Power Transfer Distance Research Articles

Efficient, Load Independent and Self-Regulated Wireless Power Transfer with Multiple Loads for Long Distance IoT Applications

This paper proposes a wireless power transfer (WPT) system by placing repeater coils to transfer power to multiple loads for the internet of things (IoT) devices and sensors in smart grid applications. The proposed system intermediate resonators (repeaters) not only function as power relays to enhance the transfer distance but also supplies power to its load attached to them. Equal power distribution and load-independent characteristics were obtained without efficiency degradation when any one of the loads was changed during system operation. Identical high-quality factor coils were designed using Litz-wire to reduce the skin effect. The coil size was 15.5 cm × 15.5 cm and the four relays achieved total efficiency of 51.7%, delivering 2 W power and output voltage of 5 V to each load with a total power transfer distance of 62 cm.

Design, Challenges, and Trends of Inductive Power Transfer Couplers for Electric Vehicles: A Review

The magnetic coupler is the heart of an inductive power transfer (IPT) system, which facilitates wireless power transfer through its air gap. The couplers are designed to maximize efficiency, power density, power transfer distance, and misalignment tolerance while minimizing leakage flux, weight, cost, and volume. The coupler design process becomes complex due to the nonlinear behavior of magnetics, sophisticated geometrical structures, and mandatory design limitations imposed by standards, such as SAE J2954/1, IEC 61980-1:2015, and ISO 19363:2020. Initially, this article reviews the advancements in coil design methodologies and their structures over the last few decades to identify the ongoing challenges and trends. The impacts of the power electronics system, industrial standards, material selection, numerical and analytical modeling methods, and thermal modeling on the coil design process are identified to formalize the design procedure. A coil design example based on finite element analysis (FEA) tools is presented to identify the drawbacks of the existing design and optimization process. A sensitivity analysis, 3-D-Pareto plots, and optimal design selection by considering misalignment variations are proposed to improve the multiobjective optimization process. A generalized guideline for coil design is proposed, which highlights the essential design stages of an IPT coupler. Current trends are identified, and future directions are proposed.

Long-distance adiabatic wireless energy transfer via multiple coils coupling

Recently, the evolution of wireless energy transfer can be described as Schrodinger equation. Thus, the transfer protocol of wireless energy transfer can be designed by coherent quantum control techniques, which can achieve efficient and robust energy transfer from transmitter to receiver. In this paper, we propose a novel design of wireless energy transfer which obtains the longer distance, efficient and robust schematic of power transfer, via multiple states of triangle crossing pattern. After our calculations, we demonstrate that our design can provide much longer transfer distance with relatively smaller decreasing transfer efficiency.

Machine Learning Approach for Wirelessly Powered RFID-Based Backscattering Sensor System

A RFID-based backscattering sensor system is low-cost and scalable wireless sensing technology. It takes advantage of RF energy harvesting technique, wireless power transfer and backscattering principle. It also has uncountable number of applications due to its versatility. In this paper, operation principle, architecture and machine learning technique for wirelessly powered RFID-based backscattering sensor system is presented. For the sensor tag-reading and power-delivering algorithm, machine learning techniques, such as support vector machine (SVM), artificial neural networks (ANN), and naive Bayes algorithm, are introduced with experimental verifications. The supervised SVM algorithm significantly improved reading accuracy of chipless RFID sensor tags due to superior signal classification performance of the SVM method. The ANN-based adaptive dynamic matching network for magnetic resonant wireless power transfer system improved wireless power transfer distance efficiently. Position estimation method based on the naive Bayes algorithm that is essential for smart wireless power transfer platform for wirelessly powered drones is also discussed in this paper.

