Inductive Links for Wireless Power Transfer: Fundamental Concepts for Designing High-efficiency Wireless Power Transfer Links

Description

This book presents a system-level analysis of inductive wireless power transfer (WPT) links. The basic requirements, design parameters, and utility of key building blocks used in inductive WPT links are presented, followed by detailed theoretical analysis, design, and optimization procedure, while considering practical aspects for various application domains. Readers are provided with fundamental, yet easy to follow guidelines to help them design high-efficiency inductive links, based on a set of application-specific target specifications. The authors discuss a wide variety of recently proposed approaches to achieve the maximum efficiency point, such as the use of additional resonant coils, matching networks, modulation of the load quality factor (Q-modulation), and adjustable DC-DC converters. Additionally, the attainability of the maximum efficiency point together with output voltage regulation is addressed in a closed-loop power control mechanism. Numerous examples, including MATLAB/Octave calculation scripts and LTspice simulation files, are presented throughout the book. This enables readers to check their own results and test variations, facilitating a thorough understanding of the concepts discussed. The book concludes with real examples demonstrating the practical application of topics discussed. Covers both introductory and advanced levels of theory and practice, providing readers with required knowledge and tools to carry on from simple to advanced wireless power transfer concepts and system designs; Provides theoretical foundation throughout the book to address different design aspects; Presents numerous examples throughout the book to complement the analysis and designs; Includes supplementary material (numerical and circuit simulation files) that provide a "hands-on" experience for the reader; Uses real examples to demonstrate the practical application of topics discussed. Preface Contents Acronyms 1 Introduction to Wireless Power Transfer 1.1 Why Wireless? 1.2 Wireless Links Classifications 1.3 Inductive Wireless Power Transfer 1.3.1 Transmitter DC-DC Converter 1.3.2 Inverter 1.3.3 Tx Matching Network 1.3.4 Inductive Link 1.3.5 Rx Matching Network 1.3.6 Rectifier 1.3.7 Receiver DC-DC Converter References 2 Inductive Link: Basic Theoretical Model 2.1 Reflected Load Theory in a 2-Coil Link 2.1.1 Underlying Physical Principles of Inductive Coupling: Self-Inductance (L), Mutual Inductance (M), and Coupling Coefficient (k) 2.1.2 Equivalent Circuit Model 2.1.3 Calculation of Link Efficiency, ηLink 2.1.4 Calculation of Power Delivered to the Rx-circuit, PMN 2.1.5 Effects of Coils' Quality Factor (Q) and Coupling Coefficient (k) on the Link 2.1.6 Effect of Tx and Rx Resonance on the Link 2.1.7 Frequency Splitting Effect 2.1.7.1 Analysis of Frequency Splitting Effect Based on T-Type Transformer Model 2.2 Reflected Load Theory in Systems with AdditionalResonant Coils 2.2.1 Link Efficiency, ηLink, and Power Delivered to the Rx-circuit, PMN, in a 3-Coil Link 2.2.2 Generalization to N-Coil Links 2.2.3 Link Efficiency, ηLink, and Power Delivered to the Rx-circuit, PMN, in a 4-Coil Link 2.3 Comparison Between 2-, 3-, and 4-Coil Links Appendices A.1 PMN Calculation for a Voltage Source and Series Tx Resonance A.2 PMN Calculation for a Voltage Source and Parallel TxResonance A.3 PMN Calculation for a Current Source and Series Tx Resonance A.4 PMN Calculation for a Current Source and Parallel Tx Resonance References 3 Inductive Link: Practical