This paper investigates effects of a step skew structure in an interior permanent magnet synchronous motor (IPMSM) to improve the output power in the field weakening control area. In this paper, effects of the step skew during the field weakening control are evaluated by three-dimensional finite element analysis (3D-FEA) as a basic investigation. On the other hand, 3D-FEA is required to reveal characteristics of skew structures, but it is time-consuming. Therefore, we constructed a design procedure for reducing development term until a suitable skew structure is obtained although 3D-FEA is performed. Additionally, the final model developed based on the constructed design procedure can achieve a large reduction in both total harmonic distortion (THD) and torque ripple under the field weakening control compared to the typical step skew models. Furthermore, it is found that the final model can suppress the voltage and has a possibility to improve the output power, especially in the field weakening control area.

This paper described the characteristics of a hybrid field motor (HEM) with a field winding on the rotor. The proposed HEM can greatly change the field magnetic flux by the field winding, and it is possible to utilize the reluctance torque and improve the power factor. In addition, the efficiency is higher than that of the conventional hybrid vehicle drive motor in wide operating area of low torque, high torque area at low speed, and constant power area. In this paper, changes in characteristics due to changes in the amount of magnets in the proposed HEM were confirmed by several electromagnetic field analyses. As a result, it was shown that the proposed HEM can reduce the efficiency in the low-speed medium-torque range, which is rarely used in electric vehicles, and significantly improve the efficiency in the low-torque range used in regular operation.

Magnetic levitation pumps can feed liquid cleanly without mechanical contact by magnetically suspending the rotor shaft integrated with the impeller. However, surfaces of the rotor and the stator need to be protected by resin bulkheads, and then the magnetic gap length is larger than generally electrical machine. Therefore, it is difficult to generate large suspension force for 1-axis active control type magnetic levitation pumps that passively stabilize the rotor in the radial direction with repulsive force of permanent magnets (PMs). This paper proposes a new structure of the repulsion PM which can generate high suspension force even wide gap length. Five structures of the repulsion PM are investigated, and the structure that is optimized for a 1-axis active control type is analyzed with 3-dimentional finite element method (3D-FEM).

This paper introduces a matrix converter control method for an isolated AC/DC converter with a resonant circuit that considers non-linearity of the diode rectifier. The method achieves a high output frequency equals to the switching frequency, a constant DC output voltage, sinusoidal input currents, and unity input power factor. Furthermore, soft switching with maximum output power factor is realized by a frequency control. In this type of circuit, the harmonics of the matrix converter output current are caused by the non-linearity of the diode rectifier. A conventional method neglects these harmonics, which cause input current distortion and DC voltage ripple. In a proposed method, the control variables are numerically calculated considering the non-linearity of the diode rectifier and implemented in a lookup table. In addition, a DC voltage feedback is applied to compensate for the effects of parameter error, e.g., voltage drop of the power semiconductor device and deadtime of the MC. The proposed method is evaluated experimentally.

We propose a frequency multiplying circuit containing a high-frequency output inverter and an impedance matching transformer that contains magnetic materials with an operation frequency lower than the output frequency. The operation principle and power loss of the proposed circuit and a conventional circuit are compared. Simple theoretical analysis shows that the proposed circuit can reduce the iron loss of magnetic materials. However, the conduction loss of semiconductor devices and the copper loss of primary windings in the proposed circuit are higher those in the conventional circuit because the number of phases in the half-bridge inverter is five times that in the conventional circuit. Experimentally, it is revealed that Mn-Zn ferrite can be used at an output frequency of 2.5 MHz, which exceeds the operation frequency of the material.

In recent years, permanent magnet synchronous motors (PMSMs) are used for many applications because of their high output density and high efficiency. On the other hand, PMSMs having low aspect ratio like flat disk are desired depending on applications. In general, PMSMs employ radial gap structure which has the air gap in radial direction. However, in flat shape, radial gap motors have relatively low torque because their effective surface area of permanent magnet (PM) is small and their coil ends occupy most of the motor volume. Therefore, in flat shape, axial gap structure which has the air gap in axial direction is frequently employed instead of radial gap motors. Since axial gap motors don't have the coil ends in axial direction, they can reduce axial length. Meanwhile, conventional axial gap motors frequently employ double stator structure. Hence, in flatter shape like `ultra-flat shape', conventional axial gap motors are not suitable because stator back yoke and PM become extremely thin. Instead of those, an axial gap motor employing C-type SMC core is proposed in this paper. Advantages of the proposed axial gap motor using C-type core in ultra-flat shape is illustrated, and then, the proposed motor is analyzed by three-dimensional finite element analysis (3D-FEA).

Magnetic suspension pumps have been attracted attention and actively developed. These pumps can realize magnetic suspension and rotation of a rotor shaft integrated with an impeller without mechanical contact. There is now a need to develop a magnetic suspension pump that is capable of 5-axis active control while retaining a small size and low power output. However, conventional structures capable of 5-axis active control are not suited to such requirements. This paper introduces a novel structure of a 5-axis active control type magnetic suspension pump for small size and low power output. The proposed structure reduces pump size by eliminating a dedicated rotor component for a thrust magnetic bearing and generating thrust suspension force in both the positive and negative axial directions with a single electromagnet. 3D-FEM analysis and experiment demonstrate that the proposed structure satisfies requirements for magnetic suspension pump applications.

Rare earth magnets that have a large energy product are generally used in high-efficiency interior permanent-magnet synchronous motors (IPMSMs). However, efficient rare-earth-free motors are needed because of problems such as the high prices of and export restrictions on rare earth materials. This paper introduces a ferrite-magnet spoke-type IPMSM that employs a W-shaped magnet placement in order to achieve high efficiency. The effectiveness of the W-shaped magnet placement is verified from the results of two-dimensional finite element analysis and experiments on a prototype.