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This paper proposes a -controller based on the structured singular value (SSV) with regard to the uncertainty of multiple parameter perturbations and external disturbances of Inductive Power Transfer (IPT) systems to achieve constant current charging. By using a boost converter as an impedance compensation network, the IPT system can obtain the maximum power transfer efficiency when the charging starts. However, the charging current varies under the load and frequency perturbation during the charging process. This paper presents a controller that ensures constant current charging and robust operations. A Generalized State-space Averaging (GSSA) is established, and a standard M- configuration by separating the uncertain parameters and a -controller are proposed to form a closed-loop control system. Simulation and experimental results show that the proposed control method has strong robustness against load and frequency perturbation, and also has certain ability to suppress other external disturbances.

In this article, a multi-load wireless power transfer (WPT) system is proposed for the power supply of autonomous underwater vehicle (AUV) cluster system. The segmented arc solenoid transmitter coil is designed to generate the concentrated magnetic field. The adjacent transmitter coils are reversely wound to form the strengthened magnetic field, which can improve the coupling between the transmitter and the receiver. The proposed coil structure is verified via finite element analysis based on ANSYS Maxwell. The transfer performance is analyzed and it is found that the transfer efficiency can be maximized against the voltage gain under the two-receiver case, which can also be extended to multiple-receiver case. An LCC-LCC compensated multi-load WPT prototype was established and the experimental results verified the theoretical analysis and simulations. The output power of each receiver and the system efficiency can reach 500 W and 90% under the different angles between any two receivers.

This article proposes a double-sided inductor–capacitor–capacitor–capacitor matrix (D-LC-CCM) impedance matching network to eliminate the impact of the load and the mutual inductance variation on inductive power transfer system. A thorough mathematical analysis is conducted and a control strategy is proposed to obtain a constant current output when the load and the mutual inductance vary. When the load changes, the equivalent impedance of the secondary side can be kept unchanged by adjusting the capacitor matrix in the receiver, then adjusting the input voltage can achieve constant current output simultaneously. The equivalent input impedance of the primary side and the output current can remain stable by adjusting the capacitor matrix in the transmitter when the mutual inductance changes. The experimental prototype was built, and the system constant current output was achieved when the load changes from 40 to 80 Ω and the mutual inductance varies from 13 to 17 μ H, which has validated the effectiveness of the D-LC-CCM impedance matching network.

A metal-rim-connected inductive coupler with series-none compensation topology is proposed for smartwatch applications. By cross-connecting the receiving coil to the metal rim with a 1 mm slot, the direction of the induced current on the metal rim is transformed to be the same as the current flowing on the receiving coil, leading to a strong magnetic coupling between the transmitting coil and receiving coil. Considering the space limitation in the smartwatch, non-compensation components are needed inside the smartwatch and only a series capacitance is integrated on the transmitter side. A prototype of the proposed inductive coupler has been built and the wireless power transfer through metal rim has been validated via experiment. The experimental results show that the prototype achieves 5 W output power with 87.4% coil-to-coil efficiency.

This article presents a maximum efficiency tracking method for an inductive power-transfer (IPT) system based on a Boost dc–dc converter. Impedance matching (IM) is achieved by maintaining the equivalent load impedance to be constant against load variations. The expression of the optimal equivalent load impedance corresponding to the maximum system-transfer efficiency is derived, and the impedance-transfer characteristics of the Boost converter in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are analyzed. The duty cycle of the Boost converter is controlled to maintain the optimal equivalent load with extended range in DCM mode, and the switching frequency of the Boost converter is further adjusted to improve the accuracy of the IM. Both simulation and experimental results have demonstrated that the proposed IM method can help achieve the maximum power-transfer efficiency under a wide range of load variations.

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.

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.

Fast charging of electric vehicles (EVs) has been the trend recently. For conductive charging, normal charging can be realised by an on-board charger, while fast charging can be realised by a DC charger which is usually off-board the vehicle. However, for wireless charging, there is a need of a transmitter on the ground and a receiver on the EV side. Therefore, there will be a high-power receiver and a low-power receiver in one EV to achieve dual charging capabilities. To reduce the EV-side cost, weight, and volume, this paper proposes a wireless charging system with a shared receiver compatible of fast wireless charging (FWC) at a small air gap and normal wireless charging (NWC) at a large air gap. The relationship between the coil size and the power level is investigated and a suitable receiver coil size is selected for FWC. The LCC-LCC topology is selected due to its characteristic of output power proportional to the coupling coefficient. Design procedures of the receiver and transmitters are investigated. The simulations and the experimental results obtained from the downscaled prototype verified the effectiveness of the compatibility design.

