https://doi.org/10.5370/KIEE.2025.74.3.377

최윤성(Yoon-Seong Choi) ; 이동호(Dongho Lee)

The integration of inverter-based renewable energy sources in power systems affects frequency stability and oscillation characteristics, posing challenges to system reliability. Complex interactions between generators' dynamic behaviors and transient electrical flows complicate oscillation detection. This study reviews oscillation theories, such as the spring-mass system and radio frequency oscillation, which help explain oscillation mechanisms but are limited in detecting power system oscillations. To address this, the study applies Prony analysis, which models time-series data as a sum of exponential functions, and compares it with RMS Energy Filtering. The proposed algorithm, combining these methods, is tested on real power system data from the U.S., successfully detecting primary oscillation modes and damping characteristics. The results highlight the method’s accuracy in identifying critical oscillation frequencies and the importance of selecting an appropriate order in Prony analysis to prevent overfitting or underfitting.

https://doi.org/10.5370/KIEE.2025.74.3.385

이학주(Hak-Ju Lee) ; 황성욱(Sung-Wook Hwang) ; 전용주(Yong-Joo Jeon) ; 최윤혁(Yun-Hyuk Choi)

As global energy conversion policies expand, the importance of distribution systems is also greatly increasing. An efficient power flow analysis method is needed to ensure stable power grid operation through large-scale integration of distributed generation and to improve the accuracy of hosting capacity calculations. Therefore, the hosting capacity estimation algorithm is implemented using network topology method. This is applied to all distribution lines within the substation connected to the Ulsan National Industrial Complex to calculate hosting capacity and use it for distribution network planning.

https://doi.org/10.5370/KIEE.2025.74.3.392

김현진(Hyeon-Jin Kim) ; 김치연(Chi-Yeon Kim) ; 윤아윤(Ah-Yun Yoon) ; 김영진(Young-Jin Kim) ; 허재행(Jae-Haeng Heo)

With climate change mitigation and carbon neutrality becoming global policy priorities, expanding renewable energy is a critical challenge. However, the conventional centralized power system faces significant limitations, including power losses from long-distance transmission, public opposition near generation and transmission facilities, and the intermittency and unpredictability of renewable energy sources. To address these challenges, the Korean government enacted the Distributed Energy Activation Special Act in June 2024, aiming to foster a transition towards a distributed energy system centered on renewable energy. Despite this legislative initiative, the lack of standardized procedures for selecting candidate sites for distributed energy-specialized regions has impeded systematic implementation. This study proposes an eight-step selection process to identify candidate sites for distributed energy-specialized regions and validates its applicability through a case study in Pohang. The framework evaluates regional energy demand and self-reliance potential while suggesting tailored distributed energy business models that address local characteristics. By providing a structured and replicable methodology, this study supports the realization of national energy self-reliance goals and the establishment of sustainable distributed energy systems, offering actionable strategies and guidelines for widespread adoption across diverse regions.

https://doi.org/10.5370/KIEE.2025.74.3.404

강상욱(Sang-Wook Kang) ; 차동철(Dong-Cheol Cha) ; 변성현(Sung-Hyun Byun) ; 최홍석(Hong-Seok Choi)

To prevent large-area blackouts due to excessive frequency drop, Under-Frequency Relay (UFR) is employed to automatically disconnect loads. Recent changes in the characteristics of the power grid, such as variations in power consumption patterns and increases in pv generation- can lead to increased deviations in the amount of load shedding, potentially affecting the reliability of UFR operation. To address this issue, it is necessary to analyze the adequacy of the load shedding quantities at each UFR stage and develop an operational system for UFRs that ensures frequency stability and optimal load shedding through frequency simulations.

https://doi.org/10.5370/KIEE.2025.74.3.411

이경민(Kyung-Min Lee) ; 박철원(Chul-Won Park)