Design and Optimization of an Electric Vehicle Wireless Charging System Using Interleaved Boost Converter and Flat Solenoid Coupler

Simple but effective output voltage/current control schemes are essential for electric vehicle wireless charging systems (EVWCSs). This article proposes an EVWCS using interleaved boost converter (IBC) and flat solenoid coupler (FSC). The closed-loop control between the primary and secondary is realized by adjusting the duty cycle of the IBC. The currents and losses in the primary are reduced in the proposed system because the dc bus voltage in the primary is increased by using the IBC. The input current ripple is diminished owing to the interleaved structure. This article also proposes a parameter optimization method to obtain the optimal FSC. Without loss of generality, the total area of the transmitter (Tx) and receiver (Rx) is assumed to be constant, and the Tx is assumed to be larger than the Rx. A scale-down prototype whose output power is 500 W was built in the laboratory to verify the theoretical analysis. The output voltage of the prototype kept constant when the misalignment was 200 mm in the winding direction or 100 mm in the magnetic direction. A highest system efficiency, from dc input to dc output, of 90.1% was achieved when the power transfer distance was 170 mm.

Constant Output-Voltage Design for Bi-Directional Wireless Power Transfer System with Multiple Stages

For the application of wireless power transfer (WPT) technology in a robot (like the snake robot), the power is supposed to be transferred to each device across multiple robot joints. This paper proposes a multi-stage bi-directional WPT (MB-WPT) system that not only provides power to multiple loads but also increases the power transfer distance. Besides, the last stage can charge for the preceding stages by reverse power transfer. The constant output voltage can be achieved whether the power is transmitted in a forward or reverse direction, and different output voltages for each stage can be achieved to satisfy the respective voltage requirement through the parameter design method. The validity of the theoretical analysis and the feasibility of the system are verified by experiments.

Development of Wireless Power Transmission System for Transfer Cart with Shortened Track

In this study, a wireless power transmission (WPT) system for high power was developed to supply the wirelessly powered transfer cart for a clean environment (such as liquid crystal display (LCD), semiconductor, and flat panel display (FPD) device industries) to improve the cleanliness of related industrial production lines and save energy. The power transmission method of WPT and the core design were optimized, and a shortened track was fabricated to enable WPT via short power lines for diverse applications in a small space-constrained workshop. In realizing the shortened Litz wire system, the amount of heat generated increased due to the increased resistance in the system, and efforts were made to improve the thermal performance. A simple approach was also proposed to estimate the skin depth caused by the skin effects in a cable made up of multiple strands of multiple wires, validated through thermal analysis by using ANSYS software in terms of heat generation by an electric field. Structure designs were implemented to improve the heat transfer performance, and the experimental results of WPT systems at a power level of 21.54 kW demonstrate that the power transfer distance of WPT was above 15 mm with a charging efficiency above 83.24%.

A Long-Range and Self-Powered Intelligent Food Monitoring System Based on Far-Field Energy Harvesting and Pressure Measurement

Introduction Radiofrequency (RF) energy harvesting has recently become a promising solution to power wireless sensors networks. As this emerging technology allows low-power sensors and systems to be charged wirelessly, it is advantageous in various applications with low cost and fewer requirements for periodical maintenance [1]. On the other hand, food quality is one of the most concerned problems of our society, foodborne illnesses caused by eating spoilt food has been a serious threat to human health. Therefore, development of a low cost, rapid and sensitive monitoring system is essential to ensure food safety and security. However, conventional food monitoring methods, which are usually based on measuring gas concentration show some drawbacks in terms of power consumption, cost, and reliability [2]. In this study, we developed a high-efficient battery-less system that can be used for food monitoring based on the far-field RF energy harvesting technique. Methods Our proposed system consists of an RF energy harvester and a sensing circuit. The RF energy harvester can harvest energy from radio waves at an ultra-high frequency (UHF) of 915 MHz to supply the power for the operation of all tag components. To improve the received power and enhance the distance of power transfer, a Yagi type structure antenna with three elements (driver, director, and reflector) was implemented to achieve a high gain and fit into a compact footprint [3]. Besides, to overcome the disadvantages of conventional food monitoring methods, our study focuses on measuring the increase in air pressure inside the food package caused by gas emission during storage. To confirm the effectiveness of the proposed system, we performed experiments on different sorts of food such as chicken, pork and fish. Results and Conclusions As a result, the sensor module is designed using a high accuracy pressure sensor and other ultra-low-power components, allowed it to consume low average power of only 1mW. The designed Yagi antenna has a high gain of 5.23dBi in the direction of the maximum radiation and voltage standing wave ratio (VSWR) better than 1.3 in approximately 60Mhz band (890-950Mhz). Finally, the increase in air pressure during food spoilage was used to categorize food freshness, demonstrating the feasibility of our proposed system.

