High Power Transmission Efficiency Research Articles

An experimental investigation of the performance of a power transmission mechanism for a flapping-foil hydrokinetic turbine

In this work, a hydrokinetic turbine that transmits the flapping power of front and rear foils to the final shaft was proposed and verified by conducting experiments in a circulating water tunnel. In particular, a crank-rocker mechanism was adopted for the transmission, with maximum actual power transmission efficiency of 92.1 % achieved, an outcome close to the maximum theoretical power transmission efficiency of 95.3 %. Although apparent negative-torque zones of the rear hydrofoil were observed due to wake effect from the front foil, maximum power efficiency up to 32.1 % was achieved at a reduced frequency of 0.117. Eventually, better transmission performance will be realized by reducing the negative-torque zones and by designing a crank-rocker mechanism with high theoretical power transmission efficiency.

High-performance optical dialogue for power electronic system

High-accuracy signal and high-quality power transmissions play an essential role in power electronics systems. Nowadays, the severe electromagnetic interference (EMI) by the switching converter threatens the stable operation of conventional signal and power transmissions. To mitigate the effects of EMI, optical fiber is a better solution due to its unmatched isolation properties. Here, we perform a transmission configuration, named optical dialogue, based on a single fiber for simultaneous bidirectional analog optical signal (AOS) and analog optical power (AOP) transmission, to ensure EMI immunity. This optical dialogue transmission not only utilizes AOS to achieve high-accuracy signal transmission, but also utilizes AOP to achieve high-quality power transmission. We validate the proposed optical dialogue transmission using discrete off-the-shelf components, demonstrating the high frequency signal transmission and high efficiency power transmission. Our proposed optical dialogue transmission offers a high-performance optical solution for signal and power transmission, which is significant step forward in the development of more accurate, reliable, and safer power electronic systems.

Broadband electrical impedance matching of sandwiched piezoelectric ultrasonic transducers for structural health monitoring of the rail in-service

To achieve high power transmission efficiency and high signal-to-noise ratio of sandwiched piezoelectric ultrasonic transducers (SPUTs) over a wide bandwidth, broadband electrical impedance matching (EIM) is investigated in-depth. Firstly, L type, T type, III type, IV type and V type EIM networks are designed and the corresponding component parameters are determined by the Smith chart with a quality factor Q constraint. Secondly, the above EIM networks are compared by reflection coefficient S11, transducer power gain (TPG) and active power. It is shown that they can effectively improve the TPG, and active power by two times and greatly reduce S11. Then the emitted voltage and received voltage under different excitation frequencies and EIM networks are analyzed. It is shown that the III type network presents optimal performance, which can make the aforementioned voltage values increase by two times over entire frequency range of interest. Finally, the effect of III type and IV type networks on electromechanical characteristics is studied by using the PSpice model of SPUTs. Compared to non-matching, the electro-acoustical gain ratio is improved almost two times, while the electro-acoustical power ratio is greatly reduced.

Misalignment tolerance improvement and high efficiency design for wireless power transfer system based on DDQ‐DD coil

SummaryThis paper addresses misalignment tolerance improvement and high‐efficiency maintenance for wireless power transmission systems. Firstly, a receiving coil is designed according to Standard J2954, published by the Society of Automotive Engineers. Next, a DDQ transmitting coil is designed to accommodate a constrained operating space. The structure and parameters of the transmitting coils are determined to obtain a high coupling coefficient when offset occurs. Subsequently, an analysis is carried out to determine the relationship between the coupler magnetic fields and power transmission ability. A current phase control strategy is developed to deal with the mismatched magnetic fields, and a switching threshold is selected to obtain high power transmission efficiency. Finally, an experimental system is set up using the designed coil. The experimental results demonstrate that the system can maintain high efficiency even when lateral misalignment occurs in different directions. A maximum transmission efficiency of 89.63% is obtained, which validates the effectiveness of the proposed method.

