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In this paper, we present a wireless power transfer (WPT) system with a two-dimensional (2-D) magnetoinductive wave (MIW) device composed by two orthogonal sets of 1-D MIW devices woven together. The device is made by 112 double-spiral coils, a geometry that we have optimized to render a low attenuation propagation. This approach enables a charging area of 22 × 22 cm2 from which a receiver device can be supplied with energy with optimum efficiency from 32 different locations with the use of a single excitation port. We present a detailed optimization of the design and fabrication of the device. To describe the behavior of the device, we use a modeling method based on the impedance matrix that allows us to include all coupling interactions among the increased number of cells. With this method, we are able to find the optimal operating conditions like the location of the excitation and the coupling conditions of the receiver device. With the proposed 2-D MIW device, we can provide up to 5 W to a load of 5  $\Omega$  located at the optimal axial separation. We corroborate our calculations with vector network analysis and dc output power measurements. Furthermore, we demonstrate the device supplying to distinct types of loads simultaneously. This paper is accompanied by a supplementary file showing the required MATLAB script and input files to calculate the mutual inductance between a receiver and the cells of the pad. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) via near-field magnetic coupling is an enabling technology for many applications. A few WPT standards are under development with frequencies ranging from kilohertz (kHz) to megahertz (MHz). Operation in kHz offers a higher power rating and that in MHz offers a smaller size. This paper presents a dual-band WPT architecture with novel transmitter and receiver topologies that can achieve high performance at both 100 kHz and 13.56 MHz with low component count and decoupled power delivery at different frequencies. On the transmitter side, we introduce an enhanced push–pull Class-E topology together with a reactance steering network (RSN), which can seamlessly compensate the load impedance variation for MHz wireless power transmitters. On the receiver side, we present a reconfigurable dual-band rectifier that can achieve a power density of 300 W/in $^3$ with low component count and low total harmonic distortion. A complete dual-band WPT system comprising an RSN-based dual-band transmitter and multiple reconfigurable receivers has been built and tested. The WPT system can simultaneously deliver a total of 30 W of power to multiple receivers (15 W maximum each) with 82.5% efficiency at 100 kHz and 74.8% efficiency at 13.56 MHz with 2.8 cm of coil distance and up to 5 cm of coil misalignment. [ABSTRACT FROM AUTHOR]

In this paper, a novel wireless servo motor drive is proposed and implemented, which artfully integrates wireless power transfer into the dc servo motor drive to achieve wireless bidirectional servo motion. Prominently, there is no power converter or controller at the servo motor side to realize the bidirectional rotation, while the motor control is fully conducted at the transmitter side. The key is to adopt only one transmitter with LCL network to achieve power equalization of two receiver coils, hence realizing bidirectional motion. Meanwhile, the phase-shift control method is newly developed to perform the desired speed control at the transmitter side, without requiring any switched capacitor arrays. As a result, the proposed wireless bidirectional servo motor drive takes the definite advantages of electrocution free and totally sealable. Both calculation and experimental results are presented to validate the feasibility and controllability. For the prototype, the transmission distance can reach up to 130 mm and the transmission efficiency can be up to 85%. [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]

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is one of the most promising WPT technologies for its remarkable capability of simultaneous noncontact power transfer for multiple independent loads. Nevertheless, diverse energy requirements of different loads and efficiency quota make it difficult to design and optimize the multiload system. In this paper, a novel driver configuration for the MCR WPT system with multiple loads is proposed, in which the transmitting resonant tank is driven synchronously by multiple inverters operating at multiple switching frequency and sharing a common dc voltage source, then a multifrequency superposition methodology is presented to achieve high efficiency and targeted power distribution. The dominant features of the methodology are listed as follows: 1) the multifrequency power components from multiple inverters can be simultaneously delivered to multiple loads through a single transmitter; 2) the receiving coils are elaborately designed at different resonant frequencies that correspond to the operating frequencies of multiple inverters to achieve targeted power transfer and high efficiency; 3) the resonant frequency of the transmitter can be modulated within the adjacent area of multiple operating frequencies, and the power distribution to meet the requirements of selective loads will be realized; and 4) the resonant frequencies of receivers can also be adjusted to effectively realize the power distribution. In this paper, a double-frequency MCR WPT system with two loads is comprehensively investigated as a representative example, and the studied methodology has been experimentally verified by two prototypes of the proposed circuit configurations. [ABSTRACT FROM AUTHOR]

A dc–dc power converter based on a two-phase synchronous buck converter that reproduces single-carrier digital modulation schemes by controlling the first switching harmonic of the output voltage ripple is presented in this paper. The dc–dc power converter carries out both the lighting and the transmission functionalities of visible light communication transmitters. Control of both the amplitude and the phase of sinusoidal currents injected toward high-brightness LEDs enable the use of efficient modulation schemes, such as quadrature amplitude modulation, carrierless amplitude and phase modulation, amplitude-shift keying, and phase-shift keying. These modulation schemes achieve higher spectral efficiency (i.e., more data can be transmitted using the same bandwidth) than previously proposed modulation schemes performed by visible light communication transmitters based on the use of dc–dc power converters. To the authors' knowledge, the ratio between the bit rate achieved and the switching frequency of the dc–dc power converter presented in this paper is the highest that can be found in the literature. [ABSTRACT FROM AUTHOR]

