Power Electronics, A First Course
Description
Enables students to understand power electronics systems, as one course, in an integrated electric energy systems curriculum
Power Electronics A First Course provides instruction on fundamental concepts related to power electronics to undergraduate electrical engineering students, beginning with an introductory chapter and moving on to discussing topics such as switching power-poles, switch-mode dc-dc converters, and feedback controllers.
The authors also cover diode rectifiers, power-factor-correction (PFC) circuits, and switch-mode dc power supplies. Later chapters touch on soft-switching in dc-dc power converters, voltage and current requirements imposed by various power applications, dc and low-frequency sinusoidal ac voltages, thyristor converters, and the utility applications of harnessing energy from renewable sources.
Power Electronics A First Course is the only textbook that is integrated with hardware experiments and simulation results. The simulation files are available on a website associated with this textbook. The hardware experiments will be available through a University of Minnesota startup at a low cost.
In Power Electronics A First Course, readers can expect to find detailed information on:
* Availability of various power semiconductor devices that are essential in power electronic systems, plus their switching characteristics and various tradeoffs
* Common foundational unit of various converters and their operation, plus fundamental concepts for feedback control, illustrated by means of regulated dc-dc converters
* Basic concepts associated with magnetic circuits, to develop an understanding of inductors and transformers needed in power electronics
* Problems associated with hard switching, and some of the practical circuits where this problem can be minimized with soft-switching
Power Electronics A First Course is an ideal textbook for Junior/Senior-Undergraduate students in Electrical and Computer Engineering (ECE). It is also valuable to students outside of ECE, such as those in more general engineering fields. Basic understanding of electrical engineering concepts and control systems is a prerequisite.
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Persons
Ned Mohan, PhD, joined the University of Minnesota in 1975, where he is currently Oscar A. Schott Professor of Power Electronic Systems and Morse-Alumni Distinguished Professor. He is a Fellow of the IEEE and a member of the National Academy of Engineering. He is also a Regents Professor at the University and Minnesota and has published six textbooks with Wiley.
Siddharth Raju is a Research Assistant Professor at the University of Minnesota and a co-author of Analysis and Control of Electric Drives: Simulations and Laboratory Implementation (2020). He is the founder of Sciamble Corp., a startup specializing in rapid real-time prototyping solutions.
Content
List of Simulation and Hardware Implementation Example and Figures xiii
Preface xv
Acknowledgment xvii
About the Companion Website xix
Chapter 1 Power Electronics: An Enabling Technology 1
1.1 Introduction to Power Electronics 1
1.2 Applications and the Role of Power Electronics 2
1.3 Energy and the Environment: Role of Power Electronics in Providing Sustainable Electric Energy 4
1.4 Need for High Efficiency and High Power Density 8
1.5 Structure of Power Electronics Interface 9
1.6 Voltage-Link-Structure 11
1.7 Recent Advances in Solid-State Devices Based on Wide Bandgap (WBG) Materials 16
1.8 Use of Simulation and Hardware Prototyping 16
References 17
Problems 18
Chapter 2 Design of Switching Power-poles 21
2.1 Power Transistors and Power Diodes 21
2.2 Selection of Power Transistors 22
2.3 Selection of Power Diodes 24
2.4 Switching Characteristics and Power Losses in Power Poles 25
2.5 Justifying Switches and Diodes as Ideal 30
2.6 Design Considerations 31
2.7 The PWM IC 34
2.8 Hardware Prototyping 35
References 36
Problems 36
Appendix 2A Diode Reverse Recovery and Power Losses 37
Chapter 3 Switch-mode Dc-dc Converters: Switching Analysis, Topology Selection, and Design 41
3.1 DC-DC Converters 41
3.2 Switching Power-Pole in DC Steady State 41
3.3 Simplifying Assumptions 45
3.4 Common Operating Principles 46
3.5 Buck Converter Switching Analysis in DC Steady State 46
