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 a new numerical formula and a design method to reduce the torque ripple while improving efficiency and the control performance of an interior permanent magnet synchronous motor (IPMSM). In previous studies, the inverse cosine function (ICF) has been used for torque ripple reduction by making the air gap flux density distribution sinusoidal under a no-load condition. However, in this paper, the advanced inverse cosine function (AICF) based on the ICF is proposed. It determines an asymmetric rotor shape for rendering the air gap flux density distribution sinusoidal, considering a certain load condition. In addition to the torque ripple reduction, lower peak values, the total harmonic distortion (THD) of the induced voltage, and a lower iron loss can be achieved by applying the AICF, compared to the other conventional methods. The lower peak value and THD of the induced voltage are important because they affect the control performance of the motor. The lower iron loss can also lead to a higher efficiency, particularly, in the high-speed region. To verify the validity of the proposed design method, the characteristics of 8-pole, 12-slot motors that have different rotor shapes are analyzed using finite element analysis (FEA) and experiments.

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.

This paper proposes the design process of an ultra-high-speed surface-mounted permanent magnet synchronous motor for a fuel-cell electric vehicle air compressor. Proposed design process enables ultra-high-speed motor design while considering mechanical stresses of the rotor materials according to the temperature. In the rotor design stage, the worst temperature condition of the permanent magnet and retaining sleeve on mechanical stress is investigated and reflected using analytical method. Rotor dimension such as permanent magnet and retaining sleeve thickness is determined considering both electromagnetic performance and mechanical characteristics. Then, from the initially designed model, the eddy current loss according to the shape ratio (SR) and torque density (TD) is analytically derived using proportional equation and finite-element analysis result. Then, SR and TD to reduce the eddy current loss and maximize the efficiency are determined while considering the first bending critical speed. Finally, to verify the proposed design process, the prototype is fabricated and tested. Test results show good agreement with the finite-element analysis results, and it is confirmed that the rotor is operated at the highest rotational speed without mechanical failure.

In this article, the electrical and mechanical characteristics of multilayer interior permanent magnet synchronous motors (ML-IPMSMs) using ferrite permanent magnets (PMs) are compared when driven at high speeds with respect to the type of electrical steel. In high-speed operation, the mechanical and electrical characteristics of ML-IPMSMs vary depending on the number of PM layers, PM shape, number of bridges, and bridge thickness. Additionally, ferrite PMs have a lower coercive force than neodymium (Nd) PMs; therefore, irreversible demagnetization (ID) must be considered, and it is affected by the number of PM layers and PM shape of ML-IPMSMs. Thus, when designing a multilayer IPMSM using ferrite PMs for electric vehicle (EV) traction, all characteristics should be considered. Compared to conventional electrical steel (CES), high-strength electrical steel (HSES) offers advantages in mechanical properties, allowing for greater flexibility in ML shape. Consequently, it is possible to design a shape with improved electrical performance when compared to CES by adjusting the ML shape. In this article, all characteristics of each ML-IPMSM using HSES and CES are reviewed via finite element analysis (FEA), and the benefits of HSES applied motors for high-speed driving motors are presented. To verify the validity of the review content in this article, experiments are conducted on the manufactured motor, and FEA results are compared with the test results.

In this paper, the design of the concentrated fluxtype synchronous motor (CFSM) using ferrite permanent magnets to improve torque is proposed for an automotive chassis actuator. The thin pancake type CFSM of this paper has considerable axial magnetic leakage flux due to structural reasons. It is therefore necessary to improve the torque. In order to meet the required specifications in a constrained installation space, this paper proposes two methods for torque improvement. The first method is the alternate-stacking core as this structure removes the magnetic leakage flux path. The second method is the rotor overhang which increases the air-gap flux density. Furthermore, the structures require a 3-D finite element method (FEM) analysis for accuracy. However, to analyze the characteristics easily and quickly, the 3-D structure is made into the equivalent 2-D FEM through an analytical method using an equivalent magnetic circuit (EMC). Finally, in this paper, the validity of the design process and the effectiveness for torque improvement is verified through experiments.