https://doi.org/10.5370/KIEE.2026.75.10.2353

김태현(Tae Hyun Kim) ; 이우남(Woo-Nam Lee) ; 정구형(Koo-Hyung Chung) ; 김창수(Chang-Soo Kim)

This study develops a 2024 PPA-adjusted grid-facing electricity-demand database for Korea using public data: Korea Power Exchange demand, KEPCO district sales, and industrial load profiles. It covers 229 districts, 38 use-sectors, and 8,784 hours. Industry-code mapping, regionally weighted profiles, and two-stage proportional scaling preserve district-sector-monthly sales and align with the national load shape. Sales are preserved exactly by construction (0.000%), with an intraday shape residual of 0.059%. A partial external cross-check against total-demand estimates separately published by KPX for Nov. 23 to Dec. 31, 2024 yielded an hourly MAPE of 0.79% at the national aggregate level. Applied to KPG 193, industrial buses show peak-to-valley ratios of 1.12?1.24 (group mean 1.18) versus 1.85?2.08 (mean 1.94) for service-dominated metropolitan buses. Compared with allocation using a single national load shape across buses, the metropolitan summer-peak share rises from 7.6% to 10.6%, whereas the industrial-complex share falls from 19.2% to 14.1%. The results support regionally differentiated demand modeling for long-term transmission planning.

https://doi.org/10.5370/KIEE.2026.75.10.2364

진호원(Ho-Won Jin) ; 김연우(Yeon-Woo Kim) ; 고백경(Baek-kyeong Ko) ; 남수철(Su-chul Nam) ; 조윤성(Yoon-Sung Cho)

Phasor measurement units (PMUs) provide time-synchronized voltage and current phasors, enabling linear state estimation in rectangular coordinates. This paper evaluates PMU-only linear state estimation for the Jeju power system using its actual PMU measurement channel configuration and proposes an observability-preserving bad-data processing method. Monte Carlo simulations were performed under voltage, current, combined bad-data, and missing-measurement conditions. The proposed observability-preserving selective reweighting and removal method (OP-SRR) was compared with measurement removal and iterative reweighting methods using a weighted least-squares (WLS)-inspired post-processing residual screening index with a fixed threshold. The results show that OP-SRR mitigates estimation instability associated with measurement removal, particularly under combined voltage and current bad-data conditions, while requiring less computation time than iterative reweighting. The missing-measurement case was evaluated under conditions in which observability was preserved.

https://doi.org/10.5370/KIEE.2026.75.10.2373

이유석(Yu-Seok Lee) ; 김우중(Woo-Jung Kim) ; 안상진(Sang-Jin Ahn) ; 전영환(Yeong-Han Chun)

This study evaluates the operational effects of power-to-electric boilers (P2eB) in the 2030 Korean power system, considering flexible nuclear operation. A reserve-constrained unit commitment model jointly optimizes the power and heat systems while representing nuclear output reduction, minimum-output holding, and recovery. P2eB capacity is varied from 0 to 10 GW under different nuclear operating and reserve-provision conditions. The results show that P2eB reduce operating costs, renewable energy curtailment, and nuclear output reduction by absorbing surplus electricity and replacing heat production from combined heat and power units and peak-load boilers. Cost reductions reach approximately KRW 7.0 billion under rated nuclear operation and KRW 5.5 billion under partial flexible operation, with primary reserve provision yielding the greatest benefit.

https://doi.org/10.5370/KIEE.2026.75.10.2384

이륜경(Ryungyeong Lee) ; 신훈영(Hunyoung Shin)

Korea is introducing demand-side bidding and locational pricing in its wholesale power market. Currently demand is set by the operator's forecast, so the buyer cannot influence the price; once demand bidding is allowed, the submitted quantity becomes the buyer's choice, and KEPCO, the de facto single buyer, gains the ability to affect it. Having this ability does not imply exercising it; that depends on a separate incentive. Distinguishing ability from incentive, we analyze when a dominant buyer would strategically underbid demand. Analysis shows underbidding yields a persistent incentive, and a simulation on Korean data quantifies it. In every representative scenario a strategic bid beats truthful bidding, and its profitable direction reverses with demand level owing to supply-curve asymmetry. This shows not that the buyer so behaves but that the incentive can arise, so surveillance must look beyond total-quantity deviations to the direction and regional pattern of bid deviations.

https://doi.org/10.5370/KIEE.2026.75.10.2393

신주영(Juyeong Shin) ; 최길수(Gilsu Choi)

This paper proposes a computationally efficient winding optimization method for reducing the position error of variable reluctance resolvers. In practical resolver design, ideal signal-winding turns are generally noninteger and must be rounded for manufacturing, causing winding-turn errors that distort SIN/COS output voltages. In addition, harmonic components of air-gap permeance caused by leakage flux and magnetic saturation contribute to position error. To address these issues, an One-Shot FEA-based analytical model is developed to extract slot-wise permeance harmonics from a single transient FEA and predict position error for various winding configurations without repeated FEA. Furthermore, a symmetry-based winding quantization method is proposed for pole combinations satisfying , where complementary floor and ceiling operations are applied to opposing slots to cancel winding-turn errors. The two methods are integrated into a hybrid winding optimization framework. For a 12?4X resolver, the proposed method reduces the average position error by approximately 64% compared with conventional rounding, while reducing computational time by approximately 99.78%. The method is further validated using an 18?6X resolver, demonstrating its applicability to other pole-slot combinations.

https://doi.org/10.5370/KIEE.2026.75.10.2400

김기목(Ki-Mok Kim)

This paper proposes a novel diode-clamped three-level interleaved double LLC resonant converter for reducing input current ripple and switch voltage stress in high-voltage DC applications. The proposed converter utilizes a three-level structure with a diode-capacitor clamping circuit, restricting the voltage stress on each main switch to exactly half of the input voltage, which enables the use of low-voltage-rated power switches. Additionally, 180-degree phase-shifted interleaved control is applied to the double LLC resonant tanks, theoretically canceling the input current ripple to zero without adding a large input filter. Furthermore, by implementing dual-function capacitors, vulnerable electrolytic capacitors are completely eliminated and replaced by long-lifespan film capacitors, significantly enhancing power density and system reliability. Experimental and simulation results are presented to comprehensively verify the performance and feasibility of the proposed converter.

https://doi.org/10.5370/KIEE.2026.75.10.2411

안진형(Jin-Hyung Ahn) ; 김용헌(Yong-Heon Kim) ; 곽상신(Sang-Shin Kwak)

Series arc faults occurring at the AC output and DC input sides of a three-phase pulse-width modulation inverter can degrade system reliability and increase the risk of electrical accidents. Because the effects of an arc on the output-current waveform vary depending on the fault location and operating condition, the diagnostic characteristics of AC and DC series arcs should be evaluated separately. In this study, the performance of several artificial-intelligence models was compared using a single A-phase output-current signal measured under various inverter operating conditions. The measured current was used as a time-domain sequence and was also transformed into a frequency-domain magnitude spectrum using the fast Fourier transform. The experimental results showed that the CNN-Transformer achieved the highest diagnostic accuracy for both AC and DC arc faults with both input representations. In particular, the frequency-domain input provided high precision and recall for both AC and DC arc conditions. These results demonstrate that both AC output-side and DC input-side series arcs can be effectively diagnosed from the output-current characteristics, while the diagnostic performance depends on the fault location, input representation, and model structure.

