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Sea ice, crucial to the Arctic and Earth's climate, requires consistent monitoring and high-resolution mapping. Manual sea ice mapping, however, is time-consuming and subjective, prompting the need for automated deep learning-based classification approaches. However, training these algorithms is challenging because expert-generated ice charts, commonly used as training data, do not map single ice types but instead map polygons with multiple ice types. Moreover, the distribution of various ice types in these charts is frequently imbalanced, resulting in a performance bias toward the dominant class. In this article, we present a novel GeoAI approach to training sea ice classification by formalizing it as a partial label learning task with explicit confidence scores to address multiple labels and class imbalance. We treat the polygon-level labels as candidate partial labels, assign the corresponding ice concentrations as confidence scores to each candidate label, and integrate them with focal loss to train a convolutional neural network. Our proposed approach leads to enhanced performance for sea ice classification in Sentinel-1 dual-polarized SAR images, improving classification accuracy (from 87% to 92%) and weighted average F-1 score (from 90% to 93%) compared to the conventional training approach of using one-hot encoded labels and categorical cross-entropy loss. It also improves the F-1 score in four out of the six sea ice classes.

Extensive literature has been produced on the investigation of eddy current losses in Surface-mounted Permanent Magnet (SPM) electric machines in presence of circumferential segmentation by analytical solution of two-dimensional (2D) models. What is missing in the present literature and constitutes the aim of this paper is a simple but accurate procedure enabling the designer to quickly and easily estimate the impact of circumferential segmentation on permanent-magnet loss reduction. The problem is hereinafter addressed in two stages: first the Helmholtz equation is solved in the permanent magnet region neglecting segmentation; then suitable gauge fixing terms are added to the vector potential and eddy current field solutions to account for segmentation. Unlike existing approaches, the method leads to manageable formulas whose accuracy is extensively assessed against finite element simulations on an example SPM machine equipped with a fractional-slot concentrated winding. Furthermore, simple practical rules are derived and validated regarding the impact of magnet segmentation on permanent-magnet losses caused by air-gap magnetic field space harmonics of different orders.

The emerging HVDC technology has been used for long-distance power transmission, increasing flexibility to the power systems, handling asynchronous interconnections, crossing long-distance submarine cables, unusual loading, and generation profiles, and improving energy market relations. The HVDC converter transformers are designed based on system parameters, that directly affect the core and windings geometries, thus the weight and operating losses. In a standard design process, the designer adjusts the active part dimensions, until the constructive and specified aspects, moreover, the technical standard restrictions, are satisfied. The main contribution is to formulate analytic equations, in a way that losses and weight can be obtained for several options of core and windings geometry. However, weight and losses are opposite objectives in the search for an optimal solution. Understanding this compromise between opposing goals is relevant to the equipment learning process. In this context, another significant contribution of the work is to carry out a formal optimization process through the analytical formulation developed. To minimize the weight and operating losses, and subject to IEC standards and constructive restrictions, the multi-objective Genetic Algorithm has been used to search for the Pareto Frontier. Far beyond the chosen solution, the non-dominated frontier obtained for each transformer design, allows the designer to learn about the equipment and its operation, leading to a continuous improvement of the proposed methodology. The analytical formulation is validated by an alternative numerical methodology for winding harmonic losses and short-circuit impedance verification, providing meaningful confidence for the applied method.

Medium-frequency transformers (MFTs) are key components in solid-state transformers, where they provide galvanic isolation and a certain voltage transfer ratio between a MV grid and a LV bus. Typically, MFTs are operated in the kilohertz range, which results in a significantly reduced volume and material usage compared to 50/60 Hz transformers. Foil conductor is an attractive solution for improving the filling factor and the cost-effectiveness of MFTs, however, the insulation clearances increase the ohmic losses due to the current crowding effect; besides, the electric field hotspots at the winding corners require shielding by equipotential rings. In this work, a new hybrid topology is presented, where the first and last turn of the foil winding package is replaced by turns of litz wire connected in series, one above and one below the foil winding, respectively, such that they act as equipotential shielding rings; besides, the current in the litz turns deflects the magnetic field lines away from the foil edges, decreasing the losses due to current crowding. The effect of the litz rings on the losses is modeled and measured on a hybrid and a standard foil winding prototype; a loss decrease higher than 15% is observed. The verified model is used to compare the conductor and footprint saving between windings designed with litz rings, and with standard equipotential shielding rings; in this respect, a minor amount of litz wire allows reducing losses up to 30%, whereas the conductor utilization and winding height can be decreased more than 20%, improving the power density of the MFT.

Accurate calculation of semiconductor losses and temperature is the foundation of any design methodology for a power electronic converter. Computation accuracy and speed play a vital role if a large set of parameters needs to be considered. Averaged loss models often neglect the temperature dependence of transistors, leading to fast, but inaccurate results. In contrast, iterative methods and simulation tools, which can include temperature dependence, take significantly longer to compute, but yield more precise results. This paper presents a best of both worlds approach, by using the harmonic balance method to obtain the steady-state solution for any inverter topology including temperature dependent conduction and switching losses. The proposed method solves for the discrete Fourier series of the device temperature, by expressing the temperature dependence and operating parameters in the frequency domain. The set of equations for each coefficient is solved by a single matrix inversion, resulting in very fast computation for steady-state temperature cycles. The steady-state operation of over one thousand possible inverter designs is calculated within less than one minute, matching iterative simulation in device temperature, conduction and switching losses, at a fraction of the computation time. In addition, the method shows good agreement with temperature measurements of a three-phase silicon-carbide inverter.