An underwater wireless power transfer system with a curly coil structure is proposed to adapt to the cylindrical symmetric hull of the autonomous underwater vehicles (AUVs). The unipolar and bipolar curly coils are optimised to minimise the weight of the receiver with the same output power. It is revealed that the bipolar curly coil structure has a heavier receiver than the unipolar curly coil structure. However, the electromagnetic field radiation in the AUV of the bipolar curly coil structure is much smaller than that of the unipolar curly coil structure, which means that the bipolar curly coil structure has a smaller influence on the electronics components in the AUV. Therefore, the bipolar curly coil is adopted for the prototype. The series−series (SS) and double-sided inductor−capacitor−capacitor (LCC−LCC) compensation topologies for the bipolar curly coil structure are also investigated. A prototype was built and the experimental results showed that distorted coil currents are generated in the SS compensation topology, while the LCC−LCC compensation has a nearly sinusoidal coil current. The efficiencies of the SS and LCC−LCC compensation topologies are approximately the same, at ∼95%, which indicates that the proposed curly coil structure is applicable.

This letter proposes a novel capacitive coupler array with free-positioning feature for mobile tablet applications. The capacitive coupler consists of three printed circuit boards, two of which constitute the transmitter and the third one is the receiver. The coupler is vertically arranged to make the charging system compact and feasible for mobile tablet applications. By applying a repetitive structure on the transmitter side and properly designing the receiver, free-positioning capacitive charging is realized and the coil-to-coil charging efficiency is not affected by the variation of the receiver position. Only two series inductances are utilized for compensation purposes, which makes the system more compact and easy to be fabricated. This proposed capacitive coupler is studied via finite-element analysis and verified by the experimental results at 1, 2.17, and 3.45 MHz.

In a wireless power transfer (WPT) system, voltage tuning and frequency tuning are two major methods to control the output power. For the design of a WPT system at the rated power, it is crucial to understand the characteristics of a WPT system with a constant-power load (CPL) under voltage tuning and frequency tuning. The model of a series–series compensated WPT system with a CPL is established based on the Thevenin equivalent circuits. The conditions to achieve the maximum coil-to-coil efficiency for the two tuning methods are obtained. For frequency tuning, the tuning zone above the resonant frequency is selected because of its wide tuning range and zero-voltage switching. The maximum output power at different operating frequencies is derived, and the required inverter dc voltage and the tuning range for a target output power can be obtained accordingly. With a strong coupling, the maximum efficiency of frequency tuning can be as high as that of voltage tuning; while with a weak coupling, the efficiency of frequency tuning is much smaller than that of voltage tuning. The model with a CPL is helpful for the design and optimization of a WPT system with the rated power.

In the wireless charging of high-power electric buses or low-power consumer electronics, the charging distance is normally very small, leading to a strong coupling. Current distortion occurs for a wireless power transfer (WPT) system with a strong coupling. This paper investigates the strongly coupled series–parallel (SP)-compensated WPT system, where the first harmonic approximation (FHA) is no longer valid. A mathematical model of an SP-compensated WPT system based on differential equations is built. There are two sinusoidal components with significantly different frequencies existing in the transmitter and receiver currents, which cause the current distortion. The proposed model and FHA are compared, and the proposed model is more accurate than FHA. The estimations of the current root-mean-square values from FHA tend to be smaller than those from the proposed model and the measured values. In addition, it is found that with the increasing rectifier dc current, the system transits from zero voltage switching to zero current switching. The critical rectifier dc current decreases with the increasing operating frequency. The experimental results verify the effectiveness of the proposed model. The proposed model promotes a better design of an SP-compensated strongly coupled WPT system.

