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In this study, magnetic field emission (MFE) of the high-power double-D (DD) coil-based wireless charging system is investigated and a shielding technique is proposed. The MFE pattern produced by the DD coils is significantly different from the MFE of the unipolar (e.g., circular, square, or rectangular) coils, and the traditional aluminum shield does not suppress the MFE from the DD coils. This study shows that a conventional aluminum shield increases the MFE, and a magnetic shield effectively suppresses the MFE of the DD coils. Therefore, a magnetic shield consisting of high-permeability magnetic material, such as ferrites, nanocrystalline, etc., is proposed for the DD pads. The shielding effectiveness of the proposed shield is evaluated through finite-element analysis and verified through experiments. An 11-kW DD coil-based wireless charging system was used to test the proposed shielding technique. The experimental results show that a traditional aluminum shield increased the MFE by 29.8%, and the proposed magnetic shield suppressed the MFE by 50.5%. [ABSTRACT FROM AUTHOR]

An ideal transformer-like (IT-like) magnetic coupling wireless power transfer system is proposed in this article, which can achieve a large constant power and efficiency output over a wide transfer range. First, the general circuit model is presented along with the analysis of fundamental and harmonic current characteristics. Then, the IT-like operation mechanism with a fixed desired secondary-primary current amplitude ratio independent of mutual inductance is proposed, based on which the transfer range capable of both power and efficiency is greatly improved. The corresponding parameter criteria and implementation methods, including the zero-phase-angle mode and the zero-voltage-switching mode are derived and verified in a practical prototype. The experimental results show that the proposed system can take the output power, transfer efficiency, transfer range, and current characteristic into account at the same time, with strong position robustness and high tolerance to variable couplings. [ABSTRACT FROM AUTHOR]

In this letter, a novel magnetic coupler with high rotational misalignment tolerance is proposed for unmanned aerial vehicles (UAVs) wireless charging. The transmitting coil consists of an inner coil and an outer circular coil connected in series, which generates a horizontal magnetic field from the center to all periphery directions within the charging range. Then, to receive the flux effectively and to adapt to UAV's structure, a vertical square air-core coil is designed and attached to the landing gear. The proposed magnetic coupler can reduce significantly the magnetic fluxes penetrating through the body of the UAV, therefore mitigating electromagnetic interference with onboard devices. Simulation based on ANSYS Maxwell and experiments based on a laboratory prototype are carried out to validate the proposal. The results show that, the proposed magnetic coupler can transmit power in all 360° of rotational misalignments, and the output voltage of the wireless charging system fluctuates only 2% around the 48 V reference. [ABSTRACT FROM AUTHOR]

Wirelesscharging for electric vehicles (EVs) enjoys many benefits, such as convenience, safety, and automation. One of the major issues concerning EV wireless charging is misalignment tolerance along the door-to-door direction of the EV. This letter proposes a misalignment-tolerant dual-transmitter EV wireless charging system with a reconfigurable topology. At central positions, the system can be reconfigured to the S-S (series-series) topology where the two transmitting coils are connected in series to feed the load. At boundary positions, the two transmitting coils form the LCCC-S (inductor-capacitor-capacitor-capacitor-series) topology to enhance power transfer capability and tolerate weak couplings. In this way, not only the output power can be smoothed with door-to-door misalignment, but also wireless charging is guaranteed at weak couplings. Experimental results reveal that within the cover area of the transmitting coils, high-efficiency stable output can be achieved. [ABSTRACT FROM AUTHOR]

This article proposes a free-positioning omnidirectional wireless power transfer (WPT) system with a reticulated planar transmitter, which enables multiple receivers to be powered simultaneously in arbitrary positions and orientations. The reticulated planar transmitter is equipped with four interleaved and overlapped meander coils, thus, a three-dimensional (3-D) rotating magnetic field is generated with the designed excitation current. Therefore, only a planar single-coil (such as a loop-type coil) is required to realize free-positioning omnidirectional WPT. According to the theoretical modeling of the magnetic field, the excitation current that can generate a 3-D rotating magnetic field is given. To obtain a uniform and strong magnetic field distribution, the transmitter grid width is optimized. Furthermore, an excitation current modulation strategy based on phase-shift control is presented to regulate the amplitude of the excitation current. The experimental results show that the output power is greater than 13.1 W no matter how the center of the receiver moves or rotates freely within 400 × 400 mm. When five receivers are powered simultaneously in different positions and orientations, 82.5 W total output power and 55.6% efficiency can be achieved. The experimental results demonstrate that free-positioning omnidirectional WPT can be realized with only planar single-coil receivers by using the proposed reticulated planar transmitter and its excitation current modulation strategy. [ABSTRACT FROM AUTHOR]

