Computationally Efficient Strand Eddy Current Loss Calculation in Electric Machines

A fast finite element (FE) based method for the calculation of eddy current losses in the stator windings of randomly wound electric machines is presented in this paper. The method is particularly suitable for implementation in large-scale design optimization algorithms where a qualitative characterization of such losses at higher speeds is most beneficial for identification of the design solutions that exhibit the lowest overall losses including the ac losses in the stator windings. Unlike the common practice of assuming a constant slot fill factor s f for all the design variations, the maximum s f in the developed method is determined based on the individual slot structure/dimensions and strand wire specifications. Furthermore, in lieu of detailed modeling of the conductor strands in the initial FE model, which significantly adds to the complexity of the problem, an alternative rectangular coil modeling subject to a subsequent flux mapping technique for determination of the impinging flux on each individual strand is pursued. Rather than pursuing the precise estimation of ac conductor losses, the research focus of this paper is placed on the development of a computationally efficient technique for the derivation of strand eddy current losses applicable in design optimization, especially where both the electromagnetic and thermal machine behavior are accounted for. A fractional-slot concentrated winding permanent magnet synchronous machine is used for the purpose of this study due to the higher slot leakage flux and slot opening fringing flux of such machines, which are the major contributors to strand eddy current losses in the windings. The analysis is supplemented with an investigation on the influence of the electrical loading on ac winding loss effects for this machine design, a subject that has received less attention in the literature. Experimental ac loss measurements on a 12-slot 10-pole stator assembly will be discussed to verify the existing trends in the simulation result

A Computationally Efficient Method for Calculation of Strand Eddy Current Losses in Electric Machines

In this paper, a fast finite element (FE)-based method for the calculation of eddy current losses in the stator windings of randomly wound electric machines with a focus on fractional slot concentrated winding (FSCW) permanent magnet (PM) machines will be presented. The method is particularly suitable for implementation in large-scale design optimization algorithms where a qualitative characterization of such losses at higher speeds is most beneficial for identification of the design solutions which exhibit the lowest overall losses including the ac losses in the stator windings. Unlike the common practice of assuming a constant slot fill factor, sf, for all the design variations, the maximum sf in the developed method is determined based on the individual slot structure/dimensions and strand wire specifications. Furthermore, in lieu of detailed modeling of the conductor strands in the initial FE model, which significantly adds to the complexity of the problem, an alternative rectangular coil modeling subject to a subsequent flux mapping technique for determination of the impinging flux on each individual strand is pursued. The research focus of the paper is placed on development of a computationally efficient technique for the ac winding loss derivation applicable in design-optimization, where both the electromagnetic and thermal machine behavior are accounted for. The analysis is supplemented with an investigation on the influence of the electrical loading on ac winging loss effects for a particular machine design, a subject which has received less attention in the literature. Experimental ac loss measurements on a 12-slot 10-pole stator assembly will be discussed to verify the existing trends in the simulation results

Power losses calculations in windings of gapped magnetic components: The i2D method applied to flyback transformers

The improved 2-D equivalent analytical calculation method to estimate conductive losses in gapped magnetic components in a wide range of frequencies is extended to the calculations of conduction losses in flyback transformers. The i2D method, that is applicable to power inductor, is extended is extended to the winding loss calculation in gapped transformers, such as flyback transformers, by means of harmonic decomposition of the current though the windings that allows the proximity field calculation and, afterward, the estimation of the losses in the windings

A Global Study of a Contactless Energy Transfer System: Analytical Design, Virtual Prototyping and Experimental Validation

International audienceThis paper presents a design methodology dedicated to a two-winding transformer with large air gap and magnetic cores. To design this kind of components, it is necessary to consider the influence of inductive parameters on electrical magnitudes and the converter, which supplies this magnetic device. Indeed, this kind of a magnetic device has a large leakage inductance and a small magnetizing inductance. Therefore, to transfer the desired power, the transformer needs important reactive energy to magnetize magnetic core and to provide leakage flux. Like inductive parameters can be determined only when geometry is known, sizing has to be iterative. Moreover, resonant converters can be used to compensate inductive behavior, but modify electrical constraints of the transformer. A robust algorithm of design and all necessary tools are presented in order to make it easier to size such components. After the analytical design, 3-D FEM simulations and experimental measurements have been carried out in order to validate the theoretical study. Moreover, the power electronics converter has been optimized in order to improve the efficiency of power transfer. A prototype of 1.6 kW 100 kHz with an air gap of 6 mm has been realized with its converter. The global efficiency is 93.3%

Energy-efficient and Power-dense DC-DC Converters in Data Center and Electric Vehicle Applications Using Wide Bandgap Devices

