Modeling failure data of overhead distribution systems

An overhead power line can be regarded as a collection of components each of which contribute in a particular way to its reliability. An overhead distribution system is a collection of such lines. A repairable system is a system which after failing, can be restored to an operational, but not a new state by repairing or replacing one or more components. This work treats the distribution system as a holistic entity with the aim of measuring the pattern of failures as an indication of reliability growth or deterioration. Comparison is made using case studies of an urban and a rural system based on trend analysis, the Laplace statistic and confidence limits. It is argued that although the pattern of failure of a distribution system may emulate a stationary point process, this can be misleading in the assessment of reliability and the impact of maintenance policies     

Modeling of transoceanic fiber-optic WDM communication systems

The rapid growth of long-haul wavelength-division multiplexing (WDM) fiber-optic telecommunications challenges lightwave system designers to increase the transmission capacity per fiber pair, while reducing the time to market. This makes it essential to have fast and accurate computer modeling tools to aid the systems design. There is a natural engineering tradeoff between simulation speed and accuracy; fast approximations tend to be inaccurate, while the exact treatment of the physical processes affecting transmission are nearly impossible to capture in a time-efficient algorithm. The proof of a successful tool development lies in the comparison of simulation results to transmission system measurements. In this paper, we discuss a new simulation technique based on careful evaluation of the key physical effects that produce system impairments. We show that this new approach can produce fast and accurate simulations of long-haul WDM transmission systems     

Modeling processes in onboard systems of cars

An approach to calculating the values of the total-resistance components of the equivalent circuits of electrical loads is proposed. This approach is used for the numerical simulation and development of digital control systems algorithms for compensating devices. Analytical expressions are given and checked for adequacy.     

Modeling the mechanical action of fiber-type biological systems

Biologically important ciliated fiber-type structures act in very complicated biological and physical situations. In this article, we model these structures and a process that is carried out by a collection of fibers, assuming that each of the fibers is connected by a small “muscle” to the surface on which the fibers are growing. The muscles act, and the fibers perform mechanical movements over the surface. Synchronization between the mechanical movements of the fibers is necessary for their mutual action, whose macroscopic relevance may be (as in the case of the cilia), for example, pushing some small obstacles in the needed direction over the (wet) surface. Synchronization only in time in the operation of the different muscles cannot be sufficient for such an effective collective mechanical action. The same direction of movement of the free ends of the fibers is also required. For this unidirectional activity, all of the muscles have to be placed at the same side of the fibers. This is a requirement of an orientational symmetry     

家用燃料电池热电联供系统的建模与仿真

家用燃料电池热电联供系统是一种清洁高效的分布式发电方式,近年来发展迅猛。开展家用热电联供系统建模与仿真,对于构建热电联供实际系统具有一定指导意义。在Matlab/Simulink平台上搭建了千瓦级燃料电池热电联供系统(包括电模型和热模型),电模型包含氢氧供应子系统、质子交换膜燃料电池模型以及功率控制模型;热模型包括热管理子系统和辅助热水器等模型。基于此热电联供模型,进行了燃料电池发电系统动态特性分析,然后采用电跟随策略,通过参考模拟工况下的电负荷与热负荷曲线研究了可变负载下系统的动态行为。仿真结果表明,该系统在热负荷与电负荷上都有较短的响应时间和较高的控制精度。     

齿隙系统的建模与自振荡分析

针对齿隙系统都有自振荡倾向的问题,给出了自振荡的条件。分析并说明了当齿隙处于系统中不同的位置上时要用不同的非线性特性来描述。当有力矩传递时齿隙的模型应该是用死区特性来描述,死区特性夹在两个动态环节之间形成了所谓的三明治系统。如果齿隙位于系统的输出端,则齿隙就具有滞环特性。无论是死区特性或滞环特性的场合,系统都有可能出现自振荡。分析指出这种三明治系统是由多重反馈回路所构成的,因而存在着固有的稳定性问题。采用描述函数法分析了这种三明治系统产生自振荡的条件,结论是齿隙的这种三明治系统与带滞环特性的系统一样,也是很容易起振的,并给出了改善起振条件的可能措施。     

一类网络控制系统的建模与稳定性分析

针对一类具有不确定网络诱导时延和线性控制对象的网络控制系统,通过将网络诱导时延描述为一个常值再叠加一个不确定值的形式,重新描述了采样控制系统的数字控制器,将网络控制系统建模为一类具有不确定时延的连续时间系统.利用Lyapunov方法和线性矩阵不等式技术,推导出了闭环系统渐进稳定的充分条件.与已有的结果相比,所提出的算法具有更低的保守性,并通过一个数值算例验证了所提出算法的有效性.     

