In Dynamic Wireless Power Transfer (DWPT), high-frequency noise voltage is applied to both ends of the power transmission coil due to switching noise, which generates a high-frequency current path from the asphalt surface through the ground back to the power source. This results in the generation of common-mode noise, which radiates a large magnetic field. Therefore, this paper focuses on filter design in a circuit configuration using common-mode choke coils and Y-capacitor, which are elements that can reduce switching noise in the power transmission side circuit. It derives a theoretical formula for common-mode voltage with respect to phase shift angle and proposes optimal parameters for common-choke Y-capacitor circuit. As a result in the experiments on proposed optimal parameter, standby loss 2.4W using 3.3nF Y-capacitor was reduced compared to 3.18W not using Y-capacitor when phase shift angle is 90°.

In Dynamic Wireless Power Transfer, it is essential to detect the vehicle, control the switching of the transmission coil, and transmit high power during low coupling to the vehicle. This is because standby loss occurs when power is applied to the transmission coil when the vehicle is not present. Therefore, this paper proposes a method to reduce standby losses and to send high power to the vehicle by using SP-PS circuit and capacitor switching. Consequently, vehicle detection was achieved without additional sensors, standby power loss was reduced by approximately 50% compared to the Double-LCC method, and sufficient receiving power was obtained—although it decreased by about 10% compared to the S-S method in simulations.

Leakage magnetic field is one of the problems of wireless power transfer, which is now used in a variety of situations. Leakage magnetic fields are feared to have adverse effects on the human body and electronic devices and must be for reducing leakage magnetic fields. Passive shielding confines leakage magnetic fields with metal or magnetic materials. Active shielding counteracts leakage magnetic fields by using magnetic fields generated by shielding coils. In this paper, it is shown that the leakage magnetic field can be reduced by shifting the phase of the current flowing in the shielding coil from that of the transfer coil. And it is also shown that the optimum phase difference differs depending on the resonance method and the location of the shielding coil. Phase difference between transfer coil and shieling coil causes leakage magnetic field reduction. The influence of the phase difference between the transfer coil and the receiver coil, and between the shielding coil and the receiver coil is negligible. The phase difference is not necessarily the optimum one to be in the opposite phase. The case of a 600 V input to the transfer coil and a shielding coil installed next to the transfer coil or around the receiver coil is considered. In all cases of S-S, Double-LCC, and LCC-S, leakage magnetic fields can be reduced to about 1 mA/m by adjusting the phase difference between the transfer coil and the shielding coil. The reduction of leakage magnetic field by the phase difference and its optimum value are shown using the theoretical equation and electromagnetic field analysis using the method of moments.

Transmission efficiency is one of the most important characteristics in dynamic wireless power transfer for battery electric vehicles. In this paper, the LCC-LCC compensation topology, which does not require complicated control in a transmission system, is used as the compensation topology. To facilitate laying and maintenance, the transmission system should be as simple as possible in configuration and control. On the other hand, there is no problem even if the receiving side uses a slightly more complicated control than the transmission side. Therefore, on the receiving side, a coupling coefficient is estimated in real time from the voltage and current values measured between the rectifier and the DC/DC converter. Then, maximum efficiency control is achieved by updating the duty ratio of the DC/DC converter to follow the optimum load. The effectiveness of the proposed method was demonstrated through the simulations and experiments.

Typical methods of wireless power transfer are Inductive Power Transfer (IPT) and Capacitive Power Transfer (CPT). Both have different characteristics such as transmission distance, cost, and impact of surrounding foreign matter. In addition, since transmission characteristics differ depending on the circuit. Therefore, in this paper, the design theory for selecting the appropriate circuit and method for various applications is made. The equations for transmission characteristics such as the compensation condition, CC(Constant Current)/CV(Constant Voltage) characteristic, efficiency, optimal load, and output power were calculated. As for compensation condition, it is found that S-P, P-S and P-P for IPT and S-S, S-P and P-S for CPT vary depending on the coupling factor. Substituting specific and impartial values into the calculated equations verified the following. As for the optimal load to achieve maximum efficiency, the value of optimal load in the receiver S is about$\boldsymbol{k}^{\mathbf{2}}$times smaller than the others for IPT, and the value of optimal load in the receiver S and LCL are about$\boldsymbol{k}^{\mathbf{2}}$times smaller than the others for CPT. Therefore, the circuits should be selected according to the value of the load for high efficiency transmission. As for the maximum efficiency, the efficiency does not depend on the transmission method or circuit, since it is the same for all circuits for both IPT and CPT. In terms of output power with voltage source, transmission S for IPT and transmission S and LCL for CPT can get about$\mathbf{1}/\boldsymbol{k}^{\mathbf{2}}$larger power than the other circuits. Regarding the output power with current source, the transmitter P and LCL for IPT and the transmitter P for CPT can get about$\mathbf{1}/\boldsymbol{k}^{\mathbf{2}}$larger power than the other circuits. Therefore, in order to get large power, an appropriate circuit should be selected depending on the type of the transmitter circuit, power source and method of transmission. Based on the above, it was found that LCL in IPT was same characteristic as S, but LCL in CPT was same characteristic as P. From the above, the design theory was made for optimal method and circuit selection by fairly evaluating representative circuits of both IPT and CPT methods under unified conditions.

