http://doi.org/10.5207/JIEIE.2025.39.6.395

Chaeeun Bae ; Hyosun Kim ; Youngjun Seo ; Youngshin Kwak

The grayscale method, which is widely used for collecting perceived color difference data, has been applied in the textile industry and in the development of color difference formulas. However, it has generally been conducted within a narrow color range and under high-luminance conditions. This study conducted a psychophysical experiment to evaluate the applicability of grayscale method under various luminance conditions and to determine whether reliable data can be obtained from non-expert participants. Three adaptation luminance conditions (99.34, 7.44, 1.56cd/m2) were implemented by attaching ND filters to a monitor. A total of ten naive observers evaluated 192 pairs of color stimuli generated based on 12 color centers. The results showed that observer repeatability increased as luminance decreased. However, the coefficient of variation for reproducibility exceeded 20%, indicating low consistency in evaluation criteria. Furthermore, for color pairs containing only hue and chroma differences, the response values were significantly lower than the CIEDE2000 predictions. This suggests that participants had difficulty evaluating chroma and hue differences based on lightness. Additionally, the luminance of grayscale used as evaluation criterion also varied, which limited the assessment of perceptual changes due to luminance variation. These findings indicate that the grayscale method has limitation when applied to naive observers and they highlight the need for a new experimental method.

http://doi.org/10.5207/JIEIE.2025.39.6.403

Gyu-Seo Lee ; Yong-Seog Kim ; Joong Kyun Kim

In this study, we explore the development process of pedestrian-friendly landscape lighting by improving the reflector design, focusing on handrail-mounted pathway lighting, while minimizing light pollution by reducing backlight. Although advancements in lighting technology have led to the widespread use of artificial lighting and enhanced human convenience, they have also had significant negative impacts on the ecological environment and human health due to increased light pollution. In response, various predictive evaluations of lighting systems and light pollution assessments have been conducted, and legal regulations also have been implemented. However, proactive research in lighting design aimed at preventing light pollution remains insufficient. We analyzed how variations in reflector material and shape influence luminosity distribution and illuminance uniformity in handrail-mounted pathway lighting. Based on these findings, we discussed reflector design directions to enhance user convenience and mitigate light pollution in landscape lighting. These improvements are also expected to reduce unnecessary energy consumption, thereby increasing energy efficiency. Also, this paper presents a lighting design in which two linear light sources are arranged on a single reflector, providing a selectable lighting environment suitable for adults taller than 1.5m and children taller than 0.8m.

http://doi.org/10.5207/JIEIE.2025.39.6.411

Hyun-Seok Choi ; Woojin Cho ; Seok-Oh Bang ; Hyun Mok Park ; Ki-Tae Kwon ; Jin-Sung Rho ; Sang-Wuk Shin ; Jong-Min Lim

This paper proposes a smart lighting system that visualizes live-broadcast context on Chzzk, a Korean live-streaming platform, through ambient lighting. The system ingests stream status and metadata (e.g., category) and maps them to color palettes while dynamically adjusting brightness and transition animations, enabling viewers to intuitively perceive changes in the broadcast environment. In particular, when a stream starts or the category changes, a category-specific color is briefly flashed to deliver an immediate alert, after which the lighting automatically shifts to a neutral white background light that is visually comfortable for display viewing. This design not only provides intuitive real-time notifications but also creates a pleasant and immersive viewing environment by reducing visual fatigue during prolonged watching. Preliminary results indicate that color and brightness-based feedback combined with comfort lighting yields higher immersion and engagement than binary on/off notifications. By extending prior Twitch-centric approaches to the Chzzk ecosystem, this study presents a transferable, real-time visual notification and comfort-lighting method for enhancing viewing experiences amid platform migration.

http://doi.org/10.5207/JIEIE.2025.39.6.420

Min-Seo Kim ; An-Seop Choi

This study conducted accelerated degradation lifetime tests for LED centerline lights and LED flashing lights under two temperature conditions, 55°C and 85°C, to estimate their lifetimes under the normal operating temperature of 25°C. The test results showed that the LED centerline light exhibited mean lifetimes of 13,246 hr at 55°C and 3,840 hr at 85°C, yielding an estimated lifetime of 58,600 hr at 25°C. For the LED flashing light, the mean lifetimes were 22,620 hr at 55°C and 9,836 hr at 85°C, with an estimated lifetime of 61,500hr at 25°C. Goodness-of-fit tests produced P-values greater than 0.05 (0.442 for the centerline light and 0.180 for the flashing light), confirming that the degradation mechanisms under both accelerated conditions were consistent. These results demonstrate that the accelerated degradation test design and the resulting data are statistically valid and reliable.

