T.J. Hammons, H.B. Ertan, J.A. Tegopoulos, W. Drury, M. Ehsani, T. Nakata, A.G. Jack
1998 ICEM Review
Highlights of the 1998 International Conference on Electrical Machines
The thirteenth International Conference on Electrical Machines (ICEM) was held 2-4 September 1998 at Swissotel Istanbul, The Bosphorus, Istanbul, Turkey. It was one of the best electrical machines conferences ever with respect to the number of papers, country representation, quality of the papers, and presentation quality. ICEM '98 was organized by the Turkish National Committee, chaired by Professor H.B. Ertan and Professor Y. Uctug of Middle East Technical University, Ankara.
This year, the conference was run in conjunction with the International Conference on the Electric Ship, which immediately preceded ICEM and at which a keynote address, an invited paper, and 21 technical papers were presented. This conference was also organized by Middle East Technical University. It was chaired by Dr. Majumdar of the U.S. Office of Naval Research (Europe) and by Professor H.B. Ertan.
ICEM is a biennial forum for academics, scientists, engineers, manufacturers and users from all over the world to come together to discuss recent developments and future trends in theory, design, operation, and applications of electrical machines, actuators, and drives. It has been the major conference in this field since its inception in 1974. After the first meeting in London, participants have met in Vienna, Brussels, Athens, Budapest, Lausanne, Munich, Pisa, Boston, Manchester, Paris, and Vigo. The general scope of the ICEM conference included analysis, development, design, and application of all types and sizes of electrical machines: inductive coils, transformers, direct current machines, alternating current machines, permanent magnet machines, variable reluctance machines, special rotating or linear machines, and actuators.
There were 404 technical papers, including 4 invited plenary papers, one on the first day, two on the second day, and one on the third day of the conference. All presentations and discussions were in English. The technical program lasted 3 full days. There were preconference and daily tours for delegates and ac companying persons.
This article focuses on hightlights of the conference and summarizes the four invited papers that were presented as Plenary Sessions:
•} The Variable Speed Drives Market: Past, Present and a View on
the Future, by W. Drury, executive vice president of Technology, Control Techniques
plc, UK
•} Sensorless Control of Switched Reluctance Motors: A Technology Ready for Applications, by M. Ehsani, professor, Texas A&M University, U.S.A.
•} Present Situation and Trends and
What is Needed for the Finite Element Method of Electrical Machines, by T. Nakata,
professor, Gakuin University,
Opening Session
H. Bulent Ertan (chair of the Local Organizing Committee) welcomed all to ICEM '98 and introduced the speakers. John A. Tegopoulos (chair of ICEM International Steering Committee), who formally opened the conference. Gulsun Saglamer (president of Istanbul Technical University) and Suha Sevuk (president of Middle East Technical University) welcomed participants on behalf of the sponsoring universities. His Excellency Hikmet Cetin (speaker of the Turkish Grand National Assembly) welcomed the conference to Turkey.
Ertan said that Turkey is a natural bridge between East and West and between North and South, and Istanbul is the jewel of this bridge. First settlements in the area of Istanbul date back to 5500 BC. The city was under Roman control in the second century BC. In the year 366, the Roman Emperor Constantine visited the city and declared the city the capital of the new Roman Empire. The city was later called Constantinople after his name. During the fifth century, the Eastern Roman or Byzantine Empire reached its peak. Constantinople was embellished with great buildings. In 1453, the city was conquered and became the capital of the Ottoman Empire. This lasted for more than 450 years. It was the symbol of the Ottoman might from the fifteenth to the seventeenth centuries; it was crowned by many monumental buildings, palaces, and mosques. Because of its unique position, it became a center of culture, commerce, and trade. By the end of the nineteenth century, the population of the city had reached about one million inhabitants. Today, Istanbul houses ten million people, is the home of an important stock market in Europe, and has operations of 235 of the top 500 companies in Turkey.
Electrical drives and motors are at the heart of most processes and transportation, which provides comfort that is taken for granted in everyday life. Developments in semiconductor technology in the past 10-15 years has provided semiconductors that are more reliable, more powerful, and have faster switching rates. Microprocessors with unimaginable computing power have become a reality. Intelligent modules have made designing a power stage for a converter relatively simple. Control techniques that were not practical a few years ago are becoming possible, and some have become a reality. High energy permanent magnets have allowed brushless motors with previously unattainable specific outputs to be produced. The switched reluctance motor has been reinvented.
