https://doi.org/10.5370/KIEE.2025.74.7.1167

구은규(Eun-Gyu GU) ; 김현진(Hyun-Jin Kim) ; 김국태(Guk-Tae Kim) ; 조윤성(Yoon-Sung Cho)

With the increasing penetration of renewable energy and rising power demand, the efficient utilization of existing transmission infrastructure has become a key issue in power system operation. However, in South Korea, conservative Static Line Ratings (SLR) based on worst-case weather conditions are still applied, while new transmission development faces significant environmental and social challenges. As a solution, Dynamic Line Rating (DLR) has gained attention for its ability to reflect real-time weather data, but its implementation remains limited due to infrastructure and operational constraints. This study explores an alternative approach by applying Seasonal Line Ratings (SAR) based on long-term historical weather data provided by the Korea Meteorological Administration. Using IEEE Std. 738, seasonal ampacity values were calculated, and PSS/E simulations were conducted to quantitatively evaluate the impact of SAR on mitigating thermal constraints. The results show that SAR application can reduce the frequency of thermal overloads by up to 45%, and during winter conditions, available line capacity increased by up to 14% compared to conventional ratings.

https://doi.org/10.5370/KIEE.2025.74.7.1174

이민행(Min-Haeng Lee) ; 김윤호(Yun-Ho Kim) ; 김세진(Se-Jin Kim) ; 장형안(Hyeong-An Jang) ; 노대석(Dae-Seok Rho)

The DC distribution system has been considered as one of the alternatives to improve the hosting capacity of renewable energy sources in the existing AC distribution system. However, researches on the worker safety and equipment protection from various electrical hazards in DC distribution system are being required due to the lack of technical guidelines of electrical facilities standards and safety operation procedures compared to the existing AC distribution system. Therefore, this paper presents systematic mechanisms of electrical hazards in LVDC distribution system such as fault current, CMV, leakage current, circuit current and surge, and also performs the modeling of electrical hazards using PSCAD/EMTDC S/W. Moreover, this paper implements a test device for the electrical hazards based on the proposed modeling, which is composed of AC source, main and section converters and generator device of electrical hazards. From the simulation and test results based on the proposed modeling and test device, it is found that electrical hazards such as fault current, leakage current, circuit current and surge may have a negative impact on the safety and stable operation in LVDC distribution system, and that it is a practical and effective tool to evaluate the electrical hazards in LVDC distribution system as the operation characteristics of simulation modeling is nearly identical as one of the test device.

https://doi.org/10.5370/KIEE.2025.74.7.1187

정진(Jin Jeong) ; 송진솔(Jin-Sol Song) ; 신광수(Gwang-Su Shin) ; 김호영(Ho-Young Kim) ; 김천호(Cheon-Ho Kim) ; 안태풍(Tae-Pung An) ; 민명환(Myung-Hwan Min) ; 김철환(Chul-Hwan Kim)

To reduce carbon emmisions, the proportion of DC-based renewable energy sources has been steadily increasing in recent years. Consequently, extensive research is being conducted on the conversion of parts of MVAC distribution systems to MVDC. In DC distribution systems, power-electronic-based DC/DC converters serve the role of traditional transformers in AC systems. In studies on protection strategies of DC power systems, multiple converters must be modeled within a single test system using EMT simulation. However, modeling multiple converters in detail increases the computational burden of the EMT simulation substantially, creating a major bottleneck in research progress. This paper analyzes the average models of various DC/DC converter topologies applicable to MVDC systems. These average models can adequately reflect the fault response characteristics necessary for developing protection strategies in MVDC distribution systems. The EMT simulation and analysis were conducted using MATLAB/Simulink software.

https://doi.org/10.5370/KIEE.2025.74.7.1196

강현구(Hyun-Koo Kang) ; 김욱원(Wook-Won Kim)

