https://doi.org/10.5370/KIEE.2024.73.7.1095

이제림(Je-Rim Lee) ; 이근준(Geun-Joon Lee) ; 차한주(Han-Ju Cha)

AC power systems incorporating HVDC are parallel to existing AC transmission networks, hence the stability of the voltage changes according to the power transmitted by HVDC. Particularly, in power systems that use HVDC to transport the output of renewable energy sources over long distances, frequent changes in transmission power occur due to high source variability, and the evaluation of voltage stability in AC power systems with embedded HVDC becomes increasingly important for ensuring system stability. This paper proposes a method to directly calculate the critical power for voltage stability in AC systems incorporating HVDC, without relying on simulations, using Thevenin equivalent circuits. This method was applied to the IEEE-30 bus system and PSS/E sample 45 bus system, and compared with PSS/E P-V simulation results, yielding practical outcomes. Additionally, the impact of HVDC operating power on voltage stability was analyzed when varying the operational power of HVDC from zero to its rated capacity, providing significant findings regarding the effect of HVDC operation on voltage stability.

https://doi.org/10.5370/KIEE.2024.73.7.1103

이샘찬(Sam-Chan Lee) ; 신석현(Seok-Hyeon Shin) ; 김동민(Dong-Min Kim) ; 배인수(In-Su Bae)

Offshore wind power has been attracting attention as a key energy source for the carbon neutralization strategy, and has the advantage of good wind resources compared to onshore wind power, and is easy to large-scale. However, the initial installation and maintenance costs of large-scale offshore wind farms are very high, so it is important to minimize the initial investment cost. Although there are preliminary studies on the economic evaluation of the inter-array of offshore wind farms in Korea, there is still a lack of research on the inter-array that considers the economic evaluation and reliability evaluation together. In this paper, therefore, the current carrying capacity and short-circuit current of a 60MW offshore wind farm with 95 mm are compared to construct the inter-array of the offshore wind farm with the new minimum size submarine cable. The inter-array is then optimized using binary integer programming model using the Bentley-Ottmann algorithm to avoid double-crossing arcs. The economic evaluation of the inter-array is conducted by comparing the installation cost and loss cost, and the reliability evaluation considering equipment failure. Then, the optimal inter-array layout of offshore wind farm with both economic evaluation and reliability evaluation is studied and reviewed.

https://doi.org/10.5370/KIEE.2024.73.7.1112

권동영(Dong-Yeong Gwon) ; 최윤혁(Yun-Hyuk Choi)

The sustained increase in the penetration of variable energy resources causes challenges to grid resilience and can lead to supply issues during faults. In response, power utilities globally have established grid integration regulations for renewable energy to manage these challenges effectively. Flexibility is enhanced through technical requirements based on the potential variability in the grid. This paper presents the implementation of a Voltage Ride Through (VRT) model using Matlab-Simulink. The model simulates low-voltage scenarios resulting from faults and allows for an analysis of the impact of smart inverter distribution system characteristics on recovery. Therefore, This contributes insights into the recovery dynamics influenced by the characteristics of distribution systems and smart inverter operating during grid faults.

https://doi.org/10.5370/KIEE.2024.73.7.1119

심상우(Sangwoo Shim) ; 김동현(Dong-Hyun Tony Kim) ; 황재홍(Jaehong Whang) ; 서정우(Jungwoo Seo) ; 임기훈(Kihoon Lim) ; 노재형(Jaehyung Roh) ; 박종배(Jong-Bae Park)

This paper suggests the necessity of establishing a bidding system for renewable energy operators to participate in the Jeju New electricity market. The introduction of renewable energy bidding, real-time market, and imbalance penalties will create risks. Therefore, it is essential to establish a bidding system that considers risks. The system required for this includes the Jeju SMP and power generation forecasting module, and the Day-Ahead market bidding strategy module. The forecasting module can be configured through machine learning or deep learning, and the Day-Ahead market bidding strategy module is configured based on Value at Risk to reflect the risk. The Day-Ahead market bidding strategy module receives the result of the remaining two modules as input and determines Day-Ahead market bidding amount. The rule changes to be introduced in the Jeju New Electric Power Market will be extended to the land, and accordingly, research for the bidding system establishment is essential.

https://doi.org/10.5370/KIEE.2024.73.7.1127

신재현(Jae-Hyeon Shin) ; 권유한(Yu-Han Kwon) ; 김진혁(Jin-Hyeok Kim) ; 김담(Dam Kim)

Microgrids are instrumental in the transition towards distributed energy systems, classified as independent or grid-connected based on the presence of interconnectivity with the main grid. In this paper, we focused on researching grid-connected microgrid systems capable of adjusting to fluctuations in power supply balance. During interconnection with the main grid, power flow occurs through interconnection lines, leading to inevitable power losses along these lines. Hence, we propose an optimal unit commitment methodology for grid-connected microgrids, designed based on mixed-integer linear programming, which considers the power losses in the interconnection lines. The power losses were modeled as a quadratic function and categorized into various cases using piecewise linear approximation. By simulating this proposed model in the IEEE 40-bus microgrid system incorporating distributed energy resources and energy storage systems, we validated the feasibility of considering the power losses in the interconnection lines as outlined in this research.

https://doi.org/10.5370/KIEE.2024.73.7.1137

곽충근(Chung-Guen Kwak) ; 김경화(Kyung-Hwa Kim) ; 김지명(Ji-Myung Kim) ; 최성문(Sung-Moon Choi) ; 김윤호(Yun-Ho Kim) ; 노대석(Dae-Seok Rho)

