https://doi.org/10.5370/KIEE.2026.75.8.1669

박영삼(Young-Sam Park) ; 모정훈(Mo JeongHoon)

This study examines the social legitimacy conditions for public-private partnerships (PPPs) in offshore transmission grid development. Offshore transmission grids are strategic infrastructures with public-good and natural-monopoly characteristics; therefore, private participation may raise concerns over privatization, public control, system operation, and local acceptance. A two-round Delphi survey was conducted with experts from government, power system operation, industry, finance, and academia. The first round identified key issues through open-ended questions, and the second round assessed importance, feasibility, content validity, response stability, and inter-group differences. The results show broad agreement on the need for PPPs, but experts emphasized public system operation, independent regulation, fair access rules, reasonable return mechanisms, local benefit sharing, and procedural participation. The OFTO (Offshore Transmission Owner) model was evaluated as less feasible in Korea. The findings suggest that social legitimacy should be secured through a hybrid governance design rather than private participation alone.

https://doi.org/10.5370/KIEE.2026.75.8.1677

권기표(Gipyo Kweon) ; 김민석(Minseok Kim) ; 김채아(Chaea Kim) ; 이대범(Daebeom Lee) ; 이동원(Dongwon Lee) ; 김범주(Beomju Kim) ; 박정후(Jeonghoo Park)

The increasing penetration of renewable energy resources (RES) in modern power grids has precipitated a significant decline in both system-wide rotational inertia and localized system strength. While prior research has often examined these factors independently, this study investigates their interdependent relationship. Specifically, the paper evaluates the impact of short-circuit capacity (SCC) on system reserve requirements by quantifying the Frequency Regulating Reserve (FRR) capacity necessary to satisfy frequency nadir constraints under the largest contingency. Through a comparative analysis of regional RES deployment within the Korean power system, simulation results indicate a consistent increasing trend in FRR requirements when RES are integrated into low-SCC areas under the tested operating conditions. These findings highlight the technical challenges and operational requirements of interconnecting RES in weak grid regions, underscoring the necessity of implementing location-aware electricity market frameworks.

https://doi.org/10.5370/KIEE.2026.75.8.1686

김준선(Junsun Kim) ; 장성호(Sung Ho Chang) ; 명성호(Seongho Myeong) ; 남태식(Taesik Nam) ; 심재웅(Jae Woong Shim)

This paper proposes a modal-analysis-based tuning framework for mitigating oscillatory instability in a grid-following inverter under reduced system-strength conditions by identifying a key tuning parameter and deriving its feasible stability region. A linearized state-space model is established, and the oscillatory behavior is investigated through eigenvalue analysis, modal assurance criterion (MAC)-based mode tracking, and participation factor analysis. The analysis reveals that the tracked oscillatory mode is not dominated by a single control loop, but instead exhibits substantial participation from PLL dynamics, P/Q outer loop states, and dq current dynamics. Based on this result, the outer loop integral gain is identified as the key tuning parameter, and its admissible range is determined by jointly considering the stabilization boundary of the high-frequency mode and the stability boundary of the low-frequency mode. The proposed approach provides a systematic procedure for selecting a critical outer loop tuning parameter and establishing a practical stability region for grid-following inverters under reduced system-strength conditions.

https://doi.org/10.5370/KIEE.2026.75.8.1694

강현구(Hyun-Koo Kang)

The increasing penetration of photovoltaic (PV) generation in distribution systems requires reliable estimation of generation output, while detailed metering data for small-scaled PV units are often unavailable. This paper proposes a method for deriving regional representative power output curves using time-series PV generation metering data. Daily generation patterns are analyzed under the assumption that PV generators within similar conditions exhibit comparable output characteristics. To identify representative generation patterns, several statistical and clustering-based approaches are examined, and k-means clustering is selected as the most effective method. The proposed approach enables practical estimation of PV generation output and supports feeder-level load estimation and distribution system planning.

https://doi.org/10.5370/KIEE.2026.75.8.1703

김우영(Woo-Young Kim) ; 조형준(Hyeong-Jun Jo) ; 김민철(Min-Chol Kim) ; 최연빈(Yeon-Bin Choi) ; 김수배(Soo-Bae Kim)

This paper proposes a proportional?resonant (PR) DC-Link voltage controller and an analytical gain design method to enhance the sub-synchronous oscillation (SSO) damping capability of conventional PI-based DC-link voltage controllers. The proposed approach derives the closed-loop characteristic equation based on the DC-link voltage dynamic model. Target closed-loop poles are then specified according to the desired damping ratio and the observed SSO frequency, from which the PR controller gains KP and KR are analytically calculated. The PR controller gains are computed using MATLAB/Simulink, and the SSO damping performance of the proposed PR controller is evaluated through PSCAD simulations in comparison with a conventional PI voltage controller. Simulation results demonstrate that the proposed PR controller more effectively damps DC-link voltage oscillations and provides improved dynamic performance, including reduced overshoot and faster settling time, compared to the PI controller.

https://doi.org/10.5370/KIEE.2026.75.8.1712

이채원(Chae-Won Lee) ; 송성윤(Sung-yoon Song)

The increasing load demand of AI data centers has raised concerns regarding its impact on power system voltage and generator output stability. Conventional active power and voltage control methods have limitations in suppressing generator output oscillations caused by rapid load fluctuations. This paper proposes an active power and voltage control scheme by integrating a Python-based external controller with a load injection method in the PSS®E environment, and validates its performance through comparison with generic models. Dynamic simulations are performed on the IEEE 118-bus test system at three buses with different short-circuit ratio (SCR) levels. The results demonstrate that applying a ramp-rate limit of 10 MW/min effectively stabilizes both bus voltage and generator output across all SCR conditions. In addition, the study suggests that AI data centers should be preferentially connected to strong grid buses, and that ramp-rate standards for large-scale power-electronics-based loads should be established.