The increasing integration of distributed energy resources (DERs), such as photovoltaics, into distribution systems has heightened the need for accurate hosting capacity analysis. To address this need, we propose a hosting capacity assessment method ensuring accuracy and computational efficiency with high granularity. To enhance computational efficiency while maintaining accuracy, we propose a Fast Iterative Method, which serves as an alternative to the straightforward Full Iterative Method. The proposed approach integrates Reference, Bisection, and Newton Methods into a hybrid framework, achieving a remarkable reduction in computation time. To validate its effectiveness, we applied the proposed method to real Korean distribution networks. The results confirm that our method maintains the same accuracy level as the Full Iterative Method while significantly reducing computational time, making it suitable for large-scale system applications.

https://doi.org/10.5370/KIEE.2025.74.7.1205

이동주(Dong-Ju Lee) ; 김종겸(Jong-Gyeum Kim)

Induction motors are a common type of linear load, but due to their resistive and inductive components, the current phase lags behind the voltage phase, resulting in a low power factor. A low power factor increases the apparent power demand from the power source, necessitating the use of power factor compensation devices. These devices are typically designed based on the assumption that the motor operates at its rated output. However, when the motor runs at a reduced load, the power factor decreases, prompting the installation of compensation devices at the motor or on the secondary side of the transformer to improve the overall power factor of the system. Despite the presence of power factor correction devices, the power factor tends to drop as the load decreases. Additionally, when the motor is idle, such as during nighttime or holidays, residual reactive power may cause the power factor to shift to a leading condition. A leading power factor can lead to voltage rise, potentially impacting system stability. This study proposes a simple method to prevent power factor from becoming leading during periods of motor inactivity by interlocking the transformer when the motor is stopped.

https://doi.org/10.5370/KIEE.2025.74.7.1211

김영우(Young-Woo Kim) ; 이도경(Do-Kyung Lee) ; 김종해(Jong-Hae Kim)

This paper presents lightning surge protection measures to protect devices damaged by lightning surges flowing into a low power AC to DC converter. Firstly, the paths of low-frequency and high-frequency surge currents are analyzed when lightning surges are applied to the line and ground of the low power AC to DC converter. Based on the analysis of low frequency and high frequency surge current paths, this paper proposes lightning surge protection measures to protect the coupling capacitor between the primary ground and secondary ground sides, Y-capacitors, semiconductor devices, and an IC controller damaged by lightning surges flowing into a low power AC to DC converter. It also proposes a lightning surge protection measure that utilizes a spark gap of a new pattern structure, which has excellent characteristics in reducing lightning surges without additional surge protection devices. Finally the effectiveness of the theoretical analysis of the lightning surge protection measures proposed in this paper was verified through theoretical analysis using the PSIM simulation tool and experimental results.

https://doi.org/10.5370/KIEE.2025.74.7.1225

박수성(Su-Seong Park) ; 김동중(Dong-Jung Kim) ; 이상혁(Sang-Hyeok Lee) ; 김래영(Rae-Young Kim)

The LLC resonant converter, widely used in DC-DC converter topologies for EV charging systems, is an isolated converter with separated primary and secondary sides, making effective transformer design essential. When applying an integrated transformer for high-efficiency and high-density LLC resonant converters, it is crucial to adjust the leakage inductance to approximate the design value in order to achieve the desired output voltage range of the converter. Although various integrated transformer structures and design techniques have been researched to adjust leakage inductance, they often require additional devices or complex winding structures, making them difficult to apply to wound transformers. This paper proposes a new wound-type integrated transformer structure that enables adjustment of leakage inductance without additional devices through sections where primary and secondary windings are completely separated and sections where they partially overlap. The proposed integrated transformer structure is elaborated based on design techniques that consider not only efficiency and power density but also reliability factors such as flux and temperature saturation. The proposed structure and design techniques were validated through Finite Element Analysis (FEA) simulations and experiments with a 10kW LLC resonant converter.

https://doi.org/10.5370/KIEE.2025.74.7.1237

김건희(Keon-Hee Kim) ; 박수성(Su-Seong Park) ; 이동근(Dong-Geun Lee) ; 김래영(Rae-Young Kim)

