http://doi.org/10.5207/JIEIE.2024.38.4.261

Soo-Gil Kim

The intensity of circular and rectangular complex holograms generated by incoherent triangular holography was derived. The light intensity of the reconstructed image using circular complex hologram is represented in the form of Bessel functions, while for rectangular complex holograms, it is represented in the form of sinc function. From the derived equations, it can be inferred that the resolution of the reconstructed image improves as the radius of circular complex hologram increases, and for rectangular complex holograms, as the length of the horizontal and vertical directions increases. Furthermore, when the radius of circular complex hologram and the lengths of the horizontal and vertical directions of rectangular complex hologram are the same, it was confirmed that the hologram’s area is larger for the rectangle, resulting in a better resolution of the reconstructed image.

http://doi.org/10.5207/JIEIE.2024.38.4.266

Won-Kuk Son ; Uh-Chan Ryu ; Chung-Hyeok Kim

In recent times, light-emitting diode (LED) lighting has asserted its dominance in the market. As a consequence, not only converter-based LED lighting but also AC direct-driven LED lighting gained prominence due to streamlined components, resulting in lower costs and enhanced reliability. However, the latter has posed inherent challenges linked to drawbacks, such as flicker, total harmonic distortion (THD), and blinking. This study delved into LED lighting products’ flicker characteristics and electrical properties, employing various AC direct-drive methods. Through a comparative analysis of flicker values and electrical traits, an enhanced AC direct-drive circuit showing less than 2% flicker, 25% THD, and a power factor (PF) exceeding 0.96 was proposed. Additionally, the relationship between the flicker characteristics and electrical properties of AC direct-driven LED lighting products was explored, aiming to put forth safer and more advanced AC direct-driven lighting solutions. Furthermore, the blinking phenomena in lighting products, which has recently been a matter of concern, was investigated.

http://doi.org/10.5207/JIEIE.2024.38.4.272

Dong-Ik Oh ; HeeJae Oh ; Hyun-Seop Kim ; Ho-Young Cha ; Hyungsik Shin

This study demonstrates the integration of an AlGaN/GaN heterojunction field-effect transistor (HFET) with a built-in micro-light emitting diode (LED), referred to as a driving switch-integrated micro-LED. AlGaN/ GaN HFETs are known for their excellent electron mobility and high current density, making them suitable for high-speed and high-power switching applications. By incorporating a p-GaN/AlGaN/GaN heterojunctionbased LED structure in the drain region of a p-GaN/AlGaN/GaN HFET, we achieved monolithic integration that allows the HFET switching transistor to control the integrated micro-LED operation. The threshold voltage of the enhancement-mode switching p-GaN/AlGaN/GaN HFET was 1.7V, and the turn-on voltage of the monolithically integrated micro-LED was 4V. This approach represents a significant advancement in monolithic switching for GaN-based devices and confirms the potential for developing optoelectronic integrated devices using a simple and cost-effective process.

http://doi.org/10.5207/JIEIE.2024.38.4.278

JuChul Kim ; SangJoong Lee

The AC two-bus system can be understood as the aggregation of the entire power system, in which the bus voltage and the load P,Q can be interpreted as the current operating voltage and the total consumers’ demand of the system. And the sending-end and receiving-end voltage of two-bus system can be the starting-point for step-by-step voltage calculation of multiple load points in a distribution line. Calculation of the voltages in two-bus system is meaningful. The voltage-power equation composed of bus voltages and load power P,Q for an AC two-bus system has been presented in publications. In addition, an explicit formula for calculating the receiving-end voltage of an AC two-bus system with line admittance G-jB recently has been announced. This formula can yield a unique and practical solution, however, the conductor parameters used in power system computation and provided by manufacturers have been mostly expressed by impedance R+jX, not by admittance G-jB. In this paper, the formulae for sending-end and receiving-end voltage of an AC two-bus system with line impedance R+jX are derived using ohmic calculation. And an explicit formula for calculating the receiving-end voltage of AC two-bus system represented by impedance R+jX is also introduced, from which a unique and feasible solution can be obtained. The line impedance data R+jX can be substituted directly into the proposed formula without any data conversion. Example calculations show that the results by the proposed formulae are exact and the same as those by existing methods.

http://doi.org/10.5207/JIEIE.2024.38.4.288

Kyung-Min Lee ; Chul-Won Park

KEPCO installed 35 PMUs at the 154kV Yeonggwang substation in Jeollanamdo through an integrated control system construction and verification project in the renewable power generation area. Measures and research are in progress to install multiple PMUs in a substation and easily utilize the vast amount of time-synchronized phasor data obtained from them.

