A Design Approach for Direct-Drive Permanent-Magnet Motors

This paper presents a design approach of a direct-drive permanent-magnet (PM) motor for a medium-sized injection-molding application. In the proposed approach, genetic-algorithm (GA) loop works to optimize the lamination design in order to meet the requirements for the target application. To achieve the design optimization within a realistic time scale, the repeated calculation required to obtain fitness evaluation does not use finite-element analysis (FEA) but consists of a geometric flux-tube-based nonlinear magnetic analysis developed specifically for this class of motors. The validity of the proposed design approach is verified through several comparative studies on the design results with FEA using a 942- 88.8-kW three-phase multipole interior PM motor, which is designed by the proposed optimizing GA approach.     

Reliability Estimation for Large-Area Solder Joints Using Explicit Modeling of Damage

The issues of available cyclic fatigue models in life prediction of large-area solder joints using finite-element analysis (FEA) are discussed. In this paper, a new FEA approach called successive initiation (SI) is modified and introduced in conjunction with energy partitioning (E-P) damage model to resolve some of the issues with available damage models such as geometry and scale dependency and provide a solution to large-area solder joints. This new technique models damage explicitly, meaning that it separates initiation from propagation by monitoring the plastic and creep damage at the tip of the crack successively. The SI technique could be easily used with continuous loadings of different types and frequencies. The modeling approach is then implemented on a power device with large-area solder. Sensitivity study is conducted with the help of the experiment to determine the right initiation threshold for smooth crack initiation and propagation. The results of modeling are then compared with available experimental data for the same power device. The comparison shows that using the damage model constants generated for small solder joints such as ball-grid array or chip-scale package could significantly overpredict the life of larger area solders. New E-P damage model constants for large-area solder joints are obtained and presented by calibrating the modeling to the experiment.     

Two-dimensional finite-element analysis of a high-force-densitylinear switched reluctance machine including three-dimensional effects

This paper presents results of a finite-element analysis (FEA) study on a high-force-density linear switched reluctance motor. Analytical study by means of an electric circuit analog of the same motor was presented in a previous paper. For this refined analysis, two-dimensional (2-D) FEA is used along with a novel way of accounting for three-dimensional (3-D) effects. It is shown that, with minimal 3-D FE modeling, the 2-D FE model can be used to satisfactorily include the third-dimensional effects due to end turns and short stack length relative to the motor axial length. FEA results are presented and compared with measured results. Comparison with measured forces shows the effectiveness of the model     

A prototype flexible robot arm-an interdisciplinary undergraduateproject

An interdisciplinary undergraduate project to set up a prototype flexible robot link is discussed. The project consists of modeling, fabrication, and control of the flexible link. The combination of already well-known Lagrange and finite-element methods seems to be a great advantage in this modeling procedure. Lightwave flexible links, although known to save a large amount of operational energy, are not popular in the industry because of difficulty in their modeling and control. Following the methodology suggested, modeling is reduced to a mechanical procedure capable of efficient computer implementation. A simple controller is suggested. The controller is designed using the MATLAB simulation package, and the results are compared graphically. The lessons learned form the project are reported     

超声电动机模型分析的研究

针对超声电动机模型，第一次对其分析方法进行了对比分析，综合解析法（能量法）、有限元法和等效电路法的特点，建立了一套行之有效的行波超声电动机分析方法。并成功设计了专利产品－均压型行波超声电动机及其驱动控制器。该方法为超声电动机的驱动控制策略和控制方法的实现奠定了理论基础，为样机设计提供了实际经验，对我国超声电动机产业及其原材料的国产化作了有效探索。     

Assessment of the Impact of Joint Bays on the Ampacity of High-Voltage Cable Circuits

Improvements in the cost and availability of computational power in recent years has led to numerical techniques such as finite-element analysis (FEA) becoming viable for cable-rating calculations. This analysis has previously been completed for the case of directly buried and force-cooled cable circuits, but without direct consideration of the joint bay. This paper presents methods by which conductor temperature profiles within joint bays may be obtained through the use of FEA. Results are presented for a number of joint bay configurations common to the U.K. for naturally and force-cooled installations. Implications of the results on circuit-rating practice are discussed and the benefits of using tools, such as FEA, are considered versus other existing methods.      

Simple nonlinear magnetic analysis for permanent-magnet motors

This paper presents a simple nonlinear magnetic analysis for a surface-mounted permanent-magnet synchronous motor as an assistant design tool of finite-element analysis (FEA). The equivalent magnetic circuit of the motor used in the proposed analysis is composed of the saturable permeance tips in the stator teeth for considering the local magnetic saturation. As a result, the proposed analysis is capable of calculating the flux distribution and the torque characteristics in the presence of magnetic saturation. The effectiveness of the proposed analysis is verified by comparing with three-dimensional (3-D) FEA in terms of the analytical accuracy. The computation time is greatly reduced as short as 1.5 s while the 3-D FEA requires as much as 32 min for the same evaluation.     

