Preface

Wireless power transfer techniques have been gaining researchers' and industry attention due to the increasing number of battery-powered devices, such as mobile computers, mobile phones, smart devices, sensors, mainly as a way to replace the standard cable charging, but also for powering battery-less equipment.

Wired charging compared with wireless charging or powering brings several benefits:






Special efforts have also been dedicated to the development of wireless charging methods for the automotive industry, as the electric cars seem to be the solution for the future public transportation. The storage capacity of batteries is an extremely important element of how a device can be used. If we talk about battery-powered electronic equipment, the average au‐ tonomy is one factor that may be essential in choosing one device or another. Also, the amount of energy stored in the battery determines the maximum distance a car can travel. As a consequence, these batteries' charging operations occur at relatively short intervals, from several hours to at most several days, and the way this recharge is done is essential.

A distinction has to be made between the two forms of wireless power transmissions, as seen in terms of how the transmitted energy is used at the receiving point:



The second form of energy transfer is the subject of this book.

This book presents some of the fundaments of wireless power transfer using inductively coupled coils, high efficiency power integrated circuits, together with recent research results for dynamic wireless power transfer for in-motion objects or vehicles.

The book starts with a chapter dealing with fundaments and operating principles of induc‐ tively coupled wireless power transfer (ICWPT) systems. The chapter begins with an outline of the ICWPT systems, highlighting their major application areas, followed by present chal‐ lenges in the field. Then the operating principle of this technology is presented including system tuning, electrical equivalent circuit, power transfer capability, and power losses asso‐ ciated with the system. The chapter ends with detailed derivations of the system coupling efficiency, which is the most important portion of the efficiency analysis of ICWPT systems for both series and parallel-tuned secondary side.

Chapter 2 deals with various compensation methods for resonant coupling of the wireless energy transfer system. A proposed analysis is particularly relevant to any application where contactless battery charging is used. Main parameters that are investigated are effi‐ ciency, as well as circuit´s electrical variables (current and voltage). To analyze the most suitable solution of coupling compensation, the relevant equations are graphically interpret‐ ed for each discussed circuit topology. Finally, this chapter gives some recommendations on how to design wireless power transfer system with the highest possible efficiency for given set of system parameters (switching frequency, transmitting distance).

Chapter 3 presents a wireless power receiver for inductive coupling and magnetic resonance applications. An active rectifier with shared delay locked loop (DLL) is proposed to achieve the high efficiency for different operation frequencies. In the DC-DC converter, the phaselocked loop is adopted for the constant switching frequency in the process, voltage, and temperature variation to solve the efficiency reduction problem, which results in the heat problem. An automatic mode switching between pulse-width modulation and pulse-fre‐ quency modulation is also adopted for the high efficiency over the wide output power range. This chip is implemented using 0.18 μm BCD technology with an active area of 5.0 mm x 3.5 mm. The maximum efficiency of the active rectifier is 92% and the maximum effi‐ ciency of the DC-DC converter is about 92 when the load current is 700 mA.

Chapter 4 focuses on a wireless power transmission system based on magnetic resonance coupling circuit. Mathematical expressions of optimal coupling coefficients are examined by the coupling model. Equivalent circuit parameters are calculated by Maxwell 3D software, and then equivalent circuit was solved by MATLAB. The transfer efficiency of the system was derived by using the electrical parameters of the equivalent circuit. The system efficien‐ cy was analyzed depending on the different air gap values for various characteristic impe‐ dances, by using PSIM circuit simulation software.

Chapter 5 describes a microwave power transmission scheme based on retro-reflective beamforming. In the retro-reflective beamforming, wireless power transmission is guided by pilot signals. To be specific, one or more than one mobile device(s) broadcast pilot signals to their surroundings, and based upon analyzing the pilot signals, a wireless power trans‐ mitter delivers focused power beam(s) onto the mobile device(s). Preliminary numerical and experimental results are presented to demonstrate the feasibility of the proposed retro-re‐ flective beamforming scheme. As microwave power transmission has the potential to supply wireless power to portable/mobile electronic devices over long distances (on the order of meters or even kilometers) efficiently, several technical challenges remain to be resolved to accomplish practical microwave power transmission systems, including (i) minimizing pow‐ er loss due to microwave propagation, (ii) preventing humans and other electrical systems from exposure to excessive microwave radiation, and (iii) reconfiguring wireless power transmission in reaction to environmental changes (such as physical movements of portable devices) in real time.

The second form of energy transfer is the subject of this book.