Comparison of Eddy Current Coupling Topologies for High Efficiency Mechanical Power Transmission

The paper is an investigation into permanent magnet eddy current couplings for high efficiency power transmission. Through extensive simulation studies, the performance of radial- and axial-field topologies, employing squirrel cage and conducting sheets, are compared in terms of torque transmission density and efficiency of power transmission. It is shown, that although using a conducting sheet (as it is often the case) results in higher torque transmission density, employing a squirrel cage is more suitable for high efficiency power transmission. A prototype of the proposed radial-field single sided permanent magnet eddy current coupling employing a copper squirrel cage is developed and tested, and a good agreement between measurements and predictions is demonstrated.

Analysis and Measurement of Large Circular Transmitting Arrays for Microwave Power Transmission

Phased arrays have been widely used in microwave power transmission. The efficiency of rectenna is closely related to the received power density. Therefore, it is necessary to accurately analyze the radiation performance of the transmitting array in order to achieve the high-efficiency power transmission. And in order to meet the long-distance and high-efficiency power transmission requirements, the transmitting array needs to have the characteristics of large electricity sizes. The direct numerical analysis method of entire array will bring huge cost in computing time and storage space. Subarray extrapolation is a method to reasonably account for the edge effects of arrays, but only for rectangular arrays. Aiming at the geometric characteristics of the array contour, this communication proposes an irregular contour recognition method. This method can expand the application of subarray extrapolation method and realizes the purpose of accurately evaluating the radiation performance of large array antennas at small calculation cost. Finally, using a large transmitting array as an example, the proposed method is verified by comparing the results of subarray extrapolation, commercial software of entire array, and the experimental measurement to validate the correctness and advancement.

High power transmission efficiency of wireless power transfer system using high-quality factor superconducting bulk coil

We developed a high-quality-factor high-temperature superconducting (HTS) bulk coil to increase the power transfer efficiency (PTE) of wireless power transfer (WPT) systems. We proposed the resonant frequency tuning by using the two sapphire substrates thickness of coil support. The configuration of a 65 mm diameter HTS bulk coil was optimized to a resonant frequency of 64 MHz. The measured quality factor of the HTS bulk coil was 9,431, which is 12 times that of the copper coil. At the transfer distance of 20 cm, the measured PTE of the WPT system using HTS bulk coils and one using copper coils were 74.8% and 20.6%, respectively.

Computational approaches for improving machining precision in five-axis flank milling of spiral bevel gears

Spiral bevel gears are a critical component in mechanical systems that offers high power transmission efficiency between nonparallel axes. The current gear manufacturing, which normally requires specialized machines and cutting tools specific to one gear type, offers limited production flexibility. An effective alternative is to utilize 5-axis computer numerical control milling on general-purpose machine tools. This paper aims to improve the machining precision in the flank milling of spiral bevel gears, particularly the tooth surfaces, using computational approaches. First, a geometric method was developed to approximate the contact path of a gear pair without solving the complex equations in tooth contact analysis. A quantitative measure was introduced to evaluate the contact path deviation from the center curve of the tooth surface. Second, we proposed an optimization scheme for generating tool paths that induce minimal geometrical errors on the finished surface. It employs a metaheuristics-based search algorithm with the errors as an objective in tool path planning. Test results on real gears verified the effectiveness of the proposed scheme. Three measures of the meshing performance, namely the average sampling error, the contact path deviation, and the transmission error, were cross-compared on different gear pairs to examine whether they consistently distinguish the performance rank. This work provides feasible solutions for controlling machining errors in 5-axis flank milling of complex gears.

Switchable compliant actuator with fast stiffness modulation and energy efficient power transmission

This article presents the design of a switchable compliant actuator (Swi-CA), capable of fast stiffness modulation over a wide range and energy-efficient equilibrium position control. Compliant actuators are designed to have a variable stiffness to generate a restoring force upon displacement. In previous studies, such actuators provided compliance by changing both output stiffness and equilibrium position using a clutch to switch between two modes. We implemented a bifurcation-based switching mechanism to shift between stiffness modulation and equilibrium position control modes via mechanical integration of a variable stiffness spring with a parallel elastic unit without the use of an additional clutch. The distinctive features of the proposed Swi-CA are threefold. First, the central bending of a leaf spring widens the range of modulated stiffness and increases the average stiffness modulation speed. Second, the developed slider-crank mechanism has high power transmission efficiency and fast stiffness modulation. Lastly, an optimized elliptical cam generated negative stiffness during output and enabled switching between the two modes without the use of a controllable clutch. Analytical models and experimental validation of the proposed design clearly demonstrated its advantages for applications requiring fast stiffness modulation and energy-efficient operation, such as some robotics applications.