https://doi.org/10.5370/KIEE.2026.75.10.2417

조준한(Junhan Jo) ; 장영훈(ounghun Jang) ; 임용준(Yong-Jun Lim) ; 성가연(Ga-Yeon Seong) ; 이상윤(Sangyoon Lee)

In this study, we propose an optimal energy management algorithm for multiple photovoltaic (PV)-integrated battery charging and swapping stations (BCSSs), considering both energy sharing among BCSSs and their PV generation uncertainties. To minimize the system-wide operating cost, we formulate a cooperative energy-sharing mechanism among BCSSs while strictly satisfying the electric vehicle (EV) charging requirements of each BCSS. In addition, to address the PV uncertainty, we formulate chance constraints based on a data-driven method using historical data. To enhance computational performance while accounting for PV uncertainties, we employ duality theory to reformulate the proposed chance constraints into a deterministic equivalent form. In the numerical investigation, we demonstrate the superior performance of the proposed algorithm in terms of cost reduction, cooperation among BCSSs, and robustness under uncertainty environments characterized by different probability distributions.

https://doi.org/10.5370/KIEE.2026.75.10.2428

하영재(Youngjae Ha) ; 이지윤(Jiyeoun Lee) ; 김성걸(Seonggeol Kim) ; 박태현(Park Tae Hyun) ; 정해성(Hae Seong Jeong) ; 윤정원(JungWon Yoon) ; 이종준(JungWon Yoon)

This study analyzes the economic feasibility of electrode boilers as Power-to-Heat in Korean district energy under two configurations. BM 1 couples an electrode boiler to a CHP plant, easing its heat burden and raising electricity sales margin; a breakeven price condition derived from generation cost, boiler efficiency, and reserve market participation was applied to actual KPX system marginal price data. BM 2 is a standalone electrode boiler with thermal storage, buffering the gap between heat production and demand; net present value was simulated from regional heat demand and daily prices, with sensitivity analysis on storage capacity. Under variable-cost criteria alone, breakeven was rarely achieved, but adequate reserve prices restore viability at average market prices. It peaked at a specific storage capacity relative to maximum regional heat load, with diminishing returns beyond. Reserve participation and storage sizing are thus decisive for viability and market design.

https://doi.org/10.5370/KIEE.2026.75.10.2437

김현진(Hyun Jin Kim) ; 석오균(Ogyun Seok) ; 김민기(Minki Kim) ; 김민재(Minjae Kim) ; 윤중락(Jung-Rag Yoon) ; 하민우(Min-Woo Ha)

Capacitors in DC-link applications for solar power systems should maintain stable electrical characteristics under high voltage and high switching frequency conditions. Recently, lead lanthanum zirconate titanate (PLZT) capacitors have attracted attention due to their high dielectric strength and stable capacitance characteristics even under high voltage. However, the electrical characteristics of PLZT capacitors for power electronics applications have not been sufficiently investigated. This study investigates the electrical characteristics of VR = 500 V, Cnom,typ = 250 nF PLZT capacitors. Our measurements indicate that the high capacitance observed even under high DC voltage is induced by its antiferroelectric dielectric response. The measured capacitance increased with DC bias, which is consistent with the field-dependent dielectric response of antiferroelectric PLZT. One device exhibited DC breakdown at 1.16 kV. These results provide baseline electrical data for evaluating PLZT capacitors in high-voltage power-conversion applications.

https://doi.org/10.5370/KIEE.2026.75.10.2445

김현진(Hyun Jin Kim) ; 석오균(Ogyun Seok) ; 김민기(Minki Kim) ; 김민재(Minjae Kim) ; 김용상(Yong-Sang Kim) ; 하민우(Min-Woo Ha)

Gate charge is an important parameter related to the switching and gate-driving characteristics of power MOSFETs. This study presents a datasheet-based empirical trend analysis of 204 commercial 650 V and 1200 V Si and SiC MOSFETs. The relationships among gate charge, gate-drain charge, rated continuous drain current, on-resistance, input capacitance, and gate-charge test voltage were evaluated using Spearman rank correlation with two-sided testing. The SiC devices were generally characterized at higher gate-source test voltages. The findings provide quantitative reference data for power-MOSFET selection and gate-driver design.

https://doi.org/10.5370/KIEE.2026.75.10.2453

김동현(Dong-Hyeon Kim) ; 고호정(Hojeong Ko) ; 장성욱(Sung-Uk Zhang)

Aluminum wire bonds in power semiconductor packages face high thermal loading, making finite element analysis (FEA) accuracy dependent on reliable temperature-dependent properties. Existing data often rely on discontinuous temperature points and overlook microstructural effects. This study proposes a Materials Studio-based molecular dynamics framework to evaluate the thermo-mechanical properties of pure aluminum using a Mishin EAM potential. Single-crystal and Voronoi polycrystalline models were constructed to analyze cell-size and grain-boundary effects. Following stepwise NVT/NPT equilibration, elastic constants were calculated via a small-strain method, and uniaxial tensile simulations were performed to derive Young’s modulus, Poisson’s ratio, linear thermal expansion coefficient, yield strength, and ultimate tensile strength across 238K to 498K. The single-crystal model revealed cell-size effects in post-peak deformation, while the polycrystalline model exhibited grain-boundary-induced softening at yielding but enhanced strength retention at ultimate tensile strength. Results were averaged and formulated into continuous regression functions. This approach supplements experimental data and provides continuous property inputs for power semiconductor FEA reliability analysis.

https://doi.org/10.5370/KIEE.2026.75.10.2460

이경렬(Gyeong-Yeol Lee) ; 길경석(Gyung-Suk Kil) ; 김성욱(Sung-Wook Kim)

While numerous studies on detection improvement of UHF sensors in GIS system have focused mainly on the geometric optimization, the properties of the electrode materials have received comparatively little attention. Therefore, from the perspective of improvement of PD detection sensitivity and output, this study used graphene for coating onto a SS UHF sensor. Surface characteristics were investigated on graphene-coated UHF sensors. Sensitivity comparison tests were conducted based on calibration procedures specified in CIGRE TB 525 and 654, and showed that the graphene-coated SS produced output voltage increases of 8.5% compared to that of bare SS. From the PD simulation test, the graphene-coated UHF sensor exhibited peak output voltage increases of 33.5% and 48.5%, respectively, and both increases were statistically significant in SNR ratio. These results indicate the low resistance and high conductivity of graphene can enhance the measurement sensitivity of UHF band PD signals.

https://doi.org/10.5370/KIEE.2026.75.10.2469

윤웅희(Ung-Hui Yun) ; 김성훈(Seong-Hun Kim) ; 김진규(Jin-Gyu Kim)

Polypropylene (PP) is widely used as an insulating material in high-voltage applications, and methods capable of inducing measurable degradation-related property changes within a short period are useful for evaluating material responses. In this study, atmospheric- pressure dielectric barrier discharge (DBD) was applied to induce degradation-related changes in PP, and the electrical characteristics of the DBD were quantified using Q?V Lissajous curves. Oxidation and electrical properties were analyzed as functions of the applied voltage and treatment time, while surface morphology was evaluated after 100 min of treatment at different applied voltages. The discharge energy per cycle and average discharge power increased with applied voltage. The carbonyl index and dissipation factor generally increased with DBD treatment, whereas the volume resistivity decreased. The cumulative dissipated energy was estimated from the average discharge power and treatment time, and the degradation-related indicators showed overall changes with increasing cumulative energy; however, the data obtained at different applied voltages did not converge to a single common relationship. Surface irregularities and localized erosion became more pronounced at higher applied voltages. These results indicate that DBD treatment can induce measurable oxidation, electrical-property changes, and surface morphological changes in PP within a relatively short treatment period, although temporal equivalence between DBD treatment and conventional accelerated aging or long-term service aging remains to be established.