Multiobjective Parameter Optimization of a Four-Plate Capacitive Power Transfer System

For a four-plate capacitive power transfer (CPT) system, the existing coupling and compensation design methods can only provide an approximate local parameter optimization solution, instead of a globally optimized solution. This article proposes an accurate calculation method for cross-coupling capacitance and a multiobjective optimization algorithm combining nondominated sorting and Kent map for an SS-type CPT system. Mathematical models of the cross-coupling capacitances and port capacitances are established based on a two-port capacitive coupling model of the four plates. Besides, the constraints considering the reasonable region of the parameter values are given. Taking the output power, efficiency, and total harmonic distortion (THD) as objective functions, with the power transfer distance, operating frequency, load resistance, and input voltage as decision variables, the Pareto-optimal fronts are obtained by the proposed algorithm. A group of global optimal parameters is chosen from the solution sets, and a simulation model and a prototype of the CPT system are constructed. The efficiency of 87.1% at 252.3-W output power has been achieved. The simulation and experimental results verified the feasibility and effectiveness of the proposed calculating method for the cross-coupling capacitance and optimization method.

A Sleeve-Type Capacitive Power Transfer System With Different Coupling Arrangements for Rotary Application

This paper presents a sleeve-type capacitive power transfer (CPT) system for contactless rotary applications. Sleeve-type capacitive couplers with different coupling arrangements between primary and secondary metal sleeves are proposed in this research, which lead to different coupling characteristics with positive, zero, and negative coupling coefficients. The effect of coupling coefficient variations caused by both the power transfer distance and the ratio between the overlapping length and the height of outer sleeves is analyzed. Combining the sleeve-type coupler, the CPT system is developed with a double-sided LC-compensated network and half-bridge inverter. For the CPT systems with positive and negative coupling coefficients, parameter design methods are presented to determine system parameters to achieve zero phase angle (ZPA) condition under the same output power. Then overall system performances of the CPT systems with local maximum positive and local minimum negative coupling coefficients are analyzed and compared by simulation in MATLAB/Simulink and Maxwell. Finally, an experimental prototype is constructed, which has demonstrated a power efficiency of 85.3% at 100.8 W. Simulation and experimental results show that the CPT system with local minimum negative coupling coefficient has clear advantages in increasing transfer distance, reducing voltage on sleeves, suppressing fringing electric field, and improving power density.

Simultaneous Magnetic Resonance Wireless Power and High-Speed Data Transfer System With Cascaded Equalizer for Variable Channel Compensation

Wireless power transfer (WPT) systems can potentially provide simultaneous power and data transfer for Internet-of-Things devices, such as smart speakers, glasses, and watches. However, due to the high quality factor of coils, the intrinsically narrow WPT channel bandwidth severely limits the data transmission capability of the system, especially for data downloading links requiring higher data rates. In addition, the channel bandwidth varies with power transfer distances, which is also undesirable for wireless communication. In this study, the channel features of a two-coil series–series matching magnetic resonance wireless power and data transfer (MWPDT) system, including the bandwidth and the roll-off slope are characterized analytically. Based on the characterization results, a receiver front-end circuit with a three-stage cascaded equalizer (EQ) is proposed and implemented to extend the bandwidth of a MWPDT system at different distances. The proposed EQ can provide a frequency response with a variable roll-up slope from 10 to 45 dB/dec to compensate for the distance-dependent channel response of an MWPDT system. A complete MWPDT system is built and tested to verify the performance of the proposed method. Experimental results demonstrate that the data rates can be extended from 650, 500, and 350 kbps to 850, 700, and 650 kbps at 0.4, 0.5, and 0.6-m distances, respectively. The highest data rate extension ratio is 85% at a transmission distance of 0.6 m, which is 2.4 times the radii of the coil employed in the system.

