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In a typical inverter-fed AC drive system, the stator windings carry a current with a large harmonics content, resulting in an increased AC loss. In this paper, the additional copper losses caused by non-sinusoidal currents are investigated for different magnet wire topologies, including the flat conductor, stranded, and litz wires. Also, a two-slot simplified model is introduced for accurate prediction of the AC losses at high frequency. It is found that one of the major issues of the conventional copper coil is that the losses are not uniformly distributed across the slot, and over 70% of the losses are concentrated near the slot opening. Moreover, using the transient finite element method, different winding topologies and arrangements are simulated at the stranded level to evaluate the losses and current density for each strand under highly distorted currents. Furthermore, different coil samples are prototyped for the same slot geometries to compare their performance under the same pulse-width modulation (PWM) waveforms for a wide range of frequencies. Finally, new hybrid coil topologies are proposed, which employ different magnet wires or materials within the same slot. The results demonstrate that utilizing a mixed wire configuration can effectively mitigate the adverse effects of eddy current losses. This approach can yield up to 16–41% lower losses while also achieving a weight savings of 36–70%. [ABSTRACT FROM AUTHOR]

In high-speed and high-frequency electric machines, one of the major issues that impacts the performance and capability of a machine is the high-frequency eddy current losses in the windings. This work deals with AC winding losses in flat rectangular conductors. Aiming for eddy current loss mitigation, two different materials are investigated and compared for the same winding design, namely copper and aluminum. Using the finite element method (FEM), the conductor loss and current density behavior are simulated at the strand level. Further, in order to verify the simulated losses, the AC losses are measured and compared over a wide range of frequencies. Finally, recommendations are provided based on the obtained measurements to identify the best winding topology that is most suitable for automotive applications. [ABSTRACT FROM AUTHOR]

In this article, a dc-link structure feasible for integration with the circumscribing polygon modular integrated drives is proposed. The proposed dc-link structure combines both the dc-link capacitors and the bus-bar together and integrates them with the machine and the converter modules without increasing the outer diameter of the integrated machine/converter structure. A generic design methodology for the proposed dc-link structure is provided and applied on a reconfigurable 15 stator coils concentrated winding axial flux machine for all its possible phase configurations. The design methodology presented in this article involves the determination of the required dc-link capacitance and the multiphysics design of the bus-bar. The parasitics of the bus-bar part of the proposed dc-link structure are evaluated using electromagnetic finite element method (FEM) models and their influence on the dc-link waveforms is evaluated. Due to the expected high ambient temperature inside an integrated drive, electromagnetic and computational fluid dynamics (CFD) models are developed for the proposed dc-link structure to evaluate the loss density and the temperature distribution of the bus-bar to ensure reliable operation. An experimental setup is built to validate the design methodology. [ABSTRACT FROM AUTHOR]

Most permanent magnet (PM) loss studies consider only eddy current loss and neglect hysteresis. In this article, the hysteresis behavior of two NdFeB PM grades with different magnetic properties is assessed when applied in a PMSM. Data from vibrating sample magnetometer measurements and hysteresis modeling are used as a base. In addition to the main magnetic phase, the samples contained magnetic phases with reduced coercivity. Such phases may contribute to hysteresis losses in a PM material. A new model is introduced to simulate the hysteresis of rare-earth magnets of any geometric shape in the second and first quadrants of the intrinsic BH-plane. The magnetic field strength distribution in the PM material of an electrical motor is analyzed by two-dimensional finite-element method. The results are used as the input data for an analytical hysteresis model. The results indicate that the hysteresis loss resulting from the structural imperfections and geometry of the magnet may introduce a considerable loss in NdFeB PMs applied in rotating electrical machines. [ABSTRACT FROM AUTHOR]

A new structure of a linear switched reluctance motor is proposed in this paper. With the permanent magnet inserted in the movers, the performance of the original motor is improved. An electromagnetic analysis is done by using the finite element analysis. The influence of the permanent magnets in different positions of the movers on the electromagnetic force is investigated. Furthermore, a theoretical analysis is made, based on the Schwarz–Christoffel transformation and the Maxwell stress tensor method. The mathematic model is also made with the consideration of the end effect and the cogging effect. The theoretical result of the electromagnetic force is compared with the simulation result. The comparison shows that the error is limited. The analysis of the flux, the magnetic field, and the inductance is then made. The results confirm that the new structure makes the motor more linearized. The new structure of linear switched reluctance motor can contribute to reducing the ripple in the electromagnetic force. [ABSTRACT FROM AUTHOR]