Modeling the polarization spectrum in composite oil/paperinsulation systems

The determination of the polarization spectrum in the low frequency region of the dissipation factor, commonly has been used in practice to diagnose insulation conditions. The recovery voltage method (RVM) is one of the methods used to estimate the polarization spectrum. Nevertheless, current analysis of the RVM tests do not use all the information available from the test. In this paper, a mathematical model of the polarization spectrum is proposed. It is shown that, from the derived model, some of the hidden RVM peaks can be identified. Since the difficulty to derive a model from RVM data increases with the number of the peaks to be identified, a simpler model is always preferable. A scheme for determining the parameters of an equivalent circuit is also given, The composite oil/paper insulation is considered which is extensively used in cables and transformers. Cellulose paper, such as the Manila-Kraft type, which is used as insulation, exerts a major influence on the life of the equipment because of its hygroscopic nature. The importance of detecting and eliminating moisture from paper is crucial in oil-impregnated HV insulation. Analysis of the polarization spectrum has been used by several utilities to determine moisture in the paper. Recently, some test results indicated that the polarization spectrum may not clearly show important peaks corresponding to local moisture ingress and thus can mislead experts in the field, The developed model has been validated using RVM data of real power transformers     

Modeling development options of electric power systems in conditions of multiple stakeholders

Methodology is presented for substantiating the development of electric power systems in modern conditions taking into account multiple interests of stakeholders. The suggested methodology is aimed at finding compromise solutions and includes several stages of research, i.e., the target analysis, target assessment of the consequences of the decisions, the identification of invariant and extreme decisions, the formation of preferable decisions, reconciliation of interests, etc. The basic principles for the implementation of such an analysis are discussed. As an illustration, an analysis of the prospects for the development of the electric power industry in the Far East is presented in the conditions of multiple stakeholders.     

高压直流输电系统功率/电压静态稳定性的建模与分析

高压直流输电系统功率/电压静态稳定性与所连接的交流系统的强弱及其所采用的控制方式密切相关.阐述了用于分析直流输电系统功率/电压静态稳定性的系统小信号模型及分析方法,对不同控制下系统静态稳定指标进行了分析,结论表明,弱交流系统的功率稳定性与电压稳定性都较差,随着SCR的逐渐增大,都将有所改善;逆变器采用定直流电压控制比采用定熄弧角控制时系统的功率稳定性与电压稳定性要好.     

Modeling by petri net with place invariants for sequential control systems

It is more difficult to model a discrete system than a continuous system. Recently, a great number of applications of Petri nets to the design and the analysis of discrete systems has been reported. However, a common problem in its applications is that the required computer memories and the computation times increase explosively in accordance with the increase in the number of systems components. Some methods to divide or to reduce Petri nets have been proposed to solve this problem. Although the liveness and boundedness of Petri nets are held in the divided or reduced Petri nets, the reachability problem cannot be solved by these methods. This paper proposes another method to model discrete systems by Petri nets with place invariants. A sequential control system will be described as a typical kind of discrete system, and its structural characteristics will be used in modeling. Each component of a sequential control system will be modeled by a sub-Petri net with place invariants. There are many components in one sequential control system, but not each one is necessarily complicated. Most sub-Petri nets do not have so many places or transitions. It is also well known that a Petri net with place invariants is bounded and can be live by placing sufficient tokens into its initial marking. Besides, the reachability problem is not so difficult to solve in a small sub-Petri net. Further, an activating relation to combine two or more sub-Petri nets is defined, and some rules to reduce conflicts among enabled transitions will be described for simulations.     

Modeling of optical waveguide structures with general anisotropy in arbitrary orthogonal coordinate systems

An extended algorithm for the analysis of arbitrary waveguide structures with general anisotropic materials is proposed and substantiated. This algorithm is based on generalized transmission line (GTL) equations which are developed here for numerical algorithms. For the purpose of analysis, a general modal matrix for the discretized transverse electric and magnetic fields is calculated. Furthermore, impedance/admittance transformation formulas are developed with the help of the GTL equations for longitudinal sections. The proposed algorithm is verified by numerical results.     

