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Über dieses Buch

Fundamentals of Power Electronics, Second Edition, is an up-to-date and authoritative text and reference book on power electronics. This new edition retains the original objective and philosophy of focusing on the fundamental principles, models, and technical requirements needed for designing practical power electronic systems while adding a wealth of new material.
Improved features of this new edition include: A new chapter on input filters, showing how to design single and multiple section filters; Major revisions of material on averaged switch modeling, low-harmonic rectifiers, and the chapter on AC modeling of the discontinuous conduction mode; New material on soft switching, active-clamp snubbers, zero-voltage transition full-bridge converter, and auxiliary resonant commutated pole. Also, new sections on design of multiple-winding magnetic and resonant inverter design; Additional appendices on Computer Simulation of Converters using averaged switch modeling, and Middlebrook's Extra Element Theorem, including four tutorial examples; and Expanded treatment of current programmed control with complete results for basic converters, and much more. This edition includes many new examples, illustrations, and exercises to guide students and professionals through the intricacies of power electronics design.
Fundamentals of Power Electronics, Second Edition, is intended for use in introductory power electronics courses and related fields for both senior undergraduates and first-year graduate students interested in converter circuits and electronics, control systems, and magnetic and power systems. It will also be an invaluable reference for professionals working in power electronics, power conversion, and analogue and digital electronics.

Inhaltsverzeichnis

Frontmatter

Introduction

1. Introduction

Abstract
The field of power electronics is concerned with the processing of electrical power using electronic devices [1–7]. The key element is the switching converter, illustrated in Fig. 1.1. In general, a switching converter contains power input and control input ports, and a power output port. The raw input power is processed as specified by the control input, yielding the conditioned output power. One of several basic functions can be performed [2]. In a dc-dc converter, the dc input voltage is converted to a dc output voltage having a larger or smaller magnitude, possibly with opposite polarity or with isolation of the input and output ground references. In an ac-dc rectifier, an ac input voltage is rectified, producing a dc output voltage. The dc output voltage and/or ac input current waveform may be controlled. The inverse process, dc-ac inversion, involves transforming a dc input voltage into an ac output voltage of controllable magnitude and frequency. Ac-ac cycloconversion involves converting an ac input voltage to a given ac output voltage of controllable magnitude and frequency.
Robert W. Erickson, Dragan Maksimović

Converters in Equilibrium

Frontmatter

2. Principles of Steady-State Converter Analysis

Abstract
In the previous chapter, the buck converter was introduced as a means of reducing the dc voltage, using only nondissipative switches, inductors, and capacitors. The switch produces a rectangular waveform v s (t) as illustrated in Fig. 2.1. The voltage v s (t) is equal to the dc input voltage V g when the switch is in position 1, and is equal to zero when the switch is in position 2. In practice, the switch is realized using power semiconductor devices, such as transistors and diodes, which are controlled to turn on and off as required to perform the function of the ideal switch. The switching frequency f s , equal to the inverse of the switching period T s , generally lies in the range of 1 kHz to 1 MHz, depending on the switching speed of the semiconductor devices. The duty ratio D is the fraction of time that the switch spends in position 1, and is a number between zero and one. The complement of the duty ratio, D’, is defined as (1 – D).
Robert W. Erickson, Dragan Maksimović

3. Steady-State Equivalent Circuit Modeling, Losses, and Efficiency

Abstract
Let us now consider the basic functions performed by a switching converter, and attempt to represent these functions by a simple equivalent circuit. The designer of a converter power stage must calculate the network voltages and currents, and specify the power components accordingly. Losses and efficiency are of prime importance. The use of equivalent circuits is a physical and intuitive approach which allows the well-known techniques of circuit analysis to be employed. As noted in the previous chapter, it is desirable to ignore the small but complicated switching ripple, and model only the important dc components of the waveforms.
Robert W. Erickson, Dragan Maksimović

4. Switch Realization

Abstract
We have seen in previous chapters that the switching elements of the buck, boost, and several other dc-dc converters can be implemented using a transistor and diode. One might wonder why this is so, and how to realize semiconductor switches in general. These are worthwhile questions to ask, and switch implementation can depend on the power processing function being performed. The switches of inverters and cycloconverters require more complicated implementations than those of dc-dc converters. Also, the way in which a semiconductor switch is implemented can alter the behavior of a converter in ways not predicted by the ideal-switch analysis of the previous chapters—an example is the discontinuous conduction mode treated in the next chapter. The realization of switches using transistors and diodes is the subject of this chapter.
Robert W. Erickson, Dragan Maksimović

