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Permanent magnet synchronous motors for electric vehicles should meet three criteria: high maximum torque, high efficiency at low torque, and constant output in a wide speed range. However, meeting these criteria has come with a trade-off in terms of the magnitude of the field magnetic flux. We propose a consequent-pole-PM-type axial-gap motor with ferrite PMs and field windings, which has structure variable field magnetic flux. In order to examine the operational characteristics of the proposed motor, we produced and tested a prototype. Experimental results show that the proposed structure meets all of the three criteria above.

This research proposes a novel low-voltage inverter-fed motor drive with variable parameters achieved through the independent armature winding for the automobile traction motor. The independent armature winding with low-voltage inverters can improve the total efficiency by reducing the converter losses. The inverters are able to change their connections to different coils groups of the armature winding in order to achieve the wide operating range. The voltage equation of each mode can be shown by using the transformation matrix when the winding connection is changed. Thus, the proposed motor is called the MATRIX motor. In this paper, the downsized model was designed to verify the principle. The principle model is able to achieve four motor parameters. It was confirmed that the principle model could extend the operating range and could achieve the high-efficiency driving in wide speed range. Furthermore, the novel winding reconfiguration method is proposed that not only avoids the surge voltage, but also compensates the torque reduction during the winding reconfigurations.

A new high-temperature superconducting (HTS) application project supported by the New Energy and Industrial Technology Development Organization (NEDO) started in July 2016. One of the targets of this project is to demonstrate the half-size of whole-body magnetic resonance imaging (MRI) system using HTS magnets with REBCO conductors. In the first phase of this project (FY2016–FY2018), a three-tesla magnet with an active shield will be manufactured. The room-temperature bore of the magnet is 480 mm in diameter. The magnet will be cooled down to lower than 20 K with a G-M refrigerator and the MR imaging will be performed to evaluate the magnetic field uniformity and stability. The design of the half-size 3-T coil has been finished: it consists of 220 single-pancake coils, and it has an inner diameter of 560 mm, an outer diameter of 1200 mm, and an axial length of 1000 mm. The rated current is 148 A and the stored energy at the rated excitation is 1.58 MJ. The designed magnetic field homogeneity is 1.7 ppm (250 mm DSV) which is adequate for MR imaging. Furthermore, the fringe field is suppressed by active shielding technology. The number of 53 single-pancake coils was manufactured in FY2016, and the yield rate was about 95%.

This paper used a finite-element magnetic field analysis (FEA) to investigate the instantaneous and average power in a single phase transformer and a three-phase rotating machine. We examined the influence of the hysteretic properties of the magnetic materials on the instantaneous power in FEA using the isotropic vector play model. We applied post-correction to estimate the accuracy of the average power from their equivalent circuits.

This paper proposes a homogenization method for a laminated iron core taking into account hysteretic property. The proposed method is applicable to a static or low-frequency problem neglecting eddy currents induced by the magnetic flux parallel to the lamination. Furthermore, we apply the proposed homogenization method to finite-element magnetic field analyses to demonstrate its effectiveness. As a consequence, it is verified that the proposed homogenization method can accurately estimate a hysteresis loss of a laminated iron core and decrease computational costs.

The superconducting magnet is effective to get a high stable and high magnetic field for magnetic resonance imaging (MRI). The current MRI superconducting magnet needed cooling in the liquid helium (4.2 K) to use NbTi superconducting wire. In the past few years, price increase and low availability of liquid helium has become a serious problem. Under such circumstances, the development of a high-temperature superconducting (HTS) coil dispensing with liquid helium cooling is greatly desired. The research and development project of the high stable magnetic field ReBCO coil system fundamental technology that started from the latter half of 2013 develops a ReBCO coil for 3 T MRI superconducting magnets. It gets a prospect of the practical use as the final aim. In this project, we will produce an HTS test coil of 300 mm bore experimentally and evaluate the magnetic field. This coil is cooled in less than 20 K by a GM refrigerator. We are going to make MRI used by the ReBCO coil field to evaluate the uniformity and stability of the magnetic field.

This paper investigates a method to increase fuel economy of motors for an electric vehicle (EV) traction system. The low-torque region of an EV motor is frequently used in everyday urban driving and in fuel economy measurement. Pulsewidth modulation (PWM) carrier harmonic iron loss accounts for a high percentage of total loss for EV motors in this region. This paper reveals the relationship between phase current and carrier harmonic iron loss for a permanent-magnet synchronous motor (PMSM) in the low-torque region. Thus, a novel carrier harmonic loss reduction technique is proposed and applied to two sets of three-phase windings for a concentrated winding PMSM. The loss is successfully reduced in a 70-kW EV motor as well as a two-dimensional finite-element method (2-D-FEM) calculation. The efficiency of the developed motor is calculated and compared with that of a conventional motor in the JC08 mode driving cycle.

This paper discusses an accurate magnetic field analysis that addresses stress distribution in the magnetic core by using the finite-element method (FEM) to estimate motor characteristics. This analysis method consists of the following steps: 1) measurement of the magnetic characteristics of electrical steel sheets in a state where stress is added; 2) calculation of deformation and stress distribution using structural analysis; 3) preprocessing of the magnetic field analysis, which generates the FEM mesh taking account of the deformation by stress and the changes of the magnetic properties in each of the core elements corresponding to stress distribution; and 4) magnetic field analysis using the data measured in step 1) and the FEM mesh generated in step 3). As an example, a result of a permanent magnet motor's cogging torque calculation is shown, focusing on stress in the stator core resulting from shrink fitting into the frame. As a result, the cogging torque waveform was shown to differ depending on the shape and the materials of the frame.

The stress that acts on the core by installing a stator in a frame influences the performance of a motor. To reflect this influence in the equipment design, the stress dependence of the magnetic property was examined for non-oriented electrical steels, which are the core materials. This time, the stress dependence of the magnetic power loss in the range of ±225 MPa was evaluated for high-grade non-oriented electrical steel sheets of 0.5 mm thickness, and the following results were obtained. (1) The influence on the magnetic power loss is larger under compression than under tensile stress. The loss increases rapidly with an increase in the compressive stress. However, when the stress exceeds -50 MPa, the saturation tendency of the loss gradually becomes strong. (2) The influence of the stress on the magnetic power loss is different in the rolling direction and the traverse direction. (3) A greater magnetic power loss that occurs with compressive stress is mainly due to an increase in hysteresis loss, and the eddy current loss also increases slightly. It is thought that this slight increase in the eddy current loss that occurs with compressive stress depends on the change in the anomalous loss.

The market of the electrical power steering is expanding rapidly because of its fuel efficiency. The DC motor is generally used in this system, whose noise reduction is demanded. The DC motor has some dispersion in contact number of segments or contact resistance between the brush and the commutator. When these conditions are different with plural brushes, currents in armature coils are in asymmetrical distribution and the unbalanced magnetic pull occurs in radial direction.We measured the radial force and currents in armature coils with the developed experimental apparatus that can also set up the eccentricity of rotor to stator. In this paper, we investigated the factor and the process of the radial force generated in the DC motor. Then we propose short circuit wires for symmetrical position that makes winding current symmetrical and realizes the noise reduction.