Wireless Power Charging System Research Articles

Development and Optimization of a Wireless Power Charging System for an Inspection Drone

Unmanned aerial vehicles (UAVs) have advanced and are now employed in a variety of industries, including aerial photography, the military, and transportation. Due to its low battery life, charging it can be difficult. A good UAV solution has been thought of as wireless charging. In this research, we suggested an inductively coupled wireless power transmission system (WPT) and examined the inductive coupling’s power efficiency. A portable energy receiving device positioned on the base of the UAV and a charging station with an induction coil array were both included in the WPT. Additionally, the WPT equivalent circuit was used to examine power efficiency, and a prototype model of the battery coupled with a quadcopter for testing power efficiency was developed. The results onboard the charging circuit design contributed with polarity modulation and safety charging the battery pack, with very light components that considerably decrease the size and weight as much as possible. The charging power conversion efficiency has achieved 83.76% at the maximum.

초고속 자기부상열차용 다중 무선충전장치에서 차폐 장벽조건에 따른 동작특성 조사

We have developed a wireless power charging(WPC) unit for the high-speed superconducting magnetic levitation train to improve the transfer efficiency and stability given that the WPC system can supply electric power without overhead wire power lines of pantographs. Various multi charging units have been required in the super high-speed transportation systems given that their utilization can improve the charging capability and reduce the construction cost of pantographs. Practically, the antenna (Tx) is installed adjacent to the shielding barriers. This way affects the transferred power considering that the Tx and multi-receiver (Rx) coils are intrinsically sensitive to impedance variation due to the external shielding barriers. Thus, the investigations of electric field (E) and magnetic field (B) between Tx and Rx coils should be conducted to control the charging rates. In this study, the authors present the intensities of electric and magnetic fields, as well as the thermal distributions and transfer efficiency between Tx and Rx coils using an RF generator of 370 kHz and 250 W.

Intracranial EEG Recordings of High-Frequency Activity From a Wireless Implantable BMI Device in Awake Nonhuman Primates.

Wireless implantable brain machine interfaces (BMIs) are a promising tool to restore communication and motor functions for individuals with severe motor disability. Prior to clinical application, recording performance must be sufficiently confirmed by animal experiments. In this paper, we aimed to evaluate the performance of a novel BMI wireless device for recording brain activity in two nonhuman primates. We customized a wireless device for implantable BMIs for clinical application. We used a battery instead of a wireless power charging system. Thirty-two electrodes were subdurally implanted over the left temporoparietal cortex. We evaluated the recording performance of the wireless device by auditory steady-state responses (ASSRs) and ketamine-induced responses. The devices successfully recorded broadband oscillatory activities up to the high-frequency band from the temporal cortex in two awake macaque monkeys. Spectral analysis of raw signals demonstrated that the devices detected characteristic results of a 40-Hz ASSR and prominent high-frequency band activity induced by ketamine injection. We confirmed the functionality of the wireless device in recording and transmitting electrocorticography (ECoG) signals with both millisecond precision and recording stability. These results provide confidence that this wireless device can be a translational tool for other fundamental neuroscientific studies in free-moving models.

Effect and Influence of Double Resonance Couplings With Dual Resonance Frequencies for Wireless Power Multi-Charging Module in Superconducting MAGLEV Train

The wireless power charging (WPC) system based on the resonance coupling method, which is composed of separate coils with same resonance frequency, is feasible for exchanging electric energy within 2 m. We have been developed the WPC unit for high speed superconducting magnetic levitation (MAGLEV) train to improve the transfer efficiency and stability since the WPC system can supply electric power without overhead wire power lines of pantographs. Practically, the various WPC units have been required in the super high speed transportation systems since it can reduce the construction cost of pantographs as well as multi charging units to inside and outside of traveling train. From this point of view, authors proposed the enhanced WPC system using multi antenna (Tx) coils with dual-resonance frequencies to expand the practical way. As the multi Tx and multi-receiver (Rx) coils of WPC unit are intrinsically sensitive to impedance variation from external factors such as double resonance coupling coils and the electromagnetic propagations, the effect and influence of charging characteristics for double resonance coupling coils with dual-resonance frequencies should be exanimated. In this paper, the effect and influence of charging characteristics and thermal distributions were investigated under the different resonance coupling modeling with 370 and 750 kHz power sources. In addition, the effect of reflected power at Tx coils was investigated under double resonance coupling coils.

Wireless Power charging system with Self-Adjusting Charge nodes for Electric Vehicles

Electrical Vehicles wireless charging emerges every year with new trends. Charging Techniques for Electric Vehicles has progressed competently in the wireless charging market. Wireless charging takes upon two coupled coils and its mutual inductance is relative to each other. In this work, a self-aligning Wireless Electric Vehicle Charging is proposed. The major idea is to upgrade the efficiency of Electric Vehicle charging through proper alignment for the Receiver and Transmitter of Electric Vehicles.

