Inductive Wireless Power Transfer Research Articles

Power Stability Enhancement in Inductive Wireless Power Transfer Systems: A Review

Power Stability Enhancement in Inductive Wireless Power Transfer Systems: A Review

Load Modulation Feedback in Adaptive Matching Networks for Low-Coupling Wireless Power Transfer Systems

This paper explores the use of load modulation feedback (LMF) in adaptive matching networks (MN) for low-coupling inductive wireless power transfer systems, with an emphasis on its use in implantable medical devices. After deriving the handy expressions of link efficiency and modulation depth in the case of LMF in the case of loose coupling, a brief overview of the most common capacitive resonance networks is presented. In particular, the MN employing two capacitors in Series–Parallel and in Parallel–Series configurations allow adaptivity with a wide range of load conditions. Then, the authors describe an effective design procedure of an adaptive matching network with LMF for an inductive wireless power transfer system, exploring the trade-off between power efficiency and modulation depth. Analytical and electrical simulations show that the proposed simple modulation strategy can successfully achieve high power transfer efficiency while maintaining steady back telemetry under varying loading conditions.

Varied-Frequency CC–CV Inductive Wireless Power Transfer with Efficiency-Regulated EV Charging for an Electric Golf Cart

Wireless electric vehicle (EV) charging is an important operation for valuable EV options in modern life. Inductive wireless EV charging needs constant current and voltage (CC–CV) charge controllers. This paper presents 750 W variable frequency CC–CV inductive wireless charging for an e-golf cart 50 Ah 72 V Li-ion battery. Due to this system’s low power, the system’s efficiency may be weak; the secondary-side (SS) maximum efficiency-controlled (MEC) converter was validated. The golf cart’s battery characteristics were evaluated to design and experiment with inductive wireless power transfer (IPT) coils and an integration system for a 42 kHz resonant frequency. The CC–CV charged control is an infrastructural part of the H-bridge inverter at varied frequencies from 50 kHz to 56 kHz when the DC input voltage is 310 V, and in the range of 44 kHz to 46 kHz at the 155 V input. The results found the charging of 9 A CC, 82 V CV and 730 W. The 310 V input voltage system without the SS MEC converter’s efficiencies was 62% to 72% and it was improved to 65% to 81% using the SS MEC converter. Finally, the best cases were validated at the 155 V DC input voltage and the system with the SS MEC converter had 76% to 86% efficiency.

Wireless power transfer technologies for electric vehicles: Principles, challenges and opportunities

Wireless power transfer (WPT) technology is a promising solution for charging electric vehicles, which have many advantages such as zero emissions, low noise, and convenience. This paper reviews the current state-of-the-art of WPT technology for electric vehicles, focusing on the classification, principle, advantages, and disadvantages of different WPT methods, such as capacitive WPT, inductive WPT, microwave WPT, and laser WPT. The paper also discusses the future trends and challenges of WPT technology, such as coil design, international standards, safety issues, multiple charging modes, and compensation networks. The paper aims to provide a comprehensive overview of WPT technology for electric vehicles and to inspire further research and development in this field.

Model-Based Optimization of Spiral Coils for Improving Wireless Power Transfer

Inductive wireless power transfer is a promising technology for powering smart wearable devices. The spiral coil shape is widely used in wireless power transfer applications. Nevertheless, during the coil design process, there are many challenges to overcome considering all the design constraints. The most important is to determine the optimal coil parameters (internal radius, external radius, spacing, wire width, and conductive wire) with the aim of obtaining the highest coil quality factor. Coil modeling is very important for the wireless power transfer system’s efficiency. Indeed, it is challenging because it requires a high computational effort and has convergence problems. In this paper, we propose a new approach for the approximation of spiral coils through concentric circular turns to reduce the computational effort. The mathematical model determines the optimal coil parameters to obtain the highest coil quality factor. We have chosen the smart textile as an application. The system operates at a frequency of 100 Khz considering the Qi guidelines. To validate this approach, we compared the approximated circular coil model with the spiral coil model through a finite element method simulation using the COMSOL software. The obtained results show that the proposed approximation reduces the complexity of the coil design process and performs well compared to the model corresponding to the spiral shape, without significantly modifying the coil inductance. For a wire width smaller than 1 mm, the total deviation is around 4% in terms of the coil quality factor in a predetermined domain of its parameters.

