https://doi.org/10.5370/KIEE.2025.74.2.221

이동현(Donghyun Lee) ; 전승찬(Seungchan Jeon) ; 이창희(Changhee Lee) ; 황순규(Sungyu Hwang) ; 배성우(Sungwoo Bae) ; 김시환(Sihwan Kim) ; 곽주식(Joosik Kwak)

This paper proposes an algorithm for determining the optimal location and sizing of a battery energy storage system (BESS) to enhance the grid hosting capacity when integrating renewable energy sources. The proposed algorithm optimizes the BESS by considering both active power absorption and reactive power supply functions, utilizing the particle swarm optimization (PSO) algorithm. By incorporating voltage sensitivity analysis, the computation time and convergence to the optimal solution of the PSO were improved. To validate the effectiveness of the proposed method, simulations were conducted based on the IEEE 300-Bus system. The P-V curve analysis indicated that the integration of BESS led to a 50.8% increase in grid capacity for renewable energy sources. Furthermore, compared to conventional methods that considered only active power, the proposed approach achieved a 9.8% increase in grid capacity.

https://doi.org/10.5370/KIEE.2025.74.2.229

송성윤(Sungyoon Song)

In this paper, an equivalent controller concept has been proposed to observe various future grid scenarios under the PSS/e dynamic simulation. The equivalent controller has been proposed to efficiently manage transient simulations with a large-scale power system planning database. Note that the sizes of renewable power plants and high-voltage direct current systems have grown to the point where their effects on the power system can no longer be neglected. To address these issues, it is imperative to create several future grid databases to ensure a stable and reliable power grid. The objective is to maximize stable dynamic simulation runs while minimizing the computing requirements. The proposed controller can be used to roughly observe stability trends. This method can efficiently manage dynamic simulations and provides a simple and fast simulation without requiring all the control blocks from manufacturers.

https://doi.org/10.5370/KIEE.2025.74.2.238

최진호(Jin-Ho Choi) ; 정재엽(Jaeyeop Jung) ; 문승일(Seung-Il Moon) ; 이규섭(Gyu-Sub Lee)

As interest in renewable energy grows due to the climate crisis, large-scale offshore wind farms are emerging as a key solution for achieving carbon neutrality. These farms can overcome the spatial and noise limitations of onshore wind; however, their intermittent nature and integration into high-voltage grids pose challenges to grid stability due to power output fluctuations. Therefore, an analysis is required for the grid connection of offshore wind farms. This paper examines reactive power compensation in accordance with the technical standards for the grid integration of offshore wind farms and calculates the required capacities for reactors and STATCOM based on the reactive power compensation strategy. Using PSS/E simulations, an offshore wind farm model was developed, and the necessary reactive power compensation was calculated.

https://doi.org/10.5370/KIEE.2025.74.2.244

주해민(Hae-Min Ju) ; 문승일(Seung-Il Moon) ; 이규섭(Gyu-Sub Lee)

This paper focuses on the analysis of frequency-dependent characteristics in transmission lines and their impact on harmonic impedance. Transmission line modeling is conducted in the time domain, incorporating existing frequency-dependent parameters, to evaluate the minimum requirements for accurate harmonic impedance modeling. The results show that these frequency-dependent characteristics significantly influence both the resonance frequency and magnitude of harmonic impedance. Furthermore, it is observed that sufficient approximation can be achieved even when the effects of ground return are disregarded.

https://doi.org/10.5370/KIEE.2025.74.2.251

박종일(Jong-Il Park) ; 박창현(Chang-Hyun Park)

This paper presents a method for estimating the equivalent model of harmonic sources using the Extended Kalman Filter(EKF) and the prediction deviation. The parameters of the equivalent model are difficult to measure directly, so they are generally estimated using data measured in the power system and numerical analysis. However, existing methods based on numerical analysis have a fundamental problem that including outliers in measured data significantly degrades the estimation performance. Additionally, the measured data before changing the equivalent model parameters can slow down the convergence speed of the estimation. To solve this problem, this paper proposed an equivalent model estimation method using the EKF and the prediction deviation. The EKF algorithm reduces outliers included in the measured voltage and current and the RLS algorithm is initialized by calculating the prediction deviation. To verify the performance of the proposed method, a comparative analysis with the previous method was conducted for the case where random data outliers were included.

