Akihiro Daikoku

Cogging torque calculation considering magnetic anisotropy for permanent magnet synchronous motors

This paper describes the cogging torque of the permanent magnet synchronous (PM) motors due to the magnetic anisotropy of motor core. The cogging torque due to the magnetic anisotropy is calculated by the finite element method using two kinds of modeling methods: one is the 2D magnetization property method, and the other is the conventional method. As a result, the PM motors with parallel laminated core show different cogging torque waveform from the PM motors with the rotational laminated core due to the influence of the magnetic anisotropy. The amplitudes of the cogging torque are different depending on the modeling methods in the region of high flux density.

PWM Carrier Harmonic Iron Loss Reduction Technique of Permanent-Magnet Motors for Electric Vehicles

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.

Research and Development of the High Stable Magnetic Field ReBCO Coil System Fundamental Technology for MRI

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.

Variable characteristics technique on permanent magnet motor for electric vehicles traction system

A traction motor system of electric vehicles (EVs) requires wide torque-speed operation range, high efficiency, and low torque ripple according to its driving point. To achieve the requirements without increasing motor size, a novel variable characteristics motor system is proposed in this paper. A winding structure is studied to reduce unprofitable conductor which makes conduction loss. The developed system is applied 48-slot 8-pole permanent magnet synchronous motor (PMSM). The motor has structural full-pitch distributed winding with 12 open-end windings connected to insulated 12 full-bridge inverter. The developed motor simulates 4 types of winding mode, and each characteristic are calculated based on static two dimensional finite element analysis (2D-FEA). The calculated results show increase torque-speed operation range, higher efficiency, and lower torque ripple by selecting appropriate winding mode.

MATRIX motor with individual winding current control capability for variable parameters and iron loss suppression

This paper describes a novel motor-drive system which includes the multi-phase open-end windings for an individual winding current control in order to realize the variable parameters. Each armature winding is connected with the insulated full-bridge inverter for the arbitrary excitation waveform. The proposed construction can extend the operating area and can distribute the high efficiency area. Furthermore, the proposed multi-phase drive can suppress the harmonic iron loss under the flux weakening operation because the individual control can regulate the instantaneous flux density in each stator tooth even though the motor consists of the full-pitch distributed winding. In this paper, the down size model was designed to confirm the principle. It was shown that the downsize model can expand the operating range, can distribute high efficiency area, and can suppress the iron loss by the controlled flux density in each stator tooth by some simulation and experimental results.

Hysteresis Loss Analysis of Laminated Iron Core by Using Homogenization Method Taking Account of Hysteretic Property

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.

PWM carrier harmonic iron loss reduction technique of permanent magnet motors for electric vehicles

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.

Wide range operation by low-voltage inverter-fed MATRIX motor with single-layer distributed winding for automobile traction motor

This research proposes a novel low-voltage inverter-fed motor drive with variable characteristics achieved through the individual winding current control for the automobile traction motor. The independent armature winding with low-voltage inverters can improve the total efficiency by reducing the converter losses. Furthermore, the motor can expand the operating range since the inverters are able to change their connections to different coils groups of the armature winding. In this paper, the down size model was designed to verify the principle. It was confirmed that the principle model can extend the operating range and can expand the high efficiency area by FEA and experimental results.

Fundamental characteristics of a claw pole motor using additional ferrite magnets for HEV

This paper presents a specification of a claw pole motor that has a field excitation coil for hybrid electric vehicles. The characteristic of the claw pole motor is no use of Dy and Tb which can increase torque capability. The filed excitation which can be generated by controlling filed current in a rotor provides us controllable efficiency. Additional ferrite magnets are installed between the rotor poles for the purpose of increasing torque capability due to moderating magnetic saturation of each claw. FE analysis and experimental results are shown in this paper.

Wide Speed Range Operation by Low-Voltage Inverter-Fed MATRIX Motor for Automobile Traction Motor

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.