Loss Calculation Method Research Articles

A Complete Switching Analytical Model of Low-Voltage eGaN HEMTs and Its Application in Loss Analysis

Low-voltage enhancement-mode gallium nitride high electron mobility transistors (eGaN HEMTs) are a kind of promising devices to realize high-efficiency and high-power-density conversion because of their fast switching speed, low conduction, and switching losses. Since the reverse conduction loss of eGaN HEMTs accounts for a large part of switching losses, it is of great importance to improve the traditional switching analytical model to predict the reverse conduction loss. In this paper, a complete and accurate switching analytical model of low-voltage eGaN HEMTs is presented, which considers the effects of low-parasitic inductances, nonlinear junction capacitances and nonlinear transconductances. The turn- on and turn- off switching processes are described in detail, and the resulting equations are solved by using mathematical software such as MATLAB to predict the switching waveforms during the switching periods. And an accurate loss calculation method based on the proposed model is proposed including the reverse conduction loss. The accuracy of the proposed model is validated by comparing the predicted switching waveforms and the efficiency of a synchronous buck converter with the experimental results, respectively. Moreover, the proposed model is compared with the traditional model, which proves the advantages of the proposed model. In the end, according to the proposed complete model, the effect of the top switch (TS) gate resistance, the TS drain-source capacitance, power loop inductance, current ripple, the bottom switch (BS) gate resistance, the BS drain-source capacitance, and dead time on the loss breakdown of the synchronous buck converter is explored and some qualitative suggestions are given to improve the conversion efficiency based on these analyzing results.

Binary Volumetric Convolutional Neural Networks for 3-D Object Recognition

To address the high computational and memory cost in 3-D volumetric convolutional neural networks (CNNs), we propose an approach to train binary volumetric CNNs for 3-D object recognition. Our method is specifically designed for 3-D data, in which it transforms the inputs and weights in convolutional/fully connected layers to binary values, which can potentially accelerate the networks by efficient bitwise operations. Two loss calculation methods are designed to solve the accuracy decrease problem when the weights in the last layer are binarized. Four binary volumetric CNNs are obtained from their corresponding floating-point networks using our approach. Evaluations on three public datasets from different domains (Computer Aided Design (CAD), light detection and ranging (LiDAR), and RGB-D) show that our binary volumetric CNNs can achieve a comparable recognition performance as their floating-point counterparts but consume less computational and memory resources.

Analysis on Eddy Current Losses in Stator Windings of Large Hydro-Generator Considering Transposed Structure Based on Analytical Calculation Method

Aimed at the problem that the existing calculation method of eddy current losses in stator windings of large hydro-generators cannot consider the transposed structure and circulating current, the equivalent circuit model considering the actual transposed structure and circulating current is established, and the analytical calculation method for eddy current losses of stator winding is proposed in this paper, which is suitable for different transposed structures. Then, eddy current losses of stator transposed winding in an 180MW hydro-generator is analyzed by the proposed method and validated by the finite element method. Finally, the influence of the transposed structure on eddy current losses of stator windings is analyzed quantitatively and compared with the existing calculation method. The results show that the value and distribution trend of eddy current losses in strands change a lot when considering the influence of circulating current and the actual transposed structure, and the influence is different for different transposed structures, which must be considered.

Method for Theoretical Line Loss Calculation of 10kV Distribution District based on Actual Electric Energy of Distribution Transformer Secondary Side

The 10kV distribution district serves the electricity customer, and its theoretical loss can reflect the real situation of the technical line loss. Adopting the equivalent resistance method based on average current, on the basis of the remotely read active and reactive electricity at the head of the 10kV line, as well as the actual copying electricity on the secondary side of distribution transformer, this paper establishes mathematical models for calculating the electricity loss in both forward and backward directions. The case analysis shows that the results of the backward mathematical model accurately reflect the actual value of the theoretical line loss, and by comparing the theoretical line loss rate calculated by the two mathematical models, the unknown loss of the line can be identified.

ВЛИЯНИЕ ОТРИЦАТЕЛЬНЫХ ТЕМПЕРАТУР НА ТЕПЛОТЕХНИЧЕСКИЕ ХАРАКТЕРИСТИКИ ОКОННЫХ БЛОКОВ ИЗ ПВХ ПРОФИЛЕЙ

The experimental studies of thermal characteristics of PVC windows at negative temperatures of the outside air are performed. The experimental studies results are compared with the requirements of regulatory documents and existing calculation methods of infiltration heat loss through the windows. The laboratory tests show, that under the influence of the temperature difference of the external and internal air (in winter) window profiles get large deformation. The temperature deformation of PVC profiles and window gaskets elasticity degradation lead to a violation of the window thermal characteristics. The effect is to increase the windows air permeability and reduce the temperature on the inner surfaces of their profile elements. This leads to an increase in infiltration heat loss through the windows and violation of the normal microclimate parameters in the room. The established effect of reducing the PVC windows thermal characteristics at negative outside air temperatures is not taken into account by the existing calculation methods.