Coil parameters variation due to manufacturing error or environment causes received power and efficiency decrease in wireless power transfer(WPT). Especially, self-inductance variation causes resonance misalignment, and the system can't maintain ideal characteristics including nominal received power. This paper proposes a power compensation method that controls only the receiving (Rx) side when coil parameters change. By using LCC circuit on the transmitter (Tx) side, wireless communication and power fluctuation due to coil parameter change on the Tx side are eliminated. On the Rx side, the received power is controlled by a DC/DC converter while the resonance misalignment is compensated by a branched capacitor. The proposed method can control the power and compensate the resonance misalignment concurrently. MATLAB Simulink simulation and experimental steady-state measurement results show that power compensation with varying capacitors on the Rx side can improve efficiency by compensating for resonance misalignment.

Several problems remain in the practical application of dynamic wireless power transfer to electric vehicles. It creates the leakage magnetic field that can be bad for people and devices nearby. There are some ways to make the leakage magnetic field smaller, like adding extra coils or materials, but they also add extra weight and cost. This paper proposes a new method to make the far-field leakage magnetic field at 10 m from the reference point smaller without additional equipment. This is a method of reducing the far-field leakage magnetic field by controlling the adjacent power transfer coils in the direction of travel of the power transfer coil that is transmitting power in a double LCC circuit. The currents flowing in the two transfer coils and the receiver coil are derived from the calculation of equivalent circuits considering the coupling between the coils. The effectiveness of the proposed method is confirmed by theoretical calculations using MATLAB and electromagnetic field analysis using Altair FEKO, and it is found that the far-field leakage magnetic field can be reduced below the regulated value without additional equipment.

There have been various types of transmitter coils proposed for dynamic wireless power transfer. This study compared three types of coils: circular (spiral) coil, DD coil, and 85 kHz self-resonant coil. The coil performance was evaluated under an ideal environment on the ground side and after coil embedment in the road, and the characteristics of each coil were clarified. In this study, the allowable current value of the litz wire was evaluated as a constraint condition. The results of the verification using actual coils showed that when the input voltage was increased to around the allowable current value of the litz wire, the 85 kHz self-resonant coil obtained approximately 30 kW of power at the input voltage conversion value of 1160 V. The output power was approximately 8 kW higher than that of the circular coil and the DD coil. It was also found that the circular coil and DD coil showed almost similar power feeding performance when compared.

Dynamic wireless power transfer to electric vehicles is attracting a great deal of attention as a solution to current battery EV issues and a contribution to decarbonization. While there are many challenges for social implementation, the selection of appropriate coils is another important topic. Coils must take into account not only transmission power and efficiency, but also safety, particularly with regard to leakage magnetic fields. In this study, all electrical characteristics of coils were obtained from theoretical equations and compared with electromagnetic field analysis, which showed good agreement. It was found that even a coreless coil can transmit 15.6 kW, 99.1% of the power, below the regulated value of the magnetic field strength. The effects of coil pitch, size, and input voltage on the magnetic field strength are also shown.

In recent years, there have been many studies on wireless power transfer. In particular, it is expected to be applied to electric vehicles, such as stationary and dynamic wireless power transfer. However, power transfer coils for electric vehicles are high cost due to the use of resonant capacitors and ferrites. In previous research, self-resonant coils without ferrite core and capacitors have been proposed to reduce the cost. However, there is not yet a self-resonant coil for electric vehicles that complies with the coil size and power class of international standards. In this paper, we propose a four-layer ferrite-less and capacitor-less coil with self-resonance in the 85 kHz band. As a result of the power transmission experiment, even without ferrites and capacitors, 5.8 kW power in conversion value was obtained with an efficiency of over 90% at a 250 mm air gap.

