Jang-Young Choi

• Professor
• Chungnam National University

This study proposes a rotational speed measurement machine based on the flux-switching principle with a 6-stator-slot/19-rotor-pole (6s/19p) topology. With a rotor shape similar to a variable reluctance sensor (VRS), the proposed machine features a simple and robust structure while ensuring the same output frequency as VRS. Additionally, compared t...

This study proposes an improved design of an eddy-current speed sensor (ECSS) by adding a ferromagnetic core to the stator, resulting in a sensitivity enhancement ranging from three to sixty times compared to a reference model according to shaft materials. An improved analytical model (AM) based on harmonic modeling (HM) is developed to account for...

This study investigates the tapering rotor surface technique in an interior permanent magnet synchronous motor (IPMSM) for electric vehicle compressors. To achieve this, this paper proposes a novel tapered rotor design with a non-uniform air gap, created by applying asymmetric shaping to the bridge region along the rotor radius. A conventional IPMS...

This paper presents an electromagnetic analysis and experimental study of permanent magnet synchronous machines (PMSMs) considering eccentricity. Rotor eccentricity caused by defects in the manufacturing or operational processes of PMSMs affects electromagnetic performances. Although rotor eccentricity can be identified using finite element analysi...

Wound rotor synchronous condensers (WRSCs) are DC-excited rotor machines that utilize rotor winding instead of permanent magnets. Their voltage regulator controls the rotor field to generate or absorb reactive power, thereby regulating grid voltage or improving power factor. A key characteristic of a WRSC is the compounding curve, which shows the r...

This study presents a two-dimensional analytical method for fast optimization, taking into consideration the influence of the eddy current in a magnet and iron loss within a coaxial magnetic gear. Subdomain modeling was utilized to obtain vector potentials in the air-gap, magnet, and modulation regions by solving Maxwell’s equations. After that, th...

As interest in eco-friendly work vehicles grows, research on the powertrains of eco-friendly tractors has increased, including research on the development of eco-friendly vehicles (tractors) using hydrogen fuel cell power packs and batteries. However, batteries require a long time to charge and have a short operating time due to their low energy ef...

This paper focuses on electromagnetic and loss analyses of an induction machine using the subdomain method. The proposed method derives an analytical solution for each subdomain using electromagnetic theory. On the basis of the derived analytical solution, electromagnetic performances are calculated and copper loss, iron loss, and rotor loss are de...

The power delivery is crucial to designing agricultural machinery. Therefore, the tractor-mounted potato harvester was used in this study to conduct the field experiment and analyze the power delivery for each step. This study was focused on an analysis of power delivery from the engine to the hydraulic components for the tractor-mounted harvester...

In this paper, an electromagnetic analysis method is proposed to improve force characteristics by using spring permanent magnets (PMs) along the axial and circumferential directions of a linear oscillatory generator (LOG). For accurate electromagnetic analysis, a detailed analysis model of the LOG is developed, and the governing equations of each s...

As the performance of permanent-magnet synchronous generators improves, research on device noise is also becoming important. This study analyzes the causes of electromagnetic noise, such as the back electromotive force, cogging torque, torque ripple, unbalanced magnetic force, and harmonics that occur during operation for each DC and AC load. In pa...

This paper presents an analytical method for analyzing the electromagnetic performance of a superconducting (SC) machine according to the 10 MW shielding configuration and the presence or absence of an armature core. To establish the SC machine design process, an analytical method considers shielding conditions and armature core type is included. T...

This study proposed an improved analytical method for electromagnetic field analysis of a wound rotor synchronous machine (WRSM) considering the permeability of soft magnetic materials. A simplified analytical model considering the magnetic permeability of each region is presented. The governing equations of each region are derived from Maxwell’s e...

This study presents an approach to optimizing the output power in a magnetically geared generator by employing subdomain modeling and particle swarm optimization. Accordingly, the subdomain analytical method is utilized to obtain the induced voltage, inductance which are used to predict output power. Afterward, the swarm intelligence optimization t...

This study proposes an innovative approach that integrates the subdomain method with sequential quadratic programming (SQP) to optimize the volume of a high-speed surface-mounted permanent magnet synchronous motor in an air compressor operating at 110 000 rpm. Unlike conventional optimization tools that often rely on finite element analysis (FEA) s...

As rare-earth permanent magnet prices continue to fluctuate, interest in non-rare-earth permanent magnet-assisted synchronous reluctance motors (PMa-SynRMs) is increasing. However, non-rare-earth PMa-SynRMs have a multi-layer structure with interior permanent magnets to compensate for the low magnetic fields. Therefore, the rotor has several design...