When a motor fault happens, the life and productivity of motor are reduced, and enormous recovery time and cost occur, so a protection plan must be established. Recently, the concept of predictive maintenance based on the prognosis according to the facility status has been attracting attention. In this paper, as part of the project to develop AI-based predictive maintenance technology for MCC's smart EOCR, state determination method using data mining is proposed. First, the data is collected from an electric motor system using an actual pump system, and then the training data and test data sets that can determine various states are configured. Among data mining technique, the state determination method is designed using the SVM model and the LSTM model, and implemented using the Python language. Finally, the performance of the two proposed data mining models are compared through evaluation metrics such as Precision, Recall, and F1_Score, etc.

https://doi.org/10.5370/KIEE.2025.74.3.417

이정범(Jeong-Beom Lee) ; 김지형(Ji-Hyoung Kim) ; 김규태(Kyu-Tae Kim) ; 최은호(Eun-Ho Choi) ; 강동주(Dong-Joo Kang)

This study presents the development of a day-ahead curtailment prediction model for the newly introduced Jeju electricity market in 2024. Using NWP (Numerical Weather Prediction) data, electricity demand and renewable energy supply were predicted. Then, based on the predicted demand and supply data, the initial curtailment was predicted using PCA (Principal Component Analysis) and MLR (Multiple Linear Regression) models. The final curtailment was then predicted using the XGBoost model. The developed model, DR-XGB (Dimension Reduction XGBoost), showed a prediction performance with an R2 of 0.41 and an RMSE of 11.0MWh, outperforming other models. Because the DR-XGB model was developed based on NWP data, it can be utilized in the future land power market. Furthermore, it is distinct from other studies because it used data from the actual electricity market. The day-ahead curtailment prediction model is expected to contribute to establishing day-ahead plans for market participants in the electricity market.

https://doi.org/10.5370/KIEE.2025.74.3.425

최재승(Jaesung Choi) ; 최길수(Gilsu Choi)

This paper examines the iron loss characteristics of a permanent magnet-assisted synchronous reluctance machine (PMa-SynRM) and a fluid-shape synchronous reluctance machine (FS-SynRM) for micro EV applications, emphasizing the impact of DC bias fields and minor loops on iron loss estimation. Iron losses are comparatively evaluated using three methods: the Steinmetz method with constant coefficients, the loss separation method with varying coefficients and FFT, and the hysteresis-based model that accounts for minor loops and DC bias fields. The results show that iron losses per unit stack length are higher in the PMa-SynRM, where the effects of DC bias fields and minor loops are more pronounced. Moreover, the Steinmetz and loss separation methods, which neglect these effects, overestimate motor efficiency by up to 1.5% and 0.3%, respectively. This study highlights the importance of incorporating DC bias and minor loops in iron loss and efficiency calculations for micro EV traction machines.

https://doi.org/10.5370/KIEE.2025.74.3.432

홍도관(Do-Kwan Hong) ; 이재길(Jae-Gil Lee) ; 정연호(Yeon-Ho Jeong) ; 김광덕(Kwang-Deok Kim) ; 박일환(Il-Hwan Park)

This study presents a design and analysis of 00kW AFPM (Axial Flux Permanent Magnet) motor for a direct-drive electric propulsion system of an underwater vehicle. In order to secure redundancy in a fault situation, the combination of the number of pole and slots that can be implemented in 3-phase/6-phase was selected. Then the electromagnetic performance according to the outer diameter of the motor and the battery voltage, various electrical steel properties (isotropic, anisotropic, cobalt steel), and the application of Halbach array of permanent magnets were compared and analyzed through 3-D electromagnetic analysis. Consequently, the design combination of outer diameter, electrical steel, and Halbach array with the high performances satisfying the required conditions was adopted. Finally, the characteristic variations according to the overhang of the permanent magnets and rotor core in radial direction were presented.

https://doi.org/10.5370/KIEE.2025.74.3.440

박광우(Kwang-Woo Park) ; 정태욱(Tae-Uk Jung)