Aspects 3.1 Coil Design 3.1.1 Square-Shaped Printed Spiral Coil 3.1.1.1 Self-Inductance, L 3.1.1.2 Equivalent Series Resistance(ESR) 3.1.1.3 Parasitic Capacitance, C 3.1.1.4 Mutual Inductance, M 3.1.1.5 Square-Shaped Printed Spiral Coil Example 3.2 Influence of Foreign Object 3.2.1 Effects of Conductive Materials 3.2.2 Effect of Ferrites 3.3 Safety and Electromagnetic Compatibility Considerations 3.3.1 Electromagnetic Compatibility(EMC) 3.3.2 Safety References 4 Back Telemetry 4.1 The Need for and Role of Back Telemetry in WPT Links 4.2 Design of Power Transfer Links that Need to Support Back Telemetry 4.3 Examples of Implementation 4.3.1 Load Shift Keying(LSK) 4.3.1.1 Example of Use in AIMDs 4.3.2 Frequency Shift Keying(FSK) 4.3.2.1 Example of Using FSK in Low-Frequency RFID References 5 Achieving the Optimum Operating Point(OOP) 5.1 Introduction 5.2 Maximum Efficiency Point(MEP) in 2-Coil Links 5.3 Maximum Power Point(MPP) in 2-Coil Links 5.3.1 MPP, Tx-circuit with a Voltage Source and a Series Resonant Capacitor 5.3.2 MPP, Tx-circuit with a Current Source and a Series Resonant Capacitor 5.4 Choosing Between MEP and MPP 5.5 MEP and MPP in N-Coil Links 5.6 Using Matching Networks to Achieve the OOP 5.7 Comparing 2-Coil and 3-Coil Links at the MEP 5.8 Design of a 3-Coil Link to Operate at the MEP Appendices B.1 Deduction of QLoptη Which Maximizes ηLink B.2 Deduction of ηLinkmax B.3 Deduction of QLoptPMN (Voltage Source Tx with a Series Resonant Capacitor) B.4 Deduction of PMNmax (Voltage Source Tx with a Series Resonant Capacitor) B.5 Deduction of QLoptPMN (Current Tx Source with a Series Resonant Capacitor) B.6 Deduction of PMNmax (Current Tx Source with a Series Resonant Capacitor) B.7 Deduction of QLoptη Which Maximizes ηLink in a 3-Coil Link B.8 Deduction of ηLinkmax (3-Coil) B.9 Deduction of QLoptPMN (3-Coil, Voltage Source, and a Series Resonant Tx) B.10 Deduction of PMNmax (3-Coil, Voltage Source, and a Series Resonant Tx) References 6 Adaptive Circuits to Track the Optimum Operating Point(OOP) 6.1 Introduction 6.2 Using the Rx DC-DC Converter to Achieve the OOP 6.2.1 Switched-Inductor Converters 6.2.2 Switched-Capacitor Converters 6.3 Using an Active Rectifier to Achieve the OOP 6.3.1 Modifying the Control Signals 6.3.2 Reconfigurable Multiple-Gain Architectures 6.4 OOP Tracking in the AC Domain 6.4.1 Q-Modulation 6.4.2 Adaptive Matching Network 6.4.3 Reconfigurable Resonant Coil 6.5 Combining Adaptive and Nonadaptive Approaches to Achieve the OOP References 7 Closed-Loop WPT Links 7.1 Output Voltage Regulation 7.2 Tracking the Maximum Efficiency Point(MEP)in a Closed-Loop 7.3 The Joint Use of Output Voltage Regulation and MEP Tracking Feedbacks 7.4 Tracking the MEP in Links with Preregulated Output Voltage 7.5 Tracking the MEP in Links with Postregulated Output Voltage 7.5.1 Effect of Rx-circuit in the Operating Point 7.5.2 2-Coil Links 7.5.2.1 Analysis with Non-resonant Tx-circuit 7.5.3 3-Coil Links 7.5.4 N-Coil Links 7.5.5 Measurement Results 7.5.6 Concluding Remarks Appendices C.1 Deduction of (7.11) and (7.12) C.2 Deduction of (7.14) and (7.16) C.3 Proof of (7.19) C.4 Deduction of Table 7.6 References 8 System Design Examples 8.1 Radio Frequency Identification(RFID) 8.1.1 RFID Link Introduction 8.1.2 2-Coil RFID Link 8.1.2.1 Charging Phase 8.1.2.2 Reading Phase 8.1.3 3-Coil RFID Link 8.1.3.1 Charging Phase 8.1.3.2 Reading Phase 8.2 Introduction to WPT Links for Visual Prosthesis 8.2.1 WPT Link for Visual Prostheses 8.2.2 Rx Matching Network Design: Series Versus Parallel 8.2.3 Tracking OOP Under Load Variations 8.3 Smartphones 8.4 Electric Vehicles References Index