The application of space-vector theory to the analysis of electrical machines with space harmonics

Contents In the present paper the space vector method is described for the analysis of uniform air-gap three-phase and two-phase machines, taking into account the effects of m.m.f. space harmonics.The space vector equations are established in a natural and also in an arbitrary reference frame. It is shown that the various harmonic models can obtained without performing matrix transformations. The relationship between matrix and space vector forms is discussed. The models derived are suitable for both steady-state and transient analysis. Methods of derivation of harmonic transformations are also presented.

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Die Anwendung der Raumzeigertheorie zur Analyse elektrischer Maschinen mit räumlichen Obserwellen

Übersicht In der vorliegenden Arbeit wird die Methode der Raumzeiger zur Darstellung räumlicher Oberwellen in elektrischen Maschinen betractet. Die allgemeinen räumlichen Vektorgleichungen werden in einem natürlichen bzw. in einem beliebigen Koordinatensystem beschrieben. Es wird gezeigt, daß die verschiedenen harmonischen Modelle ohne Matrizenoperationen erhalten werden können. Die Beziehungen zwischen den Matrizen- und Raumzeiger-schreibweisen werden untersucht. Die Darstellungen der Maschine sind für die Analyse stationärer und nichtstationärer Vorgänge anwendbar. Schließlich wird die Ableitung harmonische Transformationen berücksichtigt.

     

Field-winding fault detection in synchronous machines with static excitation through frequency response analysis

Frequency Response Analysis is a well-known technique for the diagnosis of power transformers. Currently, this technique is under research for its application in rotary electrical machines. This paper presents significant results on the application of Frequency Response Analysis to fault detection in field winding of synchronous machines with static excitation. First, the influence of the rotor position on the frequency response is evaluated. Secondly, some relevant test results are shown regarding ground fault and inter-turn fault detection in field windings at standstill condition. The influence of the fault resistance value is also taken into account. This paper also studies the applicability of Frequency Response Analysis in fault detection in field windings while rotating. This represents an important feature because some defects only appear with the machine rated speed. Several laboratory test results show the applicability of this fault detection technique in field windings at full speed with no excitation current.     

Evaluation of the efficiency of an automated system for testing synchronous round rotor machines

On the basis of analysis of normative documents and study of the technological process of tests, an automated system for testing synchronous round rotor electric machines has been developed. This system has a three-level hierarchical structure. Its lower level consists of measurement sensors and actuating units, the middle level is represented by a digital computer system on the basis of the NI PXIe platform by National Instruments, and the highest level is a computerized operator position (COP), which is based on industrial-class PCs. Algorithms and programs for automatic testing of synchronous turbomachines that we developed in the LabVIEW environment form the basis of the virtual instruments of the system. Because of their interconnections, they are combined into a unified software complex (SMTest). The approximation of the synchronous- machine characteristics that were obtained during testing is based on regression equations of different orders and the least-squares method and used in the algorithms to determine the static parameters of a machine. A combined optimizing algorithm, which is based on the least-squares method and the alternating- variable descent method, is used to determine the dynamic parameters of a synchronous machine. To filter possible noise in measuring channels of the voltage and current sensors, a newly developed efficient adaptive method of sliding trigonometric interpolation is used in the algorithms for determining the parameters of sinusoidal signals, which are picked off the voltage and current sensors in steady-state modes, and dots of signal envelopes in transient modes. To reduce the time for obtaining the static characteristics of the machine, the automated system has a designed exciting-current control loop with a PID controller, which provides the desired field forcing. The automated test system’s efficiency was estimated by mathematical simulation of the testing procedure and the experiment. Analysis of the results has shown that the use of this system makes it possible to reduce the complexity of the testing procedure and its duration by a factor of 1.5–1.7, improve the accuracy of the obtained results by a factor of 3–5, and improve testing safety by mitigating risks of injury and emergencies due to incorrect actions of the staff.     

ELMEC software system for the design and investigation of electrical machines

An implementation in the ELMEC software system is presented for the method for computing the electromagnetic field in an electrical machine, which relies on the precision numerical simulation of electrodynamical processes. The basic simulation principles are stated, along with the structural features of the ELMEC software system, the use of which allows essentially improving the quality of design and optimization in the development of electrical machines.     

A flexible instrumentation and control system applied to a powerand machines laboratory

A Microsoft Windows based instrumentation and control system has been developed around a generic Intel 80386 microcomputer with an A/D card, counter timer card, stepper motor driver card, and a GPIB port. The computer can control two DC power supplies and the tap position on a three-phase autotransformer. The ratings on the supplies are consistent with the ratings of the 2 kVA AC and DC machines. Data can be downloaded from digital storage oscilloscopes for processing and display. A virtual instrument package has been written that can create, log, and display up to 25 meters. The only analog preprocessing required are voltage dividers, current shunts, and isolation amplifiers. The package is extensible, allowing students to add their own program modules for real-time control     

On the variation with flux and frequency of the core loss coefficients in electrical machines

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.     