https://doi.org/10.5370/KIEE.2026.75.8.1721

손민환(Min-hwan Son) ; 송성윤(Sung-yoon Song)

Low-frequency oscillations (LFO) in inverter-based renewable energy systems present challenges for online grid monitoring. This paper compares three modal identification techniques?Prony analysis, full SVD-based Matrix Pencil (MP-SVD), and randomized SVD-based Matrix Pencil (MP-RSVD)?for identifying damping ratios and frequencies from time-domain voltage signals. Synthetic benchmark signals are constructed with reference to the 0.6 Hz local-oscillation frequency band reported in the April 2025 Iberian blackout?not the actual event recordings?and are analyzed across five noise conditions (SNR ∞, 40, 30, 20, 10dB). Results show that Prony analysis achieves the lowest RMSE in low-noise conditions when order is properly tuned, but exhibits high sensitivity to order selection and numerical instability at high orders. MP-SVD and MP-RSVD show comparable accuracy in low-to-moderate noise, while MP-RSVD reduces computation time by 2.0?2.7× through randomized projection. At SNR 10dB, MP-SVD experiences rank inflation leading to 3.68× higher RMSE, whereas MP-RSVD maintains stable performance through target rank constraints. These results suggest MP-RSVD offers a practical accuracy?computation trade-off for online grid monitoring, though Prony analysis remains advantageous for offline tuned applications.

https://doi.org/10.5370/KIEE.2026.75.8.1731

이혜규(Hye-Gyu Lee) ; 강제헌(Je-Heon Kang) ; 황평익(Pyeong-Ik Hwang)

The advanced distribution management system (ADMS) models a distribution line as sections bounded by in-line measurement devices (ILMDs), installed on equipment such as circuit breakers and automatic switches, and estimates section loads from ILMD measurements. Accurate phase connection information of ILMDs is therefore essential. However, recorded phase labels may disagree with actual connections owing to construction errors, equipment replacement, and post-fault rewiring. Conventional methods based on voltages or synchrophasors are not directly applicable, since feeder remote terminal units (FRTUs) provide reliable measurements only for current magnitudes and power factor angles, while their voltage measurements are inaccurate. This paper proposes a phase identification method for ILMDs using only existing FRTU measurement histories. It is shown that a phase mismatch adds a disturbance term to the calculated section load, which probabilistically increases its variability. Based on this property, a suitability index is defined as the reciprocal of the sum of three normalized variability measures, i.e., the standard deviations of the section load magnitude and power factor angle, and the standard distance in the complex power plane. The phase combination maximizing the index is then selected. For an entire system, the network is divided into zones bounded by ILMDs and phases are estimated sequentially from the circuit breaker. Case studies on a test system based on an actual distribution line demonstrate that the proposed method accurately identifies the phase connections of ILMDs under measurement noise.

https://doi.org/10.5370/KIEE.2026.75.8.1739

이광호(Kwang-Ho Lee)

This study proposes an incentive mechanism for nodal pricing to ensure that the Nash Equilibrium in electricity markets manifests as a pure strategy rather than a mixed strategy. Mixed strategies lead to various issues, including conceptual complexity, computational difficulties, and significant confusion in practical applications. In this research, the Power Transfer Distribution Factor (PTDF) is redefined to be independent of the slack bus. This new PTDF provides a more realistic quantification of the impact of generator nodes on congested lines. By incorporating this factor as an incentive into generation pricing, transmission congestion is effectively reduced. The study presents a case study demonstrating the transition from a mixed strategy to a pure strategy. Through a quantitative comparative analysis with existing research, the performance of the proposed method is validated in terms of social welfare.

https://doi.org/10.5370/KIEE.2026.75.8.1746

최형석(Hyoung-Seok Choi) ; 이민행(Min-Haeng Lee) ; 장형안(Hyeong-An Jang) ; 김윤호(Yun-Ho Kim) ; 황소연(So-Yeon Hwang) ; 노대석(Dae-Seok Rho)

Recently, according to the government's green growth and carbon-neutral policy, large-scale energy storage system(ESS) has been rapidly installing and operating. However, the safety issues in ESS have been raising according to the severe damage to the entire industry with the total of around 60 fire accidents beginning in August 2017. And also, Li-ion battery-based ESS fire cases can lead to a rapid temperature rise and propagation to adjacent cells and modules due to thermal runaway characteristics, accordingly risk evaluation methods are being required on the pre and post fire case based on the operation environment data in ESS. Therefore, this paper presents the risk diagnosis algorithm of pre-post fire case in ESS based on ESS operation environment data such as temperature, humidity, oxygen, off-gas, pressure, dust, smoke, and so on, and implements a test device for ESS fire diagnosis which contains detection section, monitoring and control section, auxiliary device section. Where, the proposed risk diagnosis algorithm of pre-post fire case in ESS can evaluate the risk degree with fire scenarios in systematical manner by considering weighting factors based on the operation environment data in ESS. From the test results based on the proposed risk diagnosis algorithm of pre-post fire case in ESS, it is confirmed that the algorithm is expected to be an effective tool to effectively evaluate the risk degree of pre-post fire for both battery and non battery fire cases.