https://doi.org/10.5370/KIEE.2026.75.10.2475

김승돈(Seung-Don KimvKyung-Hoon Jang) ; 장경훈()

In partial discharge (PD) monitoring systems, multiple PD sources and external noise can be simultaneously detected, resulting in different numbers and densities of pulses depending on the signal source. This paper proposes an automatic PD diagnosis method based on dual density-based clustering and phase-resolved partial discharge (PRPD) pattern analysis to improve the diagnostic reliability of online PD monitoring. First, Density-Based Spatial Clustering of Applications with Noise (DBSCAN) and Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) are complementarily applied to cluster pulse signals with non-uniform densities, and PRPD patterns are reconstructed from the resulting clusters. Next, to account for variations in the phase reference, trigger level associated with noise magnitude, and input signal magnitude under field measurement conditions, the PRPD data are augmented using X-axis phase shifting, Y-axis zero padding, and vertical scaling. The augmented PRPD patterns are then classified into Noise, Corona, Internal, and Surface classes using a Conv 2D-based convolutional neural network (CNN), with the classification results represented as probability scores in percentage form. Finally, Pearson correlation-based PRPD similarity analysis is applied to the CNN classification results. A True Alarm is generated when highly similar PD patterns are repeatedly detected, while PRPD patterns identified as False Alarms are stored in a Reference Memory to suppress repeated alarms caused by similar patterns. Experimental results demonstrate that the proposed method improves clustering performance under non-uniform pulse-density conditions and achieves a PD classification accuracy of 92.9%. Furthermore, the application of the PRPD similarity algorithm improves the overall diagnostic accuracy to 94.5%. By integrating pulse clustering, PRPD classification, and similarity-based alarm decision into a unified diagnostic procedure, the proposed method improves the reliability of automatic diagnosis and alarm generation for online PD monitoring systems.

https://doi.org/10.5370/KIEE.2026.75.10.2488

배영준(Young-jun Bae) ; 유찬열(Chan-yeol Ryu) ; 고건(Geon Go) ; 이방욱(Bang-wook Lee)

This paper experimentally investigates the DC breakdown characteristics of oil-impregnated pressboard with respect to specimen thickness and layer configuration. Breakdown tests were conducted ten times for each condition on single specimens of 1T, 2T, and 3T thickness (nominal 1, 2, and 3 mm) and on a stacked specimen consisting of three 1T sheets, using a sphere-sphere electrode arrangement with a diameter of 4 mm. The results were analyzed with a two-parameter Weibull distribution in accordance with IEC 62539. As the thickness of the single specimen increased from 1T to 3T, the breakdown field based on the mean electric field, normalized to the 1T condition, decreased from 1.000 pu to 0.601 pu, a reduction of 39.9 %, while the shape parameter decreased from 37.4 to 10.8. When the field utilization factor obtained from finite element analysis was taken into account, however, the reduction was 11.3 %, indicating that a substantial part of the observed decrease originates from the increased field non-uniformity associated with the electrode geometry. The corrected reduction still exceeded the 4.9 % predicted by the enlargement law. In contrast, for the same nominal total insulation thickness of 3 mm, the stacked specimen exhibited a breakdown field of 0.684 pu, which is 14 % higher than that of the single specimen of equal thickness, and the 90 % confidence intervals of the scale parameters did not overlap, confirming that the difference is statistically significant. Since the two conditions have essentially the same stressed volume, this difference is attributed not to the number of defects but to the layer configuration of the insulation. These results suggest that securing the total insulation thickness alone does not guarantee the required breakdown strength in DC insulation design, and that the layer configuration should be considered as a design parameter.

https://doi.org/10.5370/KIEE.2026.75.10.2495

임재현(Jae-Hyun Lim) ; 권도희(Do-Hee Kwon) ; 김명진(Myung-Chin Kim)

Long-term operation of oil-immersed transformers degrades the internal insulation paper, making stable insulation performance difficult to maintain. This study evaluates a forward physics-informed neural network (PINN) for predicting the degree of polymerization (DP) of transformer insulation paper using synthetic data generated from the analytical solution of the Emsley model with relative Gaussian noise. PINN, ANN and LSTM share training observations, normalization and evaluation grids, while only PINN receives the governing equation, its true parameters and a noise-free initial condition. Temperature is fixed at 98 °C. With three observations, PINN achieves a median RMSE approximately 1/11.5 that of ANN and 1/54.0 that of LSTM, both trained with fifty observations. Interpolation and extrapolation errors are reported separately, and sensitivity to physical parameter misspecification is evaluated. These comparisons quantify the benefit of exact physical prior information under controlled synthetic conditions; they do not establish the necessity of a neural solver when the analytical solution is known or demonstrate performance on field measurements.

https://doi.org/10.5370/KIEE.2026.75.10.2504

구본혁(Bonhyuk Ku) ; 김예찬(Yechan Kim) ; 고기원(Giwon Go) ; 반인후(Inhoo Ban) ; 장찬혁(Chanhyeok Jang) ; 이제희(Jehui Lee) ; 강형구(Hyoungku Kang)

Indoor switchgear is generally considered low-risk for pollution; however, dust and salt can accumulate on insulator surfaces during long-term operation, raising flashover risk under humid conditions. This study evaluated soluble and non-soluble pollution effects on 12 kV-class epoxy post insulators under Type A pollution. Soluble pollution was varied through the equivalent salt deposit density (ESDD), and non-soluble pollution through the kaolin content and resulting non-soluble deposit density (NSDD). Relative to the clean condition, flashover voltage decreased by about 30% and 44% at ESDD levels of 0.05 and 0.1 mg/cm2, respectively; these are proposed as critical pollution levels for the action and urgent management criteria. Using environment-specific accumulation rates for five service scenarios, the urgent criterion was reached after about 120 months in clean environments but only 3.2 months in coastal and offshore environments, supporting differentiated maintenance intervals.

https://doi.org/10.5370/KIEE.2026.75.10.2513

고건(Geon Go) ; 찬드라(Chandra Sekhar Reddy) ; 유찬열(Chan-yeol Ryu) ; 박상훈(Sang-hoon Park) ; 이방욱(Bang-wook Lee)

HVDC converter transformers are subjected to complex electrical stresses because AC and DC voltage components coexist on the valve winding. This study investigates time-dependent electric-field redistribution in the oil-pressboard insulation of a ±525 kV VSC-HVDC converter transformer under an earth-referenced AC/DC superimposed valve-winding voltage obtained from system-level steady-state analysis. A time-dependent finite-element electric-field analysis was performed in COMSOL Multiphysics using fixed electrical properties of insulating oil and pressboard. The electric field was initially concentrated in the oil channels but gradually shifted toward the pressboard barriers due to Maxwell-Wagner field redistribution. The Maxwell-Wagner relaxation times for the different barrier configurations ranged from approximately 3.49 to 5.79 s, and the 50 s analysis period covered a period in which the field variation became gradual following the major redistribution. With the inter-barrier oil-gap thickness fixed at 2 mm and the total insulation distance maintained at 110 mm, the pressboard barrier thickness and number were varied, thereby changing the overall pressboard fraction. At 50 s, the maximum pressboard electric field decreased from 16.9 to 10.8 kV/mm, corresponding to a reduction of approximately 36%, while the oil-channel electric field remained within a relatively similar range despite changes in the overall insulation configuration. These results highlight the need to consider time-dependent electric-field redistribution caused by the sustained DC component of AC/DC superimposed voltage in HVDC converter-transformer insulation design.