The main obstacle for the further development and commercialization of solid-state DC circuit breakers is the high ON-state power losses caused by the active power semiconductor devices. This paper presents an experimental evaluation of the electrical ON-state performance among several commercial high-power semiconductor device technologies rated at $1200V$ and $1700V$ at elevated temperatures. In addition, the potential of reducing ON-state losses by applying the maximum gate voltage, namely overdriving, has been assessed. It is shown that under nominal gate voltages, the normally-ON silicon carbide junction-field-effect transistor exhibits the lowest ON-state losses for both voltage classes, as well as at both temperatures. By using the overdriving concept, the ON-state voltage of silicon insulated-gate bipolar transistors has been minimized up to 10%. In addition to that, both the silicon carbide metal-oxide-semiconductor field effect transistors and normally-ON junction-field-effect transistors experience voltage reduction up to 16% and 33% respectively when overdriving, at elevated junction temperatures.

Applied to the production of windings, the printed circuit board (PCB) technology is promising for developing high performance slotless permanent magnet machines, since it allows for winding shapes and topologies that are difficult to obtain with the classical wire technology. However, compared with wire windings, PCB windings are more prone to eddy current losses because of the high width-to-thickness ratio of the conductor cross-section. To counteract these eddy currents, the conventional solution consists of reducing the width of the conductive tracks constituting the winding in conjunction with an increased number of turns. To keep the supply voltage within limits compatible with the power supply, parallel connections of the tracks at the winding terminals are required. This article tackles the eddy current problem differently by adding some slits distributed along the conductive tracks. This amounts to carry out local parallelizations without impacting the motor supply voltage. By means of parametric analyses carried out on different slit configurations and considering their impact on both the supply and eddy current losses, this study shows that a parallel reconnection of successive tracks two by two gives almost the same results as a classical parallel connection of all the tracks, independently of the winding shape. Furthermore, this article concludes that the optimal number of parallel slits is fixed and valid for a large range of nominal speed-torque ratios. However, it is necessary to increase the width of the slits when this ratio becomes very high and it is technically no longer possible to increase the number of slits. [ABSTRACT FROM AUTHOR]

This work investigates a 2-D vector field behavioral model to describe the anisotropic magnetic permeability and losses in Grain-Oriented Electrical Steels (GOES) within quasi-static and magneto-harmonic working conditions. The model includes the an-hysteretic magnetic field driven by the total anisotropy, the coercive force responsible for the quasi-static hysteresis losses, and the dynamic damping eddy field responsible for the extra losses. Each field contribution requires the definition of a tensor property whose diagonal and non-diagonal coupling components are experimentally identified as a function of the flux density magnitude $B$ and its angle $\theta $ with the Rolling Direction (RD). The static behavior is identified at low frequency and the dynamic one takes the frequency-dependent field diffusion into account. Diagonalization tools reveal main characteristic magnetic axis for the separate properties with deflections at the macroscale. [ABSTRACT FROM AUTHOR]

This article describes rotor shape optimization of interior permanent magnet synchronous motors to reduce both rotor core loss and torque ripples. The experimental verification by the prototype motor is also carried out to confirm the validity of the optimization. It is clarified that both the rotor core loss and the torque ripples under typical driving conditions can be significantly reduced by optimizing the rotor surface without considerable deteriorations of the other important characteristics. The mechanism of the design tradeoff for the torque ripples under different driving conditions is also clarified. [ABSTRACT FROM AUTHOR]

The design of the medium-frequency transformer (MFT) attracts increasing academic attention in recent years, in which the accuracy of the calculation method serves as the pivotal foundation. The existing 1-D based theoretical method generally fails to precisely estimate the foil winding losses under a significant 2-D edge effect. The 2-D semi-empirical methods are merely suitable for limited parameters and structures, and the pre-processing is cumbersome. The finite-element method (FEM) is accurate, yet its high computational cost makes it hard to apply in the MFT designing process. Regarding these issues, a novel 2-D semi-analytical method is proposed in this article with strict theoretical basis and sufficient generality. The foil region is divided into several rectangular elements with uniformly or linearly distributed current density, and one layer of images is placed around the magnetic core window. By deriving the basic electromagnetic relations between those rectangular elements, algebraic equations are formed with current density of the elements being the unknowns. Through the method, the whole problem turns into the process of solving algebraic equations, where all of the coefficients are obtained analytically. The new approach can achieve significantly high accuracy with acceptable computation cost, and it could suitably fit into the MFT designing process. [ABSTRACT FROM AUTHOR]