Equivalent energy function approach to power system probabilisticmodeling

A novel approach, the equivalent energy function (EEF) method, is presented for power system probabilistic modeling. The method performs convolution and deconvolution by using electric energy directly so that the probabilistic modeling is considerably simplified. The EEF method is not only more efficient than any other available method in this domain, but is also more flexible in treating assigned energy units. An approximate deconvolution algorithm and a LOLP (loss-of-load-probability) formula are also given which enable probabilistic modeling to be performed even faster. Numerical examples demonstrate that the proposed algorithm is simple, efficient and more accurate     

Cogging Torque Reduction in Permanent Magnet Machines

This paper examines two methods - magnet shifting and optimizing the magnet pole arc - for reducing cogging torque in permanent magnet machines. The methods were applied to existing machine designs and their performance was calculated using finite-element analysis (FEA). Prototypes of the machine designs were constructed and experimental results obtained. It is shown that the FEA predicted the cogging torque to be nearly eliminated using the two methods. However, there was some residual cogging in the prototypes due to manufacturing difficulties. In both methods, the back electromotive force was improved by reducing harmonics while preserving the magnitude.     

Quantification of gains and risks of static thermal rating based on typical meteorological year

The growing demand for electricity and the restructuring of power markets is forcing the power industry to change the way that power systems are planned and operated. Traditionally, transmission lines have been operated based on fixed deterministic thermal ratings, causing underutilization of their potential capacity. Efforts to overcome this limitation led to the development of alternative rating strategies based on probabilistic and dynamic methods.In this paper, a probabilistic static thermal rating method based on typical weather conditions along a transmission line is described and analyzed. The results of load and energy throughput analyses show that the use of this rating approach can significantly increase line throughput compared to traditional deterministic rating methods. However, this approach can also substantially increase the risk of thermal overload.To identify the problems associated with the use of a probabilistic static thermal rating method, we performed a sensitivity study. Statistical analysis of weather parameters shows that line ratings calculated from typical weather data are inflated. Additional results confirm that values of risk tolerance and wind direction incorporated into the rating method significantly affect the resulting rating values. We suggest values for these parameters that minimize the risk of line overloading.     

基于拉格朗日插值法的概率建模方法及其在概率潮流分析中的应用

大规模可再生能源并网给电力系统带来大量概率不确定源,这会极大地增加电力系统概率潮流分析中对不确定源概率建模的计算负担。Nataf变换能够有效完成对皮尔森相关随机变量的概率建模,其关键在于标准正态分布域的相关系数求解。然而传统的基于辛普森数值积分法和二分法的相关系数求解法,使Nataf变换的过程耗时严重,难以达到实时计算的要求。为此,采用拉格朗日插值法和简化牛顿法实现相关系数的高效计算,以加快概率建模的过程,提高概率潮流分析的效率。基于改进的IEEE 118节点算例,测试了所提相关系数求解法的计算精度与速度,并进一步测试了其误差对整个概率潮流计算结果精度的影响。结果表明,所提方法能够高效而精确地完成Nataf变换中标准正态分布域相关系数的求解,从而在保证概率潮流结果精度前提下,提高概率潮流分析的效率。     

PastA—the characterization of the inherent fluctuations in the fabrication process for circuit simulation

For worst-case analysis, Monte Carlo analysis, yield optimization and design centring, the variations and correlations of the device model parameters in the electrical circuit simulation are of fundamental significance. This paper describes a method for the complete characterization of the inherent fluctuations in the fabrication process for the simulation in IC design. the emphasis is placed on analogue simulation owing to the complex connections between circuit design and technology and the multitude of devices with correlated parameters; nevertheless, statistical requirements for digital simulation can be fully covered. This characterization works with all technologies whether CMOS, BiCMOS or bipolar. the prerequisites are accurate nominal device model parameters for the circuit simulation and information about fabrication statistics, e.g. process control monitor measurements. A new approach with connection coefficients for the calculation of the correlation coefficients is presented. Dependent parameters can be easily defined through a connection hierarchy. With the presented approach the variations and correlations of model parameters for simulation can be generated from estimates or measurements of the fabrication process. Based on sensitivity analysis, the variations and correlations of design objectives can be estimated. This enables the designer to do circuit analysis and optimization (limit parameters, worst-case distances) as well as Monte Carlo analysis.     

