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

Wireless charging is a technology of transmitting power through an air gap to electrical devices for the purpose of energy replenishment. The recent progress in wireless charging techniques and development of commercial products have provided a promising alternative way to address the energy bottleneck of conventionally portable battery-powered devices. However, the incorporation of wireless charging into the existing wireless communication systems also brings along a series of challenging issues with regard to implementation, scheduling, and power management. In this paper, we present a comprehensive overview of wireless charging techniques, the developments in technical standards, and their recent advances in network applications. In particular, with regard to network applications, we review the static charger scheduling strategies, mobile charger dispatch strategies and wireless charger deployment strategies. Additionally, we discuss open issues and challenges in implementing wireless charging technologies. Finally, we envision some practical future network applications of wireless charging.

Wireless Charging Technologies: Fundamentals, Standards, and Network Applications

Wireless power transfer system (WPTS)-based wireless electric vehicles, classified into roadway-powered electric vehicles (RPEVs) and stationary charging electric vehicles (SCEVs), are in the spotlight as future mainstream transportations. RPEVs are free from serious battery problems such as large, heavy, and expensive battery packs and long charging time because they get power directly from the road while moving. The power transfer capacity, efficiency, lateral tolerance, electromagnetic field, air-gap, size, weight, and cost of the WPTSs have been improved by virtues of innovative semiconductor switches, better coil designs, roadway construction techniques, and higher operating frequency. Recent advances in WPTSs for RPEVs are summarized in this review paper. The fifth- and sixth-generation online electric vehicles, which reduce infrastructure cost for commercialization, and the interoperability between RPEVs and SCEVs are addressed in detail in this paper. Major milestones of the developments of other RPEVs are also summarized. The rest of this paper deals with a few important technical issues such as coil structures, power supply schemes, and segmentation switching techniques of a lumped inductive power transfer system for RPEVs.

Modern Advances in Wireless Power Transfer Systems for Roadway Powered Electric Vehicles

More than a century-old gasoline internal combustion engine is a major contributor to greenhouse gases. Electric vehicles (EVs) have the potential to achieve eco-friendly transportation. However, the major limitation in achieving this vision is the battery technology. It suffers from drawbacks such as high cost, rare material, low energy density, and large weight. The problems related to battery technology can be addressed by dynamically charging the EV while on the move. In-motion charging can reduce the battery storage requirement, which could significantly extend the driving range of an EV. This paper reviews recent advances in stationary and dynamic wireless charging of EVs. A comprehensive review of charging pad, power electronics configurations, compensation networks, controls, and standards is presented.

Wireless Power Transfer for Vehicular Applications: Overview and Challenges

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

Roadway-powered electric vehicles (RPEVs) are attractive candidates for future transportation because they do not rely on large and heavy batteries but directly and efficiently get power while moving along a road. The inductive power transfer systems (IPTSs) that have been widely used for the wireless powering of RPEVs are reviewed in this paper. The development history of the IPTS is tracked from the origin of the RPEV in the 1890s to the recent RPEV. Throughout its 100-year history, the size, weight, efficiency, air gap, lateral tolerance, electromagnetic force, and cost of the IPTS have been substantially improved, and now RPEVs are becoming more widely commercialized. Important milestones of the developments of the IPTS and RPEVs are summarized in this paper, focusing on recent developments of on-line electric vehicles that were first commercialized in 2013.

Advances in Wireless Power Transfer Systems for Roadway-Powered Electric Vehicles

For commercialization of wireless stationary electric vehicles (EV) chargers, metal object detection (MOD) on a power supply coil and detection of position (DoP) of EVs are needed. In this paper, dual-purpose nonoverlapping coil sets for both MOD and DoP, which detect a variation of magnetic flux on the power supply coil, are newly proposed, where the proposed MOD and DoP methods make no contribution to any power losses. The existence of metal objects on the power supply coil is determined by an induced voltage difference of the nonoverlapping coil sets, whereas the position of the EV is determined by an induced voltage of the nonoverlapping coil sets. A sensing circuit, which has a variable resistor that is different from the conventional overlapping coil for MOD, can make the induced voltage difference zero even when the magnetic flux distribution is distorted by moving the pick-up coil. The proposed nonoverlapping coil sets with the sensing circuit have been demonstrated by simulations and experiments. When metallic coins and aluminum sheets are located on the power supply coil, the induced voltage difference of the coil sets, which is ideally zero without metal objects, significantly increases to 62.8 and 450 mV, respectively, which is more than ten times the value without metal objects throughout experiments. In addition, when the pick-up coil approaches the power supply coil, induced voltage of each coil set increased roughly 1.6 times at 10 cm air gap.

