Wireless Power Transfer E-Book

Zhen Zhang

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Serie: IEEE Press Series on Power Engineering
• Sprache: Englisch

Seitenzahl: 533

Veröffentlichungsjahr: 2022

Beschreibung

Wireless Power Transfer Presents a detailed overview of multiple-objective wireless power transfer (WPT) technologies, including the latest research developments and emerging applications Wireless Power Transfer: Principles and Applications offers comprehensive coverage of all key aspects of wireless power transfer (WPT) technologies, including fundamental theory, intelligent control, configuration analysis, and emerging power electronics techniques. This unique resource is the first book of its kind to provide in-depth discussion of energy transmission control schemes with emphasis on omni-directional vector control, energy-encryption-based security control, demand-based optimal designs for transmitter, pickup, and self-resonance coils, multiple-objective power distribution, and maximum efficiency and power control under various conditions. In addition, this text: * Presents the methodologies and approaches of emerging multiple-objective WPT technologies * Discusses various applications for wireless charging techniques, including contactless power for electric vehicles, in-flight charging for unmanned aerial vehicles, and underwater wireless charging * Covers both intermittent and continuous impedance matching methods for different classes of coils * Features more than 400 high-quality illustrations and numerous figures and tables throughout Wireless Power Transfer: Principles and Applications is an invaluable technical reference for academic researchers and industry professionals in power and energy engineering, and an excellent textbook for postgraduate courses in relevant areas of industrial and electronic engineering.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Dedication

Author Biographies

Preface

Acknowledgments

Part I: Introduction

1 The Era of Wireless Power Transfer

1.1 The Father of Wireless Power Transfer – Nikola Tesla

1.2 Wireless Power Transfer

1.3 About This Book

References

2 Inductive Power Transfer

2.1 Inductive Power Transfer

2.2 1‐to‐1 Transmission

2.3 1‐to‐

n

Transmission

2.4 What Are the Differences Between 1‐to‐1 and 1‐to‐

n

Transmission

2.A Appendix

References

Part II: Design

3 Design and Optimization for Coupled Coils

3.1 Introduction

3.2 Design Considerations

3.3 Optimal Design

3.4 Summary

References

4 Design and Optimization for Power Circuits

4.1 Impedance Matching

4.2 DC/AC Inverters

References

Part III: Control

5 Control for Single Pickup

5.1 Review of Control Schemes

5.2 Maximizing Efficiency Control Schemes

References

6 Control Scheme for Multiple‐pickup WPT System

6.1 Introduction

6.2 Transmission Strategy

6.3 Impedance Matching Strategy for Multifrequency Transmission

6.4 Others

References

7 Energy Security of Wireless Power Transfer

7.1 Introduction

7.2 Characteristics of Frequency

7.3 Energy Encryption

7.4 Verifications

7.5 Opportunities

References

8 Omnidirectional Wireless Power Transfer

8.1 Introduction

8.2 Mathematical Analysis

8.3 Design of Transmitting Coils for Synthetic Magnetic Field

8.4 Design and Control Considerations for Pickup Coils

8.5 Load Detection

8.6 Discussion

References

Part IV: Application

9 WPT for High‐power Application – Electric Vehicles

9.1 Introduction

9.2 EV Wireless Charging

9.3 Electromagnetic Field Reduction

9.4 Key Technologies

9.5 Summary

References

10 WPT for Low‐Power Applications

10.1 Portable Consumer Electronics

10.2 Implantable Medical Devices

10.3 Drones

10.4 Underwater Wireless Charging

References

Index

IEEE Press Series on Power and Energy Systems

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Different wireless power technologies.

Table 1.2 Different standard of WPT.

Chapter 2

Table 2.1 Comparison of three models.

Chapter 4

Table 4.1 Four fundamental compensation networks.

Table 4.2 Comparison of compensation characteristics.

Table 4.3

T

‐ and

Π

‐networks.

Table 4.4 Key parameters of the transmitting and the pickup coils.

Table 4.5 One pickup with inductive characteristics under the frequency of 1...

Table 4.6 Two pickups with resistive characteristics under the frequency of ...

Table 4.7 Three pickups with resistive characteristics under the frequency o...

Table 4.8 Main characteristics of the existing semiconductor materials.

Table 4.9 Characteristics of different high‐frequency inverters.

Chapter 5

Table 5.1 Comparison of the basic DC–DC converters.

Table 5.2 Parameters of the design example.

Table 5.3 An example of the experimental system devices.

Table 5.4 Parameters of the design example.

Table 5.5 Simulation results of the initial coupling coefficient estimation....

Table 5.6 Simulation results of the dynamic coupling coefficient estimation....

Table 5.7 Simulation results of the maximum efficiency tracking.

Chapter 6

Table 6.1 Comparison of four methods.

Chapter 7

Table 7.1 Switching states of the capacitor array.

Table 7.2 Key parameters of the transmitting and pickup coils.

Table 7.3 Parameters of the capacitor array.

Table 7.4 Key parameters of the transmitting, resonant, and pickup coils.

Chapter 9

Table 9.1 Basic restrictions for human exposure to time‐varying electric and...

Table 9.2 Reference levels for occupational exposure to time‐varying electri...

Table 9.3 Reference levels for general public exposure to time‐varying elect...

Table 9.4 Reference levels in EMF exposure standard.

Table 9.5 Basic restriction levels in EMF exposure standard.

Table 9.6 Typical characteristics of battery cells and supercapacitor cells....

Table 9.7 The cost of supercapacitors for EV application.

Chapter 10

Table 10.1 Comparison of wireless charging products from Xiaomi and Huawei....

List of Illustrations

Chapter 1

Figure 1.1 Nikola Tesla [3].

Figure 1.2 Demonstrations of wireless lighting by Tesla.

Figure 1.3 Tesla's unsuccessful Wardenclyffe power station.

Figure 1.4 Acoustic wireless power transfer.

Figure 1.5 Optical wireless power transfer.

Figure 1.6 Microwave wireless power transfer: (a) schematic; (b) block diagr...

Figure 1.7 Capacitive wireless power transfer: (a) Bipolar; (b) Unipolar.

Figure 1.8 Inductive power transfer.

Figure 1.9 MRC‐based wireless power transfer.

Figure 1.10 Statistics of studies on IPT: the numbers of SCIE papers from 20...

Figure 1.11 Organization of key concepts in this book.

Figure 1.12 Structure of this book.

Chapter 2

Figure 2.1 Principle of IPT.

Figure 2.2 Configuration of 1‐to‐1 IPT system.

Figure 2.3 Simplified magnetic coupling system.

Figure 2.4 Normalized magnetic field strength versus

d

/

r

.

Figure 2.5 Configuration of 1‐to‐

n

IPT system.

Figure 2.6 Different power distribution modes for single‐frequency 1‐to‐

n

tr...

Figure 2.7 Configuration of PWM‐based multifrequency 1‐to‐

n

transmission.