Accurate estimation of mutual inductance in wireless power transfer (WPT) system is a prerequisite for accurate identification of load parameters, which is critical in system constant output and efficiency tracking control. In this article, a general load decoupling method for WPT system considering soft-start process and battery initial voltage is proposed. Moreover, a double-sided LCC topology is used to explain how to calculate the boundary conditions of load decoupling. Based on the proposed load decoupling method, a mutual inductance identification method is proposed for WPT system with double-sided LCC topology. Within the frequency range recommended, the unique solution of mutual inductance can be obtained by solving high-ordered equivalent impedance equation. In this case, there is no need to discuss the situation for multiple solutions. Based on the WPT prototype, the effectiveness of the proposed load decoupling method is verified, and parameter sensitivity of the identification method is analyzed in detail. Finally, the proposed method is experimentally verified. Results show that high identification accuracy can be achieved even when the coils are misaligned. Compared with the existing identification methods, the proposed method does not need any additional switches and auxiliary circuits, which reduces the complexity and system cost effectively. [ABSTRACT FROM AUTHOR]

The wireless power supply solution has shown great advantages in rail transit applications, such as maglev trains and trams. However, research works on designing the magnetic coupler for wireless charging system in rail applications, which is a crucial problem, are not sufficient. Considering the high power and lightweight requirements, this article selects the coaxial M-shape magnetic coupler with LCL/S compensation for railway applications, which contains the transmitting rail and the receiving coil wound on an M-shape magnetic core. First, analysis was conducted on the requirements for inductance parameters of the magnetic coupler under the circuit constraints, including transmission power, input and output voltages, and component electrical stress, etc. Then, the influence of the geometric parameters of the coil structure and misalignment on its inductance parameters is analyzed. Based on these analysis results, the design method for the M-type magnetic coupler based on the lightweight principal is proposed. The geometric parameters are designed following a certain sequence to minimize the number of iterations and FEM simulation parameter sweeps, making the design procedure suitable for engineering practice. According to the proposed method, the magnetic coupler for a 360 kW wireless charging tram is designed and implemented. Through simulations and experiments, the magnetic coupler is verified to be feasible for the system with light weight. [ABSTRACT FROM AUTHOR]

This article proposes a multiobjective optimization method of a primary double-D pad for inductive power transfer systems. First, a parametric sweep analysis is conducted to choose the crucial design parameters. Then, using the nondominated sorting genetic algorithm II, the structure of the double-D pad can be optimized based on two key objectives; ensuring a good coupling coefficient while minimizing the worst-case stray leakage magnetic fields. Several useful design guidelines are found from the optimization results, including how the dimensions of both the coil and layers affect the coupling coefficient and stray leakage magnetic fields around the pad. A practical coil suitable for wireless charging of electric vehicles at level 2, similar to that recommended in SAE J2954, is used as the reference and also as the starting point for the optimization. Two of the coil structures resulting from the optimization are chosen and investigated further to assess their performance with different secondary pad misalignments using finite element methods. Finally, an experimental setup is built to validate the optimal pad structures. [ABSTRACT FROM AUTHOR]

The voltage stress of compensation capacitors in the wireless charging system could be up to several kilovolts. Things get worse for the dynamic operating condition because the resonant current gets fluctuating with the rigid variations of the coupling condition. In this article, a constant resistance (CR) control scheme on a boost converter is proposed to mitigate receiver current stress, i.e., the peak currents in the resonant tank and the boost chopper inductor. The receiver-side dynamic wireless charging (DWC) system with a postregulated boost converter is introduced by the static operating waveforms. To investigate how speed affects current stress, a receiver-side current analytical model is established based on the closed-loop input admittance of boost and the dc circuit model of resonant tanks. The modeling results illustrate that the overstress problem is prone to occur at high-speed condition under constant current charging control. CR control, which shapes boost input current and voltage in phase, is adopted to address this problem. Comparative studies for full-range speeds and nonideal coupling conditions, conducted by the DWC simulator, show that uniform low-stress performance is obtained under CR control with the same amount of energy transferred. Maximum stress improvement on the receiver resonant current is 29% for ideal condition and 44% for a nonsinusoidal condition when driving at 80 km/h. [ABSTRACT FROM AUTHOR]