On the material side, metal glass and powder metallurgy are promising interesting developments. Converter-motor integration is becoming a trend causing a review of the way motors are designed. More common use of drives is causing efficiency and harmonic generation issues to become a more important problem than ever.
The electrical machines and drives community has many problems to work on and solve. This liveliness of activity is observable from the many meetings held all over the world. ICEM has a very special place. With its invited papers and large international participation, ICEM is a good place to observe general trends in the field, to meet and make new friends, and discuss and perhaps resolve nagging questions.
Variable Speed Drives Market:
Past, Present, and Future
The first plenary session reviewed today's electrical variable speed drives market in a historical context and presented a view as to what the future will hold. The lecture was presented by Dr W. Drury, Control Techniques plc.
Past. The variable speed drives market remains a key component and beneficiary of the boom in all aspects of automation and energy saving which are becoming of ever greater importance throughout the world. Electrical variable speed drives have facilitated the automation revolution. They have developed rapidly, stretched by demands never dreamt possible a generation earlier. The development cycle of drives products is now such that product ranges have expected lifetimes of only 3-5 years. The world of variable speed drives is exciting and rapidly moving. To predict the future and the pace of development is difficult. A historical perspective is helpful and shows how rapidly things are moving.
The work of Harry Ward Leonard of 1896 marked the birth of efficient, wide range, electrical variable speed drives. His work was not universally accepted at the time, and attracted much criticism. Today, all dc drives are based on his control philosophy.
The inherently three-phase squirrel-cage induction motor was introduced in 1889, and the slip-ring induction motor a year later. The speed of these motors depended fundamentally on the number of poles and on the supply frequency. Rotor resistance control of slip-ring motors was introduced.
The first significant move with respect to frequency changing was made by Kramer in 1904 by introducing use of a dc link between the slip rings and the ac supply.. This involved two ac-dc motor sets. In 1911, Schrage introduced a system based on an induction motor with a commutator on the rotor. In 1923, the Ignitron made controlled rectification possible, grid controlled mercury rectifiers made life easier in 1928, and direct ac to ac conversion by means of cyclo-converters was introduced in 1931. In 1932, the Nyquist stability criterion was developed, followed by the Bode stability criterion in 1938.
The 1950s saw the introduction of silicon into power switches, and by 1960 thyristors (SCRs) had become available and the variable speed drives reformation had begun. The 1970s saw the introduction of packaging arid field oriented control of ac machines. Plastic moldings made their first significant im- pact in the drives industry in 1983. By 1986, great advances were being made in microprocessors, making possible cost-effective digital drives; and 1989 saw the first implementation of the field orientation or flux vector drive to the high volume, lower power market. Then, in 1992, a new packaging trend emerged where the bookform shape which had previously been applied to servo drives now was applied to the industrial ac drives market. This was followed in 1996 by the first truly universal drive that met the requirement of a general purpose open-loop vector drive, a closed-loop flux vector drive, and a servo drive with selection purely by parameter selection.
Present. The central part of the lecture focused on the variable speed drives market, and variable speed drives technology today. Development within the drives industry continues at an ever increasing pace. Fundamental changes in the product from a customer perspective are still emerging, accessing ever more applications driven by automation and quality. It is apparent that the role of marketing is becoming significant. Drives have moved from being an engineered solution to a near commodity, and development and sales trends have and will continue to reflect this. This has implications for users and the drives industry.
The big manufacturers are getting bigger and more dominant in the market. Their purchasing power outweighs their higher overheads in comparison with the smaller players. The market is still rich with special products designed for one specific user or application, though this is not as prevalent as in the past.
For any meaningful analysis of the drives market, it is helpful first to segment the market. This may be done for volume markets as follows: general purpose, high performance, and servo markets. The world market for industrial drives is of the order of US$9 billion (converters only) which can be split by market size by segment 32 percent servo, 23 percent high performance, 45 percent general purpose; market size by region 30 percent Europe, 25 percent Japan, 23 percent North America, 13 percent rest of Asia, and 9 percent rest of World. In volume terms, these figures represent over 10 million drives (some 50 percent of which are very low power low cost products); while in power terms the annual installation of drives is in the region of 40 GW.
Today's user must decide what is needed for his or her application from the vast array of drive technologies. Most users have diverse requirements, requiring different technologies. This raises issues of specification, selection, purchasing, stock control, spares, training, commissioning, etc.
