In this paper, a discussion is presented concerning the combined uncertainty when measuring residual and additional losses in the efficiency evaluation of three-phase induction motors, by evaluating some experimental results obtained on a commercial motor. The IEC 60034-2-1 standard is considered, in comparison to a previous version of this standard requiring the estimation of residual losses instead of their measurement. A major goal is to investigate if the complex measurement method introduced in the present version of the standard is justified or not by processing the actually achievable uncertainty both in additional losses and in the overall efficiency measurement. Finally, some considerations are presented about additional issues concerning the classification of the tested motor, in comparison to the IE (International Efficiency) efficiency levels.

The mathematical model of composite reservoir has been widely used in well test analysis. In the process of oil recovery, due to the injection or replacement of the displacement agent, the model boundary can be moved. At present, the mathematical model of a composite reservoir with a moving boundary is less frequently studied and cannot meet industrial demand. In this paper, a mathematical model of a composite reservoir with a moving boundary is developed, with consideration of wellbore storage and skin effects. The characteristics of pressure transient in moving boundary composite reservoir are studied, and the influences of parameters, such as initial boundary radius, moving boundary velocity, skin factor, wellbore storage coefficient, diffusion coefficient ratio, and mobility ratio on pressure and production, are analyzed. The moving boundary effects are noticeable mainly in the middle and late production stages. The proposed model provides a novel theoretical basis for well test an... [more]

Product recommendation systems are essential for enhancing customer experience, and integrating them with mobile apps is crucial for improving usability and fostering user engagement. This study proposes a hybrid approach that utilizes comparative facts from pairwise comparison data and comparison lists, with association rules as the method to formulate the recommendation system. The study employs a dataset from the New-Cars Database app, comprising 30,867 vehicle comparisons made by 5327 users across 40 car brands and 870 cars from 30 January 2015 to 2 April 2015. Two metrics are developed to measure the system’s output under varying support and confidence thresholds. The findings suggest that adjusting the support and confidence values can improve the breadth and depth of product recommendations. In addition, the unit of analysis can affect the recommendation system’s output, with comparison lists supplementing and expanding the exploration of potential outcomes. The proposed hybrid... [more]

With the further innovation of chip technology, semiconductor integrated circuits have made irreplaceable contributions to the development of microelectronic systems [...]

Acid fracturing is one of the effective techniques for developing low-permeability carbonate reservoirs economically. With the increasing reservoir depth, the reservoir temperature and closure pressure increase, posing new challenges to the acid system. In this paper, a high-temperature-resistant cross-linked acid system is selected, which maintains a viscosity above 80 mPa·s in the temperature range of 120 °C to 140 °C and can effectively reduce acid leak-off. The acid system can not only open the reservoir and ensure the extension of the fracture, but also reduce the reaction rate between the acid and the reservoir and increase the etching distance. The rock slab acid etching and conductivity tests show that the optimum injection rate is 50 mL/min, the rock etching morphology is channel type, and the conductivity remains above 110 D·cm. However, as the acid concentration decreases, the rock slab conductivity decreases considerably, especially at 10% acid concentration, where the clos... [more]

Many oil wells in closed reservoirs continue to produce in the pseudo-steady-state flow regime for a long time. The principal objective of this work is to investigate the characteristics of two key pseudo-steady-state parameters—pseudo-steady-state constant (bDpss) and pseudo-skin factor (S)—for a well penetrated by a fracture with an azimuth angle (θ) in an anisotropic reservoir. Firstly, a general analytical pressure solution for a finite-conductivity fracture with or without an azimuth angle in an anisotropic rectangular reservoir was developed by using the point-source function and spatial integral method, and two typical cases were employed to verify this solution. Secondly, with the asymptotic analysis method, the expressions of pseudo-steady-state constant and pseudo-skin factor were obtained on the basis of their definitions, and the effects of permeability anisotropy, fracture azimuth angle, fracture conductivity and reservoir shape on them were discussed in detail. Results sh... [more]