3.6 Boost Converter Switching Analysis in DC Steady State 51
3.7 Buck-Boost Converter Analysis in DC Steady State 57
3.8 Topology Selection 65
3.9 Worst-Case Design 66
3.10 Synchronous-Rectified Buck Converter for Very Low Output Voltages 66
3.11 Interleaving of Converters 71
3.12 Regulation of DC-DC Converters by PWM 71
3.13 Dynamic Average Representation of Converters in CCM 72
3.14 Bi-Directional Switching Power-Pole 74
3.15 Discontinuous-Conduction Mode (DCM) 75
References 86
Problems 86
Appendix 3A Average Representation in Discontinuous- Conduction Mode (DCM) 92
Chapter 4 Designing Feedback Controllers in Switch-mode Dc Power Supplies 97
4.1 Introduction and Objectives of Feedback Control 97
4.2 Review of Linear Control Theory 98
4.3 Linearization of Various Transfer Function Blocks 100
4.4 Feedback Controller Design in Voltage-Mode Control 106
4.5 Peak-Current Mode Control 113
4.6 Feedback Controller Design in DCM 123
References 124
Problems 124
Appendix 4A Bode Plots of Transfer Functions with Poles and Zeros 125
Appendix 4B Transfer Functions in Continuous Conduction Mode (CCM) 128
Appendix 4C Derivation of Parameters of the Controller Transfer Functions 134
Chapter 5 Rectification of Utility Input Using Diode Rectifiers 139
Rectifiers 139
5.1 Introduction 139
5.2 Distortion and Power Factor 140
5.3 Classifying the "Front-End" of Power Electronic Systems 148
Electronic Systems 148
5.4 Diode-Rectifier Bridge "Front-End" 148
5.5 Means to Avoid Transient Inrush Currents at Starting 156
5.6 Front-Ends with Bi-Directional Power Flow 157
References 157
Problems 157
Chapter 6 Power-factor-correction (PFC) Circuits And Designing the Feedback Controller And Designing the Feedback Controller 159
6.1 Introduction 159
6.2 Operating Principle of Single-Phase PFCS 159
6.3 Control of PFCS 162
6.4 Designing the Inner Average-Current-Control Loop 163
6.5 Designing the Outer Voltage-Control Loop 165
6.6 Example of Single-Phase PFC Systems 167
6.7 Simulation Results 168
6.8 Feedforward of the Input Voltage 169
6.9 Other Control Methods for PFCS 169
References 170
Problems 170
Appendix 6A Proof that I^S3/I^L2 =1/2
Appendix 6b Proof That V ~d I i~ L(s)=1 I 2 V^s/Vd R I 2/ 1+ s (R /2)C
Chapter 7 Magnetic Circuit Concepts 173
7.1 Ampere-Turns and Flux 173
7.2 Inductance l 174
7.3 Faraday's Law: Induced Voltage in a Coil Due to
Time-Rate of Change of Flux Linkage 176
7.4 Leakage and Magnetizing Inductances 177
7.5 Transformers 179
Reference 182
Problems 182
Chapter 8 Switch-mode Dc Power Supplies 185
8.1 Applications of Switch-Mode DC Power Supplies 185
8.2 Need for Electrical Isolation 186
8.3 Classification of Transformer-Isolated DC-DC Converters 186
8.4 Flyback Converters 186
8.5 Forward Converters 198
8.6 Full-Bridge Converters 204
8.7 Half-Bridge and Push-Pull Converters 209
8.8 Practical Considerations 209
References 210
Problems 211
Chapter 9 Design of High-frequency Inductors and Transformers 215
9.1 Introduction 215
9.2 Basics of Magnetic Design 215
9.3 Inductor and Transformer Construction 216
9.4 Area-Product Method 216
9.5 Design Example of an Inductor 219
9.6 Design Example of a Transformer for a
Forward Converter 221
9.7 Thermal Considerations 221
References 222
Problems 222
Chapter 10 Soft-switching in Dc-dc Converters and
Half-bridge Resonant Converters 223
10.1 Introduction 223
10.2 Hard-Switching in Switching Power poles 223
10.3 Soft-switching in Switching Power-Poles 225
10.4 Half-Bridge Resonant Converter 228
References 230
Problems 230
Chapter 11 Applications of Switch-mode Power Electronics in Motor Drives, Uninterruptible Power Supplies, And Power Systems 231
11.1 Introduction 231
11.2 Electric Motor Drives 231
11.3 Uninterruptible Power Supplies (UPS) 244
11.4 Utility Applications of Switch-Mode
Power Electronics 244
Reference 246
Problems 246
Chapter 12 Synthesis of Dc and Low-frequency Sinusoidal Ac Voltages for Motor Drives, Ups, and Power Systems Applications 249
12.1 Introduction 249
12.2 Bidirectional Switching Power-Pole as the Building Block 250
12.3 Converters for DC Motor Drives (-Vd
12.4 Synthesis of Low-Frequency AC 260
12.5 Single-Phase Inverters 261
12.6 Three-Phase Inverters 266
12.7 Multilevel Inverters 280
12.8 Converters For Bidirectional Power Flow 281
