Due to limitations of low power density, high cost, heavy weight, etc., the development and application of battery-powered devices are facing with unprecedented technical challenges. As a novel pattern of energization, the wireless power transfer (WPT) offers a band new way to the energy acquisition for electric-driven devices, thus alleviating the over-dependence on the battery. This paper presents an overview of WPT techniques with emphasis on working mechanisms, technical challenges, metamaterials, and classical applications. Focusing on WPT systems, this paper elaborates on current major research topics and discusses about future development trends. This novel energy transmission mechanism shows significant meanings on the pervasive application of renewable energies in our daily life.

Wireless Power Transfer—An Overview

The profitable commercialization and fast adoption of electrified transportation require fast, economical, and reliable charging infrastructure. This paper provides a comprehensive, state-of-the-art review of all the wireless charging technologies for electric vehicle (EVs), characteristics and standards available in the open literature, as well as sustainable implications and potential safety measures. A comparative overview of conductive charging and wireless charging is followed by a detailed description of static wireless charging, dynamic wireless charging (DWC), and quasi-DWC. Roadblocks, such as coil design of power pads, frequency, power level limitations, misalignment, and potential solutions, are outlined. The standards are then tabulated to deliver a coherent view of the current status, followed by an explanation of the crux of these standards. Necessity and progress in the standardization of wireless charging systems are then deliberated. Vehicle-to-grid application of wireless charging is reviewed followed by an overview of economic analysis, social implications, the effect on sustainability, and safety aspects to evaluate the commercial feasibility of wireless charging. This paper will be highly beneficial to research entities, industry professionals, and investment representatives as a ready reference of the wireless charging system of EVs, with information on important characteristics and standards.

A Comprehensive Review of Wireless Charging Technologies for Electric Vehicles

Electric vehicles (EVs) are regarded as one of the most effective tools to reduce the oil demands and gas emissions. And they are welcome in the near future for general road transportation. When EVs are connected to the power grid for charging and/or discharging, they become gridable EVs (GEVs). These GEVs will bring a great impact to our society and thus human life. This paper investigates and discusses the opportunities and challenges of GEVs connecting with the grid, namely, the vehicle-to-home (V2H), vehicle-to-vehicle (V2V), and vehicle-to-grid (V2G) technologies. The key is to provide the methodologies, approaches, and foresights for the emerging technologies of V2H, V2V, and V2G.

Opportunities and Challenges of Vehicle-to-Home, Vehicle-to-Vehicle, and Vehicle-to-Grid Technologies

Near-field magnetic wireless systems have distinct advantages over their conventional far-field counterparts in water-rich environments, such as underwater, underground, and in biological tissues, due to lower power absorption. This paper presents a comprehensive review of near-field magnetic wireless power transfer (WPT) and communication technologies in a variety of applications from general free-space systems, to implantable biomedical devices we find of particular interest. To implement a fully wirelessly-powered implantable system, both high-efficiency power transfer and high-rate data communication are essential. This paper first presents the history and the fundamentals of near-field WPT and communication in free-space systems, followed by technical details for their specific use in implantable biomedical devices. Finally, this paper reviews recent advances in simultaneous wireless information and power transfer and highlights their applications in implantable biomedical systems. The knowledge reviewed in the paper could provide intuition in the design of various wireless and mobile systems such as wireless body area networks, small-cell 5G cellular, as well as in-body biomedical applications, especially for efficient power and data management and higher security.

Review of Near-Field Wireless Power and Communication for Biomedical Applications

In this paper, three control schemes with variable switching frequencies are proposed and analyzed for the paralleled voltage source inverters (VSIs) fed permanent magnet synchronous motor (PMSM) drive. The proposed schemes could be applied in the low-speed operation region of high-power drive system, where the frequency modulation index is high. First, the field-oriented control (FOC) with phase-shifted chaotic space vector modulation (SVM) under synchronous frame and the FOC with phase-shifted chaotic sinusoidal pulse width modulation under stationary frame is proposed for the paralleled VSIs fed PMSM drive. The proposed phase-shifted chaotic PWM schemes not only eliminate specific switching harmonics completely but also suppress all remaining switching harmonic peaks in the spectrum. The avoidance of inherent circulating current is also considered in designing these two schemes. Second, the direct torque control (DTC) for the paralleled VSIs fed PMSM drive is proposed with circulating current suppression. Besides inheriting the advantages of DTC, the output currents of paralleled VSIs are kept balanced. The working principles of these three methods are presented in detail. Experimental results on a laboratory prototype are given to verify the validity of the three proposed control schemes for the paralleled VSIs fed PMSM with variable switching frequencies.