Modeling and damping of high-frequency leakage currents in PWMinverter-fed AC motor drive systems

This paper presents an equivalent circuit for high-frequency leakage currents in pulsewidth modulation (PWM) inverter-fed AC motors, which forms a series resonant circuit. The analysis based on the equivalent circuit leads to such a conclusion that the connection of a conventional common-mode choke or reactor in series between the AC terminals of a PWM inverter and those of an AC motor is not effective to reduce the rms and average values of the leakage current, but effective to reduce the peak value. Furthermore, this paper proposes a common-mode transformer which is different in damping principle from the conventional common-mode choke. It is shown theoretically and experimentally that the common-mode transformer is able to reduce the rms value of the leakage current to 25%, where the core used in the common-mode transformer is smaller than that of the conventional common-mode choke     

三相五电平逆变器光伏并网系统的建模与仿真

针对传统三电平逆变器光伏系统最大功率跟踪(maximum power point tracking,MPPT)响应速度慢、输出电流波形失真严重以及直流母线电压波动大的问题,提出了一种三相五电平中点箝位型(neutral point clamped,NPC)逆变器光伏并网系统。该系统采用模糊MPPT功率外环、直流电压中环以及电流内环的三环控制方案,实现了对最大功率的快速跟踪,降低了输出电流波形的总谐波畸变率(total harmonic distortion,THD),有效抑制了直流母线电压的波动。用MATLAB搭建模型,仿真结果证明了所提出的含五电平逆变器拓扑结构及其控制方法的有效性。     

Modeling and stability analysis of hybrid power systems for the more electric aircraft

This paper presents a detailed modeling and a comprehensive assessment of small-signal stability for a “more-electric” vehicular power system consisting of a synchronous variable-frequency generator which supplies power electronic controlled loads via an 18-pulse autotransformer rectifier unit for AC-DC conversion. Functional models for key power system components and loads are derived. Analytical derivations employed for small signal stability analysis based on linearized equations are described, and the influence of leading design parameters on system stability is evaluated.     

Modeling and control of distributed generation systems including PEM fuel cell and gas turbine

This paper concentrates on the modeling and control of distributed generation systems including fuel cell and gas turbine. The fuel cell is connected to the power system through a dc/ac converter, which is equipped with both voltage- and power-control loops. The gas turbine is also assumed to be equipped with both voltage-control and generation (or frequency)-control loops. Moreover the gas turbine is modeled using the d–q frame of reference. The interfacing of the gas turbine with the power system is achieved by transforming its equations from the d–q frame of reference to power system frame of reference. A multivariable supplementary fuzzy logic controller is proposed for improving the dynamics of the combined fuel cell and gas turbine system. This fuzzy logic controller is designed using the Matlab Fuzzy Logic Toolbox A distribution test system including a load, a fuel cell and a gas turbine, connected to a power grid is simulated using Matlab/Simulink software package. The dynamics of the combined distributed generation plant are analyzed for the cases of with and without controller. The accuracy of the presented model and the effectiveness of the proposed multivariable supplementary fuzzy controller are deduced from the simulation results.     

Modeling real-time balancing power demands in wind power systems using stochastic differential equations

The inclusion of wind power into power systems has a significant impact on the demand for real-time balancing power due to the stochastic nature of wind power production. The overall aim of this paper is to present probabilistic models of the impact of large-scale integration of wind power on the continuous demand in MW for real-time balancing power. This is important not only for system operators, but also for producers and consumers since they in most systems through various market solutions provide balancing power.     

Finite-element analysis of space-charge suppression ofelectrostatic-induction spray charging

A finite-element analysis of the space-charge suppression encountered during the electrostatic-induction spray-charging process is presented. This paper provides a theoretical framework in support of the experimental studies reported elsewhere of the space-charge-limiting barriers of nozzle design. Poisson's equation is solved using a finite-element axisymmetric model consisting of 3704 triangular elements and 1946 nodes for various placements of nearby earthed surfaces. Plots of constant potential surfaces in and around the dielectric embedded-electrode charging nozzle are presented. The axial droplet-charging potential gradient at the tip of the liquid jet (along the axis of symmetry) depends upon both the positive induction electrode potential and upon the presence, and substantially upon the spatial extent of the negatively charged cloud of dispensed droplets