The pulse-width modulated (PWM) switching rectification that can achieve a high power factor (PF) for increasing the energy transfer efficiency between an LC resonator and a rectifier and voltage step-up and -down conversion is proposed for a wireless power transfer (WPT) receiver. The proposed method can emulate the switching rectifier as a resistive load by using an inductor and integrated phase synchronizers. Additionally, similar to a switched-inductor converter that controls the duty cycle ratio (D), the proposed PWM rectifier can control the output voltage VOUT when the input is a rectified, wirelessly coupled voltage instead of a constant voltage. Thus, unlike a conventional PWM switching rectifier for ac mains, an additional voltage conditioning circuit would not be needed after the proposed rectifier for WPT. The proposed PWM switching rectification is implemented in the AMS 0.18 μm 1.8 V/5 V CMOS process. PF = 1 is measured, indicating the most efficient energy transfer, compared to only 0.55–0.65 in a peak detection rectifier. Additionally, 88.2% of peak power conversion efficiency of the switching rectifier is achieved, and the maximum output power is 80.3 mW at 500 kHz of the WPT frequency. Moreover, the measured voltage conversion ratios ranging between 0.73× and 2× are demonstrated in this paper. [ABSTRACT FROM AUTHOR]

An inductive power transfer (IPT) converter usually has an optimum efficiency only at a matched load. Because of wide load range variation during battery charging, it is challenging for an IPT converter to achieve the required output and maintain high efficiency throughout the charging process. In this paper, a series–series compensated IPT converter with an active rectifier is analyzed and implemented for battery charging. Appropriate operations are employed for constant-current charging and constant-voltage (CV) charging. A novel operation approach is proposed to achieve constant output voltage and to ensure load impedance matching during CV charging without the help of an extra dc–dc converter, which incurs loss. Both a frequency modulated primary inverter and a phase-angle modulated secondary active rectifier can achieve soft switching. High efficiency can be maintained during the whole battery-charging profile. [ABSTRACT FROM AUTHOR]

This two-part paper aims at providing the basic mathematical theory of omnidirectional wireless power transfer (WPT). Based on current vector control, the magnetic field vector can be generated and pointed at any direction, thus achieving genuine omnidirectional wireless power flow. Part-I of this paper contains the mathematical analysis of the two-dimensional (2-D) system. The 2-D analysis shows that the total input power and the system energy efficiency of the WPT system can be expressed as functions of the angle of the input magnetic field vector. These functions follow the Lemniscates of Bernoulli on the 2-D plane. The directional nature of such curves provides the crucial information of the locations of the receivers so that the wireless power can theoretically be directed to the loads efficiently. The 2-D theory is presented here with the support of experimental verification. Understanding the 2-D omnidirectional WPT theory would make it relatively easy to appreciate the three dimensional one reported in Part II. [ABSTRACT FROM AUTHOR]

This paper presents a maximum efficiency tracking control scheme for a closed-loop wireless power charging (WPC) system for wireless charging of mobile devices. Generally, wireless charging systems need a precise output voltage and current with the highest possible efficiency. In an open-loop system, output voltage and efficiency depend strongly on the coupling coefficient and load condition. Alternatively, a closed-loop WPC system has a constant output voltage against coupling and load variations. Many studies have been carried out regarding closed-loop systems. However, those previous studies have the drawback of efficiency degradation. In this paper, we propose a maximum efficiency tracking control scheme to achieve the highest possible efficiency. Therefore, the proposed WPC system satisfies both the requirements of a constant output voltage and high efficiency. The proposed control scheme determines the current of the transmitter based on the data received by the receiver via Bluetooth. For validation, the proposed WPC system was implemented at 6.78 MHz using loosely coupled series–series resonant coils, and we verified that the proposed system can track the maximum efficiency while maintaining a constant output voltage. [ABSTRACT FROM AUTHOR]

This paper presents a reconfigurable wide input power range radio frequency (RF) energy harvester (EH) with alliance for wireless power (A4WP) wireless power receiver (WPR). A reconfigurable RF-DC converter for RF EH and maximum power point tracking algorithm are proposed to maintain high efficiency over a wide input power range –20 to +20 dBm. The A4WP WPR is designed and merged with the EH to receive power higher than +20 dBm. In order to improve the power conversion efficiency (PCE), the delay between the ac input voltage and current is compensated by the proposed open-loop delay compensation method. The chip is implemented in 0.18 μm bipolar-CMOS-double-diffused metal-oxide-semiconductor process. The die area of the chip is 4.3 mm × 3.2 mm, including the pads. The proposed EH with WPR achieves a measured peak PCE of 48.19% with respect to the input power of 0 dBm at 900 MHz. It also has a peak PCE of 82.14% with respect to the input power of 30 dBm in an A4WP mode operation at 6.78 MHz. [ABSTRACT FROM AUTHOR]

In this paper, an efficient method is proposed to eliminate frequency splitting in nonradiative wireless power transfer via magnetic resonance coupling. In this method, two nonidentical resonant coils (NIRCs) are used as wireless power transmitter and receiver, respectively. According to the elliptic integral term in the analytical expression, the pole of the mutual inductance function with respect to transfer distance can be eliminated by using the two NIRCs, and hence overcoupling between transmitter and receiver with close transfer distance is avoided. Therefore, frequency splitting caused by overcoupling can be suppressed and stable output power can be achieved. The NIRCs are analytically calculated, numerically simulated and finally, fabricated and tested to verify the theory. All the calculated and experimental results show that frequency splitting is completely eliminated and uniform voltage across the load is achieved. Furthermore, lateral misalignment between the NIRCs barely introduces frequency splitting, and the suppression level of frequency splitting can also be controlled freely. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-coupled LCC-compen-sated inductive power transfer system with a compact magnetic coupler to improve misalignment performance. In the magnetic coupler, the main coils form the first coupling, and compensation inductors are integrated with the main coils to form a second coupling. In the design presented in this paper, the main coils are unipolar and the compensation inductors are in a Double D structure. The fundamental harmonics approximation method is used to analyze the circuit, and the couplings between the main coils and compensation inductors are considered to determine the net power flow. In misalignment cases, it is shown that the coupling between the compensation inductors, and the cross couplings between the compensation inductors and main coils, contribute to increasing the system power. A 3.5 kW prototype is designed and implemented to validate the proposed dual-coupled system. The primary coil size is \text450 mm\times \text450 mm, and the secondary coil size is \text300 mm\times \text300 mm. Experimental results show that the proposed dual-coupled system can significantly improve the misalignment performance, and retains at least 56.8% and 82.6% of the well-aligned power at 150 mm misalignment in the x- and y-directions, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a discrete sliding mode control (DSMC) scheme for a series–series compensated wireless power transfer (WPT) system to achieve fast maximum energy efficiency (MEE) tracking and output voltage regulation. The power transmitter of the adopted WPT system comprises a dc/ac converter, which incorporates the hill-climbing-search-based phase angle control in achieving minimum input current injection from its dc source, thereby attaining minimum input power operation. The power receiver comprises a buck–boost converter that emulates an optimal load value, following the MEE point determined by the DSMC scheme. With this WPT system, no direct communication means is required between the transmitter and the receiver. Therefore, the implementation cost of this system is potentially lower and annoying communication delays, which deteriorate control performance, are absent. Both the simulation and experiment results show that this WPT system displays better dynamic regulation of the output voltage during MEE tracking when it is controlled by DSMC, as compared to that controlled by the conventional discrete proportional-integral (PI) control. Such an improvement prevents the load from sustaining undesirable overshoot/undershoot during transient states. [ABSTRACT FROM PUBLISHER]