VIII Preface

for both series and parallel-tuned secondary side.

dances, by using PSIM circuit simulation software.

for dynamic wireless power transfer for in-motion objects or vehicles.

set of system parameters (switching frequency, transmitting distance).

ciency of the DC-DC converter is about 92 when the load current is 700 mA.

This book presents some of the fundaments of wireless power transfer using inductively coupled coils, high efficiency power integrated circuits, together with recent research results

The book starts with a chapter dealing with fundaments and operating principles of induc‐ tively coupled wireless power transfer (ICWPT) systems. The chapter begins with an outline of the ICWPT systems, highlighting their major application areas, followed by present chal‐ lenges in the field. Then the operating principle of this technology is presented including system tuning, electrical equivalent circuit, power transfer capability, and power losses asso‐ ciated with the system. The chapter ends with detailed derivations of the system coupling efficiency, which is the most important portion of the efficiency analysis of ICWPT systems

Chapter 2 deals with various compensation methods for resonant coupling of the wireless energy transfer system. A proposed analysis is particularly relevant to any application where contactless battery charging is used. Main parameters that are investigated are effi‐ ciency, as well as circuit´s electrical variables (current and voltage). To analyze the most suitable solution of coupling compensation, the relevant equations are graphically interpret‐ ed for each discussed circuit topology. Finally, this chapter gives some recommendations on how to design wireless power transfer system with the highest possible efficiency for given

Chapter 3 presents a wireless power receiver for inductive coupling and magnetic resonance applications. An active rectifier with shared delay locked loop (DLL) is proposed to achieve the high efficiency for different operation frequencies. In the DC-DC converter, the phaselocked loop is adopted for the constant switching frequency in the process, voltage, and temperature variation to solve the efficiency reduction problem, which results in the heat problem. An automatic mode switching between pulse-width modulation and pulse-fre‐ quency modulation is also adopted for the high efficiency over the wide output power range. This chip is implemented using 0.18 μm BCD technology with an active area of 5.0 mm x 3.5 mm. The maximum efficiency of the active rectifier is 92% and the maximum effi‐

Chapter 4 focuses on a wireless power transmission system based on magnetic resonance coupling circuit. Mathematical expressions of optimal coupling coefficients are examined by the coupling model. Equivalent circuit parameters are calculated by Maxwell 3D software, and then equivalent circuit was solved by MATLAB. The transfer efficiency of the system was derived by using the electrical parameters of the equivalent circuit. The system efficien‐ cy was analyzed depending on the different air gap values for various characteristic impe‐

Chapter 5 describes a microwave power transmission scheme based on retro-reflective beamforming. In the retro-reflective beamforming, wireless power transmission is guided by pilot signals. To be specific, one or more than one mobile device(s) broadcast pilot signals to their surroundings, and based upon analyzing the pilot signals, a wireless power trans‐ mitter delivers focused power beam(s) onto the mobile device(s). Preliminary numerical and experimental results are presented to demonstrate the feasibility of the proposed retro-re‐ flective beamforming scheme. As microwave power transmission has the potential to supply Finally, Chapter 6 presents the development of dynamic wireless power transfer (DWPT) to solve two major bottlenecks, which are battery limitation and infrastructure requirements in the commercialization of electric vehicles (EV). DWPT system in urban area ensures uninter‐ rupted power supply for EV, whether during parking, stopping at traffic light or on the run. The technology is able to extend or even provide infinite driving range with significantly reduced battery capacity. Precious space in cities and urban areas are conserved with an un‐ derground power supply network. On the other hand, railways have become indispensable for public transportation in cities and towns, to reduce pollution and traffic congestion. Wireless power transfer for train is safer and more robust than any other known method. The construction of new high-speed railway systems will be less hassle as pantograph and power rails are no longer needed. This chapter provides a review of the latest research and developments of dynamic wireless power transfer for urban EV and electric train (ET). Fol‐ lowing are the key technology issues discussed: (1) power rails and pickups, (2) segmenta‐ tions and power supply schemes, (3) circuit topologies and dynamic impedance matching, (4) control strategies, and (5) suppression of electromagnetic interference.

By presenting both state-of-the-art of the wireless power transfer technologies together with some new challenges, such as microwave and dynamic wireless power transfer, this book reaches its goal of being a short collection of current trends in this top domain, completing the series of books published by InTech, a valuable source of information for engineers and researchers, and anyone dealing with new technologies.

> **Eugen Coca** Stefan cel Mare University of Suceava Romania

**Section 1**