http://doi.org/10.5207/JIEIE.2024.38.4.294

Se-Han Lee

In this research, we designed and controlled an automatic battery swapping system based on a sliding mechanism, intended for use in mobile robots. The system removes the case holding exhausted battery from a robot, replaces it with a charged one, and returns the case to the robot. To ensure stability, the case loader of the system grabs the case holding the battery rather than the battery itself. The system’s controller manages the servo motors of the loader and the sliding mechanism through half-duplex communication. Since the controller operates on ROS (Robot Operating System), it can readily swap batteries for any mobile robots running ROS and using batteries of the same size.

http://doi.org/10.5207/JIEIE.2024.38.4.300

Younghwa Kim ; Bonhyuk Ku ; Yechan Kim ; Minkyung Jeong ; Junyoung Park ; Hobin Lee ; Jaesang Kim ; HervianaHerviana ; Hyoungku Kang

This study analyses the limitations of Korea’s Gas Insulated Switchgear (GIS) asset management approach and proposes an optimized strategy to extend the lifespan of GIS. Currently, South Korea replaces GIS after approximately 24years based on the Time-Based Management (TBM) approach, which relies on the technical standards of the late 1960s. In contrast, developed countries extend the lifespan of GIS to more than 40years, and in some cases more than 50years, through proper inspection, monitoring, testing, and maintenance. This paper elucidates the significance of GIS asset management and compares and analyses the current status of GIS lifecycle management both domestically and internationally. It identifies the limitations of the TBM approach and emphasizes the necessity of extending the lifespan of GIS through the implementation of the Condition-Based Risk Management (CBRM) technique, successfully employed in Europe and Japan. Various techniques and methodologies utilizing reliability-centred management (RCM), health index (HI), and probability of failure (PoF) metrics are examined, with case studies of successful GIS lifetime extension from Europe and Japan presented. Furthermore, the GIS lifetime is calculated based on CIGRE TB data and compared with the results from PT PLN in Indonesia to analyze the impact of various environmental conditions on GIS lifetime. In conclusion, the problems of GIS asset management in Korea are discussed, and potential improvements are suggested based on international examples.

http://doi.org/10.5207/JIEIE.2024.38.4.311

Sang-Hyeon Lee ; Yun-Hyuk Choi

The“Guarantee of Grid Connection System for Renewable Energy Projects under 1MW,” implemented in October 2016, aimed to promote small-scale renewable energy projects by ensuring grid connection and covering grid reinforcement costs by Korea Electric Power Corporation. Following this policy, applications and connections for small-scale renewable energy projects surged, with a total of 20.1GW of applications, of which 17.3GW were connected. However, indiscriminate connections have led to issues such as reverse power flow and over voltage, raising grid stability concerns. Consequently, the small-scale renewable energy grid connection system is scheduled to end in December 2023. Traditional equipment like Tap and SVR has limitations in addressing these issues, leading to the adoption of autonomous control function of the inverter for voltage control. The control function of the inverter control reactive power to adjust the point of common coupling (PCC) voltage without requiring additional equipment. This paper proposes an advanced algorithm to precisely control voltage fluctuations during line switching using the control function of the inverter. This algorithm prevents blackout caused by line outage through line switching and accurately controls voltage fluctuations using Volt-Var and DVEC functions. By modelling the inverter with Matlab/Simulink and validating voltage control results in the domestic distribution networks, the paper demonstrates how the proposed algorithm can autonomously adjust PCC voltage and maintain grid stability even during network faults.

http://doi.org/10.5207/JIEIE.2024.38.4.317

Yoon-Jae Heo ; Kyo-Beum Lee

This paper proposes an islanded operation technique using DC-DC converters. The necessity of DC-DC converters and Dual-Active-Bridge converters in distributed power is analyzed. This paper shows soft-start and voltage control using Dual-Active-Bridge converters for stable operation in the DC grid. To validate the proposed algorithm, parameters are selected and a prototype is designed. The validity of the proposed islanded operation technique is demonstrated by the experimental results.

http://doi.org/10.5207/JIEIE.2024.38.4.324

Yechan Kim ; Minkyung Jeong ; Bonhyuk Ku ; Hyoungku Kang

This paper investigates the transition from TBM (Time-Based Management) to CBRM (Condition-Based Risk Management) in global asset management trends, underscoring the importance of prioritizing asset condition in decision-making. Domestically, strategies that rely heavily on asset lifespan often result in the premature replacement of assets still in optimal condition, leading to inefficiencies. This study assesses the condition of a 25.8kV indoor GIS (Gas-Insulated Switchgear) circuit breaker, which had been in operation for 27 years and replaced under outdated management criteria. The assessment found that most of these assets were in excellent condition, highlighting the unnecessary financial and resource waste from replacing optimally performing assets. These findings advocate for a paradigm shift to a CBRM-focused strategy, indicating that such an approach could enhance economic and operational efficiency, extend asset lifespans, reduce environmental impact, and improve sustainability.