https://doi.org/10.5370/KIEE.2026.75.10.2520

김예찬(Yechan Kim) ; 구본혁(Bonhyuk Ku) ; 장찬혁(Chanhyeok Jang) ; 이제희(Jehui Lee) ; 고기원(Giwon Go) ; 반인후(Inhoo Ban) ; 장현재(Hyunjae Jang) ; 성재경(Jaekyung Sung) ; 강형구(Hyoungku Kang)

Regulation (EU) 2024/573 bans fluorinated gases in distribution switchgear rated 24kV and below from 2026. K6, a mixture of 10mol% PMVE (perfluoromethyl vinyl ether) in CO2, is an early-stage SF6 replacement whose breakdown characteristics under varying field utilization factor and moisture content have not been fully reported. This paper analyses the AC breakdown of K6 at atmospheric pressure in a quasi-uniform field. A 4mm diameter sphere-plane gap of 1, 2 and 5mm, giving field utilization factors of 0.73, 0.57 and 0.33, was tested in dry gas below 10ppmv and moist gas at 200ppmv. Ten measurements per condition were fitted to a two-parameter Weibull distribution, and the scale parameter taken as representative. Breakdown voltage increased with gap distance whereas breakdown strength decreased, so the two were least favourable at opposite gaps. Moisture lowered the breakdown strength in all cases, but the difference was statistically significant only at a utilization factor of 0.73.

https://doi.org/10.5370/KIEE.2026.75.10.2526

신효준(Hyo-Jun SHIN) ; 이세희(Se-Hee Lee)

This paper investigates the effects of electrical conductivity models of a lossy dielectric on current pulses and surface charge accumulation in a needle-plane electrode system. Two constant-conductivity cases were compared with a nonlinear model dependent on electric field and temperature. For the nonlinear model, uniform 30°C and temperature-gradient conditions were considered separately. The constant-conductivity cases showed similar pulse magnitudes but different timings, while the temperature-fixed nonlinear model caused only limited changes. In contrast, the temperature-gradient model produced clear differences in current pulses and surface charge distribution. At the same interface position, the surface charge density decreased by about 90%, and the location of maximum charge accumulation shifted. These results show that spatial variations in conductivity due to electric field and temperature significantly affect transient discharge and interfacial charge behavior.

https://doi.org/10.5370/KIEE.2026.75.10.2532

우희준(Hui-Jun Woo) ; 김선빈(Seon-Been Kim) ; 장유나(You-Na Jang) ; 안달(Dal Ahn)

This paper proposes a shielded microstrip-line diplexer capable of DC signal transmission between all ports. To secure DC transmission paths, a continuous signal-line structure connecting all ports is employed. In addition, the circuit is configured only with transmission lines and open stubs, without using short-circuited stubs, to prevent DC short-circuit paths. To suppress undesired electromagnetic coupling between adjacent signal lines and stubs in the pass band, metallic partition walls are inserted to provide physical shielding and minimize mutual coupling. The proposed diplexer has a receiving band of 1.69-1.78GHz and a transmitting band of 2.11-2.18GHz. The simulated results show an in-band return loss of less than ?14.09dB, an insertion loss of greater than -0.53dB, an attenuation characteristic of less than -51.49dB, and an isolation characteristic of less than -52.53dB. The overall size of the proposed diplexer is 138.7 × 139.7 × 17.2 [mm3].

https://doi.org/10.5370/KIEE.2026.75.10.2541

구본혁(Bonhyuk Ku) ; 김예찬(Yechan Kim) ; 이제희(Jehui Lee) ; 장찬혁(Chanhyeok Jang) ; 반인후(Inhoo Ban) ; 고기원(Giwon Go) ; 강형구(Hyoungku Kang)

This study analyzes barriers to the reuse and remanufacturing of distribution-level power equipment in Korea and proposes a multi-layer conformity framework for procurement and grid application. Domestic conditions and cases in Japan, the United States, and Europe were compared across technical, market, and institutional dimensions. The analysis identifies gaps in item-specific conformity pathways, linkage of certification, inspection, and procurement records, and core recovery systems. A five-stage pathway was derived: core recovery and screening, process control and traceability, product verification, labeling/responsibility/warranty, and procurement or grid application. The framework comprises four evidence layers (L1-L4) and three cross-cutting elements (X1-X3). Verification is differentiated according to whether interventions fall within, adjacent to, or beyond the qualified-design boundary. A staged roadmap from closed-loop pilots to broader application is also proposed.

https://doi.org/10.5370/KIEE.2026.75.10.2556

김경수(Gyeongsu Kim) ; 서기성(Kisung Seo)

Clothes-changing person re-identification aims to identify the same person under clothing changes, where conventional re-identification methods suffer from significant performance degradation due to the variation of clothing, which is one of the primary discriminative cues. Recently, CLIP-based approaches leveraging the image?text matching capability of vision-language models (VLMs) have been applied to person re-identification. However, their application to clothes-changing scenarios remains limited, and their reliance on global semantic representations makes it difficult to effectively learn local body-part features that are crucial for this task. To address this issue, this paper proposes a Parsing-guided Prompt Designframework that utilizes human parsing information to effectively learn local body-part features. The proposed method suppresses background noise while preserving only human body region information, thereby encouraging the model to focus on intrinsic human morphological characteristics. In addition, body-part-level visual features are cross-modally aligned with text prompts corresponding to each body part, enabling robust identity discrimination that is less dependent on clothing appearance. Experiments on the representative clothes-changing benchmark PRCCdemonstrate that the proposed method achieves superior performance compared with recent state-of-the-art methods.

https://doi.org/10.5370/KIEE.2026.75.10.2562

임석우(Seok-Woo Lim) ; 원찬희(Chan-Hee Won) ; 김재문(Jae-Moon Kim) ; 강정원(Jeong-Won Kang)

Railway signaling software must satisfy strict requirements?clarity, completeness, verifiability, and traceability?from the specification phase. KRS-SG-0069 requirements are written in Korean natural language, making manual structuring costly and expert-dependent. I propose a semi-automated framework combining LLM-based structuring with deterministic verification. Analysis of 94 requirements identified seven defect types mapped to EN 50128 clause 7.2.4 violations. The framework comprises four modules: M1 classifies requirements; M2 converts them into a six-element boilerplate via Chain-of-Thought prompting; M3 validates drafts through a four-layer rule engine; M4 generates state transition models, test cases, and a traceability matrix. The LLM is confined to draft generation, while safety judgments are delegated to deterministic engines and formal validators. This paper presents an architectural foundation; quantitative evaluation and broader applicability remain as future work.

https://doi.org/10.5370/KIEE.2026.75.10.2574

박유현(Yu-Hyun Park) ; 박주형(Joo-Hyeong Park) ; 이기백(Ki-Baek Lee)