The Biocompatibility of Wireless Power Charging System on Human Neural Cells

The progress in technology and science leads to the invention and use of many electrical devices in the daily lives of humans. In addition to that, people have been easily exposed to increased newly generated artificial electromagnetic waves. Exponential use of modern electronic devices has automatically led to increase in electromagnetic wave exposure. Therefore, we constructed the prototype of wireless power charging system to study the biocompatibility of electromagnetic field (EMF) generated by this system on various human cell lines. There are many studies indicating the negative bio-effect of EMF on various types of cells, such as induction of apoptosis. From the other point of view, these effects could rather be beneficial in the way, that they could eliminate the progress of various diseases or disorders. For that reason, we compared the impact of EMF (87 kHz, 0.3–1.2 mT, 30 min) on human normal as well as cancer cell lines based on morphological and cellular level. Our results suggested that EMF generated by wireless power charging systems does not have any detrimental effect on cell morphology, viability and cytoskeletal structures of human neural cells.

A coreless hybrid coil design for the wireless power charging system

In the dynamic magnetic coupling wireless charging system, the optimal design of the resonant coil structure is one of the key technologies to ensure the power transmission with the high efficiency. In this paper, based on the good static characteristics of system, a hybrid structure coil is proposed to improve the efficiency and the dynamic anti-offset ability of system. Based on the simplified circuit model of the PP compensation network, the efficiency and the output power of system under the optimal load impedance are derived based on Kirchhoff voltage law. According to the efficiency expression, the number of the turns of the hybrid coil and the radius of the coil are optimized, and the parameter design method of the hybrid coil under the specific environment is given. In order to evaluate the dynamic performance of the system, a quantitative evaluation index is given, which synthesizes three kinds of the dynamic characteristics of the axial, the radial and the angular. Finally, the feasibility of the designed coil is verified by the finite element simulation.

A coreless hybrid magnetic coupling coil structure for dynamic wireless power charging system

A coreless hybrid magnetic coupling mechanism has been studied and designed in the dynamic wireless charging system, through the mathematical model building, the parameter analysis and the model simulation comparison. The mechanism can improve the endurance of the electric vehicles, reduce the times of the power supply of the electric vehicles, and increase the offset ability. First of all, the dynamic model of the magnetic coupling mechanism is established based on the Kirchhoff’s law of the voltage and current, and the output power and the system efficiency are deduced considering the driving speed of the electric vehicle. Then, the influence of the mutual inductance between coils on the output power and the system efficiency is deeply analyzed, and the mutual inductance between coils is increased by adding the magnetic potential at a proper position, to propose and analyze a coreless hybrid magnetic coupling coil structure. Finally, the co-simulations are implemented through the finite element analysis simulations to compare and analyze the coil structure performance before and after the optimization. The results show that the designed coil structure can effectively improve the coupling between magnetic fields, and increase the offset ability. The mechanism has the characteristics of the small dynamic output power fluctuation range and high efficiency, and then can realize the stable power supply for the mobile power load.

Maximum Efficiency Point Tracking Scheme for Loosely Coupled Multiple-Receiver Wireless Power Charging System With Mutual Inductance Tracking

This article presents a maximum efficiency point tracking (MEPT) scheme for a multiple receivers and loosely coupled wireless power charging (WPC) system with a mutual inductance tracking method. In general, the WPC system should satisfy the requirements of constant output voltage and the highest possible efficiency according to sensitive variation of charging environments. To this end, a state-of-the-art MEPT scheme has been studied in this work. Additionally, one of the advantages of the loosely coupled WPC system is the ability to charge multiple devices simultaneously. However, most studies have focused on a single-input and single-output (SISO) system. In this article, we propose a MEPT scheme for a multiple receiver WPC system and a mutual inductance tracking method. The proposed control scheme determines the current of the transmitter based on the mutual inductance between the transmitter and receivers. For validation, the proposed single-input multiple-output (SIMO) WPC system was implemented at 1 MHz using loosely coupled series-series resonant coils and the proposed mutual inductance tracking method. The results verified the performance of the proposed MEPT scheme in a SIMO system regardless of changing charging environments.

Magnetic Field Mitigation by Multicoil Active Shielding in Electric Vehicles Equipped With Wireless Power Charging System

A novel design of active coil shielding is proposed to reduce the magnetic field generated by the currents flowing into the coils of a wireless power transfer (WPT) system for charging the batteries of an electric vehicle (EV). The main idea is to divide the traditional active loop used to shield a source in two separate shielding coils so as not to adversely affect the WPT performance. This concept is applied to shield the WPT coils, and, therefore, in the proposed design, there are active coils placed on the ground parallel to the primary coil of the WPT and some others on board below the vehicle, planarly located with the secondary coil. The currents on the active coils are optimized in order to minimize the magnetic field in the most critical zone accessible from humans, i.e., region besides the EV and in the cabin.