An automated approach to beat-by-beat QT-interval analysis

The present work attempts to resolve some of the problems encountered in QT interval analysis and to describe a new algorithm that uses wavelets to analyze the QT interval on a beat-by-beat basis. The QT interval is further segmented into its contributing factors to find the variability in the repolarization phase. The technique and the algorithm have been tested on control and disease data from the standard MIT ECG library to prove the reproducibility and accuracy of the system. The technique has been implemented on a PC DSP add-on card to do the analysis on a beat-by-beat basis     

改进的区域消去法在电机优化设计中的应用

将一种新的全局优化算法－－区域消去法,引入电机优化设计领域。针对电机优化问题的具体特点,提出将混合罚函数法和修正的鲍威尔法进行组合用于其中的局部寻优。典型函数验证和永磁起动机优化设计中的应用该方法适于工程问题的全局优化,且具有收敛速度快的特点。     

An automated learning system for Java programming

The increase in the numbers enrolling in university computer courses makes huge demands on resources, and maintaining standards of teaching and tutorial support is almost impossible without a massive increase in staff. To overcome this situation, the authors have developed RoboProf, an automated learning environment which, as well as generating and assessing programming exercises, provides ongoing assistance and feedback to students without extra demands on lecturer and tutors' time. This system also contains a technique for detecting plagiarism, an increasing problem in computing courses worldwide. For this research, RoboProf was used to teach Java programming to a class containing nearly 300 students in the first year of a computing degree. Use of the system by students was monitored and recorded on log files in order to investigate the extent to which usage patterns influence achieved programming skill. An analysis shows that students who complete the set of RoboProf exercises perform significantly better than those who do not. The timeliness in which these exercises are completed relative to other students is significant: early solvers get higher marks, and students solving the problems with fewer attempts get higher marks. Not surprisingly, plagiarists achieve a lower score than those who do their own work. Other factors that were found to influence programming performance included entry standards and gender. Entry qualifications impacted positively on performance, and males performed significantly better than females. There was a significant positive correlation between the score achieved in the RoboProf course and the performance in a subsequent computing course administered in the traditional manner.     

An automated laser system for eye surgery

The use of lasers in ophthalmology is discussed, and the procedure and requirements of ophthalmic laser surgery are described. An overview of a proposed laser system for eye surgery is given, and its operation is described. Progress and research to date are reviewed.     

An integrated laboratory for electric machines, power systems, andpower electronics

A new-generation laboratory for electric power is described. The design and operation results are discussed. Examples of experiments are presented. The laboratory provides safe, modern, concept-intensive study of power devices and systems. Experience with the facility demonstrated that it is possible to create an integrated approach to the broad area of power devices, systems, and their control, without compromise of the laboratory experience     

A fuzzy gain scheduling PI controller application for an interconnected electrical power system

In this study, a fuzzy gain scheduled proportional and integral (FGPI) controller was developed to regulate and to improve the frequency deviation in a two-area electrical interconnected power system. Also, a conventional integral (I), a conventional proportional and integral (PI), and a fuzzy logic (FL), controllers were used to control the same power system for the performance comparison. Two performance criteria were utulized for the comparison. First, settling times and overshoots of the frequency deviation were compared. Later, the absolute error integral analysis method was calculated to compare all the controllers. All the models were simulated by Matlab 6.0-Simulink software. The simulation results show that the FGPI controller developed in this study performs better than the other controllers with respect to the settling time and overshoot, and absolute error integral of the frequency deviation.     

An automated feedback system for computer organization projects

This paper describes a system, built and refined over the past five years, that automatically analyzes student programs assigned in a computer organization course. The system tests a student's program, then e-mails immediate feedback to the student to assist and encourage the student to continue testing, debugging, and optimizing his or her program. The automated feedback system improves the students' learning experience by allowing and encouraging them to improve their program iteratively until it is correct. The system has also made it possible to add challenging parts to each project, such as optimization and testing, and it has enabled students to meet these challenges. Finally, the system has reduced the grading load of University of Michigan's large classes significantly and helped the instructors handle the rapidly increasing enrollments of the 1990s. Initial experience with the feedback system showed that students depended too heavily on the feedback system as a substitute for their own testing. This problem was addressed by requiring students to submit a comprehensive test suite along with their program and by applying automated feedback techniques to help students learn how to write good test suites. Quantitative iterative feedback has proven to be extremely helpful in teaching students specific concepts about computer organization and general concepts on computer programming and testing.     

