We propose a new approach for predicting iron losses in soft magnetic materials with any voltage supply, starting from the knowledge of the iron losses with a sinusoidal or pulsewidth modulation supply. The model is based on the separation of the loss contributions due to hysteresis, eddy currents, and excess losses with the two supplies. Since any contribution depends on the voltage supply characteristics, it is possible to find a direct mathematical relationship between the iron loss contribution and the voltage supply characteristics. As a consequence, an iron loss prediction can be obtained with any voltage supply if it does not produce a hysteresis minor loop. The energetic model is based on coefficients that depend on the magnetic material characteristic. We performed an accurate analysis of the model on eight magnetic materials used for electrical machine construction, of different thicknesses and alloy compositions. In this way, we found the main coefficients for a large spread of magnetic materials. As a consequence, our approach can be a useful support for electrical machine designers when the energetic performance of a magnetic material has to be predicted for a voltage supply different from the sinusoidal one.

Predicting iron losses in soft magnetic materials with arbitrary voltage supply: an engineering approach

We have studied ways of predicting power losses in soft magnetic laminations for generic time dependence of the periodic magnetic polarization J(t). We found that, whatever the frequency and the induction waveform, the loss behavior can be quantitatively assessed within the theoretical framework of the statistical loss model. The prediction requires a limited set of preemptive experimental data, depending on whether or not the arbitrary J(t) waveform is endowed with local slope inversions (i.e., minor hysteresis loops) in its periodic time behavior. In the absence of minor loops, such data reduce, for any peak polarization value J/sub p/, to the loss figures obtained under sinusoidal J(t) at two different frequency values. In the presence of minor loops of semiamplitude J/sub m/, the two-frequency loss experiment should be carried out for both peak polarization values J/sub p/ and J/sub m/. Additional knowledge of the quasi-static major loop, to be used for modeling hysteresis loss, does improve the accuracy of the prediction method. A more general approach to loss in soft magnetic laminations is obtained in this way, the only limitation apparently being the onset of skin effect at high frequencies.

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Predicting loss in magnetic steels under arbitrary induction waveform and with minor hysteresis loops

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.

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On the variation with flux and frequency of the core loss coefficients in electrical machines

Core losses in rotating electrical machines have been estimated through direct use of the standard Epstein loss data of the employed magnetic laminations, without introducing empirical correcting factors. The prediction is based on a numerical finite element approach to magnetic flux distribution, coupled to a physical model of losses in ferromagnetic laminations under generic flux waveform, which takes into account the specific role of the hysteresis and classical and excess loss components. An application has been made to the case of a 7.5-kW four-pole induction motor under no-load conditions. The predicted core losses turn out to be about 20% lower than the measured ones, a fact which points to an appreciable contribution of the rotor cage Joule losses and to the detrimental role played in the material properties by the residual and applied stresses introduced by lamination punching and core assemblage. >

An improved estimation of iron losses in rotating electrical machines

Permanent-magnet (PM) motors offer potential energy savings as compared with induction motors because of the virtual elimination of rotor loss and the reduction of stator loss from operation near unity power factor. In PM machines, iron losses form a significant fraction of the total loss partly due to the nonsinusoidal flux density distribution. Design optimization therefore requires good means of predicting these iron losses. Finite-element analysis can be employed but this approach is cumbersome and costly when used in the many iterations needed in optimizing the design. This paper presents a set of improved approximate models for the prediction of iron loss. They can be used in design optimization programs and, since they are directly related to machine dimensions and material properties, they also provide quick insight into the effects of design changes. A time-stepped finite-element method is employed to evaluate the iron losses in a range of typical PM machines and the results are used to evaluate the adequacy of the models. The predictions of overall iron losses are then compared with measurements made on two PM motors.

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Modeling of iron losses of permanent-magnet synchronous motors

A numerical model for the analysis of laminated ferromagnetic cores of electromechanical devices is presented. The model is based on the finite-element solution of the two-dimensional (2-D) electromagnetic field problem in the lamination plane; a dynamical relation between local magnetic flux density and magnetic field strength is obtained by solving for the one-dimensional (1-D) eddy-current field developed in the lamination depth. The hysteresis of the magnetic material is accounted for by the Preisach approach. The model is first validated by comparison with an alternative held formulation available for axis-symmetric structures; finally, an application to a more complex 2-D laminated core is presented and the numerical results are confirmed by comparison with measured waveforms of electrical and magnetic quantities.

Advanced model of laminated magnetic cores for two-dimensional field analysis

Core loss prediction combining physical models with numerical field analysis

The paper presents a finite element solution of periodic steady state magnetic field problems in soft materials with scalar hysteresis. The Jiles-Atherton model is employed for the generation of symmetric B-H loops and it is coupled with the Fixed Point technique for handling magnetic nonlinearities. The proposed procedure is applied to a hysteretic model problem whose analytical solution is available. The results show that the Fixed Point technique can efficiently deal with non-single valued material characteristics under periodic operating conditions.

A Jiles-Atherton and fixed-point combined technique for time periodic magnetic field problems with hysteresis

The paper illustrates the evolution of Preisach-type models of hysteresis, involving mean field effect, dynamic effect and vector behaviour and their capability to be included into finite element electromagnetic field computation. The study makes reference to 1D and 2D formulations developed under different simplifying assumptions. Particular attention is devoted to the use of fixed point technique which is found to be very advantageous for the solution of hysteretic problems. Some examples of the analysis of magnetic field problems with hysteresis are finally presented.

D. Chiarabaglio

Papers

An improved estimation of iron losses in rotating electrical machines

Advanced model of laminated magnetic cores for two-dimensional field analysis

Core loss prediction combining physical models with numerical field analysis

A Jiles-Atherton and fixed-point combined technique for time periodic magnetic field problems with hysteresis

Preisach Type Hysteresis Models in Magnetic Field Computation