Extensible Low-Profile Coplanar Wireless Power Transfer System for Multiload Applications With Load-Independence Constant Current Output

This article proposes a low-profile coplanar magnetic coupling resonance wireless power transfer system, which can be expanded segment by segment to power more receivers over a long distance with load-independent constant current output. Due to the low structural profile, it can easily conform to the environment such as desktops, floors, and walls, occupying a small space. By placing low-profile ferrite plates on or under the junctions of adjacent coplanar coils, the main coupling coefficients of the adjacent coils are significantly enhanced, and therefore, the power transmission efficiency (PTE) of the system is greatly improved. With the fixed operating frequency, load-independent current characteristics, simple structure, coplanarity with the environment, good scalability, and high PTE, the system can be easily utilized in various medium and long-range multiload WPT applications. The article describes its principle in detail and clarifies the influence of losses on system performance such as output current characteristics, PTE, and the maximum number of the charging segments. The experimental platform with two and three receivers was established to verify the theory, and the measurement results are in good agreement with the theoretical analysis. The maximum measured PTE reached 93.8% and 93.6% for two and three receivers, respectively.

Modeling of Traction Drive in Elastohydrodynamic Lubrication Contact and Traction Coefficient Enhancement Using Surface Texture Under High-Speed Conditions of up to 50,000 rpm

Abstract A high-speed electric motor with a small reducer that has high-power transmission efficiency can be used to realize a high-power-density powertrain system because electric motors can be miniaturized to increase the rotational speed. A traction drive has low vibration noise due to its lack of meshing vibration, making it suitable as a transmission element for high-speed reducers. However, the traction coefficient, which greatly affects transmission performance, decreases with increasing rotational speed. In this study, to increase the traction coefficient using a surface texture, a model that takes into account transient temperature changes under high-speed conditions and the effects of micro-surface geometry was developed. The traction coefficient was measured using a high-speed test machine capable of operating at a maximum speed of 50,000 rpm. The model was able to predict the experimental values with an error of at most 6%. The high-pressure rheological properties of the oil were examined to develop design guidelines for the surface texture and a model was used to optimize the texture parameters. The designed texture was manufactured and evaluated. Experimental results show that the traction coefficient can be improved by up to 19%.

Compact, backdrivable, and efficient design of linear electro-hydrostatic actuator module

An electro-hydrostatic actuator (EHA) has high backdrivability and is suitable for robots that interact with the environment, including human. However, the challenging problem in its mechanical design is that it is difficult to achieve compact size and high power transmission efficiency, compared with standard gear reducers. To tackle this problem, this study presents the design method by macro- and micro-scale designs. A linear-type EHA consists of a cylinder and a hydraulic pump. The former includes cylinder parameters that are dominant in the total size, and the latter includes gap width in the gear pump that is important for reducing power loss. We propose the hierarchical design to determine these parameters. In the macro-scale design, we determine the cylinder radius and differential pressure to maximize the efficiency-to-volume ratio. Based on the result of the macro-scale design, the micro-scale design determines the width of internal gaps to minimize the power loss in the gear pump. We derive mathematical formulations for the designs and develop the EHA by utilizing modular design and 3D printing. Moreover, we evaluate the fundamental properties of the developed EHA module, focusing on its power transmission efficiency and backdrivability.

Maize harvester gearbox design modification for improved fatigue life

The gearbox has the advantage of being able to change the torque and rotational speed according to the gear ratio and has high power transmission efficiency by transmitting power through the contact of the gear pair. When evaluating the strength and fatigue life of a gearbox using a design load or an equivalent load, there is a possibility that the results will be very different from the actual ones. Therefore, in this study, the load duration distribution (LDD) constructed based on the actual workload was used to evaluate the strength and fatigue life of the gearbox reliably. As a result of evaluating the strength and fatigue life of the gearbox using LDD, it was confirmed that the existing gearbox did not satisfy the target lifespan in the operating environment. Therefore, the reasons for these results were analyzed, and design modification was performed based on the analyzed results. As a result of design modification, shaft deflection decreased by rearrangement of the bearings, from an overhung type to a straddle type, thereby improving the fatigue life of gears and bearings. Finally, the load distribution acting on the gear tooth surface was improved through micro-geometry modification of the gears.