Simple but effective output voltage/current control schemes are essential for electric vehicle wireless charging systems (EVWCSs). This article proposes an EVWCS using interleaved boost converter (IBC) and flat solenoid coupler (FSC). The closed-loop control between the primary and secondary is realized by adjusting the duty cycle of the IBC. The currents and losses in the primary are reduced in the proposed system because the dc bus voltage in the primary is increased by using the IBC. The input current ripple is diminished owing to the interleaved structure. This article also proposes a parameter optimization method to obtain the optimal FSC. Without loss of generality, the total area of the transmitter (Tx) and receiver (Rx) is assumed to be constant, and the Tx is assumed to be larger than the Rx. A scale-down prototype whose output power is 500 W was built in the laboratory to verify the theoretical analysis. The output voltage of the prototype kept constant when the misalignment was 200 mm in the winding direction or 100 mm in the magnetic direction. A highest system efficiency, from dc input to dc output, of 90.1% was achieved when the power transfer distance was 170 mm. [ABSTRACT FROM AUTHOR]

Megahertz-frequency inductive wireless power transfer holds the promise of compact and efficient wireless power transfer. Unfortunately, due to high-frequency losses in wide-bandgap semiconductors and low-Q high-frequency coil designs, these systems are universally less efficient, on a dc–dc basis, than wireless power systems operating at conventional frequency regimes. This letter describes the design considerations for inductive wireless power transfer systems operating at 6.78 MHz. With a novel high-frequency resonant amplifier topology, a high-Q self-resonant coil structure, and a better understanding of Coss losses in wide-bandgap power semiconductors, we demonstrate 6.78- MHz wireless power transfer systems that achieve 95% dc–dc efficiency at power levels up to and beyond 1 kW. [ABSTRACT FROM AUTHOR]

In this article, a new direct ac–ac active-clamped half-bridge converter feeding a series–series compensated inductive charging system is proposed. The proposed converter eliminates the rectification stage and bulky life-limited electrolytic dc-link capacitors, resulting in an actual single-stage (ac-to-ac) conversion with low component. The operation principles, steady-state analysis, and design considerations of the proposed converter are presented in detail. Moreover, a new predictive dead-beat technique for input current control and a linear average charging current controller are developed for the proposed converter, which enables the unity power factor and charging current regulation. The performance of the proposed battery charger is validated through experimental results on a 1-kW field programmable gate array (FPGA)-controlled silicon carbide based laboratory prototype. [ABSTRACT FROM AUTHOR]

Power fluctuation caused by the coupling variation is frequently observed in a dynamic wireless charging (DWC) system. To solve this problem, a uniform power solution based on the I-type power supply rail and DQ-phase-receiver is proposed employing receiver-side control. The outputs of DQ-phase voltages are series connected after rectifications to get a higher but less-fluctuated voltage. For further eliminating the fluctuation, the dual-input buck converter with constant resistance control is utilized. The uniform power characteristic, benefiting from the individual control on DQ-phase voltages, is demonstrated under the proposed solution. The uniform power performance is verified on a 1.5-kW prototype with wide-range driving speeds and various practical nonideal conditions. Experimental results, obtained by the DWC simulator, indicate that the output fluctuation factors under the ideal condition are 1.37%, 3.19%, and 4.69% at the driving speeds of 10, 40, and 100 km/h, respectively. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) is an enabling technology for electric vehicles (EV), as it eliminates driver intervention during charging. Major challenges to the adoption of WPT systems include coil misalignment and large air-gap WPT, both of which degrade the transfer efficiency. To address these issues, this article presents a compact WPT charger for the rear of an EV, capable of correcting lateral misalignment $\Delta$ x using two integrated electromagnetic coils. The air-gap $\Delta$ y is reduced due to the rear placement of the charging pads. The variation in $\Delta$ y, however, increases due to vehicle parking accuracy, which impacts the operation of the electromagnetic coils. This article proposes a closed-loop three-stage position-correcting control algorithm capable of detecting the impedance and resonant frequency of the system, which, in conjunction with the electromagnetic coils, results in improved vehicle alignment. The experimental prototype achieves a peak dc–dc efficiency of 90.1% at 5 kW WPT. With $\Delta$ y = 50 mm, the electromagnetic coils laterally align the pads within 1.75 s and correct $\Delta$ x as large as 240 mm. The position-correcting control was successfully demonstrated in four parking scenarios with the charging pads being corrected to within a 10-mm radius of perfect alignment. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) has recently emerged as a prominent technology to liberate various applications with small devices from limited mobility and design constraints. Among various techniques, magnetic field focusing (MFF) with multiple transmit (Tx) coils have been known as a powerful solution to enhance the efficiency of power transfer to multiple receivers (Rxs) in midrange WPT. However, in such MFF techniques, even unintended Rx may suffer from unwanted power due to leakage, which may disrupt the operations of the devices. Motivated by this issue, in this article, we consider selective magnetic resonance coupling (MRC)-based WPT, which enables WPT systems to better shape power distribution only focusing on the intended Rxs while leakages to the unintended Rx are suppressed. To this end, we first formulate the selectivity requirement of WPT as an optimization problem. Then, we propose a method to obtain the optimal Tx voltage vector for simultaneous MFF and null-steering optimization. Simulation and experimental results validate the theoretical analysis and the proposed method in practical scenarios. [ABSTRACT FROM AUTHOR]