5. The Discontinuous Conduction Mode

Abstract
When the ideal switches of a dc-dc converter are implemented using current-unidirectional and/or voltage-unidirectional semiconductor switches, one or more new modes of operation known as discontinuous conduction modes (DCM) can occur. The discontinuous conduction mode arises when the switching ripple in an inductor current or capacitor voltage is large enough to cause the polarity of the applied switch current or voltage to reverse, such that the current- or voltage-unidirectional assumptions made in realizing the switch with semiconductor devices are violated. The DCM is commonly observed in dc-dc converters and rectifiers, and can also sometimes occur in inverters or in other converters containing two-quadrant switches.
Robert W. Erickson, Dragan Maksimović

6. Converter Circuits

Abstract
We have already analyzed the operation of a number of different types of converters: buck, boost, buck-boost, Ćuk, voltage-source inverter, etc. With these converters, a number of different functions can be performed: step-down of voltage, step-up, inversion of polarity, and conversion of dc to ac or viceversa.
Robert W. Erickson, Dragan Maksimović

Converter Dynamics and Control

Frontmatter

7. AC Equivalent Circuit Modeling

Abstract
Converter systems invariably require feedback. For example, in a typical dc-dc converter application, the output voltage v(t) must be kept constant, regardless of changes in the input voltage v g (t) or in the effective load resistance R. This is accomplished by building a circuit that varies the converter control input [i.e., the duty cycle d(t)] in such a way that the output voltage v(t) is regulated to be equal to a desired reference value v ref . In inverter systems, a feedback loop causes the output voltage to follow a sinusoidal reference voltage. In modern low-harmonic rectifier systems, a control system causes the converter input current to be proportional to the input voltage, such that the input port presents a resistive load to the ac source. So feedback is commonly employed.
Robert W. Erickson, Dragan Maksimović

8. Converter Transfer Functions

Abstract
The engineering design process is comprised of several major steps:
1.
Specifications and other design goals are defined.
 
2.
A circuit is proposed. This is a creative process that draws on the physical insight and experience of the engineer.
 
3.
The circuit is modeled. The converter power stage is modeled as described in Chapter 7. Components and other portions of the system are modeled as appropriate, often with vendor-supplied data.
 
4.
Design-oriented analysis of the circuit is performed. This involves development of equations that allow element values to be chosen such that specifications and design goals are met. In addition, it may be necessary for the engineer to gain additional understanding and physical insight into the circuit behavior, so that the design can be improved by adding elements to the circuit or by changing circuit connections.
 
5.
Model verification. Predictions of the model are compared to a laboratory prototype, under nominal operating conditions. The model is refined as necessary, so that the model predictions agree with laboratory measurements.
 
6.
Worst-case analysis (or other reliability and production yield analysis) of the circuit is performed. This involves quantitative evaluation of the model performance, to judge whether specifications are met under all conditions. Computer simulation is well-suited to this task.
 
7.
Iteration. The above steps are repeated to improve the design until the worst-case behavior meets specifications, or until the reliability and production yield are acceptably high.
 
Robert W. Erickson, Dragan Maksimović

9. Controller Design

Abstract
In all switching converters, the output voltage v(t) is a function of the input line voltage vg(t), the duty cycle d(t) and the load current i load (t) as well as the converter circuit element values. In a dc-dc converter application, it is desired to obtain a constant output voltage v(t) = V, in spite of disturbances in v g (t) and i load (t and in spite of variations in the converter circuit element values. The sources of these disturbances and variations are many, and a typical situation is illustrated in Fig. 9.1. The input voltage v g (t) of an off-line power supply may typically contain periodic variations at the second harmonic of the ac power system frequency (100 Hz or 120 Hz), produced by a rectifier circuit. The magnitude of vg(t) may also vary when neighboring power system loads are switched on or off. The load current i load (t) may contain variations of significant amplitude, and a typical power supply specification is that the output voltage must remain within a specified range (for example, 3.3 V ± 0.05 V) when the load current takes a step change from, for example, full rated load current to 50% of the rated current, and vice versa. The values of the circuit elements are constructed to a certain tolerance, and so in high-volume manufacturing of a converter, converters are constructed whose output voltages lie in some distribution. It is desired that essentially all of this distribution fall within the specified range; however, this is not practical to achieve without the use of negative feedback. Similar considerations apply to inverter applications, except that the output voltage is ac.
Robert W. Erickson, Dragan Maksimović

10. Input Filter Design

Abstract
It is nearly always required that a filter be added at the power input of a switching converter. By attenuating the switching harmonics that are present in the converter input current waveform, the input filter allows compliance with regulations that limit conducted electromagnetic interference (EMI). The input filter can also protect the converter and its load from transients that appear in the input voltage vg(t), thereby improving the system reliability.
Robert W. Erickson, Dragan Maksimović

