Efficiency Of Wireless Power Transfer System Research Articles

Omnidirectional and Efficient Wireless Power Transfer System for Logistic Robots

The WPT system for logistic robots has the problems of large fluctuation of charging power and low efficiency due to the change of its position. Based on the principle of parity time symmetry, an omnidirectional and efficient wireless power transfer system for logistic robots is proposed. Firstly, the coupling coefficient of two planar spiral coils in different relative positions in space are studied. Then, a time-varying coupled-mode model of the WPT system based on the offset angle of the receiver coil is established, and its working principle and characteristics are analyzed. As long as the coupling coefficient satisfies certain conditions, the output power and efficiency of the system are always keeping constant. Finally, the proposed model is experimentally verified. The measured results show that the WPT system proposed can realize stable 150W power transfer with constant transmitting efficiency of more than 90% for a logistic robot within a confined three-dimensional space around the charging station, which are provided to further verify the correctness of theoretical analysis.

The Charging Control and Efficiency Optimization Strategy for WPT System Based on Secondary Side Controllable Rectifier

The equivalent resistance of the battery will change during charging in practical applications, so it is difficult to design a wireless power transfer (WPT) system with accurate constant current (CC) and constant voltage (CV) output characteristics. In addition, the WPT system efficiency is also affected by the change of equivalent resistance. Therefore, this paper studies the charging control and efficiency optimization strategy for the WPT system with dynamic loads. The WPT system with a structure of double-sided LCC compensation topology and containing controllable rectifier circuit at the secondary side is established, and the working process of full-bridge controllable rectifier circuit is analyzed. Then the output characteristics of the WPT system are analyzed. The expressions of the optimal transmission efficiency and the optimal equivalent impedance of the full-bridge rectifier are derived. The relationships between the equivalent impedance of the capacitor-filtered full-bridge controllable rectifier circuit and the phase shift angle, the charging current and the phase shift angle are also obtained. In this paper, the CC and CV charging strategies based on phase shift control of controllable rectifier circuit and efficiency optimization strategy based on dynamic equivalent impedance matching are proposed, which can improve the WPT system transmission efficiency while realizing CC and CV charging. Finally, the effectiveness of the proposed control strategy is verified by simulation and experiment. The WPT system realizes CC charging mode and CV charging mode in turn when the load resistance changes from $5~\Omega $ to $30~\Omega $ , and the overall efficiency is up to 90.71% at the transmission distance of 15cm.

Efficiency investigation of SS and SP compensation topologies for wireless power transfer

<span>Wireless power transfer (WPT) using inductive and resonant coupling has been widely explored in recent years for ease and safety over conventional cable charging systems. The efficiency of WPT systems is reducing drastically due to an increase in air-gaps and misalignment between transmitter (Tx) and receiver (Rx). Many circuit topologies have been analyzed to improve the efficiency of WPT system based on symmetrical coils. However, the circuit topologies have not been studied widely for unsymmetrical coils. This paper presents the investigation of two fundamental topologies i.e. Series-Series (SS) and Series-Parallel (SP) for unsymmetrical coils as well as symmetrical coils. Theoretical analysis of both the compensation topologies have been accomplished, then modeling of both the topologies have been done using two different combination of circular coils. In first case, two similar size coils have been designed and in second case transmitter coil of higher dimensions than receiver coil is designed. The efficiency of the system has been analyzed at multiple distances in both cases by integrating coil structure with the circuit. The overall result show that when Tx is bigger than Rx, the SP topology gives better efficiency than SS counterpart.</span>

Design and Interoperability Analysis of Quadruple Pad Structure for Electric Vehicle Wireless Charging Application

The power pad coil design is one of the most significant traits for wireless charging of electric vehicle charging applications. The proper design of the power pad is the most critical phase of developing an efficient and reliable wireless power transfer system. Each available coil design has its advantages suitable for specific applications. In this paper, the two objective problems of optimization are discussed involving optimized design, shape, size, and optimized current directions in subsquare structures of quadruple power pad structures. The dimensional design optimized to least area with maximum coupling coefficient, and current directions with least interference between corresponding coils were verified through finite-element analysis (FEA) using ANSYS Maxwell. The results were thoroughly compared among all the cases discussed. The other aspect of this paper is the compatibility analysis of quadruple coil structure with the rectangular, double D (DD), and double D quadrature (DDQ) coil structures. Results have been compared, and the quadruple coil structure is verified as compatible with all other coil structures.