Figure 2.8 Configuration of multifrequency superposition‐based 1‐to‐

n

transm...

Figure 2.9 Schematic diagram of loosely coupled transformer.

Figure 2.10 Loosely coupled transformer model.

Figure 2.11 T‐model for 1‐to‐1 transmission.

Figure 2.12 M‐model for 1‐to‐1 transmission.

Figure 2.13 (a) Circuit diagram of series compensation circuit; (b) Vector d...

Figure 2.14 (a) Circuit diagram of parallel compensation circuit; (b) Vector...

Figure 2.15 Simplified 1‐to‐1 IPT system with SS compensation.

Figure 2.16 Efficiency and normalized load power versus

Z

r

/

R

p

.

Figure 2.17 Simplified multiple pickups IPT system configuration.

Figure 2.18 A general two pickups IPT system.

Figure 2.19 Simplified two pickups IPT system without cross‐coupling.

Figure 2.20 Simplified multiple pickups IPT system without cross‐coupling.

Figure 2.21 Simplified two pickups IPT system with cross‐coupling.

Figure 2.22 Simplified two pickups IPT system with cross‐coupling and extra ...

Figure 2.A.1 Mutual inductance between two one‐turn loops in any shapes.

Chapter 3

Figure 3.1 Schematic of the typical WPT systems.

Figure 3.2 Circuit: (a) topology of SS compensation and (b) equivalent circu...

Figure 3.3 Relationship between maximum efficiency and

κ

2

Q

1

Q

2

.

Figure 3.4 Schematic of circular planar spiral coils.

Figure 3.5 Self‐inductance with respect to different ferrite thicknesses and...

Figure 3.6 Coupling coefficient with respect to different ferrite thicknesse...

Figure 3.7 Self‐inductance with respect to different line spacings and

D

i

/

D

e

Figure 3.8 Coupling coefficient with respect to different line spacings and

Figure 3.9 Coupling coefficient with respect to different air gaps and

D

i

/

D

e

Figure 3.10 A typical coil with shielding plate utilized in WPT systems.

Figure 3.11 Transmission efficiency with respect to the thickness of aluminu...

Figure 3.12 Transmission efficiency with respect to the distance between alu...

Figure 3.13 Magnetic field intensity for a circular planar spiral coil.

Figure 3.14 Hollow winding with track‐width ratio.

Figure 3.15 Diagram of hollow winding with track‐width ratio: (a) isometric ...

Figure 3.16 Quality factor with respect to inside radius and width ratio.

Figure 3.17 Structure of double‐layer PSC.

Figure 3.18 The introduction of wire width and wire thickness.

Figure 3.19 Influence of width and thickness on resistance: (a) with respect...

Figure 3.20 Influence of line spacing and substrate thickness on resistance....

Figure 3.21 Quality factor versus tangent of dielectric loss.

Figure 3.22 Schematics of circular pad: (a) exploded view and (b) top view....

Figure 3.23 The schematic diagram of flux density: (a) traditional circular ...

Figure 3.24 Schematics of flux pipe with two subcoils.

Figure 3.25 2‐D flux path of the circular pad and the flux pipe: (a) circula...

Figure 3.26 DD pad: (a) physical structure

Figure 3.27 Magnetic flux.

Figure 3.28 DD pad in the null position.

Figure 3.29 Simplified structure of DDQ and bipolar pad: (a) DDQ pad and (b)...

Figure 3.30 DDQ pickup pad: (a) horizontally aligned and (b) horizontally mi...

Figure 3.31 Charging zones of the circular, DD, and DDQ pads.

Figure 3.32 Simplified structure of DD2Q.

Chapter 4

Figure 4.1 Compensation topologies: (a) SS; (b) SP.

Figure 4.2 Equivalent M‐model circuit: (a) SS; (b) SP.

Figure 4.3 Compensation networks: (a) PS; (b) PP.

Figure 4.4 Equivalent M‐model circuits: (a) PS; (b) PP.

Figure 4.5 Four types of

L

‐networks: (a) I‐type

L

‐networks; (b) II‐type

L

‐ne...

Figure 4.6 I‐type

L

‐networks using input voltage source: (a)

LC

tank; (b)

CL

Figure 4.7 II‐type

L

‐networks using input current source: a)

CL

tank; (b)

LC

Figure 4.8

T

and

Π

networks: (a)

T‐

network; (b)

Π

‐network.

Figure 4.9

T

‐type topologies for constant voltage output using voltage power...

Figure 4.10

Π

‐type topologies for constant‐current output using current...

Figure 4.11 Equivalent T model of

LCC‐S

compensation network.

Figure 4.12 Equivalent T model of

LCC‐P

compensation network.

Figure 4.13 Equivalent T model of double‐sided

LCC

compensation network.

Figure 4.14 Equivalent WPT system with proposed capacitor matrix.

Figure 4.15

M

 × 

N

capacitor matrix.

Figure 4.16 Exemplified 2 × 3 capacitor matrix: (a) combination scheme; (b) ...

Figure 4.17 Topology‐reconfigurable capacitor matrix.

Figure 4.18 Exemplified 2 × 4 reconfigurable topology capacitor matrix: (a) ...

Figure 4.19 Equivalent circuit of multiple‐pickup WPT system with self‐balan...

Figure 4.20 Equivalent circuit of the proposed self‐balancing network.

Figure 4.21 Vector schematic: (a) mismatching caused by the inductive compon...

Figure 4.22 Block diagram of the proposed hybrid impedance matching method....

Figure 4.23 The respective applications of power semiconductor devices.

Figure 4.24 Schematic diagram of single‐phase half‐bridge inverters: (a) vol...

Figure 4.25 Waveforms of voltage and fundamental current with resistive load...

Figure 4.26 Schematic diagram of single‐phase full‐bridge inverters: (a) vol...

Figure 4.27 Waveforms of voltage and fundamental current with resistive load...

Figure 4.28 Schematic diagram of class‐E inverters.

Figure 4.29 Equivalent circuit model of class‐E inverters: (a) transistor Q ...

Figure 4.30 Schematic diagram of class‐EF

2

inverters.

Figure 4.31 A full‐bridge inverter with LC‐series resonant circuit.

Figure 4.32 Schematic diagram of ZCS: (a) Output waveforms of full‐bridge in...

Figure 4.33 Commutation of ZVS operation: (a)

Q

1,4

turns on,

Q

2,3

turns off;...

Figure 4.34 Schematic diagram of ZVS: (a) Output waveforms of full‐bridge in...

Figure 4.35 Schematic diagram of phase‐shift control scheme for full‐bridge ...

Chapter 5

Figure 5.1 Normalized output power versus operating frequency.

Figure 5.2 Efficiency and normalized output power versus coupling coefficien...

Figure 5.3 Efficiency and normalized output power versus equivalent load res...

Figure 5.4 Summarization of WPT control schemes.

Figure 5.5 Block diagram of ZPA‐based frequency tracking control without fre...