In the present work, the cooling efficiency of water droplets falling onto hot aluminum and stainless steel discs from heights of 12.5 cm, 25 cm, 50 cm and 100 cm, corresponding to speeds of 1.5 m/s, 2.2 m/s, 3.1 m/s and 4.4 m/s, respectively, were studied. The discs were aligned at 0° (horizontal), 30° and 60° inclination. The water application rate was 0.022 g/s and the droplet diameters studied were 2.5 mm, 3.2 mm and 3.7 mm. Acetone solutions (300 ppm and 700 ppm) as well as a NaCl (35 g/kg) solution, emulating seawater, were tested to evaluate the influence of an active surfactant on the recorded cooling efficiency. The droplets with higher impact speed resulted in lower cooling efficiency, especially at disc temperatures above the Leidenfrost temperature, likely due to more vigorous droplets bouncing. Larger inclination did, as expected, result in lower cooling efficiency. At temperatures associated with nucleate boiling, the water droplets with NaCl conspicuously displayed highe... [more]

Energies presents 10 papers selected from the 11th International Conference on Computational Heat, Mass and Momentum Transfer (ICCHMT2018) [...]

In several energy applications, DC/DC converters are one of the most important components [...]

In this paper is presented a Normally-OFF GaN HEMT (High Electron Mobility Transistor) device using p-doped GaN barrier layer regrown by CBE (Chemical Beam Epitaxy). The impact of the p doping on the device performance is investigated using TCAD simulator (Silvaco/Atlas). With 4E17 cm−3 p doping, a Vth of 1.5 V is achieved. Four terminal breakdowns of the fabricated device are investigated, and the origin of the device failure is identified.

A control technique combining pulse width modulation (PWM) and pulse amplitude modulation (PAM) is presented herein to reduce the output voltage ripple of the converter as little as possible. Such a converter requires a two-stage cascaded structure. The first stage is the buck-boost converter, which is used to adjust the output voltage of the second power stage, whereas the second stage is the two-phase interleaved buck converter, which is used to reduce the output voltage ripple. In theory, the two phases of the second stage operate under the condition of individual duty cycles of 50% with a phase difference of 180° between the two, and hence, the currents in the two phases are cancelled for any period of time, thereby making the output voltage of the converter almost voltage-free. Moreover, in order to improve the overall efficiency further, the proposed soft-switching technique based on an active clamp is presented and applied to these two stages to render the main and auxiliary swi... [more]

The flexible excitation system (FES) is a kind of novel excitation system with two channels for damping control. Besides the basic functions of traditional excitation systems, flexible excitation systems can provide reactive power support for the terminal voltage, and the large-capacity FES can improve the voltage stability and power-angle stability of synchronous generator units. However, with the increase in system capacity and the complication of control objectives, the difficulty of controller design will be increased. The randomness and fluctuation of new energy resources such as photovoltaic and wind turbines may cause disturbance and fault to the power system, which requires the coordinated control strategy for the FES to achieve stability in voltage and power angle. In this paper, the basic characteristics of FES are analyzed, and the mathematic model of the single machine infinite bus (SMIB) system based on FES is derived. The coordinated control strategy based on decoupling c... [more]

Magnetic beamforming techniques can enhance the power transfer efficiency using focused magnetic fields by the multiple transmitters to the receivers. However, the intra-couplings that cause power leakage and phase distortion among the arrayed coils inevitably occur due to the deployment of coils having strong couplings between each other. Here, we analyze the adverse influences of intra-couplings and present the advantages of magnetically independent transmitters for multiple-inputs and single-output (MISO) WPT. The independent coil array can achieve focused magnetic fields by simply adjusting the amplitude of the transmitter voltage source without phase adjustment. The system also can eliminate the reactive power with the independent coil array to efficiently use the supplying power from the source. The analytical studies are verified by numerical and circuit simulation and experiments. Our analysis can be generalized to the MISO-WPT with an arbitrary number of transmitters. It can p... [more]

Knowledge of lightning impulse (LI) voltage distribution over transformer windings during the design stage of the transformer is very important. Specific design differences in inductive voltage transformers make the transient analysis approach different to the approach to the power transformers. In this paper, a methodology for acquiring lightning impulse voltage distribution over high-voltage (HV) winding of inductive voltage transformers is presented and evaluated. Resistance, inductance, and capacitance matrices are calculated using the integral and boundary element methods (BEM) approach. Additionally, in order to improve the capacitance matrix solver, adaptive cross approximation (ACA) is applied. These parameters are then used to solve the equivalent circuit model in time domain. In order to evaluate the methodology, an experimental and numerical investigation of the layer discretisation, iron core influence, and accuracy of the proposed methodology is performed. The comparison o... [more]