The ac drive technologies remain diverse in topology and characteristics. No one system is optimum for all applications. The PWM voltage source inverter, based upon IGBTs, has gained a dominant position in the ac drives market in the power range to 1,000 kW due to its ease of application, good supply power factor, potential to provide good dynamic performance, etc. PWM drives are applied most commonly to induction motor systems but are also the basis of brushless ac servo drives.
Drury addressed ac drive control strategies, highlighting open loop inverters with fixed volts/Hertz control (induction, [synchronous or synchronous reluctance] motor); open-loop inverter with flux vector control (mainly induction motor); closed-loop inverter with flux vector control (induction motor); and closed loop inverter-brushless ac motor control (permanent magnetic ac motor). Alternative ac drive technologies are currently available on the market. Performance of the technologies varies greatly and is best quantified in terms of torque band-width performance.
Future. The dc drive is not dead nor will it die in the near future. Its market will remain flat, and consequently it will be an important market for many years.
The relatively low cost, rugged cage induction motor will re main the preferred machine for most industrial drives. Higher performance and higher power density will call upon permanent magnet synchronous (brushless dc) machines.
The call for more and more performance from open-loop drives will continue with true open loop flux vector drives coming in the near term.
The distinction between servo and industrial drives will continue to blur in terms of dynamics and hence applications.
The packaging revolution is still in its infancy. Integrated power modules will become more flexible and comprehensive, providing the basis for "drive in a block" concept to grow for small drives. Benefits in terms of size, cost, and consistency will come for the user, and a step change in manufacturing technology for the supplier.
Reliability is the key issue in the future. In this regard, good design coupled with consistency of build are vital. In striving for improved build quality, automation has a major role.
Drury addressed the market; drive technology; customer needs; component technology: processing power, power semi-conductors, materials; power circuits; motors; speed and position feedback; control strategies; and drive companies innovations.
Conclusion. The view to the future is a personal one and no guarantee can be offered. What is certain is that while drive technology has advanced rapidly in the last 20 years, the rate of growth will accelerate in coming years. In looking forward, it is useful sometimes, but not for too long, to look back. Remember Harry Ward Leonard had a lot of critics in 1896 who were skeptical about these new-fangled ideas. Not much has changed to- day for those with new ideas who lead the market and have a clear vision of the future.
Sensorless Control of Switched Reluctance Motors
The second plenary lecture was given by M. Ehsani, Texas A&M University. He presented a brief overview of the development of sensorless techniques in switched reluctance motors and the current state of the art. He covered a range of topics related to sensorless techniques, including their fundamentals, current state of research, and future trends. The presentation included a detailed description of practical laboratory implementation of a sensorless switched reluctance motor with self-tuning capability where it was concluded that reliable sensorless switched reluctance motor drives are now practical, and will make the drives of many future applications.
Foundations of Existing Sensorless Techniques. He said switched reluctance motors are structurally similar to variable reluctance stepper motors but are designed to operate efficiently for a wide range of speed. Performance of a switched reluctance motor, which is inherently a variable speed drive, depends on the synchronization of the phase excitation with respect to rotor position. Hence rotor position sensing must be an integral part of the motor control system. Conventional rotor position sensors used in a switched reluctance motor drive system include resolvers, inductive or Hall effect sensors, and optical encoders. But they have several disadvantages, like additional cost, additional electrical connections, mechanical alignment problems, and space requirement. These disadvantages make the conventional position sensors an inherent source of unreliability.
The fundamental principle of operation of a switched reluctance motors is based on variation in flux linkage with the change in angular position of the rotor. Knowledge of the magnetic characteristics plays an important role in determining the rotor position indirectly for sensorless control operation. Electrical variables have encoded rotor position information that can be extracted. Typical measurable variables include voltage, current, and chopped current rise time and fall time. The derived variables include inductance, incremental inductance, flux link-age and back EMF (motional EMF). Depending on the geometry and operating point of the motor, a suitable method is chosen such that very good resolution is obtained.
Ehsani focused on the classification of existing sensorless algorithms and said that the need to enhance reliability of switched reluctance motors resulted in the development of several sensorless techniques over the last decade. Most are based on the magnetic characteristics of the machine. They can generally be classified as open loop or synchronous control methods; intrusive methods (linear relation methods, inverse relation methods); nonintrusive methods; and other methods. He discussed the methods; and other methods including observer based methods, mutually induced voltage based methods, and design based methods which have some distinct features from the conventional non-intrusive methods.