First-principles prediction of outstanding mechanical and thermodynamic properties of YX2Si2 (X = Pd and Rh) superconductors

Superconductivity is a macroscopic quantum phenomenon with unprecedented applications in high-efficient power transmission, electric motors, generators, transportation, particle accelerators, and computing. Although the superconducting capabilities of YX2Si2 (X = Pd, and Rh) compounds have been experimentally realized, the physical aspects of these two superconductors are yet to be understood. Herein, employing first-principle-based Density Functional Theory (DFT) calculations, we realized the excellent mechanical strength of the YRh2Si2 compound. Firstly, the estimated X-ray diffraction, as well as unit cell parameters of both superconductors, show excellent conformity with prior experimental data. Also, mechanical parameters which are most fundamental, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, ductility, and Vickers hardness factors of both superconductors have been evaluated. Despite the brittle nature, YRh2Si2 shows excellent mechanical strength compared to that of YPd2Si2. Besides, the assessment of the density of states, Mulliken atomic populations, and charge density map reveals a complex chemical bonding in both superconductors including ionic, covalent, and metallic features. Furthermore, charge density data suggest that Si-Si, Si-Pd, and Si-Rh bonds are indeed covalent while Pd-Pd and Rh-Rh demonstrate metallic features. Afterward, different optical parameters such as dielectric functions, reflectivity, absorption coefficient, refractive index, photoconductivity, and loss function of both superconductors have been anticipated. Notably, it has been unveiled that both superconductors show excellent absorption and photoconductivity in the ultraviolet region of the electromagnetic spectrum. Additionally, sound velocity, Debye temperature, melting point, and minimum thermal conductivity of both superconductors have been estimated from DFT computation. Interestingly, most of the thermodynamic parameters of YRh2Si2 are notably higher compared to those of the YPd2Si2 compound. Remarkably, the DFT results suggest that YRh2Si2 exhibits excellent mechanical as well as thermodynamic properties compared to other reported superconductors of identical classes.

Analysis of frequency bifurcation and frequency splitting of IPT system under overcoupling

Wireless power transfer has gradually become a promising way for the charging of electric vehicles (EVs) and the design of a high efficiency and high stability charging system is inevitable. Inductive power transfer (IPT) systems, as one of the most important method to realize wireless power transfer, usually work under weak coupling conditions and obtain high power transmission efficiency through resonance compensation circuits. In the case of reduced power transmission distance, the IPT system will enter an over-coupled state, causing the system output power to change drastically and the system to detune, and frequency bifurcation and frequency splitting will also occur. This paper first theoretically deduces the root cause of the output power variation of several typical topological IPT systems under over-coupled conditions, and then analyzes their frequency bifurcation and frequency splitting characteristics by numerical analysis methods, which can provide a reference for the design of IPT systems. Finally, the theory of this paper is verified by simulation and a 2 kW test prototype.

Coupling and maintaining link efficiency ultrasonics in transcutaneous energy transfer systems

We present on the development of a 12.8 mm diameter ultrasonic transcutaneous energy transfer system for powering implanted hearing devices. The system was based on two custom 8mm diameter PMN-PT 1-3 composite transducers operating at 1.25MHz and featured three significant innovations. First, to ensure long-term biocompatibility and reliability of the implanted portion of the link and to ensure robust attachment to bone, the implanted transducer was designed into a 12.8 mm diameter, 3.5 mm thick hermetically sealed titanium package in an easy-to-implant form factor. The transducer was designed to deliver sound efficiently through the casing walls using a mass-spring acoustic matching technique. Second, for the external unit a “dry” acoustic coupling system based on a silicone pressure sensitive adhesive was designed that combined efficient acoustic coupling, robust adhesion to skin and that was comfortable to wear. The external unit was aligned with the internal unit using a magnetic alignment system. Third, we developed and demonstrated an efficient Class E transmit amplifier and receive electronics that incorporated compensation for changes in acoustic separation between the transducer to maintain robust, high efficiency power transmission. The system achieved 33% DC-to-DC electrical conversion efficiency through 5mm of water and 19% DC-to-DC efficiency through 5mm of porcine tissue.

