Keun-Young Yoon

The consequent-pole interior permanent-magnet (CPM) motor is a promising alternative for minimizing rare-earth magnet usage while supporting high-speed operation. However, rotor flux asymmetry often leads to distorted back-electromotive force waveforms and increased torque ripple. This study investigated a flared-type CPM motor that employs ferrite magnets arranged in a flared configuration to enhance flux concentration within a compact rotor. To address waveform distortion, structural modifications such as bridge removal and an asymmetric air-gap design were implemented. Three rotor parameters—polar angle, asymmetric air-gap length, and rotor opening length—were optimized using Latin hypercube sampling combined with an evolutionary algorithm. Finite element method analyses conducted under no-load and rated-load conditions showed that the optimized model achieved a 77.8% reduction in torque ripple, a 43.4% decrease in cogging torque, and a 0.5% improvement in efficiency compared with the basic model. Stress analyses were performed to examine the structural bonding strength and rotor deformation of the optimized model under high-speed operation. The results revealed a 5.5× safety margin at four times the rated speed. The proposed approach offers a cost-effective and sustainable alternative to rare-earth magnet machines for high-efficiency household appliances, where vibration reduction, cost stability, and energy efficiency are critical.

Interior permanent magnet synchronous motors (IPMSMs) offer high torque density. However, they are expensive owing to the rising prices of rare earth elements used in permanent magnets (PMs). This study proposes a double-layer flared-shaped IPMSM (DF-IPMSM) that achieves equivalent output torque and reduced torque ripple, while minimizing PM usage. It achieves flux concentration using C-type ferrite PMs arranged in a flared configuration and enhances reluctance torque by increasing the difference between L_d and L_q using a double-layer PM arrangement. Finite element analysis (FEA) under rated load and drive conditions demonstrates that the DF-IPMSM achieves output torque and efficiency equivalent to those of a single-layer flared-shaped IPMSM (SF-IPMSM) despite the reduced PM usage. To verify the structural advantages of the DF-IPMSM, it was compared with three alternatives, namely, SF-IPMSM, double-bar type IPMSM (DB-IPMSM), and double-spoke type IPMSM (DS-IPMSM), under rated load conditions. The FEA results indicated that the DF-IPMSM achieves the highest reluctance torque at equivalent output torque and efficiency. Although DF-IPMSM utilizes the reluctance torque more effectively than SF-IPMSM, it has the disadvantage of increasing torque ripple due to magnetic saturation and harmonic distortion. We performed an optimization rotor geometry design to improve this drawback. Sample points were generated using Latin Hypercube Sampling (LHS) and constructed a Kriging-based surrogate model. Subsequently, a genetic algorithm (GA) was employed to determine the optimal values for minimizing torque ripple. Finally, the FEA results of the optimized model were compared with the prototype measurements to verify the validity of the proposed DF-IPMSM. The proposed DF-IPMSM design offers a cost-effective alternative to conventional IPMSMs by significantly reducing reliance on rare earth PMs while maintaining high torque performance and efficiency.

This study presents a novel structure proposal of a variable inductance high-frequency transformer for enhancement power level of a dual-active-bridge (DAB) converter. The DAB converter is a solid-state transformer (SST) that requires high efficiency, power density, flexibility, and stability. Variable inductance facilitates achieving and extending maximum power levels. The proposed method adjusts the inductance based on the core insertion conditions of the transformer used in the DAB converter without requiring an additional inductor. The method was verified by analyzing the variable inductance characteristics of the transformer based on core insertion conditions via finite element analysis (FEA) and simulation and experiments within the variable inductance range.

Interior permanent magnet motors are widely used in applications requiring high power density and high efficiency due to their high torque-generating capabilities. Recently, given the price fluctuations and unstable supply of rare earth permanent magnets, alternative configurations with reduced use of permanent magnets are being sought. Among the various candidates related to this, the consequent-pole type rotor structure can halve the number of permanent magnets used compared with conventional structures. However, in a no-load analysis, the waveform of the back electromotive force becomes asymmetric, generating a harmonic component. As a result, there is a disadvantage that the torque ripple increases. To overcome these shortcomings, we propose a novel rotor structure that applies a consequent-pole structure to an embedded permanent-magnet motor structure, wherein a number of permanent magnets are arranged in a flared structure to constitute a single polarity. In the proposed flared-structured magnet arrangement, it is possible to adjust the angle of the permanent magnet and the polar angle to mitigate the asymmetry of the back-EMF waveform. The proposed structure was optimized with a genetic algorithm and a prototype of the optimal model was constructed and experimentally evaluated to verify its validity. Finally, the performance improvement and validity of the proposed structure were verified by comparing the analysis results of the optimal model with the experimental results.

Interior permanent magnets motors are widely used in applications requiring high power den-sity and high efficiency due to their high torque generating capabilities. Recently, given the re-cent price fluctuations and unstable supply of rare-earth permanent magnets, alternative config-urations with reduced use of permanent magnets are being sought. Among the various candi-dates related to this, the consequent-pole type rotor structure can halve the number of perma-nent magnets used compared with conventional structures. However, in the no-load analysis, the waveform of the back electromotive force becomes asymmetric, generating a harmonic component. As a result, there is a disadvantage that the torque ripple increases. To overcome these shortcomings, we propose a novel rotor structure that applies a consequent-pole structure to an embedded permanent-magnet motor structure, wherein a number of permanent magnets are arranged in a flared structure to constitute a single polarity. In the proposed flared-structured magnet arrangement, it is possible to adjust the angle of the permanent magnet and the polar angle to mitigate the asymmetry of the back EMF waveform. The proposed struc-ture was optimized with a genetic algorithm and a prototype of the optimal model was con-structed and experimentally evaluated to verify its validity. Finally, the performance improve-ment and validity of the proposed structure were verified by comparing the analysis results of the optimal model with the experimental results.