Of great importance is modeling for transducer design and application to predict its performance and simulate key characteristics. The equivalent circuit modeling (ECM), one of the most powerful tools, has been widely used in the transducer industry and academia due to its outstanding merits of low simulation cost and easy usage for multi-field simulation in both time and frequency domains. Nevertheless, most of the existing equivalent circuit models for Terfenol-D transducers normally ignore three material losses, namely elastic loss, piezomagnetic loss, and magnetic loss. Additionally, the magnetic leakage due to the intrinsic poor magnetic permeability of Terfenol-D is rarely considered into the piezomagnetic coupling. Both loss effects will produce substantial errors. Therefore, an improved SPICE model for a high-power Terfenol-D transducer considering the aforementioned three losses and magnetic flux leakage (MFL) is proposed in this article, which is implemented on the platform of LTspice software. To verify the usefulness and effectiveness of the proposed technique, a high-power Terfenol-D tonpilz transducer prototype with a resonance frequency of around 1 kHz and a maximum transmitting current response (TCR) of 187.1 dB/1A/ $\mu $ Pa is built and tested. The experimental results, both in the air and water of the transducer, are in excellent agreement with the simulated results, which well validates our proposed modeling methods. [ABSTRACT FROM AUTHOR]

This paper presents a new structure of a multilevel inverter with fewer components, which is suitable for renewable energy sources and industrial loads applications. The structure has three unequal input sources and ten switches that can generate a 15-level output voltage. Furthermore, it can be connected in cascade for increasing, even more, the number of levels and output voltage. The main feature of the proposed inverter is its very low harmonic distortion at the output voltage and current due to the control method, which is based on the nearest level control method for generating a high-quality output voltage. A typical application of this inverter is in solar cells and wind turbines. Both simulations in Matlab/Simulink and experimental results in a scaled-down prototype validate the proposed theoretical analysis.

Hybrid modular multilevel converters (HMMC) address the DC-fault blocking limitations of the half-bridge submodules (HB-SMs) of the standard MMC by combining HB-SMs with full-bridge submodules (FB-SMs). In order to improve the overall conversion efficiency, this article proposes two low-loss configurations for the HMMC. The main improvement in the proposed HMMCs is achieved by the combination of low-loss unipolar and low-loss bipolar SMs in the same arm of the HMMC. It is shown that the simplest structure (LLH1) can reduce the SM losses (switching and conduction losses in an SM) by 30% compared to the HMMC at the cost of limited fault blocking capabilities. The fully controlled structure (LLH2) reduces SM losses by 10% compared to the HMMC, and 30% compared to the FBSM-based MMC. These results represent an increase of 20% over the typical HBSM-based MMC for a converter (LLH2) that can provide fault-blocking capabilities. Assessment of efficiency in both HMMCs is provided over a range of operating conditions both in inverter and rectifier mode from an 800-MVA HVDC system model.

This paper presents the concept of efficiency mapping for large synchronous hydrogenerators, which are useful for evaluating hydropower generation performance vis-à-vis interconnected intermittent generation to machine efficiency-oriented design. Tests for loss segregation at rated conditions are needed, and models for loss variation along all operational areas are presented. The weighted average efficiency is obtained as the summation of all operating load point efficiencies times related weights, defined according to criteria or from a 2D-histogram of machine operation. The proposed methodology is applied and compared for two machine designs and to an existent machine under operation.

Loss allocation of the three different components (conductor, sheaths, and armor) of solidly bonded three-core separated lead-sheathed armored cables, frequently employed in offshore wind farms, is challenging due to the lack of accurate enough analytical expressions in the International Electrotechnical Commission (IEC) standard. Also, loss allocation through experimental tests leads to inaccurate results since it is based on questionable assumptions. This article improves both the IEC formulae and experimental methods by means of different analytical corrections in the conductor and sheath loss expressions. To this aim, an ad hoc application interface (Virtual Lab) based on three-dimensional numerical simulations (finite element method) has been developed. This tool virtualizes and automates different test setups to emulate, in few seconds, the most employed experimental procedures in this type of cable. The analytical corrections have been derived from an in-depth analysis of a first set of 368 cables, ranging from 30 to 275 kV. The new loss expressions were successfully applied to a second set of 645 armored cables of quite diverse features (voltages from 10 to 275 kV, sections and dimensional parameters), hence bringing a general framework for any kind of three-core armored cable. [ABSTRACT FROM AUTHOR]

The article addresses coupled loss and thermal analyses of a bearingless drive with an operating speed range of 17 000–32 000 rpm. The drive is a part of a high-temperature heat pump system integrated in a high-speed compressor. This drive system comprises two bearingless motor units and an axial active magnetic bearing. The drive can be positioned horizontally or vertically. The positioning is directly related to the force necessary to raise and suspend the rotor. Furthermore, the amplitude of the suspension current has a significant effect on the motor winding and iron losses. The iron losses, eddy current losses in the magnets, and losses in the bandage are investigated by three-dimensional (3-D) and 2-D finite-element analysis. The influence of segmentation of the magnets on losses is analyzed. Friction losses of the coolant are calculated analytically, and all the losses obtained from the electromagnetic analysis are represented as distributed heat sources and coupled with the 3-D thermal field analysis. The temperature fields are modeled under different motoring and suspension current conditions and evaluated for horizontal and vertical positions of the motor. As a precaution, demagnetization of the magnets is also considered. [ABSTRACT FROM AUTHOR]

