Wireless Power Transfer: Theory, technology, and applications
Wireless Power Transfer (WPT) enables power to be transferred from a grid or storage unit to a device without the need for cable connections. This can be performed by inductive coupling of magnetic fields as well as by direct radiative transfer via beams of electromagnetic waves, commonly radiowaves, microwaves or lasers. Inductive coupling is the most widely used wireless technology with applications including charging handheld devices, RFID tags, chargers for implantable medical devices, and proposed systems for charging electric vehicles. Applications of radiative power transfer include solar power satellites and wireless powered drone aircraft. This book covers the very latest in theory and technology of both coupling and radiative wireless power transfer. Topics covered include the basic theory of inductive coupling and resonance coupling WPT; multi-hop WPT; circuit theory for wireless couplers; inverter/ rectifier technologies for WPT systems; basic theory of WPT via radio waves; technologies of antenna and phased array for WPT via radio waves; transmitter/rectifier technologies for WPT via radio waves; applications of coupling WPT for electric vehicle charging; applications of long-distance WPT; and biological interactions of electromagnetic fields and waves.
Inspec keywords: electric vehicles; transmitters; radiofrequency power transmission; prosthetics; electromagnetic interference; antenna phased arrays; inductive power transmission; waveguide couplers; invertors; rectifiers
Other keywords: wireless couplers; transmitter-rectifier technologies; electromagnetic fields; wireless power transfer; electric vehicle; biological issue; implantable medical device; radio waves; inductive coupling; antenna; inverter-rectifier technologies; phased array; circuit theory; resonance coupling WPT system; long-distance wireless power transfer; electromagnetic interference; multihop wireless power transmission
Subjects: Prosthetics and orthotics; DC-AC power convertors (invertors); Power electronics, supply and supervisory circuits; Waveguide and microwave transmission line components; General electrical engineering topics; AC-DC power convertors (rectifiers); Electromagnetic compatibility and interference; Transportation; Antenna arrays; Wireless power transmission
- Book DOI: 10.1049/PBPO112E
- Chapter DOI: 10.1049/PBPO112E
- ISBN: 9781785613463
- e-ISBN: 9781785613470
- Page count: 250
- Format: PDF
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Front Matter
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1 Introduction
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In this book, the theory, techniques, and applications of WPT are introduced. After the introduction, the theory of coupling WPT is described. Then, we discuss circuit technologies for the coupling WPT. Next, the theory and techniques of WPT via radio waves are explained, and numerous practical WPT applications are introduced. Finally, important issues in WPT, including safety problems, are discussed.
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2 Basic theory of inductive coupling
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The noncontact electricity transmission method for supplying electricity to an electrical apparatus is based on Faraday's law and is a recent (<20 years old) development in the field of household appliances. The inductive coupling method is based on electromagnetic induction and was developed by M. Faraday in 1831. A recent application of the technology is the wireless power transfer (WPT) system. Based on the current energy situation, interest in electric vehicles (EVs) has increased, and WPT has attracted attention as a next-generation technology for charging of EV batteries. The noncontact electricity transmission technique has also attracted attention for medical applications. This chapter explains the basic characteristics of WPT systems and the basic theory of inductive coupling [1-7].
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3 Basic theory of resonance coupling WPT
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Wireless power transfer (WPT) technology has two origins of technical background. One is power electronics technology, in which WPT mechanism is considered as a transformer. The other is radio frequency (RF) technology, in which WPT mechanism is considered as a coupling of resonators. The aim of this chapter is to unveil the essence of coupled-resonant WPT by introducing a unified model that enables us to understand power electronics-based WPT and RF-based WPT in the same manner. In the first part of this chapter, unified model of resonance coupling WPT is conducted. This model enables us to understand the mechanism of resonant WPT system from the viewpoint of electric/magnetic coupling and resonance. In the later part, generalized WPT model is conducted. This model represents the whole WPT system including RF inverter and rectifier. By using this model, various kinds of WPT system can be explained from the viewpoint of impedance matching, resonance, and coupling.
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4 Multi-hop wireless power transmission
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In this chapter, the design methods of multi-hop wireless power transmission are described. First, the characteristics of multi-hop wireless power transmission are overviewed. Based on that, a design method based on bandpass filter (BPF) theory and a design method for realizing efficiency maximization in arbitrary hop are derived. Power efficiencies with the design theories presented here are evaluated in Section 4.6.
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5 Circuit theory on wireless couplers
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This chapter first introduces kQ formulas of simple inductive and capacitive couplers by way of their equivalent circuits. We then derive the optimum load impedance formula that brings the coupler into play at its best efficiency. The formulas are finally generalized to a unified theory that can apply to any kind of coupler represented by a two-port reciprocal black box.
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6 Inverter/rectifier technologies on WPT systems
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This chapter introduces a design theory of optimal magnetic-coupling wireless power transfer (WPT) systems from circuit theory viewpoint. WPT systems are generally divided into three parts: DC/AC inverter, coupling part, and AC/DC rectifier. For designs of the high-efficiency WPT systems, it is important to reduce power losses in each part. This chapter also introduces high-efficiency DC-AC inverters and AC-DC rectifiers, which achieve high power conversion efficiency at high frequencies, in particular, due to soft-switching-condition satisfactions. It is, however, not sufficient even if each part is optimized individually. Because a certain part affects other parts, it is quite important to design the optimal WPT system as an integrated system consisting of three parts, which is shown through a design example of the class-E2 WPT system.