This paper presents a comparison of 30/8 and 12/8 AC permanent magnet motors with distributed (DW) and concentrated winding (CW) designed for electric vehicle traction. Both prototypes are based on an interior permanent magnet (IPM) motor topology and contain V-shape magnets. The radial flux AC IPM motors were designed for an 80 kW propulsion system to achieve 125 N·m. Finite element models (FEM) used to design the geometry of IPM motors and the required useful parameters of electric motors are widely investigated. The accuracy of finite element models is verified and validated on the basis of test data. Numerical simulations of healthy and faulty operation states, and studies of winding faults based on the FEM offer a deeper understanding of the associated phenomena. Therefore, in this paper, a short-circuit fault in a stator winding was simulated to investigate the transient currents under an external load collapse, for all winding phases. These simulations were used to define other... [more]

To improve the efficiency of the wireless power transfer (WPT) system without increasing the system size, a central bulge ferrite core with a novel configuration is proposed. The mutual inductance between magnetic coupling structures is able to increase obviously, which is approved by eigenfunction expansion method. In this paper, the mathematical models of the planar core and the central bulge core are established, respectively, as two types of the mutual inductance are calculated in same condition. The structure parameters of the central bulge ferrite core are further optimized by Maxwell magnetic field simulation. Experiments are conducted to compare the WPT efficiency of two types of ferrite cores in improving the efficiency of WPT system, in which the influence of transmission distance, lateral misalignment, and load variation are taken into account. The results show that central bulge ferrite core has better performance in WPT efficiency than the planar one, even in the case of l... [more]

In this study, small multilayer planar spiral coils were analyzed and optimized to wirelessly charge an in-ear wearable bio-signal monitoring device in a wine-glass-shaped transmitter (Tx) based on magnetic resonance wireless power transfer (MR-WPT). For analysis of these coils, a volume filament model (VFM) was used, and an equivalent circuit formulation for the VFM was proposed. The proposed method was applied to design effective multilayer coils with a diameter and height of 6 and 3.8 mm, respectively, in the wearable device. For the coils, a printed circuit board having a 0.6 mm thick dielectric substrate and a 2 oz thick copper metal was used. Moreover, the coils on each layer were connected in series. The dimensions of the double-, four-, and eight-layer coils were optimized for the maximum quality factor (Q-factor) and coupling efficiency. The operating frequency was 6.78 MHz. The optimal dimensions for the maximum Q-factor varied depending on the number of coil layers, pattern... [more]

A computationally efficient design of interior permanent magnet (IPM) motor rotor features is investigated utilizing analytical methods. Over the broad operating range of IPM machines, interactions of MMF sources, permeances, and currents result in torque harmonics. The placement of traditional rotor features along with sculpt features are utilized to minimize torque ripple and maximize average torque. We extend the winding function theory to include the IPM rotor’s primary and secondary reluctance paths and the non-homogeneous airgap of the rotor sculpt features. A new analytical winding function model of the single-V IPM machine is introduced, which considers the sculpted rotor and how this model can be used in the design approach of machines. Results are validated with finite elements. Rotor feature trends are established and utilized to increase design intuition and reduce dependency upon the lengthy design of experiment optimization processes.

The most common type of electric vehicle traction motor is the interior permanent magnet synchronous motor (IPMSM). For IPMSM designs, engineers make use of the magnetic equivalent circuit method, which is a lumped constant circuit method, and the finite element method, which is a distributed constant circuit method. The magnetic equivalent circuit method is useful for simple design through fast and intuitive parameters, but it cannot derive the distribution of the magnetic field. The finite element method can derive an accurate magnetic field distribution, but it takes a long time and is difficult to use for analysis of intuitive design parameters. In this study, the magnetic equivalent circuit method and Carter’s coefficient were combined for rotor structure design and accurate identification and analysis of circuit constants. In this paper, this design method is called the hybrid magnetic equivalent circuit method. Intuitive design parameters are derived through this hybrid magnetic... [more]