Multiscale Method for AC Loss Calculation of HTS Coated Conductors With Magnetic Substrate

The ac loss calculation problem is the key issue for a superconducting magnet. The existing numerical models do not consider the magnetic properties of the substrate while calculating the transport ac loss of high temperature superconductor (HTS) coated conductors. In fact, the unacceptable time and memory consumption makes the ac loss calculation a tough task while considering the magnetic properties of the substrate. This paper introduces a two-dimensional multiscale method for calculating the transport ac loss of HTS YBCO coated conductors with magnetic substrate, which can greatly reduce the calculation time under the premise of high accuracy. The multiscale method is realized with three unidirectionally coupled models and only considers the nonlinear E-J characteristics in two simple models with fewer degrees of freedom, which avoids considering the E-J characteristics in the whole coil. The calculation accuracy of the multiscale method is validated by comparing the simulation results with that of Ainslie's model with the same coil structure, which consists of 2 × 50 turns of YBCO tapes with ferromagnetic substrate. The results of the multiscale method model are highly consistent with that of Ainslie's model. The calculation speed can be increased by two orders of magnitude with the multiscale method, which indicates that this method is an effective approach to handle the transport ac loss calculation problems while including the ferromagnetic substrate. It also has the ability to solve much more complex problems in the future, such as large-scale HTS magnet.

Comparison of Two Different Glenoid Bone Loss Calculation Methods using Three-Dimensional Computed Tomography

Comparison of Two Different Glenoid Bone Loss Calculation Methods using Three-Dimensional Computed Tomography

Calculation method of corona loss in EHV/UHV system based on distributed parameter characteristic

For the calculation of corona loss of extra‐/ultra‐high voltage (EHV/UHV) transmission lines, especially the estimation of real‐time corona loss, there exists no accurate method. In this paper, a calculation method of corona loss in the EHV/UHV system based on a distributed parameter characteristic is proposed. Based on the π‐shaped equivalent circuit of the long‐line distributed parameter characteristic, and considering the voltage distribution along the line, a formula for calculating the corona loss under a variety of weather and annual average conditions is derived and the power equation for the corona loss of EHV/UHV system is established by the method. The example results show that the method is quite accurate. The calculation method of this paper can consider different weather conditions of the line sections to calculate the corona loss. It is more in line with the actual weather conditions on the surface of the EHV/UHV transmission lines. And the method can analyze the corona loss and its proportion to the total loss of the system under the annual average and different weather conditions. It is of great significance to the design and operation of an EHV/UHV system. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An Improved YOLOv2 for Vehicle Detection.

Vehicle detection is one of the important applications of object detection in intelligent transportation systems. It aims to extract specific vehicle-type information from pictures or videos containing vehicles. To solve the problems of existing vehicle detection, such as the lack of vehicle-type recognition, low detection accuracy, and slow speed, a new vehicle detection model YOLOv2_Vehicle based on YOLOv2 is proposed in this paper. The k-means++ clustering algorithm was used to cluster the vehicle bounding boxes on the training dataset, and six anchor boxes with different sizes were selected. Considering that the different scales of the vehicles may influence the vehicle detection model, normalization was applied to improve the loss calculation method for length and width of bounding boxes. To improve the feature extraction ability of the network, the multi-layer feature fusion strategy was adopted, and the repeated convolution layers in high layers were removed. The experimental results on the Beijing Institute of Technology (BIT)-Vehicle validation dataset demonstrated that the mean Average Precision (mAP) could reach 94.78%. The proposed model also showed excellent generalization ability on the CompCars test dataset, where the “vehicle face” is quite different from the training dataset. With the comparison experiments, it was proven that the proposed method is effective for vehicle detection. In addition, with network visualization, the proposed model showed excellent feature extraction ability.

Evaluation of Prestress Loss Distribution during Pre-Tensioning and Post-Tensioning Using Long-Gauge Fiber Bragg Grating Sensors.