This paper presents an analysis of demagnetization of an outer rotor type brushless DC (BLDC) motor with a permanent magnet (PM) overhang structure. The proposed model converts the operating points of PM to consider such a three-dimensional (3D) structure in two dimensions (2D). In addition, the rotor yoke thickness of the proposed model is increas...

In high-speed permanent magnet synchronous motor drives, time harmonics in the current occur owing to the carrier frequency of the inverter, which affects the core losses among the electromagnetic losses. According to Steinmetz’s equation, the core loss depends on the frequency and magnetic flux density, with each term influenced by harmonic curren...

This study investigates a subdomain method for performing the characteristic analysis of an axial flux permanent magnet motor (AFPM). Initially, the AFPM was simplified for the analytical model and analysis regions were defined to apply the subdomain method. Subsequently, a general solution was derived for the governing equations of each analysis r...

This paper presents an analysis of the operating principle of magnetic geared permanent magnet machines (MGPMMs), electromagnetic analysis results according to the winding pattern, and a method for improving power factor and loss characteristics. To improve electromagnetic performance, the air gap magnetic flux density was calculated using the fini...

In this paper, a method for calculating the cogging torque and air-gap flux density of a surface-mounted permanent magnet machine (SPMSM) is studied. First, a simplified model of the SPMSM is presented for electromagnetic analysis, and the magnetic vector potential is derived using the governing equations based on Maxwell’s equations in a two-dimen...

This paper presents both analytical calculations and empirical measurements of the magnetic force between the permanent magnet (PM) and rotor yoke in a large-scale permanent magnet synchronous generator (PMSG). The assembly of PMs in large-scale PMSGs is particularly challenging owing to the substantial magnetic forces involved. Therefore, accurate...

This paper presents a method for deriving the inductance of an interior permanent-magnet synchronous motor (IPMSM) by considering magnetic saturation. To obtain accurate inductance values during the motor characteristic analysis, it is necessary to consider the influence of core saturation on the magnetic flux changes. First, two distinct inductanc...

In this article, an exact analytical model for predicting irreversible demagnetization in Permanent Magnet Synchronous Machines (PMSMs) under overload and high-temperature conditions is presented. The proposed model includes a nonlinear model combined with a process for determining demagnetization. First, the nonlinear model considers non-uniform m...

This paper presents the electromagnetic analysis and experimental verification of PMSM considering axial flux leakage and end-winding leakage inductance based on the subdomain method. To consider the axial leakage flux, an analytical solution is derived by applying the corrected relative permeability to the slot and slot opening of the simplified a...

This study presents an approach for calculating the stress and deformation increase in the modulation of magnetically geared machines using a mathematical method. An analytical method is employed to obtain the magnetic force density acting on the modulation components. Afterward, the proposed mathematical method predicts the mechanical characterist...

In this study, electromagnetic noise sources of permanent magnet synchronous motors with 8-pole 9-slot and 12-slot fractional slot concentrated windings were analyzed through finite element analysis, and the radiated noise/vibration levels were compared through structural-acoustic analysis. In addition, the stability of the rotational shaft generat...

Although the finite element method (FEM) is highly reliable, it is time-consuming and expensive, for example, substantial computing costs are incurred for coupled analysis while considering the mechanical and electromagnetic properties. Therefore, in this paper, a high-speed permanent magnet generator's electromagnetic and stress characteristics ha...

This study investigates and quantifies the electromagnetic effects of vibration and noise in high-speed, permanent magnet motors. In particular, the effects of carrier harmonics generated in the electromagnetic excitation source by the pulse width modulation method are derived based on dynamic simulations. Noise, vibration, and harshness responses...

This study presents an approach to calculating the temperature increase in the internal components of permanent magnet synchronous machines by applying lumped-parameter thermal networks and analytical methods. Accordingly, the thermal equivalent circuit method is employed to obtain the temperatures of the machine’s internal components. Furthermore,...

A surface-mounted permanent magnet synchronous motor (SPMSM) is an electric motor with a simple magnetic circuit design, fast responsiveness, linear torque–current characteristics, speed–voltage characteristics, and constant operating speed. SPMSMs use only magnetic torque; however, interior PMSMs (IPMSMs) have high power densities because they can...

This paper presents the magnetic flux density and torque calculation of coaxial magnetic gear. We obtained analytical magnetic field solutions produced by permanent magnets based on subdomain method and super position method. Then, the analytical solutions for torque characteristics were obtained. All analytical results were validated with two-dime...