This paper proposes the optimum resonance frequency of a transmitter (Tx) coil driven by a series-resonant inverter in wireless power transfer. While typical wireless power systems include a dc–dc buck converter at the receiver (Rx) side to output a constant voltage, it is revealed that the Tx design affects the operation of an Rx buck converter and Tx-to-Rx transfer efficiency. Specifically, it is found that if the resonant frequency of the Tx coil is too close to inverter switching frequency, the Rx buck converter is not allowed to operate at high duty cycle, which degrades the Tx-to-Rx transfer efficiency. Therefore, the Tx resonance frequency should be sufficiently lower than the inverter switching frequency in order to allow high-duty operation of the Rx buck converter. This is to guarantee high Q-factor of the Rx coil and thus the Tx-to-Rx transfer efficiency. The required Tx resonant frequency is proposed as a function of magnetic coupling, Rx coil property, Rx buck duty cycle, and Rx load condition. Simulation and experimental results with a constant-output-voltage system support the discussions. [ABSTRACT FROM AUTHOR]

This paper develops a 6.78 MHz multiple-receiver wireless power transfer system driven by a Class E power amplifier. Constant output voltage is achieved for each receiver with optimized overall efficiency. A novel one-receiver model is built to analyze the overall power-efficiency characteristics. The loads and input voltage are then designed as two control variables. Through tuning the loads, constant output voltage is achieved by independent controllers at the receiver side. Then, the efficiency is optimized by tuning the input voltage at the transmitter side. Finally, the theoretical analysis and control scheme are validated using a three-receiver system. It shows that different constant output voltages, 5, 9, and 12 V can be achieved independently for different receivers. When the load resistance, real coupling, and number of receivers change, the voltage can be quickly regulated, and the overall optimum system efficiency is 66.6%. [ABSTRACT FROM AUTHOR]

This paper proposes a new battery cell voltage equalization approach using multiple-receiver wireless power transfer (WPT) working at megahertz (MHz). Compared with existing multiwinding transformer, the MHz multiple-receiver WPT system is advantageous in terms of saved weight and space, ease of implementation, and improved safety. In this paper, the unique operating principle of the WPT-based equalization is first explained, through which equalization currents are naturally determined by the battery cell voltage distribution. The currents are also analytically derived. This facilitates the discussion on power amplifier (PA) design. Performance analysis is then provided to investigate the influences of system parameters on the efficiency and equalization ability of the proposed WPT-based equalization system, and thus guide following design and implementation. Considering the uncertainty in PA load due to the random cell voltage distribution, a current-model Class $E$ PA is designed that enables approximately constant PA output current. Experimental results show that the proposed multiple-receiver WPT-based battery cell equalization system can achieve high overall system efficiency (above 71%) when equalizing six lithium-ion battery cells under loosely coupling ( $k$ = 0.065). A good match between the experimental and calculation results also validates the correctness of the theoretical discussion. [ABSTRACT FROM PUBLISHER]

Both the efficiency and stray magnetic field in inductive power transfer are influenced by the design of transmitter and receiver coils. Their synergetic optimization is realized with Pareto front. The conventional method to derive the front requires thousands of finite-element simulations to sweep the physical parameters of the coils, which is time consuming especially for three-dimensional simulations. This paper demonstrates a fast method to optimize the efficiency and stray magnetic field. The windings are replaced by several lumped loops. As long as the number of turns for each loop is known, the efficiency and magnetic field are calculated using permeance matrices and current-to-field matrices. Therefore, sweeping physical parameters in simulation is replaced by sweeping turns numbers of the lumped loops in calculation. Only tens of simulations are required during the entire procedure, which are used to derive the matrices. The Pareto fronts calculated using the lumped-loops model match well with those derived from simulation using parametric sweep. An optimal design selected along the Pareto front was fabricated and measured to verify the calculation accuracy. The verification shows the same efficiency and less than 12.5% difference of the stray magnetic field, for the results from calculation, simulation, and measurement. [ABSTRACT FROM PUBLISHER]

