Miracle-dz/UniFAR-FTUs huggingface dataset:
A new modelling of cavitating flows: a numerical study of unsteady cavitation on a hydrofoil section

A new cavity model that can explain the interaction between viscous effects including vortices and cavitation bubbles is presented in this study. This model, which is named a bubble two-phase flow (BTF) model, treats the inside and outside of a cavity as one continuum by regarding the cavity as a compressible viscous fluid whose density changes greatly. Navier–Stokes equations including cavitation bubble clusters are solved in finite-difference form by a time-marching scheme, where the growth and collapse of a bubble cluster is given by a modified Rayleigh's equation. Computation was made on a two-dimensional flow field around a hydrofoil NACA0015 at angles of attack of 8° and 20°. The Reynolds number was 3 × 105. The experiments were also performed at the same Reynolds number for comparison. The computed results by the BTF cavity model can express the feature of cloud-type cavitation shed from the trailing edge of the attached cavities when the angle of attack is 8°. It shows the mechanism of cavitation cloud generation and large-scale vortices. The boundary layer separates at the cavity leading edge. Then it rolls up and produces the cavitation cloud. In other words, the instability of the shear layer may produce the cavitation cloud. When the angle of attack is 20°, the flow was fully separated from the leading edge of the hydrofoil and vortex cavitation occurs in the separated region. The BTF cavity model can also express the generation of such vortex cavitation and the effect of cavitation nuclei in the uniform flow.
Origami Inductors: Foldable 3-D Polyhedron Air-Coupled Inductors for MHz Power Conversion

This paper presents the principles of foldable 3-D polyhedron air-coupled origami inductors and their application in multiphase interleaved MHz power conversion. The polyhedron air-coupled origami inductor comprises of multiple windings forming the surfaces of a closed Euclidean structure, with each of these surfaces representing one phase of the coupled inductor. These windings can be implemented on a printed circuit board (PCB) which can be folded to form the 3-D polyhedron strcutures. Compared to discrete air-core inductors, the polyhedron air-coupled inductor offers reduced volume of flux distribution, reduced current ripple, as well as a faster transient response. A four-phase interleaved boost converter with a symmetric tetrahedron air-coupled inductor as the input inductor was built and tested at switching frequencies from 1 MHz to 10 MHz to verify the principles of the polyhedron air-coupled inductors.
Two-terminal hybrid HVDC transmission longitudinal protection based on S-transform and wave impedance characteristics

The research and application of hybrid HVDC transmission systems are still in their infancy, In order to solve the problem that backup protection is affected by distributed capacitance and transition resistance, a longitudinal protection scheme of hybrid DC line based on measured wave impedance is proposed. By analyzing the difference of measured wave impedance at both ends of the line during internal and external faults of hybrid HVDC transmission lines, the traveling wave is extracted by S-transform, so as to distinguish regional and external faults according to its phase difference construction criterion. PSCAD simulations show that the proposed protection scheme reliably and quickly identifies faults inside and outside the zone.
A Soft-Switching Zeta-Based AC-Link Universal Converter

AC-link universal converters are relatively new topologies that can transfer power from different types of sources to various kinds of electrical loads. These converters provide higher reliability by employing small film capacitors instead of large electrolytic ones, which have higher failure rates than other power electronic components. Furthermore, when isolation is needed, universal converters can use compact high-frequency transformers rather than bulky line-frequency transformers. These converters extend the principles of the operation of DC-DC converters to DC-AC, AC-DC, and AC-AC power conversion systems. This paper proposes a soft-switching Zeta-based universal converter that can step up and step down the voltage in a wide range. Compared to Cuk-based converters, the link capacitor in this topology has a lower peak voltage. This paper discusses the principles of the operation of this converter. The performance of the proposed structure is evaluated through simulations in this paper.
Comparison of Effective Permittivity Retrieval Methods of 3D-Printed Unit Cells for Dielectric Resonator Antenna Applications

In this paper, three methods to retrieve the effective permittivity of 3D-printed unit cells for dielectric resonator antenna (DRA) applications are compared: Maxwell Garnett approximation (MGA), S-parameters method, and plane wave expansion method (PWEM). More specifically, three common topologies are studied: simple cubic (SC), body-centered cubic (BCC) and face-centered cubic (FCC). From numerical analyses, we explain which method is the most appropriate for designing a DRA using 3D-printed periodic unit cells.
Efficient Integral Equation Approach for the Modelling of Glide-Symmetric Structures