This paper presents a characteristic analysis and experimental verification for predicting the electromagnetic losses in high-speed permanent magnet synchronous motors. To predict the operating characteristics (such as speed and input current), dynamic modeling is conducted that combines models for the space vector pulse width modulation (SVPWM) in...

In this paper, an analysis of electromagnetic–mechanical characteristics according to the shaft materials of a permanent magnet synchronous motor was performed. In general, the shaft of an electric motor rotating at high speed uses various materials, considering the mechanical rigidity and electromagnetic characteristics. However, because the mater...

Permanent magnet synchronous machines (PMSMs) with an overhang structure can increase power density by compensating for the increased magnetic energy of permanent magnets. To analyze the overhang structure, a three-dimensional (3D) analysis of PMSMs is essential. However, 3D analysis takes a long time and the modeling process is complicated in the...

In contrast to internal combustion engine vehicles, electric vehicles (EVs) obtain the power required for the compressor of air conditioning system from an electric source. Therefore, an optimal design for electric motor, the main component of an electric compressor, is essential for improving EV mileage. A multi-objective optimal design is require...

This paper is about the magnetic field analysis of an interior permanent magnet motor (IPM motor) by using the equivalent magnetic circuit method (EMC method), which requires a small amount of computation time compared with the finite element method (FEM). IPM motors have a specific shape of rotor in which the permanent magnets are embedded. Theref...

In this study, to analyze the effects of electromagnetic factors that are affected by the eccentricity on vibration, an overall structural model of a motor was constructed, including the stator core, rotor structure, and the other parts. Thereafter, a mode analysis was performed to verify the dynamic stiffness of the constructed model using the fin...

This study analyzed, the performance characteristics of a rotor conductor with respect to changes in the material composition. Because of the low price and high productivity of aluminum (Al) rotors, they have been used in induction motors for general applications. The Al rotor has a limitation in that the size must be increased to improve efficienc...

This study deals with the characteristic analysis of a permanent magnet synchronous generator (PMSG) with a bolting and an overhang structure. Bolting is applied to a PMSG to prevent the defects caused by scattering. To compensate the flux reduction caused by the end effect and bolting material, an overhang structure is used for the permanent magne...

In this paper, the optimal design of a brushless direct current motor with a three-dimensional (3D) structure using the response surface methodology (RSM) is presented. There were two optimization goals: reduction of the cogging torque and maintenance of the back electromotive force to prevent performance degradation. For motors with a 3D structure...

In this study, the characteristic analysis of a permanent magnet synchronous generator was performed using the analytical method, and the validity of the analytical method was compared with that of the finite element method (FEM). For the initial design, the rotor size was selected using the torque per rotor volume method, and the stator size was s...

Linear oscillating machines are electric devices that reciprocate at a specific frequency and at a specific stroke. Because of their linear motion, they are used in special applications, such as refrigerators for home appliances and medical devices. In this paper, the structure and electromagnetic characteristics of these linear oscillating machine...

In this study, we performed the electromagnetic and mechanical characteristic analyses of an 8-pole 12-slot interior permanent magnet synchronous motor (IPMSM). Permanent magnet synchronous motors are classified into surface permanent magnet synchronous motor and interior permanent magnet synchronous motors according to the type of rotor. The IPM t...

This paper presents an electromagnetic analysis and experimental verification to optimize the noise, vibration, and harshness (NVH) characteristics of a permanent magnet synchronous generator (PMSG) for wave energy converters (WECs). WECs applicable to breakwater installed in island areas require a wider operating range and a robust design for main...

In general, high-speed machines should be designed with high efficiency electromagnetic and mechanical characteristics. It is important to analyze the electromagnetic loss for a design with high efficiency. In this study, the effects of the magneto–motive force and time harmonics of the stator current according to the winding distribution of a high...

In this study, a magnetic field is analyzed using an analytical method and compared with the electromagnetic characteristics of 8-pole 9-slot and 8-pole 12-slot permanent magnet synchronous machines considering rotor eccentricity. The magnetic flux density and back electromotive force (EMF) are derived using perturbation theory and electromagnetic...

In general, high-speed machines should be designed to satisfy electromagnetic and mechanical characteristics. In this study, the design of high-speed permanent magnet synchronous generator with two different shaft materials considering overhang effect and mechanical characteristics was performed. It was confirmed that the leakage magnetic flux gene...

