This paper proposes a design method of the high-speed multi-layer interior permanent magnet synchronous motor (HSML IPMSM) employing the ferrite permanent magnet (PM). Since the maximum speed of the traction motor in this paper is 15 krpm, the mechanical stability must be considered. Additionally, in the case of the HSML IPMSM, as the number of the PM layers increases, the thickness of the PMs must be reduced to be mechanically stable. On the other hand, because the ferrite PM has a relatively low coercive force compared to the Nd PM, an irreversible demagnetization of the ferrite PM of the HSML IPMSM is likely to occur. Therefore, the mechanical stability and irreversible demagnetization must be considered at all design steps. As the irreversible demagnetization and mechanical stability can be confirmed only by finite element analysis (FEA), the proposed method in this paper is a design method that considers the irreversible demagnetization and mechanical characteristics at all design steps using the FEA. After the design of the traction motor is completed using this design method, the designed motor is manufactured. To verify the validity of the design method, experiments are conducted on the manufactured motor, and the test results are compared with FEA results.

This paper proposes the design method using a numerical formula known as the Advanced Inverse Cosine Function (AICF) to reduce vibration of the Interior Permanent Magnet Synchronous Motor (IPMSM). The proposed method reduces the vibration by modifying the rotor shape based on the numerical formula that makes the air-gap flux density sinusoidal under certain load condition. The radial electromagnetic force that is the source causing the vibration of the motor is related to the air-gap flux density under load condition. Therefore, the AICF which reduces the magnitude of the harmonic of the air-gap flux density is derived in this paper and the radial electromagnetic force due to the harmonic of the air-gap flux density decreases applying the AICF. To verify the validity of the proposed method, an 8 pole 12 slot prototype applied with the AICF is proposed. Using the Finite Element Analysis (FEA), the radial electromagnetic force and the displacement of the prototype with the AICF are compared with those of the normal model without the AICF. Finally, the results of the vibration test of the normal and AICF models are compared.

Electric vehicle (EV) systems require a high energy-efficiency traction motor so that the motors for EV traction should achieve high efficiency and power density. Hence, a permanent magnet synchronous motor (PMSM) for EV traction using a maximum slot occupation (MSO) coil has been investigated in this study. By applying the MSO coil, high torque density was achieved, but an additional loss, which decreases the efficiency, was incurred through alternating current (AC) resistance. To reduce the AC resistance of the MSO coil, the following process was performed: First, by investigation using the analytical method, pole/slot numbers, current density and number of parallel circuits affecting the frequency, the shape and number of conductors were chosen as important variables. Resistances of the MSO coil with a stator core were analyzed according to the chosen variables above. From the results, MSO coil applied PMSM with proper pole/slot numbers, current density, and parallel circuits was determined to improve the efficiencies at the base and maximum speeds. To accurately estimate the efficiency of the determined model, loss evaluation methods were explained. Subsequently, the determined MSO coil applied model was compared with the conventional model having round wires, and the improvements were verified by load testing.

To be used as a robotic actuator, a surface-mounted permanent magnet synchronous motor (SPMSM) requires a low cogging torque characteristic. The aim of this study is to analyze and reduce the cogging torque's variation due to the assembly imperfection of the segmented stator that is widely used in the SPMSM. Considering the interconnection of the stator segments, an equivalent modeling method of the segmented stator with assembly imperfection is introduced. In addition, the variation in the cogging torque caused by the assembly imperfection is mathematically evaluated. Then, a robust design process that incorporates a sensitivity analysis and a robust design optimization is proposed. By using the proposed design, a robust optimum design model was built and its validity was verified through Monte Carlo simulation and tests.

This paper proposes a novel structure for the concentrated flux-type synchronous motor (CFSM) in order to improve the torque density as well as the vibration characteristics. First, the conventional surface mounted permanent magnet synchronous motor (SPMSM) as prototype for the electric booster in the brake system is investigated through tests. Then, the relationship between the vibration characteristics and the number of poles and slots is analyzed. Based on the analysis results, a pole-slot combination for an improved CFSM is determined to enhance the vibration characteristics. Furthermore, a novel structure for the improved motor that employs three different core shapes in the rotor is proposed to increase the torque density. As a result, the improved motor with excellent vibration characteristics as well as a high torque density is designed. Finally, experiments are conducted to verify the effectiveness and the feasibility of the proposed method.

Surface-mounted permanent magnet synchronous motors (SPMSMs) usually adopt a retaining sleeve for ultrahigh-speed (UHS) applications. The retaining sleeve usually has high electrical conductivity and cannot be segmented. Accordingly, the rotor eddy current loss is high. Moreover, the higher the eddy current loss, the higher is the rotor temperature. Therefore, the rotor eddy current loss should be considered in the design stage. However, the eddy current loss is generally calculated through three-dimensional finite-element analysis (3-D FEA) and considered cumbersome because of the high computation time. This article proposes a simple estimation method for the rotor eddy current loss of a UHS SPMSM according to the motor size. In this study, the mechanically stable cross-sectional structure of the rotor was fixed, and a formula for predicting the eddy current loss of the rotor based on motor size was devised. In this method, the basic electromagnetic formula for eddy current and the frozen permeability method were utilized. The proposed method was validated via comparisons with the results of 3-D FEA.