Transient analysis of three-phase power systems,part II

The difficulties encountered with symmetrical components, as discussed in Part I, B, are eliminated when Clarke components are used. It is possible to investigate transient phenomena in three-phase systems by studying single-phase networks with the transient analyzer.The basic relationships between the three-phase problem and its equivalent representation in Clarke components are established in the first section (C) of this paper. The last section (D) of this study contains the component-network connections and the switching arrangements which are representative of the more frequent types of disturbances in three-phase systems.     

Stability analysis of sampled-data systems considering time delays and its application to electric power markets

This paper investigates the stability of linear control systems with aperiodic sampled data and communication delays. A systematic analysis method is presented and then it is applied to an electric power market. Firstly, the sampled-data system is transformed into a system with a special time-varying delay via the input delay method. Secondly, a less conservative stability criterion is derived based on Lyapunov theory. Several augmented terms and an extra integral term are introduced during the constructing of candidate Lyapunov–Krasovskii functional (LKF); and an improved free-weighting matrix approach is used to handle with the LKF itself and its derivative for obtaining the relaxed conditions ensuring the positive and decreasing requirements of the LKF. The benefit of those treatments on the conservativeness-reducing is analyzed and verified based on a simple numerical example. Finally, the application of the proposed method to a simplified electric power market is investigated, including modeling the system with market clearing time and communication delay, and determining the stability region. The application also shows the practical significance of the reducing of the conservativeness.     

Geographical information systems as part of the corporate information strategy

In the past, Geographical Information Systems (GIS) have been used and developed by small groups of professionals within organizations, for example, town planners within local authorities. Champions from such enthusiastic groups have made enormous contributions to the development of working GIS in practice. However, GIS implementations that are ad hoc developments primarily designed to improve the operations of the organization are potentially underutilizing the benefits of GIS. In business applications GIS must be seen as another potential tool. Managers need to see GIS among a range of management support tools, in a way that other information systems might be viewed. The integration of GIS into corporate information systems is vital for gaining the maximum benefit from the information resources of the organization. The paper explores issues such as: How can GIS be integrated into the information strategy? What are the benefits of such an integration? The paper puts forward a framework for considering GIS within the corporate information strategy.     

Thermodynamics,part I: The second law from the standpoint of the equation of state

In this paper the concepts “equilibrium” and “reversibility” are examined from the standpoint of the number of independent variables which define a thermodynamic system. The endeavor is made to show that the number of independent variables which are selected is crucial to the basic concepts as well as to the second law of thermodynamics. If this number is less than the minimum required to define the system completely, the equation of state for the internal energy will be incomplete. It is our practice to employ incomplete equations of state, and this results in processes which we consider to be irreversible. The Kelvin-Planck and Clausius principles are shown to be somewhat related to the first law of thermodynamics, and their validity arises from the fact that the equations of state which are used are incomplete. If these equations were complete, that is, if the number of independent variables were not less than the minimum required to describe the systems completely, we should have complete conversion of heat into work, as well as work into heat. The difficulties in realizing complete equations are considered.The entropy concept is considered in detail, and it is shown that there are serious limitations in its application.     

Analysis of integrated STATCOM-SMES based on three-phase three-level multi-pulse voltage source inverter for high power utility applications

This paper is aimed to investigate the operating characteristics of a static synchronous compensator (STATCOM) integrated with superconducting magnetic energy storage (SMES) for high power applications in the transmission network level. The STATCOM controller topology comprises multi-level multi-pulse neutral-point clamped-type (NPC) voltage source inverters (VSIs) using the harmonics cancellation technique, and incorporates a SMES coil. An innovative two-quadrant multi-level dc-dc converter is proposed to effectively interface the STATCOM with the superconducting coil using a buck-boost topology with neutral point voltage control capabilities; thus enabling to simultaneously control both active and reactive power exchange with the high voltage power system. A detailed analysis of major system variables is presented, including analytical results and digital simulations using the MATLAB/Simulink environment. Moreover, a three-level control scheme is designed, including a full decoupled current control strategy in the d-q reference frame with a novel controller to prevent the STATCOM dc bus capacitors voltage drift/imbalance and an enhanced power system frequency controller.     