Development of an undergraduate structured laboratory to supportclassical and new base technology experiments in communications

This paper describes an effective method of teaching a communications laboratory course that supports classical as well as new base technology experiments to undergraduate electrical engineering students. Primarily, experiments dealing with the design of the basic building blocks of analog and digital communications systems are targeted, which provides an opportunity for the student to become familiar with various signal processing techniques applied in modern communications systems, to learn how to operate the communication laboratory test equipment, and to obtain exposure to some hardware/software design and implementation of these subsystems. The second level of experimentation involves a small system in which discrete or integrated devices are used to build small systems. Level three involves experimentation with a complete communications system, such as a fiber optics communications system or a simulated satellite link. Four sample experiments are described in some detail     

An automated system for remote energy monitoring of mobile objects with electric drives

An approach to automation of remote energy monitoring of a mobile object with an electric drive is suggested. The approach is focused on solving the problem of generating statistics using analysis of energy consumption profiles. Structural solutions to arranging a system providing collection, transmission, and processing of measuring information from mobile object energy customers are considered. Based on the mixed implementation, a scheme of the measuring unit including a set of temperature, voltage, current, and speed sensors is developed. A data exchange scheme corresponding to the upper level of energy monitoring automation is developed. The control level in the scheme is established by JEVis local and global information systems with an open source. It is proposed to use a VIDA44M module remote telemetry and control line as a controller to collect data. The modules of the energy monitoring system can be supported by one server or distributed among several ones forming a cloud server. The data collection controllers communicate wirelessly with the server. The main calculation parameters of mobile object power supply, as well as the results of energy profile processing using hardware-in-the-loop simulations of the static and dynamic electric drive load, are considered. Based on the graphic profiles obtained by automated energy monitoring, one can assess the energy consumption of mobile objects, including public transport vehicles in a specific form, compare flow rates between similar objects, reveal faults or improper adjustment of the equipment, rank objects in power consumption, work out solutions to replace inefficient parts and mechanisms, predict power consumption, etc. As a result, power supply indices can be calculated and energy efficiency can be estimated; in addition, as energy audit of a transport company can be carried out and management decisions concerning energy efficiency can be suggested.     

A systematic approach to the implementation of final year projectin an electrical engineering undergraduate course

This paper describes a computerized management system for the processing of a final year project in an electrical engineering undergraduate course including a structured project allocation to students, a comprehensive assessment procedure, an automated processing of marks, and a management supporting system. An optical reader is used to scan the project selection made by all the students, and the allocation algorithm allocates as many projects as possible in meeting the students' preferences. A new attempt using a grading category index for each assessment criterion is implemented and the assessment of the student's performance is evaluated through five main components with 31 assessment criteria. The marks for each student are scanned by an optical reader and calculated by a weighted linear conversion of all the grading category indexes. The assessment system is more valid as it has many specific criteria and is more reliable as the process is consistent. The management supporting tools and experiences in handling very large groups of students especially in the maintenance of a uniform marking standard to all the students are highlighted. It is hoped that some of our approaches can be selectively adopted for undergraduate course work on continuous assessment even for a smaller student population     

基于改进MSER算法的电力设备红外故障区域提取方法

红外图像处理中因目标边界模糊、区域灰度变化等因素,导致传统的极大稳态区域方法区域提取效果低下。为此,提出一种基于改进极大稳态区域方法的电力设备红外故障区域提取机制,提升区域提取效果。首先,从灰度相似度聚类出发,采用Meanshift算法对分割区域的邻域像素进行聚类。其次,结合阈值分割机制,快速将相似像素进行分割,最终通过迭代得到电力设备故障所呈现的亮度区域信息。实验结果表明该提取区域方法性能优于极大稳态区域算法,具有较低的误分类错误,且相比于Mean shift算法,具有高效的处理速度。     

Assessment and analysis of the reliability of an electrical distribution system integrated with a wind energy system

From the results of a report previously prepared by Systems Control Inc., it was recommended that a wind turbine generator (WTG) should be integrated with a conventional system to assess the reliability of the combined systems, estimated on yearly-based data. In contrast, in this paper, the issue is reinvestigated to get an accurate estimation of the capacity and energy credits, and the reliability level using monthly average daily climatic data.The second main contribution of this work is to find the effect of the WTG penetration level on its power and energy credits, reliability and costs and eventually on the distribution system reliability. In addition, the influence of different configurations of the distribution system on its reliability in the presence of the WTG will be investigated for all seasons of the year.New mathematical models explicitly describing these impacts are developed.     

Midterm stability analysis of a multimachine system by the frequency response method

The eigenvalue method, Routh—Hurwitz method and other conventional methods used for steady-state stability analysis are not suited for a multimachine system consisting of several hundred machines with automatic voltage regulators and speed governors. This paper shows that the frequency response method is very useful for such a large-scale system. The critical stability condition obtained by the proposed method is compared with that obtained by conventional simulation and it is shown that the proposed method is sufficiently accurate and efficient. This algorithm is applicable to a decomposing system.     

计及异步电机频率响应的电力系统最低惯量评估

随着大规模新能源等电力电子器件的并网,电力系统惯量水平逐渐降低,系统转动惯量需求产生新的变化,负荷侧频率支撑能力显得愈发重要。针对这一问题,系统分析了异步电机的频率响应特性。基于小信号分析法提出一种机电暂态下异步电机建模方法,构建计及异步电机频率响应的电力系统频率响应模型。在深入分析新型电力系统惯量特性的基础上,考虑系统最大频率变化率、最大频率偏差以及备用容量限制等频率安全约束,构建了电力系统最低惯量评估模型并通过遗传算法进行求解。最后,在Matlab和PSASP平台上进行算例仿真和分析,验证了所提异步电机频率响应模型以及最低惯量评估结果的正确性和有效性。