input can be transfered into an uncertain nonlinear dynamical system subject to a linear input with time‐varying input coefficient. Then, by making use of the self‐tuning design approach, a class of adaptive robust output tracking control schemes with a rather simple structure is synthesized. Thus, the proposed direct and simple self‐tuning design approach can be easily understood by the engineering designers, and the resulting simple adaptive robust control schemes can be well implemented in most practical engineering control problems. By combining the proposed self‐tuning design approach with other control methods, one may expect to obtain a number of interesting results for a rather large class of uncertain nonlinear dynamical systems with dead‐zone in the actuators. Finally,the simulations of some numerical examples are provided to demonstrate the validity of the theoretical results. Copyright © 2016 John Wiley & Sons, Ltd.     

Deterministic analysis of sigma–delta modulation for linear and non-linear signal reconstruction

Deterministic analysis is becoming increasingly popular to study the theoretical mechanisms of ΣΔ modulation, as opposed to the classical noise-shaping approach. This paper gives an overview of its application to the specific problem of signal reconstruction. Once an input signal has been processed through a ΣΔ modulator of given specifications, the fundamental question is to know what deterministic information can be retrieved about this signal from the ΣΔ output. The paper summarizes all results obtained in this research under a unified presentation framework. © 1997 by John Wiley & Sons, Ltd.     

Production of large‐diameter uniform plasmas and control of electron temperature

In order to produce large‐diameter uniform plasmas, we have proposed two plasma sources: a plane electron‐cyclotron‐resonance (ECR) slotted antenna (PESA) source for ECR plasma production and a modified magnetron‐type (MMT) radio frequency (RF) source for RF plasma production. The PESA has magnet rings behind the slotted antenna to provide the magnetic field for the ECR. The MMT RF source provides high‐density uniform plasmas with the help of the LC resonance of auxiliary electrode placed parallel to the substrate. Both plasma sources produce large‐diameter uniform plasmas exceeding 30 cm in diameter. We have proposed a grid method for electron temperature control. By applying a negative dc voltage to the grid which separates a plasma‐processing region from a plasma production region, the electron temperature is decreased by one order of magnitude in the processing region. The same effect is obtained by changing the mesh size of a floating grid. The change of a slit between two grids also causes variation of the electron temperature. These techniques are quite effective for chemical reaction control in processing plasmas. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 1–7, 2000     

Electrical breakdown characteristics of nitrogen and air at cryogenic temperature in a quasi‐uniform electric field

The breakdown voltages of the longer‐gap configurations in gaseous nitrogen and air that are necessary in designing superconducting electrical power apparatuses are measured at temperatures of 293 and 93 K. The quasi‐uniform electric field made by a sphere‐to‐sphere electrode with a diameter of 150 mm and a gap length of about 10 to 100 mm is used in the measurement of the breakdown voltages. When 50‐Hz ac and dc voltages are applied to the sphere‐to‐sphere gap, the breakdown voltages in nitrogen and air obey Paschen's law even at cryogenic temperatures (93 K). When a 1.4/50‐μs lightning impulse voltage is applied to the gap, the 50% breakdown voltage of nitrogen also obeys Paschen's law under UV irradiation of the cathode electrode. However, the breakdown voltage in air at 93 K is higher in the case of lightning impulse voltage applications, and the delay from impulse voltage application to breakdown occurrence is apparently longer at 93 K than at 293 K. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 28–33, 2000     

I.W. Sandberg, '𝒵+ fading memory and extensions of input‐output maps'. International Journal of Circuit Theory and Applications 29(4) 2001, 381–388.

The original article to which this Erratum refers was published in International Journal of Circuit Theory and Applications 29 (4) 2001 381–388.     

Absorbing boundary conditions for the FD‐TLM method : the perfectly matched layer and the one‐way equation technique

This paper investigates the absorbing boundary conditions for the frequency domain transmission line matrix method. Two approaches are presented, namely the perfectly matched layer (PML) technique and the one‐way wave equation. Concerning the PML technique, two‐dimensional and three‐dimensional transmission line matrix (TLM) nodes, already used in time domain, are exploited in frequency domain where a rigorous formulation of these PML–TLM nodes is presented. In addition, two types of one‐way wave operators are also transposed from time to frequency domain TLM approach: Taylor expansion and Higdon's boundary conditions. The simulation of a wideband matched load WR‐28 rectangular waveguide is presented for validation. Excellent results are obtained with a very thin PML layer. Results concerning one‐way operator techniques also show very good return loss performances. For instance, Higdon's boundary condition was extended beyond third‐order approximation, and a return loss better than 160 dB was obtained. Copyright © 2013 John Wiley & Sons, Ltd.     