The aim of the paper is to find the optimal geometry of a passive shield for the reduction of the magnetic stray field of an axisymmetric induction heater. For the optimization, a space mapping algorithm is used that requires two models. The first is an accurate model with a high computational effort as it contains finite element models. The second is less accurate, but it has a low computational effort as it uses an analytical model: the shield is replaced by a number of mutually coupled coils. The currents in the shield are found by solving an electrical circuit. Space mapping combines both models to obtain the optimal passive shield fast and accurately. The presented optimization technique is compared with gradient, simplex, and genetic algorithms. [ABSTRACT FROM AUTHOR]

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star-delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star-delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star-delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star-delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts. [ABSTRACT FROM AUTHOR]

A time-harmonic analytical model is presented for a combined study of demagnetization and rotor eccentricity in single-stator double-rotor axial flux permanent magnet synchronous machines (AFPMSM). Demagnetization defects are modeled by scaling the magnetization “square wave” by magnetization factors for each individual magnet on both rotors. Static, dynamic, and mixed rotor eccentricities are modeled using a permeance function. The original contribution of the model is that asymmetrical defects in the two air gaps of the machine can be described with acceptable accuracy and limited additional calculation time. The model is validated with a finite element method and experiments in both healthy and defected operations. Because the model has a short computation time, it is useful for real-time condition monitoring of any AFPMSM with double air gap and either concentrated or distributed windings. [ABSTRACT FROM PUBLISHER]

In synchronous reluctance motors (SynRMs), the d- and q-axis inductances ( Ld and Lq) are nonlinear functions of d- and q-axis currents (id and iq) and rotor position ( \theta r). The main research question for dynamic studies of SynRMs in this paper is how accurate should the inductance model be to have a reliable computation of dynamic behavior and stability limits? The stability limits are important in the case of $V/ f$ control without position feedback. To answer the question, we consider three cases: 1) inductances are function of id , iq, and \theta r; 2) inductances are function of id and iq, averaged over the position \theta r; and 3) inductances are constant values, with properly chosen values. The cases 1 and 2 include saturation and cross saturation, while case 3 does not. It is found that averaging the rotor position \theta r is almost not jeopardizing accuracy of the SynRM model. However, including magnetic saturation is crucial: it is observed that using constants Ld and Lq to represent the SynRM modeling leads to a large deviation in the prediction of the torque capability compared to the practical motor. In addition, including the magnetic saturation effect in the closed-loop control of SynRMs is necessary. Then, maximum torque per ampere can be achieved. Finally, the proposed method of including the magnetic saturation and the rotor position effects in the SynRM modeling has been validated by experimental measurements. [ABSTRACT FROM AUTHOR]

This paper analyzes and compares the synchronous reluctance motor (SynRM) performance for a conventional star winding and for a combined star-delta connected winding under healthy and faulty conditions. The finite element method is used to simulate the SynRM characteristics in case of normal star and in case of combined star-delta connected windings. For the healthy case, it was found that for the same current, the SynRM output power increased by about 5% for the star-delta connected windings compared with the conventional star connection. Moreover, the efficiency increased slightly by 0.20%. Probably the strongest advantage of the combined star-delta winding is observed when a phase fault occurs. When one phase is missing, for the same current, the star-delta connected motor keeps 80% of the rated torque in the healthy case, while the star connected motor only keeps 40%. Furthermore, the torque ripple of the star wound machine is extremely high in case of a missing phase, compared to the star-delta wound machine. Simulation results were validated by experimental results to show the effectiveness of the star-delta connected windings on the SynRM. [ABSTRACT FROM PUBLISHER]