This article proposes a novel and generalized single-carrier (SC) pulsewidth modulation (PWM) scheme suitable for multilevel converters. Compared with the existing SC-PWM schemes, the proposed one presents a simpler approach to replicate the behavior of the phase disposition PWM method at any operating point. Besides having an easier digital implementation, the proposed SC-PWM scheme results in great control flexibility to optimize the operation of multilevel converters. Based on the rationales of the proposed SC-PWM scheme, an optimized switching strategy for a cascaded H-bridge (CHB) multilevel inverter architecture is developed. The proposed optimized switching strategy imposes appropriate switching sequences with a minimum number of power device commutations per cycle, leading to both half-wave and quarter-wave symmetries at the individual H-bridge cell level, which subsequently improves the converter harmonic performances and reduces the overall switching losses. The validity and effectiveness of both proposed modulation and switching strategies are demonstrated through the intensive simulation and experimental test results provided both in time and frequency domains. The experimental results are obtained on a three-phase seven-level CHB inverter for an 18-kW laboratory prototype. [ABSTRACT FROM AUTHOR]

In this paper, a novel voltage equalization technique based on the hybridization of total cross-tied configuration and switching capacitor concept for enhancing the power generation of PV arrays during partial shading is proposed. The technique uses the charge balancing concept to maintain the voltage ratio between the total cross-tied array modules and ensures higher power output and convex power curves during partial shading. The validation of the proposed system is carried out in the MATLAB environment for three different size PV arrays under partial shading and compared with the conventional and three reconfiguration techniques in terms of power generation, losses, and conversion efficiency. Also, the insertion losses encountered by the proposed system are derived mathematically. The study concludes that the proposed system tends to generate higher power than any other techniques during shading with conversion efficiency of more than 97%. [ABSTRACT FROM AUTHOR]

This paper proposes a comprehensive study of uplink scheduling in multi-cell OFDMA networks. We first focus on two scenarios for the homogeneous case, one without and one with a Cloud-RAN (C-RAN), and explore how to design efficient practical uplink schedulers for those scenarios. To compute the best achievable performance (BAP) under complete information, we study a centralized multi-cell scheduler. To this end, we formulate an MINLP problem and show how to solve it quasi-optimally. Then, we study the performance of an existing practical local benchmark scheduler (LBM) in terms of goodput and losses. We compare its performance to BAP and show that LBM only yields 44 percent of BAP. To reduce this performance gap, we propose two practical enhancements for LBM, one per scenario. The enhanced scheduler for the first scenario yields 51 percent of BAP (70 percent for the second). To reduce the gap further, we propose a new scheduler inspired by soft-frequency reuse (SFR). Its performance is 69 percent (resp. 83 percent) of BAP. It outperforms LBM by 56 percent for the scenario without C-RAN (84 percent with C-RAN). We finally extend our SFR-based scheduler to heterogeneous networks and show that it outperforms LBM by 53 percent for the scenario without C-RAN (96 percent with C-RAN). [ABSTRACT FROM AUTHOR]

A synchronous condenser (SC) used in an ultrahigh-voltage direct current system often operates under overexcitation and underexcitation conditions, which can dramatically change the field in the end region. A metal shield plays an important role in the end region of SC, and different metal shield materials have an effect on the distribution of the magnetic flux and loss. The selection of the metal shield is, therefore, a key factor that should be carefully considered in the design of SC. For a 300-Mvar SC with different metal shields, this article presents the mathematical models of the three-dimensional (3-D) transient electromagnetic field in the end region. The flux densities and losses of the end structural components are compared under the rated excitation and loss of excitation. From the detailed performance evaluations by the 3-D finite-element analysis, the variation laws of the flux densities at the key points and the losses of the end structural components along with the conductivity of the metal shield are revealed. The regions of the maximum loss in the end structural components are obtained. The results provide the theoretical basis for the improvement of the loss distribution in the end region of the SC. [ABSTRACT FROM AUTHOR]

In this article, an improved model for the beam–wave interaction of sheet beam in traveling wave tubes (TWTs) considering ohmic losses and reflections is presented. The ohmic losses are obtained by field analysis and equivalent method. The space charge magnetic field is derived from the active Helmholtz’s equation. An algorithm to obtain the S-matrix by the equivalent circuit method is presented. The relativistic Boris method is applied to accelerate macroparticles. The exchanged power is computed by the work the electromagnetic field applied to the macroparticles. The theoretical model is applied for validation to a G-band staggered double vane TWT and validated in comparison with CST Particle Studio and simulations without losses and reflections. The convergence of this algorithm is also discussed. The simulation time of the model is substantial faster than 3-D particle-in-cell (PIC) simulations. [ABSTRACT FROM AUTHOR]

In this article, we propose a method to separate the losses generated in armature windings of permanent magnet motors by using a combination of two different eddy current formulations and frozen permeability technique. The total Joule loss of the winding is separated into three components, which are produced by armature current from the terminal, eddy currents in each wire, and circulating currents between the wires. By using the proposed method, advantages and disadvantages of various kinds of winding configurations are investigated. The experimental verification of the calculated loss is also carried out. [ABSTRACT FROM AUTHOR]

