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This paper describes the development of highspeed motor with high power density and high efficiency by using the ultra-thin electrical steel sheet in 80μm thick. This steel sheet has a low core loss reduction in high speed motor. These contents are based on the ultra-thin electrical steeleddycurrent loss, The developed high-speed motor is for the Mars rover rover, and requires a power supply voltage of 40V, an output of 50W and a weight of 25g as the high efficiency and high power density motor.

The iron loss of an induction motor powered by the sinusoidal wave of a commercial power source has been remarkably decreased by improving the electrical steel sheet used in a motor. However, in recent years, the permanent magnet motor and induction motor used in electric vehicles are often powered by a Pulse Width Modulation (PWM) inverter which shows good controllability. Iron loss in a stator core is increased by the carrier wave used in the PWM inverter. The iron loss of a ring core specimen made of electrical steel sheets of three kinds of thicknesses was evaluated under PWM inverter excitation. The thicknesses of the prepared electrical steel sheets were 0.08 mm, 0.1 mm, and 0.35 mm, respectively. In addition, in this paper, a number of problems that present when iron loss is evaluated under PWM excitation were investigated. For instance, the influence of switching-noise and dead-time of the PWM inverter on the iron loss were examined. Moreover, relationships between the carrier frequency, the modulation index and the iron loss were investigated. As a result, it was found that the iron loss of the ultrathin electrical steel sheet does not increase much even under PWM excitation.

This paper proposes core loss reduction of a surface mounted permanent magnet (SPM) motor with a segment stator core. First, it is shown that core loss of a motor is decreased by segmentation of a stator core made of nonoriented electrical steel sheet. The non-oriented electrical steel sheet used as the segment stator core has an anisotropy which is easy to magnetize in the rolling direction. Therefore, it is important to investigate core loss of the segment stator core in consideration of the rolling direction of electrical steel sheet. The rolling direction of the steel sheet can be taken into consideration in magnetic field analysis by using Enokizono & Soda (E&S) model which is one of the vector magnetic property utilization technique. Accordingly, the finite element method which introduced the E& S model is used in order to evaluate core loss of the motor. Secondly, core loss of the segment stator core is further reduced by applying corner radius to each tooth root. Finally, relation between core loss and the rolling direction in the segment stator core applying corner radius is investigated.

This paper proposes ways to reduce motor losses and improve efficiency. The purpose of this paper is to review the magnetic properties of vector magnetic characteristic techniques and to suggest the use of magnetic characteristic analytical methods. In this shows the vector magnetic properties of the non-oriented electrical steel sheet of the motor core material. An engineering model considering vector magnetic characteristics in the magnetic characteristic analysis has been proposed. The utility of this technique and examples of its use is shown.

In this paper, a stator core shape design method is proposed for an improvement in power density of a small surface-mounted permanent magnet (SPM) motor. In order to improve power density of a motor, it is necessary to increase torque of a motor or to reduce weight of a motor. However, when a stator core shape is miniaturized to reduce weight of motor, winding regions in a motor frequently decrease. Our stator core shape design method improves power density of a motor by reducing weight of a motor without decreasing torque and keeping winding regions constant. Moreover, core loss of a motor decreases by using our method. A Bezier curve is used for determination of a stator core shape. The finite element method in consideration of the vector magnetic properties is used to evaluate iron loss of the motor shaped by our method. As a result, power density of a SPM motor is improved, and core loss of the motor decreases.

This paper describes the development of the high speed motor of 50 [W] at 25 [g] as a space probe rover motor. Furthermore, this motor was required to have high power density. Ultra-thin electrical steel sheet with the thickness of 80μ was used for the iron core of this motor. The iron core shape was designed by vector magnetic characteristic analysis, introducing vector magnetic characteristics representing the magnetic characteristics in arbitrary direction of this electrical steel sheet.

This paper describes the necessary technical issues for the development of high-speed motors. Especially, it aims at high efficiency by reducing core loss. Its breakdown is the necessary magnetic properties of materials for high speed motor iron core, its vector magnetic characteristics and magnetic characteristics analysis of the magnetic circuit design. Finally, the stator core of the permanent magnet motor is shown as a design example.

This paper describes the technical problems in upgrading efficiency by core loss reduction on high speed motor. These contents are based on the ultra-thin electrical steel sheet for motor core and vector magnetic characteristic technology. It is difficult to get successful results by replace of high performance core materials. Because the utilization technique of these materials is necessary as a recipe for research and development of high efficiency high speed motor.