This letter proposes a rotation-free wireless power transfer system based on a new coil structure to achieve stable output power and efficiency against rotational misalignments for charging autonomous underwater vehicles. The new coil structure has two decoupled receivers composed of two reversely wound receiver coils and the magnetic flux directions of the two receivers are perpendicular to each other, guaranteeing a relatively constant total mutual inductance and a decoupled characteristic under rotational misalignments. The proposed coil structure is verified via finite element analysis based on ANSYS Maxwell. A rotation-free LCC–LCC compensated WPT prototype is built and the experimental results verify the theoretical analysis and simulations. The system can deliver 664 W with a dc–dc efficiency of 92.26% under the best case and 485 W with a 92.10% dc–dc efficiency under the worst case.

Accurate modelling is necessary for designing a wireless power transfer (WPT) system and currently, first harmonic approximation (FHA) is widely used. However, it is not accurate for WPT systems with a strong coupling, such as fast charging of electric vehicles with a coupling coefficient of 0.80, compared to the conventional wireless charging with a coupling coefficient of 0.15-0.30. This study develops accurate models for WPT systems with series-series (SS) and LCC-LCC compensations. For the SS compensation with a strong coupling, the transmitter and receiver currents are distorted, leading to much larger values than the estimations from FHA, which determines the selection of power switches and resonant capacitors. For the LCC-LCC compensation, the transmission coil currents are only highly distorted with rich third-order harmonics at the vicinity of the 0.889 coupling coefficient, leading to low efficiency and large coil current ratings. For the experimental prototype, the efficiency drop can be over 3%, which is significant, especially for high-power systems. The WPT system with the LCC-LCC compensation should avoid operation in the vicinity of this particular coupling coefficient. Furthermore, experiments are conducted, and the results perfectly match the calculations, demonstrating the accuracy of the proposed models.

Dynamic wireless power transfer can reduce the battery capacity of charged devices. This paper proposes a dynamic capacitive power transfer (CPT) system with a compact receiver structure and a reduced transmitter cost. Compared with the conventional solution, the specially designed coupler can reduce the transmitter copper usage by 50% while still achieving stable output. A series compensation with a compensating inductor is adopted on the transmitter side and there is no compensation on the receiver side to minimize the element count and size, especially on the receiver side. Design procedures of the coupler and the compensation network are provided. The mathematical model of the dynamic CPT system is established. Simulation results have verified the effectiveness of the proposed method.

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.

An LCL-none (LCL-N) topology is proposed in this paper for high-power strongly-coupled wireless charging systems. The receiver-side compensation is eliminated to achieve a compact and lightweight receiver. The efficiency is still high due to the strongly-coupled characteristic. 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 is achieved. The model of the LCL-N topology is built and the output power and the efficiency are analyzed. A full-scaled system of 100 kW is designed and simulated. A downscaled 1 kW system is implemented. The simulations and experiments have verified the effectiveness of the analysis.

Wireless Power Transfer (WPT) for autonomous underwater vehicles (AUVs) has been a research focus in recent years. This paper studies the inductor-capacitor-capacitor and parallel (LCC-P) compensation topology to achieve a compact receiver for AUVs. Unlike the series-series (SS) compensation topology, the LCC-P topology retains the advantages of the double-sided LCC topology and has a more compact receiver than the double-sided LCC topology with fewer elements used on the receiver side. The analytical model of such a WPT system is established to analyze the output power and transfer efficiency. The LCC-P topology has a higher efficiency compared to the SS topology due to the smaller conduction loss of the inverter. Moreover, a method of eliminating the DC filter inductor L0 is proposed to further decrease the size and weight of the receiver. The amplitude of the withstanding voltage on the receiver compensation capacitor without L0 is approximately decreased by 40% compared to that with L0. Both cases of with and without L0 have a constant current output and the peak efficiency without L0 is about 94%, which is 1% lower than that with L0. A prototype was built and the experimental results verified the theoretical analysis.

Underwater Wireless Power Transfer (WPT) has attracted much attention in recent years. In an underwater WPT system, the eddy current loss tends to be non-negligible as the frequency and current increase. Thus, it is crucial to analyze the eddy current loss in an underwater WPT system. The analytical model of the eddy current loss of a coreless WPT system in seawater is established with Maxwell’s equations. The expressions of the electric field intensity and the eddy current loss are derived and the eddy current loss is analyzed in different circumstances. An underwater WPT prototype is set up and the experimental results verify the theoretical analysis.

