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In this paper, we investigate the losses caused by circulating currents generated in armature windings of permanent magnet synchronous machines by using electromagnetic field analysis. In the analysis, each parallel connected wire in the windings is modeled by finite elements in order to consider the difference in the electromotive forces and the generation of the circulating currents. The calculated losses are compared with experimental results. It is clarified that the armature copper loss in permanent magnet machines with parallel connected wires considerably increases by the circulating currents. [ABSTRACT FROM AUTHOR]

In this study we investigate a method for accurately calculating the characteristics of salient-pole synchronous machines assisted by permanent magnets. First, the operating principle of the machines is investigated by using both finite element analysis and a simple magnetic circuit. Then, a theoretical representation of the assist effect on the permanent magnets is derived based on the magnetic circuit. Finally, the measured and calculated results are compared in order to confirm the validity of the proposed calculation method. We show that the load characteristics of the proposed machine can be accurately estimated from the no-load and short-circuit characteristics of the conventional machine without permanent magnets, and the size and magnetization of the inserted permanent magnets. [ABSTRACT FROM AUTHOR]

The arrangement of permanent magnets in double-layer interior permanent-magnet motors is optimized for variable-speed applications. First, the arrangement of magnets is decided by automatic optimization. Next, the superiority of the optimized motor is discussed by considering d- and q-axis equivalent circuits that take into account the magnetic saturation of the rotor core. Finally, experimental verification is carried out with a prototype motor. It is confirmed that the maximum torque of the optimized motor under both low-speed and high-speed conditions is higher than that of conventional motors because of the relatively large q-axis inductance and small d-axis inductance. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 54-63, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22348 [ABSTRACT FROM AUTHOR]

In this study, we investigate the loss reduction effect by stator-teeth slits in turbine generators on the basis of electromagnetic field analysis and basic experiments. First, the loss reduction effect in the generator is estimated by the 3D finite element method and the theoretical solution of eddy current loss. Next, an experiment using a simple model that simulates the stator-core ends of the turbine generator is carried out. It is clarified that the loss reduction effect by the slits depends on the frequency, flux density, and permeability of the stator teeth because the loss reduction effect weakens with the skin effect. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(3): 17-25, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22345 [ABSTRACT FROM AUTHOR]

A method for calculation of iron loss in rotating machines is proposed. The calculation employs the finite element method while taking into consideration the eddy currents in electrical steel sheets. First, the electromagnetic field distribution and iron loss of several types of electrical steel sheets are calculated by the proposed method, formulated as a one-dimensional model. The results are compared with those of experiments and the conventional method in order to verify the validity of the proposed method. The influence of the skin effect and magnetic saturation in the electrical steel sheets on the iron loss characteristics is also investigated. Next, the proposed method formulated as a three-dimensional model is applied to several types of rotating machines. It is shown that the skin effect is significant in the case of high-frequency harmonic fields and that direct consideration of eddy currents by the finite element method is indispensable in such cases. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 69-80, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21053 [ABSTRACT FROM AUTHOR]

In this paper, we present the development of interior magnet motors reducing iron loss at high rotational speed under the flux weakening control. The rotor core and magnet shapes are determined by the automatic numerical calculation using combination of the optimization method and the adaptive finite element method. The optimized motor is manufactured to prove the effectiveness by the measurement of the iron loss. Both results of the calculation and the measurement indicate that the iron loss of the proposed motor at the high rotational speed under the flux weakening control is reduced by half compared with the initial rotor shape while the torque is nearly constant. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(3): 59–66, 2009; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20827 [ABSTRACT FROM AUTHOR]

A method for the modification of finite element meshes based on adaptive meshing for optimization of electric machines is proposed. In the optimization of the machine, the proposed method generates the mesh for the new shape from the previous mesh with minor modification. The locations of the nodes for the new shape are decided by solving a Laplacian equation whose unknowns are the displacements of the nodes. The advantages are illustrated by application to the shape optimization of an IPM motor. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(1): 21–28, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20773 [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel algorithm of the nonlinear time-stepping finite element method for analyses of rotating machines. In the method, the adaptive finite element meshing is applied at each nonlinear and time-stepping iterative calculation with the interpolate calculations of the potentials from the previous step. The primary finite element mesh at each time step is obtained from the final mesh of the previous time step with minor modification due to the movement of the rotor. The proposed method is applied to the characteristics calculations of a permanent magnet motor and an induction motor to verify the method's validity and its usefulness. It is clarified that the proposed method gives almost identical results to the conventional adaptive meshing method whereas the calculation time is reduced to less than 1/10 in most cases. As a result, the proposed method can reduce not only the time of making mesh manually but also the calculation time compared with the usual finite element method without adaptive meshing. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(3): 78–91, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20308 [ABSTRACT FROM AUTHOR]

A method of loss calculation for induction motors is proposed. The combined 3D-2D time-stepping finite element analysis is carried out to obtain the copper loss and the time variation of the magnetic field in the motor. The iron loss is calculated approximately considering the time variation of the magnetic field direction and the minor hysteresis loops caused by the time-harmonic fields using practical computer resources. The proposed method is applied to four types of induction motors, which are the solid rotor induction motors with/without slot and the cage induction motors with/without skew. The measured and the calculated total losses and the iron losses agree well in all cases. The differences of the loss distributions of each motor are also compared and investigated. [ABSTRACT FROM AUTHOR]

This paper proposes a method of eddy current analysis which can accurately calculate characteristics of electric machines including several conductors moving at different velocities. In the formulation of the proposed method, different moving coordinate systems are used separately in each conductor region to set relative velocities at zero between every conductor and the coordinate system. The method can avoid the numerical disadvantages of a fixed coordinate system that has relative velocity to the conductors. First, the difference of definitions between electromagnetic potentials introduced in the moving coordinate system and potentials introduced in the fixed coordinate system is discussed to determine theoretical background of the proposed method. Potentials introduced in each coordinate system can be of the same value introducing appropriate gauge conditions. Second, the results of numerical tests which clarify the consideration are shown. Finally, advantages of the proposed method are discussed through the practical analysis of a canned motor. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (1): 1–14, 1997 [ABSTRACT FROM AUTHOR]