Full-Range Soft-Switching Pulse Frequency Modulated Wireless Power Transfer

This article proposes and implements a full-range soft-switching pulse frequency modulated (PFM) wireless power transfer (WPT) system, which not only offers high efficiency but also high controllability, selectivity, and security. Although the phase-shift control (PSC) has been widely used in various WPT applications, the high-frequency hard-switching operation will inevitably degrade the system performances in terms of power losses, and hence, efficiency during power regulation. Thus, a soft-switching PFM is newly conceived to suppress the switching frequency and power losses while maintaining full-range soft switching for effective power control, hence improving the system efficiency. In addition to realizing the controllability, the full-range soft-switching PFM can be further derived to implement the selectivity and security. The system efficiency of a multiobjective PFM-WPT system prototype can reach 86.27% at 220-W output power and 135-mm transfer distance. During wireless power control, it can effectively be improved by up to 5.68% as compared to its counterpart using the PSC. Theoretical analysis, computer simulation, and hardware experimentation are given to verify the feasibility of proposed full-range soft-switching PFM-WPT system.

Efficiency Enhancement in a Wireless Power Transmission System Using Parasitic Components

In this paper, we present a rigorous optimization method to design a wireless power transmission (WPT) system. In order to enhance the power received by the receiver, parasitic components are integrated into the system. Our analysis shows that a system with square parasitic wire actually gives better performance than its circular counterpart. From our results, it can be seen that the presence of square parasitic wires in the system improves considerably the efficiencies, as well as the distance of effective power transfer. By implementing two square parasitic wires and using an optimization algorithm to carefully select the positions of the receiving antennas, we show that power coupled to one receiver can be significantly enhanced; while the other suppressed – the peak power at the receiving antenna is improved to 15.7% and the power detected by the adjacent antenna is minimized to as low as 2.6%. This result is important as it shows that the parasitic components do not only enhance the power coupled to the receiving antenna, it also effectively reduces crosstalk in adjacent antennas. Indeed, it can be observed that the peak efficiency obtained using two parasitic wires (with the transmitter sandwiched in between the two wires) is almost twice of that using a single wire.

A novel three-coil wireless power transfer system and its optimization for implantable biomedical applications

The technology of wireless power transfer (WPT) has broad applications especially in implantable biomedical devices. Because of the limitation of the size of the receiver coil, how to lengthen the power transfer distance is crucial in biomedical applications. In order to address this problem, in this paper, a novel three-coil WPT system is proposed and analyzed. In the system, there are two transmitter coils and one receiver coil. Based on the Biot–Savart’s law, the electromagnetic property of the square coil is analyzed using finite element method. Moreover, the structural design of the system is optimized by a memetic algorithm. The memetic algorithm combines features of the artificial bee colony method and the covariance matrix adaption evolutionary strategy method. The simulation and experiment results show that the receiver coil can receive about dozens of millivolt when the power transfer distance is about 15 cm. This means the proposed system is suitable for implantable biomedical devices. Compared with the two-coil WPT system, in addition, the power received in the receiver coil of three-coil WPT system can increase about 48%.

A 3D wireless charging cube with externally enhanced magnetic field for extended range of wireless power transfer

More mobile devices such as mobile phones and robots are wirelessly charged for convenience, simplicity, and safety, and it would be desirable to achieve three-dimensional (3D) wireless charging with high spatial freedom and long range. This paper proposes a 3D wireless charging cube with three orthogonal coils and supporting magnetic cores to enhance the magnetic flux outside the cube. The proposed system is simulated by Ansoft Maxwell and implemented by a downsized prototype. Both simulation and experimental results show that the magnetic cores can strengthen the magnitude of B-field outside the cube. The final prototype demonstrates that the power transfer distance outside the cube for getting the same induced electromotive force in the receiver coil is extended approximately by 50 mm using magnetic cores with a permeability of 2800. It is found that the magnitude of B-field outside the cube can be increased by increasing the width and the permeability of the magnetic cores. The measured results show that when the permeability of the magnetic cores is fixed, the induced electromotive force in the receiver coil at a point 300 mm away from the center of the cube is increased by about 2V when the width of the magnetic cores is increased from 50 to 100 mm. The increase in the induced electromotive force at an extended point implies a greater potential of wireless power transfer capability to the power pickup.