Advantages and Shortcomings of Existing Methods. He said open loop control methods are based on directly controlling output torque by adjusting controllable input parameters. They are relatively inexpensive but are not reliable during starting of the motor as it can lead to mechanical resonance. Intrusive methods are based on probing the passive (unenergized) phases. Since the time window for this probing is reduced at high speeds, these methods are suitable only for speed restricted applications. The test signals used must be chosen such that it produces no or very less negative torque and have little saturation effects. Probing methods using existing power circuitry need compensation for mutual effects. Most of the probing methods require additional electronics resulting in restricted control flexibility.
Nonintrusive methods offer the advantage of a wide spread range and fewer additional electronic circuitry. Some of these methods are based on chopping current waveform, hence have restricted speed range. Another disadvantage of this method is that position encoded signals are at the power level rather than at the signal level. Observer based methods offer better accuracy but are computationally intensive. They also require a very accurate model of the motor and a fast processor to compute the complicated algorithm. But the rotor position information is inadequate if the control is aimed at performance optimization of the machine. Sensorless techniques with self-tuning capability are necessary for performance optimization in the presence of parameter variations.
Ehsani discussed a practical four-quadrant sensorless switched reluctance motor drive with self-tuning capability that he had developed. The main attributes of the sensorless method are: speed range 0-3,000 rpm; position error 0.5 degrees (mechanical) at 3000 rpm and better at lower speeds; resolution of 0.1 degrees (mechanical) at 3,000 rpm and better at lower speeds; transient performance good at high speeds and moderate at low speeds; and four-quadrant capability. An amplitude moderation scheme in conjunction with an internal timer available in the micro-controller is used for achieving a robust sensorless scheme. The principle of operation of the scheme along with experimental results obtained were then presented. Discussed was implementation of the sensorless scheme, self-tuning control to achieve maximum torque per ampere in the presence of parameter variations, and optimization with balanced inductive profiles.
Addressing commercially available sensorless control methods, he said that some of the sensorless methods have been successfully implemented and are commercially available. A flux integrator method based on inductance estimation is commercially available in Europe. A method based on rate of change of current has also been successfully implemented.
Future Trends. Existing sensorless techniques can be perfected by making use of new advancements in power electronics and digital signal processing. Significant switched reluctance motor parameter variations have been found to occur in mass production or with motor aging. This necessitates sensorless techniques with self-tuning to allow for parameter variations. Self tuning control methods with sensor and without position sensor have already been developed. It has been found that self-tuning control techniques are essential to obtain best performance of switched reluctance motors in the presence of parameter variations.
If control is based on rotor position obtained from a conventional sensor which is insensitive to these variations, optimal performance cannot be extracted from the machine. Since control of switched reluctance motors is essentially based on the inductance profile which changes with parameter variations, an on-line self-tuning control strategy is necessary for optimal performance. Sensorless techniques based on inductance estimation will have a better performance than conventional position sensors. Since sensorless techniques are based on the electrical variables which alter due to parameter variations, the control can he made to adapt to these variations to give better performance.
Conclusion. Switched reluctance motor drives are ready to use in many manufacturing, aerospace, and consumer applications. Sensorless technology in switched reluctance motors has come a long way. Recent advances in power electronics, digital signal processing and control systems have made sensorless switched reluctance motors a commercially acceptable drive. Further research is necessary in some important issues such as self-tuning to manufacture sensorless switched reluctance drives that gives optimal performance in low-cost mass production.
Finite Element Methods
Analysis of Electrical Machines
The third plenary lecture was presented by T. Nakata, Kanto Gakuin University. He introduced the important techniques that contributed to the widespread use of finite element methods in electrical engineering, examined the present states and necessity of 3-D analysis, and discussed future problems that require solutions.
Advances in computing technology and progress made in the area of numerical analysis has resulted in 2-D electrical and magnetic field analyses being used routinely for designing electrical machines, and the 3-D finite element method is becoming more practical in use.