Single-Layer Transmitter Array Coil Pattern Evaluation toward a Uniform Vertical Magnetic Field Distribution

A uniform magnetic field distribution is a critical aspect in the transmitter array coil design process for achieving a homogenous vertical magnetic field distribution. The free position and orientation features can thus be implemented in the wireless power charging system. This paper presents vertical magnetic field distribution generated by a single-layer circular flat spiral air core transmitter array coil model analysis and evaluation using a numerical analysis method. This method is developed based on the off-symmetry axis magnetic field distribution due to a circular current loop derived from the Biot-Savart law. The proposed evaluation criteria are used to obtain the vertical magnetic field distribution characteristic of the evaluated array coil model. The vertical magnetic field distribution of several circular flat spiral air core coils, in both single and array coil models with different coil geometries were investigated to obtain the relation between the coil parameters and the distance between the adjoining coil centers to generate uniform vertical magnetic field distribution. A case study was also conducted to analyze and evaluate several array coil model patterns (1 × 2 array coil, 1 × 3 array coil, 2 × 2 array coil, 2 × 3 array coil) to meet uniform vertical magnetic field distribution. The array coil model is composed of an identical single circular flat spiral air-core coil. Every single coil has inner coil diameter (Di), outer coil diameter (Do), wire diameter (W), pitch (P) and a number of turns (N) at 25 mm, 47.8 mm, 0.643 mm, 0.03 mm, 17 respectively. The study and evaluation of several array coil pattern models show that the distance between the adjoining coil centers should be defined close to the half of coil outer diameter (1/2Do) to generate close to uniform vertical magnetic field distribution. The vertical magnetic field distribution average and magnetic field effective transmitting areas array coil model with the given coil parameters changing as the effect in variation in distances between the adjoining coil centers.

Operating Characteristics for Different Resonance Frequency Ranges of Wireless Power Charging System in Superconducting MAGLEV Train

Our research team has developed a wireless power charging system for a high-speed superconducting magnetic levitation train based on the strong resonance coupling method to improve the transfer efficiency and stability. Especially, the range of resonance frequency is one of main key design parameters to fabricate the system since the high resonance frequency can improve the transfer distance easily. On the other hand, since the sensitivity of impedance matching between antenna and receiver coils is increased in the range of higher frequency, the technique of stable impedance matching design including elaborated rectifying subcircuit has been required to commercialize under high-power transfer applications. For this reason, the various transfer characteristics under different ranges for resonance frequency conditions should be evaluated to accomplish improve the transfer efficiency. Thus, in this paper, the transfer efficiency of the moving position of receiver (Rx) coil and consumption of liquid nitrogen were measured at 100 and 370 kHz with 250 W, respectively. In addition, the operating characteristics of the cooled copper Rx and HTS Rx coil were evaluated under 100 and 370 kHz with 250 W, respectively.

Design Considerations of Cooling Vessel to Improve Power Charging under Magnetic Shielding Structure in Wireless Power Charging System in Magnetic Levitation Train

The wireless power transfer (WPT) using magnetic resonance coupling method has been known to have the advantage of being able to transfer power across large air gap with considerably high efficiency. As well as, as such a method can eliminate the physical contact loss in the system, it provides an ideal solution for the problem of contact losses in the power applications. From these reasons, WPT technology has started to be applied to the wireless charging for various power applications such as transportations (train, underwater ship, electric vehicle). In the high speed superconducting magnetic levitation (MAGLEV) train, antenna (Tx) coils, which are installed both sides of train, are placed on the guidance rail, as well as, superconducting receiver (Rx) coils can be installed in traveling train. In the superconducting system, a cooling vessel, which is made by steel materials, is a requisite subsystem. However, since the steel materials can shield electromagnetic field, the structure design of cooling vessel can affect the transfer efficiency. In this study, we presented transfer efficiency and operating characteristics from copper Tx to superconducting Rx coil under different structures of cooling vessel with radio frequency power of 370 ㎑ below 500 W.

Operating characteristics and cooling cost evaluation for HTS receiver arrays of wireless power charging system in superconducting MAGLEV train

Since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety and fearless transmission of power during movement. Above all, the WPT technology in the MAGLEV can reduce the cost of tunnel construction since the space of conventional power line doesn’t required. From these merits, the WPT systems have been started to be applied to the wireless charging for various power applications such as transportations (train, underwater ship, electric vehicle). In this study, as a practical approach, authors investigate transfer efficiency and cooling cost for multi-Tx and multi-sized single Tx coils under different size of Rx coils arrays, respectively. Additionally, authors investigated transfer ratio at HTS Rx with helix and spiral Tx coils under different interval. As well as, authors evaluate cooling cost of different sizes of HTS receiver under long single and multi-copper antenna arrays based on nitrogen evaporation method.

