Iron Loss Measurement Research Articles

High-Frequency Characterization of Losses in Fully Assembled Stators of Slotless PM Motors

The recent emergence of wide-bandgap power transistors enables higher switching frequencies in electrical motor drives. Their full utilization from a system point of view requires quantification of the corresponding time-harmonic motor losses. As an initial step, this paper presents a unique study of stator losses for three different commercially available nonoriented silicon–iron steel grades (with lamination thicknesses 0.1, 0.2, and 0.3 mm). The investigations cover a wide frequency range (10–100 kHz) at different levels of dc bias (up to 1.6 T). Iron losses are identified from measurements on fully assembled stators deploying a novel technique. By utilizing fully assembled stators, no additional samples are required. Manufacturing influence is inherently incorporated. Results show that measured iron losses are twice as high at 10 kHz compared with Epstein test results, which emphasizes the need to incorporate manufacturing influence on iron losses at high frequencies. The level of dc bias is also observed to have a significant impact on iron losses (up to 30%). Even though thinner laminations are known for reducing iron losses, the reduction is much lower than anticipated in the studied frequency range due to skin effect. Using a 0.1-mm lamination gauge instead of 0.3 mm reduces losses by 50% at 10 kHz, while the same substitution at 100 kHz only reduces losses by 30%. Future work includes loss separation in complete converter-fed machines.

Time-resolved detection of vaporization during laser metal processing with laser-induced fluorescence

Element loss during high-power laser processing of metals can lead to deleterious chemical and mechanical effects that negatively impact the processed material’s quality. Currently, there is no suitable way to measure time-resolved element loss in situ during laser processing. In this work, we show that laser-induced fluorescence (LIF) can be used to temporally resolve individual element vaporization during a laser spot welding of 316L stainless steel. As a proof-of-concept, we measured iron loss during a 500 µs laser spot weld with a time resolution of 5 microseconds. We found that keyhole formation could clearly be identified by a dramatic increase in iron emission from the weld pool. This conclusion was validated by independent, time-resolved measurements of laser absorptance during laser spot welding from our previous work.

Accuracy of time domain extension formulae of core losses in non‐oriented electrical steel laminations under non‐sinusoidal excitation

This study presents a comparative study on the accuracy of three iron loss prediction models. The models are based on the decomposition of core or iron losses into the hysteresis and the eddy current loss components. The time domain extensions of two frequency domain models have been used to predict the iron losses due to a number of non-sinusoidal waveforms with and without the presence of minor loops. A third model, by Boglietti, that has been proposed recently to predict core losses for non-sinusoidal and pulse-width modulated (PWM) waveforms has also been studied. The unknown coefficients of each model have been determined by data fitting iron losses obtained from Epstein frame experiments for induction levels and fundamental frequencies up to 1.6 T and 2 kHz, respectively. Core losses due to PWM waveforms have been measured at various fundamental and switching frequencies in unipolar and bipolar modes. The experimentally measured iron losses have been compared to those predicted using the three models and the accuracy and applicability of each model have been discussed.

Impact of Mechanical Stress on Characteristics of Interior Permanent Magnet Synchronous Motors

In this paper, we investigate the impact of mechanical stress on characteristics of interior permanent magnet synchronous motors from both results of measurement and calculation. First, the basic experiments by using stator cores with/without shrink fitting of housings are carried out. The measured iron loss is compared with the calculated results obtained by combined stress and electromagnetic field finite-element analysis. Next, the measured torque and iron loss of the motor under load conditions are compared with the analysis that considers the mechanical stress caused by both the stator shrink fitting and the rotor centrifugal force. The measured and calculated results are found to be in good agreement. From these results, it is clarified that the mechanical stress causes not only an increase in the stator iron loss, but also an increase in the rotor-iron loss, and a decrease in the reluctance torque of interior permanent magnet synchronous motors.

Analysis and identification of influential phenomena on iron losses in embedded permanent magnet synchronous machine

AbstractThis paper presents magnetic flux density behaviour in laminated electrical sheets which affects the results and precision of iron losses calculation in imbedded permanent magnet (IPM) machine. Objective of the research was to analyse all the influential phenomena that were identified through iron loss models analysis, finite element method simulations and iron loss measurements. The presence of phenomena such as harmonic content and rotational magnetic fields are confirmed with finite element method analysis of concentrated and distributed winding IPM machine. A significant magnetic flux density ripple in the rotor of concentrated winding IPM machine in comparison to distributed winding IPM machine is revealed and analysed. Behaviour that affects iron loss in the rotor of synchronous machines in the absence of first order harmonic is analysed. The DC level added to alternating magnetic flux density was used in experiment to mimic magnetic behaviour on the rotor of IPM machine and further to calculate iron losses.