Figure 5.6 Phase angle between the primary current and voltage varying with ...

Figure 5.7 Block diagram of ZPA‐based frequency tracking control with PLL co...

Figure 5.8 Block diagram of ZPA‐based frequency tracking control with freque...

Figure 5.9 Equivalent WPT system with

M

×

N

capacitor matrix: (a) System con...

Figure 5.10 Equivalent circuit model of a four‐coil WPT system with reconfig...

Figure 5.11 Equivalent circuit of a WPT system with the DC–DC converter conn...

Figure 5.12 Basic DC–DC converter topologies: (a) buck type; (b) boost type;...

Figure 5.13 Diagram of the optimal load resistance closed‐loop control schem...

Figure 5.14 Equivalent circuit of a WPT system with the active rectifier in ...

Figure 5.15 Input voltage of active rectifier in the secondary side with dif...

Figure 5.16 Flowchart of P&O‐based maximum efficiency point tracking scheme ...

Figure 5.17 Flowchart of P&O‐based maximum efficiency point tracking scheme ...

Figure 5.18 Diagram of P&O‐based maximum efficiency point tracking control s...

Figure 5.19 Diagram of the maximum efficiency point tracking control scheme ...

Figure 5.20 Flowchart of the maximum efficiency point tracking control schem...

Figure 5.21 System configuration of P&O‐based maximum efficiency tracking.

Figure 5.22 Results of the maximum efficiency tracking: (a) tracking of opti...

Figure 5.23 Diagram of the maximum efficiency point tracking control scheme ...

Figure 5.24 Efficiency tracking results with dynamic coupling coefficient.

Chapter 6

Figure 6.1 Structure diagram of 1‐to‐

n

transmission.

Figure 6.2 Simplified two‐pickup WPT system under single‐frequency time‐shar...

Figure 6.3 Efficiency versus operating frequency under two‐pickup selective ...

Figure 6.4 Efficiency versus operating frequency with and without cross‐coup...

Figure 6.5 Simplified two‐pickup WPT system under multifrequency simultaneou...

Figure 6.6 (a) Unipolar multifrequency programmed PWM; (b) Bipolar multifreq...

Figure 6.7 Unipolar multifrequency programmed PWM under

U

ac

29

= 0.6,

U

ac

87

 =...

Figure 6.8 Bipolar multifrequency programmed PWM under

U

ac

29

= 0,

U

ac

87

 = 0....

Figure 6.9 Configuration of dual‐frequency full‐bridge resonant inverter.

Figure 6.10 Control signal and output voltage of the dual‐frequency modulati...

Figure 6.11 Inverter output voltage and two load currents.

Figure 6.12 Configuration of transformer‐based multifrequency superposition....

Figure 6.13 Waveform of dual‐frequency transformer‐based multifrequency supe...

Figure 6.14 Methodology for transformer‐free multifrequency superposition. (...

Figure 6.15 Configuration of the proposed artful inverter.

Figure 6.16 Waveforms of transformer‐free superposition‐based WPT system.

Figure 6.17 Dual‐frequency resonating compensation network: (a) Circuit diag...

Figure 6.18 Verification results of

Z

p

: (a) |

Z

p

|; (b) Impedance angle of

Z

p

....

Figure 6.19 Triple‐frequency resonating compensation network: (a) Circuit di...

Figure 6.20 Roots distribution: (a)

x

1

,

x

2

< 0,

x

3

> 0; (b)

x

1

,

x

2

,

x

3

> 0....

Figure 6.21 Impedance characteristics of triple‐resonating compensation unde...

Figure 6.22 Circuit diagram of multifrequency resonating compensation networ...

Figure 6.23 Simplified two‐pickup IPT system with cross‐coupling and extra r...

Chapter 7

Figure 7.1 Relationship between load power and frequency with respect to dif...

Figure 7.2 Distribution of the induced electromagnetic field. (a) Optimal op...

Figure 7.3 Curve of the output power at different frequencies.

Figure 7.4 Equivalent circuit of two‐coil WPT systems. (a) Primary side; (b)...

Figure 7.5 Process of encryption and decryption.

Figure 7.6

X

n

concerning different values of

A

.

Figure 7.7 Basic circuit of two‐coil WPT systems.

Figure 7.8 Capacitor arrays of the primary and secondary sides.

Figure 7.9 Procedure of exemplified energy encryption scheme.

Figure 7.10 Simulation results of Case 1: (a) Load voltage; (b) Load current...

Figure 7.11 Simulation results of Case 1: Load power.

Figure 7.12 Simulation result of Case 2: (a) Load voltage; (b) Load current;...

Figure 7.13 Simulation results of Case 1: Load power.

Figure 7.14 Simulation result of Case 2: (a) Load voltage; (b) Load current;...

Figure 7.15 Simulation result of Case 2: Load power.

Figure 7.16 Electromagnetic field analysis of Case 2.

Figure 7.17 Experimental prototype.

Figure 7.18 Experiment waveforms: (a) Load voltage of authorized pickup (X: ...

Chapter 8

Figure 8.1 Two‐dimensional omnidirectional WPT system with a loaded pickup c...

Figure 8.2 Schematic diagram of the two orthogonal transmitting coils and a ...

Figure 8.3 Geometrical relationship of a loaded pickup coil resonator in a 2...

Figure 8.4 Energy efficiency of the 2D WPT system when the pickup load is pl...

Figure 8.5 Efficiency when the magnetic vector is rotating around the origin...

Figure 8.6 Schematic diagram of load power (in the form of a Lemniscate of B...

Figure 8.7 Schematic diagram of the power picked up by the pickup (in the fo...

Figure 8.8 Schematic diagram of the input power (in the form of a deformed L...

Figure 8.9 Energy efficiency plots when the pickup is placed at different an...

Figure 8.10 (a) Relative location of the pickup coil with the two orthogonal...

Figure 8.11 Trajectory of the magnetic field vector at the center under cont...

Figure 8.12 Three‐orthogonal‐coil structure for the proposed omnidirectional...

Figure 8.13 Three‐dimensional omnidirectional WPT system comprising three or...

Figure 8.14 Amplitude modulation description of currents

,

, and

, where ...

Figure 8.15 Current vector plotted in space [9]: (a) the resultant current v...

Figure 8.16 Variations of the amplitude modulation functions of Eq. (8.23) a...

Figure 8.17 Load power: the surface of revolution of Lemniscate of Bernoulli...

Figure 8.18 Power picked up by the pickup: the surface of revolution of Lemn...

Figure 8.19 Total input power of the three transmitters: the surface of revo...

Figure 8.20 Block diagram of the proposed WPT system.

Figure 8.21 Detailed structure of the proposed coils.

Figure 8.22 Use of three separate orthogonal coils A, B, and C connected in ...

Figure 8.23 The structure of the magnetic coupler (3D view of the magnetic c...

Figure 8.24 Proposed crossed dipole coils for six degrees of freedom.