The mass and volume of wireless power transfer (WPT) systems for charging electric vehicles are directly related to the rated power of the system. The difficulties of high-power wireless charging are exacerbated by the need to meet the same practical constraints associated with vehicle integration as lower power systems. Therefore, more advanced techniques are necessary to improve power density and specific power of wireless charging systems for high-power applications. This article presents theory and analysis of three-phase inductive WPT systems with bipolar phase windings. Magnetic coupler topologies and the theoretical and practical aspects of series three-phase resonant compensation networks are discussed. The systems under consideration are designed to utilize rotating magnetic fields to achieve a power transfer characteristic that is temporally smoother than single-phase systems. Other benefits associated with rotating magnetic field based WPT, including reduced ferrite mass, filter component requirements, and electromagnetic field emissions, are discussed. Experimental results of a prototype system are presented in both aligned and misaligned configurations. The system is demonstrated transferring 50 kW with 95% dc-to-dc efficiency over a 150-mm airgap in the aligned case. On a per-pad basis, the magnetic couplers achieve a power density of 195 kW/m $^2$ and a specific power of 3.65 kW/kg. This article is accompanied by a video of the rotating magnetic field produced by a simulated three-phase WPT system. [ABSTRACT FROM AUTHOR]

A three-coil wireless charging system is proposed for full metal-cover smartphone applications. Considering the space limitation and other antennas in the smartphone, the receiver coil embedded in the smartphone is designed to be miniaturized as 16 mm × 65 mm. By integrating a series capacitance at the end of the 2-mm width narrow horizontal slot loading on the metal cover, the metal cover is converted to a relay coil of the three-coil system and wireless power transfer (WPT) through the metal cover is thus achieved. A prototype of the proposed three-coil system has been built and WPT through metal cover has been validated via experiment. The experimental results show that the prototype achieves 5 W output power with 71% coil-to-coil efficiency. [ABSTRACT FROM AUTHOR]

Expandable and flexible wireless power transfer (WPT) systems have been in demand in numerous industry applications, especially for dynamic chargers in electric vehicles. Those systems, however, bring about certain technical issues such as modulation technique and topology of the transmitter side, and transferred power profile of the transmitters. In this article, a new converter topology to drive closely spaced segmented dynamic wireless power transfer (DWPT) systems is proposed. The proposed converter can be expanded to cater for different number of transmitters, and it can provide a uniform transferred power profile throughout the path of transmitter coils, known as track. Furthermore, this article focuses on analyzing the operation of the converter and the effect of closely spaced transmitters over its operation. To show the effectiveness of the proposed topology and its modulation technique, the converter is simulated and experimentally tested using a laboratory prototype. The results are compared and analyzed, and their close agreement shows the validity of the proposed technique. [ABSTRACT FROM AUTHOR]