Active Shielding Design for Wireless Power Transfer Systems

The shielding technique by active coils is proposed to mitigate the magnetic field produced by a wireless power transfer (WPT) system based on near field coupling. General guidelines are provided for the active shielding design to shield the source for emission reduction or to shield the victim for immunity enhancement. Then, a method is proposed to identify the suitable excitation of the active coils. The proposed method permits the mitigation of the magnetic field in a specific point or of the induced effects in a loop area. Furthermore, the influence of the active shielding on the performance of a WPT system is also investigated. Finally, the proposed solution for active shielding is validated by measurements. A shielding effectiveness (SE) of about 20 dB on the considered area is obtained with a negligible degradation of the WPT system efficiency.

Efficient wireless charging system for supercapacitor-based electric vehicle using inductive coupling power transfer technique

Wireless charging has become an emerging challenge to reduce the cost of a conventional plug-in charging system in electric vehicles especially for supercapacitors that are utilized for quick charging and low-energy demands. In this article, the design of an efficient wireless power transfer system has been presented using resonant inductive coupling technique for supercapacitor-based electric vehicle. Mathematical analysis, simulation, and experimental implementation of the proposed charging system have been carried out. Simulations of various parts of the systems are carried out in two different software, ANSYS MAXWELL and MATLAB. ANSYS MAXWELL has been used to calculate the various parameters for the transmitter and receiver coils such as self-inductance ( L), mutual inductance ( M), coupling coefficient ( K), and magnetic flux magnitude ( B). MATLAB has been utilized to calculate output power and efficiency of the proposed system using the mathematical relationships of these parameters. The experimental setup is made with supercapacitor banks, electric vehicle, wattmeters, controller, and frequency generator to verify the simulation results. The results show that the proposed technique has better power transfer efficiency of more than 75% and higher power transfer density using a smaller coil size with a bigger gap of 4–24 cm.

A Metamaterial-Coupled Wireless Power Transfer System Based on Cubic High-Dielectric Resonators

In this paper, a metamaterial-coupled, highly efficient, miniaturized, and long-range wireless power transfer (WPT) system based on a cubic high-dielectric resonator (CHDR) is explored. The proposed WPT system consists of two CHDR metamaterials separated by a distance and excited by two rectangular coils. Initially, this WPT system is analyzed by considering the cube dielectric permittivity, $\varepsilon _{r}$ = 1000, and loss tangent, tan $\delta$ = 0.00001. From the Ansoft HFSS simulation, it is observed that the system operates in the hybrid resonance mode resonating as a horizontal magnetic dipole providing more than 90% power transfer efficiency at a distance of 0.1 $\lambda$ . In addition, parametric studies regarding the transmitter and receiver sizes, loss tangent, receiver misorientation, cube periodicity, etc., are carried out. One of the significant findings of this parametric study reveals that the suggested WPT system is less sensitive to the displacement of the receiver coil, and the WPT efficiency due to misorientation of the receiver can be increased by changing the CHDR cube rotation. Due to inaccessibility of the very high $\varepsilon _{r}$ = 1000, 18 microwave ceramic samples of EXXELIA TEMEX E5080 (Oxide composition: Ba Sm Ti), which has a permittivity, $\varepsilon _{r}$ = 78, permeability, $\mu _{r}$ = 1, and a loss tangent, tan $\delta$ = 0.0004, was made for experimental verification. These cubes are surrounded by Teflon to make the CHDR resonators. From simulations and measurements, it is found that the proposed system outperforms the most recent high-dielectric or copper-based WPT systems in terms of efficiency, range, size, and specific absorption rate.

Reconfigurable transmitter coil structure for highly efficient and misalignment-insensitive wireless power transfer systems in megahertz range

The structural optimization of coils is a key issue in wireless power transfer (WPT) applications owing to size limitations. In this study, a novel planar-spiral transmitter coil (TX-coil) with an outer-tight and inner-sparse configuration is proposed to achieve a high quality factor (Q-factor) and uniform magnetic field, which ensures high efficiency and improves the misalignment tolerance for several-megahertz WPT systems. Furthermore, a closed-form expression for the Q-factor is provided and analyzed for coil optimization. By using this method, a TX-coil with an outer diameter of 100 mm and a wire diameter of 1.5 mm is designed and tested at 1 MHz. Finite element method simulations and experimental results demonstrate that the Q-factor is increased by about 8% in comparison with evenly spaced planar spiral coils, which is achieved while ensuring a relatively uniform magnetic field.

