In Chapter 11, we studied the forces in machine systems in which all forces on the bodies were in balance, and therefore the systems were in either static or dynamic equilibrium. However, in real machines this is seldom, if ever, the case except when the machine is stopped. We learned in Chapter 4 that although the input crank of a machine may be driven at constant speed, this does not mean that all points of the input crank have constant velocity vectors or that other links of the machine operate at constant speeds. In general, there will be accelerations, and therefore machines with moving parts having mass are not balanced.

In Part I we examined the form and function ofthe major families of power electronic converters.Our goal was to show how the intended powerconversion function is achieved in each case byappropriate configuration of the circuitcomponents and by proper operation of theswitches. Throughout those earlier chapters, ourconcern was with nominal operating conditions, that is,the ideal operating conditions in which aconverter is designed to perform its primaryconversion function. As nominal operation in mostpower electronic circuits involves a periodic steady state, wefocused on situations in which circuit operationand behavior are the same from cycle to cycle.

The existence of vibrating elements in a mechanical system produces unwanted noise, high stresses, wear, poor reliability, and, frequently, premature failure of one or more of the parts. The moving parts of all machines are inherently vibration producers, and for this reason engineers must expect vibrations to exist in the devices they design. But there is a great deal they can do during the design of the system to anticipate a vibration problem and to minimize its undesirable effects.

In this chapter, we begin by defining the concept of the angular momentum for a point mass, systems of discrete masses, and continuous rigid bodies. We then use the most general form of Newton’s Second Law for rotational motion to study the impulse due to a torque, the angular momentum impulse theorem, and finally the conservation of angular momentum. To develop these theorems, we draw from our understanding of the analogous theorems in linear motion.

In the last chapter we presented evidence tying intelligence differences among individuals to quantified details of brain structure and function. There were never doubts that intelligence is a function of the brain, so modern neuroimaging findings were not controversial in principle.

Changes in intellectual ability over the adult years are complex and important to understand because they can inform social policies. There are 97 million people in the European Union at least sixty-five years old. Three out of 10 live alone, and only 9 out of 100 between sixty-five and seventy-five are economically active. In the United States, the number of people sixty-five or over is 48 million now, in 2023, and this number will rise to 98 million by 2060. In China, the estimate is 487 million people aged sixty-five or older by 2050. The number for Japan will be a quarter of its total population.

Power magnetics are often constrained by loss.Consequently, the ability to accurately predictthe loss of a magnetic component is extremelyvaluable for design. The techniques for modelingmagnetics loss introduced in the previous chaptersare useful, but do not adequately cover allsituations. In this chapter we introduce refinedmethods to predict winding and core losses inmagnetic components, with particular emphasis onfactors (such as proximity effect) that becomedominant at high frequencies and on cases wherethe waveforms are not purely dc or sinusoidal.

We add transformers to the topology of ahigh-frequency converter for three reasons: toprovide electrical isolation between two (or more)external systems; to reduce the component stressesthat result when the input/output conversion ratiois far from unity; and to create multiple relatedoutputs in a simple manner. (We showed therelationship between switch-stress factor and theconversion ratio in Fig. 5.26.) There are manyways in which we can include the transformer inthe topology of a dc/dc converter; we present anddiscuss some of them in this chapter.

Balancing is defined here as the process of correcting or eliminating unwanted inertia forces and moments in rotating machinery. In previous chapters, we have seen that shaking forces on the frame can vary significantly during a cycle of operation. Such forces can cause vibrations that at times may reach dangerous amplitudes. Even if they are not dangerous, vibrations increase component stresses and subject bearings to repeated loads that may cause parts to fail prematurely by fatigue. Thus, in the design of machinery, it is not sufficient merely to avoid operation near the critical speeds; we must eliminate, or at least reduce, the dynamic forces that produce these vibrations in the first place.

Power electronic circuits change the characterof electrical energy: from dc or ac to ac or dc,from one voltage level or frequency to another, orin some other way. We refer to such circuitsgenerically as converters, staticconverters (because they contain nomoving parts), powerprocessors, or powerconditioners. The part of the system thatactually manipulates the flow of energy is thepower circuit. It isthe scaffold for the system’s other components,such as the control circuit or the thermalmanagement parts.

The rapid switching transitions of a powerconverter are potential sources of electromagneticinterference (EMI), both for the converter itselfand for the systems to which it is connected.Adequate filtering at the input and output of theconverter is important, both to obtain acceptableperformance and to prevent interference with otherequipment. In this chapter, we consider thesources of EMI in a converter, how EMI is measuredand modeled, and how it can be mitigated, with afocus on conducted (rather than radiated) EMI.

The previous chapters on magnetics provided thekey concepts needed to analyze, model, and designmagnetic components such as inductors andtransformers. The purpose of this chapter is torefine and extend the methods introduced there,with a focus on techniques for magnetic componentdesign. In particular, we introduce design methodsand sizing considerations for efficientlyconverging on an appropriate design. Thisincludes, for example, approximate methods forsizing the magnetic core for an inductor ortransformer, and metrics for comparing magneticmaterials.

AC/AC converters take power from one ac systemand deliver it to another with waveforms of thesame or different amplitude, frequency, or phase.The ac systems can be single phase or polyphase,and reactive power can exist at the input, output,or both, depending on how we configure theconverter. The simplest and most common ac/acconverter is the transformer.