In high-power electric vehicle wireless charging systems, the charging distance is short, and the coupling is strong in order to increase the power density and reduce the coil size and the system cost. With a strong coupling, the receiver-side compensation can be eliminated, and a high efficiency can still be obtained. The inductor-capacitor-inductor-none (LCL-N) topology is formed with the LCL compensation on the primary side. The phase difference between the transmitter and receiver currents is larger than 90°, leading to the magnetic flux cancelation in the ferrites. Thus, the required ferrite thickness of the LCL-N topology is smaller than the fully-compensated topologies. Therefore, a compact, lightweight, and low-cost receiver structure is achieved with the omitted compensation and thinner ferrite. Moreover, the LCL-N topology can achieve zero voltage switching for all loading conditions, withstand open-circuit and short-circuit faults, and is suitable for constant-current and constant-voltage charging due to the fact that it has neither a CC nor a CV output characteristic. A 100-kW system is designed and simulated. A downscaled 1-kW system is implemented. The simulations and experimental results verify the effectiveness of the analysis. [ABSTRACT FROM AUTHOR]

In this paper, a detailed lumped model of the shield is developed, and an optimization method is proposed to minimize the shield loss while suppressing the emission within the standard limit. The electromagnetic emission in a wireless charging system (WCS) is a serious concern for health and safety, especially for medium- and high-power applications, where strong magnetic field propagates through a large air gap. Usually, a flat aluminum plate is used as a shield to suppress the emission outside the charging area. This field emission increases proportionally with the coil ampere turn; therefore, a much higher shield current is required to suppress the additional emission under the limit set by the International Commission on Non-Ionizing Radiation Protection. In this paper, a novel hybrid shield structure is proposed to limit the electromagnetic field (EMF) emission, as well as to minimize the shield loss. The proposed shielding is evaluated on a laboratory prototype of 7-kW WCS designed for electric vehicle application. The experimental result shows that, while suppressing the EMF under the limit, the shield loss has been reduced by 21% compared to the commonly used aluminum shield. [ABSTRACT FROM AUTHOR]

Battery-to-battery (B2B) wireless charging can take place in many scenarios, such as using a mobile phone to charge another mobile phone, wearable devices, or low-power sensor nodes. To facilitate this wireless power transfer (WPT) function with the minimum additional cost, we propose a monolithic reconfigurable bidirectional WPT transceiver designed for the first time in CMOS, which can be reconfigured between a differential class-D power amplifier (PA) and a full-wave rectifier. Meanwhile, we employed a maximum current charging mode to maximize the B2B charging efficiency, by directly charging the loading battery with the rectifier, and by powering the PA with the sourcing battery. Then, we reduced the number of cascaded WPT stages from five in the conventional design to three. This bidirectional WPT transceiver fabricated in 0.35 μm CMOS occupies 3.9 mm2 of silicon area. The bidirectional WPT function, verified at 6.78 MHz with only one off-chip capacitor, exhibits peak efficiencies of 91.5% and 58.6% for the receiver and the overall system, respectively, when the output power is 1.55 W. [ABSTRACT FROM AUTHOR]

This paper introduces a primary pad for wireless charging applications, which is able to transfer high power over large air gaps and is tolerant to lateral displacements suitable for electric vehicle charging applications. The developed pad is an improved solenoid designed specifically to address issues such as flux leakage and loss while retaining good coupling. It is a hybrid structure that consists of a combination of rectangular- or square-shaped coils and a central solenoid, all connected in series. When energized, it produces a single-sided, polarized flux similar to the flux pattern of the solenoid and double D (DDP) pads. The power transfer capability of this pad is investigated through finite-element analysis simulations. The results are compared first to a similar sized solenoid from which it was derived, and also a DDP primary pad and are verified through measurements on prototype systems in the laboratory. The aim of this paper is to provide an improved hybrid solenoid pad showing higher coupling factors and lower stray field emissions with a performance (coupling and stray field emissions) similar to that of DDPs. [ABSTRACT FROM AUTHOR]

The multiphase receiver for more steady output is proposed in this paper. The conventional power supply rail with multipole such as I-type, S-type, and n-type for dynamic wireless charging (DWC) system has a main drawback: the induced voltage of the double-D coil of receiver has a sinusoidal fluctuation along the driving direction and the fluctuation factor is 1.0. Therefore, the multiphase receivers including two-phase, three-phase, and four-phase receiver are proposed to solve the problem. The fluctuation factor, effective value (rms) of induced voltage and mutual inductance, cost, and loss of different numbers of phase in different connection modes are analyzed and compared. The applicable conditions of different types are given. The structure size of single-phase coil is optimized to achieve larger coupling coefficient. The influence of distance between phases on fluctuation factor and induced voltage (rms) are calculated and the design principle of the distance between phases is determined. Based on above research, design guideline for the multiphase receiver is proposed including the constraints of installation environment and the distribution of different phases. The structure size of single-phase coil and the distance between phases are optimized to improve the coupling coefficient and reduce cost, loss, and voltage level of resonator. Considering the practical application environment, a four-phase receiver of 10-kW DWC system is designed. A prototype system is also established and the analysis and simulation are verified. In the dynamic 10-kW experiment, the fluctuation factor is reduced to 0.146 from 0.3 of two-phase receiver and 1.0 of single-phase receiver. [ABSTRACT FROM AUTHOR]