Inductance Calculation of Multilayer Circular Printed Spiral Coils

In the past few years, implanted biomedical devices have been widely used in healthy and medical applications and wireless power transfer (WPT) techniques used in these devices have been become a research hot topic. The printed spiral coils (PSCs), which have characteristics of small volume, low cost, high precision and high-integration, are better suited for WPT system. It is noteworthy that mutual inductance value of PSCs is a significant parameter which can influence the transfer efficiency of WPT system. Considering the geometry of multilayer circular PSCs and the distance between two adjacent layers, the previous methods are not suitable for calculating the mutual inductance of multilayer circular PSCs. In this study, an approximate calculation formula of mutual inductance between two single-layer circular PSCs is presented based on the existing research. On this basis, the self-inductance values of double-layer circular PSCs are calculated by MATLAB, the calculation results are verified by the ANSYS Q3D simulation and measurement results.

Miniaturization of SCMR Systems Using Multilayer Resonators

Multilayer elements are used to miniaturize the size of highly efficient wireless power transfer systems based on the Strongly Coupled Magnetic Resonance (SCMR). Specifically, inspired by miniaturization techniques used in antennas, multilayer resonators in conformal SCMR systems (instead of single-layer resonators traditionally used) are tightly stacked to significantly shrink the size of CSCMR systems. An analytical methodology is developed, based on Kirchhoff's law and Maxwell's mutual inductance formula using elliptic integrals, which can predict the system's resonance. Excellent agreement is shown between analytical, simulated and measured results. Based on our results the proposed multilayer CSCMR systems can operate at significantly lower frequencies than traditional CSCMR systems, while maintaining significantly smaller size as well as providing significantly higher efficiency and transmission range than traditional CSCMR systems.

Capacitor-Less High-Strength Resonant Wireless Power Transfer Using Open Bifilar Spiral Coil

A highly efficient wireless power transfer (WPT) system is required in many applications to replace the conventional wired system. The high temperature superconducting (HTS) wires are examined in a WPT system to increase the power-transfer efficiency (PTE) as compared with the conventional copper/Litz conductor. The HTS conductors are naturally can produce higher amount of magnetic field with high induced voltage to the receiving coil. Moreover, the WPT systems are prone to misalignment, which can cause sudden variation in the induced voltage and lead to rapid damage of the resonant capacitors connected in the circuit. Hence, the protection or elimination of resonant capacitor is required to increase the longevity of WPT system, but both the adoptions will operate the system in nonresonance mode. The absence of resonance phenomena in the WPT system will drastically reduce the PTE and correspondingly the future commercialization. This paper proposes an open bifilar spiral coils based self-resonant WPT method without using resonant capacitors at both the sides. The mathematical modeling and circuit simulation of the proposed system is performed by designing the transmitter coil using HTS wire and the receiver with copper coil. The three-dimensional modeling and finite element simulation of the proposed system is performed to analyze the current density at different coupling distances between the coil. Furthermore, the experimental results show the PTE of 49.8% under critical coupling with the resonant frequency of 25 kHz.

Highly Efficient WPT System With Negative Impedance Converter for Q-factor Improvement

A negative impedance converter (NIC) has been combined with a wireless power transfer (WPT) system to maximize the system efficiency based on non-foster theory. The NIC is composed of transistor, voltage divider, capacitor, and inductor for impedance matching, and resonant circuit operating at 6.78 MHz. The desired negative impedance can be controlled by tunable impedance in the NIC. In this paper, the loss of the transmitting coil is reduced to 0.1 Ω, yielding a quality factor of 7,050, which is 19.1 times higher than that of the conventional coil. The WPT system with the NIC provides high power transfer efficiency (PTE) at various transmission distances. The experimental results are improved from 64% to 96% and from 5% to 55% at the transmission distances of 50 and 200 mm, respectively. Furthermore, the PTE is enhanced from 38% to 87% and from 2% to 38% at the diagonal misalignment distance of 0 and 150 mm, respectively, at a transmission distance of 100 mm. The proposed technology for increasing the receiving power in the receiving coil with a higher PTE can be utilized for numerous applications in the industrial, scientific, and medical band, with a restricted radio frequency power on the transmitter side.