This paper presents an edge-based system for detecting post-fall non-recovery states in a predefined indoor monitoring area. The target of the proposed system is not the instantaneous fall event itself, but a fall-like abnormal posture that persists without recovery. Human keypoints and a person bounding box are extracted using a pretrained YOLO26n-Pose model. Torso orientation is used as the primary posture feature, and the bounding-box width-to-height ratio is used as an auxiliary horizontal-posture feature. A finite-state machine separates frame-level abnormal-posture candidates from emergency decisions by assigning Normal, Warning, and Emergency states according to the accumulated posture duration. In the self-recorded scenario evaluation, no Emergency transition was observed in the normal-posture and daily-motion scenarios, whereas sustained abnormal postures produced sequential Warning-to-Emergency transitions. The average pose inference time on the Jetson AGX Orin was 53.12 ms/frame. The UR Fall Detection Dataset, consisting of 30 fall and 40 ADL RGB clips, was additionally used to examine the external applicability of the posture features and their threshold sensitivity. Under the conservative sensitivity setting, abnormal-posture candidates were detected in 90.0% of the fall clips, while the moderate Warning setting achieved a clip-level F1-score of 0.6552. These results should be interpreted as a feasibility and sensitivity analysis under the evaluated conditions rather than as a general performance validation for unrestricted fall-detection environments.

https://doi.org/10.5370/KIEE.2026.75.10.2583

정소영(So-Yeong Jung) ; 서경욱(Kyeong-Wook Seo) ; 최형준(Hyeong-Jun Choi) ; 최보경(Bo-Kyung Choi) ; 송진우(Jin-Woo Song)

In global navigation satellite system (GNSS)-denied environments, auxiliary navigation sensors are commonly employed for position estimation. However, in multirotors with limited payload, cost, and computational resources, the use of additional sensors may be constrained. As an alternative, dynamics-model-based dead reckoning can be applied. Under real-world conditions, disturbances such as wind can cause dead reckoning errors to accumulate. Therefore, dedicated sensors such as anemometers may be required to obtain disturbance information. This paper proposes a model-based indirect disturbance estimation algorithm that estimates disturbances during GNSS-available periods using only inertial measurement unit(IMU), GNSS receiver and dynamics model. The estimated disturbance is then used to compensate for dead reckoning during GNSS outages. Simulation results show that compensating for the disturbance estimated by the proposed algorithm improves dead reckoning performance.

https://doi.org/10.5370/KIEE.2026.75.10.2594

모영규(Young-Kyu Mo) ; 이훈서(Hun-Seo Lee) ; 전혜련(Hye-Ryeon Jeon) ; 김영석(Young-Seok Kim) ; 오명국(Myung-Kooc Oh)

This study evaluates the power quality of a full-scale PV-ESS demonstration facility integrating PV generation, ESS, EV chargers, and office loads. Two field datasets were combined: 1-min VCB relay data at the high-voltage grid connection point and 1-s high-resolution measurements from eight operating events. The VCB data were used to analyze long-term active/reactive power flow, voltage, current, and frequency, while the high-resolution data were used to evaluate THD, waveforms, and transient P-Q characteristics. The grid connection point repeatedly changed between receiving and reverse power flow conditions, with reverse power flow accounting for 38.7% of the analysis period. Voltage THD remained relatively stable at an average of 1.68%, whereas current THD showed greater event-dependent variation. A temporary reactive power transition was also observed. Based on these results, an event-based assessment procedure integrating long-term operating data and high-resolution power quality measurements is proposed for monitoring and improving PV-ESS integrated facilities.

https://doi.org/10.5370/KIEE.2026.75.10.2606

김기성(Kisung Kim) ; 정병욱(Byeong-Wook Jung) ; 신성수(Seong-Su Shin) ; 송동우(Dongwoo Song)

As MVDC systems expand along roadways, overhead conductors face fire hazards from under-line vehicles and containers. Using FDS 6.9.1, this study evaluates thermal responses of an ACSR-OC 160 mm² XLPE-insulated conductor for seven scenarios ? passenger car, two cars, van, bus, standard and large containers, and electric vehicle ? at heights of 5?10 m, load factors of 50?70 %, and ambient temperatures of 20?40 °C. Failure thresholds are 299 °C for XLPE insulation and 538 °C for structural steel. Passenger-car fires remain safe at 5?6 m, whereas van and large-container fires exceed the threshold even at 10 m. A 70 % load factor shortens time-to-failure, but a 1?2 m height increase restores safety margins. Steel surfaces do not exceed 102 °C across all scenarios. A minimum clearance of 10 m is suggested for logistics and congestion-prone zones, with fire-protective conduits for container areas. Future work should address wind-induced flame tilt and EV re-ignition.

https://doi.org/10.5370/KIEE.2026.75.10.2616

최병우(ByungWoo Choi) ; 김영훈(Young-Hoon Kim) ; 김희균(Hui-Kyun Kim)

This study examines a smart inspection model for pre-use inspection of fixed offshore wind power facilities with gearless direct- drive turbines. Of the 170 inspection items specified in Annex 9 of the relevant notification, 135 items were selected for reviewing offshore execution. After excluding six items not applicable to the representative turbine configuration, 129 items were classified into 80 pre-installation onshore inspection items, 13 post-installation offshore field inspection items, and 36 post-installation non-field verification items. The non-field category comprises remote measurement verification, remote witnessing, and records-based verification. Non-field verification was limited to items for which compliance could be assessed using SCADA data, remote witnessing, or test and design records under defined verification conditions. Items requiring direct confirmation of actual construction conditions, underwater components, and submarine cables were retained as offshore field inspection. In a comparison scenario for three turbines, the total inspection time was estimated to decrease from 106.5 h to 42.7 h, a reduction of 59.9%. Assuming WTIV standby or charter conditions, the estimated cost difference was KRW 2.16 billion. These results are scenario-based estimates and require validation using field inspection and remote verification data.

https://doi.org/10.5370/KIEE.2026.75.10.2627

장주희(Ju-Hee Jang) ; 김종민(Chong-Min Kim) ; 조성구(Sung-Koo Cho) ; 오수정(Su-Jeong Oh) ; 강해권(Hae-Gweon Kang)

These days, the installation of photovoltaic (PV) systems is rapidly increasing. Fault diagnosis of PV systems has been extensively studied to improve electrical safety. A PV system is largely divided into five main components: PV modules, cables, connectors, combiner boxes, and inverters. Among these, faults in PV connectors and cables can cause fire accidents. In this paper, a PV system where a fire accident occurred is analyzed. Furthermore, the causes of the failure are identified through experimental and theoretical analyses. First, power losses were evaluated based on the conductor type and cross-sectional area; aluminum cables exhibited 10.6% higher power losses than copper cables. Next, the allowable current of the cable was calculated, revealing that it could be exceeded depending on the cable installation methods and reduction factors. Lastly, the suitability of PV connector workmanship was evaluated against relevant standards, showing that 28.6% of the connectors were improper. Overall, to improve the safety of PV systems, conductor types, cable installation methods, and connector workmanship must be carefully considered during the design and construction phases.

https://doi.org/10.5370/KIEE.2026.75.10.2633

모영규(Young-Kyu Mo) ; 최원나(Won-Na Choi) ; 전주현(Ju-Hyeon Jeon) ; 김영석(Young-Seok Kim) ; 오명국(Myung-Kooc Oh)

As renewable energy and inverter-based resources expand, voltage and frequency support is shifting from synchronous machines to power-electronic resources. Battery ESS power conversion systems are thus evolving into key assets for grid support, islanded operation, and system restoration. Grid-forming (GFM) PCS can provide voltage and frequency formation, active and reactive power control, fault ride-through, black start, and resynchronization, requiring a safety framework beyond that for conventional grid-following PCS. This study proposes an integrated framework linking pre-use inspection, periodic inspection, and detailed safety checks from the perspective of electrical safety inspection in Korea. Domestic regulations and international standards were reviewed, GFM-specific risks were identified, and inspection and diagnostic items were mapped to design, commissioning, operation, and abnormal conditions. A conceptual industrial ESS case matrix was used to demonstrate applicability.