Wireless Power Transfer (WPT) has attracted much attention in recent years. Voltage tuning and frequency tuning are two major tuning methods to control the output of a WPT system. For the design of a WPT system at the rated output power, it is crucial to analyze the WPT system with a constant-power load under voltage tuning and frequency tuning. The analytical models of a WPT system with a constant-power load both at and off the resonant frequency are established. The expressions of the transmitter current, the receiver current, the DC voltage of the rectifier, and the coil-to-coil efficiency are derived. The conditions to achieve the maximum coil-to-coil efficiency for voltage tuning and frequency tuning are obtained. An experimental prototype is implemented. The experimental results agree well with the analysis and the calculations. With a strong coupling, the maximum efficiency of frequency tuning can be as high as that of voltage tuning.

Wireless power transfer (WPT) has a promising application prospect due to its convenience and feasibility to special occasions. Inductive power transfer (IPT) uses the magnetic field for power transfer and it is currently the most popular and mature WPT technology. However, the strong magnetic field will heat up metal objects falling in the charging area due to eddy currents generated in the objects. It can also harm animals or toddlers staying in the charging area. To deal with these issues, foreign object detection (FOD), including metal object detection (MOD) and living object detection (LOD), should be developed for the safe operation of IPT systems. FOD can be divided into system parameter detection methods, wave-based detection methods, and field-based detection methods. System parameter detection methods are normally used in low-power systems for MOD. Wave-based detection methods are suitable for high-power applications, for both MOD and LOD. Field-based detection methods work for both high-power and low-power applications, for both MOD (in an inductive way) and LOD (in a capacitive way). This paper reviews and summarizes the state-of-the-art development of FOD technology in IPT systems.

For power supply of autonomous underwater vehicles (AUV), a novel underwater contactless power transmission (CPT) system based on the arc electromagnetic coupler (EC) is proposed in this paper. The equivalent circuit model of EC is established to analyze the transmission efficiency theoretically, thus the working frequency and the load resistance are optimized. Then the additional eddy current (AEC) loss and the transmission efficiency are analyzed by finite element analysis (FEA) method. Finally, theoretical analysis and simulation results are verified by underwater experiments, which have a maximal transmission efficiency of 82% with a 5 mm gap length.

In the marine environment, the inductive power transfer (IPT) technology offers many benefits such as increased flexibility and complete rejection of the winding problem. However, for underwater vehicles, the impact of seawater flow vibration will affect the stability of the power transmission. In this paper, a symmetrical double coil structure named 1×1×1 system is proposed to reduce the eddy current loss (ECL) and enhance the power transmission stability of the system under the impact of seawater flow vibration. Firstly, based on the discretization of the electric fields excited by each turn of two transmitting coils, the novel calculation method proposed is that the synthetic electric field at each discrete point is the sum of the electric field vector. Then the synthetic electric field and induced voltage of the 1×1×1 system are simulated by the finite element simulation software COMSOL to verify the calculated results. Finally, experiments are conducted to illustrate that the 1×1×1 system has good ability to resist Z-axial interference and reduce the impact of the seawater flow vibration.

Underwater wireless power transfer (WPT) has gained a lot of popularity in recent years. In the seawater environment, the electrical conductivity is non-negligible compared with that in the air. Therefore, the eddy current loss is generated by the high-frequency alternating currents in the coils. The eddy current loss of the aligned coils has been analyzed while the eddy current loss of the misaligned coils has not been explored yet, which is crucial because misaligned coils are more common in practical applications. In this paper, an analytical model for the eddy current loss of a coreless WPT system in the seawater with misalignments is established with Maxwell’s equations. The theoretical expressions of the electric field intensity and the eddy current loss are derived. Then the eddy current loss is analyzed under different misalignments and frequencies. It is found that the efficiency in the seawater remains stable at a frequency range of 215.5 kHz to 248.4 kHz. Moreover, the efficiency is relatively unchanged under a small lateral misalignment and decreases sharply when the lateral misalignment keeps growing. An underwater WPT prototype is built and the experiments verify the theoretical analysis.