Multiple transmitters powering a single receiver simultaneously is a good alternative to upgrade the power capacity of the wireless power transfer (WPT) system by using multiple modular inverters manufactured in a larger quantities, since the demand for high power applications is on the rise. A multiple overlapped transmitters based WPT system is presented in this paper. In order to alleviate the effects of the cross couplings between the transmitters, additional capacitors are adopted in the transmitters and the configuration of additional capacitors is provided. Virtual active and reactive powers are defined to decompose the transmitter current into active and reactive components. A transmitter current control scheme based on the proposed current decomposition method consisting of one reactive current control loop and one active current control loop is also presented in this paper. Finally, a low-scale experimental setup using two overlapped transmitters WPT system is provided to verify the proposed approach. The experimental results indicate that the proposed method could improve the stability of output voltage control and achieve minimal current difference amongst transmitters. Besides, the overall system efficiency is improved to 90.34% with the proposed control method at 1.45 kW output power, which demonstrates that the proposed method is a potential solution for high power applications. [ABSTRACT FROM AUTHOR]

In a wireless power transfer (WPT) system via the magnetic resonant coupling, one of the most challenging design issues is to maintain a reasonable level of power transfer efficiency (PTE), even when the distance between the transmitter and the receiver changes. When the distance varies, the PTE drastically decreases due to the impedance mismatch between the resonator of the transmitter and that of the receiver. This paper presents a novel serial/parallel capacitor matrix in the transmitter, where the impedance can be automatically reconfigured to track the optimum impedance-matching point in the case of varying distances. The dynamic WPT matching system is enabled by changing the combination of serial and parallel capacitors in the capacitor matrix. An interesting observation in the proposed capacitor matrix is that the resonant frequency is not shifted, even with capacitor-matrix tuning. In order to quickly find the best capacitor combination that achieves maximum power transfer, a window-prediction-based search algorithm is also presented in this paper. The proposed resonance WPT system is implemented using a resonant frequency of 13.56 MHz, and the experimental results with 1W power transfer show that the transfer efficiency increases up to 88 % when the distance changes from 0 to 1.2 m. [ABSTRACT FROM AUTHOR]

A traditional strongly coupled magnetic resonance (SCMR) system is highly sensitive to the alignment between the transmitter and receiver elements, which is an issue that has limited their applicability in practical wireless power transfer systems. This paper proposes, for the first time, a novel set of SCMR-based topologies that are less sensitive to misalignment while providing large wireless powering efficiencies. Specifically, instead of using planar coils for the transmitter and the receiver, we connect two orthogonal coils together into a 3-D model to provide misalignment insensitivity. Three SCMR systems (standard SCMR, conformal SCMR, and hybrid SCMR systems) are studied and compared to the proposed 3-D SCMR system in terms of angular azimuth, angular elevation, and lateral misalignment. Also, the ranges of these SCMR systems are compared. It is shown that the proposed misalignment system achieves above 40% efficiency for the entire range of 360° of angular misalignment. Also, our results show that the proposed misalignment system provides longer range. [ABSTRACT FROM AUTHOR]

Coordinated control of distributed energy resources (DER) is essential for the operation of islanded microgrids (MGs). Conventionally, such coordination is achieved by drooping the frequency of the reference voltage versus active (or reactive) power. The conventional droop method ensures synchronized operation and even power sharing without any communication link. However, that method produces unwanted frequency fluctuations, which degrade the power quality. In order to improve the power quality of islanded MGs, a novel decentralized control method is proposed in this paper. In this method, the GPS timing technology is utilized to synchronize the DERs to a common reference frame, rotating at a nominal frequency. In addition, an adaptive Q–f droop controller is introduced as a backup to ensure stable operation during GPS signal interruptions. In the context of the common reference frame, even sharing of active ( id) and reactive ( iq) components of the current are achieved based on vd\,\-\,id and vq\,\-\,iq droop characteristics. The method has been tested on a laboratory-scale MG. Experimental results demonstrate the efficacy of the proposed method in terms of dynamics, power quality, and robustness with respect to GPS interruptions. [ABSTRACT FROM PUBLISHER]

This paper proposes a wireless power transfer with automatic feedback control of load resistance transformation to maintain high efficiency over wide variations of coupling current and load current. The receiver (Rx) first determines the desired current level of transmitter (Tx) coil such that the receiver-side converter can transform the load resistance into optimum effective resistance, based on load current and Tx-to-Rx distance information. The determined Tx coil current data are sent to the transmitter, which then adjusts the Tx coil current accordingly. In this way, the effective resistance transformed by the receiver-side converter remains optimum under the variations of distance and load current. One of the advantages of the proposed automatic feedback control is faster response and simple hardware because it does not use operating point sweep and observation. The receiver-side switching converter also incorporates the ability to send data from receiver to transmitter by modulating the duty cycle of converter at data frequency, eliminating the need for separate RF communication hardware. This proposed communication does not require shunt current dissipation from dc output to ground, resulting in low loss. Experimental result demonstrates that the system maintains high efficiency under wide variations of coupling and load current. [ABSTRACT FROM PUBLISHER]

