Switch-Mode Power Converters: Design and Analysis
by Keng C Wu, Published by Academic Press
ISBN 0-12-088795-9, hardback, 408 pp, $89.95

ZONE Reviewer: Dennis L. Feucht

Keng Wu is a Lead Member of the engineering staff at Lockheed-Martin. The opening paragraph of the back cover sets the tone for the book: It says the book offers "a highly analytical approach to symbolic, close-form solutions for switched-mode power converter circuits. This mathematically rigorous approach is designed for readers who have already been exposed to the basics…"

The first nine chapters each analyze a particular, major converter topology. Besides familiar ones, Wu includes the "phase-shifted full-bridge converter." This scheme places an inductor in series with the transformer, which results in zero-voltage switching (ZVS) of power switches. This chapter also includes a nifty circuit that power circuits engineers should know: the secondary-side, current-doubling rectifier-filter. This circuit uses two diodes and two inductors, as shown below.

It has an impedance-reducing effect of doubling current and halving voltage. The duty ratio is also effectively divided by 2. Another chapter is on a quasi-resonant converter and the one after, on a "class-E" resonant converter.

After this, Wu takes up power-factor correction (PFC), mainly concentrating of the dominant boost-circuit approach. Included is a three-phase PFC. The book then turns towards a circuits focus, with a chapter on error amplifiers that includes some discussion of the control aspects of converters. Switch drivers, soft-starting, snubbers, charge pumps, and an analysis of the peak-sampling single-phase full-wave rectifier with RC filter is included in a following chapter. The last three chapters take up specialized topics: state-space averaging, simulation, and power quality and integrity. The appendices include MathCAD and MATLAB listings.

After reviewing several hand-waving books lacking much content, it is refreshing to have an author who strives for rigor and mathematical completeness. However, I can give this book only a feeble recommendation. It contains plenty of math but I found little of it actually useful in circuit design. The problem is that the author has not learned the essential art of managing complexity through conceptual abstraction. Everything is analyzed at the same conceptual level, beginning with massive application of Kirchhoff's Laws, followed by pages of matrix crunching. When all the equations have been derived and values substituted, abstraction from them of useful insights does not occur. There is no way of telling whether the values are what should be expected.

The author tries to include in his circuit models all the parasitic elements that he believes are important. This results in a conceptually flat approach that minimizes insight into circuit function. Instead of beginning with a simple, more idealized model, to gain intuition for the circuit, and then add complications one at a time to note their effects on circuit behavior, the total complexity is analyzed in one shot. The result is the symbolic equivalent of running a circuit simulation: monstrous expressions not very amenable to interpretation in higher-level circuit concepts. The approach taken is high in formal completeness but low in conceptual enhancement.

The completeness is also selective, and lacking in some crucial ways. For instance, some s-domain expressions are worked out, but hardly ever placed in normalized form for ease of interpretation. Not a single s-domain plot of poles and zeros, or their loci with parameter variation, is presented. A few Bode plots appear. Tradeoffs among key criteria of design are not discussed, nor design constraints and how to get around them. I did not get the impression that this book was so much engineering as an opportunity for the author to do math. It has plenty of trees but too little forest.

I would not recommend this book for students, not even graduate students. It teaches the wrong mental habits for excelling at engineering. However, it might be useful as an occasional reference for academic (mainly) and industrial (occasionally) engineering work. Before reading it, I recommend brushing up on advanced calculus.