Benchmarking of cutting-edge wireless power transfer for electric vehicles

Wireless power transfer (WPT), which can transfer energy though magnetic field, electronic field, laser beam, microwave and other methods without wire, provide electric vehicles (EVs) a better prospect. Compared to cars with internal combustion engines, Electric vehicles are more environmental-friendly, and do not need any fossil fuel, which is a ideal transportation in the future, however, for electric vehicles, battery technology is the major barrier: high cost, low energy density and large weight, which make electric vehicles very expensive and difficult to improve the endurance mileage, by applying wireless power transfer technology, using dynamic wireless charging can solve these problems perfectly. This paper reviews basic information of wireless power transfer technologies: four basic classification of WPT, basic compensation networks for inductive wireless power transfer, coil designs to improve the transferring efficiency, and wireless power transfer applications on EV charging, additionally, challenges and potential solutions for wireless power transfer of EV are presented.

Experimentally verified numerical model for asymmetric ferrite core wireless power transfer with on-chip interfacing circuits

This paper presents a novel numerical model for asymmetric ferrite core wireless power transfer, which has been experimentally verified. The research focuses on addressing the challenge of reducing the resonance frequency in wireless power transfer technology, particularly for cost reduction in power transfer systems. To achieve this, a toroidal ferrite core is utilized to decrease the self-resonant frequency, and the transmission parameter is measured using a vector network analyzer. Inductive wireless power transfer designs operating at MHz frequencies often suffer from low current efficiency due to the quality factor of the resonant coils. To overcome this limitation, finite element analysis is employed to optimize the cross-sectional area of the inductors, specifically for high-frequency wireless power transfer. The results demonstrate the effectiveness of the optimized coils, achieving an impressive transfer efficiency of nearly 98% at 5 cm, with an operating frequency of 21.6 MHz. Furthermore, the system is enhanced with a CMOS-based interfacing circuit, designed to enable system-on-chip power transfer for Internet of Things (IoT) applications. This integrated system design contributes to the advancement of wireless power transfer technology by not only addressing resonance frequency reduction but also proposing a cost-effective and efficient solution for power transfer in IoT applications.

Joint Real-Time Identification for Mutual Inductance and Load Charging Parameters of IPT System

Accurate and fast identification for mutual inductance and load charging parameters of inductive wireless power transfer (IPT) system is essential for impedance matching, and the output control of communication-free IPT system. A joint real-time identification method for mutual inductance and load charging parameters of IPT system is proposed in this paper. Only via measuring the RMS value of fundamental voltage and current on primary side, the double equivalent impedance modulus equations about mutual inductance and equivalent load resistance are established. To obtain real-time identification results of mutual inductance and equivalent load resistance from the high-order implicit function equations, an improved adaptive filtering algorithm based on Least Mean Squares (LMS) is proposed. Then, the identification values of load charging parameters are obtained according to the identified mutual inductance and equivalent load resistance. Finally, a 3.6kW platform is built to verify the validity of the proposed method. And the experiment results show that, compared with other existing achievements, the proposed method can identify <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U_Bat</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_Bat</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_L</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> simultaneously in real-time without changing the system operation, and it has faster rate and higher accuracy of identification.

Wearable Transmitter Coil Design for Inductive Wireless Power Transfer to Implantable Devices.

Wireless endovascular sensors and stimulators are emerging biomedical technologies for applications such as endovascular pressure monitoring, hyperthermia, and neural stimulations. Recently, coil-shaped stents have been proposed for inductive power transfer to endovascular devices using the stent as a receiver. However, less work has been done on the external transmitter components, so the maximum power transferable remains unknown. In this work, we design and evaluate a wearable transmitter coil that allows 50 mW power transfer in simulation.Clinical Relevance-This allows more accurate measurements and precise control of endovascular devices.