Figure 8.25 Schematics of (a) omnidirectional WPT system and (b) quadrature‐...

Figure 8.26 Power and efficiency with respect to

l

.

Figure 8.27 Power and efficiency with respect to

w

.

Figure 8.28 Schematic of magnetic field strength.

Figure 8.29 Induced pickup coil voltages with angular misalignment around: (...

Figure 8.30 Comparative analysis: (a) roll, (b) yaw, and (c) pitch.

Figure 8.31 Configuration of the proposed pickup coil with minimum number of...

Figure 8.32 Diagrams indicating how induced voltage is generated or canceled...

Chapter 9

Figure 9.1 EV static wireless charging system.

Figure 9.2 Transformer between the inverter and the primary circuit.

Figure 9.3 Experimental prototype.

Figure 9.4 Qualcomm Halo wireless charging system.

Figure 9.5 WiTricity wireless charging system.

Figure 9.6 Plugless wireless charging system.

Figure 9.7 Momentum dynamics wireless charging system.

Figure 9.8 EV dynamic wireless charging system based on lumped track: (a) ov...

Figure 9.9 EV dynamic wireless charging system based on stretched track: (a)...

Figure 9.10 Top view and cross section of typical power track designs: (a) E...

Figure 9.11 The ORNL prototype of EV dynamic wireless charging.

Figure 9.12 Bombardier prototype.

Figure 9.13 The FABRIC test site in Satory.

Figure 9.14 The FABRIC test site in Torino.

Figure 9.15 The VICTORIA dynamic wireless charging system.

Figure 9.16 Statistics of patents related to wireless charging for EVs.

Figure 9.17 Proportion of patents among various enterprises.

Figure 9.18 Front view of measurement.

Figure 9.19 Front view of EMF regions.

Figure 9.20 Overall configuration of V2G.

Chapter 10

Figure 10.1 Wireless charging products. (a) Xiaomi 10W; (b) Huawei 15W; (c) ...

Figure 10.2 Disassembly diagram of Xiaomi 10W wireless charging board.

Figure 10.3 Disassembly diagram of wireless charging products. (a) Huawei 15...

Figure 10.4 Cooling design of Huawei 40W wireless charger.

Figure 10.5 Schematic of the capacitive coupling method.

Figure 10.6 Schematic of the ultrasonic energy transfer method.

Figure 10.7 Schematic diagram of cochlear implant.

Figure 10.8 Retinal prosthesis system: (a) wearable external unit and (b) im...

Figure 10.9 Structure of the cortical implant.

Figure 10.10 Schematic diagram of the peripheral nerve implant.

Figure 10.11 Application of WPT for electric‐driven drones.

Figure 10.12 Schematic of wireless in‐flight charging for drones.

Figure 10.13 WPT coils: (a) transmitting coil and (b) receiving coil.

Figure 10.14 Simulation result of radiation resistance in seawater and air....

Figure 10.15 Equivalent circuit of UWPT systems.

Figure 10.16 Underwater wireless charging for AUV.

Figure 10.17 Underwater wireless charging for ocean buoy.

Guide

Cover

Table of Contents

Title Page

Copyright

Dedication

Author Biographies

Preface

Acknowledgments

Begin Reading

Index

IEEE Press Series on Power and Energy Systems

End User License Agreement

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Peter (Yong) Lian

Thomas Robertazzi

Wireless Power Transfer: Principles and Applications

Zhen Zhang and Hongliang Pang

Tianjin University, China

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To my baby girl, Olivia Yiqing Zhang.

              Zhen Zhang, Ph.D.

Author Biographies

Zhen Zhang, Ph.D., is a full professor with the School of Electrical and Information Engineering at Tianjin University. He has authored and co‐authored numerous internationally refereed papers as well as two books published by Wiley‐IEEE Press and Cambridge University Press. Prof. Zhang is currently the Chair of IEEE Beijing Section IES Chapter (Tianjin) and an Associate Editor for the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, and IEEE INDUSTRIAL ELECTRONICS MAGAZINE. He is the recipient of the Humboldt Research Fellowship, Carl Friedrich von Siemens Research Fellowship, Japan Society for the Promotion of Science Visiting Fellowship, 2020 Outstanding Paper Award for IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, and IEEE J. David Irwin Early Career Award.

Hongliang Pang received the B.Eng. and M.Eng. degrees from Tianjin University, Tianjin, China, in 2017 and 2020, respectively. He is currently working toward the Ph.D. degree in electrical and electronic engineering at the Department of Electrical and Electronic Engineering, the University of Hong Kong, Hong Kong. He has published several technical papers and industrial reports in these areas. His current research interests include electric vehicle technologies, wireless power transfer, and power‐electronic‐based impedance matching.

Preface

Electrically isolated inductive magnetic coupling provides the wireless power transfer (WPT) with flexibility, noninvasivity, cleanliness, and security, enabling to deliver the power without any physical contact. This epoch‐making technique has been favored by various electric‐driven applications, thus fueling the industry with a new breed of technology. It is broadly expected that the WPT industry will grow persistently in the coming decades. Accompanied by the increasing penetration trend of practical niches as well as the rising development of WPT techniques, various scenarios pose complexity, diversity, and challenging issues on this emerging technique. Hence, a book that covers wide areas for WPT technologies, which concurrently takes theoretical analysis, optimal design, intelligent control, and emerging applications into consideration, is highly desirable. This book aims to achieve this mission in the research of WPT, especially for multiple‐pickup WPT.

The purpose of this book is to offer readers a panoramic view of WPT technologies with emphasis on the multiple‐pickup WPT which is different from single‐pickup WPT. Along with the in‐depth research on the WPT, the practical‐demand‐based optimal design and intelligent energy transmission control have attracted increasing attention from the academia and the industry. Hence, this book also aims to offer readers with hot‐pot research topics in the current and near future. Most importantly, a whole chapter regarding the latest control scheme for multiple‐pickup WPT is presented, which addresses the first systematic elaboration on this topic. Furthermore, this book discusses several typical applications for the wireless charging technique, including the high‐power EV wireless charging, and low‐power applications, e.g. portable consumer electronics, in‐flight charging for unmanned aerial vehicles, and underwater wireless charging, wherein, WPT shows significant, profound, and irreplaceable roles. Thus, this book explores and provides the current methodologies, approaches, and foresight of the emerging technologies of multiple‐objective WPT which nearly have not been published before.

This book covers the multidisciplinary aspects and is organized into the following four parts:

Part I

presents an introduction and addresses the differences between 1‐to‐1 and 1‐to‐

N

transmission. It consists of

Chapters 1

and

2

, which introduce the basic theory of inductive power transmission and conclude the system analysis.

Part II

focuses on the design and optimization of coupled coils and power circuits. It comprises two chapters,

Chapters 3

and

4

, respectively, which discuss the design consideration for coupled coils, coil topology, impedance matching compensation, and DC/AC inverters.