https://doi.org/10.5370/KIEE.2025.74.2.258

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

Recently, as inverter-based VREs are connected to the power grid, fault phenomena different from those of conventional synchronous generator-based power grids are appearing. This paper was conducted as a preliminary step in the development of an improved protective relaying algorithm that can prevent malfunctions in transformer systems. First, we describe the RDR based on the second harmonic using FFT, and the transformer protection technique based on DWT. We model a 345/161/23kV, 600MVA three-winding power transformer system using real system data. After reviewing the accuracy of the result of the steady-state simulation, we analyze the transients of magnetizing inrush, winding ground fault, and winding short-circuit fault. Finally, we simulate and implement the RDR protection technique with second-harmonic restraint using FFT of PSCAD library in EMT tools, and the protection of power transformer using DWT of EMT library and verify its performance.

https://doi.org/10.5370/KIEE.2025.74.2.266

권용준(Yong-Jun Kwon) ; 최대선(Dae-Sun Choi) ; 왕창현(Chang-Hyeon Wang) ; 오호진(Ho-Jin Oh) ; 윤한준(Han-Joon Yoon) ; 정상용(Sang-Yong Jung)

Interior Permanent Magnet Synchronous Machines (IPMSMs) are widely used not only as drive motors for Electric Vehicles (EVs) but also in various industrial fields due to their high efficiency and high power output characteristics. However, because of the embedded magnets, IPMSMs exhibit significant torque ripple during operation, necessitating the use of optimization algorithms to address this issue. For IPMSMs, which have a large number of design variables, the feasible design space is defined by multiple constraints, increasing the complexity of the design optimization process. Therefore, this paper proposes a Random Forest-based Modified PSO-GA hybrid method to perform optimization in the presence of multiple constraints and applies it to the torque and torque ripple improvement design of a Double V-Type IPMSM.

https://doi.org/10.5370/KIEE.2025.74.2.273

최의진(Eui-Jin Choi) ; 한지훈(Ji-Hoon Han) ; 송승민(Seung-Min Song) ; 박종훈(Jong-Hoon Park) ; 홍선기(Sun-Ki Hong)

In the field, unsupervised learning-based fault diagnosis is necessary due to the lack of fault data. However, conventional auto-encoder models face challenges in fault classification. To address this issue, this study proposes an unsupervised learning-based auto-encoder model enhanced with an ensemble approach. The proposed model performs fault classification using gear, bearing, and eccentricity fault data, and employs the Layer-wise Relevance Propagation (LRP) technique to improve fault classification. Through the LRP technique, the key frequency bands relevant to each fault are identified and incorporated into the learning process, allowing for frequency band-based training. As a result, the proposed auto-encoder model improves classification performance and effectively distinguishes between different types of faults.

https://doi.org/10.5370/KIEE.2025.74.2.280

양준원(Jun-Won Yang) ; 김태성(Tae-Seong Kim) ; 김용주(Yong-Joo Kim) ; 이윤석(Yoon-Seok Lee) ; 신경훈(Kyung-Hun Shin) ; 최장영(Jang-Young Choi)

In this paper, an improved analytical method for axial flux permanent magnet machines considering leakage flux is presented. Based on the assumption that the magnetic vector potential in the r direction is uniform, the analytical model in the polar coordinate system is simplified from a three-dimensional model to a two-dimensional model dependent on z and θ. and the magnetic vector potential is then derived for analysis region. The electromagnetic characteristics of the analysis model are calculated using the derived magnetic vector potential. A magnetic equivalent circuit for calculating the leakage flux in the r-z plane is defined and the leakage coefficient is derived. The electromagnetic characteristics derived from the proposed analysis method are compared with the results from 3D finite element analysis to verify its validity.

https://doi.org/10.5370/KIEE.2025.74.2.287

이수진(Soo-Jin Lee) ; (Nguyen Manh Dung) ; 엄석현(Seok-Hyeon Eom) ; 김태성(Tae-Seong Kim) ; 김상협(Sang-Hyeop Kim) ; 김용주(Yong-Joo Kim) ; 신경훈(Kyung-Hun Shin) ; 최장영(Jang-Young Choi)