https://doi.org/10.5370/KIEE.2026.75.10.2643

이호성(Ho-Seong Lee) ; 김정기(Jeong-Gi Kim) ; 이진식(Jinsik Lee) ; 김재현(Jae-Hyun Kim) ; 전정채(Jeong Chay Jeon) ; 방준호(Junho Bang)

Over-discharge of large-format lithium-ion cells can cause electrochemical and mechanical degradation, leading to safety concerns. This study investigated a 67 Ah NCM pouch cell using electrochemical impedance spectroscopy (EIS), acoustic emission (AE), and X-ray computed tomography (X-ray CT). Repeated low-rate discharge under 0% SOC changed the EIS spectrum from two arcs to one dominant arc, suggesting a possible overlapping of SEI-related relaxation and charge transfer processes. During forced over-discharge, burst-type AE signals were detected irregularly, particularly near the voltage reversal region. Post-test X-ray CT showed pouch swelling and displacement or separation of the internal electrode stack. The results demonstrate that EIS and AE/X-ray CT have the potential to serve as complementary diagnostic indicators for estimating gradual electrochemical degradation and abrupt structural changes during severe over-discharge. Further repeated tests are required to improve the reliability of AE-based diagnosis.

https://doi.org/10.5370/KIEE.2026.75.10.2652

정인주(Inju Jung) ; 김형표(Hyungpyo Kim)

This study proposes a conceptual AI-based predictive maintenance architecture for residual current devices (RCDs) using time-series analysis of leakage current and evaluates the preliminary embedded applicability of deep learning models. Leakage current data were collected at 1 s intervals for 120 h using two ACS712 current sensors. LSTM, GRU, and Transformer models were trained and evaluated using the same dataset configuration and evaluation framework. Their performance was compared using MAE, RMSE, trainable parameter count, estimated FP32 weight memory, and CPU inference time. LSTM and GRU showed lower prediction errors than the Transformer. GRU achieved prediction accuracy comparable to LSTM while requiring the fewest parameters and the shortest CPU inference time, suggesting its potential as a lightweight candidate for future MCU-based implementation. Based on these results, the proposed architecture is designed to support early warning and predictive maintenance while retaining the conventional RCD protection function.

https://doi.org/10.5370/KIEE.2026.75.10.2660

강해권(Hae-Gweon Kang) ; 방준호(Jun-Ho Bang) ; 김종민(Chong-Min Kim) ; 조성구(Sung-Koo Cho) ; 오수정(Su-Jeong Oh) ; 장주희(Ju-Hee Jang)

Fixed-type offshore wind power facilities operate under harsh marine conditions?salinity, corrosion, combined wave and current loading, and severe access restrictions?that increase the likelihood of component failure while making periodic inspection and maintenance difficult and costly. Conventional Failure Mode and Effects Analysis (FMEA) based on the Risk Priority Number (RPN) evaluates failure modes only at the component level and cannot reflect the relative importance of higher-level subsystems, which biases the risk ranking toward frequently occurring failures. This paper proposes a two-stage hybrid safety assessment framework that combines the Analytic Hierarchy Process (AHP) with RPN-based FMEA. A component classification aligned with the inspection and diagnostic capability of an electrical safety authority is first derived, comprising four major categories, fifteen sub-elements, and eighty-one failure modes. AHP assigns relative weights to the four top-level categories, while a marine-adapted seven-point RPN scheme evaluates each failure mode; the two are combined into a Weighted Risk Priority Index (WRPI) on a 100-point scale. Both the pairwise comparisons and the S?O?D ratings were elicited from a panel of six field-inspection experts of an electrical safety authority, covering the electrical, civil and mechanical disciplines. The AHP analysis yields the highest weight for electrical facilities (0.565), followed by wind facilities (0.262), the SCADA system (0.118) and the civil foundation (0.055), with a consistency ratio of 0.043. The resulting WRPI ranking shows closer qualitative agreement with published wind-turbine accident statistics than either a raw-RPN ranking or an equally weighted single-stage FMEA, and the framework is expected to support the prioritization of inspection items for future SCADA-based remote assessment.

https://doi.org/10.5370/KIEE.2026.75.10.2669

임승택(Sueng-Taek Lim) ; 오찬혁(Chan-Hyeok Oh) ; 이기연(Ki-Yeon Leen)

With the growing interest in low-voltage direct-current (LVDC) systems, various types of new electrical equipment are being introduced, increasing the need for technical research and revisions to relevant installation requirements. However, from the perspective of electrical safety, adequate requirements have not yet been established for either newly introduced or existing equipment in LVDC systems. Surge protective devices (SPDs) are widely used to protect electrical installations against transient overvoltages caused by lightning and switching events and are also applied in DC systems. Nevertheless, detailed requirements for the selection and installation of SPDs considering DC system configurations and grounding arrangements remain insufficient. Therefore, this study investigates appropriate SPD installation methods for DC systems by analyzing SPD connection schemes according to system configuration and grounding arrangement, as well as the selection of impulse discharge current ratings. Conventional SPD installation methods used in AC systems were analyzed and adapted to DC systems, and the impulse-current sharing characteristics in two-wire and three-wire DC systems were experimentally evaluated. Based on the analysis and experimental results, suitable SPD application methods for different system configurations and a method for selecting the required impulse discharge current rating are proposed. The findings provide practical guidance for applying SPDs to DC installations, whose electrical characteristics differ from those of conventional AC installations, and can serve as a basis for establishing safer installation requirements for LVDC systems.

https://doi.org/10.5370/KIEE.2026.75.10.2677

전주현(Juhyeon Jeon) ; 최원나(Wonna Choi) ; 모영규(Young-Kyu Mo) ; 김영석(Young-Seok Kim)

Energy Storage Systems store large amounts of electrical energy and may therefore supply high short circuit currents from the battery during a short circuit fault, requiring appropriate short circuit protection. In this study, the short circuit current characteristics of an ESS battery and the operating characteristics of fuses under different short circuit conditions were experimentally investigated. The state of charge and short circuit resistance were varied, and the short circuit current and fuse clearing time were measured. In addition, fuse melting behavior was compared according to the fuse installation position. The experimental results showed that the magnitude of the short circuit current varied with both SOC and short circuit resistance, with the effect of short circuit resistance being relatively greater under the tested conditions. The fuse clearing time and melting behavior also varied depending on the magnitude of the short circuit current. These results indicate that the actual short circuit current characteristics, fuse operating behavior, and fuse installation position should be considered together when designing short circuit protection for ESS battery systems.

https://doi.org/10.5370/KIEE.2026.75.10.2683

최원나(Wonna Choi) ; 전주현(Juhyeon Jeon) ; 김지연(Ji-Yeon Kim) ; 김영석(Young-Seok Kim)