https://doi.org/10.5370/KIEE.2026.75.8.1760

정민규(Min-Kyu Jung) ; 임현준(Hyeon-Jun Im) ; 이민영(Min-Young Lee) ; 김상원(Sang-Won Kim) ; 이두희(Duehee Lee)

This study proposes a risk-based scheduling strategy for energy storage systems (ESS) in power systems with high renewable penetration, where reliability and economic operation must be balanced under load variability, renewable uncertainty, and equipment outages. A multi-dimensional risk index is developed by integrating supply margin, equipment reliability, renewable uncertainty, and expected shortfall energy. Based on this index, the ESS is operated using dynamic SOC floor policies and 24-hour look-ahead control logic to coordinate reserve retention and price-based arbitrage. The strategy is evaluated on an expanded IEEE RTS-24 system through annual sequential Monte Carlo simulation with DC-OPF transmission constraints. Compared with Rule-Based Arbitrage, it reduces LOLE by 32.8% and EENS by 35.9% while achieving higher ESS operating revenue. It also achieves the highest ELCC of 169.53MW, or 84.8% of the ESS rated power, highlighting ESS operating strategy as a key design factor.

https://doi.org/10.5370/KIEE.2026.75.8.1773

명준(Jun Myeong) ; 임재성(Jae Seong Lim) ; 이현식(Hyeon Sik Lee) ; 이환규(Hwan Gyu Lee) ; 이진환(Jin Hwan Lee)

This paper presents a performance evaluation of a Permanent Magnet Vernier Motor (PMVM) as a candidate for enhancing the output density of Direct-Drive In-Wheel Motors, compared to a conventional Permanent Magnet Synchronous Motor (PMSM). The torque and power factor characteristics are systematically analyzed by examining their correlations with the magnetic gearing effect and key design parameters, such as the winding factor, axial length, and rotor pole pair number. Through comparative analysis of motor models, the influence of each parameter on the electromagnetic characteristics is clarified. Based on these results, the optimal model with respect to torque density and power factor is identified.

https://doi.org/10.5370/KIEE.2026.75.8.1783

이성규(Seong-Kyu Lee) ; 손영우(Young-Woo Son) ; 이승현(Seung-Hyun Lee) ; 황상원(Sang-Weon Hwang) ; 김종훈(Jong-Hoon Kim)

In this paper, a model is developed to simultaneously estimate the battery state of charge (SOC) and state of temperature (SOT). Initial electrical parameters are identified through hybrid pulse power characterization tests, and a recursive least squares (RLS) method is applied to update these parameters in real time based on current and voltage data. The updated parameters are coupled with a battery heat-generation model, and COMSOL and MATLAB/Simulink are integrated to validate the joint SOC?SOT estimation performance. Validation is conducted for two cells under UDDS and 1 C-rate capacity test conditions at an ambient temperature of 25°C. The results show that the proposed model reproduced SOC with low error and captured the overall SOT trend for both cells under the tested 25°C conditions, although transient mismatch was observed in some discharge intervals. These results support the feasibility of the proposed RLS-EKF-based joint SOC-SOT estimation framework under the tested conditions.

https://doi.org/10.5370/KIEE.2026.75.8.1792

이도현(Do Hyeon Lee) ; 김채린(Chae-Lyn Kim) ; 임성원(Sung-Won Lim) ; 이병국(Byoung Kuk Lee)

This paper presents an optimal phase-driving algorithm to improve the power transfer performance of a three-phase pad in a 50-kW wireless charging system for electric vehicles (EVs). The pad consists of vertical- and horizontal-flux coils. Under misalignment, variations in the coupling coefficients can cause flux-linkage cancellation at the receiver pad, reducing the output power capability and phase power balance. Accordingly, this paper analyzes the flux-linkage characteristics with respect to receiver-pad position, identifies the optimal driving phase for each misalignment condition by minimizing the flux-cancellation, and proposes a phase-driving algorithm based on identified phase. Experimental validation was conducted using a 50-kW inductive power transfer (IPT) system employing a double-sided LCC compensation network. The results demonstrate that the proposed algorithm improves the output power and power balance among the phases under representative misalignment conditions.

https://doi.org/10.5370/KIEE.2026.75.8.1801

홍기준(Gi-Jun Hong) ; 공태현(Tae-Hyeon Gong) ; 이상승(Sang-Seung Lee) ; 김태윤(Tae-Yoon Kim) ; 김종훈(Jong-Hoon Kim)

This paper proposes an offline parameter identification framework based on the Levenberg-Marquardt (LM) algorithm with parameter transformation techniques to improve the accuracy and numerical stability of one-RC equivalent circuit model (ECM) parameter optimization for lithium-ion batteries. Since ECM-based state-of-charge (SOC) estimation accuracy is strongly dependent on parameter quality, it is important to mitigate the numerical instability caused by the large scale disparity between polarization resistance ? ??? and capacitance ? ??? . To address this issue, this study compares two transformation-based methods: log-scale transformation (LM-Log) and sigmoid function transformation (LM-Sig). LM-Log mitigates scale imbalance through relative rate-of-change updates in logarithmic space, while LM-Sig provides both scale normalization and absolute parameter bounds through sigmoid mapping. An extended Kalman filter (EKF) is constructed using the identified parameters, and terminal voltage and SOC estimation performance is evaluated under two scenarios: an OCV-based pulse discharge profile for a Samsung SDI INR21700-50E cylindrical cell and a photovoltaic energy storage system (PVESS) dynamic charge-discharge profile for an SK pouch cell. In the PVESS validation, the parameter set identified and optimized from the OCV test is applied without additional re-optimization. The results show that LM-Sig achieves the best overall performance in both scenarios. For the INR21700-50E cell, LM-Sig reduces the maximum terminal voltage and SOC errors by 63.4% and 68.4%, respectively, compared with non-optimized parameters. For the SK pouch cell under the PVESS profile, LM-Sig reduces the maximum terminal voltage and SOC errors by 14.0% and 21.5%, respectively. These results indicate that the proposed framework can provide physically reasonable and numerically stable initial parameters for ECM-based SOC estimation, and may serve as a useful basis for subsequent online adaptive algorithms in applications where post-deployment maintenance is structurally constrained.