Pulse Density Modulated ZVS Full-Bridge Converters for Wireless Power Transfer Systems

Pulse density modulation (PDM) is an advanced technique for maximum efficiency point tracking of wireless power transfer (WPT) systems. By using PDM, both voltage regulation and efficiency maximization can be achieved without dc/dc converters. PDM is also compatible with the dual-side soft switching technique that utilizes resonant tanks and synchronous rectification. However, this soft switching technique depends on coupling and load conditions. Hard switching may occur when the coupling of coils gets stronger or the equivalent load is not properly controlled. To eliminate the dependence and ensure the soft switching under various operating conditions, this paper proposes a PDM zero-voltage-switching (ZVS) full-bridge converter for WPT systems. The converter employs a ZVS branch between switching nodes to provide a ZVS current, and uses a specially designed modulator to obtain the valid ZVS current waveforms. Experimental results verified the proposed operating principles and showed that the additional power loss caused by the ZVS current is insignificant. The overall efficiency of the WPT prototype was 93 ∼ 73% when the power transfer distance was 0.1 ∼ 0.4 m, among which up to 85% efficiency was observed when the distance equaled the coil diameter.

Pulse Density Modulation for Maximum Efficiency Point Tracking of Wireless Power Transfer Systems

Maximum efficiency point tracking (MEPT) control has been adopted in state-of-the-art wireless power transfer (WPT) systems to meet the power demands with the highest efficiency against coupling and load variations. Conventional MEPT implementations use dc/dc converters on both transmitting and receiving sides to regulate the output voltage and maximize the system efficiency at the expense of increased overall complexity and power losses on the dc/dc converters. Other implementations use phase-shift control or on-off control of the transmitting side inverter and the receiving side active rectifier instead of dc/dc converters but cause new problems, e.g., hard switching, low average efficiency, and large dc voltage ripples. This paper proposes a pulse density modulation (PDM) based implementation for MEPT to eliminate all the mentioned disadvantages of existing implementations. Delta-sigma modulators are used as an example to realize the PDM. A dual-side soft switching technique is proposed for the PDM. The ripple factor of the output voltage with PDM is derived. A 50 W WPT system is built to validate the proposed method. The system efficiency is maintained higher than 70% for various load resistances when the power transfer distance is 0.5 m, which is 1.67 times the diameter of the coils.

Comparative Study and Simulation of Mid-range Wireless Power Transfer at Various Transmission Distance

Wireless power transfer would be the niche of research in next decade which is significant to reduce the cable and charges consumption for electronic devices. This paper presents the simulation result of electric and magnetic wave behaviour in mid-range wireless power transfer and various transmission distance in the range of 8 – 16 cm. Simulation result using CST microwave studio shows that scattering parameter in the power transmission decreases from 0.6509 down to 0.5137 with the increase in distance. The transmitted electric field at the receiver decreases from 1615 V/m to 1086 V/m whereas the magnetic field decreases from 32.63 A/m down to 24.85 A/m. Results show that 4-coils magnetic resonance coupling is an ideal approach for mid-range wireless power transfer.

An optimal operating frequency selection scheme for maximizing inductive power link efficiency

AbstractImproving the efficiency of the inductive wireless power transfer (WPT) is an effective way to increase the power transfer distance, reduce the power exposure, and popularize the WPT application. If the geometrical sizes of the transmitting and receiving coils and the distance between them have been determined, an operating frequency exists to maximize the power transfer efficiency. In this work, a method to find this optimal frequency is introduced by virtue of analytical models of self‐ and mutual‐inductances and parasitic resistances and capacitances of the coils, and verified via simulations and measurements.

Encryption Techniques and Wireless Power Transfer Schemes

<p>Wireless power transfer (WPT) is one of the most useful ways to transfer power. Based on power transfer distances, the WPT system can be divided into three categories, namely, near, medium, and far fields. Inductive coupling and capacitive coupling contactless techniques are used in the near-field WPT. Magnetic resonant coupling technique is used in the medium-field WPT. Electromagnetic radiation is used in the far-field WPT. This paper reviews the techniques used in WPT. In addition, energy encryption plays a major role in ensuring that power is transferred to the true receiver. Therefore, this paper reviews the energy encryption techniques in WPT. A comparison between different techniques shows that the distance, efficiency, and number of receivers are the main factors in selecting the suitable energy encryption technique.</p>