For the design of advanced microwave and antenna components, efficient and accurate electromagnetic methods are required. In this work, we present a technique to fast simulate mirror- and glide-symmetric periodic structures. More concretely, a novel Green’s function is proposed which allows to reduce the computational domain to one half of the unit cell. Full dispersion diagrams are computed for metallic glide- and mirror-symmetric structures with three stages of mesh refinement. The results converge with the meshing and agree well with conventional eigenmode analyses.
A Self-Powered Two-Terminal MEMS Based Relay with Advanced Control Functions

In this paper, the application of a micro-electromechanical switch (MEMS) as a power relay is presented. A local energy harvesting circuit is proposed to generate auxiliary power from the ac mains. The proposed circuit is suitable for two terminal switch operation. Further, gate drive and control logic to operate the in soft switching condition is proposed and presented in order to increase the device lifetime and reliability. Analytical and experimental results are presented to verify the proposed approach.
Investigating UU Powder Core Inductor Winding Configurations Influence on DC Bias Inductance

Powder core materials are popularly used in design of line-frequency filter inductors. Designing with toroidal shape cores is well understood and its performance well predictable from datasheet values. Recently the use of “E” and “U” core shapes is gaining popularity for SiC applications. These new core shapes enable the use of flat-wire technology with automated assembly process improving efficiency and cost. But for these new core shapes, the Inductance Factor (AL) value provided by the core manufacturer is accurate only for the reported test condition. Other winding arrangements can result in considerably different AL values. This discrepancy is high for low permeability cores. This paper aims to highlight this discrepancy, provide technical insights on expected performance and design trade-offs. Finite element analysis (FEA) is used to support this, and the results match experimental measurements for the two mock inductors fabricated. When designing with low Perm U -cores the leakage fields effect the resultant inductance at nominal and overload conditions. Leakage field distribution between two common winding (one-leg and two-leg) configurations is also provided. It is shown that additional inductance in one-leg winding is relatively independent of permeability of core.
Four legs Clamping Modulation Technique of Dual Inverter with Isolated DC Bus for Reduction of Switching Loss considering Power Factor

This paper proposes a technique for reducing of switching losses in a dual inverter with isolated DC Bus. The dual inverter consists of six-legs with 12 switching devices. This means that switching losses double that of a single inverter with three legs. The switching losses depend on the angle by power factor (PF) and the magnitude of the stator current. In this paper, the four legs clamping modulation technique that considers PF is proposed. In the proposed technique, for clamping the four of six legs of the dual inverter during a switching period, voltage vectors of the primary and secondary inverters are determined through the combinations of active and zero voltage vectors. Furthermore, the combinations are selected differently according to 12 sectors divided by the angle of the current to consider PF. The validity of the proposed technique is verified by simulation results.
Shaped-Beam Subarrays for Equi-Power Urban Area Coverage With Modularity and Low Cost

Design of millimeter-wave arrays for base stations operating in dense urban environment is investigated. Innovative designs for linear subarrays with shaped beam patterns for hybrid beamforming are proposed. The number of elements and element spacings in the subarrays are optimally selected based on a pattern matching technique. The subarrays are designed and verified in series edge-fed slotted substrate integrated waveguide technology at 26 GHz. A novel phase shifter unit is proposed to reduce the subarray width for grating lobe-free beam steering in the plane orthogonal to the sub-array axis. Infinite array simulations are performed to observe the coupling effects on the subarrays.
Shared-Volume Millimeter-Wave Substrate Integrated Step Horn Antennas and Arrays

Two substrate integrated step horn antennas sharing the same volume in the millimeter-wave band are proposed in this paper. The step horns are implemented using the substrate integrated waveguide technology and the multiple layer printed circuit board (PCB) technique. Two step horns radiate from their individual aperture with independent feedings, but are integrated in the same substrate cube. After elaborate designs, both the two horns operate in a wide band from 24 to 30 GHz with the reflection coefficients below -10 dB. The two perpendicular radiating aperture on the top and front, contribute together to a radiation in the 0-plane, resulting in an increased space coverage efficiency. Moreover, a linear broadside array with eight antenna units is investigated to obtain the beam scanning property. Simulation results demonstrate that the radiation beams of the eight-unit array in both directions can steer continuously from -45° to +45° with scanning loss less than 3 dB. The antenna unit and array proposed in this paper are promising for millimeter-wave communication systems on mobile devices.
Prediction of PEMFC Life decay based on Machine Learning