浅谈火力发电厂筒仓的结构设计

以往对于火力发电厂的筒仓结构通常采用分块简化方法进行分析计算,大多数计算结果均十分保守。本文剖析了筒仓的一般设计前处理过程,包括荷载输入以及有限元模型建立。以湛江新建筒仓为工程实例,建立不同的模型,通过对比分析,揭示了一般电厂筒仓结构有限元模型建立的注意要点及设计思路,供今后筒仓结构设计以及研究人员参考。     

Composite system well-being evaluation based on non-sequential Monte Carlo simulation

The reliability evaluation of composite power systems has historically been assessed using deterministic and probabilistic criteria and methods. The well-being approach was recently proposed in order to combine deterministic criteria with probabilistic methods and evaluates the system by healthy, marginal and risky states. This paper presents an efficient method for composite system well-being evaluation based on non-sequential Monte Carlo simulation. It is assumed that the system is coherent, and the frequency and duration indices are calculated by the conditional probability method. The system adequacy is evaluated by a non-linear power flow solved by the Newton–Raphson method and by an optimal power flow solved by the Interior Points method. Results are presented for the IEEE-RTS system with a constant load and with a variable load curve. It is demonstrated that the proposed method, as well as the assumed hypothesis, are valid and provide an efficient alternative for the well-being analysis of large scale power systems.     

基于最优化算法的污秽绝缘子模型计算

笔者以有限元分析软件Ansys8．0为工具,讨论了基于最优化算法的污秽绝缘子模型临界条件的计算,包括建模、仿真和计算流程,并对典型实验模型进行了计算。由于该法可以动态地控制寻优范围和叠代步长,所以收敛迅速、结果准确。不仅可以计算简单模型,对于形状不规则或表面污染物分布不均匀的模型也同样适用。与传统的模拟电荷法和电路分析法相比,更加适合于绝缘子闪络特性的仿真和计算。     

机炉协调系统的鲁棒非线性控制

文中将一种近似反馈线性化方法和概率鲁棒分析设计方法结合起来设计机炉协调控制器。近似反馈线性化方法采用积分观测器估计并补偿系统的扩张状态，不仅实现了系统的近似线性化，而且减弱了外扰、参数不确定性和限幅限速对系统的影响。控制器的参数采用基于遗传算法的概率鲁棒分析设计方法得到，在设计阶段可直接考虑鲁棒性能设计要求。最后设计了两种典型情况进行仿真，并与回路成形H∞方法进行了比较，结果显示文中的方法具有更好的鲁棒性和适应性。     

Simulation and analysis of induction machines with rotor asymmetries

The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. An important issue in such an effort is the modeling of the induction machine including rotor bar and end-ring faults, with a minimum of computational complexity. A new and simpler method is employed in the simulation and analysis of an induction motor with rotor asymmetries. Simulation, finite-element analysis, and experimental results are presented to support the proposed approach.     

基于Ansoft的新型磁阻式旋转变压器的设计及优化

介绍了新型磁阻式旋转变压器的的基本结构和工作原理,给出了定子激磁绕组和输出绕组的的分布方式,分析了正弦绕组和凸极转子的设计方法。通过Ansoft/Maxwell有限元仿真分析软件对所设计的磁阻式旋转变压器进行了分析,得到了旋转变压器的仿真输出参数,进行了样机制作并对其完成了测试,通过测试结果和仿真分析结果的对比,验证了设计方案的正确性和可行性,为新型磁阻式旋转变压器的设计提供了设计依据。     

A New Method to Measure the Switched Reluctance Motor's Flux

This paper presents a method to measure the flux linkage curves of a switched reluctance motor (SRM) that avoids the inherent errors introduced by iron and copper losses using the classic method of applying a voltage to the phase of the SRM and integrating it, minus a resistive voltage drop to get the flux. In the proposed method, the flux is computed from the measured static torque using conservation of energy and from the SRM's measured unaligned inductance. In this paper, the method is applied to measured torque data from an experimental SRM and to torque calculated by finite-element analysis (FEA). The experimental results and FEA results are compared with the results obtained using the classic method and an analytical model.     

The present status of maintenance strategies and the impact ofmaintenance on reliability

In this paper, the most frequently used power system maintenance strategies are reviewed. Distinction is made between strategies where maintenance consists of replacement by a new (or “good as new”) component and where it is represented by a less costly activity resulting in a limited improvement of the component's condition. Methods are also divided into categories where maintenance is performed at fixed intervals and where it is carried out as needed. A further distinction is made between heuristic methods and those based on mathematical models; the models themselves can be deterministic or probabilistic. From a review of present maintenance policies in electric utilities, it is concluded that maintenance at fixed intervals is the most frequently used approach, often augmented by additional corrections. Newer “as needed”-type methods, such as reliability-centered maintenance (RCM), are increasingly considered for application in North America, but methods based on mathematical models are hardly ever used or even considered. Yet only mathematical approaches where component deterioration and condition improvement by maintenance are quantitatively linked can determine the effect of maintenance on reliability. Although more complex, probabilistic models have advantages over deterministic ones: they are capable of describing actual processes more realistically, and also facilitate optimization for maximal reliability or minimal costs