Finite
Element Methodology. Historically, finite element
methods were first introduced for analyzing magnetic fields in electrical machines
in the early 1970s. Development of the 2-D techniques to solve electrical problems
took place in 1980-1985; the 2-D finite element method was applied to the analysis
of electrical machines in 1986-1989; development of
3-D techniques took place in 1990-1994; and 3-D finite element methods have been applied to the analysis of electrical machines since 1995. Techniques that have contributed to the practical use of finite element methods in numerical analysis include: the Newton-Raphson iterative method for solving non-linear problems, analysis methods for electrical machines excited from a voltage source, time-period finite element methods, special elements, and quasi 3-D analysis methods.
The Newton-Raphson iteration method is the most popular technique in the analysis of nonlinear magnetic circuits. Analysis of electrical machines excited from a voltage source such as a capacitor motor requires the knowledge of current in the main and auxiliary windings. The waveforms of these currents are distorted due to nonlinearity of the magnetic materials. In such a case, which is usual in electrical machines, Poisson's equation should be solved simultaneously combined with the circuit equations obtained from Kirchhoff's second law.
Time-period finite element methods to solve nonperiodic phenomena have been developed to reduce computing time. Special elements, for example gap elements; and quasi 3-D analysis methods, for example in the approximate analysis of magnetic circuits composed of axi-symmetric and regular regions, also contribute to reduce computing time and increase accuracy.
Examples for flux distributions in laminated cores include double lap joints, and five step lap joints at low flux density and practical flux density. He then explained how to model the skew problem using quasi 3-D analysis. In this case, the machine is divided into several segments and each segment is solved using the usual 2-D analysis.
In the 1990s, the 3-D finite element method drew consider- able attention due to progress in computer technology and developments in numerical analysis. The speed and memory size of the computer have increased very much, 3-D visualization has been improved by multicolor displays, and the price has come down rapidly.
The 3-D finite element method analysis techniques include the incomplete Cholesky conjugate gradient (ICCG) method; edge elements; automatic mesh generation; and benchmark testing. With respect to the ICCG method in 3-D analysis, first order simultaneous equations with several hundred thousands of unknown variables have to be solved. The conventional Gause elimination method cannot be applied to such a large matrix due to limitation of computer memory. The ICCG method reduces considerably the memory and computing time used for 3-D analysis. As the method is an iterative method, convergence is not guaranteed.
Advantages of edge elements include less memory, shorter computing time, and greater accuracy.
With respect to automatic mesh generation, accurate computation of leakage flux distribution is very important in electrical engineering. The leakage impedance, electromagnetic force, etc. are produced by the leakage flux. Therefore, not only the subdivision of the iron part, but also that of the air space is needed. This is quite difficult and differ from other fields, for example, structural analysis. Although many automatic mesh generation methods have been proposed, no satisfactory software for mesh generation in 3-D analysis is available. The mesh generation of a machine which has a complicated 3-D construction is tedious and in practice nearly impossible.
Benchmark testing is necessary to verify software. In the case of 2-D analysis, there are some analytical solutions and software can be checked by comparing results with those obtained analytically. In the case of 3-D analysis, there are no analytical solutions. Therefore, verification of software can be done only by the following: comparison with experimental results; comparison with results obtained by other methods; and comparison with results obtained by other groups. Defects of many software packages have been found and have been improved by benchmark testing.
Future Requirements and Applications. With respect to finite element methods as a tool for design of electromagnetic devices, the tools were adequate for 2-D problems, and were also adequate for 3-D problems if the construction of the machine was not too complicated.
Concerning the question whether 3-D analysis is always necessary, he thought 2-D analysis was sufficient to assess tendency, for example, to examine the effect of a factor (conductivity, dimension, etc.). Sometimes the linear solution was adequate.
If an accurate solution within 5 percent
is required, the 3-D analysis might be needed. However, the computing time for
the 3-D analysis is 100 to 1,000 times longer than for the 2-D analysis. Further,
it is very difficult to make a magnetic measurement
to within a few percent error.
If the problem to be solved is an eddy current problem, 3-D analysis is absolutely necessary. For example, if the axial length of the rotating machine is not large compared with the diameter, the eddy current has to be analyzed three-dimensionally. There-fore, analysis of induction machines is one of the most difficult machines to analyze.
Discussing whether finite element analysis can estimate power losses in electrical machines, he said if it were a simple problem, the power losses could be estimated. Usually, the waveform of the flux in an iron core is distorted due to the magnetic saturation. The iron loss has to be estimated taking into account the higher harmonics. Although a rotational power loss occurs in three-phase transformer cores, etc., the relationship between the flux density and the power loss is not clear.