Proton exchange membrane fuel cell (PEMFC) has the advantages of fast cold start and zero pollution, however, the safety stability, reliability and durability of mainstream PEMFC restrict its large-scale industrial application and commercialization. In this paper, we propose a method combining wavelet threshold denoising algorithm and machine learning technology to address the problems of low model prediction accuracy due to the high noise of the original PEMFC data set and the unknown influence of PEMFC feature quantity on its lifetime prediction. Firstly, the noise interference in the original data is removed and the PEMFC attenuation information is retained by equal interval sampling and wavelet threshold denoising algorithm, and then the XGBoost-RFECV algorithm is used to calculate the importance of different features of PEMFC and filter out the optimal feature subset, and at the same time, a two-layer bi-directional long and short-term memory (BiLSTM) based neural network is built, and the filtered optimal feature subset is input into the model is trained to achieve life span prediction. The experimental results show that the average absolute error and root mean square error of this method are 0.0013 and 0.0022, respectively, and the coefficient of determination R2 is 0.980, which is more accurate than XGBoost-RNN, XGBoost-LSTM and XGBoost-RFECV-LSTM methods, and can effectively improve the prediction of PEMFC lifetime.
Seamless Grid-Following to Grid-Forming Transition of Inverters Supplying a Microgrid

A control method for grid-interactive inverters to operate in grid-following (GFL) and grid-forming (GFL) modes is presented in this paper. The proposed controller uses two sets of semi-parallel control paths in which each set provides the phase angle and amplitude of the PWM reference signal. Based on the mode of operation of an inverter, the PWM generator receives only one set of reference signals at a time. The proposed controller can keep the two sets of paths synchronized so that when a group of inverters operating in GFL mode is suddenly disconnected from the grid, multiple inverters can seamlessly and simultaneously transit to GFM mode to form a microgrid. The efficacy of the proposed controller has been verified in a microgrid fed by two 5kVA 208V inverters and a 30kVA grid emulator under several scenarios, and the results are presented in this article.
A 155W −95.6 dB THD+N GaN-based Class-D Audio Amplifier With LC Filter Nonlinearity Compensation

Silicon MOSFETs-based medium-power (< 50W) Class-D amplifiers (CDAs) switching in the MHz range have gained popularity in recent years, which achieves better linearity thanks to a higher loop gain in the audio band while enabling the use of LC filters with higher cut-off frequencies. However, for high-power (>100 W) CDAs, such switching frequency and high load current could lead to significant power loss. Furthermore, in the presence of a large current and voltage applied to the load, the linearity of the system can quickly degrade due to LC filter component voltage/current dependency. Without any LC filter nonlinearity compensation technique, LC components with high voltage/current rating must be used to reach high system linearity, which are often expensive and bulky. This paper presents a CDA using a GaN-based output stage to achieve high switching frequency and good efficiency simultaneously, and an integrated controller implemented in a 180nm CMOS technology to compensate for the LC filter nonlinearity. Switching at 1.8 MHz, the CDA can deliver a maximum of 155W from a 50V supply into a $4\Omega$ load with a peak efficiency of 91.7%. It achieves a peak THD+N of −95.6 dB (0.0017%) while allowing the use of cheaper and smaller nonlinear LC components.
A Novel Digital Energy Management Control Strategy of a Fully Active Hybrid Converter for Unmanned Aerial Vehicle Applications

A combination of multiple energy sources, known as a hybrid energy system (HES), has been considered to increase flight time for unmanned aerial vehicle applications. Two separated or combined converters, which can be defined as a fully active hybrid converter, can be placed between energy sources and the load to manage energy flows from sources. This paper proposed a novel digital energy management control strategy for fully active hybrid converters, mainly comprised of the mode identification strategy and digital control algorithm, which can realize four crucial functions: 1) regulation of the output voltage, 2) energy management control, 3) charging and discharging operations of battery, and 4) protection for energy sources. And the control strategy has been validated by the experiment based on a hybrid converter prototype, which is designed for 400 W (16.8 V/ 24 A) output and two energy sources, a 450 W fuel cell (FC) and 12 stack Li-Po battery with 39.6-50.4 V voltage range and 44.4 V nominal voltage.
Universal Bridgeless Reconfigurable Battery Charger with Wide Output Voltage Range for Next-generation EV Compatibility

The main concern for the adoption of electric vehicles (EVs) is the long idle period for charging. Next-generation EVs are coming with high voltage (HV) powertrains to enhance the battery charger's power rating without increasing the charging chord size. This paper proposes a new isolated bridgeless reconfigurable battery charger to charge the traditional and next-generation EVs from a universal ac input power supply (85–264 V, 50/60 Hz). Two distinct controllers are presented to maintain the unity power factor and input current total harmonic distortion at the input power supply. Furthermore, these controllers regulate the charger output voltage/current in accordance with the charging technique. The proposed reconfigurable charger and its control design are provided in detail. Moreover, a 3.3 kW reconfigurable battery charger and the controller are implemented to validate the proposed battery charger. The simulation and test results demonstrate that the proposed charger maintains the ripple-free dc current/voltage at the battery terminals for both traditional and next-generation EV charging. Furthermore, the charger extracts a sinusoidal current, which is in phase with the supply voltage.
A Novel Transformer Leakage Energy Recovery Active Clamp Control Technique for High Power AC/DC Flyback Converters