This paper proposes a method for analyzing power loss in a full-bridge LLC resonant converter based on the enhanced Time-Domain Analysis (TDA) technique. The proposed enhanced TDA method demonstrates that the power loss in an LLC resonant converter can be expressed through a complete equation. The necessary initial values are represented in equations, showing a deviation of less than 5% compared to simulation results. Furthermore, based on an 8.4kW full-bridge LLC resonant converter prototype, the proposed method and experimental values are compared in terms of efficiency across different loads, with a maximum error of 1.7% under light loads, while exhibiting highly similar values in other regions.

https://doi.org/10.5370/KIEE.2025.74.7.1248

송영훈(Younghun Song) ; 김남기(Namgi Kim) ; 정경용(Kyungyong Chung)

In this study, we propose a YOLO-LSTM-based model for real-time traffic accident detection, verified using the CarCrashDataset (CCD), which contains 4,500 curated videos covering a diverse range of driving conditions. Our approach integrates YOLOv5 for rapid object detection focusing on vehicles, motorcycles, and pedestrians with an LSTM module that captures critical time-series ? ? patterns indicating imminent collisions. By leveraging both pre-extracted features from CCD and dynamically generated YOLO outputs, the model achieves robust performance in challenging scenarios such as night driving, inclement weather, and partial occlusions. Experimental results demonstrate high accuracy and recall, confirming the system’s ability to reliably identify accidents, often before collisions occur. Furthermore, the fusion of YOLO-based detections with advanced feature representations enhances detection precision while minimizing false alarms. These findings highlight the system’s potential for deployment in intelligent transportation infrastructures, where proactive warnings can significantly mitigate accident-related damage. Future work will explore transformer architectures and multi-sensor data fusion, thereby offering a strong foundation for next-generation traffic safety applications demanding reliable, real-time accident prevention.

https://doi.org/10.5370/KIEE.2025.74.7.1257

문주영(Joo-Young Moon) ; 김혜진(Hye-Jin Kim) ; 황영미(Young-Mi Hwang) ; 김준호(Joon-Ho Kim) ; 박성호(Sung-Ho Park) ; 김희겸(Hee-Kyum Kim)

Due to the rapidly changing climate environment, power facility failures and increasing social concerns, it is essential to secure basic data for deriving optimal design standards and preventive maintenance strategies through wind speed estimation and downscaling technology that reflects climate change outlook. This paper developed a model that downscaling low-resolution wind speed data to high-resolution and a model that estimations the average wind speed as the maximum wind speed to ensure stable operation of overhead power transmission facilities in response to climate environment changes. Based on the SSP scenario and AWS and ASOS data provided by the Korea Meteorological Administration, the Downscaling model secured 95.96% accuracy, and the maximum instantaneous wind speed estimation model secured 90.18% accuracy. This paper presents a new paradigm for improving the design and operational efficiency of transmission facilities and will serve as an essential technological foundation for responding to climate change.

https://doi.org/10.5370/KIEE.2025.74.7.1266

송민섭(Min-Sup Song) ; 김재원(Jaewon Kim) ; 조환희(Hwan-Hee Cho) ; 김형철(Hyungchul Kim) ; 정호성(Hosung Jung)

This paper presents the multi-neighboring reference vector discontinuous PWM (MNRV DPWM) methodology for effectively controlling DC-link voltage imbalance in multilevel diode-clamped topologies. MNRV DPWM utilizes multiple neighboring reference voltage vectors to balance capacitor charging while ensuring volt-time compliance through the additional degrees of freedom provided by outermost voltage vectors. A duty compensation mechanism further simplifies closed-loop control and enhances system stability. The proposed approach is applied to three-phase PWM inverters and full-bridge (FB) LLC resonant converters, demonstrating its effectiveness in DC/AC and DC/DC power conversion systems. By interpreting FB circuits as two symmetric half-bridge circuits, MNRV DPWM can be efficiently implemented through offset voltage (Voffset) injection. Experimental results confirm the effectiveness of MNRV DPWM in mitigating voltage imbalance and enhancing power conversion efficiency. This study highlights the broad applicability of MNRV DPWM across multilevel DC/AC, AC/DC, and DC/DC converters and its potential for high-voltage, high-power conversion systems.