Part III

is the core section of this book, namely, the control scheme for WPT. It contains four chapters,

Chapters 5

–

8

, in which the maximum efficiency/power control, excitation modulation as well as power allocation for multiple‐pickup WPT, energy‐encryption‐based security consideration control, and omnidirectional vector control are elaborated.

Part IV

unveils promising applications adopting the WPT technique. It includes

Chapters 9

and

10

, which emphasize electric vehicles (EVs), portable consumer electronics, implantable medical devices, drones, and underwater devices.

It is anticipated that WPT will experience explosive development. Hope this book to be a key reference for researchers, engineers, and administrators who need to make such progress.

My baby girl, Olivia Yiqing Zhang, was born in Hong Kong in the year 2011, which is right at the beginning of the place and the date for my research on WPT technologies. Today, more than 10 years have passed; my girl gradually realizes the importance of self‐learning and independent thinking, while I also gradually realize the challenges and opportunities of WPT technologies. As a similarity as my girl is finishing her primary stage of education, my understanding on WPT technologies is shaping which seems a wonderful beginning for me. Hence, it is very necessary for me to summarize past work, re‐understand basic concepts, and think about the future of WPT technologies, which is the reason why I decided to write this book. After the next 10 years, I firmly believe WPT technologies will embrace rapid development stage and draw increasing attention from various applications, similar to my baby girl who is growing up and has her own wonderful life. Lastly, this book is dedicated to my girl, as well as my wife who has been accompanying me to appreciate life all the time.

Hereby, I would therefore like to take this opportunity to express my heartfelt gratitude to my girl, Olivia Yiqing Zhang, and my wife, Zhenyan Liang, for their presence in my life.

PEIYANG Campus, Tianjin University Written by Zhen Zhang, Ph.D.

Acknowledgments

The authors wish to acknowledge many exceptional contributions toward the content of this book from our research team, namely Tianjin University Laboratory of Embedded Computing and Control (TJU‐ECC), especially Mr. Lin Yang, Mr. Xingyu Li, Mr. Cong Xie, Mr. Shen Shen, Mr. Zhichao Wang, Mr. Yu Gu, Mr. Yitong Wu, and Mr. Yantian Gong. In particular, a large portion of the supporting materials presented are the results of our research groups.

The authors are deeply indebted to our tutors, colleagues, and friends worldwide for their continuous support and encouragement during the years. A note of gratitude to the editors and staff at Wiley who were instrumental in undertaking a diligent review of the text and editing the book through the production process.

The authors would like to express our gratitude to the National Natural Science Foundation of China (Grant No. 51977138), the International Teaching Project for Postgraduates of Tianjin University (Project No. ENT19021), and the Hum‐boldt Research Fellowship (Ref. 3.5‐CHN‐1201512‐HFST‐P) for their financial support.

Last but not least, the authors also owe debts of gratitude to their families, who gave tremendous support during the process of writing this book.

Part IIntroduction

1The Era of Wireless Power Transfer

As one of the most epoch‐making technologies, the wireless power transfer (WPT) can realize the energy transmission in a cordless way [1, 2], which is obviously changing our traditional usage pattern of the energy, thus promoting the pervasive application of sustainable energies into our daily life. Surprisingly, such a miracle technique is not anything new, yet the original concept can date back more than 100 years ago. The story should begin with a great man, namely Nikola Tesla, as shown in Figure 1.1.

1.1 The Father of Wireless Power Transfer – Nikola Tesla

About 130 years ago, the wirelessly transmitting power was successfully demonstrated by Nikola Tesla's series of experiments, where the Geissler tubes and incandescent light bulbs can be lighted from across a stage based on near‐field inductive and capacitive coupling, as depicted in Figure 1.2. The key technique of such amazing experiments is to use Tesla coils, which are spark‐excited radio‐frequency resonant transformers, to generate a high alternating current (AC) voltage [3, 4]. More importantly, Tesla found that the transmission distance could be increased if the LC circuit of receivers can be tuned to resonance with the LC circuit of transmitters [5], namely resonant inductive coupling [4]. Nevertheless, such an imaginative technique failed to proceed with commercialization due to various limitations at that time, such as semiconductor materials, power electronic technologies, and manufacturing.

Tesla's attempting efforts on WPT technologies have never stopped since the beginning of this story. Then, his focus moved to a wireless power distribution system, which can wirelessly deliver the power directly to everywhere in the world. Borrowing from the idea of Mahlon Loomis [3], he developed a demonstrating system composed of balloons to suspend transmitting and receiving electrodes in the air above 9100‐m altitude, because he believed that the low‐pressure air at high altitude would allow higher voltage for long‐distance power transmission. In 1899, Tesla build up a test facility at high altitude in Colorado Springs to further study the conductive characteristics of low‐pressure air [3]. It is this famous experiment that led Tesla to incorrectly conclude that the entire Earth can be utilized to conduct electrical energy [3]. In addition, the potential of the Earth can be oscillated by driving AC pulses into the Earth at its resonant frequency using a grounded Tesla coil. In such a way, he believed that the AC power can be picked up at everywhere around the world using a similar capacitive antenna tuned to resonance with the Earth [3, 6].

Figure 1.1 Nikola Tesla [3].

Source: Wikimedia Commons.

Figure 1.2 Demonstrations of wireless lighting by Tesla.

Source: Ref. [2] Nikola Tesla/Wikimedia Commons/Public Domain.

Figure 1.3 Tesla's unsuccessful Wardenclyffe power station.

Source: Ref. [2] Nikola Tesla/Wikimedia Commons/Public Domain.

Then, Tesla boldly proposed a “World Wireless System” to deliver both the information and the power around the world [3]. In 1901, a large high‐voltage wireless power station, namely Wardenclyffe Tower, was built at Shoreham in New York, as depicted in Figure 1.3. Unfortunately, this project had to be halt due to dried‐up investment by the year 1904. Despite all this, Nikola Tesla really redefined the energy transmission and opened up a brand‐new research field, who is well deserved to be called the Father of Wireless Power Transfer [7].

1.2 Wireless Power Transfer

As one of the revolutionary technologies, WPT can realize the transmission of electric energy from the transmitting end to the desired pickup device in a contactless manner. From the perspective of the transmission distance, the WPT can be mainly divided to near‐field transmission and far‐field transmission. On the one hand, the near‐field power transfer is based on the electromagnetic field coupling theory, including the inductive and capacitive coupling mechanisms. On the other hand, the far‐field power transfer can be realized by means of acoustic, optical, and microwave methods, which are applied in low‐power sensor networks and military fields. The different wireless power technologies are shown in Table 1.1.

1.2.1 Acoustic

The acoustic power transfer can achieve the wireless power transmission in the form of acoustic waves or mechanical vibrations. As shown in Figure 1.4, the system of the acoustic power transfer mainly includes four constituent units, namely the primary AC power supply, the primary and pickup sensors that realize the conversion of electrical energy and mechanical acoustic energy, and the energy pickup side.