Tree counting polynomials for labelled graphs part I: Properties

The properties of special pairs of tree counting polynomials that relate to a class of incomplete graphs and their complements are presented. These polynomial pairs are related by the previously defined binary complementing operation.In contrast with alternative graph representations, they offer the possibility of serving as a convenient signature for the specific configurations.In Part II, a new constructive procedure is presented for deriving these polynomials. It is shown that the new algorithmic approach facilities obtaining the polynomials for cases not readily obtained by use of generic factors of the basic subgraphs.     

A note on L2-gain analysis for power systems with delayed load frequency control schemes

This paper investigates $L_2$-gain analysis of power systems with delayed load frequency control schemes. Based on a new delay form, new functionals which may be more general than some existing Lyapunov-Krasovskii functionals are developed. Then, new $L_2$-gain criteria are derived with the help of the functionals. Finally, some comparisons are made to show that the obtained criteria are effective.     

汽车某B柱零件的成形皱曲仿真分析

文章针对汽车某B柱上零件模型,模拟仿真其冲压成形过程,对由不均匀拉应力引起的内皱进行改善措施。     

Operational analysis of library systems

Mathematical models are developed for describing and optimizing the way libraries organize information sources. By ordering the sources in a more relevant manner, the users' search and retrieval costs are reduced, which leads to an increase in the value and amount of information processed. The cost of organizing collections so as to minimize user effort is dependent on the scatter of relevant sources in the literature and the specification of core classes.     

Load frequency composite control for multi-region interconnected power systems

This paper investigates a composite controller for load frequency control (LFC) in multi-region interconnected power systems via sliding mode observer design. State observers (SOs) and disturbance observers (DOs) are implied for the LFC based on the load variations with communication delays and quantization output measurements. A nonlinear integral sliding surface combined with a composite controller is developed to optimize control performance. Moreover, a three-area power system model is used to demonstrate the effectiveness of the proposed scheme in the illustrative example, confirming that frequency deviations can be rejected despite delays, uncertainties, and quantization during transmission.     

Analyzing inter-organizational systems from a power and interest perspective

Inter-organizational systems (IOS) are Information and Communication Technology (ICT)-based systems that enable organizations to share information and to electronically conduct business across organizational boundaries. Especially since the increasing availability of the Internet, there have been less technological barriers to implement IOS. However, that does not imply that IOS possibilities are implemented successfully in all occasions: other barriers may remain. Innovation is not only a technical process of ‘solving problems’; it also involves economic and political processes in which interests are articulated, alliances are built and outcomes are struggled over. To explore this observation, this paper presents a model that helps to describe and analyze IOS from a power and interest perspective of multiple parties. To illustrate this model, eight case studies of IOS are discussed, of which one is in more depth. After that, we will put the findings of the analysis in a broader perspective. The paper concludes with the assertion that the scope for the design of an effective IOS depends on a combination of technical, economic and social factors, which are intertwined. The model may help users to assess and discuss these factors.     

锂离子动力电池专利信息分析

通过对锂离子动力电池领域的专利情况进行统计和分析,揭示当今锂离子动力电池的研发现状,指出我国在该技术领域的专利申请特点和存在的问题并提出相应建议,为相关企业和科研机构的进一步研发提供参考。     

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.     

Travelling-wave analysis of generalized multiconductor systems

The behaviour of multiconductor systems is analysed from a fundamental travelling-wave point of view. Generalized wave parameters are derived for a two-port multiconductor system from which image and iterative parameters follow as special cases. The relationship of these to short-circuit parameters is also given.     

On the analysis of discontinuous systems

An effective procedure, employing an operational approach, is demonstrated for the analysis of constant parameter continuous systems with multiple lumped parameter attachments and concentrated forces. Convenience of the method and of the form in which the results are obtained are evaluated in comparison with other applicable methods. Systems with piecewise constant parameters are also investigated. The desirability of obtaining a complete closed-form steady-state solution and various methods of obtaining it are examined. Finally, an example is treated which illustrates the application of the operational method to system with jump discontinuities in deflection and slope.     

Taylor series analysis of multi-delay systems

The Taylor delayed operational matrix is extended to the analysis of multi-delay dynamic systems. A simple example is given to compare the exact solution and the solution obtained by the method shown in this paper. The result proves to be quite satisfactory.     

Walsh series analysis of multi-delay systems

A matrix, called the “delay operational matrix”, is constructed from the Walsh matrix. This matrix, together with some matrices obtained from the delay operational matrix after performing right-shift operations, is used to solve multi-delay linear dynamic systems. A simple example is given to compare the actual solution and the solution obtained by the techniques of this paper.