In this paper, a new method to estimate the mutual inductance and load resistance in a series–series compensated wireless power transfer system is presented. Reasonably accurate estimations can be obtained from measurements of the input voltage and current obtained at one operating frequency only. The proposal can be used to dynamically monitor both the coupling relationship between the transmitter and receiver coils and the load conditions without any direct measurement on the receiver side. It can also be used as a simple method to measure the mutual inductance of any pair of coupled coils. A novel impedance spectrum analysis method is further presented to show that series–series compensation has special characteristics in its input impedance spectrum. Experimental results with acceptable tolerance are included to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Multi-phase dynamic inductive power transfer (D-IPT) systems are capable of achieving uniform power transmission with low control complexity and high efficiency. To achieve acceptable power capabilities, D-IPT systems have to work in resonance configurations. In contrast to transformers, and due to the low coupling coefficient, the compensation is carried out separately in the primary and secondary sides. Consequently, an effect known as bifurcation or pole splitting is created. This causes extra losses in the semiconductors because zero voltage switching (ZVS) is lost. The main objective of this paper is to derive the bifurcation limits for a three-phase D-IPT system. First, the meander coil configuration is introduced. Because this is a system with multiple variables, five assumptions are made to achieve closed-form equations. Therefore, the 36 inductance system is converted into an ideal three inductance problem. With these assumptions, the equations of the coupling, power, and inductance ratio limits are obtained. Afterward, the repercussion of these assumptions is analyzed using illustrations that depict the input impedance angle for various non-ideal conditions. Finally, a 9-kW prototype is used to validate the calculations, analyzing two different operating points: incomplete ZVS and complete ZVS. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) technology has shown its significant role in various applications, such as electric vehicles and consumer electronics. In this paper, an input-parallel output-series circuit topology based on a compact double-sided decoupled coupler is presented to upgrade the power capacity of the WPT system with low-power and low-cost semiconductors. To avoid the potential risk of magnetic saturation, the phase difference between the transmitter currents is controlled to be 90° to achieve a symmetrical magnetic flux distribution for the magnetic coupler. Most importantly, an analytical model, which illustrates the relation between the efficiency and the ratio of the output voltages of the transmitter-side inverters under various misalignments, has been derived. Based on this, a control strategy is developed to maximize the energy efficiency under various misalignment conditions. The experimental results based on a 2.5-kW laboratory prototype show that, in comparison with the traditional method with identical inverters output voltages, the overall efficiency is improved by 2.32% by using the proposed method. [ABSTRACT FROM AUTHOR]

In the inductive power transfer (IPT) system, coil misalignment, load variation, and external disturbance will unavoidably cause power fluctuation and worsen system performances. Currently, robust control has been successfully introduced in the IPT system for promoting its stability and performances. However, due to the diversity of poles distribution, all possible IPT subsystems always show different overshoot, settling time, and resistance capacity to uncertainty factors. So, robust control design for the IPT system via pole placement constraints in linear matrix inequality (LMI) region is studied in this paper. An IPT system model with structured parametric uncertainty relevant to mutual inductance and load is first established. Based on the derived closed-loop system with a two-degrees-of-freedom control structure, a method of variable replacement is then proposed to transform the robust D-stability problem with pole region constraints into the LMI form, which can be solved to obtain a robust controller. After analyzing the influence of the LMI region change on poles distribution and system performances, an optimized robust controller is finally chosen. Experimental results show that a robust controller can reach the prescribed dynamic performances even if mutual inductance or load may change into another value, and also a good steady-state performance by resisting parametric uncertainty and external disturbance. [ABSTRACT FROM AUTHOR]

Techniques of long-term in vivo electrophysiological recording play important roles in brain research and neural rehabilitation. To avoid interruption of experiment and risk of infection, use of wireless power transfer (WPT) technique has been suggested to eliminate cumbersome wires and batteries attached to the animals in rodent electrophysiological applications. This paper presents a holistic assessment of the relationships among the physical sizes of the transmitting and receiving coils, power transfer characteristics, and specific absorption rate (SAR) in animals of a simple WPT system using two rectangular coaxial transmitting coils. With given space for the animal and size of the receiving coil, a procedure for designing the minimum driving current, and the transmitting coil dimensions and separation to deliver sufficient power to the receiver, and interactions between the transmitting and receiving coils is derived. A π-capacitor network that can match the impedances of the receiving coil and the load to operate the receiver at the maximum power transfer condition is proposed. It is also optimized for the overall volume. A 100-mW prototype with an operating zone of 400 × 240 × 40 mm3 and a receiving coil with a diameter of 11.45 mm is built and studied. The SAR in the animal is evaluated and compared with the recommended restriction level. [ABSTRACT FROM AUTHOR]

This paper presents a full-CMOS wireless power receiving unit (WPRU) with a high-efficiency 6.78-MHz active rectifier and a dc–dc converter for magnetic-resonant alliance for wireless power (A4WP) applications. The proposed high-efficiency active rectifier with delay-locked loop (DLL) is a highly efficient receiver circuit intended for use in resonant wireless charging applications with a resonant frequency of 6.78 MHz. Each MOSFET of the proposed rectifier is turned on and off based on the ac input voltage. The delay between the ac input current and the ac input voltage due to the delays of internal blocks such as voltage limiter, level shifter, gate driver, and comparator will cause the reverse leakage current, degrading the power efficiency. Thus, the proposed active rectifier adopts the DLL to compensate for the delay caused by internal blocks, which leads to the removal of reverse leakage current and the power efficiency maximization. Moreover, to maximize power efficiency, negative impedance circuit (NIC) is also adopted to minimize switching loss. In the case of dc–dc converter, phase-locked loop is adopted for the constant switching frequency in process, voltage, and temperature (PVT) variation to solve the efficiency reduction problem, especially by heat. This chip is implemented using 0.18 μm BCD technology with an active area of 3.5 mm × 3.5 mm. When the magnitude of the ac input voltage is 8.95 V, the maximum efficiencies of the proposed active rectifier and dc–dc converter are 91.5% and 92.7%, respectively. The range of ac input voltage is 3–20 V, and the efficiency of the WPRU is about 80.86%. [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]

Recent research in wireless power transfer has highlighted the potential benefits for relaying power from source to receiver by a number of resonating relay coils coupled via mutual inductance. A number of researchers have reported experimental systems based on relay coils and have noted that power transfer efficiency to loads located at different points on the structure can vary widely. Such structures, often known as magnetoinductive waveguides are well known to carry signals known as magnetoinductive waves (MIW) when excited with a frequency in their passband. This paper presents an investigation into their impact on wireless power systems and methods by which negative effects may be minimized. Using the physics of magnetoinductive waves it becomes possible to understand the behavior of relay coil systems and to model them in a closed form. The effects of reflections and standing waves on a one-dimensional system are considered and their effect on the input impedance and the variation of matching conditions determined. An optimum receiver load is proposed based on the results and tested experimentally. A simple experimental demonstrator is used as a model for study, which achieves 58% efficient power transfer to a single load at any point on its length. [ABSTRACT FROM AUTHOR]