The far‐field power transfer can be realized in the acoustic mechanism with the help of the ultrasonic frequency of vibration. Meanwhile, a variety of transmission media, including living tissue, metal materials, and air, are suitable for the acoustic mechanisms. Nevertheless, the acoustic power transfer faces the following three challenges. Firstly, the principle of spatial resonance puts forward special requirements for the placement position of the pickup coil, which limits the application scenario of this technology. Secondly, the technology lacks complete and clear theoretical analysis, which hinders the further development and wide application of the technology. Finally, the design of sensor is an important part of this technology which needs to comprehensively consider the power, efficiency of the system, and the impact of reflections [8].

1.2.2 Optical

As shown in Figure 1.5, the optical WPT uses the laser as the medium to transmit energy to the pickup coil. This technology is mainly used in military or aerospace fields that require long‐distance energy transmission. Compared with other energy transmission mechanisms, this technology has the following characteristics: the realization of the ultralong‐distance transmission, the realization of the centralized and directional energy transmission, and zero interference to radio‐frequency applications. Meanwhile, the optical WPT faces the challenges including the low conversion efficiency between light and electricity and the danger of laser radiation. Since the twenty‐first century, optical WPT has also been used in industrial consumer electronics or low‐power sensors [9].

Table 1.1 Different wireless power technologies.

Technology

Range

Directivity

Frequency

Antenna devices

Current and/or possible future applications

Inductive coupling

Short

Low

Hz to MHz

Wire coils

Electric tooth brush and razor battery charging, induction stovetops, and industrial heaters

Resonant inductive coupling

Mid

Low

kHz to GHz

Tuned wire coils and lumped element resonators

Charging portable devices (Qi), biomedical implants, electric vehicles, powering buses, trains, MAGLEV, Radio frequency identification (RFID), and smartcards

Capacitive coupling

Short

Low

kHz to GHz

Metal plate electrodes

Charging portable devices, power routing in large‐scale integrated circuits, smartcards, and biomedical implants

Magnetodynamic coupling

Short

N.A. (Not applicable)

Hz

Rotating magnets

Charging electric vehicles and biomedical implants

Microwaves

Long

High

GHz

Parabolic dishes, phased arrays, and rectennas

Solar power satellite, powering drone aircraft, and charging wireless devices

Light waves

Long

High

≥THz

Lasers, photocells, and lenses

Charging portable devices, powering drone aircraft, and powering space elevator climbers

Figure 1.4 Acoustic wireless power transfer.

Figure 1.5 Optical wireless power transfer.

1.2.3 Microwave

Microwave power transfer technology is a typical far‐field wireless power transmission mechanism, which is applied in the low‐power sensor networks, space, and military fields. The principle and components of the microwave power transfer system are depicted in Figure 1.6. At the transmitting part, the microwave is generated by the microwave generator and transmitted through the coax‐waveguide‐adapted and waveguide circulator, which reduces the external radiation caused by microwave. Then, the tuner and directional coupler device are used to realize the separation of radiation signals according to different propagation directions, ensuring the propagation of radiation in the air. In the pickup part, the microwave radiation is received through the receiving antenna and then converted into DC power through the low‐pass filter, matching network, and rectifier [10]. To obtain the best energy conversion efficiency in the wide‐range input power levels, a novel rectifier antenna architecture was proposed in the microwave WPT system [11].

Figure 1.6 Microwave wireless power transfer: (a) schematic; (b) block diagram of working principle.

1.2.4 Capacitive

The capacitive WPT system mainly consists of the transmitting and receiving electrodes, where the transmitting plate voltage generates an induced AC electromotive force on the receiving plate through electrostatic induction. In this technology, the transmitting power is related to the switching frequency of the system and the capacitance between the plates. According to the number of plates, the capacitive WPT can be divided into unipolar and bipolar systems. As shown in Figure 1.7a, the bipolar system includes two sets of transmitting and pickup plates. Different transmitting plates have 180° voltage phase difference, and AC potentials with opposite phase are induced at the pickup plates to realize wireless power transmission in the bipolar method. In addition, as depicted in Figure 1.7b, the unipolar system can achieve the energy transmission with a set of plates, where the passive plates form the return path at the same time [12].

Figure 1.7 Capacitive wireless power transfer: (a) Bipolar; (b) Unipolar.

Compared with other energy transmission mechanisms, this technology reduces the need for alignment between the transmitter and the pickup coils and provides a closed energy field to reduce the external interferences. Nevertheless, since the high voltage on the electrode plate will lead to the generation of harmful gases, the technology can only be applied to some low‐power wireless charging scenarios.

1.2.5 Inductive

As depicted in Figure 1.8, the common inductive WPT system is composed of the primary and secondary parts. In the primary part, the high‐frequency AC is generated by DC power supply and inverter. Then, based on the electromagnetic induction mechanism, the high‐frequency current is wirelessly transmitted from the primary coil to the pickup coil. In fact, the induced power transfer system is similar to the transformer system with weak coupling strength. Besides, the magnetic materials such as the ferrite can enhance the coupling strength between the primary and pickup coils [13].

Figure 1.8 Inductive power transfer.

Figure 1.9 MRC‐based wireless power transfer.

Moreover, the magnetic resonant coupling (MRC) mechanism can help to increase the transmission performance of inductive power transmission, which has broad application prospects in medium‐distance and low‐power applications. In Ref. [14], the effectiveness of MRC mechanism was proved by the WPT experiment with a transmission distance of 2 m and a power of 60 W. Figure 1.9 describes the basic components of four‐coil MRC‐based WPT system, including high‐frequency AC power supply, compensation network of the transmitting and receiving coils, and the load side. Different from the inductive power transfer, the MRC‐based system must use the capacitance compensation network to ensure that the system works in a resonant state.

Based on the MRC mechanism, the energy can be simultaneously transferred to different pickups in a wireless way [15]. Besides, to maximize the transmission efficiency and distance of the system, the theoretical analysis was proposed based on the equivalent circuit and Neumann formula [16]. Also, the coils with noncoaxial and circular structures were proposed to achieve the domino‐resonator WPT system [17]. Furthermore, to avoid the adverse effects of system detuning, an adaptive impedance matching system was implemented by matching the primary and secondary compensation networks to the resonant frequency of the system [18].

As a typical application scenario of inductive power transfer technologies, electric vehicle (EV) wireless charging system has obtained abundant achievements. For instance, to realize the online charging of EVs, an inductive power transfer system was proposed to provide energy for EVs on the whole road [19]. Besides, a bidirectional interface of inductive power transmission was designed to achieve the simultaneous charging and discharging of multiple EVs [20]. Also, to ensure the safe operation of wireless charging system, a load detection model was proposed to monitor the load state of the inductive power transfer system in real time [21]. In addition, the theoretical model of the mutual coupling effect between inductors was introduced to predict the mutual inductance [22].