https://doi.org/10.5370/KIEE.2026.75.8.1814

정승민(Seung-min Jung) ; 김민성(Minseong Kim) ; 김도현(Do-Hyeon Kim) ; 이준석(June-Seok Lee)

This paper analyzes and compares two carrier-based zero-sequence pulse-width modulation (PWM) methods, Double-Zero-Sequence (DZS) PWM and Common-Zero-Sequence (CZS) PWM, for dual-motor drives fed by a five-leg voltage-source inverter (FLVSI). Although both methods use offset-voltage injection to expand the linear modulation range and reduce output-voltage harmonics, their performance depends on the phase difference between the voltage vectors of each motor. To compare the two methods, the linear modulation ranges are derived based on the pole-voltage references of each method. In addition, the zero-vector dwell-time allocation is analyzed with respect to the phase difference. The analysis shows that CZS PWM provides a wider linear modulation range and lower output-voltage harmonics than DZS PWM at small phase differences. However, as the phase difference increases, the modulation characteristics of the two methods become comparable.

https://doi.org/10.5370/KIEE.2026.75.8.1824

응우옌딘푸응이아(Nghia-Phu Nguyen Dinh) ; 이준엽(Jun-Yeop Lee) ; 딘민차우(Minh-Chau Dinh) ; 이석주(Seok-Ju Lee)

This paper develops a continuous-time current-based state-space model of a Doubly-Fed Induction Generator (DFIG) wind turbine for use as a reusable virtual generator in wind turbine digital twin frameworks. The model is formulated in the synchronous dq frame and incorporates rotor-side PVdq control, mechanical shaft dynamics, and a grid Thevenin equivalent to capture dominant electromechanical behavior in a compact form. Model parameters are derived from SCADA data, and the virtual generator is implemented as a reusable simulation block. The model is validated using three SCADA datasets by comparing simulated active power with measured references over the same time intervals. The results show consistent tracking of SCADA active power trends across the tested operating range, achieving an average MAPE of 6.83% and %RMSE of 6.29%, supporting its applicability to power system studies and digital twin integration.

https://doi.org/10.5370/KIEE.2026.75.8.1831

한재수(Jaesu Han)

This study analyzed a fuel cell-battery hybrid power system under real ship power demand conditions. A load profile was constructed using measured data from an electric propulsion ferry, including propulsion and hotel load power. Three rule-based power distribution strategies were compared: power-following, SOC-step, and reference power-based strategies. The power-following strategy reduced battery power burden but increased fuel cell power fluctuation and showed saturation in high-load regions. The SOC-step strategy enabled intuitive SOC management but caused stepwise fuel cell power changes and increased battery participation. The reference power-based strategy reduced rapid fuel cell power variation by assigning the average load to the fuel cell and transient load to the battery. The results indicate that ship power distribution strategies should be evaluated by considering fuel economy, SOC behavior, battery burden, and fuel cell power stability.

https://doi.org/10.5370/KIEE.2026.75.8.1843

안정훈(Jung-Hoon Ahn) ; 이영달(Young-Dal Lee)

Although autonomous driving technologies are automating vehicle driving and parking, EV charging still remains a major operational bottleneck that requires physical driver intervention. Accordingly, wireless charging is gaining attention not only as a convenience technology replacing conductive charging, but also as a key technology for redefining energy supply in autonomous vehicles. This paper examines EV wireless charging by extending the conventional alignment- and maximum-output-oriented design perspective toward an energy-operation-oriented perspective. It discusses the distinct roles of static and dynamic wireless charging, the possibility of compatible operation, and key research directions including AI-based coupling coefficient prediction, power transfer control, abnormal-state diagnosis, route-infrastructure-grid coordinated operation, and future standardization and demonstration strategies.

https://doi.org/10.5370/KIEE.2026.75.8.1854

한성희(Seong-Hee Han) ; 김동욱(Dong-Wook Kim)

This paper presents a high-gain power amplifier(PA) monolithic microwave integrated circuit(MMIC) tailored for Ka-band satellite and next-generation communication systems. To mitigate gain degradation at millimeter-wave frequencies, a gain-boosting technique utilizing an embedding feedback network?derived from gain-plane analysis?is proposed and experimentally validated. The three-stage PA MMIC was fabricated using a 0.15-μm GaN HEMT process. The first stage incorporates an embedded transistor structure for enhanced gain, while the final stage employs parallel-combined transistors to achieve high output power. The chip occupies a compact area of 2.5 × 2.1 mm2. Measurement results demonstrate a power gain of 22.6?25.5 dB over a very wide frequency range of 32?38 GHz, corresponding to a remarkable 7.53?8.5 dB per stage. Input and output reflection coefficients remain below -10 dB across the same range. Furthermore, within the 30?40 GHz band, the PA delivers a saturated output power(Psat) of 36.4?37.8 dBm and a power-added efficiency(PAE) of 28.5?31.1%. Compared to the previously published state-of-the-art works, this PA achieves superior gain per stage and high output power density.