CPT is cheaper and lighter than Inductive Wireless Power Transfer (IPT). In addition, Capacitive Wireless Power Transfer (CPT) doesn’t have risks of rising temperature of metallic foreign objects. Owing to these advantages, CPT will be able to use in various applications. But, No studies have made circuit comparisons considering differences between voltage and current sources. In this study, the typical circuits S-S, S-P, P-S and P-P circuits in CPT are compared, taking into consideration the difference in load value and the difference in power supply. In compensation condition, the conditions based on the gyrator characteristics and the ideal voltage transformer/current transformer characteristics are adopted. By satisfying this condition, CV characteristic or CC characteristic can be obtained in each circuit. As a result, it was found that the efficiency under the optimal load was the same value in all the circuits regardless of power supply, and the optimal load of S-S and P-S circuits was k2(coupling coefficient) times that of S-P and P-P circuits. When a voltage source is used, the output power of P-S and P-P circuits is k2times that of S-S and S-P circuits, and when a current source is used, the output power of S-S and S-P circuits is k2times that of P-S and P-P circuits. From the above results, it is concluded that when using a voltage source, S-S or S-P circuit should be selected. S-S should be selected when load resistance is low. S-P should be selected when load resistance is high. On the other hand, when using a current source, P-S or P-P circuit should be selected, P-S should be selected when load resistance is low. P-P should be selected when load resistance is high. These results could also be confirmed from experiments using actual circuits.

Wireless power transfer has been attracting a lot of attention in recent years to improve our convenience. Wireless power transfer to electric vehicles is very important to contribute to the spread of electric vehicles and to reduce global warming. Since power supply to electric vehicles often requires high output power, it is essential to design coils to increase the output power by focusing on the coupler part in a specific frequency band from the viewpoint of practicality. In this study, based on SAE J2954 Test station GA-WPT1 and Test station VA-WPT1/Z3 at 85kHz band, we propose a coil design method to obtain the output power while maintaining the efficiency within the required coil size. Although the WPT1 requires 3.3 kW output, the highest efficiency of 99.2% was achieved at 10.9 kW with 600 V input in the simulation. It also achieved 99.0% efficiency at 20.2kW output. The simulation and measurement results show that the inductance of the coil on the transmission side has a significant effect on the output power, which is applied to all wireless power transfer in SS circuits.

In-motion charging technology can drastically improve electrical mileage of Eclectic Vehicles (EVs). Therefore, it is expected as a game-changing technology. In this paper, we investigated cost-effective arrangement design of in-motion charging facilities that can maximize supply energy in the shortest section length as possible. In order to simulate that, we analyzed the actual driving data on urban area in Japan. We focused on the staying time near crossroads with traffic light and found the appropriate in-motion charging section length. Finally we did an electrical mileage simulation using actual driving data and confirm the effectiveness of the in-motion charging facility for electrical mileage extension.

Wireless power transfer (WPT) via magnetic resonant coupling has been widely studied for many applications. In the control of WPT systems with variable power load such as motor, achieving high efficiency and desired power corresponding to the load at any time is important. Some methods which increases efficiency by secondary side power converters has been proposed. In these research, however margin between possible transmission power which is determined by the primary and secondary side voltage and received power is necessary because WPT systems with variable power load is unstable. This paper proposes a method for maximum efficiency operation by dynamic voltage control of the primary and secondary side DC-link. Margin in the transmission power is unnecessary in the system configuration which has supercapacitor and DC/DC converter on the secondary-side because supercapacitor compensates power fluctuation. Simulations and experiments demonstrated feasibility of the proposed method and effectiveness of the controllers.

Due to the extremely low temperature of Moon surface at lunar night, lunar rover has suffered from heat leakage along the wire connection between solar battery and rover body. In this paper, a wireless power transfer system has been proposed to transfer energy from solar battery to rover body in order to aovid the heat leakage at lunar night. The solar battery is controlled by a buck converter to be switched between the Maximum Power Point Tracking (MPPT) mode and buck mode to output appropriate amount energy to load and battery in rover body through the wireless power transfer system. The load and battery is connected to the DC bus which is controlled by a DC-DC converter to stabilize the voltage. Based on the experiment results, the whole system efficiency is about 48.7% at 22 W. It has been demonstrated the system efficiency is closely related with system power level due to the power electronics wasted power, and the efficiency can be improved to 62.1% with higher system power at 48.6 W.