In fact, due to the development of inductive WPT technology, wireless charging has attracted a lot of attention from academia and business. Figure 1.10 shows the statistics of the published SCIE papers and issued patents about inductive WPT from 2011 to 2020. Besides, many world‐famous companies have been engaged in the application and promotion of this technology, such as BMW, Audi, Tesla, Apple, and Huawei, among others. Hence, to standardize the application of the inductive WPT technology, a number of organizations (International Telecommunication Union, SAE International, and Wireless Power Consortium, among others) have issued relevant standards as shown in Table 1.2.

Figure 1.10 Statistics of studies on IPT: the numbers of SCIE papers from 2011 to 2020 and patents from 2011 to 2020. CN: China

Table 1.2 Different standard of WPT.

Standard

Title (Content)

Application

Recommendation ITU‐R SM.2110

Guidance for the use of frequency ranges for operation of non‐beam wireless power transmission for electric vehicle

EV

Report ITU‐R SM.2303‐2

Wireless power transmission using technologies other than radio frequency beam

All

Recommendation ITU‐R SM.2110

Frequency ranges for operation of non‐beam Wireless Power Transmission systems

All

IEC61980‐1

Electric vehicle wireless power transfer (WPT) systems ‐ Part 1: General requirements

EV

IEC61980‐2

Electric vehicle wireless power transfer (WPT) systems ‐ Part 2: Specific requirements for communication between electric road vehicle (EV) and infrastructure

EV

IEC61980‐3

Electric vehicle wireless power transfer (WPT) systems ‐ Part 3: Specific requirements for the magnetic field wireless power transfer systems

EV

ISO 19363:2017

Electrically propelled road vehicles? Magnetic field wireless power transfer? Safety and interoperability requirements

EV

ISO 19363:2020

Electrically propelled road vehicles? Magnetic field wireless power transfer? Safety and interoperability requirements

EV

SAE J2954

Wireless Power Transfer for Light‐Duty Plug‐in/Electric Vehicles and Alignment Methodology

EV

SAE J2847/6

Communication for Wireless Power Transfer Between Light‐Duty Plug‐in Electric Vehicles and Wireless EV Charging Stations

EV

Qi standard

The world's de facto wireless charging standard for providing 5‐15 watts of power to small personal electronics

Phone

1.3 About This Book

As mentioned in the preface, this book is trying to introduce working mechanisms, summarize recent research works, and discuss about classic applications of WPT technologies, especially during the past 20 years. It is expected to provide a big picture of WPT technologies for academic researchers, industrial engineers, postgraduate students, and readers who are interested in this research topic. Figure 1.11 shows the organization and the relationship among basic concepts, key technique, and main contents of this book, which is utilized to help readers understand WPT technologies more readily, more intuitively, and more in‐depth. As depicted in Figure 1.12, this book covers the multidisciplinary aspects and is organized into the following four parts as:

Part I

presents an introduction and addresses the differences between 1‐to‐1 and 1‐to‐

N

transmission. It consists of Chapters 1 and

2

, which introduce the basic theory of inductive power transmission and conclude the system analysis.

Part II

focuses on the design and optimization of coupled coils and power circuits. It comprises two chapters,

Chapters 3

and

4

, respectively, which discuss the design consideration for coupled coils, coil topology, impedance matching compensation, and DC/AC inverters.

Part III

is the core section of this book, namely the control scheme for WPT. It contains four chapters,

Chapters 5

–

8

, in which the maximum efficiency/power control, excitation modulation as well as power allocation for multiple‐pickup WPT, energy‐encryption‐based security consideration control, and omnidirectional vector control are elaborated.

Part IV

unveils promising applications adopting the WPT technique. It includes

Chapters 9

and

10

, which emphasize EVs, portable consumer electronics, implantable medical devices, drones, and underwater devices.

Figure 1.11 Organization of key concepts in this book.

Figure 1.12 Structure of this book.

References

1

   Zhang, Z., Pang, H., Georgiadis, A., and Cecati, C. (2019). Wireless power transfer – an overview.

IEEE Transactions on Industrial Electronics

66 (2): 1044–1058.

2

   Wireless Power Transfer.

https://en.wikipedia.org/wiki/Wireless_power_transfer

.

3

   Carlson, W.B. (2013).

Tesla: Inventor of the Electrical Age

. Princeton University Press.

4

   Lee, C.K., Zhong, W.X., and Hui, S.Y.R. (2012). Recent progress in mid‐range wireless power transfer.

Proceedings of 2012 IEEE Energy Conversion Congress and Exposition

, Raleigh, NC, USA (15‐20 September 2012)

https://ieeexplore.ieee.org/document/6472081

.

5

   Wheeler, L.P. (1943). II – Tesla's contribution to high frequency.

Electrical Engineering

62 (8): 355–357.

6

   Tesla, N. (1904). The transmission of electric energy without wires.

Electrical World and Engineer

43: 23760–23761.

7

   Tesla, N. (1900). System of transmission of electrical energy. US Patent 645,576, filed 02 September 1897 and issued 20 March 1900.

https://patents.google.com/patent/US645576A/en

.

8

   Roes, M.G.L., Duarte, J.L., Hendrix, M.A.M., and Lomonova, E.A. (2013). Acoustic energy transfer: a review.

IEEE Transactions on Industrial Electronics

60 (1): 242–248.

9

   Sahai, A. and Graham, D. (2011). Optical wireless power transmission at long wavelengths. In:

Proceedings of 2011 International Conference on Space Optical Systems and Applications

, Santa Monica, CA, USA, 146–170.

https://ieeexplore.ieee.org/document/5783662

.

10

  Reddy, M.V., Hemanth, K.S., and Venkat Mohan, C.H. (2013). Microwave power transmission – a next generation power transmission system.

IOSR Journal of Electrical and Electronics Engineering

4: 24–28.

11

  Marian, V., Allard, B., Vollaire, C., and Verdier, J. (2012). Strategy for microwave energy harvesting from ambient field or a feeding source.

IEEE Transactions on Power Electronics

27 (11): 4481–4491.

12

  Liu, C., Hu, A.P., and Nair, N.K.C. (2011). Modeling and analysis of a capacitively coupled contactless power transfer system.

IET Power Electronics

4: 808–815.

13

  Govic, G.A. and Boys, J.T. (2013). Inductive power transfer.

Proceedings of the IEEE

101 (6): 1276–1289.

14

  Kurs, A., Karalis, A., Moffatt, R. et al. (2007). Wireless power transfer via strongly coupled magnetic resonances.

Science

317 (5834): 83–86.

15

  Cannon, B.L., Hoburg, J.F., Stancil, D.D., and Goldstein, S.C. (2009). Magnetic resonant coupling as a potential means for wireless power transfer to multiple small receivers.

IEEE Transactions on Power Electronics

24 (7): 1819–1825.

16

  Imura, T. and Hori, Y. (2011). Maximizing air gap and efficiency of magnetic resonant coupling for wireless power transfer using equivalent circuit and Neumann formula.