Diagnostic data of transformers are essential in determining their integrity and to estimate their reliability. Such diagnostic data is not available for distribution transformers as only meagre attempts are made to accumulate this information. The reason for lack of such attention is attributed to the compromise made to meet financial constraints and cost-cutting measures. It is needless to emphasize the significance of these diagnostic data in evading premature failures and enhancing the accuracy of the maintenance program. Overall, the concepts of diagnostic methods are well defined regarding power transformers, but cannot be extended to distribution transformers. This paper attempts to fill this gap by measuring the diagnostic data from in-service and defective distribution transformers. For this purpose, eight transformers (six in-service, two defective) showing deviations in their diagnostic status were selected from a group. As per their kVA rating and operating status, the chos... [more]

This paper presents a straightforward step-by-step procedure to design salient-pole synchronous generators, starting with its main specifications and finishing with all necessary data to put it on production. As most of the electricity is generated by synchronous generators, the design of these machines remains an interesting subject, but, although it is important, it is difficult to find a complete step-by-step procedure in the literature. The proposed procedure can be followed by an electrical engineer or student and, distinctively from most papers and books, all steps are presented. Such a procedure is based on analytic calculations, eventually relying on finite element simulation to verify if everything is all right and to adjust some design parameters. All calculations have been chosen to keep the design as simple as possible; otherwise, it would not be possible to present all steps and procedures. Therefore, it can be used for beginners in the art of design-synchronous generators... [more]

In the article, a wireless charging system with the use of periodically arranged planar coils is presented. The efficiency of two wireless power transfer (WPT) systems with different types of inductors, i.e., circular and square planar coils is compared, and two models are proposed: analytical and numerical. With the appropriate selection of a load resistance, it is possible to obtain either the maximum efficiency or the maximum power of a receiver. Therefore, the system is analyzed at two optimum modes of operation: with the maximum possible efficiency and with the highest power transmitted to the load. The analysis of many variants of the proposed wireless power transfer solution was performed. The aim was to check the influence of the geometry of the coils and their type (circular or square) on the efficiency of the system. Changes in the number of turns, the distance between the coils (transmit and receive) as well as frequency are also taken into account. The results obtained from... [more]

Communication between the primary and secondary sides is pivotal to the wireless power transfer (WPT) system. The system control commands and feedback information need simultaneous wireless information and power transfer (SWIPT). In this paper, a FSK-based SWIPT system with full-duplex communication via a shared channel is provided. Considering the complexity of the coupling relationship in this kind of full-duplex SWIPT system, this paper proposes an analysis method based on the transmission channel, studies the crosstalk between the power channel and the information channel, and between the forward and reverse transfer of information. A design method of full-duplex communication SWIPT system based on shared coupling channels is provided. A 60 W SWIPT prototype with a full-duplex communication rate of 20 kbps is built to verify the proposed method.

The computation of self and mutual inductances of coils is a classic problem of electrical engineering. The accurate modeling of coupled coils has received renewed interest with the spread of wireless power transfer systems. This problem has been quite well addressed for coplanar or perfectly coaxial coils but it is known that the misalignment conditions easily lead to a sharp decrease in the efficiency. Hence, it is crucial to take misalignment into account in order to properly design the overall wireless power transfer system. This work presents a study to compute analytically the mutual inductance of non-coaxial pancake coils with parallel axes. The accuracy of the proposed methodology is tested by comparison with the numerical results obtained using the tool Fast-Henry. Then, a wireless power transfer system, comprising a full bridge inverter is considered, showing the impact of the misalignment on the coupling between two pancake coils and, thus, between the source and the load.

Induction machines have been key components in the industrial sector for decades, owing to different characteristics such as their simplicity, robustness, high energy efficiency and reliability. However, due to the stress and harsh working conditions they are subjected to in many applications, they are prone to suffering different breakdowns. Among the most common failure modes, bearing failures and stator winding failures can be found. To a lesser extent, High Resistance Connections (HRC) have also been investigated. Motor power connection failure mechanisms may be due to human errors while assembling the different parts of the system. Moreover, they are not only limited to HRC, there may also be cases of opposite wiring connections or open-phase faults in motor power terminals. Because of that, companies in industry are interested in diagnosing these failure modes in order to overcome human errors. This article presents a machine learning (ML) based fault diagnosis strategy to help m... [more]