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Iron losses are one major origin of losses in highly utilized electrical machines. This work presents how iron losses can be modeled including material deterioration due to manufacturing processes. The obtained model is used to improve the machine design process and understand currently used building factors. These factors are state-of-art in descr...
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Citations
... Literature is full of examples of research focused on studying the impact of the technological process on changes in the properties of ferromagnetic material used in the production of motor cores [8,9]. Among them, there are works showing a significant impact of the punching process on a change in magnetic permeability, as well as material specific loss [10,11]. ...
The effective design of energy-saving electric motors with efficiency class IE4 and higher requires the use of material characteristics that take into account the core shaping process. Therefore, it becomes necessary to use analytical or numerical models that take into account the change of local properties of Fe-Si material. The aim of the work is to indicate a useful analytical model for estimating the local magnetic permeability of the material, as well as to understand the reasons for these changes. For this purpose, low-loss ferromagnetic materials cut with a guillotine and a laser were tested. Rectangular samples, cut at an angle of 0 degrees in relation to the rolling direction, were subjected to macroscopic and microscopic examinations. Finally, the main reasons for changes in material characteristics for both cutting technologies were indicated. Therefore, the proposed model takes into account not only the cutting technology used, but also the current width of the tested strip, for which the material characteristics are to be determined. The parameters of the analytical model are determined on the basis of a limited number of measurements carried out on samples of a simple geometric shape.
... Another group of researchers tried to find a proper relationship concerning change in iron loss, suggesting modified classical dependence [27] ...
... In practice, a two-subregion model is used, i.e., containing a damaged fragment with homogeneous material properties and the remaining part that is undamaged. As these examples show, even such a simplified approach guarantees the achievement of acceptable accuracy of the results obtained [22,27,32,33]. The herein presented paper uses a different approach, using a homogeneous material with its characteristics depending on the current width of selected subregions. ...
Many technologies for cutting the magnetic laminations, from which electric motors cores are built, change material properties, among which are magnetizability and iron loss, thus affecting the motor parameters such as motor efficiency. This problem is particularly important for low-power motors, in which the dimensions of the magnetic circuit elements are relatively small. The correct estimation of the motor efficiency is important as early as at its design stage. This is possible when the correct material characteristics are used. This knowledge and analytical model enabling fast estimation of material properties (depending on the actual size) are necessary for engineers, who design electrical motors by analyzing many solution variants in a short time. The author proposes an analytical model of changing material properties, implemented in SPICE software. Its effectiveness was compared with measurement results while being a competitive solution in relation to other analytical models. The proposed SPICE model allowed evaluating material properties for lamination of any width. In the end, the knowledge concerning the material properties was used to calculate the iron loss in the stator of the SyRM motor, showing the need to use the material characteristics calculated for the specified width of the core piece.
... The stator core is the essential component in the electrical motors used in electrical systems [13,27]. The manufacturing technologies used in the making of stator core are the large contributors in terms of increased losses in motors [28][29][30][31][32]. ...
The Cold Rolled Non-Oriented (CRNO) electrical steel of M-43, M-45 and M-47 grade is widely used in Medium Capacity Rotating Electrical Systems and Small Motors. The stator core of the motors is manufactured by joining the thin sheets using conventional TIG welding process. The total core losses in the stator cores are increased due to the welding of the sheet laminations. The welding of the stator core also significantly deteriorates the material properties of the CRNO sheets. The joining of the thin laminated sheets is unavoidable, and the motor manufacturing industries are exploring for alternative joining techniques for reducing the welding losses in stator cores. The Laser welding technique has already been investigated and found reducing the welding losses, in comparison to the TIG welding technique, but lacks in practical applicability due to its higher cost of operations. Hence, the arc welding process, due to its high flexibility and economical operations is explored as alternative in processing the stator cores. The Cold Metal Transfer (CMT), a modified arc welding process, based on pulse operated control system with mechanized short circuiting push-pull wire buffer system is a potential method implemented by many industries such as automobile, heavy construction, aerospace etc., for sheet metal joining due to its low heat input.
The research project implies the investigation of thin stacked welded CRNO cores of M-43, M-45 and M-47 grades for exploring the impact of CMT welding on the performance (Core Loss, Magnetic Field Strength and Magnetic Permeability) of the sample CRNO cores. Total 30 toroidal shape sheets (30 x 0.5 mm) were clamped and welded on 6 sides around the outer periphery, to replicate the standard operating industry conditions. The performances of the CMT processed cores were compared with a TIG welded core at identical weld input conditions, with similar weld current and weld speed and a reference non-welded toroidal core prepared by sticking the sheets. The CMT and TIG processed samples were examined on the basis of Microstructural (Grain size, Orientation), Macroscopic (Weld characterization), Mechanical (Micro-hardness, Residual stress) and Magnetic performance observed by varying the magnetic flux density (B).