IEEE Transactions on Industrial Electronics

58 (10): 4746–4752.

17

  Zhong, W.X., Lee, C.K., and Hui, S.Y.R. (2012). Wireless power domino‐resonator systems with noncoaxial axes and circular structures.

IEEE Transactions on Power Electronics

27 (11): 4750–4762.

18

  Beh, T.C., Kata, M., Imura, T. et al. (2013). Automated impedance matching system for robust wireless power transfer via magnetic resonance coupling.

IEEE Transactions on Industrial Electronics

60 (9): 3689–3698.

19

  Huh, J., Lee, S.W., Lee, W.Y. et al. (2011). Narrow‐width inductive power transfer system for online electric vehicles.

IEEE Transactions on Power Electronics

26 (12): 3666–3679.

20

  Madawala, U.K. and Thrimawithana, D.J. (2011). A bidirectional inductive power interface for electric vehicle in V2G systems.

IEEE Transactions on Industrial Electronics

58 (10): 4789–4796.

21

  Wang, Z., Li, Y., Sun, Y. et al. (2013). Load detection model of voltage‐fed inductive power transfer system.

IEEE Transactions on Power Electronics

28 (11): 5233–5243.

22

  Raju, S., Wu, R., Chan, M., and Yue, C.P. (2014). Modeling of mutual coupling between planar inductors in wireless power applications.

IEEE Transactions on Power Electronics

29 (1): 481–490.

2Inductive Power Transfer

2.1 Inductive Power Transfer

In this chapter, the basic theories and fundamental principles of the inductive power transfer (IPT) are first presented, where no distinction between the definition of IPT and that of magnetic resonant coupling (MRC) is made. From the perspective of the quantity for pickups, the IPT system is divided into 1‐to‐1 transmission and 1‐to‐n transmission. Then, the general configuration, coupled modeling, and compensation and power transfer characteristics of the aforementioned two transmission forms are illustrated in detail. Finally, the differences between 1‐to‐1 and 1‐to‐n transmission are explained, with emphasis on the unique characteristics of 1‐to‐N transmission.

Specific discussions on design, control, and application are extended in the remaining chapters of the book.

2.1.1 Principle

Some other literature reviews may divide the magnetic induction‐based wireless power transfer (WPT) into IPT and MRC. However, there only remain slight differences between IPT which requires actual capacitors to resonate with the inductance coils and MRC which utilizes the designed parasitic capacitance to compensate the inductance reactance. Consequently, the fundamental principles and operation of these two classifications are inherently the same, although various quality factors (Q) of the winding coils may cause the theoretical analysis differences between IPT and MRC, where the extremely high Q is often adopted in the MRC system [1, 2]. Hence, this chapter makes no distinction between them and focuses on the IPT which possesses more representatives compared with MRC to elaborate the magnetic induction‐based WPT.

The principle of the IPT system is shown in Figure 2.1 where power is transmitted wirelessly through two loosely coupled coils, namely the transmitting coils and the pickup coils. The specific power transmission procedures will be elaborated step by step as follows:

(1) Firstly, the resonant inverter/converter is adopted to modulate the DC power source or utility AC power source at the power frequency (50 or 60 Hz) into high‐frequency AC power which is utilized in WPT system with the scope of about 20 kHz [

3

–

5

] to a few MHz (6.78 or 13.56 MHz) [

6

].

(2) Then, the time‐varying AC current flows through the transmitting coils, accordingly, producing an alternatingly induced magnetic field nearby.

(3) Meantime, based on the Faraday's law, the alternatingly induced voltage with the same frequency is excited in the pickup coils through a weak magnetic coupling.

(4) Finally, after power electronics conversion, the power will be delivered directly to the load that is connected to each pickup coil.

Figure 2.1 Principle of IPT.

Similar to the conventional transformer theory, the aforementioned IPT principle is well illustrated; however, where are the differences between transformer theory and IPT principle? Four slight but noticeable features for IPT compared with transformers will be discussed as listed below:

Low mutual inductance and large leakage inductance

 –

 Unlike the traditional transformers, due to the large winding separation, the IPT system has a relatively large leakage inductance, where the leakage inductance holds 10 times larger than the magnetizing inductance in IPT system compared with the magnetizing inductance that holds about 50 times larger than the leakage inductance in conventional transformers. Moreover, the relatively long distance also leads to a significant reduction in magnetic flux, which results in the weaker coupling coefficient

κ

 < 0.2

[

7

] and lower mutual inductance

M

; thus, the IPT is also called loosely coupled power transmission. Hence, both the reasonable selection of compensation circuit so as to eliminate the large leakage inductance reactance and the elaborate design procedure for the transmitting and pickup coils with emphasis on high

Q

[

8

] prove to be the critical technical challenges in the IPT system.

The hollow inductor

 –

 The transmitting and pickup devices are both inductors in the IPT system, while most of them are hollow inductors to eliminate core loss (except the EV charging pad and EV track coils). However, regarding the transformers, the iron cores around the windings form a magnetic path and avoid magnetic leakage losses. Consequently, whether adopting the iron core as the magnetic circuit or not turns into a key factor for the differences between traditional transformers and the IPT system.

The phase between primary‐ and secondary‐side current

– Ignoring the loss and hysteresis, the currents of the primary and secondary sides are in phase or of opposite phase in conventional ideal transformers; however, for IPT system, there often exists approximately 90° phase difference between the primary and the secondary currents, which is completely different from that of the transformers.

The parameters perturbation and parasitic parameters

– With the changing transmission distance, misalignment of coupled coils, variable load values, and uncertainty quantity for pickups, the inherent or reflected parameters of the IPT system suffer violent fluctuations, which result in the extreme degradation of transmission efficiency and power. Besides, IPT systems employ the frequency band within 6.78 MHz ± 15 kHz [

6

] and a low band of several kHz [

3

–

5

]. Hence, the parasitic resistance and capacitance become severe through the high‐frequency IPT system, thus impeding the normal operation. As a result, the maintenance of high efficiency and stable output current/voltage under the circumstance of complex parameters perturbation falls into the focal concerns of the IPT system.

After conducting an overall discussion aiming at the principles of IPT, as well as revealing the differences between conventional transformers and IPT principle, the detailed introduction with emphasis on the essential theories for IPT system will follow up for the readers.

From the perspective of the quantity for pickups, the IPT system is divided into 1‐to‐1 (single transmitter single pickup) transmission and 1‐to‐n (single transmitter multiple pickups) transmission. As for the n‐to‐n (multiple transmitters multiple pickups) transmission, it could be considered as the cascaded connected operation mode for 1‐to‐1 transmission system with varying frequencies. Hence, this chapter will not regard n‐to‐n transmission as a separate classification and incorporate it into a special circumstance of 1‐to‐1 transmission.

2.1.2 1‐to‐1 Transmission

As shown in Figure 2.2