Reliability remains an issue for the Si/SiC hybrid switch adopting the conventional switching strategy of the internal SiC MOSFET that turns on earlier, and off later. Such issue is attributable to the overcurrent stress under the heavy load operating condition, which adversely affects the SiC MOSFET during the gate delay time. To solve this problem without increasing the extra power loss, a novel variable-frequency current-dependent switching strategy combining the variable switching pattern strategy, and the variable pulsewidth modulation (PWM) frequency strategy is proposed. Variable switching pattern strategy can avoid the overcurrent stress of the SiC MOSFET at the heavy load operating condition, and the designed optimal delay time in different switching patterns can achieve the compromise between the excellent reliability, and the power loss of Si/SiC hybrid switch. Variable PWM frequency strategy can effectively reduce the switching loss of the Si/SiC hybrid switch by decreasing the switching frequency around the peak current region. An Si/SiC-hybrid-switch-based single-phase inverter platform is constructed and tested. Test results show that the power loss of the single-phase inverter adopting such switching strategy outperforms the current-dependent switching strategy with 9.4% reduction of power loss, and overcurrent stress of SiC MOSFET is avoided. [ABSTRACT FROM AUTHOR]

The utilization of wide band-gap semiconductor devices provides the possibility of higher switching frequency and power density for power converters. However, the influence of parasitic parameters becomes more significant. It deteriorates the converter performance and leads to extra loss. In this article, the extra loss caused by the parasitic capacitance of printed circuit boards (PCBs) is studied. The mechanism is explained, and the model of full bridge topology with PCB parasitic capacitance is proposed as an example. Both the capacitance in power loops and control circuits are considered in the proposed model. Besides the capacitive loss in power loops, losses are also introduced by the capacitive coupling between the power and control circuits due to the potential pulsation of the control ground. This potential pulsation is analyzed and the calculation method of corresponding losses is presented. The formation of PCB parasitic capacitance is analyzed in detail and corresponding layout optimization methods are proposed. Theoretical analyses are verified on a gallium nitride based full bridge prototype with calorimetric loss measurement. The comparison of calculated and measured losses is presented, which shows a switching loss deviation of 26% without the consideration of parasitic capacitance and a 40% reduction on the extra losses after the proposed optimization. [ABSTRACT FROM AUTHOR]

Enhancing the performance of distribution systems is crucial work for their operators. It involves the high necessity for reducing the power losses besides their related costs, enhancing the voltage profile, and minimizing the investment costs of allocated shunt capacitors. Uncertain power demand is also augmented to achieve reliable operation of distribution systems. To fulfill the previous techno-economic merits, this article proposes a multiobjective framework. In this line, a multiobjective salp swarm optimizer (MSSO) is developed. MSSO is characterized by its simplicity, good convergence, and high capability of driving the solutions toward true optimal Pareto front. The developed MSSO optimizes the technical and economical objective functions considering integer, discrete, and continuous natures of control variables. The proposed MSSO is successively tested on two Egyptian distribution networks. Significant merits are achieved with reduction of 20–25 k$/year in the total costs for single and multiobjective cases. In addition, it preserves the voltage deviations at very low levels compared with the flat value. The superiority and scalability of the proposed MSSO are satisfied for large-scale 118-node radial system. Best compromise solutions at acceptable convergence rates and competitive statistical indices are achieved. [ABSTRACT FROM AUTHOR]

The impact of granular microstructure on permanent magnets on eddy current losses is investigated. A numerical homogenization procedure for electrical conductivity is defined. Then, an approximated simple analytical model for the homogenized conductivity able to capture the main features of the geometrical and material dependences is derived. Finally, analytic calculations of eddy current losses are given, and the two asymptotic expressions for losses in the stationary conduction limit and advanced skin effect limit are derived and discussed. [ABSTRACT FROM AUTHOR]

This article proposes a novel approach for operating hybrid fuel cell and battery power systems in marine vessels. The target of the approach is to reduce energy losses in drivetrain devices. In the proposed approach, the dc bus voltage of the hybrid power system is adjusted according to fuel cell operating points, which enables operation in freewheel mode, and thus significantly reducing power conversion losses. Feasibility of the proposed approach is verified using a real-time hardware-in-loop simulation setup consisting of prevalidated virtual models and real industrial power converter controllers. The results presented in the work illustrate that the variable dc approach enables significant improvements in drivetrain efficiencies, and thus providing significant savings for vessel operators. Additionally, variable dc approach is shown to eliminate high-frequency current ripple at the fuel cell terminals, which can further improve the efficiency and the lifetime of the fuel cells. [ABSTRACT FROM AUTHOR]

This article presents a method for designing converter systems embedding power modules for a specified degradation monitoring performance in real-time applications. It builds upon prior work which identified specific variations in three-dimensional transient heat transfer with interface and interconnect state-of-health. This article contributes a joint, module-converter concurrent design method to quantify opportunities and limits in using chip-based temperature sensing to integrate electrothermal impedance spectroscopy in situ. Challenges intrinsic to modules, such as many, closely packed heat sources, are quantified. This article also examines spatial degrees-of-freedom for placing additional degradation sensing temperature detectors. Experimental measurements of transient thermal frequency response show trends that can be exploited to push temperature sensors against their signal-to-noise ratio limits. Overall, the design method relies on circuit topology and modulation details; it is directed toward early-stage converter development. To that end, an included harmonic loss modeling step immediately provides a designer with feedback about the feasibility of a degradation sensing concept. [ABSTRACT FROM AUTHOR]