The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is a good tool for the optimization. However, the computation time is an obstacle as there are many geometrical parameters to be optimized. The flux-barrier widths and angles are the two most crucial parameters for the SynRM output torque and torque ripple. This paper proposes an easy-to-use set of parametrized equations to select appropriate values for these two rotor parameters. With these equations, the reader can design a SynRM of distributed windings with a low torque ripple and with a better average torque. The methodology is valid for a wide range of SynRMs. To check the validity of the proposed equations, the sensitivity analysis for the variation of these two parameters on the SynRM torque and torque ripple is carried out. In addition, the analysis in this paper gives insight into the behavior of the machine as a function of these two parameters. Furthermore, the torque and torque ripple of SynRMs having a rotor with three, four and five flux-barriers are compared with three literature approaches. The comparison shows that the proposed equations are effective in choosing the flux-barrier angles and widths for low torque ripple and better average torque. Experimental results have been obtained to confirm the FEM results and to validate the methodology for choosing the rotor parameters. [ABSTRACT FROM AUTHOR]

A comparison between different analytical and finite-element (FE) tools for the computation of cogging torque and torque ripple in axial flux permanent-magnet synchronous machines is made. 2D and 3D FE models are the most accurate for the computation of cogging torque and torque ripple. However, they are too time consuming to be used for optimization studies. Therefore, analytical tools are also used to obtain the cogging torque and torque ripple. In this paper, three types of analytical models are considered. They are all based on dividing the machine into many slices in the radial direction. One model computes the lateral force based on the magnetic field distribution in the air gap area. Another model is based on conformal mapping and uses complex Schwarz Christoffel (SC) transformations. The last model is based on the subdomain technique, which divides the studied geometry into a number of separate domains. The different types of models are compared for different slot openings and permanent-magnet widths. One of the main conclusions is that the subdomain model is best suited to compute the cogging torque and torque ripple with a much higher accuracy than the SC model. [ABSTRACT FROM AUTHOR]

An electrical variable transmission (EVT) is an electromagnetic device with dual mechanical and electrical ports. In hybrid electric vehicles (HEVs), it is used to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. The most important feature is that the power splitting is done in an electromagnetic way. This has the advantage over mechanical power splitting devices of reduced maintenance, high efficiency, and inherent overload protection. This paper gives a conceptual framework on how the torque on both rotors of the EVT can be simultaneously controlled by using a field-oriented control (FOC) scheme. It describes an induction-machine-based EVT model in which no permanent magnets are required, based on classical machine theory. By use of a predictive current controller to track the calculated current reference values, a fast and accurate torque control can be achieved. By selecting an appropriate value for the flux coupled with the squirrel-cage interrotor, the torque can be controlled in various operating points of power split, generation, and pure electric mode. The conclusions are supported by simulations and transient finite-element calculations. [ABSTRACT FROM PUBLISHER]

The importance of extensive optimizations during the design of electric machines entails a need for fast and accurate simulation tools. For that reason, Fourier-based analytical models have gained a lot of popularity. The problem, however, is that these models typically require a current density as input. This is in contrast with the fact that the great majority of modern drive trains are powered with the help of a pulse-width modulated voltage-source inverter. To overcome that mismatch, this paper presents a coupling of classical Fourier-based models with the equation for the terminal voltage of an electric machine, a technique that is well known in finite-element modeling but has not yet been translated to Fourier-based analytical models. Both a very general discussion of the technique and a specific example are discussed. The presented work is validated with the help of a finite-element model. A very good accuracy is obtained. [ABSTRACT FROM AUTHOR]

The goal of this paper is to investigate the accuracy of modeling the excess loss in electrical steels using a time domain model with Bertotti’s loss model parameters n0 and V0 fitted in the frequency domain. Three variants of iron loss models based on Bertotti’s theory are compared for the prediction of iron losses under sinusoidal and non-sinusoidal flux conditions. The non-sinusoidal waveforms are based on the realistic time variation of the magnetic induction in the stator core of an electrical machine, obtained from a finite element-based machine model. [ABSTRACT FROM AUTHOR]

This paper presents an analytical method for permanent magnet demagnetization detection in an axial flux permanent magnet synchronous machine. First, a forward model is built to calculate the three phase terminal voltages with inputs of three phase currents, the geometry of the machine, and the electromagnetic properties of the machine. To model the demagnetization fault, the scalar potential equation is solved. The magnetization waveform is a square wave corrected with magnetization factors that represent the individual magnetization of every magnet. Second, the forward model is inverted so that the magnetization factors are computed out of the three phase currents and the three phase terminal voltages. The forward model is validated with experimental data and finite element simulations. [ABSTRACT FROM AUTHOR]