12.9 Matrix Converters (Direct Link System) 283
References 284
Problems 284
Chapter 13 Thyristor Converters 287
13.1 Introduction 287
13.2 Thyristors (SCRs) 287
13.3 Single-phase, Phase-controlled Thyristor Converters 289
13.4 Three-Phase, Full-Bridge Thyristor Converters 294
13.5 Current-Link Systems 300
Reference 301
Problems 301
Chapter 14 Utility Applications of Power Electronics 303
14.1 Introduction 303
14.2 Power Semiconductor Devices and Their Capabilities 304
14.3 Categorizing Power Electronic Systems 305
14.4 Distributed Generation (DG) Applications 306
14.5 Power Electronic Loads 311
14.6 Power Quality Solutions 312
14.7 Transmission and Distribution (T&D) Applications 313
References 317
Problems 317
Index 319
1
POWER ELECTRONICS: AN ENABLING TECHNOLOGY
Power electronic systems are essential for energy sustainability, which can be defined as meeting our present needs without compromising the ability of future generations to meet their needs. Using renewable energy for generating electricity and increasing the efficiency of transmitting and consuming it are the twin pillars of sustainability. Some of the applications of power electronics in doing so are as mentioned below:
- Harnessing renewable energy such as wind energy and solar energy using photovoltaics .
- Storage of electricity in batteries and flywheels to offset the variability in the electricity generated by renewables.
- Increasing the efficiency of transmitting electricity.
- Increasing efficiency in consuming the electricity in motor-driven systems and lighting, for example.
This introductory chapter highlights all the points mentioned above, which are discussed in further detail in the context of describing the fundamentals of power electronics in the subsequent chapters.
1.1 INTRODUCTION TO POWER ELECTRONICS
Power electronics is an enabling technology, providing the needed interface between an electrical source and an electrical load, as depicted in Figure 1.1 [1]. The electrical source and the electrical load can, and often do, differ in frequency, voltage amplitudes, and the number of phases. The power electronics interface facilitates the transfer of power from the source to the load by converting voltages and currents from one form to another, in which it is possible for the source and load to reverse roles. The controller shown in Figure 1.1 allows management of the power transfer process in which the conversion of voltages and currents should be achieved with as high energy efficiency and high power density as possible. Adjustable-speed electric drives, for example in wind turbines, represent an important application of power electronics.
FIGURE 1.1 Power electronics interface between the source and load.
1.2 APPLICATIONS AND THE ROLE OF POWER ELECTRONICS
Power electronics and drives encompass a wide array of applications. A few important applications and their role are described below.
1.2.1 Powering the Information Technology
Most of the consumer electronics equipment such as personal computers (PCs) and entertainment systems supplied from the utility need very low DC voltages internally. They, therefore, require power electronics in the form of switch-mode DC power supplies for converting the input line voltage into a regulated low DC voltage, as shown in Figure 1.2a. Figure 1.2b shows the distributed architecture typically used in computers in which the incoming AC voltage from the utility is converted into DC voltage, for example, at 24 V. This semi-regulated voltage is distributed within the computer where onboard power supplies in logic-level printed circuit boards convert this 24 V DC input voltage to a lower voltage, for example, 5 V DC, which is very tightly regulated. Very large-scale integration and higher logic circuitry speed require operating voltages much lower than 5 V; hence 3.3 V, 1 V, and eventually, 0.5 V levels would be needed.
FIGURE 1.2 Regulated low-voltage DC power supplies.
Many devices such as cell phones operate from low battery voltages with one or two battery cells as inputs. However, the electronic circuitry within them requires higher voltages, thus necessitating a circuit to boost input DC to a higher DC voltage as shown in the block diagram of Figure 1.3.
FIGURE 1.3 Boost DC-DC converter needed in cell-operated equipment.