Observer-Based Control of Inductive Wireless Power Transfer System Using Genetic Algorithm

In this paper, we studied the feedback stabilization of an inductive power transfer system based on available output measurement. The proposed controller relies on a full-order state observer in order to estimate the unmeasured state. The control design problem is challenging due to the large dimension of the closed-loop system, which requires too many tuning parameters to be determined when conventional control methods are employed. To solve this issue, we propose an LQR methodology based on a genetic algorithm such that the weighing coefficients of the cost function matrices can be automatically computed in an optimized manner. The proposed approach combines the method of eigenstructure assignment and the LQR technique in order to design both the controller and the observer gain matrices. The design methodology provides a systematic way to compute the parameters of the LQR technique for a wireless power transfer system in an optimized manner, which can be a useful design tool for many other applications. The effectiveness of the approach was verified by numerical simulation on the dynamic model of the wireless power transfer system. The results show that the proposed design outperforms conventional design methods in terms of a better performance and reduced design iterations effort.

Design of a Highly Compatible Underwater Wireless Power Transfer Station for Seafloor Observation Equipment

Conventional cabled seafloor observatories (CSOs) power in-situ instruments via wet-mated or dry-mated direct electrical contact (DEC) connectors to achieve long-term and real-time observation. However, the DEC connectors have high risks of water leakage and short circuits in power feeding, especially under high water pressure. This paper proposes a highly compatible underwater station based on inductive wireless power transfer (IPT) technology to address the above reliability issue. A novel energy transmitter with runway-structure coils is applied to the proposed underwater station to cover a sufficient power feeding area so that various in-situ equipment can be powered with desirable misalignment tolerance. The magnetic field distribution is analyzed by both derivation and finite element analysis (FEA) methods, and the principal parameters of the transmitter are further optimized and compared with both the mixed-integer sequential quadratic programming (MISQP) algorithm and the evolutionary algorithm (EA) for better performance. The same results show a reliable optimization process. The WPT circuit characteristics are also investigated to power different loads and improve the power transmission efficiency. The output power decreases, and the transmission efficiency rises and then decreases as the load increases. In addition, receivers with higher mutual inductance have better transmission performance. A prototype of the underwater station has been tested both in air and in water, and the experimental results have proven it can power multiple seafloor observation instruments stably and achieve compatibility requirements. The maximum output power of the station prototype for testing is 100 W, and the maximum overall transmission efficiency is 61%.

Implementation of an Accurate Measurement Method for the Spatial Distribution of the Electromagnetic Field in a WPT System

In an inductive wireless power transfer (WPT) system, the transferred power depends on the coupling between the transmitter coil and the receiver coil and, consequently, on their spatial positioning with respect to each other. Since this positioning needs to be as flexible as possible, one can design various construction shapes for the coils, in terms of both winding geometry and core geometry. The system efficiency for different positionings and configurations can be assessed if the structure and distribution of the electromagnetic field (EMF) in the space close to the system are determined. In this context, this paper proposes an investigation method based on measuring the intensity of the electromagnetic field generated by the emitting coil in the WPT space in terms of both modulus and direction. The measurements needed to be performed at a sufficient number of points, so that the entire field was determined. The EMF value was estimated by linear spatial interpolation between the measured points. Moreover, this paper presents the method and the results of investigations carried out only in the presence of the emitting coil. Calibration or correction solutions were also proposed to obtain sufficient accuracy, and the viability of the method was therefore demonstrated.