非线性电路平衡点全局渐近稳定的充分必要条件

利用向量比较原理,得到了确定非线性电路平衡点全局渐近稳定的充分必要条件。结果表明,非线性非自治电路的唯一稳态的充分必要条件,可以用一个常数矩阵的Hurwitz条件决定。     

Evaluation of load division among transformers of different capacities in the grounded wye–delta and open wye–open delta banks under balanced loading and various power factor conditions

This paper evaluates the load division among transformers of different capacities in the grounded wye–delta and open wye–open delta banks under balanced loading and various power factor conditions. In some contingency cases two or three single-phase transformers of different kVA ratings are connected as a three-phase transformer bank to provide three-phase service for critical customers. In these cases, the load division among transformers becomes unequal and results in an unbalanced distribution system. The results of this study corroborate power company experience. Even when both three-phase sources and loads of the bank are balanced, the load division among transformers is unequal if transformers of different capacities are used in a bank, or an open wye–open delta connection is adopted.     

非线性输出反馈控制的理论改进及其在电力系统励磁控制中的应用

介绍一种新的适用于一般结构非线性多输入多输出系统的输出反馈控制理论,提出该理论的一种改进形式,从而扩展其应用范围,并进而应用于电力系统励磁控制.针对单机无穷大系统,采用角速度、机端电压及电流为反馈信号,首次推导出系统的可观域,并基于上述改进理论设计一种新的非线性输出反馈励磁控制器.该控制器不需要转子角信号,从而比一般的非线性状态反馈励磁控制器实践性强.最后利用PSCAD/EMTDC对该控制器进行暂态仿真,以验证其对电力系统扰动的抑制效果.     

Development of –1 MV DC Filter and High‐Voltage DC Measurement Systems for ITER NBI

This paper presents the development results of a ?1 MV dc filter and dc measurement systems for an ITER (International Thermonuclear Experimental Reactor) neutral beam injector (NBI) system. High accuracy of 0.5% and fast responsivity of 3.3 μs, ?3 dB are required for the dc measurement systems: both dc voltage dividers and DCCTs. Circuit design and thermal flow design were carried out to clarify and minimize their effects on the accuracy and responsivity. The validity of the established design was demonstrated by the actual‐product tests; temperature rise of each components fell below the allowable value; inner components of dc filter withstood dc ?1.2 MV; each voltage divider accurately measured the voltage during the dc ?1.2 MV withstand voltage test; the voltage dividers and the DCCTs were adequate to the requirements of responsivity (3.3 μs, ?3 dB).     

Experimental proof of voltage‐current waveform sensor output of resin molded type for measurement of power factor and harmonics in general power distribution system

We have proposed a voltage‐current sensor of resin molded type for measurement of the power factor and harmonics. To understand the characteristics of the conventional prototype sensor and the problems of its practical use, we conducted a finite element analysis. Problems involving the cost and practical usage of the sensor were identified. Therefore, we have redesigned the prototype sensor, incorporating the current sensor designed on the basis of the FEM and a ready‐made voltage sensor. In this paper, we describe feasibility field experiments with the present sensor in a practical 6.6‐kV distribution system and show that the sensor can measure the power factor and harmonics of horizontal and vertical power line systems successfully. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(3): 1–10, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21213     

Proposal for a benchmark model of a laminated iron core and a large‐scale and highly accurate magnetic analysis

This paper describes a benchmark model proposed for the clarification of the characteristic of various methods for modeling the laminated iron core. In order to obtain a reference solution of the benchmark model, a large‐scale nonlinear magnetostatic field analysis with a mesh fine enough to represent the microscopic structure of the laminated iron core is carried out by using the hybrid finite element–boundary element (FE‐BE) method combined with the fast multipole method (FMM) based on diagonal forms for translation operators. The computational costs and accuracy of two kinds of homogenization methods are discussed, comparing them with the reference solution. As a consequence, it is verified that the homogenization methods can analyze magnetic fields in laminated iron core within acceptable computational costs. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 26–35, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20809