The CMT processed core sample revealed improved performance with reduced total core losses (W/Kg), and relatively much controlled grain size and hardness variation. In case of M-43 grade CRNO electrical steel, the percentage increase in core loss (W/Kg) of 21.24 %, 21.83 %, 45.54 %, 46.55 % for 50A, 70A, 90A, 110A TIG weld sample and 20.66 %, 21.45 %, 38.38 %, 41.64 % for 50A, 70A, 90A, 110A, for CMT weld sample respectively, in comparison to the non-welded punched core sample at 1.0 T is observed. Similarly, at B of 1.8 T, the percentage increase in core loss of 8.81%, 10.85 %, 27.41 %, and 30.26 %, for TIG weld sample and 5.20 %, 8.54 %, 10.37 %, and 37.54 % respectively for CMT weld samples, in comparison to non-welded punched core sample is obtained.
The Magnetic Field strength (H) revealed an percentage increase of 99.46 %, 102.99 %, 108.52 %, 113.51 %, for TIG and 67.20 %, 108.67 %, 155.83 %, 225.19 %, for CMT at 1.0 T and 16.68 %, 16.88 %, 13.94 %, 14.39 %, for TIG and 4.34 %, 14.57 %, 27.29 %, 91.44 %, for CMT at 1.8 T respectively, in magnetic field strength for 50A, 70A, 90A, 110A weld samples is observed in comparison to non-welded punched core sample. Overall, the GTAW core sample experienced a percentage decrease of 7.36 % and 15.69 % in relative permeability at B of 1 T. Whereas, it is 52.04 % for TIG sample and 52.08 % for CMT sample, in case of M-45 grade, and for M-47 grade sample, it is 44.04 % for TIG sample and 47.64 % for CMT sample, in comparison to the non-welded punched core sample.
The CMT processed cores were also found superior to the TIG weld core samples with controlled mechanical properties (hardness, residual stress), microstructure (grain size) variations. The micro-hardness investigation summarized that weld pool zone in the TIG welds contains the higher hardness magnitude among the other zones (BM, HAZ), in comparison with the CMT weld samples. The finer grains in the center of weld pool have higher magnitude of hardness and residual stresses, increasing with the weld current (heat input). The HAZ region due to the existence of coarse grains showed significant variation in hardness, residual stress and uncontrolled distribution of grain sizes in the samples. The TIG weld samples due increased heat input have higher magnitude of hardness, with reference to the CMT weld samples. Overall, the investigations performed on CMT processed samples are showing improved results with reference to TIG welded core samples and can be a potential process in joining the thin laminated CRNO sheets.
... Once the global magnetic properties are measured, the results are defined as a function of the variable which is presumably related to the degree of degradation . This approach was applied in [80], [26], [20], [8], [13] and [75]. With the magnetic properties defined as a function of the total width and cutting degradation, magnetic material models are built as a function of the width of the test strip and the severity of the cutting degradation. ...
... Within this volume, a certain degradation distribution is assumed which is either exponential or homogeneous ( Fig. 4.2). After obtaining the global magnetic measurements at several induction levels and frequencies, the BH-curve models and core loss models are adapted correspondingly with cutting effect correction factors, such as in [41], [75] and [68]. These models can be fitted accurately and succeed in estimating the global magnetic properties after separation. ...
... Once the modified material models are fitted, they can be applied in FEmodels of full machines. Some models are characterized by assigning separate material characteristics to each region of the machine [13], [75], by defining a cutting edge region with degraded but homogeneous properties [8], or by defining several edge layers with increasing levels of degradation towards the outer edge layer, as in [71] and [7]. In the stator tooth regions near the air gap, the cutting effect can be seen as an additional 'extended' air gap due to its worsened magnetic permeability, as was proposed by [56]. ...
... This method is known to have the least impact on the magnetic properties of the material, even though it still generates mechanical stresses in the steel sheets [68]. The influence of the cutting technique, including mechanical punching and laser cutting, on the magnetic properties of electrical steels has been quantified in amongst others [26,68,204,223], and they show that the quasi-static hysteresis losses and the magnetic permeability are the most impacted. In particular, the influence of different material width, i.e. the cut edge length to mass ratio, is characterized in [223] and a linear relationship with regard to the hysteresis losses coefficient is demonstrated. ...