Analysis and identification of influential phenomena on iron losses in embedded permanent magnet synchronous machine

Abstract This paper presents magnetic flux density behaviour in laminated electrical sheets which affects the results and precision of iron losses calculation in imbedded permanent magnet (IPM) machine. Objective of the research was to analyse all the influential phenomena that were identified through iron loss models analysis, finite element method simulations and iron loss measurements. The presence of phenomena such as harmonic content and rotational magnetic fields are confirmed with finite element method analysis of concentrated and distributed winding IPM machine. A significant magnetic flux density ripple in the rotor of concentrated winding IPM machine in comparison to distributed winding IPM machine is revealed and analysed. Behaviour that affects iron loss in the rotor of synchronous machines in the absence of first order harmonic is analysed. The DC level added to alternating magnetic flux density was used in experiment to mimic magnetic behaviour on the rotor of IPM machine and further to calculate iron losses.

Reducing Losses Due to Fringing Flux in an Axial-Flux Permanent-Magnet Synchronous Machine

This paper deals with iron losses caused by fringing fluxes generated by the concentrated stator windings of an axial-flux permanent-magnet synchronous machine. Fringing fluxes enter the laminated stator stack perpendicularly to the plane of the laminated silicon steel sheets. They cause additional eddy currents and losses in the sheets. Three approaches for reducing these losses are compared experimentally with a dedicated setup. The setup has no moving parts and makes accurate iron loss measurement possible. The first method directly restricts the eddy-current losses by segmenting the lamination surface. The second method deflects the fringing flux by using soft magnetic composite. The third method magnetically short circuits the fringing flux using ferromagnetic wires. The first method gives the best results, with a reduction of 6% of the total iron loss at an induction level of 0.6 T and a frequency of 200 Hz.

Design of a measurement system for investigating the magnetic characteristics of soft magnetic materials for non-sinusoidal periodic excitations

Abstract This article is about the design of a measurement system for measuring the iron losses in soft magnetic materials exerted by periodic flux density characteristics. The losses are due to hysteresis and eddy currents effects. The aim is to predict the iron losses which occur in electric machines. Common loss modeling techniques are derived by considering sinusoidal flux density characteristics. As nowadays highly-utilized machine designs with special winding topologies are employed, the periodic flux density characteristics in a big part of the ferromagnetic components are far off from being sinusoidal. Hence, the here presented measurement system and the associated control are especially developed for analyzing any periodic flux density characteristics. A further part of this article is dedicated to the comparison of state-of-the-art iron loss modeling techniques and measurement results. Several scenarios with different flux density harmonic magnitudes and frequencies are considered. It turns out that currently available loss modeling techniques show significant modeling errors for non-sinusoidal periodic flux density excitations. Thus, future work has to be on deriving more accurate models by considering their applicability for computer-aided engineering software.

Evaluation of stress distribution due to shearing in non-oriented electrical steel by using synchrotron radiation

The influence of the shearing process on the iron loss of non-oriented electrical steels with grain sizes of 10 μm-150 μm was investigated. The deterioration ratio of iron loss was clearly smaller in sample with small grain sizes. The droop height, reflecting the amount of plastic deformation, displayed a good relationship with the deterioration of iron loss under the effect of the material grain size. To clarify the strain distribution around the sheared edge, the elastic strain in a sheet sample with the thickness of 0.30 mm and grain size of 10 μm was evaluated by using synchrotron radiation. The width of the region of elastic strain due to shearing was two or three times of the material thickness. The results of the plastic strain distribution obtained by the measurements were then used to estimate the iron loss deterioration rate in 5 mm width sheared samples. The estimated loss deteriotation coincided with the actual measured iron loss.