Currently, research is being carried out on the performance improvement of permanent-magnet-synchronous motors (PMSM) used in air conditioning and blowing systems for marine, as well as structural research, regarding their high-speed operation. Surface-mounted permanent magnet (SPM) motors used in marine propulsion and air-conditioning systems have the advantages of easy rotor manufacturing and a simple structure. However, owing to the structural characteristics associated with attaching a permanent magnet to the surface of the rotor, there is a risk of permanent magnet scattering when turning a rated load at high speed, and the rotor assembly is directly affected by the heat generated in the stator winding. Therefore, in this study, additional protrusions were proposed to prevent rotor scattering during high-speed operations. Additionally, optimization was performed to reduce the torque ripple at the rated load and the total harmonic distortion (THD) of the no-load-induced electromotive-force waveform generated by the protrusion. Consequently, the risk of scattering at high speeds was improved by securing the bonding force of the permanent magnet using the proposed structure, and the THD and torque ripple were reduced compared with those of the basic model through optimization. In addition, rotor structural stress analyses were conducted to solve the problem of scattering at high speeds and eigenmode analysis.

Unlike the winding structure of existing three-phase single winding motors, the winding structure of the dual winding motor (DWM) contains a master part and two slave parts. Thus, when the master part fails, it can be driven using the remaining slave part. It is applicable to various electric parts driving the integrated electric brake (IEB) system; thereby securing the high reliability of vehicle parts. However, in the existing DWM, there is an overheating problem owing to the increase in current because it operates with half the motor during the faulty mode. Therefore, a compensation method for the increase in current in a faulty mode was employed by increasing the stacking length of the DWM. However, although it solves the overheating problem of the DWM in the faulty mode, the motor output performance and braking performance of the IEB system are degraded in the normal mode because of the change in the motor control parameters. Thus, in this paper, we propose a DWM with winding switching (WS) to simultaneously solve the DWM overheating problem in the faulty mode and the DWM’s performance degradation problem in the normal mode. The output performance of the DWM with an increased stack length and the previously developed base model are compared to verify the performance of the proposed DWM with WS. As a result of the comparison, unlike the DWM with an increased stack length, in which the maximum speed is reduced by 20.5% compared to the existing base model during quick braking in the normal mode, the proposed DWM with WS has no performance degradation. In other words, it is confirmed that the proposed DWM with WS effectively solves the overheating problem during faulty mode, while simultaneously solving the performance degradation problem of the IEB system during the normal mode.

A system-level fault-tolerant design process of a dual-winding three-phase permanent magnet (PM) motor for overheat problem is introduced. Conventional dual-winding three-phase PM motors have been designed with a focus on the redundant system without considering the overheating. However, in the introduced design process, the overheating problem is considered of the motor that occurs in a faulty operation mode in an integrated electric brake (IEB) system. In the design process, the faulty operation mode is investigated in the system level. The design variables are selected as the main components of the IEB system such as the motor and pump piston. Then the selected design variables are optimized to operate without performance degradation even in the faulty operation mode. To analyze the coil temperature rise during the faulty operation mode of a dual winding motor by motor and pump piston size, a lumped-parameter thermal network with piecewise stator-housing modules (LPTN with PSMs) is utilized. In addition, to conduct the optimal design, latin hypercube sampling (LHS), kriging modeling, and a genetic algorithm (GA) are utilized. A prototype of the optimized model is manufactured and tested for verification of design results. It was confirmed that the dual-winding motor for autonomous vehicles, which is robust against overheating, even in faulty operation mode, is well designed.

In this paper, a novel fault-tolerant design process of the spoke type interior permanent magnet (IPM) motor is proposed to prevent the increase of cogging torque and torque ripple due to partial demagnetization fault, and to minimize the motor size. First, unlike other research papers on the irreversible partial irreversible demagnetization of PM, in this paper, the effect of partial irreversible demagnetization faults on the cogging torque and torque ripple for the fault cases are investigated. Then a novel fault-tolerant design process is proposed to solve the problem of partial demagnetization faults that increase the cogging torque and torque ripple. In the novel fault-tolerant design process, first, to solve the problem of increasing cogging torque and torque ripple due to the partial demagnetization fault, a process for implementing a uniform irreversible PM demagnetization is proposed. Second, to compensate for the motor torque constant decreased by degraded PM, which is caused by irreversible demagnetization of PM, a torque compensation coefficient is also proposed. The proposed fault-tolerant design process is applied to the motor design for the integrated electric brake (IEB) system that requires high torque density. In the optimal design process, Latin hypercube sampling (LHS), the kriging method, and a genetic algorithm are utilized. To verify the effectiveness of proposed fault-tolerant design process, it is compared with the conventional optimized design results in which irreversible demagnetization of PM is not allowed at all to prevent the partial demagnetization faults. As a result of comparing the optimal design results, the proposed optimization model utilizing the fault-tolerant design process can significantly reduce the motor volume by 12.9%, compared to the conventional optimization model.