In this work, directly perforated substrate integrated waveguides (SIWs) in the form of periodic air holes are studied with a focus on the electromagnetic shielding effect by examining its bandpass and stopband filtering characteristics. Two different configurations of the air-filled holes are considered for this electromagnetic bandgap structure, which are called shielded and unshielded cases. In both the scenarios, the relationship between the center frequency of the bandgap and the structural material and geometric parameters is established and used for the bandgap investigation. In addition, the impact that the shielding of the air-filled holes yields on the loss of the structure is systematically examined. Finally, equivalent circuits for both the cases are formulated and experimentally verified up to 30 GHz. [ABSTRACT FROM AUTHOR]

We study the influence of the damper bar pitch, the stator slot skewing degree, and the damper bar number per pole on the no-load voltage waveform harmonic distortion factor (HDF) and the damper winding heat of a tubular hydro generator. We implemented 288 different design schemes using a 36-MW fractional-slot tubular hydro generator. The following influence factors were investigated: continuous variation, variation range, variation step, and higher-order harmonics of no-load voltage. Thus, the relation among these structure parameters and the HDF, the losses, and the highest temperature of the damper bars is revealed. In addition, the calculated models and results are validated directly by test data, and measures are proposed for their improvement. The present research not only corrected the errors in the related papers we published before, but also provides guidelines for optimizing the no-load voltage waveform and decreases the damper bar losses and heat, as well as a more comprehensive, accurate, and effective reference for improving tubular hydro generator design and manufacture.

Ultrasonic wireless power transfer (UWPT) has been a promising technology to recharge the sensor batteries that locate in enclosed metal containers. An accurate and comprehensive analytical model is the key enabling tool for designing the UWPT system. In this article, a novel equivalent circuit model has been proposed for a typical UWPT system with two symmetric piezoelectric transducers bounding onto an aluminum plate coaxially. The proposed model is a two-port network equivalent circuit that can be described by T parameters. By considering the losses of the UWPT system, the accuracy of this model has been enhanced in comparison with the widely used equivalent circuit model, which ignores its losses. The experimental results show that the average error of output power decreases about 6.4 times in the proposed model compared to the existing model. Moreover, the proposed model is tested under various working conditions to validate the enhanced accuracy. [ABSTRACT FROM AUTHOR]

High-efficiency energy conversion, primarily limited by internal losses of piezoelectric materials, is an important target for piezoelectric actuators or sensors. There are three internal losses in piezoelectric materials: dielectric, elastic, and piezoelectric. In this article, a new equivalent circuit of a piezoelectric ring in radial vibration mode is proposed considering three types of fundamental losses. First, the decoupled equivalent circuit with inherent losses is derived based on the conventional electromechanical equivalent circuit. In order to verify the feasibility of the new circuit, an ultrasonic motor operating in radial vibration mode is explored and simulated. The resonance and antiresonance frequencies and their corresponding mechanical quality factors are obtained from the new circuits and then compared with those of an actual stator sample. The simulation results match well with the experimental measurements of the stator. Finally, a prototype is fabricated due to the simulation results and a maximum torque of 270 mNm is acquired. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing enables production of copper and aluminium parts exhibiting unmatched geometric freedom, giving rise to new possibilities in the winding design of electrical machines and wound passive components. Early adopters of additive manufacturing are primarily concerned with improving power-density or efficiency by increasing slot fill-factor, optimizing end-winding topology or incorporating cooling channels into the conductors. In this article, a method of minimizing the elevated ac loss present in open slot electrical machine topologies is presented, in which individual conductor profiles are shaped according to their magnetic environment. Such shaped profile windings are shown to exhibit operating mode dependent loss behavior giving them potential for efficiency improvement in applications with a dominant operating mode such as electric vehicle traction, aerospace propulsion fans, and generators. For the first time, the conductor shaping method and associated benefits are demonstrated by the retrospective design, additive manufacture, and experimental test of a three-phase set of shaped profile windings for a concentrated wound, open slot, permanent magnet electrical machine. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for network reconfiguration which could help in the operation and expansion planning of three-phase distribution systems. Considering the fact that power losses lead to decrease utility benefits, and the three-phase unbalanced voltage can damage electrical machines, the proposed algorithm is presented as a multi-objective optimization problem based on Evolutionary Algorithms where the power losses and three-phase unbalanced voltage are simultaneously minimized. In order to validate the efficiency of the proposed reconfiguration algorithm, a large-scale radial electric distribution system, under maximum load conditions, is considered for operation planning. In addition, different scenarios are compared to test the algorithm as an expansion planning tool. The proposed algorithm maximizes the utility profits and improves system performance reducing power loss and unbalanced voltage. [ABSTRACT FROM AUTHOR]

In this article, we investigate rotor design of claw-pole alternators for automobile applications to increase output and decrease core loss. First, the electromagnetic field distribution is calculated by the three-dimensional (3-D) nonlinear time-stepping finite-element method, which considers eddy currents generated at a solid rotor core and a laminated stator core. From the results, a novel rotor design is proposed. Experimental verification is carried out to confirm the advantage of the proposed design. The mechanism of output increase and loss reduction by the proposed alternator is revealed by analyzing detailed 3-D flux paths in the rotors. [ABSTRACT FROM AUTHOR]

