In this paper, a design of six-phase surface inset permanent magnet synchronous machine (SIPMSM) with the open slots is performed considering the power factor and torque ripple. Because of the reluctance torque component by the q-axis core thickness of rotor, a surface inset permanent magnet synchronous machine (SIPMSM) has the high torque density but the large torque ripple. To overcome the large torque ripple, there are the various design method. In case of SIPMSM with the open slots, the tapering of shoe and the notch of stator and rotor cannot apply the tapering is applied to magnet, but the torque density and power factor decrease because the linkage flux by the permanent magnet reduce. Therefore, the thickness of q-axis core and tapering magnet has the trade-off between the performance and torque ripple. In this paper, the characteristic according to the q-axis core thickness and tapering magnet is analyzed based on a finite element analysis (FEA). Furthermore, the optimal design is proposed using the performance map based on the tapering of magnet and q-axis thickness of core. For the design of a basic model, pole-slot combinations are compared with the torque of SIPMSGM according to the current phase angle. Considering the performance, the basic SIPMSGM is selected for the optimal design. Based on the basic SIPMSGM, the optimal design is performed based on the optimal design parameters considering the power factor and torque ripple.

This study facilitated the improvement of no-load back electromotive force (back-EMF) wave form, total harmonic distortion (THD) of back-EMF, and torque ripple using a novel skew angle formula, considering the specific order of a no-load THD. In real usage environments, it is taken into consideration for the fully enclosed cooling system and limited inverter switching frequency of urban railway car traction motors. Since the most railway car traction motors use high-withstand voltage rectangular wires in slot-open structure, a no-load back EMF waveform includes large space slot harmonics, which should be smaller as possible. For 6-step control, the no-load back EMF waveform is important because switching for motor control is performed once after the rotor position is determined. To improve the no-load back EMF waveform and THD, two-dimensional and three-dimensional finite element analysis (FEA) were performed using a novel skew angle formula considering specific harmonic order reduction, while the fundamental amplitude was minimally reduced. A prototype with the novel skew was fabricated and verified. In addition, it was designed by calculating a low current density for a fully enclosed cooling system. A temperature saturation experiment was also performed, and successfully verified. Therefore, we suggest that the no-load back EMF characteristics and torque ripple are improved by applying the novel skew angle instead of a traditional skew angle.

This study focused on the efficiency improvement and acoustic noise reduction of brushless DC (BLDC) motors by reducing current harmonics using a novel BLDC commutation method. To achieve these goals, we designed an improved 150° commutation method for a three-phase permanent magnet BLDC motor that can improve the current waveform. Although the 120° commutation method is generally employed for BLDC motors, an improved 150° commutation method is introduced to operate the BLDC with increased efficiency and acoustic noise similar to a brushless AC motor. This study investigated the attributes of various commutation methods, both theoretically and experimentally, to determine the optimal commutation method. The results of this study indicate that the improved 150° commutation method is optimal in terms of harmonic attributes and reduced torque ripple, allowing it to improve motor efficiency and reduce acoustic noise.

Generally, cogging torque derives from motor using permanent magnet such as interior permanent magnet synchronous motor (IPMSM) and surface permanent magnet synchronous motor (SPMSM). The cogging torque works for smoothness in rotation of the rotor, but it is a kind of root cause mechanical vibration and acoustic noise. Consequently, cogging torque must be reduced by all manner of means. There are various methods to reduce the cogging torque, but this paper deals with two ways in the IPMSM. One is tapping the rotor and the other is design of barrier shape. Besides, this paper proposes best design of the IPMSM to reduce cogging torque, and the analysis of cogging torque by using FEM is compared with experimental results to verify.

Improving the efficiency of buck–boost converters has long been a major focus in power electronics. To enhance efficiency and overcome existing limitations, this paper proposes a soft-switching technique for a cascaded buck–boost converter (CBBC). The proposed approach integrates high-frequency switching of four gallium nitride (GaN) devices, improving both dynamic and steady-state performance from hardware and control perspectives. First, a soft-switching modulation scheme based on negative-current pulse width modulation (PWM) is implemented by introducing a new switching sequence in the CBBC, controlled by a modulation variable. This scheme ensures that the GaN switches operate under zero-current switching (ZCS) and zero-voltage switching (ZVS) conditions during transitions. Furthermore, the CBBC operating modes are divided into four intervals for modeling and analysis, upon which a model predictive control (MPC) strategy is developed to achieve fast closed-loop regulation of both output voltage and current. To further minimize current ripple and device losses, the MPC cost function is optimized by constraining the control parameters. Experimental results obtained from a 300-W hardware prototype verify the effectiveness and feasibility of the proposed soft-switching control method.

With the rapid growth of the electric vehicle (EV) market, the demand for high-efficiency and high-power motors has steadily increased. Consequently, the use of rare-earth materials such as neodymium (Nd) permanent magnets has also risen. However, the monopolistic supply chain and price volatility of rare-earth elements limit their wide adoption. In this study, we propose a motor structure that eliminates the use of dysprosium (Dy)—a rare-earth element critical for maintaining coercivity in high-temperature environments—to address concerns related to supply instability and cost escalation. While Dy plays a key role in preventing irreversible demagnetization by preserving magnet coercivity under elevated temperatures, this research demonstrates that stable performance can still be achieved at high temperatures without Dy by integrating a heat pipe into the motor design. The heat pipe effectively reduces the temperature of the permanent magnets; however, poor structural design may exacerbate eddy current losses, leading to further temperature increases. Hence, we conducted a thermal equivalent circuit analysis to verify that the heat pipe successfully controls magnet temperature rise and prevents irreversible demagnetization. The proposed structure is expected to reduce the consumption of rare-earth materials while enhancing both the efficiency and reliability of the motor.