This paper compares inductance calculation methods for IPMSM (Interior Permanent Magnet Synchronous Machine) considering core non-linearity and analyzes electromagnetic performance based on different types of inductance. Inductance is classified into inductance based on matrix, obtained through d-q transformation, and incremental inductance, depending on the calculation method. The torque and output characteristics are analyzed accordingly. By applying motor operating limit conditions, torque and voltage results are compared at the point of maximum torque. The validity of the proposed inductance calculation method is verified by comparing results obtained through finite element analysis. In conclusion, an inductance calculation method that considers core non-linearity while offering superior control simplicity is proposed.

https://doi.org/10.5370/KIEE.2025.74.2.295

왕창현(Chang-Hyeon Wang) ; 김남호(Nam-Ho Kim) ; 최호용(Ho-Yong Choi) ; 정상용(Sang-Yong Jung)

The advancements in electrified drive systems have enabled the design of high-power density electric vehicle (EV) motors. However, the increased operating frequency necessary for achieving high-power density amplifies AC copper losses, primarily due to skin and proximity effects. This study focuses on reducing AC copper losses in an 8-pole, 48-slot Interior Permanent Magnet Synchronous Motor (IPMSM) using 2D finite element analysis (FEA). The analysis evaluates the contributions of skin and proximity effects to total copper losses and investigates the influence of slot leakage flux. Additionally, the impact of slot and conductor geometries on leakage flux, its variation over time, and the resulting AC copper losses were systematically analyzed. By balancing manufacturability and performance, optimal design parameters were derived to minimize AC copper losses. The results demonstrate that adjustments in slot width, slot depth, and conductor placement significantly affect leakage flux and copper losses. The proposed design strategies improve motor efficiency and thermal performance under high-speed operating conditions, contributing to the development of high-performance EV motors.

https://doi.org/10.5370/KIEE.2025.74.2.302

지태혁(Tae-Hyuk Ji) ; 송인석(In Seok Song) ; 김형우(Hyung-Woo Kim) ; 정상용(Sang-Yong Jung)

Surface-mounted permanent magnet synchronous motors (SPMSMs) are widely used in high-performance system. However, they suffer from torque ripple and cogging torque, which degrade output quality and cause noise and vibration, necessitating optimized design. While finite element analysis offers high accuracy for optimization, it comes with significant computational cost. To address this limitation, this paper proposes an attention mechanism-based convolutional neural network (CNN) regression model to predict SPMSM electromagnetic performance. CNNs capture spatial structures of motor designs, while attention mechanisms highlight key design features, boosting prediction accuracy and efficiency. This study analyzes the effects of attention mechanisms and proposes a CNN-based regression model incorporating them, confirming the effectiveness of the attention mechanism through comparisons with conventional CNN models.

https://doi.org/10.5370/KIEE.2025.74.2.310

김영현(Young-Hyun Kim) ; 이중호(Jung-Ho Lee)

This paper examines the demagnetization characteristics of rare earth permanent magnets (PMs) used in electric machinery. An analytical model was designed considering a controllable shape, temperature, and the external magnetic field in PMs used in the rotor of an interior permanent magnet synchronous motor (IPMSM) for driving an electric railway vehicle (ERV). The demagnetization process was analysed based on the magnetization and demagnetization theory for PM materials in computer simulation. The result of the analysis can be used to calculate the magnetization and demagnetization phenomenon according to the input B-H curves. So, this paper presents the conditions of demagnetization by the external magnetic field in the running and stopped states and proposes a simulation method that can analyse demagnetization phenomena according to each condition and be used to design the IPMSM that maximizes efficiency and torque characteristics. This was experimentally verified.

https://doi.org/10.5370/KIEE.2025.74.2.316

박하민(Ha-Min Park) ; 이형우(Hyung-Woo Lee) ; 박찬배(Chan-Bae Park) ; Youguang Guo(Youguang Guo) ; 이재범(Jae-Bum Lee)