https://doi.org/10.5370/KIEE.2026.75.8.1861

류주완(Juwan Ryu) ; 박기훈(Kihun Park) ; 나완수(Wansoo Nah)

This paper presents the design and performance evaluation of a 5 kV, 20 kHz high-repetition-rate pulse generator for evaluating the vulnerability of automotive electronic components to IEMI-induced conducted transient overvoltage pulses in future mobility environments. Conventional spark-gap-based Marx generators suffer from voltage control instability due to gap spacing errors and low pulse repetition rates (PRR) below tens of Hz. To overcome these limitations, this study proposes a 5-stage MOSFET Marx generator topology employing power MOSFETs as switching elements, combined with a single active gate driver and multi-stage passive gate driver structure. Steady-state current was derived through R-L time-constant analysis to ensure component ratings and thermal stability. Insulation distance design based on IPC-2221B standards and partial inductance analysis were applied to enhance the electrical reliability of high-voltage PCBs. Stable pulse output was verified at an output voltage of ?5 kV and PRR of 20 kHz through comparison of ADS simulation and experimental results.

https://doi.org/10.5370/KIEE.2026.75.8.1872

이주봉(Ju-Bong Lee) ; 권구영(Gu-Young Kwon) ; 이춘권(Chun-Kwon Lee)

Reflectometry-based cable diagnosis is used to detect impedance discontinuities and estimate fault locations in submarine and power cables. Among various reflectometry methods, time-frequency domain reflectometry (TFDR) evaluates the similarity between incident and reflected signals in the time-frequency domain. In conventional TFDR, real-valued measured signals are converted into analytic signals using the Hilbert transform before Wigner-Ville distribution (WVD) and time-frequency cross correlation (TFCC) analysis. However, for Gaussian-enveloped linear chirp (GELC) signals, the Hilbert-transform-based analytic signal may include approximation errors due to nonstationary AM-FM characteristics, finite-length FFT implementation, spectral leakage, and approximate Bedrosian conditions. These errors can distort the WVD representation and degrade TFCC-based detection reliability. In this paper, a phase-sweep-based complex signal estimation method is applied to improve TFDR detection performance. Multiple real-valued responses acquired with different initial phases are modeled using cosine and sine components, and the complex response is estimated using least squares. Experimental results show that the proposed method reduces out-of-band WVD energy leakage and increases TFCC similarity coefficients at factory joint locations. The results demonstrate that phase-sweep-based complex signal estimation can improve weak reflection detection in TFDR-based cable diagnosis.

https://doi.org/10.5370/KIEE.2026.75.8.1879

윤성호(Sung-Ho Yoon) ; 이권준(Kwon-Joon Lee) ; 최진욱(Jin-Wook Choe)

This paper analyzes reflectometry signal characteristics according to metallic sheath damage severity in dry type (lead sheath) and wet type (copper wire sheath) submarine cables for offshore wind farms. Three reflectometry methods time domain reflectometry (TDR), time-frequency domain reflectometry (TFDR), and frequency domain reflectometry (FDR) were applied to cable specimens with incremental damage levels from 0% to 100%. DC resistance of metallic sheath was simultaneously measured at each damage level to establish a quantitative relationship with reflectometry signals. FDR, which employs broadband impedance spectroscopy via a vector network analyzer, showed high sensitivity to partial damage in wet type cables, detecting characteristic impedance deviation and normalized reflection voltage changes from approximately 60% wire damage. In contrast, TDR and TFDR required complete sheath fracture (100%) for reliable detection in both cable types. For TFDR, cross-term interference arising from closely spaced reflection sources can reduce fault localization accuracy. The dry type lead sheath exhibited negligible impedance change below 100% damage owing to its continuous tubular structure, whereas progressive wire cutting in the wet type cable produced cumulative impedance perturbations detectable by FDR. DC resistance of metallic sheath in the wet type cable increased progressively with damage level, showing a quantitative correlation with FDR reflection coefficient changes. These findings provide practical guidance for selecting reflectometry based diagnostic methods for offshore wind submarine cable health monitoring.

https://doi.org/10.5370/KIEE.2026.75.8.1887

김가현(Ga-Hyun Kim) ; 서예슬(Ye-Seul Seo) ; 임장섭(Jang-Seob Lim)

This paper compares the MMU Index R with the newly proposed KEPCO Index to improve insulation diagnostics for underground distribution cables. The MMU Index R, used in Very Low Frequency (VLF) tanδ diagnostics, relies on the Skirt factor, which was unobtainable for about 15% of the field data studied. The KEPCO Index excludes this volatile factor, applying instead the trend line slopes and standard deviations of Tangent Delta (TD) and its differential (DTD) as weights. Across about 6,000 field data points, the indices differed in virtual versus trend line use, normalization, and Skirt factor use. Some data judged defective by the MMU Index R were judged normal by the KEPCO Index; for these, DTD lay solely within Grade C to E. Such discrepancies could misclassify a defective cable as normal, a latent risk to supply stability. Whether this stems from the KEPCO Index design or from Skirt calculation errors remains unclear, requiring further study of the groups where the indices disagree.

https://doi.org/10.5370/KIEE.2026.75.8.1893

서예슬(Ye-Seul Seo) ; 김가현(Ga-Hyun Kim) ; 최현준(Hyen-Jun Choi) ; 임장섭(Jang-Seob Lim)