SPMSM is used as an actuator that drives each system of automobiles according to the trend of automobile electrical equipment. When designing an automobile, it is required to reduce the vibration and noise of the SPMSM according to the miniaturization of an actuator and the need for motor control and quietness to reduce fuel efficiency. Cogging torque has a great influence on the noise and vibration generation of the motor, so it should be reduced as much as possible during design. Several studies have been conducted to reduce the cogging torque of SPMSM, but a comparative analysis of a method of minimizing cogging torque by designing a stator shape having an auxiliary pole is not widely known. Therefore, in this paper, a method that can effectively reduce the cogging torque of SPMSM using auxiliary poles was designed through finite element analysis, electrical characteristics were analyzed through finite element analysis for basic models without auxiliary poles and models with auxiliary poles. For the optimal design of motors with auxiliary poles, the main design factors of stators and rotors were derived to obtain the optimal design shape that meets the design goals using the reaction surface method.

https://doi.org/10.5370/KIEE.2025.74.3.447

김한빛(Han-Vit Kim) ; 이준희(June-Hee Lee) ; 김도현(Do-Hyeon Kim) ; 이준석(June-Seok Lee)

This paper proposes a flux-weakening control methods using the feed-forward compensation of a wound field synchronous motor (WFSM). Typically, in the high-speed region, the voltage applied to the motor is limited by the maximum output of the inverter and Proportional-Integral (PI) controller is used to maintain this constant voltage. However, as the speed increases, the control performance deteriorates when the bandwidth of the controller is small. Therefore, this paper applies a feed-forward compensation method to improve controller performance during high-speed operation. Due to the control characteristics of WFSM, the feed-forward compensation components can be mathematically derived into d-axis current compensation and field current compensation, depending on the two flux-weakening methods. As a result, the proposed methods can use a small bandwidth that is robust to noise and enhances control stability. The validity of the proposed method is verified by experimental results.

https://doi.org/10.5370/KIEE.2025.74.3.455

홍창완(Chang-Wan Hong) ; 오귀운(Gwi-Un Oh) ; 김승택(Seung-Taik Kim) ; 윤인식(In-Sik Yoon) ; 고종선(Jong-Sun Ko)

In this paper, a torque feed-forward compensation method with discrete flux observer is proposed for voltage per frequency (V/f) control of induction motors. Induction motors are widely used in various industries such as large pumps and water supply systems due to their simple structure and low cost. V/f control is one of the driving methods for induction motors, offering the advantage of simple implementation. However, it has the drawback that slip causes a difference between the commanded speed and the rotor speed when the load changes. Therefore, this paper proposes a method to compensate the torque with the load in a feed-forward manner through a discrete flux observer. This method can quickly respond to load fluctuations during operation and improve the speed control performance of the motor. The control method proposed in this paper shows better speed control performance than the conventional V/f control through simulation using MATLAB/Simulink and experiments.

https://doi.org/10.5370/KIEE.2025.74.3.468

권경현(Gyeonghyun Kwon) ; 이동인(Dongin Lee) ; 정성욱(Seongwook Jeong) ; 정연호(Yeonho Jeong) ; 윤한신(Hanshin Youn)

This paper proposes an Active-Clamp Forward-Flyback (ACFF) converter with three planar transformers to achieve 4 kW output power. As autonomous driving technology rapidly advances, the demand for higher output power from low-voltage DC-DC converters (LDC) in electric vehicles has significantly increased. Conventionally, two 2 kW ACFF converters with four magnetic cores connected in series-parallel have been used to meet 4 kW power requirement, but this configuration has proven inefficient in terms of size, power density, and cost. The proposed converter improves power density by integrating the four magnetic cores of the conventional 4 kW ACFF converter into three, reducing the overall magnetic volume and allowing for a more compact design. Furthermore, the use of planar magnetic components enables the winding to be embedded in a 4-layer PCB.

https://doi.org/10.5370/KIEE.2025.74.3.477

장민우(Min-U Jang) ; 차주홍(Ju-Hong Cha) ; 이호준(Ho-Jun Leeark)