As the number of electric vehicles grows, the development of fast chargers is advancing rapidly. A DC-DC converter that can deliver high output power, a fixed input voltage, and a wide output voltage range is critical for electric vehicle fast chargers. While the LLC resonant converter is commonly used in these converters, it requires a low magnetizing inductance, which increases the transformer air gap, causing additional AC losses in the windings due to the fringing effect. To mitigate these issues, this study explores design solutions in LLC resonant converters. By using two transformers per module, with the primary sides connected in series and the secondary sides in parallel, the number of primary turns can be reduced, minimizing the air gap. This reduction also allows for structural changes in the windings, improving heat dissipation. Magnetic field analysis and circuit simulations were conducted to validate the proposed DC-DC converter design.

https://doi.org/10.5370/KIEE.2025.74.2.326

전태현(Tae-Hyun Jun) ; 곽병섭(Byeong-Sub Kwak) ; 김아름(Ah-Reum Kim) ; 임병훈(Byung-Hun Lim) ; 박현주(Hyun-Joo Parkark)

In recent years, the number of failures caused by oil impregenated paper(OIP) bushings applied to long-term power transformers has been increasing, and some of them have progressed to fires, increasing the possibility of facility damage. As OIP bushings are more than 70% of the long-term bushings in operation, there is a high probability of fire in case of failure, so it is necessary to develop diagnostic technology for aging bushings. Although KEPCO is implementing insulation oil gas analysis to prevent the continued occurrence of failures and recurrence of failures due to bushing insulation breakdown. However, since KEPCO currently does not have its own bushing oil gas maintenance standards, it is necessary to establish management standards that reflect the differences in insulation oil types among manufacturers. Therefore, in this study, we evaluated the generation characteristics of major decomposed gases by failure type based on KEPCO's accumulated bushing dissolved gas analysis database for major bushing manufacturers in operation, bushing internal dismantling inspection, and accelerated aging experiments for each manufacturer. Based on this, it is expected to contribute to the establishment of abnormal diagnosis criteria for OIP bushings and improvement of facility inspection efficiency.

https://doi.org/10.5370/KIEE.2025.74.2.332

주영준(Youngjun Joo)

This paper deals with an iterative proportional-integral-derivative (PID) gain tuning algorithm to maximize the proportional (P) gain while guaranteeing the stability of the closed-loop system. Indeed, by increasing P-gain, the performance of the closed-loop system, such as the steady-state error, disturbance rejection, and transient response, is improved. However, increasing P-gain alone generally destabilizes the closed-loop system, and thus, the control designer also needs to increase the derivative (D) gain. To improve the control performance and guarantee stability simultaneously, P- and D-gains are sequentially increased in an iterative manner. Furthermore, if necessary, the integral (I) gain is selected to achieve the desired steady-state performance with the pre-designed PD controller. With its strong control performance, the proposed algorithm makes it easy to design PID gains and can be applicable to the fine-tuning of PID gains selected by other PID gain tuning algorithms. In addition, the stability conditions of designing PID gains are presented for linear time-invariant systems. Thus, the stability of the closed-loop system is guaranteed while separately increasing each P-, I-, and D-gain. To validate the effectiveness of the proposed algorithm, simulations for a single-link flexible robot manipulator system have been conducted.

https://doi.org/10.5370/KIEE.2025.74.2.339

원형식(Hyeong-sik Won) ; 조현종(Hyun-chong Cho)

Skin diseases in companion cats can worsen if not treated promptly, and this can increase the financial burden on pet owners. To prevent this, early and accurate diagnosis is essential. This study introduces a deep learning-based Computer-Aided Diagnosis (CADx) system designed to classify cat skin diseases into non-inflammatory and inflammatory lesions by comparing them with normal images. The system employs the EfficientNetV2 model and incorporates image augmentation techniques like AutoAugment and AugMix to enhance classification performance. The study results indicate that the developed model achieved an 84.68% accuracy for non-inflammatory lesions, reflecting a 10.06% improvement, and a 97.19% accuracy for inflammatory lesions, reflecting a 2.45% improvement. Furthermore, we applied Grad-CAM to visualize the regions of interest in the images, offering veterinarians critical insights into the location and characteristics of the lesions. This system has the potential to significantly improve the precision of diagnosing skin diseases in companion cats, thereby supporting better veterinary care.