Dual-Purpose Nonoverlapping Coil Sets as Metal Object and Vehicle Position Detections for Wireless Stationary EV Chargers

An ultraslim S-type power supply rail, which has a width of only 4 cm, for roadway-powered electric vehicles (RPEVs) is proposed in this paper. The cross section of the core has a thin S-shape, and a vertically-wound multiturn coil is displaced inside the core. In this way, the most slim power supply rail is designed, which is crucial for the commercialization of RPEVs. The construction of roadway infrastructure, which is responsible for more than 80% of the total deployment cost for RPEVs, can be much easier when the width of the power supply rail is so small. To increase portability and to minimize construction time, a foldable power supply module is also proposed in which flexible power cables connect each foldable power supply module such that no connectors are needed during deployment. An effective winding method for minimizing the cable length is proposed, and an optimum core thickness of the proposed power supply rail is determined by FEA simulations and verified by a prototype power supply module. By virtue of the ultraslim shape, a large lateral displacement of 30 cm at an air gap of 20 cm was experimentally obtained, which is 6 cm larger than that of the I-type power supply rail. In addition to the larger lateral displacement, it is estimated that the S-type one has lower EMF than the I-type one because the width of the S-type one is narrower than that of I-type one. The maximum efficiency, excluding the inverter, was 91%, and the pick-up power was 22 kW.

Ultraslim S-Type Power Supply Rails for Roadway-Powered Electric Vehicles

A narrow-width power-invariant inductive power transfer system (IPTS) along the driving direction is newly proposed in this paper. The conventional I-type power supply rail for on-line electric vehicles (OLEVs) has a very narrow power supply rail with 10-cm width and exposes pedestrians to a very low electromagnetic field due to its alternatively arranged magnetic poles along the driving direction of electric vehicles; however, it has a major drawback: Sinusoidal variation of the induced pick-up voltage depending on pick-up positions on the power supply rail along driving direction. To overcome this disadvantage, a dq -power supply rail fed by two high-frequency ac currents of the d -phase and q -phase is introduced in this paper. The d -phase and q -phase magnetic poles are alternatively arranged in a line; hence, the induced voltage of a pickup becomes spatially uniform. The power invariant characteristic of the proposed IPTS for OLEV has been verified by analysis, simulations, and experiments. A practical winding method is suggested as well.

Uniform Power I-Type Inductive Power Transfer System With DQ -Power Supply Rails for On-Line Electric Vehicles

In this paper, a metal object detection (MOD) system, a kind of foreign object detection (FOD), which is based on mistuned resonant circuits and utilizes the variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers. The sensing pattern that consists of multiple loop coil sets is mounted on the transmitting (Tx) pad of an EV charger, where a loop coil set has two coils connected in series with the opposite polarity to cancel out the induced voltage generated by the Tx coil. Variation of self-inductance of the loop coil set is detected by a parallel-resonant circuit, driven by a current source and operating at near 1 MHz, in order to enhance the resolution of the proposed MOD system. To increase the detection sensitivity of the proposed MOD system, instead of an exact resonant frequency, a mistuned operating frequency near the –3 dB point is utilized for the parallel-resonant circuit. In this way, the proposed MOD system can detect very small metal objects regardless of their position and orientation on the Tx coil without any blind zone. Through simulations and experiments, it is found that the proposed MOD system detects not only horizontal but also standing upright metal objects. A prototype MOD system, operating at 85 kHz to satisfy the standard J2954, was fabricated to verify its feasibility. The results showed that output voltage change of the proposed MOD system becomes 22.7% for a piece of the aluminum foil of 3 × 3 cm2 and 40.9% for 100 Korean Won coin.

Seog Y. Jeong

Papers

Advances in Wireless Power Transfer Systems for Roadway-Powered Electric Vehicles

Dual-Purpose Nonoverlapping Coil Sets as Metal Object and Vehicle Position Detections for Wireless Stationary EV Chargers

Ultraslim S-Type Power Supply Rails for Roadway-Powered Electric Vehicles

Uniform Power I-Type Inductive Power Transfer System With DQ -Power Supply Rails for On-Line Electric Vehicles

Self-Inductance-Based Metal Object Detection With Mistuned Resonant Circuits and Nullifying Induced Voltage for Wireless EV Chargers