The SiO2 films are widely used as sidewall spacers and insulating liners in microelectronic devices. One of the main challenges in depositing thin SiO2 films is precisely tuning their mechanical, optical, and electrical properties. Additionally, the films must be deposited in high aspect ratio structures for various applications. The properties of these films are determined by active species such as ions and radicals, as well as clusters formed by collisions between electrons and gaseous under certain conditions. To enhance the efficiency of thin film deposition and improve process control, we investigated plasma properties at different gas mixture ratios and pressures through two-dimensional fluid simulations of capacitively coupled Ar/O2 discharges. This study confirmed that as the mole fraction of O2 increases, the density of O2 + and O+ increases, which in turn increases the recombination reaction with O- . This provided insight into the behavior of each ion and radical.

https://doi.org/10.5370/KIEE.2025.74.3.484

장승완(Seungwan Jang) ; 윤희철(Heechul Yoon)

Ultrasound stimulation for the treatment of osteoarthritis has proven to alleviate patient pain and has shown the potential for cartilage cell regeneration. To improve the treatment efficacy and ultrasound focusing, the use of larger aperture and higher frequency signals is desired, but it could result in grating lobe artifacts. To resolve this challenge, this study proposes a new ultrasound stimulation technique that modulates the frequency during transmission to dynamically shift the temporal and spatial position of the grating lobes. The proposed method disperses the angle of the grating lobes over time by continuously modulating the frequency within a specific frequency range, including both linear and nonlinear modulations. To validate our approach, we produced 3-D acoustic beam fields under beam steering conditions. A transmit pulse with a single frequency at 2 MHz was compared to linear and nonlinear frequency-modulated pulses with a frequency ranging from 1-to-3 MHz. Additionally, we modeled a 64-channel 8x8 2-D array with a center frequency of 2 MHz and a 60% fractional bandwidth using MATLAB and Field II programs. For quantitative evaluation, we estimated the beam width at 3 dB and the intensity variation between the main and ? grating lobes, and the peak intensity at the focus. Overall, we found that the grating lobe decreased by up to 9.83 dB in our ? configurations and demonstrated that frequency modulation-based ultrasound stimulation shows the potential for reducing grating lobe, which is expected to be applicable to improve the safety and performance of osteoarthritis treatment.

https://doi.org/10.5370/KIEE.2025.74.3.491

황동윤(Dong-Yun Hwang) ; 서경욱(Kyeong-Wook Seo) ; 이민호(Min-Ho Lee) ; 김용훈(Yong-Hun Kim) ; 송진우(Jin-Woo Song)

In this paper, we propose an algorithm that equips a drone with a monocular camera and a laser range finder to derive position measurements for smooth mission execution and return to the home position, even in situations where GNSS is not available. This algorithm stores images and create an orthoimage when GNSS is available, and from the time the GNSS signal is lost, it matches the current image with the database image based on image feature point matching to determine the drone's current location and to employ return to home mission. We validated the algorithm with data acquired from actual drone flights and confirmed that the proposed algorithm could be used practically and effectively with sufficient accuracy for return to home mission.

https://doi.org/10.5370/KIEE.2025.74.3.500

임채영(Chae-Young Lim) ; 여채은(Chae-Eun Yeo) ; 김경호(Kyung-Ho Kim)

In smart factory manufacturing processes, irregular and uncertain environmental factors can lead to unexpected equipment failures or abnormal operations, resulting in product defects, safety incidents, and energy waste, which ultimately reduce productivity. To prevent these issues and ensure stable equipment operation, it is essential to accurately predict not only equipment failures but also energy consumption. Maximizing energy efficiency requires a predictive model that comprehensively considers both equipment status and energy usage patterns. This study proposes a machine learning-based flow pattern prediction model using power data from smart factory manufacturing processes. The model utilizes Multi-Layer Perceptron (MLP), Convolutional Neural Network (CNN), and Long Short-Term Memory (LSTM) algorithms to predict equipment power consumption and flow patterns. By applying these prediction models to a digital twin framework, the study demonstrates the potential to optimize energy consumption.

