The core design elements of the motor for the co-robot joint are miniaturization and high torque. In this paper, a dual rotor axial-flux permanent magnet (DRAFPM) motor is proposed to improve the performance of robot joints. DRAFPM motors have the advantage of reducing iron loss and minimizing volume because they can remove stator yoke. When designing a motor with the same volume, it can be designed to increase the height of the fixed ruler by the thickness of the yoke of the fixed ruler and increase the number of turns. In the case of existing axial-flux permanent magnet (AFPM) motors, the shape of the three-dimensional structure is limited by radial laminating of stator. Therefore, considering the production of 3D printing, the shape of stator shoe is designed. The optimal design problem of DRAFPM motor consists of real and integer design variables. In addition, due to the structural characteristics of DRAFPM motors, 3D finite element analysis (FEA) is required, so it takes a long time to interpret. Therefore, this paper proposes an efficient optimal design process to optimize the remaining real design variables after prioritizing the integer design variables. The proposed optimization process is applied to the DRAFPM motor for robot joints, and the optimal design plan satisfying the design function is derived from various design variables to prove the validity of the optimization process.

The spoke-type permanent magnet synchronous motor (PMSM), which is a general ferrite magnetic flux-concentrated motor, has a low portion of reluctance torque at the total torque magnitude. Therefore, as a way to increase the reluctance torque, there is a double-layer spoke-type PMSM that can maximize the difference in inductance between the d-axis and the q-axis. However, in the double-layer spoke-type PMSM, cogging torque, torque ripple, and total harmonic distortion (THD) increase with reluctance torque, which is the main cause of vibration and noise. In this paper, a method is proposed that provides the same effect as skew without dividing stages of the permanent magnet by dividing the core of the rotor into two types so that it is easy to manufacture according to the number of stages, unlike extant skew methods. Based on the method, the reduction in cogging torque and THD was verified by finite element analysis (FEA).

Permanent magnet synchronous motors (PMSMs), with their high power density, high efficiency, and thermal stability, are widely used nowadays. PMSM magnets are composed of rare earth elements. However, rare earth elements are subject to severe price fluctuations because of their limited availability and the monopoly of some countries. Therefore, extensive research on magnets devoid of rare earth elements has been conducted recently. Although a magnet devoid of rare earth elements has a high irreversible demagnetization rate at high temperatures owing to its low coercive force, an irreversible demagnetization improvement process is proposed in this paper to compensate for this disadvantage. This process analyzes the contribution of the magnet’s back EMF (electromotive force) using the flux linkage equation, which does not change with time. Next, the location of irreversible demagnetization is moved to a position with a low contribution to the back electromotive force. Consequently, even if irreversible demagnetization occurs at the same size, the irreversible demagnetization ratio is reduced. The proposed process can minimize irreversible demagnetization while maintaining performance.

Axial flux motors have a large output density with a large outer diameter of the motor and a short axial length. Since it is advantageous in short axial length, the axial thickness of motor components becomes a very important parameter when designing axial flux motors. Among the components, the back yoke exists to serve as a path for magnetic flux and must have a certain thickness to prevent magnetic saturation. However, as the thickness of the back yoke increases within the axial size limit of the motor, the output of the motor may decrease. In this paper, same-direction skew that increases the cross-sectional area of the magnetic flux path without increasing the thickness of the back yoke is presented. Same-direction skew is a way to increase the cross-sectional area of the back yoke by skewing the rotor and stator in the same direction. The back yoke thickness that can be reduced by same-direction skew was calculated. Performance with same-direction skew designed using the equations was analyzed and compared, and the effectiveness of each type of rotor was verified. The validity of the proposed model was examined using the finite element analysis method.

Permanent magnet synchronous generators (PMSGs) with high output density per unit volume are becoming widespread in wind-power generation systems. Among them, spoke-type PMSGs are more challenging to magnetize than other PMSGs, owing to their structural characteristics. Magnetization performance is critical because it is directly related to the demagnetization and mass productivity of permanent magnets, and load performance is reduced when non-magnetization occurs due to the low magnetization performance. Additionally, the starting performance is crucial in wind turbines and is influenced by the cogging torque of the PMSG. This is because starting a wind turbine with a large cogging torque is more challenging. Therefore, this study proposes a spoke-type PMSG rotor shape design for low capacity wind turbines that considers magnetization and cogging torques. We analyzed the principle of magnetization and the factors influencing magnetization performance, and designed a rotor shape with improved magnetization performance. Additionally, we applied an asymmetric rotor barrier structure to reduce the cogging torque and analyze the performance of the final model using finite element analysis. We analyzed the temperature saturation during the operation of the final model using a thermal network method and validated the irreversible demagnetization accordingly.