A variety of U.S. government agencies have contributed to research efforts which contributed to this book, including the Army, Navy, DOE, Sandia National Labs, NREL, ORNL, and NASA. The Office of Naval Research in particular has provided steady support for my entire career which directly and indirectly supported this work, and without which this work would not have been possible. The support of the Grainger Foundation has also been very important to the program at Purdue.
I would thank my colleagues at Purdue. A key attribute of any institution is the people your work with. With this regard, my colleagues at Purdue, namely Oleg Wasynczuk, Steve Pekarek, and Dionysios Aliprantis, are a great group.
Finally, I had some extra help with the second edition. Special thanks to Dr. Harshita Singh, who thoroughly reviewed Chapters 10 and 12. Dr Paul Ohodnicki (University of Pittsburg) and Drummond Fudge (Continuous Solutions) provided great feedback on Chapters 13, 14, and 15. Dr. Jamal Alsawalhi (Khalifa University) provided detailed reviews on Chapters 6 and 16. Finally, Dr Steve Pekarek (Purdue University) also reviewed Chapter 16. I am greatly indebted to all of these individuals for contributing so much time to the second edition of this book.
About the Companion Site
This book is accompanied by a companion website:
www.wiley.com/go/sudhoff/Powermagneticdevices
The website includes the following materials: Powerpoint slides, Solutions manual, Matlab code
1 Optimization‐Based Design
We will begin our study of power magnetic device design with a general consideration of the design process. A case will be made to approach the design process rather formally by converting the design problem into an optimization problem. Next, single‐objective optimization is discussed, with particular emphasis on optimization using genetic algorithms (GAs). This is followed by a discussion of multi‐objective optimization. Practical aspects of formulating design problems as optimization problems are then considered. The chapter concludes with a design example that focuses on a UI‐core inductor.
1.1 Design Approach
It is appropriate to begin this work by considering the design process. Clearly, there are a myriad of different approaches by which components may be designed. For example, a possible manual design process is illustrated in Figure 1.1. In order to consider this process in a more concrete way, suppose that the component we are designing is an electromagnet and that we wish to design an electromagnet so that a certain set of specifications are met.
Using the design process in Figure 1.1, our first step would be to perform a detailed mathematical analysis of the device. Typically, when we analyze a device, our analysis predicts device performance (mass, loss, force) in terms of the device parameters (geometry, materials) rather than directly addressing the design problem by deriving expressions for what the device parameters should be in terms of the device specifications (allowed loss, required force). Therefore, we must manipulate our detailed analysis into a set of design equations that are used to calculate the design parameters as a function of device specifications. However, going from detailed analysis to design equations invariably requires numerous assumptions and approximations, even beyond the ones found in our original “detailed” analysis. As a result, we check our design, either against our original analysis or using some numerical tool such as a finite element analysis. Based on the results from the numerical analysis, we will revise the design and repeat the numerical analysis until specifications are met, at which point we have arrived at a final design. Of course, we often use a more involved design process; for example, another iteration of the design may be made based on physical prototypes.
The manual design process we have been considering involves an engineer in the iteration process. Variations of this process are successfully used ubiquitously throughout the engineering community. However, the process has some significant drawbacks. First, it requires a great deal of engineering time. Second, it requires a great deal of engineering experience. This experience comes into play in the development of the design equations, which often take the form of rules‐of‐thumb based at least partially on experience. Experience is also a factor in making changes to the design based on the numerical analysis. Finally, while the process has been very successful in yielding working designs, it may not lead to the best design.
Figure 1.1 A manual design process.
Figure 1.2 Optimization‐based design process.
An alternate design process is illustrated in Figure 1.2. Therein, an optimization‐based design process is shown. In this case, the process is not illustrated in a sequential manner as in Figure 1.1, but rather in an organizational manner. The process again starts with a detailed analysis of the device or component. However, unlike the manual design process, in the optimization‐based process, the detailed analysis is not used to formulate design equations. Instead, the detailed analysis is used to calculate design metrics such as mass, cost, and loss. The detailed analysis is also used to check constraints such as achieving some minimum acceptable level of performance. The metrics and constraints are combined into an objective or fitness function. This function is defined so that its optimization results in optimization of the design metrics subject to all design constraints being met.
At the outermost level of this design process, an optimization engine will select the parameters of the design (geometry, materials, etc.) so as to maximize the objective function. In terms of computational algorithm, Figure 1.2 depicts an optimization engine at the outer level. This engine operates on an objective function that is calculated based on the detailed analysis.
There are several advantages of this approach. First, it is unnecessary to formulate design equations. This is beneficial in that it reduces the number of approximations and assumptions made and reduces the amount of design experience needed for a good design. Second, the design is formally optimized with regard to the design metrics, potentially leading to better designs, at least in terms of the design metrics. Third, since the engineer is out of the optimization loop, less engineering time is generally required. There are some disadvantages of the procedure. First, the process can be numerically intense and require significant computing time, sometimes on the order of hours and, in extreme