https://doi.org/10.5370/KIEE.2025.74.2.345

강현민(Hyun-Min Kang) ; 이재호(Jaiho Lee) ; 문영섭(Young-Seob Moon) ; 이호영(Ho-Young Leek)

In this study, numerical analysis of pyrolysis fire modeling using a FDS(fire dynamics simulator) was performed to evaluate the fire stability of electrical cable fires in nuclear power plants. For this purpose, a standardised fire modelling procedure applicable to electrical cable fires was developed, and fire modelling was performed for two and five cable tray conditions in an open space using FDS according to the proposed fire modeling procedure. A grid sensitivity analysis was performed to analyse the effect of grid size on the simulation results and to select the optimal grid size for use in pyrolysis fire modeling. The quantitative comparative analysis of fire simulation results was conducted by applying the analytical blind method to assess the thickness of the cable, heat release rate, and fire duration, along with the primary input parameters of the pyrolysis model, including the reference temperature for pyrolysis, heating rate, and pyrolysis range.

https://doi.org/10.5370/KIEE.2025.74.2.353

노수영(Soo-Young Noh) ; 김창현(Chang-Hyun Kim)

Magnetic levitation conveyor systems enable frictionless and contamination-free transport, making them suitable for sensitive environments such as semiconductor cleanrooms. However, their inherent nonlinearities, along with uncertainties such as noise, disturbances, and time delays, pose significant challenges to conventional controllers. To overcome these limitations, this study proposes a reinforcement learning based control strategy utilizing the deep deterministic policy gradient algorithm, selected for its effectiveness in handling continuous state-action spaces and learning stable control policies in complex nonlinear environments. The developed reinforcement learning based controller is designed to handle the system’s nonlinear dynamics and various uncertainties more effectively than traditional PID controller. Simulation results demonstrate that the proposed controller not only produces smoother transient responses and robust steady-state performance but also maintains stable operation under time delays. The proposed controller is applicable to magnetic levitation systems with various uncertainties.

https://doi.org/10.5370/KIEE.2025.74.2.361

정기석(Ki-Seok Jeong) ; 정태영(Tae-Young Jyung)

Recently, with the global expansion of hydrogen energy adoption, research and demonstration projects on hydrogen-integrated microgrids for carbon emission reduction are actively being carried out in conjunction with renewable energy and ESS. However, for the energy independence of microgrid users in an island operation mode, technical issues such as regulatory compliance, system stability, and power quality arise, necessitating prior verification of expected operational conditions during the system design stage. Therefore, this paper proposes a computational analysis model for the stable operation of hydrogen-integrated microgrids, including hybrid distributed power sources like photovoltaics, fuel cells, ESS, and water electrolysis, using the power system transient analysis program EMTP/RV. Simulations are conducted under independent operation transition and continuation conditions following KEPCO grid separation, considering the control modes of each DERs’ PCS, load variations, and inverter control modes of the grid-forming method. The analysis results confirm that the inertia and damping response of the ESS with a VSM-based GFM inverter contribute to frequency stability improvement under load variation conditions. Additionally, the control performance of the ESS’s GFM inverter under conditions of short-term output variations of photovoltaics due to changes in irradiation can be maintained more stably in terms of power, frequency, and bus voltage compared to the traditional inverter method.

https://doi.org/10.5370/KIEE.2025.74.2.370

김규원(Gyu-Won Kim) ; 지평식(Pyeong-Shik Ji)

In this paper, we studied a Lattice grounding electrode satisfying KEC and verified its performance through CDEGS simulation and experimental demonstration. In order to evaluate the performance of the grid grounding electrode, the touch voltage, step voltage, grounding electrode resistance, and ground potential rise were analyzed in case of ground fault to verify the validity of the proposed method. In addition, in order to evaluate the performance of the proposed grounding electrode under transient conditions such as lightning, various frequencies were applied to the grounding electrode considering the transient conditions and its characteristics were analyzed. The maximum frequency was set to 1[MHz], which is the maximum frequency of the lightning impulse, and the utilization of the grid grounding electrode was studied.