The efficiency of permanent-magnet (PM) synchronous machines with outer rotor and concentrated windings is investigated as a function of the mass of magnets used, keeping the power, volume, and mechanical air-gap thickness constant. In order to be useful for electric vehicle motors and wind turbine generators, the efficiency is computed in wide speed and torque ranges, including overload. For a given type and amount of magnets, the geometry of the machine and the efficiency map are computed by analytical models and finite-element models, taken into account the iron loss, copper loss, magnet loss, and pulsewidth-modulation loss. The models are validated by experiments. Furthermore, the demagnetization risk and torque ripple are studied as functions of the mass of magnets in the machine. The effect of the mass of magnets is investigated for several soft magnetic materials, for several combinations of number of poles and number of stator slots, and for both rare earth (NdFeB) magnets and ferrite magnets. It is observed that the amount of PM material can vary in a wide range with a minor influence on the efficiency, torque density, and torque ripple and with a limited demagnetization risk. [ABSTRACT FROM PUBLISHER]

For electrical machines with a 3-D geometry, such as axial flux permanent magnet machines, the computation of iron and magnet losses in the case of pulsewidth modulation (PWM) supply could be performed by a transient 3-D finite element model (FEM) coupled with an electrical circuit. To reduce the CPU time, in this paper, these losses are computed with acceptable accuracy without using a 3-D transient FEM. The multislice technique is used with a 2-D static FEM, combined with a state space model of the machine. A Preisach hysteresis model is considered to evaluate the iron loss during minor loops. The loss in the electrical steel and in the magnets is evaluated for several PWM frequencies as well as for different segmentations of the magnets. [ABSTRACT FROM AUTHOR]

SUMMARY The stray field outside outer rotor permanent magnet synchronous motors can be used for rotor position detection. The focus of the research is on the optimal position of the sensors in order to provide accurate rotor position information. By using 2D and 3D models, the effect of the radial, circumferential and axial position of the sensors on the output signal is shown. Furthermore, the effects of the rotor yoke thickness and the stator current are studied: a thick rotor yoke obviously reduces the stray field amplitude, and high stator currents slightly shift the switching points of the Hall sensors, making the position information less accurate. Also, the rotor temperature and the orientation of the sensors towards the direction normal to the rotor surface are important: modifying the orientation causes a phase shift and is a way to tune the sensors without changing the position. Experiments show that an accurate brushless DC control is possible based on Hall sensors in the stray field. The motor and brushless DC control are used for a wheel drive of an ultra-light electric vehicle. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The effect of the magnetic and thermal properties of four electrical steel grades were compared for a permanent magnet synchronous generator (PMSG). The low loss grades are expected to have less iron loss in the stator laminations, but their thermal conductivity may be lower. Therefore, the evacuation of the heat may be less effective. This has an influence on the temperature distribution, which is crucial in case of PMSG. The investigated generator is a 5 MW, radial flux machine designed for direct-drive wind turbines. A thermal finite-element model was used to simulate the temperature distribution in the generator. The influence of the steel grade on the thermal distribution was compared for four geometries of PMSG with varying air-gap diameter and pole-pair number. In conclusion, the number of pole pairs has a major influence on the importance of electrical and thermal properties of the steel grades applied. [ABSTRACT FROM AUTHOR]

On the rotors of an axial-flux PM machine, NdFeB permanent magnets (PM) are very often placed because of their high energy density. As the NdFeB-magnets are good electric conductive, electric currents are induced in the magnets when they are exposed to a varying magnetic field. This varying magnetic field has two causes: variation of the airgap reluctance due to the effect of stator slots and armature reaction due to the stator currents. As axial-flux PM machines have an inherent 3-D-geometry, full 3-D-finite-element modeling seems necessary to calculate the eddy currents in the PM and to evaluate their corresponding losses. In this paper, however, the 1-D airgap magnetic fields of multiple multilayer 2-D finite-element simulations are combined to a 2-D airgap magnetic field using static simulations. In a subsequent step, this 2-D airgap magnetic field is imposed to a 2-D finite-element model of the PM to calculate the eddy currents and eddy current losses. The main benefit of this multilayer 2-D–2-D coupled model compared to 3-D finite-element modeling is the reduction in calculation time. Accuracy of the suggested multilayer 2-D–2-D coupled model is verified by simulations using a 3-D finite-element model. [ABSTRACT FROM AUTHOR]