To secure the reliability of extra high voltage power cables, evaluating the properties of TR XLPE is essential. This study fabricated pinhole defect specimens of commercial XLPE and TR XLPE A, B to verify their water tree suppression and initial dielectric strength. FEM analysis quantified an electric field concentration of 475kV/mm at the defect tip, which coincided with the actual water tree initiation site in accelerated aging tests. The maximum water tree growth lengths were 331μm for TR XLPE A and 212μm for TR XLPE B. Weibull analysis of initial AC breakdown strength showed that the scale parameter of TR materials, 11.8kV/mm, improved by 5.4% over commercial XLPE, and the shape parameter of TR XLPE B increased by 15.4%. By correlating numerical electric field stress with physical degradation and statistical breakdown thresholds, this study provides baseline indicators that can be utilized as a standard for evaluating the secondary dielectric strength of aged cable insulation.

https://doi.org/10.5370/KIEE.2026.75.8.1899

류재현(Jae-Hyun Ryu) ; 권구영(Gu-Young Kwon) ; 이춘권(Chun-Kwon Lee) ; 장승진(Seung Jin Chang)

This study examines whether propagation constants estimated by reflectometry can track insulation-property changes relevant to wet-type submarine cable diagnosis. Time-frequency domain reflectometry (TFDR) and stepped-frequency waveform reflectometry (SFWR) were applied under identical conditions to a calibrated XLPE cable model. Relative permittivity and input loss tangent were varied separately while the other parameter was fixed. Attenuation and phase constants were estimated from the reflected signals, and an effective loss tangent including conductor and dielectric losses was calculated. Increasing relative permittivity increased both constants, with a larger relative increase in the phase constant, resulting in a lower effective loss tangent. Increasing the input loss tangent increased the estimated effective loss tangent in both methods. The consistent trends demonstrate the feasibility of tracking dielectric-property changes using reflectometry and provide a basis for future validation on wet-type submarine cables.

https://doi.org/10.5370/KIEE.2026.75.8.1908

노우진(Woo-Jin Noh) ; 김선혁(Seon Hyeog Kim) ; 이용태(Yongtae Lee) ; 권구영(Gu-Young Kwon)

This paper presents an adaptive time-window integration method for Mixed-Signal Reflectometry (MSR)-based fault location in an 800 mm MI submarine cable model. In MSR, the DC component of the squared response is extracted at each swept frequency and transformed into a distance response using FFT. Since the squared signal contains a ripple, a fixed integration window may cause frequency-dependent DC estimation errors. The proposed method adjusts the integration window according to the ripple period at each frequency. An Advanced Design System (ADS) model with a 100 m cable, a 50 Ω shunt fault at 70 m, and an open terminal was used for verification. The fixed 1 μs and adaptive 1-cycle windows estimated the fault at 76.831 m and 70.343 m, respectively. Under white Gaussian noise, the 32-cycle window showed the lowest RMSE for all tested SNRs, indicating improved robustness of MSR-based submarine cable fault diagnosis.

https://doi.org/10.5370/KIEE.2026.75.8.1915

양철민(Chul-Min Yang) ; 정현철(Hyun-Chul Jung) ; 정재철(Jae-Cehol Jeong) ; 홍동석(Dong-Suk Hong) ; 김현주(Hyeon-Ju Kim)

This study investigated the chemical and space charge characteristics of Tree-Retardant Cross-Linked Polyethylene (TR-XLPE) for DC insulation applications. XLPE and TR-XLPE were thermally aged at 140°C for up to 30 days and analyzed using DSC, OIT, FTIR, and space charge measurements. Both materials showed decreases in crystallization enthalpy and OIT during the early stage of aging, while crystallization enthalpy gradually recovered with prolonged aging. FTIR analysis revealed changes in carbonyl and ester groups caused by additive depletion and oxidation. Before aging, TR-XLPE showed better space charge suppression than XLPE; however, space charge accumulation increased with aging and exceeded that of XLPE after long-term aging. Yellowing and degradation of space charge characteristics were also observed. These results show that thermal aging significantly changes the chemical and space charge characteristics of TR-XLPE.

https://doi.org/10.5370/KIEE.2026.75.8.1922

이경문(Kyungmun Lee)

This paper proposes a modular UV-C sterilizer system design concept and control algorithm for sanitary treatment of agricultural waste nutrient solution and circulation water. The proposed system adopts a parallel lego-type combination structure of a single sterilization module, securing both variability in processing capacity and manufacturing economy. Each module consists of an integrated unit comprising a UV-C lamp, quartz tube, independent flow channel, and inlet/outlet port, applying the TUV 36T5 HO 4P SE rated lamp (75W, total lamp length 850mm). The sterilization control algorithm includes water level detection, automatic pump and lamp operation, optimal temperature maintenance using a heater rod, and automatic valve control cleaning function. This structure is verified to be an optimized design for large-scale agricultural waste nutrient solution processing systems in terms of flow flexibility, ease of maintenance, manufacturing economy, and stable sterilization performance.

https://doi.org/10.5370/KIEE.2026.75.8.1929

김지환(Ji-hwan Kim) ; 조현종(Hyun-chong Cho)

Timely identification of sow farrowing is important for farm management and piglet welfare. This study proposes RAR-LbC, a loss-based ROI-aligned training strategy for classifying top-view farrowing-pen images into farrowing and non-farrowing classes. EfficientNetV2 is used as the backbone, and the proposed method improves training by modifying the loss function without changing the network architecture. RAR-LbC combines ROI-based Activation Regularization (RAR), which suppresses activation probability mass outside a predefined ROI, with Localization by Classification (LbC), which aligns the attention distribution used for feature aggregation with the ROI. Experiments showed that RAR-LbC improved overall classification performance compared with the original-image baseline, increasing recall from 72.58% to 74.42%, which indicates improved detection of farrowing frames. Paired t-test, ablation, and sensitivity analyses further confirmed the effectiveness of the proposed ROI-aligned loss design. These results suggest that RAR-LbC can improve sow farrowing status classification by guiding the model toward farrowing-relevant regions during training.