Capacitive power transfer (CPT) with resonance coupling has various advantages compared with inductive power transfer (IPT) with resonance coupling. There are some difficulties of the circuit design because the circuits in CPT with resonance coupling such as SS and SP topologies are not sufficiently analyzed. Therefore, this paper analyzes the SS and SP topologies based on power factor consideration and presents the design methods for resonant conditions and target load to achieve higher efficiency. Furthermore, theoretical formulas and characteristics of the transmission efficiency and output power in SS and SP topologies of CPT are investigated. The feasibility of theoretical formulas is verified with simulation and experiment.

In wireless power transfer, high voltage can breakdown the resonance capacitor due to magnetic resonance coupling in S/S topology. Then, an open-end coil can be self-resonant with parasitic capacitance and can be maintenance-free for primary-side system even if the coupling is weak. It is necessary for high-power and high-efficiency transfer to reduce the resistance of coils. However, the internal resistance of the coil is not sufficiently low to transfer high power. In this paper, in order to reduce the resistance of the coil, the dielectric property is explored. The experiments demonstrated that the internal resistance of the proposed coil can be reduced by considering the dielectric loss.

The most critical problem in high-precision stages for semiconductor and LCD manufacturing is cable disturbance, which can be caused by power cables and communication lines. In our previous study, we designed a novel single-axis high-precision stage using wireless power transfer technology, which avoids cable disturbance. Here, we further develop this concept and propose a multi-axis wireless high-precision. Experimental results demonstrate the effectiveness of the multi-axis wireless high-precision stage.

Wireless power transfer (WPT) via magnetic resonance coupling has gathered attentions because of its high transmitting efficiency and robustness to misalignment. The efficiency characteristics of the WPT system are expressed by kQ product, which is given by coupling coefficient and quality factors of a transmitter and receiver. However, a conventional measuring method of the kQ product is quite burdensome because it requires to remove the resonance capacitors of the transmitter and receiver and to change connecting points of measuring equipment. In this paper, a simplified measuring method of the kQ product is proposed based on the input impedance of the WPT system. The experiments demonstrate that the proposed method is simple yet effective and the measurement results not only evaluates the maximum transmitting efficiency but also estimates an optimum load condition for designing an efficiency control system.

Semiconductor and LCD manufacturing equipment, which needs to position the stage in high-speed and high-precision, has been developed on both the mechanism and control. The experimental results, however, is often different from theoretical results because of a cable disturbance caused by such power cables and communication lines. Therefore, in order to eliminate the high-voltage cable disturbance, this paper proposes a next generation high-precision stage with lightweight moving coil type linear motor powered by wireless power transfer via magnetic resonance coupling. The experimental results demonstrate effectiveness of the proposed high-precision stage.

A dynamic wireless charging system for electric vehicles (EVs) is expected to extend the limited driving distance of EVs. As the transmitting efficiency changes according to motion of the vehicle in dynamic charging, an efficiency maximization method is important. Previous research has proposed secondary-side efficiency control based on mutual inductance estimation to simplify the ground facilities, which would be installed over long distances. However, the ground facilities have to regulate the primary voltage to achieve maximum efficiency control on the secondary side without signal communication. In this paper, a calculation method of the reference value for maximum efficiency control is proposed using simultaneous estimation of the primary voltage and the mutual inductance on the secondary side to eliminate the need for the primary voltage regulation. Simulations and experiments demonstrate that the proposed method is available for maximum efficiency control on the secondary side.

The differences between electromagnetic induction and magnetic resonant coupling were presented in the first study on electromagnetic resonant coupling. However, there is no clear technical comparison between the two phenomena. Therefore, in this study, four circuits are compared. The transition from typical electromagnetic induction to magnetic resonant coupling is demonstrated. The superiority for a high efficiency and high power transfer across a large air gap and displacement is discussed, where the primary and secondary resonant frequencies are the same. From the discussions, the superiority of magnetic resonant coupling over the other topologies is proposed at large air gap and verified experimentally.

Electric vehicles are an efficient alternative to gasoline-fuelled vehicles, but suffer from limited cruising range and long battery charging time. Wireless power transfer is among the solutions for these problems. By using it, the control of the power converters is essential for achieving high efficiency and desired power to the load at any time. Simultaneous regulation of both power and efficiency on the secondary side of WPT systems has already been proposed in past research. However, such control is still not verified in a dynamic scenario. Therefore, in this paper, the aforementioned control is applied to a dynamic charging scenario. The controllers are based on the online mutual inductance estimation, performed with recursive least square filter by constant trace algorithm. The experimental results show that the proposed control effectively works in dynamic charging.