To increase the efficiency of commercial induction machines, especially at part load and speed, these machines are converted into permanent magnet synchronous machines. The stators are not changed at all; only the rotors are modified. The appropriate size of the rotor iron and the magnets is found by a numerical optimization, using finite element software. The parameters that are optimized are: the magnet thickness (tm), the number of magnet segments per pole (Nps) and the magnet pole angle (am). The objectives are high efficiency, low magnet volume, low cogging torque and with sufficient mechanical power. The high robustness and reliability of the original induction machines remain high because the stators, the shafts and the bearings are not modified. The resulting synchronous machines still have a rather low torque to weight ratio, but they have low rotor losses, a good power factor and high efficiency. A financial analysis is made in order to assess if the payback time of the conversion is reasonable. Two induction machines with approximately the same outer dimensions (a 2-pole 3 kW machine and a 6-pole 1.5 kW machine) were converted into synchronous machines by different production techniques for the rotor. The efficiency maps were simulated and measured. For both machines, the peak efficiency increases by 5% and 10% respectively, and the average efficiency (between 0.5 and 1 times nominal torque, and 0.5 and 1 times nominal speed) by 4% and 14%, while the cogging torque and magnet volume are low. Conversion of induction machines with many poles to synchronous machines improves the efficiency much more than conversion of two-pole induction machines. [ABSTRACT FROM AUTHOR]

In this paper, a combined wye-delta connection is introduced and compared with a conventional wye-connection of a concentrated winding. Because the combined wye-delta connection has a higher fundamental winding factor, the output torque is higher for the same current density when a sinusoidal current is imposed. As the combined wye-delta connection has only a minor influence on the losses in the machine, the efficiency of the machine is also increased. The combined wye-delta connection is illustrated in detail for an axial-flux permanent-magnet synchronous machine with a rated power of 4 kW at a fixed speed of 2500 r/min, using finite element computation and measurements on a prototype machine. [ABSTRACT FROM PUBLISHER]

This paper presents the efficiency study of a 6-pole and 2-pole induction motor (IM), converted into a 6-pole and 2-pole permanent magnet synchronous machine (PMSM). Firstly, the stator of the IM was kept unchanged and the rotor was converted into a permanent magnet (NdFeB magnets) rotor, resulting in higher average efficiency. Secondly, we investigated how much the efficiency can be increased by replacing the electrical steel in the stator by another material grade. The numerical approach is based on the finite element method (FEM), taking into account the rotor movement. Iron losses are computed according to the loss separation theory. From measurements and simulations, it is observed that the efficiency increases significantly compared to the original IM. The average efficiency of the original 1.5 kW IM converted into the 1.5 kW PMSM led to a 14% higher efficiency in a speed range 0.5\Omeganom-\Omeganom and torque range 0.5Tnom-Tnom. When the stator iron is replaced by M235-35A laminations with the same geometry, the average efficiency increases by an additional 2% for the 1.5 kW PMSM with modified stator. [ABSTRACT FROM PUBLISHER]

At low speed, the rotor-position estimation in sensorless control is often carried out based on the evaluation of the phase-current ripples resulting from the supply of high-frequency voltage test signals. However, the rotor-position estimation is affected by cross-saturation in the machine, resulting in less accurate position estimations at higher loads. As the importance of sensorless control of interior permanent-magnet synchronous machines (IPMSMs) increases, it is useful to design IPMSMs in such a way that they are optimized for accurate sensorless control. The goal of this paper is to determine design aspects in the rotor geometry of an IPMSM to minimize the position estimation error due to cross-saturation. Simulations of a sensorless drive are usually based on a state-space model with constant q- and d-axis inductances and no mutual inductances. In this paper, this technique is improved by calculating the inductance matrix from several finite-element models, which allows the study of the effect of variable q- and d-axis inductances and cross-saturation on the performance of the sensorless control. The rotor design is discussed, for both IPMSMs with and without flux barriers, in order to reduce the estimation error caused by cross-saturation. [ABSTRACT FROM PUBLISHER]