The double-sided LCC topology provides a highly efficient compensation method for electric vehicle (EV) wireless charging systems. However, the two compensated coils occupy a large volume. In order to address the volume increase as well as to be compatible with unipolar coil structures, which are widely applied in EV wireless charging systems, an integration method is introduced in this paper. Aspect ratios of the compensated coils are studied to minimize the respective coupling effect. With the proposed integration method, the extra coupling coefficients are either eliminated or decreased to a negligible level. A wireless charging system with the proposed integration method is built and the experimental results show that the system resonates at 85 kHz and delivers 3.09 kW with a dc–dc efficiency of 95.49% at an air gap of 150 mm. Furthermore, a comparison with the integration method into bipolar coil structures is presented and the results demonstrate that the system with the proposed integration method is more immune to front-to-rear and vertical misalignments. [ABSTRACT FROM AUTHOR]

A wide-range ubiquitous wireless power environment, called a ubiquitous Wi-power zone, where any electric devices can be charged by three-dimensional (3-D)-omnidirectional wireless charging, is newly proposed in this paper. By virtue of the proposed direct-quadrature (DQ) transmitting (Tx) coils composed of multiple Tx modules with same size, a ubiquitous Wi-power zone having the transmitting (Tx) coils can be provided over wide-range 3-D space. In this area, a number of electric devices can be simultaneously charged during operation. Therefore, the proposed IPT is expected to be the next generation of wireless power transfer (WPT), as the internet of things (IoT), mobile devices, and sensor technologies evolve. For magnetic shielding behind the Tx coils and high power efficient operation of the proposed DQ Tx coils, providing an evenly distributed magnetic field, a conductive plate is adopted, and the effects of the conductive plate for the dipole coil structure were thoroughly evaluated by a 3-D FEM simulation. To create the proposed ubiquitous Wi-power zone, simulation-based optimum design procedures are established based on four design considerations and the optimized number of modularizations for the DQ Tx coils can be found by an optimum point of figure of merit (FoM). The DQ Tx module composed of the DQ Tx coils and series resonant capacitors was adopted as a standard unit of the proposed IPT so that different sizes and shapes of 3-D space can be utilized for universal use of the proposed ubiquitous IPT; hence, a general solution to create the proposed ubiquitous IPT is provided in this paper. A prototype 5 × 5 modularized IPT composed of 25 DQ Tx modules having the same size of ${\text{10 cm}} \times {\text{10 cm}}\times {\text{2 cm}}$ was fabricated and experimentally verified for a ${\text{1 m}}\times {\text{1 m}}\times {\text{0.7 m}}$ ubiquitous Wi-power zone. Experimental results showed that 95.5%, 92.1%, and 98.8% of high magnetic field uniformity for $z_{1}= {\text{25}}$  cm, 50 cm, and 75 cm, respectively, and 3-D omnidirectional wireless power delivery have been achieved; thus, meeting essential requirements for the proposed ubiquitous Wi-power zone. Nine Rx coils can be simultaneously charged with 14.2 W of total received load power and 8.2% power efficiency at $z_{1}= {\text{70}}$  cm. [ABSTRACT FROM AUTHOR]

Lightweight autonomous underwater vehicles (AUVs), powered by rechargeable batteries, are widely deployed in inshore surveying, environmental monitoring, and mine countermeasures. While providing valuable information in locations humans have difficulty accessing, limited battery capacity of such systems prevents extended mission times. In order to extend mission times, this paper proposes a three-phase wireless charging system that could be used in a field-deployable charging station capable of rapid, efficient, and convenient AUV recharging. Wireless charging should not, however, affect instrumentation located inside the AUV. Thus, a three-dimensional finite element analysis tool is employed to study the characteristics of magnetic fields inside the AUV during three-phase charging. Simulation results reveal that the magnetic field generated by the proposed three-phase coil structure is concentrated away from the center of the AUV, where instrumentation would nominally be located. Detailed circuit analysis and compensation method to achieve resonance on both transmitter's and receiver's sides are also given. To validate the proposed concept, a three-phase wireless charging system is developed. Experimental results demonstrate that the system is able to transfer 1.0 kW with a dc–dc efficiency of 92.41% at 465 kHz. [ABSTRACT FROM AUTHOR]