Integro-Differential Analysis of Resonant Magnetic Metasurfaces With Equivalent Medium Approximation

This paper proposes a strategy to consider the dielectric effects in the thin-wire integro-differential formulation and applies it to analyzing microstrip metasurfaces that support magnetic resonances. These structures comprise a periodic arrangement of subwavelength unit cells; therefore, the thin-wire approximation can be applied to analyze them. However, the substrate is usually disregarded. This work achieves more accurate results with a homogeneous equivalent medium approximation considering the dielectric properties. Moreover, an experimental methodology is presented to validate this implementation for each device as well as for the complete system. The proposed formulation is numerically solved with the Method of Moments, and the results show close agreement with experimental data. Besides, it leads to a significant reduction in the computation time compared to a full-wave analysis, which makes this approach also compelling for designing inductive wireless power transfer systems and magnetic resonators.

Simple Enhancement of Series–Series-Compensated Inductive Wireless Power Transfer Links Operating With Load-Independent Voltage Output at Fixed Frequency to Attain Zero Inverter Phase Angle

It is well-known that series-series compensated resonant inductive wireless power transfer links (SS-IWPTL) may be designed to attain load independent voltage output (LIVO) for given operating frequency and coupling coefficient. Unfortunately, corresponding inverter output impedance is either highly-inductive or highly-capacitive (inductive region is typically preferred due to natural zero-voltage switching (ZVS) of inverter transistors), significantly increasing inverter volt-ampere (VA) rating. The letter demonstrates that designing the SS-IWPTL for operation in the capacitive region and then adding a shunt inductor across AC-side terminals of either inverter or rectifier while allows attaining inverter zero phase angle (ZPA) thus minimizing its VA rating.

Inductive Wireless Power Transfer Systems for Low-Voltage and High-Current Electric Mobility Applications: Review and Design Example

Along with the technology boom regarding electric vehicles such as lithium-ion batteries, electric motors, and plug-in charging systems, inductive power transfer (IPT) systems have gained more attention from academia and industry in recent years. This article presents a review of the state-of-the-art development of IPT systems, with a focus on low-voltage and high-current electric mobility applications. The fundamental theory, compensation topologies, magnetic coupling structures, power electronic architectures, and control methods are discussed and further considered in terms of several aspects, including efficiency, coil misalignments, and output regulation capability. A 3D finite element software (Ansys Maxwell) is used to validate the magnetic coupler performance. In addition, a 2.5 kW 400/48 V IPT system is proposed to address the challenges of low-voltage and high-current wireless charging systems. In this design, an asymmetrical double-sided LCC compensation topology and a passive current balancing method are proposed to provide excellent current sharing capability in the dual-receiver structures under both resonant component mismatch and misalignment conditions. Finally, the performance of the proposed method is verified by MATLAB/PSIM simulation results.

A review of underwater inductive wireless power transfer system

AbstractThe IPT system has been studied for underwater applications such as autonomous underwater vehicles (AUVs) and subsea sensors. However, it rarely comparatively shows the performance of the IPT system in air, freshwater, and seawater. Based on the fore‐mentioned research background, this paper presents a survey of the properties of the IPT system in different mediums. Here, a 100 W power‐level experimental IPT prototype is built and tested. The resonant frequency is set at 300 kHz with a gap range from 10 to 190 mm. The comparison is focused on the efficiency, mutual inductance, coupling coefficient, coil resistance, and quality factor of the IPT system. The IPT system is placed in air, freshwater, and seawater with the same settings. What's more, the magnetic fields of coupling coils in air, freshwater, and seawater are presented in this paper. This paper could be acted as a reference to optimize the IPT system and facilitate future IPT research for underwater applications by analysing the performance of the IPT system in different mediums. The 3D Ansys Maxwell simulation of the IPT system is also given here to study the magnetic fields.

A Wireless Power Transfer System Using a Double DD Quadrature Coil Structure

This paper presents the evolution of an inductive wireless power transfer using a multicoil system. The double DD coil structure on the transmitter and the receiver side using two perpendicular bipolar DD coils is upgraded with an additional nonpolar quadrature coil. The proposed structure can be called the double DDQ coil structure. All three coils are not coupled, due to the nature of the directional double DD coil. If the transmitter and the receiver are not misaligned to one another, the system behaves as three separate, uncoupled IPT systems. The main advantage of the proposed coil topology is additionally increased power density and increased misalignment tolerance. Additionally, when the transmitter and the receiver coil are perfectly aligned, the proposed pad structure can transmit three different voltages and can be excited with different frequencies. In the case of this paper, the three coils on the transmitter side were excited by the same frequency. The proposed coil was evaluated experimentally and compared to the system using double DD coil structure.