In this paper, a simple lamination stacking method for the teeth of an axial flux permanent-magnet synchronous machine with concentrated stator windings is proposed. In this simple lamination stacking method, only two lamination profiles are used and are stacked alternately. To evaluate the performance of this stacking method, a comparison is made between the proposed method with two profiles and a conventional stacking method that uses different profiles for each lamination layer, using a multilayer 2-D finite element model. [ABSTRACT FROM PUBLISHER]

The identification of the magnetic material characteristics for the switched reluctance motor by solving an inverse problem is presented. The inverse problem aims at identifying the magnetic material parameter values of the magnetic circuit, starting from measured torque profiles. The computational time of the inverse problem is appreciably reduced by implementing a space mapping-based inverse approach. Using the space mapping technique, we combine the computationally intensive finite element model with a much faster magnetic network model. The proposed approach is very helpful for the material identification problem on the electrical machine, and the obtained results reveal the success and the reliability of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, the efficiency optimization of an axial flux permanent-magnet synchronous generator with concentrated pole windings is examined for a 3.6 kW/2000 rpm combined heat and power application. Because the efficiency of the machine is important, specific measures are taken in order to reduce losses in the machine: thin laminated grain oriented material in the teeth, concentrated pole windings, and segmented magnets. A study of the influence of a limited set of geometry parameters on the efficiency of this type of machine is done, using both analytical and finite-element methods. In the analytical as well as in the finite-element model, the inherent 3-D geometry of the axial flux machine is approximated by multiple 2-D models at different radii in circumferential direction. Afterwards, the influence of mass on the optimal values of the geometry parameters and the efficiency is considered, and it is found that mass can be seriously decreased with only a small reduction in efficiency. Finally, the results of both methods are compared with measurements on a prototype to evaluate their validity. [ABSTRACT FROM AUTHOR]

Magnetic shielding of levitation melting induction heating devices does not only reduce the stray field of the device; it has also an influence on the position of the workpiece. The aim is to investigate the change in magnetic field, and the change in steady-state position of the workpiece caused by adding copper or soft magnetic shields to the device. The calculation of the force on the workpiece and the magnetic field around the induction heater is done by either a 2-D or 3-D finite element model, or by a circuit model combined with analytical expressions for the magnetic field and the force. By adding an axisymmetric copper shield surrounding the inductor (shielding by induced currents), the levitated workpiece moves downward, for the same excitation current. By adding a nonaxisymmetric wall of soft magnetic ferrite tiles at one side of the induction heater (shielding by flux-shunting), the workpiece moves upward, and it shifts away from the axial symmetry axis. [ABSTRACT FROM AUTHOR]

The aim of the research is to investigate how much the losses in a permanent-magnet synchronous machine (PMSM) increase by the test pulses that are injected for sensorless control, i.e., to obtain rotor position information without using a position sensor. The current responses to the voltage test pulses in the machine are used as input of a 2-fl transient finite element model (FEM) of the PMSM, to compute the field distribution. The magnet losses are calculated by a 3-D FEM of one magnet and a part of the rotor yoke only. To find the iron losses in the SiFe part of the magnetic circuit, quasi-static and dynamic BH-loops were measured at various amplitudes by using an excitation winding and a measurement winding around the stator yoke of the PMSM. For field waveforms recorded in the 2-D FEM, the corresponding induction is calculated by a static Preisach model. The dynamic field is added based on the theory of loss separation. The test pulses cause minor hysteresis loops. Measurements and simulations show that losses due to the test pulses are usually small and have the same order of magnitude in the permanent magnets and the yoke. [ABSTRACT FROM AUTHOR]

