[No. 52] JMAG goes to work

Fig. 1

This new book is written for engineers concerned with the design and development of electric machines.

It addresses two aspects of the modern design environment, in which powerful software tools are widely used:

(i) How should we start a new design to meet a given specification?
(ii) How can the classical theory inform and support the design process?

Some answers are attempted through a series of numerical design examples, including the surface magnet motor (SPM), the interior magnet motor (IPM), the asynchronous induction motor, the synchronous reluctance motor, the wound-field synchronous motor, and the switched reluctance motor. After the SPM, all the remaining motors are designed to the same AC drive specification with many common parts.

Working with numerical design examples, the book

(a) provides a platform for the use of CAE tools, starting with the same geometry, winding layout, etc., so that more difficult aspects can be studied;
(b) uses the finite element method to help with several basic classical calculations, greatly improving the accuracy; and
(c) presents and explains many of the theoretical principles of electric machine design without overburdening the subject with pure theory.

The use of numerical design examples helps to keep the length of the book to a manageable scale (450 pages).

The Blue Book has two chapters devoted to the theory and design of windings in AC machines, one on synthesis and the other on analysis. It covers all the main theoretical principles of winding layout (for both integral-slot and fractional-slot windings), including detailed treatment of terminal inductances and inductance components, and a rare English-language treatment of the Görges diagram and its application to the calculation of differential (harmonic) leakage inductance. The origins of AC windings are developed from the DC armature winding in the 1880s, and we argue that winding theory is a vital element of modern machine design that does not reside in the numerical solution of the equations of physics, but is an independent engineering discipline in its own right. While winding theory is indispensable for winding design, it must also be coupled to modern numerical analysis and it must also conform to manufacturing requirements, not least in the context of advanced ‘coil-winding’ technology as well as the established crafts of the winding shop. Modern hair-pin windings and fractional-slot windings provide ample evidence of these couplings, which in fact apply to all windings.

The Blue Book is unique in its use of coils instead of conductors as the basis for winding theory.  Although it is traditionally used as a building block, the isolated conductor is useless with the finite-element method, and we argue that it should be replaced by the complete coil, which obeys Faraday’s law directly. Along with this, we emphasize the importance and recognition of flux-linkage. Following these principles, the slot star becomes a star diagram of the space-vectors of space-harmonics of the winding distribution, producing the same results (with examples from integral- and fractional-slot windings) but based more securely on the laws of Faraday, Ampere, and Gauss, and rigorously consistent with modern finite-element formulations.

The Blue Book devotes a whole chapter to the subject of complex numbers, which we may often take for granted. Three applications are explained in detail: (i) the phasor, (ii) the space-vectors of the space-harmonic components of ampere-conductor distributions and MMF; and (iii) the space-vectors or (space-phasors) of field-oriented control. Although the terms seem horribly theoretical, these three entities are ingrained in the language of electric machine design and control, and they are often voiced in casual familiar terms that belie the important distinctions between them.

Finally there is a chapter of plates or illustrations from the industry and from advanced numerical analysis; a detailed glossary of terms used in the field; and a detailed index.

In the last 20 years we have seen the publication of several substantial new textbooks on electric machines : for example, by Ponick, Müller and Vogt; by Binder; by Pyhrönen, Jökinen and Hrabovcova; by Boldea; and by other distinguished authors. There can be no doubt that these works have been prepared to serve the extraordinary expansion in the design and use of electric machines (‘electrification’); but it remains the case that only a few of these works contain extended numerical examples, and only a few of them address the remarkable transformation in design methods that has resulted from the development of numerical methods in all disciplines of analytical engineering. It is an enormous challenge to bridge the gap between the classical theory of machines and the modern environment of digital simulation, even within the narrow confines of one discipline such as the electromagnetic design. It takes such a long time for any one engineer to master these skills, that it is almost more than a lifetime’s work to combine the old with the new in a thoroughgoing way. We haven’t done all of that, but we’ve made a start.

In the case of the Blue Book we have certainly used extended numerical design examples and we have used a great deal of classical theory. We would also claim to have described ways in which the finite-element method can be used more efficiently than is often the case, most of them developed very recently. Although the examples have been developed with collaboration from Powersys, it is fair to claim that the methods are rooted in the classical theory and they could be used with any competent finite-element program. Since they are based on what we describe as ‘classical’ theory, they are readily accessible in the ‘classical’ literature. We must also respect the fact that all the examples are elementary relative to the analysis that is now possible and performed regularly by specialists at a very high level, not only in electromagnetic engineering but also in all the cognate disciplines that go into the design of electric machines. And it is also important to state that the Blue Book is not an instruction manual for JMAG or any other program.

The Blue Book also widens the scope to include machines not treated in the Green Book (Fig. 2), which focussed on brushless permanent-magnet machines. This is important in the steady development of rare-earth-free machines. It also has a chapter reviewing the calculation methods and facilities from Blondel and Steinmetz all the way up to the present day.

Lastly the book has been designed with a high-quality hardback cover and exceptionally clear print, intended for study in the old-fashioned way, with the book lying open and flat on a cluttered or uncluttered desktop, Fig. 3.

Both books are available in Japan from MS-TECH, in the USA from sales@motordesignbooks.com, and in Europe from Maccon.  Also listed on Amazon.  For corrections and technical comments / enquiries please contact TJEMiller@ieee.org.


Bibliography

Binder A., Elektrische Maschinen und Antriebe, Springer, 2017 (2 vol.)
Müller G. & Ponick B., Grundlagen elektrische Maschinen, Wiley-VCH, 2014
—, Vogt K. & Ponick B., Berechnung elektrischer Maschinen, Wiley-VCH, 2008
—, & Ponick B., Theorie elektrischer Maschinen, Wiley-VCH, 2009
Pyrhönen J., Jokinen T. and Hrabovcová V., Design of Rotating Electrical Machines, Wiley, 2014
Boldea I., Induction Machines Handbook, CRC Press, 3rd edition, 2020
—, Electric Generators Handbook, CRC Press, 2015, (2 vol.)

Fig. 2

Fig. 3

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PROFILE

Prof. Miller was educated at the universities of Glasgow and Leeds, U.K., and served an industrial apprenticeship with Tube Investments Ltd. He worked for G.E.C. in the U.K. and General Electric in the United States. From 1986-2011 he was professor of electric power engineering at the university of Glasgow, where he founded the Scottish Power Electronics and Electric Drives Consortium. He has published more than 200 papers and 10 books and 10 patents, and he has given many training courses. He has consulted for several industrial companies in Europe, Japan and the United States. He is a Life Fellow of I.E.E.E. and in 2008 he was awarded the Nikola Tesla award.

The Green Book: “Design of Brushless Permanent-Magnet Machines”