The ever increasing demands in the energy conversion market propel power converters towards high efficiency and high power density. With fast development of data processing capability in the data center, the server will include more processors, memories, chipsets and hard drives than ever, which requires more efficient and compact power converters. Meanwhile, the energy-efficient and power-dense converters for the electric vehicle also result in longer driving range as well as more passengers and cargo capacities. DC-DC converters are indispensable power stages for both applications. In order to address the efficiency and density requirements of the DC-DC converters in these applications, several related research topics are discussed in this dissertation. For the DC-DC converter in the data center application, a LLC resonant converter based on the newly emerged GaN devices is developed to improve the efficiency over the traditional Si-based converter. The relationship between the critical device parameters and converter loss is established. A new perspective of extra winding loss due to the asymmetrical primary and secondary side current in LLC resonant converter is proposed. The extra winding loss is related to the critical device parameters as well. The GaN device benefits on device loss and transformer winding loss is analyzed. An improved LLC resonant converter design method considering the device loss and transformer winding loss is proposed. For the DC-DC converter in the electric vehicle application, an integrated DC-DC converter that combines the on-board charger DC-DC converter and drivetrain DC-DC converter is developed. The integrated DC-DC converter is considered to operate in different modes. The existing dual active bridge (DAB) DC-DC converter originally designed for the charger is proposed to operate in the drivetrain mode to improve the efficiency at the light load and high voltage step-up ratio conditions of the traditional drivetrain DC-DC converter. Design method and loss model are proposed for the integrated converter in the drivetrain mode. A scaled-down integrated DC-DC converter prototype is developed to verify the design and loss model

Design optimization of integrated rotor-less inductors for high-speed AC drive applications

Discrete sub-system due to passive elements in motor drive require functional and structural integration to make efficient and power dense overall system. Such power dense system is the prerequisite in aerospace and marine applications. This paper presents the design optimization of integrated rotor-less inductors for high speed AC drive applications. Different slot-pole combinations are considered in this process. The single layer (SL) and double layer (DL) windings are chosen with concentrated winding (CW) and distributed winding (DW) configurations. The rotor-less inductors are optimized and compared in this paper with EE core inductor in terms of total losses, weight and AC copper resistance at both fundamental frequency and switching frequencies (10, 15 and 20 kHz). The comparative analysis between EE core and rotor-less inductors has shown a significant reduction in total losses and AC copper resistance at both fundamental frequency and all switching frequencies

Radio frequency and capacitive sensors for dielectric characterization of low-conductivity media

Low-conductivity media are found in a vast number of applications, for example as electrical insulation or as the matrix polymer in high strength-to-weight ratio structural composites. In some applications, these materials are subjected to extreme environmental, thermal, and mechanical conditions that can affect the material\u27s desired performance. In a more general sense, a medium may be comprised of one or more layers with unknown material properties that may affect the desired performance of the entire structure. It is often, therefore, of great import to be able to characterize the material properties of these media for the purpose of estimating their future performance in a certain application. Low-conductivity media, or dielectrics, are poor electrical conductors and permit electromagnetic waves and static electric fields to pass through with minimal attenuation. The amount of electrical energy that may be stored (and lost) in these fields depends directly upon the material property, permittivity, which is generally complex, frequency-dependent and has a measurable effect on sensors designed to characterize dielectric media. In this work, two different types of dielectric sensors: radio frequency resonant antennas and lower-frequency (\u3c1 MHz) capacitive sensors, are designed for permittivity characterization in their respective frequency regimes. In the first part of this work, the capability of characterizing multilayer dielectric structures is studied using a patch antenna, a type of antenna that is primarily designed for data communications in the microwave bands but has application in the field of nondestructive evaluation as well. Each configuration of a patch antenna has a single lowest resonant (dominant mode) frequency that is dependent upon the antenna\u27s substrate material and geometry as well as the permittivity and geometry of exterior materials. Here, an extant forward model is validated using well-characterized microwave samples and a new method of resonant frequency and quality factor determination from measured data is presented. Excellent agreement between calculated and measured values of sensor resonant frequency was obtained for the samples studied. Agreement between calculated and measured quality factor was good in some cases but incurred the particular challenge of accurately quantifying multiple contributions to loss from the sensor structure itself, which at times dominates the contribution due to the sample material. Two later chapters describe the development of capacitive sensors to quantify the low-frequency changes in material permittivity due to environmental aging mechanisms. One embodiment involves the application of coplanar concentric interdigital electrode sensors for the purpose of investigating polymer-matrix degradation in glass-fiber composites due to isothermal aging. Samples of bismaleimide-matrix glass-fiber composites were aged at several high temperatures to induce thermal degradation and capacitive sensors were used to measure the sensor capacitance and dissipation factor, parameters that are directly proportional to the real and imaginary components of complex permittivity, respectively. It was shown that real permittivity and dissipation factor decreased with increasing aging temperature, a trend that was common to both interdigital sensor measurements and standard parallel plate electrode measurements. The second piece of work involves the development of cylindrical interdigital electrode sensors to characterize complex permittivity changes in wire insulation due to aging-related degradation. The sensor was proven effective in detecting changes in irradiated nuclear power plant wiring insulation and in aircraft wiring insulation due to liquid chemical immersion. In all three cases, the results indicate a clear correlation of measured capacitance and dissipation factor with increased degradation