Virtual control method applied to Modular Multilevel Converter

The DC transformer based on the Modular Multilevel Converter (MMC) structure has the advantages of robust scalability, low output voltage harmonic content, easy realization of back-to-back connection, and high power transmission efficiency. It is widely used in DC distribution networks. However, traditional control methods hardly provide inertia for the DC distribution network, thereby reducing the stability of the distribution network when new energy output fluctuations, DC distribution network failures, or other disturbances occur. Aiming at the problem that the DC bus voltage is easily affected by power fluctuations, the paper proposes a virtual inertia control method applied to the DC transformer with MMC structure. Similar to the introduction of virtual synchronous generators in the AC distribution network to enhance the system inertia, the paper designs a control strategy for dynamically adjusting the virtual inertia with a virtual capacitor added, which is based on the traditional two-phase shift control. The paper also presents the calculation method of the virtual capacitance. When the power in the DC microgrid fluctuates significantly, the strategy can effectively enhance the inertia of the DC distribution network and suppress the voltage fluctuation of the DC bus. The paper finally establishes a DC distribution network model with distributed power sources in the PLECS simulation software, and verifies the effectiveness of the control strategy compared with the traditional strategy.

Topology optimization of metamaterial microstructure for wireless power transfer with high power transmission efficiency

An efficient short-range magnetic coupling wireless power transferring (WPT) system by embedding metamaterials (MTM) resonator between the source coil and load coil, whose configuration was designed based on topology optimization, was proposed in this paper. The topology optimization model for designing the MTM microstructures to achieve WPT with maximum power transfer efficiency (PTE) at the required frequency was established. The different MTM microstructures were realized by different conductor patch combination in the discretized pixelated design domain. As a designing example, a short-range magnetic coupling MTM-based WPT system with high efficiency at specific frequency 1 GHz was designed. Taking two classical MTM microstructures as reference, the PTE of WPT system with the topology optimized MTM was improved considerably. The variation of the transmission characteristics of the designed WPT system caused by misalignment was analyzed. The comparison between the MTM-based WPT system and the typical 4-coil WPT system was also discussed.

Kilowatt-Level 4 × 1 Fiber Combiner of Low Brightness Loss With a Square Core Output Fiber

We present the design and fabrication of a 4 × 1 fiber combiner with low brightness loss. The effective area ratio (AR) of light transmission was first introduced to estimate the brightness loss. A square core fiber was used as the output fiber of the fiber combiner to achieve a high AR. The adiabatic criterion for tapering multimode fibers was investigated to obtain the structure parameters required for the fabrication. We used an auxiliary fiber of appropriate size to achieve a regular squared fiber bundle and improve bundle cutting and splicing quality. The fiber combiner yielded a high average power transmission efficiency of 97.8% when the brightness ratio was 1.05. In addition, the output power of 1030 W was obtained by combining two LDs. This type of fiber combiner can produce multi-kilowatts laser by combining high power LDs or fiber lasers. And it can be flexibly applied in laser welding, laser cladding, and laser cleaning.

A Heterogeneous Inductive Power Transfer System for Electric Vehicles with Spontaneous Constant Current and Constant Voltage Output Features

An inductively coupled wireless power transfer system is proposed in this paper, which is designed to comply with the battery’s load characteristics. A loosely coupled transformer with high coupling coefficient is proposed. A heterogeneous compensation topology is proposed which is able to switch between constant current and constant voltage output mode according to the load resistance. The output characteristic curve agrees with the charging curve of the battery in a whole cycle. The proposed topology has a misalignment range of 300 mm where the coupling coefficient is 0.2. A 3 kW experimental platform is established to verify the theoretical analysis, and the experimental results show that the proposed loosely coupled transformer has high coupling coefficient and high power transmission efficiency (95.2% in aligned position) within a large misalignment range, which agrees with the charging scenario of the electric vehicle.