11. AC and DC Equivalent Circuit Modeling of the Discontinuous Conduction Mode

Abstract
So far, we have derived equivalent circuit models for dc-dc pulse-width modulation (PWM) converters operating in the continuous conduction mode. As illustrated in Fig. 11.1, the basic dc conversion property is modeled by an effective dc transformer, having a turns ratio equal to the conversion ratio M(D). This model predicts that the converter has a voltage-source output characteristic, such that the output voltage is essentially independent of the load current or load resistance R. We have also seen how to refine this model, to predict losses and efficiency, converter dynamics, and small-signal ac transfer functions. We found that the transfer functions of the buck converter contain two low-frequency poles, owing to the converter filter inductor and capacitor. The control-to-output transfer functions of the boost and buck-boost converters additionally contain a right half-plane zero. Finally, we have seen how to utilize these results in the design of converter control systems.
Robert W. Erickson, Dragan Maksimović

12. Current Programmed Control

Abstract
So far, we have discussed duty ratio control of PWM converters, in which the converter output is controlled by direct choice of the duty ratio d(t). We have therefore developed expressions and small-signal transfer functions that relate the converter waveforms and output voltage to the duty ratio.
Robert W. Erickson, Dragan Maksimović

Magnetics

Frontmatter

13. Basic Magnetics Theory

Abstract
Magnetics are an integral part of every switching converter. Often, the design of the magnetic devices cannot be isolated from the converter design. The power electronics engineer must not only model and design the converter, but must model and design the magnetics as well. Modeling and design of magnetics for switching converters is the topic of Part III of this book.
Robert W. Erickson, Dragan Maksimović

14. Inductor Design

Abstract
This chapter treats the design of magnetic elements such as filter inductors, using the K g method. With this method, the maximum flux density B max is specified in advance, and the element is designed to attain a given copper loss.
Robert W. Erickson, Dragan Maksimović

15. Transformer Design

Abstract
In the design methods of the previous chapter, copper loss P cu and maximum flux density B max are specified, while core loss P fe is not specifically addressed. This approach is appropriate for a number of applications, such as the filter inductor in which the dominant design constraints are copper loss and saturation flux density. However, in a substantial class of applications, the operating flux density is limited by core loss rather than saturation. For example, in a conventional high-frequency transformer, it is usually necessary to limit the core loss by operating at a reduced value of the peak ac flux density ΔB.
Robert W. Erickson, Dragan Maksimović

Modern Rectifiers and Power System Harmonics

Frontmatter

16. Power and Harmonics in Nonsinusoidal Systems

Abstract
Rectification used to be a much simpler topic. A textbook could cover the topic simply by discussing the various circuits, such as the peak-detection and inductor-input rectifiers, the phase-controlled bridge, polyphase transformer connections, and perhaps multiplier circuits. But recently, rectifiers have become much more sophisticated, and are now systems rather than mere circuits. They often include pulse-width modulated converters such as the boost converter, with control systems that regulate the ac input current waveform. So modern rectifier technology now incorporates many of the dc-dc converter fundamentals.
Robert W. Erickson, Dragan Maksimović

17. Line-Commutated Rectifiers

Abstract
Conventional diode peak-detection rectifiers are inexpensive, reliable, and in widespread use. Their shortcomings are the high harmonic content of their ac line currents, and their low power factors. In this chapter, the basic operation and ac line current waveforms of several of the most common single-phase and three-phase diode rectifiers are summarized. Also introduced are phase-controlled three-phase rectifiers and inverters, and passive harmonic mitigation techniques. Several of the many references in this area are listed at the end of this chapter [1–15].
Robert W. Erickson, Dragan Maksimović

18. Pulse-Width Modulated Rectifiers

Abstract
To obtain low ac line current THD, the passive techniques described in the previous chapter rely on low-frequency transformers and/or reactive elements. The large size and weight of these elements are objectionable in many applications. This chapter covers active techniques that employ converters having switching frequencies much greater than the ac line frequency. The reactive elements and transformers of these converters are small, because their sizes depend on the converter switching frequency rather than the ac line frequency.
Robert W. Erickson, Dragan Maksimović

Resonant Converters

Frontmatter

19. Resonant Conversion

Abstract
Part V of this text deals with a class of converters whose operation differs significantly from the PWM converters covered in Parts I to IV. Resonant power converters [1–36] contain resonant L-C networks whose voltage and current waveforms vary sinusoidally during one or more subintervals of each switching period. These sinusoidal variations are large in magnitude, and hence the small ripple approximation introduced in Chapter 2 does not apply.
Robert W. Erickson, Dragan Maksimović

20. Soft Switching

Abstract
In addition to the resonant circuits introduced in Chapter 19, there has been much interest in reducing the switching loss of the PWM converters of the previous chapters. Several of the more popular approaches to obtaining soft switching in buck, boost, and other converters, are discussed in this chapter.
Robert W. Erickson, Dragan Maksimović

Backmatter

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