https://doi.org/10.5370/KIEE.2026.75.8.1937

박재성(Jaesung Park) ; 김경호(Kyungho Kim)

This paper proposes a butterfly-shaped wire dipole antenna, referred to as the Butterfly Broadband Dipole (BBD), for ionospheric- radiation-based HF communication systems, and presents a comprehensive performance analysis. The conventional BBD antenna, widely employed over the HF band (2?30 MHz), requires a large installation footprint, with an approximate height of 26 m, length of 76 m, and width of 45.7 m. To enable deployment in height-restricted environments, the proposed design increases the number of antenna wires from 8 to 10 while reducing the overall height relative to the conventional structure. The proposed antenna has a butterfly geometry with a total length of 76 m, a total width of 45 m, and a maximum height of 18 m. Broadband impedance matching is achieved by employing a 1:300 impedance transformer. The target performance is to maintain a VSWR of 2.5:1 or less and a realized gain of at least 5 dBi across the entire 2?30 MHz band. The antenna characteristics are systematically evaluated by comparing the impedance and radiation behavior as functions of installation height and number of wire elements, thereby verifying the design validity and practical applicability of the proposed structure.

https://doi.org/10.5370/KIEE.2026.75.8.1943

임재우(Jae-Woo Lim)

This paper proposes a proportional-integral (PI) control scheme utilizing a feedforward gain for zero adjustment in the pitch-axis attitude control of wing-controlled missiles. Conventional PI controllers suffer from excessive overshoot, while 3-loop autopilots exhibit slow tracking performance. To resolve this issue, an independent feedforward gain is introduced to shift the closed-loop zero. Mathematical analysis proves this decouples the transient response from relative stability without altering the open-loop characteristic equation. Numerical simulations demonstrate that the proposed method effectively suppresses overshoot and minimizes the ITAE index while perfectly preserving original stability margins, offering a robust autopilot design for highly maneuverable aerospace vehicles.

https://doi.org/10.5370/KIEE.2026.75.8.1951

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

In modern power systems, the proliferation of non-linear loads has led to significant harmonic distortion. This study aims to re-evaluate power quality assessment methods by comparing Displacement Power Factor (DPF) with True Power Factor (TPF) in the presence of these non-linear loads. The research utilizes a "Power Tetrahedron" model, which extends the traditional 2-dimensional power triangle into a 3-dimensional structure by incorporating Distortion Reactive Power(D). A simulation was conducted using an electromagnetic transient analysis program, modeling a system that combines linear loads and non-linear loads. Additionally, the effectiveness of a 5th harmonic passive filter was tested to analyze improvements in power quality. The study demonstrates that DPF-centered monitoring fails to account for distortion losses, potentially leading to revenue loss for power providers and efficiency degradation for consumers. It is imperative to establish new power factor compensation standards and billing systems that reflect TPF. Future research should explore the economic and technical advantages of active filters capable of mitigating multiple harmonic orders simultaneously.

https://doi.org/10.5370/KIEE.2026.75.8.1958

구자영(Ja-Young Koo) ; 곽준호(Jun-Ho Kwak) ; 윤호열(Ho-Yeol Yoon) ; 김희동(Hee-Dong Kim)

Analyzing the temporal trends of AC current, dissipation factor (tanδ), and partial discharge (PD) magnitude enables the evaluation of insulation degradation and the proactive prediction of potential defects in long-term operational generator stator windings. Stator windings in newly manufactured generators often exhibit numerous internal micro-delaminations within the groundwall insulation, which initially leads to elevated baseline measurements for AC current, tanδ, and PD magnitude. However, once the generator enters commercial service, high operational currents induce thermal expansion that gradually minimizes these micro-delaminations over successive operating years. Specifically, the PD magnitude decreases to its minimum after 2～3 years of operation and subsequently increases as insulation aging initiates. Conversely, the AC current increase rate (△I) and dissipation factor increase rate (Δtanδ) require more than a decade of operation to decrease, after which they progressively rise as structural degradation commences within the groundwall insulation. In this study, off-line insulation diagnostic tests were performed to evaluate the degradation state of a steam turbine (S/T) generator (374 MVA, 20 kV) stator winding operated for over 23 years. Based on the diagnostic test results, a detailed trend analysis was conducted using data collected over six measurement intervals during planned maintenance outages over a 15-year period from 2011 to 2026, focusing on AC current, tanδ, and PD magnitude.

https://doi.org/10.5370/KIEE.2026.75.8.1965

이재희(Jae-Hee Lee) ; 박시형(Si-Hyung Park) ; 김지섭(Ji-Sub Kim) ; 서창진(Chang-Jin Seo)

This study presents the design and implementation of an advanced, real-time portable License Plate Recognition (LPR) system optimized for edge computing environments using the Raspberry Pi 5. To ensure high-speed processing and enhanced accuracy, a comparative performance analysis was conducted on AI accelerators, specifically the Coral USB Single TPU and M.2 Dual Edge TPU. For detection, YOLOv8n and EfficientDet-Lite0 were evaluated, while LPRNet was adopted for recognition. To optimize these models for edge deployment, transfer learning and integer quantization were strategically applied. Results revealed that EfficientDet- Lite0 outperformed YOLOv8n by a margin of 0.16 in mAP@50-95. Furthermore, by leveraging transfer learning and model format conversion, the LPRNet model size was reduced to one-tenth of its original footprint, achieving significant architectural efficiency. Robust real-time performance was successfully validated by integrating the Coral M.2 Dual Edge TPU.