Regulation of spatial fields in wireless power transfer with artificial magnetic conductor

In order to improve the efficiency of wireless power transfer (WPT) system, the spatial fields are regulated on a two-non-resonant-coil WPT system by hexagon artificial magnetic conductors (AMC). In our configuration, the AMC is located by the side of the two-non-resonant-coil WPT system and close to the transmitter coil. The AMC structure consists of small hexagon copper patches periodically arranged on the dielectric substrate. Each patch is grounded by a via passing through its center hole. Chip capacitors are soldered in the gaps between the adjacent patches. We can design the working frequency of WPT system through the capacitance of these chip capacitors. The results show that the electromagnetic fields are changed between the transmitter coil and the receiver coil in WPT system due to the introducing of the AMC structure. There are two main reasons. First, many resonant modes are excited by near magnetic fields on the AMC structure. Second, near magnetic fields are shielded by the AMC structure. The variation of space electromagnetic field improves the transmission efficiency of WPT system. When the working frequency is 27 MHz and the transmission distance is 3 cm, the experiment verifies that the transmission efficiency increases by 22% in the WPT system with the AMC structure compared with the WPT system without the AMC structure. Simultaneously, the transmission efficiency is raised by 25% at different transmission distances. The simulation results are almost consistent with the experimental results. There is a little difference that the number of resonant modes is different between the simulation and the experiment due to the resistance loss of the chip capacitors in experiment. Therefore, we correct the simulation results under consideration of resistive loss. In addition, the excited multiple resonant modes can supply multiple and adjustable working frequencies in the WPT system with the AMC structure. In practical applications, AMC is low in cost and easy to implement.

Circuit modeling and efficiency analysis for wireless power transfer system with shielding

SummaryIt is an effective way to use magnetic shielding scheme in magnetic coupled wireless power transfer (WPT) system to reduce magnetic flux leakage. However, the additional shielding material would affect the equivalent circuit model and the power transmission efficiency of WPT system. Although the impact of some common shielding materials on the transmission efficiency has been studied using finite element simulation, there is still a lack of understanding about the impact to the equivalent model in theory. In this paper, the equivalent circuit and transmission efficiency of WPT system are analyzed theoretically under the influence of different shielding materials, and the relationship between material electrical characteristics and transmission efficiency is presented. In our WPT prototype with two 166‐mm diameter coils under ferrite shielding and aluminum shielding, the achieved maximum transmission efficiencies are 95.7% for 100‐kHz resonant frequency and 97.9% for 1‐MHz resonant frequency under the ferrite shielding, and the efficiency errors between the analytical and experimental results are less than 5% for 100‐kHz resonant frequency and 10% for 1‐MHz resonant frequency.

Compact and efficient WPT systems using half-ring resonators (HRRs) for powering electronic devices

This work presents a novel efficient and compact size coupled resonator system for wireless power transfer (WPT) based on compact half-ring resonators defected ground structure (HRRs-DGS). The proposed design is capable of supplying low power electronic devices. The suggested system is based on coupled resonators of DGS. An HRR-DGS band-stop filter is designed and proposed, and when two HRRs-DGS are coupled back-to-back, it transfers to a band-pass filter leading to a compact and highly efficient WPT system working at 3.4 GHz. The measured efficiency of the proposed coupled HRRs-DGS system is around 94% at a transmission distance of 12 mm which is filled with foam for stable measurements. The proposed design is suitable for charging electronic devices such as wireless sensor nodes at 3.4 GHz. Simulation and experimental results have shown acceptable agreement.

Design Approach for Efficient Wireless Power Transfer Systems During Lateral Misalignment

This paper methodizes efficiency improvement during lateral misalignment for the wireless power transfer (WPT) system using two coupled semielliptic defected ground structure (DGS) resonators. We design the WPT system using a scaled value of the available mutual coupling between the resonators at perfect alignment. This scaled mutual coupling value enforces over-coupling regime, and the WPT efficiency is lower than the peak one. Then, during lateral misalignment, WPT efficiency improves until it peaks at critical coupling. Next, with further misalignment, the efficiency drops as the system enters loose coupling regime. The proposed method consists of two steps. First, we derive an analytical approach to determine the scaled mutual coupling value for efficiency design during lateral misalignment, and second, we improve the maximum obtainable efficiency by careful designing of the DGS structures’ profile. We verify the proposed method by implementing the WPT system at 300 MHz, which shows a peak efficiency of 80% for a size $D_{o} \times D_{o} = 40 \times 40$ mm2 with a transfer distance $d = D_{o}$ . During misalignment, the efficiency is higher than 50% for a lateral shift up to ±0.75 $D_{o}$ .