The performance and iron losses of an axial flux permanent-magnet synchronous machine (AFPMSM) using nonoriented (NO) steel are compared with the performance and iron losses of an AFPMSM using grain-oriented (GO) material. The machine is modeled by several 2-D finite element models in circumferential direction, at different radii. The material model for the GO material is an anhysteretic anisotropic model based on the magnetic energy. The magnetic energy is computed by using several measured quasi-static BH-loops on an Epstein frame in seven directions starting from the rolling direction to the transverse direction. The losses are calculated a posteriori, based on the principles of loss separation and dynamic loop measurements. A loss model was made for each of the seven directions, assuming unidirectional fields. In comparison with the more usual NO material, both the saturation induction and the torque are higher with GO -material. The magnetic field in the GO material is lower than for NO material in the major part of the iron, but higher in the tooth tips where the field is not in the rolling direction. The stator iron losses are about 7 times lower for the considered GO compared to the NO material. [ABSTRACT FROM AUTHOR]

Abstract: Three types of methods are studied to calculate the shielding efficiency of a cylindrical ferromagnetic shield in Fe–Si steel, i.e. an analytical method, a finite element method and a neural network method. The methods take into account nonlinear hysteretic behaviour in the shield. All of the methods are compared with each other and with measurements: the shielding factor is computed and measured for several shield radii, thicknesses, field amplitudes and frequencies. The mean absolute error rates are calculated for AM, FEM and NN to be 9.16%, 6.45% and 5.54%, respectively. The analytical model is very fast and accurate for materials with mild nonlinearity. In case of highly nonlinear material and a strongly non-uniform field distribution in the shield, the modeling of the nonlinear behavior in the analytical model is not accurate. The FEM is very accurate for all considered shielding configurations if the mesh density is well chosen, but its evaluation time is high. The neural network has the disadvantage that it should be trained. It is, however, a fast method with the additional advantage that it can be used without any knowledge of the shield geometry and material properties if the training is based on measurements. [Copyright &y& Elsevier]

Sensorless control of permanent-magnet synchronous machines (PMSMs) at low speed and standstill is often based on a difference between q- and d-axis inductances. By determining the inductances, i.e., by evaluating current responses that result from the supply of voltage test vectors, an estimation of the rotor position is obtained. These inductances are dependent on the stator current-because of (cross-)saturation-and on the geometry of the PMSM. Changing inductances strongly affect the accuracy of the rotor position estimation. This paper investigates the influence of geometrical parameters of the rotor on the inductances and on the position estimation. First, for several angles, widths, heights, and radial positions of the buried magnets in the rotor, finite element models (FEMs) calculate the inductances and the torque as a function of the stator current. Second, to study the effect of the variable q- and d-inductances on the position estimator, time-domain simulations are carried out in combination with FEM evaluations. The simulated control is validated on an experimental interior PMSM. The FEM is not needed by the controller in the experiments. [ABSTRACT FROM AUTHOR]

To find the induced currents in conductive objects, the circuit method (CM) replaces these objects by a set of magnetically (mutually) coupled filaments. The unknown induced currents are obtained by solving an electrical circuit and the magnetic field is found by the Biot-Savart law. In the literature, the CM is described as a fast and easy-to-implement alternative for the finite-element method (FEM), with however some limitations: the objects to be modeled in the CM should be nonferromagnetic and much thinner than the penetration depth. In this paper, the CM is extended. It also models ferromagnetic behavior and objects thicker than the penetration depth, by adding extra filaments carrying proper currents. To validate the CM, an axisymmetric shielding problem is solved both with CM and FEM for a conductive shield, a nonlinear hysteretic ferromagnetic shield, and a double (multilayer) shield. [ABSTRACT FROM AUTHOR]

We present a model that evaluates in the frequency domain the magnetic behavior of laminated SiFe alloys caused by a magnetic field imposed at the material edge. The model is based on plane wave theory describing how an electromagnetic wave penetrates a material. As the nonlinear material with hysteresis can cause harmonic frequency components of the field and induction inside the material, the model takes into account several harmonics simultaneously by applying the harmonic balance principle. The plane wave model is solved iteratively with a classical Preisach model as constitutive law. We compare the model with a time domain finite-element model and with measurements on a ring core and find a good correspondence. The CPU time is low if only a few harmonics are considered and if the nonlinearity of the material is rather mild. [ABSTRACT FROM AUTHOR]