This paper demonstrates the presence of spurious power losses or generation in the Arm Equivalent Model (AEM) of Modular Multilevel Converters. Such power losses can occur if model equations are not solved simultaneously with surrounding power circuit equations, which is the case when the AEM is implemented using control system blocks in electromagnetic transient simulation software. Depending on operating conditions and simulation parameters, these additional losses can represent a significant part of the total converter station losses or even surpass them, thus making simulation results inaccurate. Analytical demonstration of the losses is presented, and several models that eliminate the losses are proposed. Based on simulation studies, only the variable resistance model and equivalent voltage source model can give accurate simulation results without significantly increasing simulation time and generating or consuming spurious power. [ABSTRACT FROM AUTHOR]

Loss estimation in power semiconductor components is an important research topic for a long time with various methods that have been proposed in the literature. Although these methods have been implemented and allow estimating the losses with satisfactory results, the junction temperature of the component is generally controlled poorly while it influences the losses. This article presents a dynamic calorimetric method used to estimate the losses in power semiconductor devices, taking into account their evolution as a function of the junction temperature. The proposed method is based on the temperature measurement in a metal block fixed under the component. Through a thermal model based on the notion of thermal impedance, the transient temperature measurement in the block allows determining the losses and the junction temperature of the device. In order to size the test bench and determine the robustness of this method with respect to measurement or implementation uncertainties (heat transfer coefficients and thermal conductivity of materials), thermal simulations were performed using the Flotherm software. Due to the presence of noise in the measurements, post signal processing is also necessary. By applying the chosen setting, a corresponding experiment was conducted to verify the proposed method. This experiment showed promising results for both loss and junction temperature determination. [ABSTRACT FROM AUTHOR]

This article describes a fast characteristics calculation of large transformers with step-lap joints by dividing regions of finite-element analysis (FEA). The flux of the core in each divided region is given by fixing the magnetic vector potential at the divided surface due to Stokes’ theorem. The exiting current of the coil is calculated from the magnetic field with Ampere’s law. The validity and advantage of the proposed method are confirmed by comparing the calculated iron loss and exciting current with those of the FEA applied to the whole region. The usefulness of the proposed method is clarified by the application of characteristics improvement of the transformers. [ABSTRACT FROM AUTHOR]

In this article, an unstructured–partial element equivalent circuit (PEEC) method for modeling electromagnetic thin regions is proposed. Two coupled circuits’ representations are used for solving both electric and/or magnetic effects in thin regions discretized by a finite-element surface mesh. Dynamic effects across the thickness of the sheet are modeled by equivalent complex conductivity and reluctivity. Nonsimply connected regions are treated with fundamental branch independent loop matrices coming from the circuit representation. The formulation enables the computation of eddy current losses and can be coupled with external circuits, PEEC cables or coils, thanks to the circuit representation. [ABSTRACT FROM AUTHOR]

This article describes a method to calculate iron loss of permanent-magnet machines by considering the hysteresis loops affected by multi-axial stress. A simple hysteresis model is introduced and modified by reluctivity and hysteresis loss increase ratios, which can be determined by core material experiments under uniaxial stress. This model is coupled with time-stepping finite-element analysis. The validity of the proposed method is confirmed by the core material experiments under multi-axial stress and measured characteristics of permanent-magnet machines. It is clarified that the accuracy of the proposed method is acceptable. [ABSTRACT FROM AUTHOR]

This article describes a fast calculation method for harmonic losses caused by inverter carrier in interior permanent-magnet synchronous motors (IPMSMs) under a large number of driving conditions. In the proposed method, the harmonic loss caused by the largest component of the harmonic voltages is calculated by the linear frequency-domain finite-element analysis (FEA) with the differential permeability distribution obtained by the time-domain FEA. The total carrier loss is predicted by the variation in this largest harmonic component and sum of the square of harmonic voltages. The proposed method is applied to the efficiency-map calculation of an IPMSM. It is clarified that the total computational time is reduced to be 1/20th when compared with the conventional method. [ABSTRACT FROM AUTHOR]

In this article, we investigate the loss reduction of permanent magnet machines, whose armature windings consist of parallel wires. First, the impact of the loss caused by the circulating currents in the parallel armature wires is estimated by finite-element analysis. The calculated total electrical loss is compared with the experimental result of a prototype motor. The measured and calculated results are found to be in good agreement. In addition, it is revealed that the circulating armature current loss is larger than the usual copper loss, which is estimated only by the total armature current and the armature winding resistance. Next, the loss reduction by reducing the number of parallel wires is discussed. The optimal number of parallel wires is found by considering the tradeoff between the reduction of circulating current loss and increases in the other losses, such as usual copper loss and core loss. [ABSTRACT FROM AUTHOR]