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7 Basic theory of wireless power transfer via radio waves
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Combining the magnetic and electric fields, an electromagnetic field can wirelessly transfer power to a receiver at longer distances. The fields create an electromagnetic wave when the wavelength of the field or the wave becomes shorter. We often use electromagnetic waves with frequencies in the MHz-GHz range. When a high-frequency electromagnetic wave is created, power can be wirelessly transferred to a distant receiver. The electromagnetic waves and fields were originally based on Ampere's law and Faraday's law; however, they can be better described by Maxwell's equations.
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8 Technologies of antenna and phased array for wireless power transfer via radio waves
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The idea of transferring power over long distances via radio waves has emerged shortly after the development of high-power microwave amplifiers. The potential applications and impact of wireless power transmission (WPT) has motivated an always increasing interest from the academic and industrial communities in the research and development of effective WPT transmitting and receiving devices. Within such a framework, this chapter is aimed at introducing and formulating the problem of designing WPT antennas and arrays for power transmission via radio waves, and at illustrating the theoretical motivations, fundamentals, and technological guidelines behind state-of-the-art strategies for the synthesis of such systems. A discussion on the current trends and envisaged development within this research area will be also provided.
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9 Transmitter/rectifier technologies in WPT via radio waves
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As described in Chapter 6, an inverter circuit with lumped elements is always applied for coupling wireless power transfer (WPT) because its frequency is usually in the kHz-MHz range and its wavelength is very low compared to the circuit size. As described in Chapters 7 and 8, radio waves with frequencies in the GHz range that are below tens of cm-1 are used for WPT to extend the WPT distance. At frequencies above 1 GHz, the size of the circuit and the wavelength are essentially the same; therefore, distributed constant lines are often applied to the circuit at frequencies greater than GHz instead of the lumped elements (Figure 9.1). We must consider a phase and an amplitude at each point in the circuit and the characteristic impedance of the circuit given by the amplitude and the phase of the voltage and current in the circuit. We should additionally consider parasitic capacitances and inductances at GHz frequencies. While the inverter circuits and design method described in Chapter 6 can be applied for WPT via radio waves, other transmitter/receiver circuits and design methods with the distributed constant lines are more suited for WPT via radio waves and should be used instead of the circuits described in Chapter 6.
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10 Applications of coupling WPT for electric vehicle
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Availability to deploy wireless power transfer (WPT) on electric vehicle (EV) has opened at the report of MIT Team at 2007 where they proved wide and variable airgap power transfer. That is called “MIT's revolution or Columbus's egg (2007)”[1]. After the MIT report, many concept EV cars with WPT capability have displayed and demonstrated at various motor shows. At Tokyo Motor Show 2011 Japan, many Original Equipment Manufacturers (OEMs), such as Toyota, Nissan, Mitsubishi motors, Yamaha, and GM, displayed their concept EVs with WPT option [2]. At next year of the Tokyo Motor Show 2011, at New York International Auto Show 2012, Nissan announced that they will deliver the Infiniti LE Concept with the wireless charging option within 24 months [3]. It was doubtless the world first announcement to install the WPT system on mass production passenger EV. Unfortunately the plan does not realized.
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11 Applications of long-distance wireless power transfer
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In principle, the distance of wireless power transfer (WPT) via radio waves from a transmitting antenna to a receiving one can be extended if the medium of wave propagation is lossless, e.g., vacuum in space. Technically, the distance limitation of WPT via radio waves is dominated by the power required by users as well as the limitation of system size and efficiency in practical applications. It is easy to develop multiuser WPT systems using WPT via radio waves because they are electromagnetically uncoupled and no interference between circuit parameters at a transmitter occurs even with increasing number of users. Besides, since the beam efficiency between a transmitting antenna and a receiving one is not high, multiuser WPT systems are also suitable when WPT systems via radio waves are applied in far field.
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12 Biological issue of electromagnetic fields and waves
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Wireless communication devices emit nonionizing electromagnetic radiofrequency (RF) fields in the range of 300 MHz to 300 GHz, raising public concern regarding the increasing use of mobile phones and their potential health related risks. The intermediate frequency (IF) EMF (300 Hz to 10 MHz) is also now widely used for wireless power transmission (WPT) or domestic kitchen appliances such as induction heating cooking. Unfortunately, although plenty of research has been conducted on RF, little information exists on the potential health effects associated with the exposure to IF magnetic fields. With growing concerns regarding the potential health hazards, it has become necessary to investigate the risks of IF magnetic fields in more detail.This chapter discusses the biological effects of IF and RF exposure. This chapter is divided into the following three parts: epidemiological study, animal study, and cellular study. In the RF field, the frequency of 2.45 GHz is mainly discussed because of the future use of WPT.
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13 Impact of electromagnetic interference arising from wireless power transfer upon implantable medical device
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Wireless power transfer systems (WPTSs) using nonradiative resonant coupling have attracted considerable research attention and are expected to achieve novel wireless charging and power supply functions for low-and high-power applications such as home appliances, electric vehicles (EVs), and other electric systems. Because these systems can generate high-strength reactive electromagnetic fields (EMFs), electromagnetic interference (EMI) issues and human safety must be assessed.
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Back Matter
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