The technique of wireless power transfer (WPT) via magnetic coupling resonance provides a way to transfer power wirelessly to cardiac pacemakers from external source. For wireless charging system to be used in clinical environment, this paper gives priority consideration to three technical difficulties, i.e., implantation, efficiency, and safety. The LCC-C compensation topology for pacemaker wireless charger is presented, where only one secondary side resonance capacitor needs to be implanted, and resonance compensation parameters are derived. The compensation network can make the WPT system operate at stable resonance and high efficiency. The prototype of the wireless charging system for implantable cardiac pacemaker is developed, where a thin flexible receiving unit was designed to effectively shield eddy currents in the pacemaker shell. The experiments of wireless charging through pork tissues reveal that 3.072-W power can be received from a 3.919-W power source at 300 kHz, reaching a rather high WPT efficiency of 78.4%, such that the charging is fast, i.e., the 1050 mA·h, 4.2-V Li-ion battery voltage increases from 3.98 (80% residual capacity) to 4.2 V within only 27 min, and only 3.3 °C maximum temperature rise of the pork is in safe limits. The feasibility and safety of the charging system were further evaluated by simulations of specific absorption rate and temperature rise in human tissues and electromagnetic fields in the pacemaker case. [ABSTRACT FROM AUTHOR]

In this paper, a new ferrite-less wireless charging pad, called circular nonferrite pad, for roadway applications is introduced. The pad is characterized by having the ability to control leakage flux to reduce the electromagnetic fields outside the charging region. In addition, the pad shows low sensitivity to changes in the self-inductance due to secondary pad misalignment. A comparison of this new pad with similar-sized ferrite pads and single spiral couplers is presented. A formal mathematical description of the pad is shown here with finite element method simulations along with lab measurements to verify the validity of the models. The costs, advantages, and limitations of the new pad are also investigated. [ABSTRACT FROM AUTHOR]

Inductive power transfer is a highly attractive option for powering unmanned aerial or underwater vehicles, in harsh environments and while in continuous motion. This study presents a variable frequency controller for series–series compensated contactless chargers operating in dynamic conditions. The controller tracks, in real time, the frequency for which the output voltage is load independent. The criterion for that is the zeroing of the phase difference between the secondary current and the primary-side inverter output voltage. Control is performed by a phase-locked loop with optical communication between the two sides. Experimental results on a 1-kW prototype, for power transfer while in motion, show fast frequency response, along with steady output voltage, despite load variations. Comparison is performed with two other fixed frequencies of operation; the natural frequency of the primary resonant circuit and the maximum output power frequency at nominal gap. The proposed control is proven superior in terms of output power level and stability, as well as safety to highly misaligned conditions. [ABSTRACT FROM PUBLISHER]

There is a need for charging electric vehicles (EVs) wirelessly since it provides a more convenient, reliable, and safer charging option for EV customers. A wireless charging system using a double-sided LCC compensation topology is proven to be highly efficient; however, the large volume induced by the compensation coils is a drawback. In order to make the system more compact, this paper proposes a new method to integrate the compensated coil into the main coil structure. With the proposed method, not only is the system more compact, but also the extra coupling effects resulting from the integration are either eliminated or minimized to a negligible level. Three-dimensional finite-element analysis tool ANSYS MAXWELL is employed to optimize the integrated coils, and detailed design procedures on improving system efficiency are also given in this paper. The wireless charging system with the proposed integration method is able to transfer 3.0 kW with 95.5% efficiency (overall dc to dc) at an air gap of 150 mm. [ABSTRACT FROM PUBLISHER]

Recently, wireless charging via coupled magnetic resonances gains attention because it has a potential of efficient mid-range wireless charging. Here, functions such as sensing at the transmitter and wireless communication from the target are the essential elements to realize the standard wireless charging system. Currently, the sensing and communication protocol of hardware (i.e., high-frequency power source and antenna configuration) compatible with wireless charging is gaining attention in terms of cost and space reduction due to the use of common components in multiple functions. However, these protocols have the problem of narrow effective areas. Therefore, this paper presents a method for wide-area sensing and communication with slight modification of the configuration. The basic concept is to expand the effective area related to antenna Q factor by using the Q controllable antenna acting as though the Q factor increased. The underlying theory was described with electric circuit theory. The experimental results showed that the Q factor can be increased until the resonance collapses, and the increase of Q factor has the potential to widen the effective area of sensing and communication. [ABSTRACT FROM AUTHOR]