Laboratory system for measurement of iron losses in high speed drives

Iron loss measurement has always been a concern for the engineers designing electrical machines. A novel test method developed for fast and accurate measurement of iron losses in permanent magnet synchronous machines and a dedicated laboratory system for performing automatic measurements are presented. The principle of the measurement technique, the main building blocks of the laboratory system and the procedures of tests are described. Furthermore a method for the separation of the iron loss into hysteresis and eddy current components, the correction of the change in the magnetic flux density due to varying temperature of the rotor permanent magnets and the calculation of the instantaneous permanent magnet temperature are presented in more detail.

Design and Performance of a Segmented Stator Permanent Magnet Alternator for Aerospace

In this paper, a permanent magnet alternator which presently relies on magnetic slot wedges is redesigned to give lower iron loss. The new segmented stator design is used as the basis for a validated loss study—comparing bonded lamination stacks with those held together with a punched notch. Segmentation is shown to improve the production process, reduce losses, and remove the need for wedges, while not significantly altering the acoustic performance. In the first series of prototypes, however, where notching is used to secure lamination packs, the process is shown to have adversely affected material properties of the nickel iron laminations and overall measured losses increased. In the second prototype, with thinner laminations and glued stacks, iron loss predictions and measurement agree and are less than the present slot wedge design.

ステータ巻線励磁法による製造工程が誘導機用ステータコアの磁気特性に及ぼす影響評価

Past magnetic property measuring methods such as the single sheet test (SST) and the Epstein method cannot quantitatively evaluate magnetic properties of an actual stator core that shows complex shape. Therefore, we are researching the stator winding excitation method as a new method to evaluate magnetic properties (iron loss and maximum magnetic flux density at a tooth) of an actual stator core after each manufacturing process. This method can directly measure them using a dummy rotor and a three-phase stator winding. To actualize this method, we constructed a new measuring system that consists of an iron loss measurement system and a multichannel data acquisition system. According to our experimental result using the proposed iron loss measurement system, the iron loss of the actual stator core that completed all manufacturing processes was about 2.3 times larger than an iron loss of an unprocessed electrical steel sheet. In addition, the proposed multichannel data acquisition system shows observation results of the magnetic flux density waveform and of maximum magnetic flux density at each tooth of the shrink fitting processed actual stator core. From our observation result, maximum magnetic flux density at each tooth was influenced by the compressive stress of a frame.

Phase Correction for High Precision Measurement of Iron Loss Using H‐coil Method

SUMMARYThe accurate magnetic properties of electrical steel sheets are important for the development of high‐efficiency electromagnetic devices. In particular, the H‐coil method is a useful technique for accurately measuring magnetic field strength in a single sheet tester. Therefore, we developed a tester for magnetic field properties using the H‐coil method, referred to as the stress load type single sheet tester (S‐SST), and a problem was found in iron loss measurement at a high flux density of 1.6 T or more. In this paper, it is shown that the cause of this problem is the phase difference between the induced voltage in the H‐coil and the B‐coil. Because the phase difference makes the B–H loop slightly twisted near the tip point, the iron losses are evaluated low. Thus, we propose a method of determining the phase correction values. These values are measured in the absence of a specimen in the S‐SST measurement system, and the phase correction method for induced voltage in a coil is investigated. Finally, ideal results for the correction of iron loss in nonoriented electrical steel sheets are shown. The proposed method is effective for the calibration of a single sheet tester using the H‐coil method.

Measurement and Comparison of Iron Loss in Bonded- and Embossed-Type Segmented Stator Cores for IPMSM

According to the manufacturing process of the laminated stator core for an inserted permanent magnet synchronous motor (IPMSM), the iron loss may be different. It is because the mechanical stress imposed to electrical steel sheet is strongly dependent on the manufacturing process. This paper proposes a new iron loss measurement algorithm which utilizes the induced voltage of a search coil and exciting current. The method is effective even when the distribution of magnetic flux density is not uniform along the magnetic flux path as well as uniform. The developed iron loss measurement system is applied to bonded- and embossed-type segmented stator cores of an IPMSM, and the iron losses are quantitatively compared.