https://doi.org/10.5370/KIEE.2025.74.3.506

곽성우(Seong Woo Kwak) ; 양정민(Jung-Min Yang)

The paper proposes a novel checkpoint management method for a real-time system with a quintuple modular redundancy (QMR) structure wherein multiple fault detections are performed between checkpoints. If the detected faults can be overcome within the context of the QMR structure, they are recovered by simply synchronizing the state values. Otherwise, the system rollbacks to the most recent checkpoint and re-executes the task to recover from the faults. The real-time system having the QMR structure and incorporating the proposed checkpoint scheme is modeled by a Markov chain. Based on the Markov chain model, a probability equation is derived to calculate the likelihood of completing the real-time task within the deadline. The optimal number of checkpoints and fault detections maximizing the probability value are also determined. Numerical experiments are conducted to illustrate the optimization procedure of the real-time system with a QMR structure using the proposed checkpoint management method.

https://doi.org/10.5370/KIEE.2025.74.3.516

김유민(Yu-Min Kim) ; 이재복(Jae-Bok Lee) ; 이경주(Kyoung-Joo Lee) ; 최승규(Seung-Kyu Choi) ; 곽지혜(Ji-Hye Kwak) ; 정현학(Hyun-Hak Jung) ; 김명진(Myungchin Kim) ; 강성만(Sung-Man Kang)

This study aimed to evaluate the electrical performance of a M.V.(Micro Varistor) based FGM(Field Grading Material) to maximize the field-relaxation effect in HVDC(High Voltage Direct Current) systems. The research applied the in house developed FGM to a 525 kV class HVDC cable joint and conducted electromagnetic field analysis under S/IMP(Superimposed Impulse) and LC(Load Cycle) test conditions. As a result, in the joint model with FGM, the maximum electric field under S/IMP conditions significantly decreased from approximately 36.3 /mm to 17.8 /mm, confirming its effective mitigation of voltage concentration. Although a ㎸ ㎸ slight increase in maximum electric field was observed under LC conditions due to FGM application, the field relaxation effect under S/IMP conditions was predominant, resulting in a substantial improvement in overall insulation stability. These findings provide a technical foundation for enhancing the long term insulation performance and reliability of HVDC systems, suggesting the practical applicability of FGM based insulation technology in high voltage environments within future HVDC power grids.

https://doi.org/10.5370/KIEE.2025.74.3.523

김명현(Myong-Hyon Kim) ; 김진석(Jin-Seok Kim)

In this paper, we identified a problem in which distance relays did not operate properly near the boundary of the protection zone due to the impedance of the SFCL(superconducting fault current limiter) when a fault occurred in a transmission line. As a solution to this problem, we proposed a composite relaying method that utilizes the operation status of the superconducting fault current limiter. The operation of the superconducting fault current limiter means a fault, it was judged that a relaying method utilizing the operation of the superconducting current limiter would be appropriate. In addition, a method considering fault current was proposed to increase the reliability of the proposed method due to the failure of the SFCL itself. As a result of performing fault detection using the proposed method, it was shown that effective fault detection was possible based on the operation of the superconducting current limiter even when the under reach occurred near the boundary of the protection zone of the distance.

https://doi.org/10.5370/KIEE.2025.74.3.529

서재필(Jae-Pil Seo) ; 이동호(Dongho Lee) ; 이재형(Jaehyeong Lee)

In power systems with a high share of renewable energy, the reduced number of synchronous generators in operation leads to weakened system strength. This lack of robustness causes challenges in frequency stability analysis simulations, as voltage instability often occurs before frequency dynamics can be adequately analyzed. This paper proposes an equivalent model for frequency stability assessment in power systems with high renewable energy penetration. The model enables frequency analysis independently of system strength. By aggregating multiple synchronous generators while preserving frequency response characteristics and reducing the system to minimize localized voltage instability issues, the proposed approach ensures accurate frequency analysis. The validity of the proposed model is verified using the Modified IEEE 39-bus system.