Transient analysis of three-phase power systems,part I

The application of symmetrical components to the solution of steady state problems in power systems engineering suggests the application of the same or similar components in the study of transient phenomena on the network calculating board by means of oscilloscope and synchronous switch. However, it is found upon rigorous examination that symmetrical components are applicable to such problems in but a few types of switching. Part II of this paper will deal with a system of components which serve well in all cases of transient phenomena produced by short circuits, the operation of circuit breakers or other apparatus.     

Flatness-based adaptive fuzzy output tracking excitation control for power system generators

In this paper, a novel approach for the design of an indirect adaptive fuzzy output tracking excitation control of power system generators is proposed. The method is developed based on the concept of differentially flat systems through which the nonlinear system can be written in canonical form. The flatness-based adaptive fuzzy control methodology is used to design the excitation control signal of a single machine power system in order to track a reference trajectory for the generator angle. The considered power system can be written in the canonical form and the resulting excitation control signal is shown to be nonlinear. In case of unknown power system parameters due to abnormalities, the nonlinear functions appearing in the control signal are approximated using adaptive fuzzy systems. Simulation results show that the proposed controller can enhance the transient stability of the power system under a three-phase to ground fault occurring near the generator terminals.     

Application of “stability index” to assess the stability of multi-machine systems

A new stability index is presented in this paper which may easily be calculated using the information obtained from the load flow study and the fault location and time. No information from previous transient stability studies of the system is required.The conventional methods of studying transient stability require long computing time whereas the use of stability index is a very fast method of assessing the system's stability. Application of the index provides a very quick insight into the behaviour of the generator under a three-phase fault and identifies the critical situations.Results of the calculation of this index for a sample power system are included and within a reasonable accuracy agree with the results of a full transient stability analysis.     

Control of switch-sharing-based multilevel inverter suitable for photovoltaic applications

Owing to the higher amount and the better quality of power transferred, three-phase multilevel inverters have strengthened their presence in low-power photovoltaic (PV) applications. However, the existing topologies investigated for low-power PV systems are basically meant for medium- and high-power applications, thus making them underutilized for low-power range. In order to address this shortcoming, this paper proposes a three-phase multilevel inverter with a switch-sharing capability and its control solution. It combines the characteristics of the two-level full-bridge topology and the diode-clamped multilevel structure. As a result, the inverter can be used with full capacity and without being underutilized, and significantly improves the output quality. A control strategy that is able to maximize the full potential of the inverter is developed. A digital proportional-integral (PI) controller with a new tuning algorithm is designed to effectively deal with the load changes. The result reveals that the load current is always retained at the intended quality level despite the variations in load. The performance of the inverter is validated from the experimental work conducted on a laboratory prototype under closed-loop conditions.     

A new mathematical analysis of series and shunt faults on three phase power networks

A mathematical analysis of sequential fault transients due to series and shunt faults is important in the study of circuit breaker pole openings and reclosings with arc resistances. The line loading itself becomes unbalanced momentarily due to load switching. Each double fault is developed in sequence, therefore the initial currents in the second and third fault must be treated properly under transient conditions. New sequence component variables λμ0 and ρσ0 are used with αβ0 components. This study is useful for small power systems as well for large power systems. A digital simulation of various series and shunt faults is presented in a generalized manner using αβ0, λμ0 and ρσ0 components.     

从国有商业银行的行为分析不良贷款的生成机制

本文从日本、中国的国有商业银行具有高不良贷款的现实出发研究商业银行各分支机构的经理人员(代理人)的行为,第一部分的引言强调研究国有商业银行各分支机构的经理人员行为的必要性,并且对现有文献进行了回顾。第二部分扩展了基本的监管模型,研究了国有商业银行各分支机构的经理人员(代理人)在支付矩阵下的行为,第三部分得出结论:在我们的研究范围内,银行不良贷款的产生是因为商业银行在不同的行为参数下,依赖自己的行为参数从效用最大化出发进行博弈的结果。     

A nonsmooth Newton method for the design of state feedback stabilizers under structure constraints

The paper proposes a method for structured state-feedback controllers design for linear time-invariant systems. A necessary and sufficient condition for structured state-feedback stabilizability of linear systems, making an appeal to the linear-quadratic (LQ) regulator theory, is first proposed. The latter is presented in the form of a nonlinear matrix equation. Then, it is recast as a nonsmooth unconstrained equation using projection onto the positive semi-definite matrices cone. Thereby, a nonsmooth Newton’s iterative algorithm, based on the Clarke generalized Jacobian of said projection, is proposed. This method has a guaranteed local convergence. Finally, numerical examples illustrate the effectiveness of the proposed method.     