http://doi.org/10.5207/JIEIE.2025.39.6.427

Sang-Wuk Shin ; Seok-Oh Bang ; Seong-Sik Yoo ; Min-Su Lim ; Jong-Min Lim

This study investigates the impact of illuminance and correlated color temperature (CCT) on melanopic responses mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) to characterize the non-visual optical properties of indoor lighting. Eleven commercial fixtures-four human centric lighting (HCL) products and seven smart lighting devices?were measured in a darkroom using CIE S 026 metrics, including melanopic efficacy of luminous radiation (MELR), melanopic daylight efficacy ratio (MDER), melanopic equivalent daylight illuminance (MEDI), and M/P ratio. Results showed that MELR, MDER, and M/P ratio increased proportionally with CCT but were largely unaffected by illuminance. Conversely, MEDI increased with illuminance rather than CCT. No significant differences were observed between HCL and general smart lighting products under equivalent CCT and illuminance conditions. These findings highlight the importance of spectral power distribution, particularly in the 480?490 nm range, for optimizing circadian effects and suggest the need for further research using larger datasets and additional circadian metrics, such as circadian stimulus (CS) and circadian light (CLA), to support standardized evaluation and design of non-visual lighting performance.

http://doi.org/10.5207/JIEIE.2025.39.6.435

Younjoo Cho ; An-Seop Choi

This study investigates how the mounting height and direct?indirect light ratio of pendant luminaires affect non-visual lighting performance(M-EDI, Melanopic Equivalent Daylight Illuminance) and visual metrics(UGR, uniformity, etc.) in a small office, compared to flat panel luminaires. Relux-based simulations were conducted with horizontal illuminance(Eh) normalized to 500lx. Among the 28 pendant lighting scenarios, 11 met the M-EDI ≥ 250lx criterion; however, 6 were excluded because they required luminous flux beyond the rated 4,100lm. The compliant 5 scenarios showed high Ev/Eh ratios(0.74?0.95) but also high UGR values(25.2?25.6), exceeding the office recommendation(UGR ≤ 19). In contrast, flat panel luminaires did not meet the M-EDI criterion(250lx) but exhibited UGR values that met or neared the threshold. These results reveal a trade-off between visual comfort and non-visual performance, indicating that hybrid lighting strategies combining both luminaire types may be necessary.

http://doi.org/10.5207/JIEIE.2025.39.6.442

Ui-Chang Mun ; Seung-Ho Song

This paper discusses the method of estimating the output voltage and output current of the Series-Parallel(LCC) resonant converter applied to high voltage capacitor chargers. Voltage and current sensors located at the output stage are exposed to high withstand voltage in high voltage application. Accordingly, it is difficult to ensure the long term durability and consistent reliability of the sensors. Moreover, directly sensing such high output voltages necessitates high specification sensors. To address this, the output voltage and current were estimated using voltage and current on the low-voltage side of transformer. The operating principles of LCC resonant converter are analyzed. Based on these principles, the estimation algorithm is derived that using information of series resonant current and parallel resonant current. The proposed method is validated through simulations, achieving errors within 1% for output voltage and within 2% for output current.

http://doi.org/10.5207/JIEIE.2025.39.6.448

Giwan Seo

In this manuscript, we experimentally investigate the effect of DC voltage bias on laser-induced bistable switching behavior in a two-terminal device based on vanadium dioxide (VO2) thin films. To explore this phenomenon, a DC voltage source was connected in series with the device and a resistor to form a closed-loop circuit. The static and transient responses of the circuit current (I) were measured as the optical power (PL) of a ~1.55μm laser beam, incident on the VO2 film, was varied under different bias voltages (VS). In the static response, current I exhibited hysteresis with respect to PL, but only within a narrow range of VS (6 ~ 9 V). Within this range, decreasing VS shifted the hysteresis loop toward higher PL values and narrowed its width, while increasing VS had the opposite effect. Outside this voltage range (VS < 6 V or VS > 9 V), the hysteresis behavior disappeared. At low VS, the device showed no switching, and at high VS, the switching became irreversible rather than bistable. In the transient response, clear laser-induced bistable switching was observed only in a narrower VS range (8 ~ 9 V), suggesting that dynamic bistability requires more stringent bias conditions compared to static hysteresis.