This paper describes a technique for multifrequency wireless power transfer systems in which the wireless power can be transmitted through the wireless power transfer channel or channels from the transmitter to the targeted loads with receiver coils specifically tuned for energy reception. Auxiliary circuits comprising bandpass and/or bandstop circuits are proposed for incorporation into the receiver circuits and optional relay circuits so as to facilitate the selection and enhancement of the wireless power transfer to the designated load without causing significant cross interference due to the use of multifrequency wireless power flow control. A unique feature of this technique is that the nontargeted receiver will automatically act as a relay resonator to enhance 1) magnetic coupling, and thus, 2) the power transfer between the power transmitter and the targeted receiver. A second novel feature is that the chosen operating frequencies for the tuned receivers need not be widely apart because the auxiliary circuits consist of bandpass and/or bandstop filters to reduce any cross interference from the nontargeted frequency. The proposed technique has been practically verified in experimental prototype. [ABSTRACT FROM AUTHOR]

Multiple output chargers have widely been adopted in various electronic devices due to their benefit concerning cost, power density, and space for installation. On the contrary, inductive power transfer (IPT) has been applied increasingly in electric vehicles (EVs) since it is safer and more convenient as compared to conductive chargers. However, research works on multiple output chargers using an IPT system for EV charging applications are rarely presented. This paper proposes a new concept of a multiple output IPT charger, which can charge several output batteries independently and simultaneously by adopting only one full bridge inverter at the primary side combining with multiple transmitters. A total of two possible IPT-coil structures are analyzed, and the minimum distance between each channel's coils is determined to neglect the cross-coupling between them. A total of two options are proposed to attain a zero phase angle (ZPA) condition for the primary inverter of the proposed system. First option is to operate the compensation tanks of every output channel at exact ZPA frequencies. The other option is to let one channel work in the inductive region of its input impedance and other channel work in the capacitive region. By adopting an appropriate design, the reactive powers of these tanks can be nearly canceled by each other and the phase of inverter current can be nearly in-phase with the input voltage as a result. A total of two proposed options are compared to give recommendation whether option 1 or 2 should be selected according to various applications’ requirements. To simplify control complexity, IPT output current sources topologies are selected, compared, and analyzed to construct the proposed multiple output system in both above-mentioned options. Double-sided LCC and series–parallel topologies are adopted to demonstrate the proposed idea for options 1 and 2, respectively. In order to verify feasibility and validity of the proposed method, experimental results of two output channels with the total output power of 1.5 kW are provided. Experimental results indicate that the ZPA is achieved for the primary inverter with both of the above-mentioned options even under different load conditions. Some comparisons between the conventional and the proposed IPT charging structure in terms of cost, reliability, and complexity are included in the discussion section. [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]

Laser power transmission (LPT) is one of the most promising technologies in the long-range wireless power transfer field. LPT research has been driven by the desire to remotely power unmanned aerial vehicles, satellites, and other mobile electric facilities. However, the low overall efficiency is the main issue that limits the implement of high-intensity laser power beam (HILPB) system. As seen from the contemporary understanding of efficiency of laser power transmission channel, the efficiencies of laser and PV array are the main limiting factors to the HILPB system from the perspective of power conversion. Thus, a comprehensive overview of LPT technology is presented from the point of efficiency optimization view in this paper. First, the basic principles of laser power transmission are briefly summarized. Then, a survey of the efficiency optimization methods for HILPB system with regard to the laser and PV technologies is provided in detail. Additionally, the open issues and challenges in implementing the LPT technology are discussed. [ABSTRACT FROM AUTHOR]

In some applications of wireless power transfer, such as wireless charging of consumer electronics and electric buses, the coupling between the transmitter and the receiver is strong in order to improve efficiency. With a strong coupling, the compensation on the receiver side can be eliminated to achieve a high-level integration of the receiver device and a smaller receiver-side loss, forming a series-none (SN) topology, which has not been fully investigated before. The commonly used first harmonic approximation method for the SN topology has discrepancies with a low-power output and cannot fully reveal the characteristics of the SN topology. Therefore, this paper establishes a model of the SN topology and derives the analytical expressions of the transmitter and receiver currents based on differential equations. The distortion of the receiver current is studied. The coil-to-coil efficiency is obtained and its maximum condition is investigated. The SN topology offers approximately the same efficiency as the SS topology when the coupling is strong and the coil quality factors are large. Theoretical calculations and experimental results confirm the analysis. [ABSTRACT FROM AUTHOR]

A new methodology for ensuring that a three-coil wireless power transfer system is more energy efficient than a two-coil counterpart is presented in this paper. The theoretical proof and the conditions for meeting the objective are derived and practically verified in a practical prototype. The key features of the magnetic design are to: 1) shift the current stress from the primary driving circuit to the relay resonator; and 2) generate a large relay current for maximizing magnetic coupling with the receiver coil for efficient power transfer. Consequently, the current rating and cost of the driving circuit can be reduced and the overall quality factor and system energy efficiency are improved. This approach utilizes the combined advantages of the maximum efficiency principle and the use of relay resonator to overcome the energy efficiency problem for applications with extended energy transfer distances. [ABSTRACT FROM AUTHOR]