The magnetic shielding efficiency of a cylindrical shield is studied starting from the experimentally determined hysteresis loops of the nonlinear shielding material. The magnetic transfer relation model is used in the frequency domain. This analytical model can be evaluated very fast, but works only for linear material. Therefore, the nonlinear shield is divided into a number of linear sublayers with constant complex permeability, which is modelled by an analytical complex function, fitted from the experimental hysteresis loops. The shielding factors are calculated by the analytical model as a function of the imposed field amplitude. They are validated by a finite element model and compared with measured shielding factors of cylindrical tubes. The correspondence is good for the three considered shields: a shield in aluminium (shielding by induced currents), a shield in Fe-Si steel (mainly shielding by flux shunting) and a multilayered shield in aluminium and Fe-Si steel. [ABSTRACT FROM AUTHOR]

The direct coil cooling method is one of the existing cooling techniques for electric machines with concentrated windings, in which cooling tubes of conductive material are inserted between the windings. In such cases, eddy current losses are induced in those cooling tubes because of the time variant magnetic field. To compute the cooling tubes losses, either a transient finite element simulation (mostly based on commercial software), or a full analytical method, which is more complex to be constructed, is required. Instead, this paper proposes a simple and an accurate combined semi-analytical-finite element method to calculate the losses of electric machines having cooling tubes. The 2D magnetostatic solution of the magnetic field is obtained e.g., using the free package "FEMM". Then, the eddy current losses in the tubes are computed using simple analytical equations. In addition, the iron core losses could be obtained. In order to validate the proposed method, two cases are investigated. In Case 1, a six-toothed stator of a switched reluctance machine (SRM), without rotor, is employed in which six cooling tubes are used while in Case 2 a complete rotating SRM is studied. The proposed method is validated by a 2D transient simulation in the commercial software "ANSYS Maxwell" and also by experimental measurements. Evidently, the proposed method is simple and fast to be constructed and it is almost free of cost. [ABSTRACT FROM AUTHOR]

In this paper, the effect of some geometrical parameters on the steady state average temperature of the stator core, the winding and the permanent magnets of the yokeless and segmented armature (YASA) axial flux permanent magnet synchronous machine (AFPMSM) is studied. The geometrical parameters selected for the study are the air gap length, the inward heat extraction fin thickness and the permanent magnet thickness. These parametric studies make it possible to obtain a better trade-off between power density and efficiency. These investigations are very helpful in correlating the values of the geometrical parameters to some specific desired performance criteria like not going below some desired minimum efficiency, limiting the temperature of specific part to some maximum value for maximization of lifetime and also determination of the allowed speed range to limit the temperatures lower than the critical values. This is important specifically for the synchronous machines due to the fact that the speed value affects both the losses and the heat transfer convection coefficients. The air gap length has a direct effect on the overall machine losses and the air gap convection coefficient and hence on the temperature of the machine. As the fins are between the stator windings, a thicker fin reduces the space for copper windings and hence increases the losses, but at the same time improves heat evacuation. In addition, the effect on the temperature is studied of the speed variation, which influences both the losses and the convection coefficients of the machine. Every study is made based on coupled electromagnetic and thermal models. The results are obtained from analytical electromagnetic and thermal models verified by finite element simulations and validated experimentally on a 4 kW yokeless and segmented armature axial flux machine. [ABSTRACT FROM AUTHOR]

• Effect of core welding on an induction machine performance. • Magnetic measurements on welded and unwelded ring cores. • Finite element modeling of induction machine including the welding effect. • Measurement of stator core losses with blocked dummy rotor test setup. There is a growing interest towards increasing the efficiency of electrical machines to reduce the ecological footprint. The efficiency of an electrical machine is closely related to the understanding and accurate estimation of the associated losses. One loss component is related to the welding of the electrical steel sheets as a part of manufacturing. This paper studies the effect of the core welding on a typical industrial induction motor. The effect of core welding on the magnetic permeability and core losses is first analyzed with the help of magnetic measurements on the unwelded and welded ring cores assembled from the stator sheets. Further, the derived material parameters are applied in finite element analysis of the induction machine and the effect of welding on the machine performance parameters is analyzed. It was observed that stator core losses increased about 10% due to the welding effect. A mock-up prototype is then manufactured to measure the stator core losses which follow the simulated values closely. [ABSTRACT FROM AUTHOR]