Prestress loss evaluation in prestressed strands is essential for prestressed structures. However, the sensors installed outside the duct can only measure the total prestress loss. The sensors attached on strands inside the duct also have several problems, such as inadequate durability in an aggressive environment and vulnerability to damage during tensioning. This paper proposes a new installation method for long-gauge fiber Bragg grating (LFBG) sensors to prevent accidental damage. Then the itemized prestress losses were determined in each stage of the pre-tensioning and post-tensioning according to the LFBG measurements. We verified the applicability of the LFBG sensors for prestress monitoring and the accuracy of the proposed prestress loss calculation method during pre-tensioning and post-tensioning. In the pre-tensioning case, the calculated prestress losses had less deviation from the true losses than those obtained from foil-strain gauges, and the durability of the LFBG sensors was better than foil-strain gauges, whereas in post-tensioning case, the calculated prestress losses were close to those derived from theoretical predictions. Finally, we monitored prestress variation in the strand for 90 days. The itemized prestress losses at each stages of post-tensioning were obtained by the proposed calculation method to show the prospect of the LFBG sensors in practical evaluation.

Semiconductor loss calculation of DC–DC modular multilevel converter for HVDC interconnections

DC–DC modular multilevel converter (DC–DC MMC) is an attractive candidate for high-voltage DC (HVDC) interconnections since it can provide the required voltage matching, galvanic isolation and flexible power control abilities. The semiconductor loss of such a DC–DC MMC is a major concern for both system evaluation and parameter design. However, it cannot be measured directly since it is out of the precision range of the high-voltage measuring equipment, and thus, mathematical analysis is considered as a feasible alternative. This paper proposes an accurate off-line loss calculation method for DC–DC MMC modulated by fundamental frequency modulation. Based on the characteristics of the modulation, the switching moments along with the instantaneous voltage and current can be calculated exactly, and the conduction loss and switching loss of each submodule can be expressed in a mathematical way. The calculation results are compared with the simulation results from a comprehensive switched model and show good accuracy performance within a relative error of ± 2% under different operating conditions.

Accurate Calculation of Eddy Current Loss in Litz-Wired High-Frequency Transformer Windings

The winding power loss of a high frequency transformer is strongly influenced by the high frequency eddy current skin and proximity effects. The litz-wire can reduce effectively the eddy current effects. The precise loss calculation method of litz-wire remains however a difficulty. At present, the Dowell model [1] and Ferreira model [2], [3] are two commonly used methods to calculate the winding loss. The Dowell model is originally derived to calculate the eddy current effects in foil conductors and later on extended to packed windings composed of litz-wire by introducing a porosity factor [4]. The accuracy however declines quickly when porosity factor reduces, and the characteristics of eddy current distribution is not adapted to the litz-wire. On the other hand, the magnetic field of round conductors analyzed by Ferreira model is excellent, but the error become significate at high frequency at high porosity factor [5] because it neglects the interaction between conductors in the same layer [6]. In this paper, an improved model is proposed for calculating the eddy current distribution in litz-wire windings due to the skin and proximity effects. This model can have much more accurate prediction of eddy current distributions in the cross-section of a round litz-wire conductor, and can be used for electromagnetic design of high frequency devices.

Comparative Analysis of Core Loss Calculation Methods for Magnetic Materials Under Nonsinusoidal Excitations

Magnetic components in power electronic equipment usually suffer from nonsinusoidal excitations. In this paper, a brief description about the existing core loss calculation methods for nonsinusoidal excitations is given. Then calculation formulas of aforementioned methods for two typical excitation waveforms, that is, square and rectangular with variable duty cycle D, are derived. Core loss of nanocrystalline FT-3KS, under above two nonsinusoidal excitations, is measured on an established test setup. The accuracy and applicability of each method are discussed theoretically and verified experimentally, especially in terms of different duty cycles and frequencies. It is found that the waveform coefficient Steinmetz equation (WcSE) is more applicable for the case of relatively small harmonics content of magnetic field intensity H (normal duty cycle region), while the improved generalized Steinmetz equation (IGSE) has better precision where the harmonics count (extreme duty cycle region). In addition, the IGSE can better follow the changing trend of core loss with D and have better frequency applicability than WcSE, which is proven to be not valid in low frequency (where the static hysteresis loss dominates). The results can provide reference for core loss prediction under nonsinusoidal excitations.

