This paper presents the design of an ultra-high speed PM Motor/Generator driven at a rated output and speed of 10kW and 70,000 rpm, respectively, for use in an Electric-Turbo Compounding System (E-TCS). When designing the very-high speed Motor/Generator, the mechanical and structural safety of the rotor and losses that occur when the motor operates at high speed should be considered for safe operation. In this paper, the optimal design of the ultra-high speed PM motor is performed with Finite Element Analysis (FEA) and structural analysis. Especially, the electromagnetic and structural characteristics based on the sleeve material are analyzed. The optimal design for PM motor, using carbon fiber is proposed not only to reduce the eddy-current loss, which prominently occurs at very-high speed, but also to ensure its structural safety. Finally, the validity of the design method and the effectiveness of the fabricated prototype of PM motor is verified through experimental tests.

Owing to the development of electric vehicles (EVs), research and development are underway to minimize torque ripple in relation to vibration and noise in EV motors. Although there are various ways to reduce torque ripple, this study analyzes the torque ripple, cogging torque, total harmonic distortion (THD), and magnetic flux density distribution for the three rotor shapes of interior permanent magnet synchronous motors, which are widely employed in EVs. To reduce the torque ripple while retaining the required average torque, the barrier shape is optimized, and wedge skew is applied. First, regarding the rotor barrier shape, torque ripple is primarily reduced by designing the rotor barrier shape with the response surface method, which is an experimental design method. Additionally, the wedge skew shape considering the bidirectional rotation and fabrication was applied to the stator shoe as a step and analyzed using three-dimensional finite element analysis. When designing the wedge skew, the layer subdivision according to the axial length, wedge skew diameter, and wedge skew position was analyzed and improved. The torque ripple reduction method in this paper can be applied not only to motors for EVs or Hybrid EVs (HEVs) but also all types of permanent magnet synchronous motors.

In this paper, the optimal design for a permanent magnet-assisted synchronous reluctance motor (PMA-SynRM) is proposed in terms of efficiency, maximum torque, and minimum torque pulsations. Design variables, objective functions, and constraints are selected for this optimal design, which is divided into two steps. Step I utilizes the pole/slot combination of the PMA-SynRM and winding methods. The chosen 4-pole/36-slot model with distributed winding maximizes the rated efficiency. In Step II, the optimal design of the stator parameters is obtained using the response surface method and the precise torque and torque ripple are calculated using the finite-element analysis (FEA). The proposed stator slot openings are minimized to minimize the air-gap flux leakage, and consequently, realize a smooth electromagnetic torque. Finally, a few FEA results are validated by experimental results.

This paper proposes a quasi-semi-closed (QSC) slot design method for an open-slot-type interior permanent magnet synchronous motor (IPMSM) for independently rotating wheelsets necessary to reduce the total harmonic distortion of no-load back-electromotive force and the torque ripple in the IPMSM. Four different slot-opening models were selected--the basic model, hairpin coil model, magnetic-wedge model, and QSC-slot model--and 2-D finite-element analysis was performed under open-circuit and load operations for each of the four models. Next, the relationships among the cogging torque, the torque ripple, and the saturation phenomenon in the core were analyzed. In addition, the manufacturing process, manufacturing cost, fill factor, end-winding resistance, copper loss, and efficiency were investigated. The experimental results verify the accuracy of the proposed method.

Torque ripple and radial electromagnetic (EM) vibration can lead to motor vibration and noise, which are crucial to the motor’s NVH (Noise, Vibration, and Harshness) performance. Researchers focus on two main aspects: motor body design and control strategy, employing various methods to optimize the motor and reduce torque ripple and radial EM vibration. Rotor notching and segmented rotor skewing are frequently used techniques. However, determining the optimal notch and skew strategy has been an ongoing challenge for researchers. In this paper, an 8-pole, 36-slot ISG motor is optimized using a combination of Q-axis and magnetic bridge notching (QMC notch) as well as segmented rotor skewing to reduce torque ripple and radial EM vibration. Three skewing strategies—step skew (SS), V-shape skew (VS), and zigzag skew (ZS)—along with four segmentation cases are thoroughly considered. The results show that the QMC notch significantly reduces torque ripple, while skewing designs greatly diminish radial EM vibrations. However, at 14 $f_e$, the EM vibration frequency is close to the motor’s third-order natural frequency, leading to mixed results in vibration reduction using skewing techniques. After a comprehensive analysis of all skewing strategies, four-segment VS and ZS are recommended as the optimal approaches.

There are complex physical phenomena for the interpretation of a molded case circuit breaker (MCCB) in a distribution system. Most of the studies of MCCB interruption phenomena were conducted with numerical analysis and experiments. This traditional approach may help improve the performance of the MCCB itself, but it is difficult to find connectivity with other systems. In this paper, the circuit model is proposed and the interruption phenomenon of MCCB is analyzed. The interruption of the MCCB is divided into three sections to deal with physical phenomena occurring in each area. A simplified model is proposed considering the characteristics of each section. Based on this model, the circuit model is proposed. To implement the features of each section, the calculation of physical phenomena is carried out, and this is expressed in the circuit model with resistance and zener diode. Comparing the results of the simulation with the experimental results is as follows. For 7-plates (basic state), the error rate is −5.6% in section II and 16.8% in section III. For 1-plate, the error rate is 36.5% in section II and −17.0% in section III. This case shows much difference from the simplified model in this paper, resulting in the largest error rate. The 7-plates and 5-plates cases, which are available in the general MCCB owing to the shortest distance from the arc, represent a relatively small error rate. Using the proposed circuit model, it is expected that the entire system, including the interruption phenomenon, can be interpreted as a single circuit model.