The following is important in applying finite element methods: accurate modeling of material constants, for example the correct BH curve; selection of the most suitable solving method to decrease computing time; and close cooperation of machine designers and investigators using finite element methods.
In the future, the following areas should be studied:
· Accurate modeling of the anisotropy and hysteresis
· Software for 3-D automatic mesh generation
· Standardization of pre- and post-processors
· Education programs on computational electromagnetics.
There are many problems to be discussed in respect of machines. For example, in rotating machines, the analysis method for moving conductors, the analysis of the magnetization process of a permanent magnet, etc. should be investigated. The optimization processes will not be in practical use in the near future.
Experience with Use of Soft
Composites in Electrical Machines
The final plenary lecture was given by A.G.
Jack, University of Newcastle-upon-Tyne. He reviewed experience with using soft
magnetic composites for electrical machines. Soft magnetic composites are formed
from bonding iron powder (plus possible alloys) under pressure. The material
allows new design free-doms and for some motors significant advantages have
been demonstrated.
Soft Magnetic Composites. The basis for soft magnetic composites is bonded iron powder. The powder is coated, pressed into a solid material using a die, and heat treated to anneal and cure the bond. The material should not be confused with powder materials that are sintered. All materials so far made via this latter rout have inter-metallic contact between the powder grains.
Restricting attention to bonded materials forces limitations. High density is required to avoid the distributed air gap that is implied by porosity. This means high pressures are needed (up to 800 MPa) in the forming process. This is perfectly normal in powder metallurgy components for structural parts, but it does dictate the size of the press for a given component and place practical limits on the maximum size of the component. The high pressure results in strains and, coupled with the rather small powder size used to date, results in rather high hysteresis loss (which is only partially relieved by the annealing step). The bonding process prevents really high density and figures in the range of 7.2g/cm3 (c.f., 7.8 for solid steel) are good. This adversely affects saturation and permeability. The bonding process also affects mechanical strength and maximum operating temperature.
The presentation examined the exploitation of the material rather than making a detailed exposition of the material itself. The major points were:
· The material is isotropic. This opens up crucial design benefits: magnetic circuits can be designed with three dimensional flux paths.
· The material tends to have very low eddy currents because in bonded materials there is very little conduction between grains.
· The routes to mass production are good with a number of processes removed and automation techniques already established in the production of structural components.
·
Unlike laminations, the parts can be made without sharp
corners in crucial areas.
Unfortunately, the material is not good at everything. The major drawbacks are: permeability is poor; saturation flux density is reduced as compared to the base iron powder; high hysteresis loss resulting from strain and poor domain structure at low frequencies; bonding the powder makes the material rather weak; nature of the binder makes the material brittle; porosity needs, consideration in respect of corrosion protection.
The desired fabrication route is a die pressing operation followed by heat treatment. This will produce a finished part with good dimensional tolerance and good surface finish.
The material is likely to be most easily applied in machines that need a high frequency, benefit from a 3-D magnetic circuit, and have a large effective airgap in comparison to iron circuits.
Experience with Prototypes and Commercial Applications. Experience with prototypes built by the group include: axial field brushless dc machine; permanent magnet servo motor; radial/axial permanent magnet machine; induction machine; universal motors; reluctance machines; claw pole armature machine; transverse flux motor; and transverse flux/claw pole motor. Design, construction, performance, ad- vantages and disadvantages of each prototype were described.
Soft magnetic powder composites have been around for a long time but until fairly recently the insulation between powder grains was thick resulting in very poor magnetic properties. The market was restricted to very high frequencies where low eddy current loss more than offset the poor permeability and saturation flux density. New coating, pressing, powder grain shape control and heat treatment have resulted in a sharp improvement in properties. Relative permeability has improved from 70 to 800 in the past 6 years, losses at 1.5 T, 50 Hz have fallen from 20W/kg to less than 10W/kg in the same period. Further improvements will occur as attention is switched to the relatively low frequencies typical of electric machines. For instance, thinner insulation coatings, better grain shapes, and improved heat treatment are all being explored and evaluated in research laboratories. Materials which are more dense and have higher permeability and saturation yet have lower losses and are significantly stronger are being reported.
The other research direction is for sintered materials. They have metal-to-metal contact between grains, and hence their bulk resistivity is low severely restricting their area of application. Large alloy contents are forcing up resistivity but it seems unlikely that this will ever be high enough for a wide range of application.