https://doi.org/10.5370/KIEE.2026.75.8.1971

박종복(Jong-Bok Park) ; 지평식(Pyeong-Shik Ji)

This paper presents an experimental analysis of distance-dependent variations in arc fault signal features and their rankings in residential electrical loads. In practical systems, current signals are measured at distribution panels rather than at the arc source, where characteristics can be affected by cable length and load-dependent propagation effects. To investigate this, arc and normal current signals were acquired at cable lengths from 0 m to 30 m. Time- and frequency-domain features were extracted and evaluated using the effect size measure η² to derive feature rankings across distances. The analysis focuses on a microwave oven and an electric fan. Results show that in the microwave oven, feature values and rankings vary significantly with distance, leading to reduced discriminative performance. In contrast, for the electric fan, key features such as variance, RMS, and normalized harmonics maintain consistent performance, showing high ranking stability across distances. These results indicate that distance effects depend on load characteristics and highlight the need for distance-aware feature analysis for reliable panel-level arc fault detection.

https://doi.org/10.5370/KIEE.2026.75.8.1979

안한웅(Hanwoong Ahn)

Precision sun-pointing of a solar array drive assembly (SADA) requires both high reliability and accurate pointing. In a gearless direct-drive configuration, microstepping improves pointing resolution, but the achievable open-loop accuracy is limited by the motor's detent torque. This paper proposes a detent feedforward compensation method using a position-indexed compensation map to reduce detent-induced pointing errors. Integrated motor-drive simulations are performed to analyze the relationship between resolution and accuracy, the sensitivity to detent ratio and compensation effectiveness, and the open-loop dynamic characteristics. The results show that the proposed method significantly reduces the detent-induced accuracy floor while preserving a sensorless open-loop structure. Design conditions on detent ratio, compensation effectiveness, and equivalent damping ratio required to satisfy a given pointing-accuracy target are also derived.

https://doi.org/10.5370/KIEE.2026.75.8.1986

김지열(Gi-Yeol Kim) ; 김성열(Sung-Yul Kim) ; 임채옥(Chae-Og Lim) ; 한종부(Jong-Boo Han) ; 이여진(Yeo-Jin Lee) ; 손은태(Eun-Tae Son)

This study presents a model of a closed cathode Polymer Electrolyte Membrane Fuel Cell (PEMFC) system for submarine Air Independent Propulsion (AIP) applications. The proposed model separately represents the PEMFC stack and Balance of Plant (BOP) components, including fuel and oxygen supply, humidification, exhaust, recirculation, and cooling systems, each implemented as independent modules. This modular structure enables quantitative analysis of BOP component power consumption and stack performance interaction, and allows individual modules to be updated without reconstructing the entire system model. The model was implemented in a Python-based simulation environment and validated against manufacturer test data for a 300 W class PEMFC stack and a MATLAB/Simulink-based model using the MathWorks Simscape library, showing voltage and power errors of approximately 8 % and 5 % compared with the manufacturer data. The MATLAB/Simulink-based model showed voltage and power errors of approximately 10 % and 6 % compared with the same manufacturer data. The model also demonstrated stable load-following performance under rapid load variation conditions. Based on the model with confirmed fidelity, temperature and relative humidity effects on system efficiency were analyzed. Stack efficiency was highest at 35 ~ 45 ℃ and 70 ~ 80 % relative humidity, while system efficiency showed significant degradation under low-temperature and low-humidity conditions due to increased BOP load. The ratio ranged from 8.96 % to 9.59 %, confirming that BOP power consumption has a non-negligible impact on overall system efficiency. The proposed model can be utilized as a foundational tool for operational analysis, component improvement, and future energy management studies of submarine PEMFC systems.

https://doi.org/10.5370/KIEE.2026.75.8.2000

이영재(Young-Jae Lee)

This study proposes an ESS-based Energy Control Protocol (E-ECP) to efficiently manage regenerative energy generated by regenerative elevators in apartment complexes. Based on real-time IoT sensor data, E-ECP comprehensively evaluates ESS remaining capacity, predicted regenerative power, and emergency reserve power, then dynamically determines four operating states?normal, overload, conserve, and emergency?and supplies power according to load priority. Computer simulations were conducted for a 200-household apartment complex in Korea under normal (S1), peak load (S2), and emergency (S3) scenarios, and the results were compared with Baseline, SOC-band, and Greedy strategies. The results showed that E-ECP reduced peak demand by 14.85?18.66 % as ESS capacity increased under peak-load conditions, and achieved emergency load protection rates of 10.76?21.53 % under emergency conditions, demonstrating superior protection performance for essential facilities compared with other methods.

https://doi.org/10.5370/KIEE.2026.75.8.2007

김채린(Chae-Lyn Kim) ; 김도연(Do yeon Kim) ; 임성원(Sung-Won Lim) ; 이병국(Byoung Kuk Lee)

This paper proposes a design and control method for an LCC-LCC compensation network for high-efficiency operation of an 11 kW 2-stage wireless power transfer system for electric vehicles. The limitations of applying a conventional compensation network design to a 2-stage IPT converter are analyzed, and a design and control method is developed based on the output characteristics with respect to the coupling coefficient and battery charging profile. The proposed method is validated through PSIM-based loss analysis, and experimental results from a hardware prototype verify its effectiveness.