The increasing use of energy storage systems has intensified the need for effective battery thermal management. This study investigated the location-dependent temperature characteristics of an ESS battery cell under different C-rates and cooling conditions. A 94 Ah prismatic lithium-ion cell obtained from a ESS module was instrumented with eleven thermocouples on its surfaces, terminals, vent hole, and side faces. Cooling conditions were defined as operation with and without heating, ventilation, and air conditioning (HVAC), and charge-discharge tests were conducted at 0.3C, 0.5C, and 1.0C. Without HVAC, the maximum temperatures were 29.9°C, 32.6°C, and 42.0°C, and the corresponding differences between the maximum cell and ambient temperatures were 7.3°C, 9.4°C, and 18.4°C, respectively. With HVAC, these values decreased to 29.2°C, 28.7°C, and 31.7°C and to 3.0°C, 2.4°C, and 5.4°C, respectively. Without HVAC, the hotspot was consistently observed at the negative terminal. With HVAC, it remained at the negative terminal at 0.3C but shifted to the lower front surface at 0.5C and 1.0C. Under the tested conditions, HVAC operation suppressed temperature rise and altered the spatial temperature distribution, providing useful data for temperature-sensor placement and thermal management design in ESS battery modules.

https://doi.org/10.5370/KIEE.2026.75.10.2691

박재경(Jae-Kyung Park) ; 이기연(Ki-Yeon Lee) ; 한가람(Ga-Ram Han) ; 문영채(Youg-Chae Mun)

Ensuring the safety of electric vehicle DC charging facilities requires not only verification of the conditions of installed facilities but also consideration of the verification scope for DC output-side insulation monitoring and fault-response protective functions. This study compares the verification objects and objectives across three distinct layers: facility safety inspections based on the Korea Electro-technical Code (KEC) and the Korea Electrical Safety Code (KESC), product safety verification based on KC 61851-23, and the self-diagnostic functions embedded in the charging system itself. The analysis is limited to System C, which corresponds to the DC Combo (CCS) fast-charging interface used in Korea. The proposed 2026 amendment to KC 61851-23 is treated separately as comparative material for identifying the direction of future technical requirements rather than as a currently effective legal basis. The analysis shows that facility-side earthing and insulation inspections differ in both verification object and purpose from DC output-side protective-conductor continuity monitoring and insulation-monitoring functions on the DC output side. It also confirms that the charging system independently performs insulation verification before charging and continuous insulation monitoring during operation. The fundamental requirements for insulation monitoring and protective actions are already included in the currently effective KC 61851-23, while the main differences introduced by the proposed amendment lie in terminology and the level of detail in the associated test procedures rather than in the underlying assessment principle. Accordingly, this study proposes a staged safety verification framework consisting of product safety verification, installation and field safety confirmation, utilization of operational diagnostic information, and conditional verification of protective functions. Prior to institutionalization, available diagnostic information is used as supplementary information for maintenance and technical diagnosis, while detailed verification through fault-state reproduction is performed only when clearly defined conditions arise, such as recurring safety-related anomalies or the repair or replacement of major protective components. Incorporation into statutory inspections should be considered only after field validation and standardization and only when the KESC and related public notices are amended accordingly. Because resistance values and response times differ in meaning and applicable conditions across standards, this study does not propose a single new acceptance criterion.

https://doi.org/10.5370/KIEE.2026.75.10.2701

김정기(Jeong-Gi Kim) ; 이호성(Ho-Seong Lee) ; 김재현(Jae-Hyun Kim) ; 이진식(Jinsik Lee) ; 전정채(Jeong Chay Jeon)

The increasing deployment of photovoltaic (PV) generation has raised concerns regarding the fire safety of outdoor power conversion systems (PCS). This study investigates a fire accident involving a 250kW grid-connected PV PCS through field inspection, event analysis, damaged components, and 3D X-ray CT analysis. Fire damage was concentrated around the DC-link capacitor bank, plate busbars, insulation layer, and IGBT stack. The observed localized melting, perforation, and insulation damage indicate that insulation degradation and surface discharge between the plate busbars may have contributed to the accident progression, although the initial ignition source could not be conclusively identified. The creepage distance of the insulation structure was additionally evaluated with reference to IEC 60664-1 considering pollution degree and material group. Based on the accident analysis, improvements including strengthened busbar insulation design and inspection, PV-side rapid shutdown, and coordinated DC/AC isolation are proposed. The results will provide a basis for improving PCS fire prevention, inspection, and protection designs.

https://doi.org/10.5370/KIEE.2026.75.10.2711

조성구(Sung-Koo Cho) ; 김종민(Chong-Min Kim) ; 오수정(Su-Jeong Oh) ; 강해권(Hae-Gweon Kang) ; 장주희(Ju-Hee Jang)

Vertical bifacial photovoltaic (PV) systems differ from conventional tilted PV systems in irradiance on the front and rear sides, orientation-dependent output profiles, and thermal conditions. Although these characteristics have been widely studied, their implications for electrical design values and the applicability of current safety-related design standards have received relatively limited attention. This study reviews previous studies on vertical bifacial PV systems to identify installation and operating characteristics relevant to electrical safety and to derive key electrical design variables. Based on their direct linkage to current design standards, maximum current and maximum system voltage are selected for the applicability analysis. The study then examines the applicability of IEC 61215-1 and IEC 62548-1 together with relevant domestic requirements. For maximum system voltage, low-temperature and available-irradiance conditions relevant to voltage determination are reviewed. The results indicate that the current standards are generally applicable to vertical bifacial PV systems, while consideration of site-specific irradiance and installation conditions is important for their practical application. These findings provide a technical basis for electrical safety design and subsequent field validation of vertical bifacial PV systems.

https://doi.org/10.5370/KIEE.2026.75.10.2721

신승권(Seung-Kwon Shin)

Railway stations run continuously with flat, base-load-dominated electricity demand, so the value of photovoltaics (PV) and energy storage (ESS) differs from buildings with daily peaks. This study analyzes PV-ESS integrated operation for SRT station using twelve months of metered hourly electricity and within-hour 15-minute maximum demand, the 202 kW rooftop PV scaled to its 2024 measured yield, and the industrial time-of-use (TOU) tariff with weekend and holiday rules. The load averages 685 kW with a load factor of 0.55 and an annual 15-minute peak of 1,245 kW as short spikes; PV covers 4.1% of demand with no export. Expanding rooftop PV to about 1,000 kW keeps self-consumption at 100% but raises self-sufficiency only to 20% and cuts the annual peak by only 38 kW. For flat-load stations the value of storage lies in demand-charge reduction rather than arbitrage or self-sufficiency.

https://doi.org/10.5370/KIEE.2026.75.10.2727

유비(Bi Yu) ; 최현준(Hyun-Jun Choig)

This paper proposes an enhanced three-phase Phase-Locked Loop (PLL) algorithm based on Cascaded Delayed Signal Cancellation (CDSC) for accurate per-phase detection under unbalanced grid conditions. PLL is essential for extracting grid frequency and phase in grid-connected power converter applications. However, conventional three-phase PLLs are mainly used for inverter control and have limitations in accurately estimating independent per-phase quantities under voltage unbalance and grid distortion. To address this limitation, an enhanced CDSC-PLL is proposed, in which each phase is independently processed and an average-based compensation method is applied. Through this approach, the effects of the harmonic components in the estimated angular frequency are reduced. The performance of the proposed algorithm was verified under unbalanced grid conditions. The results show that the proposed method achieves improved harmonic suppression and effective per-phase phase estimation compared with a Moving Average Filter (MAF)-based PLL and a conventional CDSC-PLL.ㅍ

https://doi.org/10.5370/KIEE.2026.75.10.2733

구병준(Byeong-Jun Gu) ; 이상준(Sang-Jun Lee)