... The influence of the cutting technique, including mechanical punching and laser cutting, on the magnetic properties of electrical steels has been quantified in amongst others [26,68,204,223], and they show that the quasi-static hysteresis losses and the magnetic permeability are the most impacted. In particular, the influence of different material width, i.e. the cut edge length to mass ratio, is characterized in [223] and a linear relationship with regard to the hysteresis losses coefficient is demonstrated. Furthermore, it is shown in [26] that compared to a reference without degradation, mechanical cutting increases the iron losses by 15 %, while laser cutting increases the losses by 31 % to 51 % depending on the power and speed of the laser, the faster being beneficial. ...
... The distance between cut edges is 30 mm and 10 mm for the bar and ring sample, respectively. When comparing the cut edge proportion [223], the bar and ring samples give 18.7 m/kg and 25.6 m/kg, respectively. For the slitted core, the inter-slit distance along the radial direction is 12.4 mm, while along the angular direction it ranges from 12 mm to 17 mm, and the cut edge proportion is 16.8 m/kg. ...
The demands for highly-efficient and high-force density electrical machines are ever-increasing in the transportation, manufacturing, and medical industries. To satisfy these challenging requirements, complex design topologies are researched to mitigate the performance-limiting phenomena, which include the slitting or trimming of parts. This is done for weight reduction, electrical windings junctions, mechanical interfaces, or cooling channels. Moreover, these geometrical features can lead to thermal hotspots, which locally modify the material properties, such as electrical conductivity or magnetic remanence, and impacts the penetration depth of the electromagnetic field. It is evident that multi-physical models are needed to simulate these complex phenomena accurately while a seamless coupling from one field to another is critical. Moreover, it becomes necessary to be able to modify the topology, e.g. deform the shape or trim elements at any moment during the design stage, without impacting the model complexity dramatically. Accurate, efficient, and flexible models are therefore needed to take into account local features during the design stage and to predict their impacts on the system.
This is realized by utilizing the isogeometric paradigm, which enables the design-through-analysis of computer-aided-design models. The particularity of this class of numerical methods is the use of the same basis functions for an exact description of the geometrical shapes and the approximation of the solution of partial differential equations. These spline-based basis functions can be adaptively refined to resolve geometrical and physical singularities as well as local features. Furthermore, the construction of the high-order basis functions can be tailored to yield structure-preserving spaces that embed within their properties the characteristic behaviors expected from the physical fields, and reduce spurious modes.
In this thesis, different classes of solvers are detailed for solving low-frequency approximations of Maxwell's equations in the framework of isogeometric analysis. Concerning the evolution of the fields through time: magnetostatic, magnetoharmonic, and transient solvers are described. Two nonlinear methods are used, namely the general Newton-Raphson method and a specific fixed-point method, to resolve the nonlinearities caused by the B-H characteristics of the soft-magnetic materials. Eddy current solvers are presented, which can predict the additional losses in electrically conducting solid regions due to time-varying fields from coil carrying current and from the motion of permanent magnet arrays. Coupled problems are introduced that include the interaction among electromagnetic and thermal fields. This multiphysics coupling is of paramount influence, since the temperature is often one of the most important constraints in the design of an electrical machine.
A specific modeling approach is proposed to simulate the steady-state solution of nonlinear eddy current problems. It uses an adaptive truncated hierarchical B-spline discretization of curl-conforming spaces in combination with the harmonic balance method to avoid the computationally expensive time-stepping approach. It yields an efficient time-frequency alternating scheme that can handle nonlinearities, motion and trimming. It solves the Fourier coefficients of the solution progressively with increasing harmonic content. This approach is also compared with a space-time discontinuous Galerkin method for solving nonlinear motional eddy current problems.
The industrial relevance and benefits of the proposed modeling approach are demonstrated on a complex multiphysics problem: computing efficiently the steady-state electromagnetic and thermal behavior of a single-sided axial-flux permanent magnet machine topology. The geometry is three-dimensional and curved. The stator core is slitted radially through multiple trimming operations along the angular direction. The motion of the permanent magnet array induces eddy current losses in the slitted core, which is both electrically conducting and magnetically permeable with nonlinear characteristics. The slits act as eddy current barriers, reducing the losses and heat generation. Both the eddy current and temperature distributions are influenced, since they are coupled through temperature-dependent material properties.
An experimental setup is manufactured to validate the developed multi-physical model, which couples magnetic, eddy current, and thermal fields pointwise in the isogeometric framework. A variable airgap is considered, which affects the magnetic flux density in the slitted core. The stronger magnetic saturation excites higher-order time harmonics, which are efficiently captured by the harmonic balance method. In addition, it increases the amount of both eddy current losses and temperature. A good agreement between the simulations and measurements is obtained with less than 10 % discrepancy for both quantities over a wide range of speeds and two different core materials.