http://doi.org/10.5207/JIEIE.2025.39.6.453

So-Young Jun ; Byeung-Jun Lim ; Jae-Sung Heo ; Seon-Hwan Hwang

This paper proposes a switch open fault detection method for a dual three-phase inverter system by using the DC-link current ripple analysis in an asymmetric six-phase permanent magnet synchronous motor (PMSM). When a switch open fault occurs, specific ripple components appear in the DC-link current at either the fundamental or double the fundamental frequency, depending on the type of open fault. To extract these ripple components, the proposed method applies a variable high-pass filter (VHPF), followed by a variable all-pass filter (VAPF) to introduce a 90-degree phase shift and enable peak value estimation. A low-pass filter (LPF) is then used to suppress high-frequency noise, and correlation analysis with phase current signals is conducted to detect the fault. The proposed algorithm requires no additional hardware and has been experimentally validated using a propeller benchmark system. The experimental results demonstrate its effectiveness in identifying not only the occurrence of faults but also the specific faulty phase.

http://doi.org/10.5207/JIEIE.2025.39.6.460

Geonu Jeon ; Sang-Joon Cho ; Ji-Yeon Park ; Chae-Yeon Lee ; Dong-Geun Lee

This paper proposes a DC distribution plug and power outlet system using power semiconductor devices to address issues such as sparks, surges, and fault currents that may arise during the operation of products using plug and power outlet configurations, similar to existing AC power usage, as the adoption of DC power networks increases in households. DC power lacks a zero-crossing point like AC power, which can frequently cause sparks and surges during contact when using plugs and sockets. Additionally, if overcurrent occurs due to system or device issues, DC power presents a challenge of excessive current rise compared to AC power, necessitating rapid interruption of overcurrent. To resolve potential problems in households with the introduction of DC distribution networks, the proposed plug and power outlet system in this paper enables real-time monitoring using magnetic field detection sensors and current sensors. This allows for the implementation of a circuit breaker system utilizing power semiconductor devices, enabling quick ON/OFF operations of the circuit breaker during plug-in/out actions and overcurrent situations, thus preventing electrical hazards and enhancing safety. It also efficiently detects and interrupts fault currents. The proposed system has been constructed, and its performance and validity were verified through experiments implementing the algorithm.

http://doi.org/10.5207/JIEIE.2025.39.6.466

Sang-Wook Park ; Kyo-Beum Lee

This paper analyzes the effectiveness of reducing EMI noise in digital audio signals in the HDMI mode of a soundbar by using resistors and chip ferrite beads. To select the resistor value and the impedance of the chip ferrite bead that do not distort signals, an oscilloscope is used to measure the synchronization timing of the digital audio signals. For the verification of momentary synchronization timing errors between signals, a 1kHz audio signal is employed, and audio dropouts are detected through listening tests. The EMI noise levels at various frequencies embedded in the signals are confirmed by measuring the FFT of the 1MHz to 1GHz frequency range with a spectrum analyzer. By comparing test results measured in the EMI chamber, the paper proposes the use of the most effective component?either the resistor or the chip ferrite bead?for EMI noise reduction.

http://doi.org/10.5207/JIEIE.2025.39.6.474

Sung-Min Park

This study proposes a hybrid system combining wind power generation complexes utilizing rural reservoirs and Distributed pumped storage power plants to mitigate the intermittence problem of renewable energy. Moreover, optimization analysis was performed based on this using the Homer Pro model. Analysis results discount rate of 4.5% inflation of 2% was analyzed as NPC $127,210,800 LCOE 3.20 ($/kWh). In addition, it was confirmed that both LCOE and NPC decreased as the wind speed intensity increased. It was confirmed that 791.3 billion won was reduced when a pumping storage power plant was built using rural reservoirs. The results indicated that if the energy capacity of pumped storage power plants is secured, it could increase the reliability of the power system by compensating for the variability of renewable energy. Furthermore, the introduction of a hybrid pumped storage power plant can have attractive potential for reduced initial costs as it utilizes existing rural reservoirs.