Iron Loss Measurement on 6.5wt%Si Composite Plate Prepared by Clad Casting and Conventional Rolling Processes

The 6.5wt%Si composite plate, which contains three layers and the middle one is about 10wt% ferrosilicon alloy, is fabricated by clad casting and conventional thermomechanical processes. Experimental results reveal that the high silicon composite plate could get lager plastic deformation on the traditional rolling mill. Microstructure of different stages such as hot rolling, warm rolling and heat treatment are observed by optical microscope. Defects appeared in core layer of 6.5wt% high silicon composite plate could be eliminated in the diffusion annealing process. The values of iron loss are investigated at different frequencies which thickness of these homogenous thin sheets are near 0.3-0.5mm. Measurement results of 6.5wt%Si alloy samples produced by chemical vapor deposition (CVD) and powder rolling processing (DPR), and 3wt%Si grain oriented steel are compared with samples prepared by laminar composite technique.

Uni- and Bidirectional Flux Variation Loci Method for Analytical Prediction of Iron Losses in Doubly-Salient Field-Excited Switched-Flux Machines

Field-Excited Flux-Switching machines are doubly-salient machines with complex flux-density waveforms in the core. Hence, prediction of iron losses is difficult. In this article, we propose a method to determine flux loci in iron parts in an analytical manner, accounting for bidirectional field in back-irons of stator and rotor. The analytical model for flux-density prediction in the core at no-load was first validated with 2D FE simulations. Then measured iron losses on a prototype machine were used to calibrate an iron loss model. It was shown that in FE-SF machines rotor iron losses are not negligible and represent 28% of total iron losses. This model could be advantageously used in a design optimization procedure.

Three-Dimensional Eddy Current Loss Modeling in Steel Laminations of Skewed Induction Machines

The effects of skewing on the loss behavior of a megawatt rated slip-ring induction machine are studied. The iron loss evaluation is performed by postprocessing the field solution obtained from a multi-slice finite element model. A novel method to compute the three-dimensional eddy current distribution in the steel sheets is employed for the eddy current analysis. The iron loss models are validated against no-load iron loss measurements. Simulation results under load show that skewing leads to a highly non-uniform iron loss distribution along the machine length. The sum of the iron and copper losses increases slightly compared to a machine with straight rotor bars.

Behavior of Minor Loop and Iron Loss Under Constant Voltage Type PWM Inverter Excitation

The pulse width modulation (PWM) inverter is widely used for the control of motors. We showed that the iron loss under PWM inverter excitation is affected by the impedance of the excitation circuit. The dc voltage of PWM inverter, which is widely used, is constant and the control of motor is carried out by changing the modulation index. Therefore, the evaluation of iron loss under PWM excitation with constant dc voltage is necessary in order to investigate the behavior of iron loss in an actual motor. In this paper, we measured iron losses of non-oriented electrical steel sheets under the shingle-phase full-bridge PWM inverter excitation and examined the influence of modulation index m, carrier frequency fc and dc voltage Vdc on the iron losses. It is shown that the iron loss under PWM inverter excitation can be reduced when dc voltage Vdc is reduced and modulation index m is increased.

정현파 자속밀도 제어와 디지털 궤환을 이용한 AC 손실 측정방법

New digital feedback algorithm was developed to measure iron loss of soft magnetic materials under a condition of sinusoidal flux waveform. (B) curve was used instead of H(B) curve to decide next input waveform in the feedback module so that adjusting phases of current waveform, flux waveform, and input waveform could be removed. The effectiveness of the developed algorithm was verified when iron loss of ferrite cores was measured under frequencies of 1 and 10 kHz.

Phase Correction for High Precision Measurement of Iron Loss using H-coil Method

SUMMARY The accurate magnetic properties of electrical steel sheets are important for the development of high-efficiency electromagnetic devices. In particular, the H-coil method is a useful technique for accurately measuring magnetic field strength in a single sheet tester. Therefore, we developed a tester for magnetic field properties using the H-coil method, referred to as the stress load type single sheet tester (S-SST), and a problem was found in iron loss measurement at a high flux density of 1.6 T or more. In this paper, it is shown that the cause of this problem is the phase difference between the induced voltage in the H-coil and the B-coil. Because the phase difference makes the B–H loop slightly twisted near the tip point, the iron losses are evaluated low. Thus, we propose a method of determining the phase correction values. These values are measured in the absence of a specimen in the S-SST measurement system, and the phase correction method for induced voltage in a coil is investigated. Finally, ideal results for the correction of iron loss in nonoriented electrical steel sheets are shown. The proposed method is effective for the calibration of a single sheet tester using the H-coil method.