... We can observe that the difference between BH is not significant but specific losses for second sample are much higher. This confirms the statement already known from the literature [1,[29][30][31][32][33] that laser cutting increases losses in the core material. A similar phenomenon is observed when cutting EDM or mechanical, but it is not so pronounced. ...
The method of cutting motor core sheets causes a change in their magnetic properties and core losses, especially additional losses. Reducing motor losses is very important because of the fulfillment of increasingly stringent requirements set by international regulations for reducing electricity consumption. Due to fact that more and more often induction motors are supplied with high-frequency voltage, core losses are beginning to play a dominant role in the motor’s loss balance. That is why accurate determination of these losses is very important and cutting has a significant impact on them. This report shows how the method of cutting sheet metal affects losses in the finished induction motor working in a wide frequency range. The paper presents the impact of various motor core fabrication technologies on its operational parameters and an approximate way of including this impact in analytical calculations at the design stage of new machine designs, as it is necessary to use sheet metal cutting technologies such as laser or electrical discharge machining (EDM) at the prototype stage. The proposed method is based on measurements of sheet parameters made on toroidal samples with appropriately selected dimensions, so that the width of the sample corresponds to the average width of the motor core elements.
... These parameters are adjusted to account for occurring deterioration effects due to induced mechanical stresses. In order to map the effect of mechanical stress due to cutting into the iron loss estimation scheme used for machine calculation, the hysteresis losses which are most prone to manufacturing processing are modified using the overall cut edge length per unit mass being a measure of the induced cutting stress instead of using empirical building factors [21], [22]. This approach was validated using a loss parameter set solely based on single sheet tester measurements of samples with varying proportion of cutting surface per unit volume [22] and applied in this paper using Epstein datasets. ...
... In order to map the effect of mechanical stress due to cutting into the iron loss estimation scheme used for machine calculation, the hysteresis losses which are most prone to manufacturing processing are modified using the overall cut edge length per unit mass being a measure of the induced cutting stress instead of using empirical building factors [21], [22]. This approach was validated using a loss parameter set solely based on single sheet tester measurements of samples with varying proportion of cutting surface per unit volume [22] and applied in this paper using Epstein datasets. Table I A comparison of loss predictions and measurements is depicted in Fig. 1. ...
Iron losses have a large share in the overall losses of high power density electrical machines operating as variable speed drives. Especially in the partial load area the ratio of iron losses is dominant with respect to the copper losses. Therefore, commonly used control strategies such as Maximum Torque per Ampere or Maximum Torque per Voltage aiming at minimizing the current for given restrictions as the maximum voltage do not select the best direct- and quadrature currents to maximize the efficiency or minimize the overall losses at each operating point. This paper elaborates a stator current vector determination strategy considering the iron loss distribution at all operating points, comparing different iron loss models in a machine with distributed windings. Depending on the operating point and the operational conditions of the machine, the overall losses can be reduced up to 7 %.
The magnetic properties, namely the iron losses and the relative permeability, of SiFe electrical steel laminations after guillotine shearing and cutting by means of fiber and CO
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lasers are studied. The magnetic measurements are conducted on the Epstein frame for lamination strips with 1, 2, and 3 additional cutting edges along their length, in order to increase the cutting effect and the characterization data. The quantified effects of manufacturing (cutting and welding) are presented for three different material grades: M270-50A, M400-50A, and a nonoriented electrical steel of gauge 0.2 mm called NO20. Usage of the Epstein frame method allows any electrical steel company to reproduce the measurements for any specific grade. Data presented in normalized values facilitate utilization of the presented results and comparison between materials. An original model that incorporates the cutting effect considering homogenously damaged areas is developed and implemented in a finite-element method-based motor design software. Its originality is that it includes dependence on the geometry, included in the material magnetic properties. Simulations made for an industrial low voltage induction motor indicate a more than 15% increase in the iron losses compared with a model that does not consider the mechanical cutting effect. In the case of laser cutting, this increase reaches 30% to 50%, depending on laser settings. These relatively large increases of iron losses justify the implementation of the effect of cutting in industrial finite-element design tools, using a method that does not increase the simulation time.
This paper focuses on mapping the different losses present in an Insert Permanent Magnet Synchronous Machine (IPMSM). The machine is designed as a traction machine according to the requirements of a parallel hybrid electric heavy vehicle. This includes a wide constant power range and overload capability, all to be fitted in a strictly limited space in the vehicle. In order to meet the requirements, the machine is designed with a speed higher than that of the conventional powertrain and connected via a fixed speed reduction. The electromagnetic power loss estimation is performed in the post processor of a 2D FE simulation tool. The outcome from the study compares the initial rough power loss calculation to extensive calculation in order to distinguish and separate different sources of power losses and correlate the characteristics to the measurements.