The rotor of turbogenerator is made of solid steel, instead of laminated steel, for its high-speed rotation. The asynchronous torque resulting from the eddy current in the rotor core plays an important role in the asynchronous operation of turbogenerator after loss of excitation. On the other hand, the rotor loss and temperature rise restrict the operation of turbogenerator. The selection of solid steel is therefore a key factor that affects the operation limit and should be carefully considered in the design of turbogenerators. For a turbogenerator with the rotor core made of different solid steel, this paper presents time-stepping finite element calculation of the asynchronous performances and the experimental validation. The influences of different rotor solid steel on the dynamics, saturation, asynchronous operation ability, and rotor loss of turbogenerator with the loss of field are studied. The losses in different areas of rotor are calculated and compared. The results provide steel manufacturers and generator designers with the theoretic basis for improvement of the asynchronous operating ability of turbogenerator. [ABSTRACT FROM AUTHOR]

Fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSMs) have been a research hotspot over the past few decades. Recently, the magnetic gearing effect in FSCW PMSMs is revealed along with its gear ratio, which is a function of slot/pole number combination. At the design stage of FSCW PMSMs, one of the key issues is the selection of the slot/pole number combination. This paper shows that the gear ratio can contribute to a proper slot/pole number selection in any multiphase FSCW PMSMs by acting as a unified index for a quick overall performance comparison. In this paper, first, the magnetic gearing effect in FSCW PMSMs is explained and the gear ratio is further discussed. The advantages of adopting gear ratio as the overall performance index over other indices are revealed. The influence of the gear ratio on the winding factor, torque output, cogging torque, inductance, and rotor losses of three- and six-phase FSCW PMSMs is analyzed and validated by experiments, thus proving the analyses. [ABSTRACT FROM AUTHOR]

In this paper, the intermittent control is proposed for switched reluctance machine (SRM) drive to both increase the efficiency and decrease the cost of the traction system for low-cost electric vehicles. With the purpose of maintaining the average machine torque required by the load, the intermittent control imposes a higher phase torque during a shorter time. The simulation and experimental results achieved with three different SRMs show that the intermittent control increases the system efficiency by reducing the converter losses and the core losses. Additionally, three different strategies of the control have been proposed to analyze their impact automotive application based on the criteria of efficiency, machine vibration, and torque pulsation. It can also be easily applied for any SRMs using average-torque-control-based methods. [ABSTRACT FROM AUTHOR]

In this paper, we propose a loss calculation method considering minor hysteresis loops for permanent magnet (PM) motors driven by pulsewidth modulated (PWM) inverters. In the governing equation of the proposed method, both the effects of the major and minor hysteresis phenomena are expressed by a reaction magnetic field. This field is determined by iterative calculations of finite-element analysis (FEA) with a simple hysteresis modeling that considers the minor loops. The proposed method is applied to a PM motor, and the experimental verification is carried out. It is clarified that the minor hysteresis loops affect not only the hysteresis loss but also the eddy current loss because the skin depth varies with the differential permeability of the minor loops. [ABSTRACT FROM AUTHOR]

This paper analyzes the effect of the operation frequency of an inductive charging system on the heat generation and its impact on the overall system efficiency. This is done considering the change of the material properties due to both frequency and temperature changes. The analysis is achieved using FEA modeling software ANSYS workbench. For faster subsequent optimization, an order-reduced model is implemented in a system-level simulation. Various tests show the good agreement of the results between the reduced order model and those of dynamically coupled-field solvers. Our implementation allows for precise calculation of the losses of the different system parts. Furthermore, an experiment has been conducted to validate the simulation results. [ABSTRACT FROM AUTHOR]

Electrostatic motor can work as a supplement to the electromagnetic motor due to its simple structure, low cost, light weight, and high efficiency. This paper presents a dielectric-gas-based single-phase electrostatic motor with simplified construction. The motor design is focused on increasing the capacitance, subsequently the torque, to make the electrostatic motors competitive with the electromagnetic ones. Three-dimensional (3-D) finite element analysis (FEA) simulation and optimization process of the electrostatic motor is performed. A 50 W electrostatic motor with the torque of 0.25 N·m, which is the same order in magnitude with the fluid-filled electrostatic machine and induction machine at the similar power level, is designed. Losses including the friction loss, windage loss, and dielectric loss are predicted. Thermal fields are analyzed using FEA and the electrostatic motor presented can work stably at high ambient temperature. 3-D printing is used to build a prototype machine to eliminate the process of mould manufacture and achieve a weight reduction. Predicted capacitance of machine is compared with measured result and good agreement is achieved. [ABSTRACT FROM AUTHOR]

The high-power pulsed power supply based on homoploar inductor alternator (HIA) was successfully used as a primary power supply of the pulse load. This type of power supply has the advantages of high-power density and high reliability. The efficiency of this power supply is an important parameter in the design of this power supply. This paper presents the analysis and test efficiency of it. The theoretical calculation is consistent with the test, and the results show that the efficiency is 75%–80%; the armature copper losses account for the largest proportion of total losses, and the iron losses take the second proportion. The large armature copper losses are due to the extremely serious skin and squeezing effects. The analysis and test results are benefit for estimating the required inertial energy storage. Finally, the design aspects about the losses of pulsed HIA are discussed, and it is helpful for the optimal design of a high-efficiency pulsed HIA for capacitor charge power supply. [ABSTRACT FROM AUTHOR]