Comparison of Series/Series and Parallel/Series Resonance Circuit in 1.5 kW Inductive Wireless Power Transfer for EV Applications

Wireless power transfer system plays a key role in the present and future days, because of their upgraded comfort and safety and their merits of less green-house gas (GHG) emissions, cell phones, laptops and electric vehicle charging. In this paper, the basic two resonance circuits were analyzed using an inductive wireless power transfer (IWPT) system, at 1.5 kW, 120-mm, and 85 kHz resonance frequencies. It includes analyzing, designing, and comparing this resonance circuit to choose a suitable resonant circuit for the particular application of an IWPT system. The main analysis and comparison were: Mutual Inductance Effect (Misalignment), stresses on the components, Effect of mutual inductance on the efficiency, Effect of distance on the efficiency, Effect of frequency on the efficiency, Effect of the coupling coefficient (k) on the efficiency and transferred power, Effect of coupling coefficient (k) on the input impedance, Effect of distance on the coupling coefficient (k) and Mutual inductance, and both S/S and P/S circuits have same battery output dc power, current, voltage levels. Both resonance circuits designing formulas derived, electrical parameters are calculated for the given wireless power charger level reaches SAEJ2954 standards. In the end, both resonance circuits are verified through MATLAB simulation of the equivalent circuits.

Spatial filtering magnetic metasurface for misalignment robustness enhancement in wireless power transfer applications

In this paper, we present the design of spatial filtering magnetic metasurfaces to overcome the efficiency decay arising in misaligned resonant inductive Wireless Power Transfer systems. At first, we describe the analytical framework for the control of currents flowing on a finite-size metasurface, avoiding classical truncation effects on the periphery and opportunely manipulating, at the same time, the spatial magnetic field distribution produced by the closely placed RF driving coil. In order to validate the theoretical approach, we conceive a numerical test case consisting of a WPT system operating at 12 MHz. By performing accurate full-wave simulations, we prove that inducing a uniform current in the metasurface results in a more robust WPT system in terms of misalignment with respect to conventional configurations, also including standard metasurfaces. Therefore, while the use of metasurfaces in WPT systems has been already demonstrated to be beneficial in terms of efficiency enhancement, we confirmed that a proper control of the metasurfaces field filtering response can be advantageous also for the misalignment issue. Notably, the free space wavelength at the operating frequency (12 MHz) is 25 m, whereas the proposed metasurface dimensions are only 0.0024λ × 0.0024λ. Despite the extremely reduced dimensions, the spatial magnetic field distribution produced by the closely placed RF driving coil can be nevertheless opportunely manipulated. Finally, experimental measurements conducted on fabricated prototypes validated the numerical results, demonstrating the effectiveness of the proposed approach. These achievements can be particularly helpful in WPT applications where the position of driving and receiving coils frequently changes, as in consumer devices and biomedical implants.

Battery-Free and Real-Time Wireless Sensor System on Marine Propulsion Shaft Using a Wireless Power Transfer Module

In this paper, we present a wireless sensor system (WSS) that integrated an inductive wireless power transfer (I-WPT) module for battery-free real-time monitoring of the status of rotating shaft in ships. Firstly, an optimized I-WPT module for seamless power supply was implemented using multiple Tx and Rx coils, and its power capability of 1.75 W with an efficiency of 75% was achieved. Secondly, as a result of the high-power transfer performance of the implemented I-WPT module, an entire WSS that integrated four sensors was designed on the rotary shaft. Finally, the designed WSS was installed on a small-scale test bench system with a shaft diameter of 200 mm; it was demonstrated that the status of a propulsion shaft could be monitored in real time without a battery.