This study deals with the analysis of electro-mechanical characteristic analysis on permanent magnet synchronous machines (PMSMs) for electrically driven tools primarily used in industrial applications. This study compares the noise, vibration and harshness(NVH) characteristic results generated by fractional pole/slot combinations. The electromagne...

Field-oriented control of permanent magnet synchronous machines, used in high-precision control applications, suffers from significant problems due to the delay effect of the filter. To address these problems, this study focuses on the analysis, design, and realization of various analog and digital filters. Based on the analysis results, it is math...

Permanent magnet (PM) type linear oscillating actuators (LOAs) are used in various types of equipment owing to their high efficiency, thrust density, and good control performance. However, the disadvantage of the LOA is the side force inevitably generated by the magnetic coupling structure of the stator and the PM mover. Therefore, side force reduc...

In this study, analysis of core-loss occurring in the magnetic flux modulation core of a linear magnetic gear and the core of each mover is presented, using an analytical method. Losses in electric machines were generally calculated and analyzed using the finite element method (FEM). However, in the case of core-loss, the exact loss value could not...

In this study, the iron losses of high flux density concentrated winding-type interior permanent magnet synchronous motors for three different magnet shapes (single-V, single-flat, and dual-delta) and rotor structures are analyzed and compared. Iron loss is analyzed using the classical Steinmetz equation (CSE) based on the frequency separation appr...

This study presents detailed analytical modeling for electromagnetic performance analysis of actively shielded superconducting machines with air-cored slotless armatures. An actively shielded superconducting machine is composed of a type of nonmagnetic material to prevent saturation of the magnetic flux path, as the field coil has a high magnetic f...

This paper presents the design for a high-speed permanent magnet synchronous machine (PMSMs) considering the demagnetization and mechanical characteristics of rare-earth magnets based on the operating temperature. The TRV equation and plane stress analytical method are considered for the temperature, the rotor size is derived from the analysis resu...

This study presents an optimal double-pole magnetization brushless DC (BLDC) motor design, compared to a single-pole magnetization BLDC motor in terms of electromagnetic performance. Initially, a double-pole model is selected based on the permanent magnet (PM) of the single-pole model. The pole separation space, which is generated in the magnetizat...

This study deals with the noise, vibration, and harshness (NVH) characteristic analysis of permanent magnet synchronous motors (PMSMs) for electrical machines, such as electrically driven tools that are used in industries. An improved NVH design is needed for application to industrial tools. In general, the electromagnetic NVH characteristics of PM...

In this study, we performed an electromagnetic characteristic analysis of a permanent magnet synchronous machine considering the current waveform based on static rotor eccentricity. First, the characteristics of the back electromotive force were analyzed through the no-load analysis of the analysis model according to static rotor eccentricity. Next...

In general, permanent magnet (PM) motors are driven by a pulse width modulation (PWM) voltage source inverter for vector control. The generated PWM signals cause high-frequency voltage components at the carrier frequency. Such components can increase the electromagnetic losses, thereby necessitating the consideration of the phase current correspond...

This study analyzes and verifies the electromagnetic performance and thrust characteristics of linear magnetic gears using subdomain-based analytical methods. By simplifying the analytical model, the governing equations of each domain are calculated based on the Maxwell equation. In addition, the undetermined coefficients of the governing equations...

This paper proposes an improved analytical approach to the electromagnetic performance of a linear oscillatory actuator, considering the end and stacking effects of the outer and inner cores. A simplified analytical model is defined with several assumptions taking into account the end effect of the outer and inner core in the z-axis direction. Maxw...

This paper presents an evaluation system to experimentally verify the performance of a double-sided linear permanent magnet synchronous generator (PMSG) prototype. In general, research on wave power generation systems has concentrated on the optimum design technology of PMSGs, power generation performance analysis technology, loss analysis, and per...

This study proposes a semi three-dimensional analysis method for a permanent magnet linear device with a radially laminated structure. After the magnetic flux density was calculated using two-dimensional finite element (FE) analysis, the magnetic flux density in the iron core was estimated by considering the volume of the divided core. Finally, a c...

This study investigates the design and characterization of a permanent magnet torque motor with a limited operating range. The design method and configuration that satisfy the range and torque at a specific applied current were determined. The motor was designed and analyzed through finite element analysis. This motor was then fabricated, and an ex...

In this work, the design and experimental analysis of a high-speed permanent magnet (PM) synchronous generator (PMSG) with a magnetic bearing without mechanical friction were per-formed. The rotor size was derived using the torque per rotor volume method and an analytical method. Rotor structure analysis was performed to verify the validity of the...