Dual-Phase-Shift Control Scheme With Current-Stress and Efficiency Optimization for Wireless Power Transfer Systems

Traditional wireless power transfer (WPT) systems usually adopt the single-phase-shift (SPS) control method to maintain a constant output current or a constant output voltage for various applications. However, the current-stress on one side is much higher than that of the other side especially under operating conditions with high voltage conversion ratio and light-load. This phenomenon actually can be proven by the established mathematical model of the current-stress of WPT systems using SPS control. This large current-stress will damage power devices and lower the efficiency of WPT systems. In addition, it will result in an increase of system total cost because of the need for the devices with the higher volt-ampere rating. A control strategy based on dual-phase-shift control is developed for WPT systems with an active rectifier to reduce the maximum value of current-stresses on both sides as well as to maintain a constant output voltage or current. Consequently, the system efficiency can be improved compared to traditional WPT systems with SPS control. A scaled-down experimental prototype is constructed to verify the effectiveness of the proposed WPT topology and the control method. Experimental results show that the proposed method can reduce the maximum current-stress significantly and improve the system efficiency compared to traditional WPT systems under SPS control.

Experimental and Numerical Study of a Magnetic Resonance Wireless Power Transfer System Using Superconductor and Ferromagnetic Metamaterials

In this paper, a magnetic resonance wireless power transfer (WPT) system with two coils using superconductor and ferromagnetic (SC-FM) metamaterials was constructed and tested. SC-FM metamaterials were used in the WPT system to improve the transfer efficiency of the magnetic resonance WPT system. Three kinds of resonance coils were designed and the effects on the WPT system of different resonance coils using SC-FM metamaterials were investigated. This involved designing and conducting several kinds of WPT experiments with, and without, the SC-FM metamaterials. The results are then presented and analyzed. It is shown that the SC-FM metamaterials are able to improve the transfer efficiency of a WPT system.

Asymmetric Coil Structures for Highly Efficient Wireless Power Transfer Systems

A transmitter coil (TX-coil) as well as a receiver coil (RX-coil) has been designed at 6.78 MHz for magnetic resonant wireless power transfer systems not only to have high efficiency at medium distances, which is comparable to the coil dimensions, but also to provide stable efficiency over the position variation of the RX-coil. For mobile devices, the coils should be compact and have low profile and asymmetric, meaning that TX- and RX-coils have different dimensions. In this paper, TX-coil is designed by adding a small coil in series to achieve high quality factor (Q-factor) as well as relatively uniform magnetic field distribution. On the other hand, the scaling factor is introduced for wire width to design RX-coil with higher Q-factor. As a result, the proposed asymmetric coils reveal improved efficiency and degree of freedom in terms of position variation. This has been verified by measuring the system performance, including a power amplifier, full-wave rectifier, regulator, and load. The proposed TX-coil has size of $200 \times 200 \times 1$ mm3, while the size of the RX-coil is $100\times 100\times0.4$ mm3. The power transfer efficiency is 96% and 39% at the transmission distances of 50 and 300 mm, respectively.

Efficient Wireless Power Transfer System Integrating With Metasurface for Biological Applications

Wireless power transfer (WPT) is a key technique for many existing and emerging applications in biomedical devices. This paper presents a novel implantable magnetic coupling resonate WPT system by integrating with metasurface for biological applications. The receiver element is implanted under the skin surface 3 mm and has the dual-band property for transferring power and data telemetry simultaneously. A conformal strongly coupled magnetic resonator coil is used as the transmitting coil to construct the wireless power link. In addition, we integrate the proposed WPT system with negative permeability (MNG) metasurface over the human skin surface as a miniaturized wearable device to improve the WPT efficiency. The property of the MNG and its effect on the WPT efficiency are analyzed. Considering the special implantable environment, various misalignment tolerances between the metasurface and the receiver are discussed to evaluate the coupling response of the proposed WPT system. Finally, the efficient WPT system integrating with MNG has been verified by the experimental measurements, and the measured result shows that 15.7 dB coupling enhancement can be obtained by integrating with the MNG metasurface.