Impact Investigations and Characteristics by Strong Electromagnetic Field of Wireless Power Charging System for Electric Vehicle Under Air and Water Exposure Indexes

Our research team has been developing a wireless power charging (WPC) system for electric vehicle (EV) using superconducting and normal conducting resonance coils in order to improve the transfer efficiency and stability. In the practical approach, the EV, which is installed outside, is wirelessly charged without moving. The antenna (Tx) coil is disclosed by rain or snow and so on. From this reason, the transfer characteristics surrounded by water circumstance, i.e., fresh water or salt water, should be evaluated to commercialize In addition, the high-voltage WPC system generates strong electromagnetic fields (EMFs) around Tx and receiver (Rx) coils. As the human safety with respect to EMFs is an important measure, it is required to identify the condition under which human exposure complies with the safety regulations. Thus, in this paper, as a fundamental approach, the spatial spots of current around Tx and Rx coils were measured. As well as, the transfer efficiencies of a WPC unit under different water circumstances of Tx and Rx coil were measured with an RF generator of power of 150 W, 370 kHz.

A Simple Wireless Power Charging Antenna System: Evaluation of Ferrite Sheet

We report a simple wireless power charging (WPC) antenna system (50 mm $\times40$ mm $\times0.1$ mm) for use in simulating power transfer efficiency ( $\eta $ ) with and without ferrite and a metallic object (battery case), thereby identifying suitable magnetic parameters and ferrite sheet thickness. The simulation results suggest that magnetic loss tangent (tan $\delta _{\mu }$ ) and permeability ( $\mu '$ ) need to be less than 0.05 and higher than 125 at 13.56 MHz, respectively, to achieve at least 75% of the transfer efficiency ( $\eta _{\mathrm {max}}$ ) of the WPC antenna without ferrite and the metallic object. Accordingly, we have fabricated Ni x Zn0.85– x Cu0.15Fe2O4 (x = 0.32 – 0.38) spinel ferrites using a one-step sintering process and obtained relatively high $\mu '$ of 169 and low tan $\delta _{\mu }$ of 0.1 with a nickel (Ni) concentration of 0.38. This magnetic loss is still too high to achieve 75% of the $\eta _{\mathrm {max}}$ value. In order to further reduce the magnetic loss, a two-step sintering process was used. The two-step sintered Ni0.38Zn0.47Cu0.15Fe2O4 shows $\mu '$ of 132 and a tan $\delta _{\mu }$ of 0.03 at 13.56 MHz, respectively. Therefore, this ferrite meets criteria identified by the transfer efficiency simulation and is a good candidate for 13.56-MHz wireless power transfer charging antenna system. In addition, our designed WPC system is capable of evaluating other magnetic materials that are suitable for WPC antenna applications.

Conceptual Design and Operating Characteristics of Multi-Resonance Antennas in the Wireless Power Charging System for Superconducting MAGLEV Train

Recently super high-speed magnetic levitation (MAGLEV) using high-temperature superconducting (HTS) magnet has been expected as next-generation transportation since superconducting magnet can keep mighty levitation force. The superconducting magnet at MAGLEV train should be continually charged with high power in order to keep stronger and stable levitation force. Practically, since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance-coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications, such as transportations (train, underwater ship, electric vehicle). However, it has obstacles to commercialize, such as delivery distance and efficiency. To solve the problems, authors proposed the technical fusion using HTS resonance coil in the WPT system since the superconducting wire has merits a larger current density and higher Q -value than normal conducting wire. In this study, authors described the conceptual design of HTS receiver (Rx) coil with multi-copper antenna (Tx) coils. The priority characteristics of moving HTS receivers under multi-copper Tx coils are compared with and various copper Rx coils with radio frequency power of 370 kHz below 300 W.

Influence of fields and SAR evaluation for 13.56 MHz EV resonance-based wireless power charging systems

Influence of fields and SAR evaluation for 13.56 MHz EV resonance-based wireless power charging systems

Design of Maximum Efficiency Tracking Control Scheme for Closed-Loop Wireless Power Charging System Employing Series Resonant Tank

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.

Design of a Rechargeable Battery Wireless Charging System

This paper presents a wireless power charging system for rechargeable batteries. Recently, misalignment between transmitting coil and receiving coils has been a significant factor to wireless power charging systems, which are prone to lateral and angular misalignment. Unfortunately, the batteries can be easily rolled because of the shape, and coils are often misaligned while charging devices, in practical situations. This paper presents the wireless power battery charging system. In order to solve the angular misalignment, two perpendicular coil having structure of ‘plus (+)’ shape was proposed. To validate the results, the proposed wireless power charging system was implemented at 6.78 MHz using loosely coupled resonant coils, and the system was verified as being robust to misalignment.