This paper focuses on the interoperability analysis of a resonating contactless charging system for electric vehicles (EVs). The design uses different inductive loops realized by industrial partners. It highlights an advanced electromagnetic modeling (EM) concerning the geometrical characteristics, the resonant topologies, and the control loop. It is shown that the EV chassis plays a major role in the calculation of the electrical parameters and the radiation of the interoperable system. Furthermore, the position of the interoperable magnetic couplers with respect to the EV (middle or backend) has an important effect on the values of the coupling factor and also for the radiation of the system. Finally, an efficiency of 90% is realized in the experimental test with the interoperability which gives flexibility for the driver to use charging stations with different technologies. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency wireless power transfer system with an asymmetric four-coil resonator. It presents a theoretical analysis, an optimal design method, and experimental results. Multicoil systems which have more than three coils between the primary and secondary side provide the benefits of a good coupling coefficient, a long transfer distance, and a wide operating frequency range. The conventional four-coil system has a symmetric coil configuration. In the primary side, there are source and transmitter coils, and the secondary side contains receiver and load coils. On the other hand, in the proposed asymmetric four-coil system, the primary side consists of a source coil and two transmitter coils which are called intermediate coils, and in the secondary side, a load coil serves as a receiver coil. In the primary side, two intermediate coils boost the apparent coupling coefficient at around the operating frequency. Because of this double boosting effect, the system with an asymmetric four-coil resonator has a higher efficiency than that of the conventional symmetric four-coil system. A prototype of the proposed system with the asymmetric four-coil resonator is implemented and experimented on to verify the validity of the proposed system. The prototype operates at 90 kHz of switching frequency and has 200 mm of the power transmission distance between the primary side and the secondary side. An ac–dc overall system efficiency of 96.56% has been achieved at 3.3 kW of output power. [ABSTRACT FROM AUTHOR]

This paper describes a method for monitoring multiple loads from the front end of a wireless power transfer system without using any wireless communication systems. A mathematical approach based on scanning the frequency around the resonant frequency has been developed for deriving the load conditions. The proposal requires only information of the input voltage and current, thereby eliminating the requirements of using wireless communication systems for feedback control. The proposal has been practically confirmed in hardware prototype with good results. [ABSTRACT FROM PUBLISHER]

A wireless charging or inductive charging electric vehicle (EV) is a type of EVs with a battery that is charged from a charging infrastructure, using a wireless power transfer technology. Wireless charging EVs are classified as stationary or dynamic charging EVs. Stationary charging EVs charge wirelessly when they are parked, and dynamic charging EVs can charge while they are in motion. The online electric vehicle developed at the Korea Advanced Institute of Science and Technology is an example of a commercially available dynamic charging transportation system. Numerous studies have reported that one of the benefits of dynamic charging is that it allows smaller and lighter batteries to be used, due to frequent charging using the charging infrastructure embedded under roads. In this paper, we quantitatively analyze the benefits of dynamic charging with an economic model of battery size and charging infrastructure allocation, using a mathematical optimization model. Particularly, we analyze by how much battery size can be reduced and what the cost saving of reducing the battery size is with the model. We also show that the dynamic charging can be beneficial to battery life. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) is an emerging technology with an increasing number of potential applications to transfer power from a transmitter to a mobile receiver over a relatively large air gap. However, its widespread application is hampered due to the relatively low efficiency of current Wireless power transfer (WPT) systems. This study presents a concept to maximize the efficiency as well as to increase the amount of extractable power of a WPT system operating in nonresonant operation. The proposed method is based on actively modifying the equivalent secondary-side load impedance by controlling the phase-shift of the active rectifier and its output voltage level. The presented hardware prototype represents a complete wireless charging system, including a dc–dc converter which is used to charge a battery at the output of the system. Experimental results are shown for the proposed concept in comparison to a conventional synchronous rectification approach. The presented optimization method clearly outperforms state-of-the-art solutions in terms of efficiency and extractable power. [ABSTRACT FROM AUTHOR]