The detuning of an inductive power transfer (IPT) system caused by the component tolerance and aging of the inductors and capacitors can decrease the system efficiency, accordingly. To tune the receiver circuit of the IPT system dynamically, an inductor is parallelly connected with a diode full-bridge rectifier cascaded with a buck converter serving as a tuning circuit in this paper. By changing the duty cycle of the buck converter, the impedance of the tuning circuit can be adjusted to compensate the reactance caused by detuning. The tuning range of the proposed method is analyzed in detail. A corresponding control method, in which an auxiliary measurement coil is utilized, is proposed to tune the receiver circuit dynamically while regulating the output voltage. Because the buck converter is with the dc side of the receiver, no synchronization is required for the switches of the buck converter, and the switching frequency of the buck converter can be much lower than the inverter frequency. A 400 W prototype is established to validate the proposed method. The experimental results show that with 15% tolerance of the resonant capacitor in the receiver side, the system efficiency with the proposed tuning method can reach 91% with an improvement by 7.9% compared to the detuned system. [ABSTRACT FROM AUTHOR]

Electrical and electromagnetic methods have long played an important role in mineral exploration. For example, in active source prospecting methods, when measuring the values of many electrical parameters, the signal-to-noise ratio can be improved by increasing the transmitting power. In this paper, we present a multifunction borehole ground electromagnetic transmitting system that transmits rectangular waves at a frequency of 0.01–10 kHz with a frequency error less than 10−8 Hz @ 1 Hz (depending on the high-precision temperature compensation crystal) and the initial synchronization error between the transmitter and receiver is less than $ \pm \text{0.1}\,\mu {\text{s}}$. During operation, either the maximum transmitting voltage output can reach 950 V or the maximum transmitting current can exceed 90 A, but both cannot be achieved simultaneously. We tested the transmitting system at its maximum power output continuously for over 8 h and the power output was more than 48 kW at a current above 60 A. The energy was delivered above ground or underground using existing drill casings to produce the high-power transmissions. The field experiments show that the system meets the demands of the controlled-source audio-frequency magnetotelluric and induced polarization methods used in mineral exploration. [ABSTRACT FROM AUTHOR]

In typical multi-MHz inductive power transfer (IPT) systems, a change in coupling or load resistance can significantly deteriorate the end-to-end efficiency due to a deviation from the optimal load of the IPT link and suboptimal operation of the resonant inverter due to the loss of soft switching condition. This paper proposes solutions for an IPT system to operate efficiently when large changes in coupling take place. To achieve high power efficiency independent of coupling, we utilize inherent regulation properties of resonant converters to avoid losing soft switching for any coupling value, and present the optimal load to the IPT link at the maximum energy throughput coupling. A probability-based model is introduced to assess and optimize the IPT system by analyzing coupling as a distribution in time, which depends on the dynamic behavior of the wireless charging system. The proposed circuits are a Class D rectifier with a resistance compression network in the receiving end and a load-independent Class EF inverter in the transmitting end. Experiments were performed at 6.78 and 13.56 MHz verifying high efficiency for dynamic coupling and variable load resistance. End-to-end efficiencies of up to 88% are achieved at a coil separation larger than one coil radius for a system capable of supplying 150 W to the load, and the energy efficiency was measured at 80% when performing a uniformly distributed linear misalignment of 0–12.5 cm, corresponding to a receiver moving at a constant velocity over a transmitter without power throughput control. [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]

Optimum energy efficiency in a wireless power transfer (WPT) system usually occurs only at a specific load value while the load such as a battery is normally not constant. A major challenge in WPT is, therefore, to achieve high energy efficiency over a wide load range. Previously, impedance transformation methods such as dc–dc converters and use of a relay coil have been used to transform the practical load resistance to the optimum (or near-optimum) value. In this paper, a new approach based on reconfigurable magnetic resonant structures is proposed to achieve high energy efficiency and low volt-amp ratings. This basic principle is to create more than one efficiency–load curve. The WPT system is controlled to be operated within the top regions of the energy efficiency curves of the reconfigurable circuits so that high energy efficiency can be achieved over a very wide load range. The principle of this new approach is explained with an analysis and verified with practical measurements. [ABSTRACT FROM PUBLISHER]

The paper proposes optimal driving conditions of two transmitters (TXs) in magnetic wireless power transfer, where the couplings from each TX to an RX are not identical. First, for the case of identical TX coil currents, a criterion for deactivating a specific TX element is proposed. Specifically, one TX element among the two TXs often has weaker coupling coefficient than the other TX element. It is found that the TX element with weaker coupling should be deactivated if its coupling coefficient is less than 0.414 times of the stronger coupling. Second, for the case of adjustable TX coil currents, the optimal current ratio between the two TX coils is proposed. It is found that the TX coil current ratio should be equal to the coupling coefficient ratio, e.g., the TX coil with twice coupling with an RX should carry twice current. The results are widely applicable regardless of absolute coupling strength and load condition because it turns out that the results only depend on the ratio of couplings. Finally, it is discussed that the required component values of an LCC inverter should be adjusted based on the current ratios and coupling between adjacent TXs. [ABSTRACT FROM AUTHOR]

This paper presents the framework for the applications of double-source wireless systems in charging for movable electronic devices. To acquire the real-time mutual inductances between the receiving coil and the transmitting coils, a detection strategy on the basis of primary parameters (currents and voltages) is introduced, which can replace the wireless communications between the receiving side and the transmitting side. Coordinated control of two source voltages is employed to deal with the power fluctuation of load, which is caused by load position variations. In specific, the constraint of two source voltages, which can maintain the output power stable, is derived. Based on these feasible combinations of source voltages, numerical calculations are further carried out to identify the optimized voltage combination, which can achieve high power transfer efficiency. Finally, an experimental prototype is built up and the results show that the proposed coordinated control strategy can minimize power fluctuation and maintain relative high efficiency at the same time. [ABSTRACT FROM PUBLISHER]

Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the use of magnetic resonance technique at a certain load resistance value. However, practical load resistance is not constant. Previously, a switched mode dc–dc converter was used in the receiver circuit to emulate an equivalent load resistance for maximum energy efficiency. In this paper, a new approach based on the On–Off Keying is proposed to achieve the high energy efficiency operation over a wide range of load power without using an impedance-matching dc–dc power converter. This simple and effective method has reduced average switching frequency and switching losses. It can be applied to any series-series resonant WPT system designed to operate at a constant output voltage. Practical measurements have confirmed the validity of the proposal. [ABSTRACT FROM PUBLISHER]

Resonance tracking technology is indispensable in inductively coupled wireless power transmission applications to counteract the detuning. In this paper, an ultrafast resonance tracking method is proposed that can accomplish resonance tracking within one-half oscillation cycle. The proposed method is implemented by synchronizing the operating frequency to the damped natural frequency, which occurs in close proximity to the resonance frequency. In addition, the tracking principle and tracking error theory are described in detail based on unloaded and loaded circuit models. A prototype is implemented and performance aspects including tracking accuracy, transient characteristics, induction voltage stability, and efficiency improvement are tested. The experimental results validate both the half-cycle tracking principle and the tracking error theory, where the tracking error is within 1.3% over the full range. Using the proposed method, the resonance tracking performance reaches the dynamic characteristic limit of the resonance loop, and is ten times that of a classical phase-locked loop-based tracking solution. This method could compensate for high-frequency detuning of up to several of kilohertz, caused by mechanical vibration and the chopper actions of the loads. The proposed method can be widely applied in the field, where both accurate and fast resonance tracking are required. [ABSTRACT FROM PUBLISHER]

A new wireless power transfer (WPT) system based on ball-joint structure is presented in this paper. A ball-joint WPT system consists of a ball structure with a mechanical rod attached to the ball and a ball socket that accommodates the ball structure. This ball-joint structure comprises at least one winding in the ball structure and at least one winding in the ball socket structure. The ball structure can be flexibly rotated over a wide range of angle inside the ball socket, while wireless power can still be transferred from the transmitter winding to the receiver winding through magnetic resonance. The magnetic coupling coefficient between the transmitter and receiver coil over a wide rotating angular range has been analyzed and experimentally checked. Experimental results confirm that an energy efficiency of up to 81% can be achieved. [ABSTRACT FROM PUBLISHER]

The efficiency of wireless power transfer (WPT) systems is highly dependent on the load, which may change in a wide range in field applications. Besides, the detuning of WPT systems caused by the component tolerance and aging of inductors and capacitors can also decrease the system efficiency. In order to track the maximum system efficiency under varied loads and detuning conditions in real time, an active single-phase rectifier (ASPR) with an auxiliary measurement coil (AMC) and its corresponding control method are proposed in this paper. Both the equivalent load impedance and the output voltage can be regulated by the ASPR and the inverter, separately. First, the fundamental harmonic analysis model is established to analyze the influence of the load and the detuning on the system efficiency. Second, the soft-switching conditions and the equivalent input impedance of ASPR with different phase shifts and pulse widths are investigated in detail. Then, the analysis of the AMC and the maximum efficiency control strategy are provided in detail. Finally, an 800-W prototype is set up to validate the performance of the proposed method. The experimental results show that with 10% tolerance of the resonant capacitor in the receiver side, the system efficiency with the proposed approach reaches 91.7% at rated 800-W load and 91.1% at 300-W light load, which has an improvement by 2% and 10% separately compared with the traditional diode rectifier. [ABSTRACT FROM PUBLISHER]

The paper proposes a method to suppress the anticurrent and magnetic canceling in a dual-band transmitter (Tx) and receiver (Rx) for wireless power transfer. The problem of intracoupling between the two coils in a dual-band resonator is analyzed. During 6.78-MHz operation, the intracoupling causes antidirectional current at 200-kHz coil which cancels the magnetic field and degrades efficiency. To solve the problem of antidirectional current, a new resonator design method is proposed. The proposed technique suppresses the 6.78-MHz anticurrent by specially selecting the impedance values and coil-winding direction that manipulate the magnitude and phase of 6.78-MHz voltage, such that total voltage across 200-kHz path is zero. One of the advantages is that the spatial separation between 6.78-MHz coil and 200-kHz coil can be reduced, which allows the maximum diameter for inner coil. Also, smaller discrete inductor can be used. The two coils share an inverter (or a rectifier), thus minimizing the number of inverter and rectifier. The 24-W system with dual-band Tx achieves 70.3% and 70.8% efficiencies at 6.78 MHz and 200 kHz, respectively, whereas the system with dual-band Rx achieves 66.3% and 74.3% at 6.78 MHz and 200 kHz, respectively. The efficiency improvement due to anticurrent suppressing is 4.8∼23.6%. [ABSTRACT FROM PUBLISHER]

The power transfer efficiency and power transfer characteristics of wireless inductive links are determined by several intrinsic and extrinsic factors, such as coupling coefficient, quality factors, matching conditions of the transmitting and receiving coils, and operating frequency. The nominal component values, such as the capacitors used in matching the coils, are chosen by considering the optimal power transfer efficiency and power transfer requirement at the nominal operating condition. However, due to manufacturing tolerance, temperature effect, and aging, electronic components are subject to parameter variations. Such unavoidable issue would cause performance degradation of the link. Typically, it is tackled by conducting on-the-spot measurements of the electrical quantities together with sophisticated communication links and protocols to provide the transmitter with the operating condition of the receiver. To reduce system complexity, this paper presents another perspective by processing transmitter-side electrical information with an evolutionary computation technique to estimate several system parameters, including coil inductances and quality factors, resonant frequencies of the transmitting and receiving networks, and coupling coefficient, for the transmitter to manage power transfer. The proposed technique has been applied to a 4-W wireless-powered LED driver prototype for regulating the load power under parametric variations. [ABSTRACT FROM PUBLISHER]