This paper proposes a multimodal data-based deep learning model for partial discharge detection in solid- and liquid-insulated electrical equipment to support early fault diagnosis and electrical accident prevention. Existing approaches often rely on a single data modality, which may limit their ability to capture complementary characteristics of different partial discharge types. The proposed model independently extracts spatial features from phase-resolved partial discharge (PRPD) images and temporal features from time-series signals, and combines them through Late Fusion for final classification. Experiments were conducted using 60,000 multimodal samples acquired from ACSR-OC with solid insulation and an oil-immersed power transformer with liquid insulation, covering normal, noise, void discharge, surface discharge, and corona discharge states. The training, validation, and test sets were constructed without overlapping identical files, and experiments were repeated using five random seeds. Compared with ResNet-18, LSTM-AE, and Cross-Attention Transformer, the proposed model achieved the highest average performance, with an Accuracy of 99.4733 ± 0.3301% and a Macro F1-score of 99.4716 ± 0.3315%. These results show that combining complementary spatial and temporal information can improve partial discharge detection performance and contribute to more reliable electrical equipment condition diagnosis.

https://doi.org/10.5370/KIEE.2026.75.10.2743

강민찬(Min-Chan Kang) ; 조윤진(Dong-Il Cho) ; 조동일(Yun-Jin Cho) ; 남준혁(Jun-Hyuk Nam) ; 문원식(Won-Sik Moon)

This study evaluates location-dependent feasible connection capacity intervals for AI inference data centers in a distribution network with photovoltaics. A synthetic 24-hour facility load profile is constructed from public inference request traces, measured processor power characteristics, and power usage effectiveness data. OpenDSS simulations assess 53 candidate buses under three line current limits. In the identified intervals, existing overvoltage determines the lower bounds, while undervoltage or line current constraints determine the upper bounds. The maximum interval width increases from 1.141 MW at 350 A to 1.938 MW at 450 A. Sites selected by the upper-bound and interval-width criteria differ under all three conditions. The results support joint assessment of capacity bounds, interval width, and limiting constraints when planning data center location and size under a fixed load profile.

https://doi.org/10.5370/KIEE.2026.75.10.2752

강민찬(Min-Chan Kang) ; 조동일(Dong-Il Cho) ; 조윤진(Yun-Jin Cho) ; 이달우(Dal-Woo Lee) ; 하중훤(Jung-Hweon Ha) ; 문원식(Won-Sik Moon)

Asset management for MVDC distribution systems faces two obstacles: the modular multilevel converter couples hundreds of components so that one asset's aging accelerates its neighbors', and no operating MVDC system has failure records to learn this coupling from. This paper answers both with a data representation. First, an MVDC station is modeled as an attributed graph whose nine edge types are split by a FMEA into an operational and a degradation topology; in the KEPCO Naju ±35 kV, 30 MW testbed, 358 of 417 edges are degradation edges. Second, a synthetic dataset is built from published failure rates by assigning per-type Weibull parameters and modulating each asset's characteristic life along the adjudicated paths; generating parameters are withheld from the inputs. Using a graph model as a validation tool over 12 seeds, the 358 degradation edges alone match the full graph, whereas the 59 operational edges alone degrade error by 38.7%, no better than no edges.

https://doi.org/10.5370/KIEE.2026.75.10.2760

신재호(Jaeho Shin)

Metal additive manufacturing can introduce internal defects such as porosity, inclusions, and cracks, yet supervised ultrasonic C-scan detectors are hard to deploy at process introduction, where labeled images are scarce and rare defect classes are imbalanced. We propose a physics-informed C-scan augmentation method that explicitly models six ultrasonic effects, automatically synthesizing labeled images over ten classes. All evaluation is confined to the synthetic domain. Within that scope we verify that input physical parameters are quantitatively transferred to the rendered images: defect contrast increases monotonically with the theoretical reflection coefficient across six impedance levels, and the attenuation coefficient recovered from the images agrees with the input value. The best detector reached mAP@0.5 of 0.705 at a fixed compute budget, and targeted synthetic augmentation of the most signal-sensitive class raised its AP@0.5 from 0.516 to 0.583, while a same-size neutral control gained only 0.009. Public measured laser-ultrasonic amplitude maps of an additively manufactured specimen are included as a quantitative external reference: under a common domain-distance measure the measured domain lies farther from the training distribution than any synthetic shift tested here, which bounds applicability and quantifies the adaptation scale required in future work.

https://doi.org/10.5370/KIEE.2026.75.10.2768

김상호(Sang-Ho Kim) ; 김일송(Il-Song Kim)

This paper proposes a novel high efficiency, high step-up boost converter and its precise modeling technique, utilizing a magnetic clamp structure to suppress leakage inductance surges and efficiently recover energy. Under identical load conditions, the converter exhibits a unique mode transition based on a critical duty ratio (0.6?0.7), shifting dynamically between a first order DCM and a second order CCM. To analytically unify this non-linear behavior within a single framework, a unified (CCM based) state-space averaging(SSA) modeling technique introducing the inductor current conduction ratio() is proposed. By applying symmetrical winding conditions, the analytical complexity is simplified to only inductance() and coupling coefficient(), ensuring practical design guidelines. A robust double loop controller is optimized and designed via MATLAB SISOTOOL to secure sufficient stability margins across all operating regions. The validity of the proposed model and controller is verified via PSIM simulations. Notably, the system achieves stable and seamless voltage tracking without control discontinuities or voltage overshoot, even during harsh transient states where the duty ratio passes through the critical threshold under a fixed load condition.

https://doi.org/10.5370/KIEE.2026.75.10.2781

조승현(Seung-Hyeon Cho) ; 장진수(Jin-Su Jang) ; 이기영(Gi-Young Lee)

LLC resonant converters can achieve zero-voltage switching (ZVS) of the primary-side switches by utilizing the characteristics of the resonant tank, and are therefore widely employed in various power conversion applications requiring high efficiency. Conventional dead-time design methods for LLC resonant converters have mainly focused on determining a sufficiently long dead time to ensure ZVS, while body-diode conduction loss during the dead-time interval has received relatively limited consideration. To address this issue, this paper proposes an adaptive dead-time algorithm that estimates the time required to achieve ZVS according to the operating condition using the resonant current measured at the switch turn-off instant and adjusts the dead time based on the estimated value. The proposed algorithm is evaluated under abrupt load-change conditions, and the results confirmed that the dead time was appropriately adjusted according to the operating condition, thereby maintaining ZVS operation while minimizing the body-diode conduction interval. In addition, compared with the conventional fixed dead-time method, the proposed algorithm effectively reduced both body-diode conduction loss and total switch loss. In particular, the reduction in total switch loss was approximately 66.12~69.85 % at rated load, whereas it increased to approximately 82.37~85.79 % under light-load conditions, demonstrating that the loss-reduction effect of the proposed algorithm is more pronounced at light load.

https://doi.org/10.5370/KIEE.2026.75.10.2794

신석현(Seok-Hyeon Shin) ; 송우창(Woo-Chang Song)

This paper analyzes the effect of pre-clustering methods on inter-array network optimization in offshore wind farms with multiple offshore substations (OSSs). A binary integer programming (BIP)-based model is used to compare integrated optimization with distance-based and angle-based pre-clustering followed by separate optimization of each cluster. Case studies are conducted for 60 MW and 400 MW offshore wind farms. In both cases, an additional OSS is assumed to be asymmetrically placed. In the 60 MW case, distance-based clustering yields a total cost comparable to that of integrated optimization, whereas angle-based clustering increases the total cost. In the 400 MW case, integrated optimization achieves the lowest total cost. The results show that pre-clustering can restrict cable routing and cable type selection, leading to less economical inter-array network designs.