This paper presents relation between stator core shape and torque ripple for a surface-mounted permanent magnet (SPM) motor. An SPM motor with different stator core shapes is analyzed to clarify the influence of tooth width on torque ripple. In order to consider detailed magnetic properties of non-oriented electromagnetic steel sheet used for a stator core, a motor is analyzed by using 2-D finite element method which introduced an E&S (Enokizono & Soda) model. Furthermore, torque ripple reduction is attempted by chamfering the corner of tooth-tips. As a result, it is shown that tooth-end width and tooth-tip shape are very important for not only torque increase but torque ripple reduction.

It is well-known that iron loss in the stator core of a motor increases when the rotational speed of the motor increases. An eddy-current generated in the stator core is the cause of the increased iron loss. To decrease the eddy-current loss in the stator core, it is effective to reduce the thickness of the electrical steel sheet used for the stator core. We developed a 0.08-mm-thick ultrathin electrical steel sheet for the stator core of a high-speed motor. To demonstrate its effectiveness, we prepared two ring cores including one made of the 0.08-mm-thick ultrathin electrical steel sheet and another made of a 0.35-mm-thick electrical steel sheet. We compared the iron loss excited by a sinusoidal wave with the iron loss excited by a Pulse Width Modulation (PWM) wave using the two ring cores. In both specimens, the iron loss excited by the PWM wave was larger than the iron loss excited by the sinusoidal wave. Particularly in the specimen made of the 0.08-mm-thick ultrathin electrical steel sheet, the increasing rate of iron loss caused by an increase in the carrier frequency of the PWM wave was lower. In this paper, the effectiveness of a high-speed motor stator core made of a 0.08-mm-thick ultrathin electrical steel sheet is shown.

Improvement of the self-propelled rotary actuator in consideration of shape and rolling direction of steel sheets.

In order to design a high-efficiency motor, the iron loss that is generated in the motor core should be reduced.

This paper presents the newly proposed heating method named “secondary current heating method” to reduce the iron loss on laminated electrical steel sheet cores for high-efficiency electrical motors. It is well known that the magnetic properties of electrical steel sheets, which are used for electrical motor cores, are deteriorated by the residual stress during manufacturing of the electrical motors, and then the iron loss of the laminated electrical steel sheet cores of the electrical motors increases inevitably. The newly proposed secondary current heating method can improve the magnetic properties on laminated electrical steel sheet cores and reduce the iron loss of them in the very short time in comparison with conventional methods. In this paper, the electromagnetic and heating characteristics of the specimens by the proposed method were confirmed, and then it was applied into the laminated cores to reduce iron loss.

It is well known that the magnetic properties of a stator core in a rotating machine such as an induction motor are influenced by residual stress and external force. Residual stress is generated during manufacturing processes such as punch, laminate, and shrink fit processes. Magnetic properties such as iron loss of the stator core increases dramatically during the punching process and the shrink fit process. However, it is not easy to evaluate the magnetic properties of the actual stator core which has a complex shape. To evaluate the growth rate of iron loss in an actual stator core by manufacturing processes, the excitation inner core method was developed. The excitation inner core method can successfully evaluate changes in magnetic properties in an actual stator core. Then, the excitation inner core method was applied to examine the influence given to iron loss of the stress that caused by a motor frame. Moreover, iron loss consists of hysteresis loss and eddy-current loss. The iron loss measured using the excitation inner core method was separated into hysteresis loss and eddy-current loss by the dual frequency method. Experiments showed the compressive stress from a motor frame greatly influenced hysteresis loss, but the influence of this stress on eddy-current loss was small.

The Barkhausen signal was used for the nondestructive evaluation methods in order to evaluate residual stress levels in ferromagnetic materials. However, it cannot be said that this technique has been established completely because the evaluation is usually not done under controlled magnetic flux conditions. When the magnetic field is applied into the materials by the exciting coil, material characteristics will change, therefore, controlling the magnetic flux condition is required for the precise evaluation of magnetic materials. Some results of the residual stress level evaluation using Barkhausen signals under the controlled magnetic flux condition measured from different tensile stressed specimens are shown and discussed them for high efficiency motors in this paper.

This paper describes about the core loss (magnetic power loss, iron loss) reduction method for upgrading high efficiency motor. It is difficult to achieve the core loss reduction of motor by using conventional technique. Therefore we proposed the vector magnetic characteristic technology which is constructed magnetic characteristic analytical method, evaluation method of magnetic materials, and the building factor problem. Furthermore as an important magnetic characteristic, magnetostriction phenomena based on new viewpoint are introduced and its numerical simulation results.