Step-skew is a common technique for eliminating the cogging torque of a target harmonic order in permanent magnet synchronous motors (PMSMs). However, when step-skew is applied to the rotor, the cogging torque of the target harmonic order is not completely eliminated due to 3-D leakage flux. Therefore, the 3-D leakage flux should be considered in designing a PMSM with step-skew for cogging torque reduction. The most accurate way to consider the 3-D leakage flux is to perform 3-D finite element analysis (FEA), but it has the disadvantage of high computation time. To resolve this challenge, this paper proposes a design method that utilizes transfer learning to reduce the time for 3-D FEA while maintaining accuracy. Through the proposed method, a large amount of 2-D FEA-based data and a small amount of 3-D FEA-based data are used instead of a large amount of 3-D FEA-based data, with similar accuracy as using a large amount of 3-D FEA-based data, and the computational time is highly reduced. Finally, a prototype is fabricated and tested to verify the validity of the proposed design method for cogging torque reduction.

In this study, the causes of significant radial vibration at pole-frequency in an 18-slot 16-pole (18S16P) permanent magnet synchronous motor (PMSM) are thoroughly analyzed, and an improved model is proposed. First, the spatial phase relationship of the lowest order radial and tangential air-gap electromagnetic force densities (AEFDs) of the 18S16P PMSM is derived analytically. Then, using 3-D structural finite element analysis, the radial vibration-enhancing effect of the lowest order radial and tangential AEFDs is revealed. Furthermore, the tooth modulation effect of the 18S16P PMSM is investigated. The analysis results show that the modulated radial vibration is also enhanced by the radial vibration caused by the lowest order radial and tangential AEFDs, leading to significant pole-frequency radial vibrations. Afterward, a vibration reduction model is proposed to minimize the tooth modulation effect and utilize the vibration suppression effect caused by the lowest order radial and tangential AEFDs considering the spatial phase relationships. As a result, radial vibrations are greatly reduced, and the results are validated through simulations and tests.

The high power density, high efficiency, and wide speed range of permanent magnet synchronous motors (PMSMs) are attractive features. However, the cogging torque and unsuppressed torque ripple of PMSMs degrade torque quality and reliability and cause vibration. This article compares the effectiveness of PMSMs in reducing the cogging torque, torque ripple, and vibration by applying each stator tooth chamfer types: inner eccentricity chamfer, outer eccentricity chamfer, linear chamfer, and circular chamfer. First, stator tooth chamfers were applied to the reference model to confirm the tendency of cogging torque, torque ripple, and electromagnetic force according to the design variables by chamfer types, and it was demonstrated that the chamfer needs to be applied in a way that reduces the harmonics of the air-gap magnetic flux density to improve the performances through finite element analysis (FEA). Next, the optimum design for reducing cogging torque, torque ripple, and electromagnetic force was performed for each stator tooth chamfer types for a valid comparison. As a result, it was confirmed that there are advantageous stator tooth chamfer types based on each performance. Finally, a prototype was fabricated and tested to validate the FEA results of the optimum model for performance comparison.

Urban lightweight electric vehicles (EVs) for personal mobility have the advantage of being convenient and economical. Vehicles with low vibrations and high energy efficiency are suitable for use as urban electric vehicles. The torque ripple of the motor that induces the vibration of the EV can be improved by reducing the harmonics of the magnetic flux density. The energy efficiency of an EV can be improved by increasing the efficiency at the main operating points (MOPs) by considering the driving cycle. Through the proposed design process, optimization was performed to improve the harmonic characteristics of a high-efficiency lightweight EV with a stator chamfer and rotor notch structure. The harmonics of the magnetic flux density due to the teeth and slots are improved through the stator chamfer, and the fundamental component of the magnetic flux density is increased through the rotor notch structure. The optimum model designed through the proposed design method has improved the efficiency at the MOPs and harmonic characteristics.

In this study, the radial vibration of fractional-slot concentrated winding (FSCW) permanent magnet synchronous motor (PMSM) was analyzed according to pole/slot combination considering phase relationship of modulated radial, tangential forces, and moment. First, to calculate the modulated forces and moment according to pole/slot combination, the amplitude and phase of modulated radial, tangential force and moment converted by radial air-gap electromagnetic force density (AEFD) are analytically derived. Since the lever arm effect by tangential force varies according to the tooth length, tangential force was translated on the yoke and an equivalent modulated moment was derived. Subsequently, to analyze the radial vibration caused by modulated forces and moment, the radial displacement response owing to a unit radial AEFD is calculated using 3D structural finite element analysis by applying unit modulated forces and moment. It was found out that the tooth modulation effect hardly varied with pole/slot combination and shape of the PMSM such as tooth length. Rather, it was confirmed that the tooth modulation effect was significantly influenced by the slot opening width. Especially, it was analyzed that the radial vibration of PMSM is not simply reduced by optimizing the slot opening width with reduced modulated radial force, but the amplitude and phase of the modulated tangential force and moment should also be considered. Finally, four prototypes of the PMSM with different slot opening widths of two 12-slot 10-pole and two 12-slot 14-pole are fabricated, and the test and simulation results are compared and verified.

During the motor design stage, it is crucial to accurately predict the characteristics of the motor at various operating points. Performing finite-element analysis (FEA) for each point is time-consuming and impractical. Therefore, the motor parameters and losses are typically calculated for each load point and used to solve the voltage and torque equations, thereby reducing the time required for motor characteristic analysis. Thus, the accurate prediction of motor parameters is essential for optimizing the motor design. This study proposes a parameter estimation method for the design process of induction motors (IMs). Accordingly, the circuit parameters are estimated using a reduced amount of FEA data. A common approach for evaluating the circuit parameters of IMs is through locked-rotor and no-load tests. However, these methods have limitations, because they use a fixed frequency that may not be suitable for electric vehicle traction motors owing to their various driving points, high torque, and high power density. This article introduces an iterative method for estimating the magnetizing inductance in IMs, owing to its significant impact on torque. This method is based on the changes in saturation according to current and slip frequency.