1.2.2 Robotics and Flexible Production
Robotics and flexible production are now essential to industrial competitiveness in a global economy. These applications require adjustable-speed drives for precise speed and position control. Figure 1.4 shows the block diagram of adjustable-speed drives in which the AC input from a 1-phase or a 3-phase utility source is at the line frequency of 50 or 60 Hz . The role of the power electronics interface, as a power-processing unit, is to provide the required voltage to the motor. In the case of a DC motor, DC voltage is supplied with an adjustable magnitude that controls the motor speed. In the case of an AC motor, the power electronics interface provides sinusoidal AC voltages with adjustable amplitude and frequency to control the motor speed. In certain cases, the power electronics interface may be required to allow bidirectional power flow through it, between the utility and the motor load.
FIGURE 1.4 Block diagram of adjustable-speed drives.
Induction heating and electric welding, shown in Figures 1.5 and 1.6, respectively, by their block diagrams, are other important industrial applications of power electronics for flexible production.
FIGURE 1.5 Power electronics interface required for induction heating.
FIGURE 1.6 Power electronics interface required for electric welding.
1.3 ENERGY AND THE ENVIRONMENT: ROLE OF POWER ELECTRONICS IN PROVIDING SUSTAINABLE ELECTRIC ENERGY
As mentioned in the preface of this textbook, power electronics is an enabling technology in providing sustainable electric energy. Most scientists now believe that carbon-based fuels for energy production contribute to climate change, which is threatening human civilization. In the United States, the Department of Energy reports that approximately 40% of all the energy consumed is first converted into electricity. Potentially, the use of electric and plug-in hybrid cars, high-speed rails, and so on, may increase this to even 60%. Therefore, it is essential that we generate electricity from renewable sources such as wind and solar, which, at present, represent only slightly over 4%, build the next-generation smarter grid to utilize renewable resources often in remote locations, and use electricity in more energy-efficient ways. Undoubtedly, using electricity efficiently and generating it from renewable sources are the twin pillars of sustainability, and power electronic systems discussed in this textbook are a key to them both!
1.3.1 Energy Conservation
It's an old adage: a penny saved is a penny earned. Not only does energy conservation lead to financial savings, but it also helps the environment. The pie chart in Figure 1.7 shows the percentages of electricity usage in the United States for various applications. The potential for energy conservation in these applications are discussed below.
FIGURE 1.7 Percentage use of electricity in various sectors in the US.
1.3.1.1 Electric-Motor Driven Systems
Figure 1.7 shows that electric motors, including their applications in heating, ventilating, and air conditioning (HVAC), are responsible for consuming one-half to two-thirds of all the electricity generated. Traditionally, motor-driven systems run at a nearly constant speed, and their output, for example, the flow rate in a pump, is controlled by wasting a portion of the input energy across a throttling valve. This waste is eliminated by an adjustable-speed electric drive, as shown in Figure 1.8, by efficiently controlling the motor speed, hence the pump speed, by means of power electronics [2].
FIGURE 1.8 Role of adjustable-speed drives in pump-driven systems.
One out of three new homes in the United States now uses an electric heat pump, in which an adjustable-speed drive can reduce energy consumption by as much as 30% [3] by eliminating on-off cycling of the compressor and running the heat pump at a speed that matches the thermal load of the building. The same is true for air conditioners.
A Department of Energy report [4] estimates that operating all these motor-driven systems more efficiently in the United States could annually save electricity equivalent to the annual electricity usage by the entire state of New York!
1.3.1.2 Lighting Using LEDs
As shown in the pie chart in Figure 1.7, approximately one-fifth of the electricity produced is used for lighting. LEDs (light-emitting diodes) can improve this efficiency by more than a factor of six. They offer a longer lifetime and have become equally affordable as incandescent lamps. They require a power-electronic interface, as shown in Figure 1.9, to convert the line-frequency to supply DC current to the LEDs.
FIGURE 1.9 Power electronics interface required for LED.
1.3.1.3 Transportation
Electric drives offer huge potential for energy conservation in transportation. While efforts to introduce commercially viable electric vehicles (EVs) continue with progress in battery [5] and fuel cell technologies [6] being reported, hybrid electric vehicles (HEVs) are sure to make a huge impact [7]. According to the US Environmental Protection Agency, the estimated gas mileage of the hybrid-electrical vehicle shown in Figure 1.10 in combined city and highway driving is 48 miles per gallon [8]. This is in comparison to the gas mileage of 22.1 miles per gallon for an average passenger car in the United States [9]. Since automobiles are estimated to account...