Global Mittag-Leffler consensus for fractional singularly perturbed multi-agent systems with discontinuous inherent dynamics via event-triggered control strategy

In this paper, the global Mittag-Leffler consensus tracking issue is considered for fractional singularly perturbed multi-agent systems (FSPMASs) based on event-triggered control strategy, where the inherent dynamic is modeled to be a discontinuous function with nondecreasing property. Firstly, a differential inequality with respect to fractional-order derivative of convex function is developed. As the special cases, the inequalities about fractional-order derivative of three known functions are also addressed. Secondly, a distributed event-triggered control scheme is designed to guarantee that the considered FSPMASs can achieve the global Mittag-Leffler consensus. Moreover, the Mittag-Leffer convergence speed of tracking the leader for followers can be adjusted to any desired values in advance. In addition, under fractional Filippov differential inclusion framework, by applying Lur’e Postnikov-type Lyapunov functional with variable upper limit integral item and Clarke’s non-smooth analysis technique, the global Mittag-Leffler consensus conditions are addressed in terms of matrix inequalities (MIs). Finally, two numerical simulations are provided to illustrate the validity of the proposed design method and theoretical results.     

CLAIRE: A combinatorial visual analytics system for information retrieval evaluation

Information Retrieval (IR) develops complex systems, constituted of several components, which aim at returning and optimally ranking the most relevant documents in response to user queries. In this context, experimental evaluation plays a central role, since it allows for measuring IR systems effectiveness, increasing the understanding of their functioning, and better directing the efforts for improving them. Current evaluation methodologies are limited by two major factors: (i) IR systems are evaluated as “black boxes”, since it is not possible to decompose the contributions of the different components, e.g., stop lists, stemmers, and IR models; (ii) given that it is not possible to predict the effectiveness of an IR system, both academia and industry need to explore huge numbers of systems, originated by large combinatorial compositions of their components, to understand how they perform and how these components interact together.We propose a Combinatorial visuaL Analytics system for Information Retrieval Evaluation (CLAIRE) which allows for exploring and making sense of the performances of a large amount of IR systems, in order to quickly and intuitively grasp which system configurations are preferred, what are the contributions of the different components and how these components interact together.The CLAIRE system is then validated against use cases based on several test collections using a wide set of systems, generated by a combinatorial composition of several off-the-shelf components, representing the most common denominator almost always present in English IR systems. In particular, we validate the findings enabled by CLAIRE with respect to consolidated deep statistical analyses and we show that the CLAIRE system allows the generation of new insights, which were not detectable with traditional approaches.     

Pole placement LMI constraints for stability and transient performance of LPV systems with incomplete state measurement

In this paper, new conditions for the stabilisation and transient performance improvement of linear parameter-varying (LPV) systems considering the gain-scheduling (GS) strategy are proposed. Our work is focused on dealing with LPV systems under the major practical constraint of incomplete state measurement. In that sense, we propose two new control design strategies based on linear matrix inequalities (LMI). First, for coping with the general case where only a subset of the state variables is measured, we propose a new static output feedback (SOF) strategy. Second, for dealing with the particular case where only accelerometers signals are available, we bring new synthesis conditions for the design of state derivative feedback (SDF) controllers. Further from stability, our proposed methods are able to induce better transient response by including pole placement LMI constraints in the control design. For illustrating our contribution efficacy, we present a couple of design examples.     

基于三单相多重化ASVG的研究

针对输电电网电压水平低,电能质量差的现状,根据ASVG在改善电力系统供电质量,提高电力系统暂态稳定性方面表现出的优越性,提出了一种采用三单相二重化电压逆变器为主要结构,以直流电压和无功综合控制为策略,实现对三相三线制输电系统进行静态无功补偿的方法。     

轮钟花属的恢复及其花粉和种皮证据

光学显微镜和扫描电镜观察表明,金钱豹属(广义)花粉明显分为两个类型:Campanumoea inflata和C.javanica subsp.laponica的花粉5～8沟,外壁具相对密的短刺,刺高不过1μm,而C.lancifolia,C.celebica和C.parviflora的花粉3孔沟,外壁刺稀疏,高于2μm。种子表面纹饰也同样可分为  两类,前两个种一类,其种子表面网状,网眼规则而多角形,直径大于网脊宽度,网脊上的次级纹饰为念  珠状,而后三种为一类,其种子表面网眼不规则,直径与网脊宽度近相等,网脊上的次级纹饰绳索状。可  见花粉特征与种皮性状是高度相关的。后三个种所属的分类群就是被归并了的属Cyclocodon Griffith。  综合花粉、种皮及外部形态,这个属应予恢复。其近缘属应是Platycodon,而不是Campanumoea。     