A novel twin-pulse active clamp has been proposed for flyback converters that can efficiently recover the transformer leakage energy and route it to the output with reduced clamp current ratings and clamp capacitance compared to existing active clamp methods. This extends the application power range for ac/dc flyback converters by enabling a cost-effective leakage energy recovery method for high-power applications. In the case of a 2.5 kW flyback converter, the proposed clamp offers a potential reduction of the required clamp capacitance by 500x and the clamp current by more than 2x at the expense of a higher peak switch voltage stress when compared to an equivalent conventional active clamp. The operating principle and the design criteria for the proposed clamp method are discussed. Experimental results for a 2.5 kW ac/dc flyback converter prototype with the proposed clamp have been presented, validating the clamp operation. Its performance and efficiency improvement compared to a dissipative clamp with active discharge has also been evaluated over the entire operating region.
A 400W, 99.3% Efficient GaN Buck-Boost Converter

This paper presents a high-efficiency high-power density 500kHz gallium nitride (GaN) based buck-boost converter. State-of-the-art silicon-based buck-boost converters are limited by the poorer device figure of merit (FOM) of silicon technology, namely these converters suffer from large capacitance related switching losses which limit the switching frequency and deteriorate the efficiency and power density. GaN power devices with much better FOM provide lower conduction loss and switching loss at the same time even at elevated switching frequencies. However, quantitative benefits of replacing Si-MOSFETs with GaN FETs are not well-defined in many cases. The focus of this paper is to quantify the impact in a buck-boost converter which is becoming increasingly important due to the proliferation of battery-powered electronics systems. Experimental results are presented in order to show the superior performance of the GaN-based converter in comparison to the state-of-the-art Si-MOSFETs converters. The experimental results show very high efficiency (up to 99.3%) in a wide range of operations and high-power density. The prototype achieves a power density of 110W/cm3 using IHLP6767GZ01 inductor and 35W/cm3 using IHLP8787MZ5A inductor.
Propagation Characteristics of UHF Partial Discharge Signals in GIS

Partial discharge measurement is one of the main methods for condition monitoring of gas insulated switchgear. Built-in ultra-high frequency (UHF) sensors can be used to capture PD propagating electromagnetic signals within the GIS. Placing PD sensors inside a GIS is one of the main challenges in designing an online PD measurement system. For this purpose, the influence of different GIS components on the propagation of PD electromagnetic waves should be studied. In this paper, based on the real GIS, the simulation models of straight cavity, L shape and T shape are established, and the influence of different partial discharge positions and different structures on the propagation of electromagnetic waves generated by partial discharge is compared and analyzed by CST simulation software. In addition, in order to study the attenuation characteristics of partial discharge UHF signals in GIS, the S parameters after passing through different numbers of basin insulators were analyzed. The research results show that the degree of attenuation of the measured PD electromagnetic wave is mainly affected by the structure of the sensor. GIS designers can use these results to select the appropriate PD sensor and its installation location.
Electrical Fault Detection Based On Infrared Temperature Measurement Technology

This paper mainly analyzes the infrared temperature measurement equipment of power system. Its hardware architecture mainly includes three parts: monitoring front-end, wireless communication network and monitoring center. The monitoring front-end hardware is installed with a main control module, which is successively linked with image acquisition, image compression module and infrared alarm module; An infrared thermal imager is linked to the image acquisition; The monitoring center is also equipped with a computer host server and an infrared camera display device. In this paper, the distribution of high temperature of transmission line is detected online by infrared thermal image, and the security status of transmission line is judged through the online measurement technology of transmission line infrared thermal image, and the early warning signal of high temperature thermal anomaly is accurately provided. In order to effectively protect the safety of existing transmission line from high temperature thermal overshoot, it plays a great role.
A Bandwidth-Enhanced Substrate Integrated Waveguide Cavity-Backed V-Band Antenna Using Double-Sided Complementary Annular Slots

This work presents a 64-GHz substrate integrated waveguide (SIW) cavity-backed antenna, whose bandwidth is extended through the complementary multiple annular slots on the front and back sides of the SIW cavity, respectively. A perturbed TE210 mode with two broadside radiation patterns in opposite directions can be observed under the double-sided slots. A Rogers RO4003C substrate is used to manufacture this antenna through a printed circuit board process. With the -10- dB S11 criteria, the measured impedance bandwidth is 3.2 GHz. The measured realized gains at 64 GHz in the two broadside directions are 6.4 dBi and 3.4 dBi, respectively. Furthermore, an over-the-air experiment with a QPSK modulation signal was conducted to validate the double-sided radiation.