The biggest commercial application thus far of soft magnetic composite materials lies in car ignition coils. In comparison with electric motor production, this is very small. All powder metallurgy output (including structural parts which currently constitutes the vast majority of production) is several orders of magnitude smaller than the amount of steel used in motors.
In conclusion, a number of different machines have been produced that offer significant performance and/or material utilization benefits. Only the surface has been pricked of the possibilities for soft composite materials. It is a new technology which demands very different design, construction and production methods. The introduction of soft composite materials in volume markets will require a large investment in new production techniques. Supplies to motor manufactures will need to change, for instance pressers instead of punchers, different insulating systems and so on. The best design for motors using soft composite materials is very different from current practice. Simple component replacement nearly always results in inferior performance. Not every motor type can gain advantage from use of the current material. However, preliminary work with induction motors points the way to what can be done even in the most unpromising applications. Permanent magnet motors of all types, universal motors and all high speed motors are the most fruitful areas of application.
The most pressing need at this time is to investigate the difficulties and cost of production. Performance advantage has been demonstrated, but is it a commercial proposition?
Technical Sessions
Topics debated in the three groups of oral sessions (nine) and the poster sessions (two) on the first day included synchronous machines; induction machines; switched reluctance machines; losses; testing; actuators; permanent magnet machines; diagnostics; noise and vibrations; transformers; teaching; and mis-cellaneous topics.
On the second day, there were parallel oral sessions (nine) and poster sessions (two) on direct current machines; finite element methods; magnetic devices; linear machines; induction machines; permanent magnet machines; transformers; synchronous machines; and miscellaneous topics.
Topics debated on the third day in the three groups of oral sessions (nine) and in the poster sessions (two) included induction machines; switched reluctance machines; wind energy applications; noise and vibration; electric vehicles; losses; inductive coils; and diagnostics. Approximately 43 percent of the papers were presented orally; the remainder were presented in poster sessions. It was emphasized that all papers were of equal status. The high standard of the presentations and technical discussions was particularly gratifying.
Technical Visits and Awards
There were technical visits to some of the important production facilities in the field of electrical machines and drives on the day following the conference.
Prizes were awarded for the best paper and the best poster, based on relevance as well as quality of the presentation.
Exhibition
The ICEM/Electro '98 International Electrotechnics and Electronics Exhibition was held in conjunction with the conference at the World Trade Center, Istanbul. Its scope included:
· Electricity: power generation, transformation, transmission, automatic control, regulation, compensation, lightening, protection and grounding, measurement and testing.
· Electronics: microelectronics, fiberoptics, optoelectronics, electroacoustics, factory and building automation, energy management, security systems, telecommunications, audiovisual equipment, projection systems, electronic apparatus and materials, electromedical devices, household electronics, automotive electronics, mobile electronics, hobby electronics.
Closing Session
The conference was closed by J.A. Tegopoulos. He thanked authors and presenters for their effort in preparing papers properly, concentrating on the essentials, and for their presentations. He thanked session chairs who skillfully managed the technical sessions. It was with their assistance that vivid presentations and discussions were forthcoming.
On behalf of all participants, he congratulated and thanked very warmly the organizers of ICEM '98. Judging from the results, the conference has been very successful, more than the previous ones, so that the course of constant progress has been maintained.
Approximately 385 participants attended the conference, 87 percent were from other countries, 18 percent were from industry, and 82 percent were from the universities.
ICEM '98 Proceedings
All papers were incorporated in the ICEM '98 Proceedings, which were distributed to delegates at the conference. ICEM '98 Proceedings (3 volumes, 2,220 pages) may be purchased for US$130, including postage (supplement by air), until current supplies are exhausted, from H.B. Ertan, Department of Electrical and Electronics Engineering, Middle East Technical University, 06531 Ankara, Turkey, +90 312 210 2359/1332, Fax: +90 312 210 1261, E-mail Ertan@metu.edu.tr.
The 2000 ICEM will take place in Helsinki, Finland,
28-30 August 2000 and will be organized by T. Jokinen and J. Perho, Helsinki University of Technology, Espoo, Finland. Further
information may be obtained from the ICEM '2000 Secretariate, +358 9 451 2384,
FAX +358 9 451 2991 E-mail icem2000@hut.fi,
Web http://www.hut.ft/Misc/ICEM2000.
The 2002 ICEM will be convened in Leuven, Belgium.