中国齿鳞草属和假野菰属的订正

The present paper deals with taxonomic studies on the genera Lathraea Linn. and Christisonia Gard. (Orobanchaceae) in China.  In the genus Lathraea, only a single species in China, L. japonica Miq., is recongnized in the paper. It occurs in sou- thern Shaanxi, southern Gansu, southeastern Sichuan, northern Guizhou and northern   Guangdong, also in Japan. L. miqueliana Franch. et Sav., L. chinfushanica Hu et Tang and L. japonica Miq. var. miqueliana (Franch. et Sav.) Ohwi are treated as new synon- yms of L. japonica Miq. in this paper.       In the genus Christisonia, the most of collections from China, which were identi- fied as C. sinensis G. Beck before, are treated as a new synonym of C. hookeri C. B. Clarke.  A few collections of this genus from China, which were mistakenly described as Gleadovia lepoense Hu snd G. kwangtungense Hu, should be transferred to Christi- sonia hookeri C. B. Clarke.  It is distributed in southeastern and south China, westwards to the Himalayas.     

囊状嵩草(莎草科)及相关类群的分类

 根据外部形态学和小坚果表皮的微形态学资料，研究了囊状嵩草及其相关类群的分类。在这一 群植物中，有13个相关的学名。根据以前学者用于区别这些植物的形态性状，无法清楚地将它们划分 开。因此作者深入地研究了有关植物的89号200多份标本，重新评价了形态性状的分类学意义。为了 更深入地理解这类植物的分类，应用扫描电子显微镜对其小坚果表皮的微形态进行了研究。根据研究 的结果，确认了囊状嵩草Kobresia fragilis和弧形嵩草K．curvata，其他名称做为囊状嵩草的异名，K．clar- keana、K．clarkeana var．megalantha和K.curticeps var．gyirongensis被处理为囊状嵩草的新异名。弧形嵩 草从形态学和微形态学两个方面都明显不同于囊状嵩草。研究中还发现囊状嵩草的一号标本采自甘肃的碌曲，是其分布的省级新记录。     

Power load identification

The number and power of loads that pollute the electric network, from an electric point of view, are constantly increasing. For this reason this study aims to define a parameter to assess, in terms of distortion and unbalance, the quality of an electric network. Taking as a starting point the advantages and limitations of wavelet methods proposed in the literature, a new index useful to quantify the load characteristics is introduced. The efficiency of this index has been verified by computer simulations to assess the applicability of the method to three-phase systems using three-wire measurements based on the instantaneous power theory, in several typical situations.     

西藏五福花属一新种和一新记录种

A new species and a new record for China of the genus Adoxa L.are reported from Xizang, China. They are Adoxa xizangensis G.Yao and Adoxa inodora (Falc.ex C.B.Clarke)  Nepomn.     

Dynamic harmonic balance principle and analysis of rocking block motions

The harmonic balance (HB) principle is a powerful and convenient tool for finding periodic solutions in nonlinear systems. In the present paper, this principle is extended to transient processes in systems with one single-valued odd-symmetric nonlinearity and linear plant not having zeros in the transfer function, and named the dynamic HB. Based on the dynamic HB, first the equations for the amplitude, frequency, and amplitude decay of an oscillatory process in the Lure system are derived. It is then applied to analysis of rocking block decaying motions. An example is provided.     

Decentralized optimal controller design for multimachine power systems using successive approximation approach

In this paper, we propose to develop algorithmically and implement a nonlinear decentralized optimal control for multimachine power systems, based on a successive approximation approach for designing the optimal controller with respect to quadratic performance index. The advantage of this approach is to transform the high order coupling nonlinear two-point boundary value (TPBV) problem into a sequence of linear decoupling TPBV problem, which uniformly converges to the optimal control for nonlinear interconnected large scale systems. We apply this approach to a 3-machine power system which generators are strongly nonlinear interconnected, and containing possible uncertainties on the parameters. We demonstrate clearly via advanced simulations that this approach brings better performances than other decentralized controller, improving effectively transient stability of these power systems in few iterative sequences for different cases of perturbations.     

Mathematical aspects of static and dynamic stability problems in power systems

A power system is modelled by a system of parameterised differential-algebraic equations (DAEs) when it is operating normally; it is modelled by time-piecewise DAEs when a transient process occurs. The normal operation of power systems is related to the static stability problem; while the transient process is related to the dynamic stability problem. After categorising the stability problems in power systems into static and dynamic cases, mathematical formulations are proposed and mathematical problems related to them are studied using different mathematical tools. In the static case, the determination of feasibility region is related to solving algebraic equations; while in the dynamic case, identifying attraction domain is related to solving a DAE. For a power system, the determination of feasibility region is usually reduced to optimisation problems, while the determination of attraction domain and critical clearing time is related to the study of transient energy functions.