Field-Oriented Control and Direct Torque Control for Paralleled VSIs Fed PMSM Drives With Variable Switching Frequencies

This paper presents a novel energy encryption strategy for wireless power transfer (WPT) systems, which can effectively improve the security performance of wirelessly transferred energy. In a WPT system, energy is expected to transfer to specific receptors as well as to switch off other unauthorized energy transmission channels, so the security of energy transmission is an important issue. In the proposed secure WPT system, the energy is encrypted by chaotically regulating the frequency of the power source. Then, the authorized receptor can receive the energy by simultaneously adjusting the circuit to decrypt the encrypted energy based on the security key obtained from the power supply, while the unauthorized receptor cannot receive the energy without knowledge of the security key. Hence, a secure energy transmission channel is established to effectively prevent unauthorized receptors from stealing the energy. In this paper, both simulation and experimental results are provided to verify the validity of the proposed encrypted WPT system.

Energy Encryption for Wireless Power Transfer

This paper presents a homogeneous wireless power transfer (WPT) technique to continuously energize the moving target. Due to the mobility of the charging target, the misalignment between the primary and secondary coils inevitably deteriorates the energy transfer performance by adopting the conventional WPT technique, so the constant energization mechanism is the most important issue for move-and-charge systems. The proposed homogeneous WPT technique utilizes the alternate winding design to gaplessly assemble primary coils, aiming to enhance the magnetic flux density. Besides, the vertical-and-horizontal secondary coil is also implemented to further improve the capability of acquiring energy for charging targets, especially in the area of the coils gap. In such ways, the proposed homogeneous WPT technique can effectively fulfil a continuous charging mechanism for moving targets. Also, this paper deduces the equivalent circuit model to analyze the mutual effect among multiple primary coils, which offers the theory-based view for the design of move-and-charge systems. Besides, both simulation and experimental results are provided to verify the feasibility of the proposed homogeneous WPT technique for move-and-charge systems.

Homogeneous Wireless Power Transfer for Move-and-Charge

In this paper, the concept of double stators and the concept of magnetic gears are artfully integrated to form a novel class of machines. By utilizing the modulation-ring structure, the proposed machines can modulate the high-speed rotating armature field of the stators to match the low-speed rotating permanent-magnet (PM) field of the rotor. Hence, the machines readily achieve the low-speed high-torque merit. In addition, the fractional-slot structure can be adopted for the inner-stator design to remove the modulation-ring of the inner stator. Two possible machine structures are discussed and compared. Their characteristics and performances are calculated by using the time-stepping finite-element-method. The results well verify the validity of the proposed machine design.

Novel Design of Double-Stator Single-Rotor Magnetic-Geared Machines

This paper proposes and implements the concept of flexible induction heating based on the magnetic resonant coupling (MRC) mechanism. In conventional induction heating systems, the variation of the relative position between the heater and workpiece significantly deteriorates the heating performance. In particular, the heating effect dramatically reduces with the increase of vertical displacement or horizontal misalignment. This paper utilizes the MRC mechanism to effectuate flexible induction heating; thus, handling the requirements of varying vertical displacement and horizontal misalignment for various cooking styles. Differing from a conventional induction heating, the proposed induction heating adopts one resonant coil in the heater and one resonant coil in the workpiece, which can significantly strengthen the coupling effect, and, hence, the heating effect. Both the simulation and experimental results are given to validate the feasibility and flexibility of the proposed induction heating.

Zhen Zhang

Papers

Wireless Power Transfer—An Overview

Energy Encryption for Wireless Power Transfer

Homogeneous Wireless Power Transfer for Move-and-Charge

Novel Design of Double-Stator Single-Rotor Magnetic-Geared Machines

Flexible Induction Heating Using Magnetic Resonant Coupling