In-Wheel Motor (IWM) which is a driving system of Electric Vehicles (EVs) is effective for expanding driving range and reducing vehicle weight. However, IWM has not been put in practical use because of a possibility of power lines disconnection. Therefore, we have proposed Wireless In-Wheel Motor (W-IWM) in which Wireless Power Transfer (WPT) is used to remove these lines and to enhance practicability of IWM. Moreover, we have proposed the advanced system of W-IWM which has Lithium-ion Capacitor (LiC) and circuit on its wheel side for dynamic charging. In this paper, a State of Charge (SOC) control of LiC on the wheel side in the advanced system is proposed. By applying the proposed control, the SOC control of the LiC and power management on the wheel side are achieved simultaneously. The proposed control is verified by simulations and experiments.

Wireless Power Transfer (WPT) has been widely researched in many application fields. Typical application to vehicle field is wireless charging for electric vehicles while parking and driving. Some power conversion circuit structures and its control method have been proposed in previous researches, for example, transmitting power control and efficiency maximizing control using a secondary-side DC-DC converter. However, selection method of optimal circuit structure for desired control is not clear. In this research, we propose generalized power conversion circuit structure on Series-Series compensated WPT circuit. Load current and power transfer efficiency are analyzed using equivalent AC resistance model about WPT circuit with constant voltage load. Then, we formulate operation points for desired control with consideration for operating condition.

Wireless power transfer (WPT) via magnetic resonance coupling provides highly efficient mid-range transmission. Its transmitting power can be controlled using a diode rectifier and a DC-DC converter on the secondary side. Previous research replaces the load and the rectifier circuit with an equivalent load resistance or a fundamental harmonic sine wave voltage source to analyze the charging power of WPT. In such a case however, the effect caused by the rectifier circuit becomes unclear because the harmonic components are neglected. As a result, the theoretical charging power and its true value have an error due to the harmonic current distortion. In this paper, a novel WPT circuit model is proposed for the analysis of the harmonic current distortion on the secondary side. The proposed model uses the secondary voltage as the input variable of transfer functions and makes clear the effect caused by the rectifier circuit. Experiments demonstrate that the harmonic current distortion is increased with the increase in the secondary voltage. These results accord with the analysis using the proposed model and verify the effectiveness of the proposed model.

Transmitting efficiency is able to be controlled by changing the input impedance on the receiving side using a DC-DC converter for static wireless power transfer system. However, the control method has never been applied for dynamic wireless power transfer system where coupling coefficient changes drastically. The information of coupling coefficient is needed constantly to achieve the control. Moreover, the considerations about dynamics of the transmitting circuit and coupling coefficient are necessary in dynamic wireless power transfer system. In this paper, a simple method of coupling coefficient estimation with RLS (Recursive least squares) filter and maximum efficiency control using a PID feedback controller are proposed. The simulation and experimental results of dynamic maximum efficiency control are provided and indicating the effectiveness of the proposed control in a real dynamic wireless power transfer system for EVs.

Electric vehicles (EVs) are very useful but suffer from limited range and long battery charge time. Using wireless power transfer (WPT) allows these issues to be solved. In WPT, the control of the power converters is very important in order to achieve high efficiency and be able to extract the desired power from the source at any time. Until now, it was possible to perform either power control or efficiency control in the secondary side, but not both at the same time. Therefore, the authors propose a novel control for power and efficiency with two converters entirely performed on the secondary side of the wireless system, independently from the primary side. The proposed control allows achieving high transmitting efficiency for the desired power by means of a half active rectifier. Simulations and experiments shows that this method effectively allows achieving high efficiency even when the desired power is varied.

In this paper, a novel dynamic wireless power transfer system is designed for roadway EV powering application. Multiple LCL resonators are parallel connected in a high-power inverter and are turned on/off through vehicle positioning result. Compared to the conventional long-rail manner, firstly, the miniaturized transmitter can greatly reduce the electromagnetic radiation. Secondly, construction costs are significantly reduced due to both the transmitter and receiver do not require ferrite. Finally, the generalized state-space averaging and small signal model are built to analyze both the steady-state and transient response process. Experimental results validate the proposed dynamic model and system performance.

The In-Wheel Motor (IWM) is the most preferable driving mechanism of electric vehicles for vehicle motion control, energy efficiency, and vehicle design flexibility. One technical issue of the IWM is the reliability of power and signal wires. Wireless power transfer technology is the best solution. In this paper, a bidirectional wireless power transfer circuit using a primary inverter and a secondary converter is proposed. We propose a control method of both the inverter and the converter to stabilize the secondary DC-link voltage. The proposed method is verified by simulation and experiments using simulated test equipment.