http://doi.org/10.5207/JIEIE.2025.39.6.481

Da-Woon Choi ; Geo-Seung Choi ; Yun-Hyun Cho

Recently, the switched reluctance generator (SRG) is emerging to complement the shortcomings of PM machine in renewable energy applications because of its advantages. However, the SRG have fundamental disadvantages such as vibration and noise due to the pulse-driven operation and the reluctance torque variation. This paper is focused on overcoming the disadvantages of the SRG; the rotor geometry is proposed to reduce the torque pulsation and it is designed considering the variation of inductance when the SRG is operated in a generating mode. As a result, it is available to reduce the effect of the torque ripple and vibration. In order to verify the effectiveness, the analysis result of SRG with the proposed rotor structure is compared with a conventional rotor structure under the same specifications and stator dimension. Each model is built as prototypes and the experimental verification is conducted as a result.

http://doi.org/10.5207/JIEIE.2025.39.6.486

Sang-Hyuk Lee ; Kyo-Beom Lee

This paper proposes a temperature-dependent degradation modeling approach for lithium-ion batteries using PyBaMM. A DFN-based model is extended by integrating sub-models for solid electrolyte interphase (SEI) growth, lithium plating, and loss of active material to more accurately represent the underlying degradation mechanisms. Charge?discharge simulations are conducted under various temperature conditions to identify the dominant degradation mechanisms at each temperature. Simulation results show that lithium plating and mechanical stress primarily contribute to degradation at low temperatures, whereas SEI growth becomes more significant at high temperatures.

http://doi.org/10.5207/JIEIE.2025.39.6.493

Sung-Min Kim ; Tae-Uk Jung

This paper presents a design method for small BLDC motors used in vehicle actuators. To simplify the winding process and reduce manufacturing costs, a stator structure without tooth shoe was adopted, enabling coil bobbin insertion. However, this causes efficiency loss due to insufficient magnetic flux. To address this, stator tooth tip shape and asymmetric air-gap structures were selected as design variables, and an optimized model was derived using finite element analysis (FEA) and response surface methodology (RSM). The optimized model improved efficiency by 1.61% and torque by 0.37% compared to base model. Therefore, the proposed design method is suitable for small motors and other motors with complex winding processes.

http://doi.org/10.5207/JIEIE.2025.39.6.499

Eun-Hyeok Choi

Pole-mounted transformers are essential components of distribution systems, requiring reliable fault diagnosis to prevent outages and ensure stable operation. Conventional methods?ultrasonic testing, infrared thermography, and wireless load monitoring?depend heavily on human judgment and are affected by environmental factors such as weather and temperature, making accurate detection of internal faults difficult. To overcome these limitations, a radiated electromagnetic wave detection technique based on partial discharge (PD) is necessary. Effective PD detection requires identifying the frequency characteristics of emitted electromagnetic waves and using a high-sensitivity sensor capable of detecting signals at distances of at least 10 meters. This study designs and simulates a high-sensitivity conical dipole sensor optimized for broadband performance to detect PD-induced electromagnetic radiation in distribution-level transformers. The proposed sensor improves bandwidth and detection sensitivity, and its application is expected to help prevent insulation-related outages and enhance the reliability of distribution network operation.

http://doi.org/10.5207/JIEIE.2025.39.6.503

Da-Woon Choi ; Myung-Soo Kim ; Yun-Hyun Cho

Recently, the demand for alternative energy sources has increased due to energy exhaustion and environmental concerns, and renewable energy systems such as wind and tidal power have received significant attention. As system capacities continue to grow to improve energy conversion efficiency, the development of direct-driven wind turbines exceeding 10 MW is actively progressing. To address these needs, this study deals with the design and experiment of an axial flux permanent magnet(AFPM) generator for a 2.5 MW direct-driven wind turbine system. The overall design process of the AFPM generator is presented, and a quasi-3D finite-element analysis model is proposed to accurately predict electromagnetic characteristics. The model is verified through comparison with 3D analysis results. Finally, a full-scale prototype of the AFPM generator is manufactured, and experimental evaluation is conducted to validate the proposed design and analysis approach.