Comparison of FDTD and TDWP Methods for Simulating Electromagnetic Wave Propagation above Terrains

Abstract — Researchers have always been in favor of path loss calculation in different media for applications such as telecommunication link design. Wave propagation calculations in large spaces using the FDTD method is time-consuming and imposes a great computational burden. For this reason, to replace the classical FDTD method for wave propagation simulation and path loss calculation in large spaces, optimized methods, namely TDWP, have been provided. In this paper, the use of the TDWP method for wave propagation simulation and path loss calculation above a terrain is investigated. Longitudinal components of ground-waves are taken into account (including direct waves, ground reflections, and surface waves). Propagation space is longitudinally divided into smaller FDTD windows with finite length. The electromagnetic pulse travels through these windows from left to right to the desired point. But despite its capability in reducing computational burden and increasing processing speed, TDWP has lower precision in instantaneous field simulation and calculation of propagation coefficients, so that results obtained from FDTD and TDWP are clearly different. In this paper, some efficient methods are proposed, which yield an increase in method accuracy.

The analysis of heat engineering parameters of building’s thermal protection

Energy efficiency is a one of most important goals in a building sector, namely reduction of heat losses for heating of housing stock. The article presents the results of analysis of heat engineering parameters calculation of building’s enclosing sheath by applicable building codes. Purpose. To define an optimal parameters of heat resistance of constructions on an example different design schemes of building walling. Methodology. The calculation method of building heat losses with considering its architectural and design features was implemented. Conclusion. The difference in calculations of thermal insulation systems in a different codes was researched. Originality. The numerical data concerning results of the insulation parameters selection in systems with a ventilated facade and industrial finishes was received. Practical value. The practical recommendations concerning insulation of existing building in the Ukraine's conditions was represented.

Management of Effective Factors in Components’ Supply Chain on Losses of Electric Distribution System

Restructuring in the electrical distribution utilities, the loss management is one of the critical activities to enhance network efficiency. Accordingly, management of technical loss would be the main target of the asset managers. For loss management, the usual methods of loss calculation and estimation need numerous data which is not used to real networks. In this research, a practical method for loss management is introduced from the viewpoint of components’ supply chain to the network. For this purpose, sub-indictors are extracted using focus group for each process of this chain and their probability distribution functions are calculated. Then, permissible values of sub-indicators are determined by the Delphi method and to calculate new probability functions, the deviation of each process is calculated. Finally, a real network with historical data is used here to study the proposed method. The results illustrate that the most deviation is in the sub-indicator design process about 91% in the viewpoint losses.

Optimisation of the HVDC auto transformer by using hybrid MMC modulation

Over the recent years, the modular multilevel converter has become the state-of-the-art technology for high-voltage (HV) alternating current (AC) to direct current (DC) converters and also upcoming HV DC to DC converters. Especially modular multilevel converters (MMCs) with half-bridge (HB) sub-modules (SMs) are already widely established. Due to the increasing requirements, such as a DC fault ride through and active DC fault current suppression, also MMCs with full-bridge (FB) SMs become more and more attractive. However, the higher losses of the FB SMs require further optimisation to achieve full market acceptance. With the new hybrid modulation technique, combining the advantages of HB and FB SMs, more efficient DC fault resilient converters can be designed. In this study, a new hybrid modulation technique is investigated and implemented for the new HV DC-DC auto transformer, to create a highly efficient, DC fault resilient HV DC-DC converter. A theoretical loss calculation method for hybrid MMCs is developed. The theoretical analysis is validated by means of a full-scale simulation model.

A novel method for the core loss calculation in the surface-mounted permanent magnet synchronous machine

The core loss is of great significance in the machine designing and optimization. In the paper, an analytical method for calculating the flux density of surface-mounted permanent magnet synchronous machine is first presented based on the equivalent magnetic circuit and conformal mapping method. The model takes into account the slotting effect and stator saturation. Subsequently, the core loss was calculated by improved Bertotti’s formula in terms of the analytical model of flux density. Finally, experiment and finite element analysis (FEA) are used to validate the accuracy of the proposed analytical method for core loss. It shows that the analytical results for core loss can keep excellent agreement with the experimental results and FEA results. Therefore, the analytical model provides a great potential to the machine designing and optimization.

Core loss calculation for magnetic materials employed in SMPS under rectangular voltage excitations

Magnetic materials are widely used in switching-mode power supplies (SMPS) and magnetic components in SMPS usually work under two typical rectangular excitations (with or without the period of zero voltage). Extensive experimental results have shown that there is quite a difference of core loss between sinusoidal excitations and rectangular excitations, which means the traditional core loss calculation methods are no longer applicable. In this paper, two formulas for core loss calculation under the above rectangular excitations are derived based on the Improved Generalized Steinmetz Equation (IGSE). Core loss of different magnetic materials, under both sinusoidal excitations and rectangular excitations with different frequencies and duty cycles, are measured. Experimental results show that the formulas are accurate enough and very useful to predict the core loss.

Roughness evaluation in shotcrete-lined water tunnels with invert concrete based on cases from Nepal

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.