Recently, the researches on lightning and surge protection system are being actively conducted due to development of the information technology and large scale interconnection of renewable energy sources in power distribution system. Because the exsiting methods have dealt with prevention of human electric shock and equipment protection only considering reference frequency when the faults such as grounding and short-circuit are occurred, operation method of grounding impedance considering both reference and transient frequencies is being required. Therefore, this paper presents a calculation method of transient grounding impedance in rods and mesh grounding types to evaluate the transient grounding impedance in high frequency bandwidth, and proposes an evaluation algorithm to reduce the transient grounding impedance. Where, the proposed algorithm calculates grounding impedance in both reference and transient frequencies, and designs proper configuration of rods and mesh grounding types in order to meet the code of KEC. And also, this paper performs the modeling which is composed of distribution system, PV system and detecting device of transient grounding impedance using PSCAD/EMTDC S/W. From the simulation results based on the evaluation algorithm and modeling, it is confirmed that the proposed algorithm is useful tool to maintain the transient impedance and surge current within the allowable limit in KEC code.

https://doi.org/10.5370/KIEE.2024.73.7.1147

정성인(Sung-In Jeong)

This study focuses on the modeling and analysis of the cylindrical linear generator for a bladeless wind power generation to overcome the limitations and drawbacks of conventional wind turbines. A bladeless wind power generation system has the advantages of low land requirement for installation and maintenance cost compared to a blade wind power turbine. As a results, it is practicable to microgrid by installation on the roof of apartments and buildings, which can maximize unused efficiency. However, a comprehensive study of generator for bladeless wind power generation is still missing in terms of design process such as design and evaluation method. The goal of the research is to analyze the characteristics of cylindrical linear generator oscillating with back-iron and PM for bladeless wind power systems. The proposed generator will be analyzed using magnetic energy by two-dimensional equivalent magnetic circuit network method, and then it has been proved by finite element method and evaluated by manufacture and experiment. Finally, the results of this project will give elaborate information about new generator structures for wind power system and provide insights into the characteristics of bladeless wind power generation.

https://doi.org/10.5370/KIEE.2024.73.7.1155

장관희(Gwan-Hui Jang) ; 최길수(Gilsu Choi) ; 김세환(Sehwan Kim)

Minimizing the torque ripple of the electric machines used in electric power steering (EPS) systems is essential to improve the drivability of vehicles. This study introduces mathematical expressions to reduce torque ripple. It also describes an efficient design process to meet multiple design objectives and constraints. A surrogate model-based optimization algorithm with adaptive sampling is applied to perform the optimal design of a fractional-slot surface-mounted permanent magnet synchronous machine (SPMSM). The results show that the optimized design achieves significant improvements in torque density, efficiency, and cost-effectiveness while meeting both torque ripple and cogging torque constraints.

https://doi.org/10.5370/KIEE.2024.73.7.1162

김지헌(Ji-Heon Kim) ; 구본관(Bon-Gwan Gu) ; 임종경(Jong-Kyong Lim) ; 김래영(Rae-Young Kim)

This paper proposes a deformed zero-sequence flux model of open-end winding (OEW) Interior Permanent Magnet Synchronous Motor (IPMSM), which takes into account non-linearity and structural features of IPMSM. The flux and phase voltage of the IPMSM are investigated using finite element analysis (FEA). This analysis confirmed the existence of the zero sequence voltage (ZSV) that causes the zero sequence current (ZSC) when utilizing an OEW inverter. Additionally, the presence of coupled components between the zero-sequence and DQ axes due to the winding structure and core saturation is identified. The proposed model effectively expresses the properties of zero-sequence components in IPMSM.

https://doi.org/10.5370/KIEE.2024.73.7.1170

김동수(Dong-Su Kim) ; 정시욱(Si-Uk Jung) ; 정재우(Jae-Woo Jung)

This paper covers the design and optimization steps of a surface-mounted permanent magnet synchronous motor (SPMSM) applied to robotic joint actuation using d-q axis equivalent circuit and Phi-L map. d-q axis equivalent circuit analysis and Phi-L map are effective ways to shorten the time of the initial design process. During initial design, various combinations of pole slots are analyzed and the combination that shows the highest efficiency is selected. Based on this selected combination, the main parameters of the motor, inductance and back electromotive force, are determined using d-q axis equivalent circuit analysis and Phi-L map. The selected parameters determine the design dimensions and key parameters that meet the required performance of the motor. In addition, based on the initial design, multi-objective optimization is utilized to reduce torque ripple and cogging torque of continuous rating and maximum rating. In addition, optimal design is performed to reduce weight and heat generation, and the performance of the initial design model and the optimized model is compared and analyzed through finite element analysis.

https://doi.org/10.5370/KIEE.2024.73.7.1182

강경호(Kyongho Kang) ; 박종덕(Jongdeok Park)

In this paper, we calculate and analyze the effects of the magnetization characteristics of the solenoid valve of the MR damper on the generation of damping force and the vehicle. First, to calculate the damping force of the MR damper, an analytical calculation program based on MATLAB/GUI is combined with a finite element analysis that can consider geometrical shape and magnetization characteristics. Second, the magnetization characteristics of various magnetic material candidates are measured through experiments. Third, in order to verify the consistency of the damping force characteristics for each speed obtained through analysis, it is compared with the test results measured by the damper test equipment. Finally, the calculated damping force characteristics are combined with the vehicle dynamics model to analyze the vehicle's driving behavior and vibration under various road conditions. After analyzing vehicle behavior and vibration damping effects depending on the magnetic material, a magnetic material suitable for the MR damper is finally proposed.

https://doi.org/10.5370/KIEE.2024.73.7.1190

신용진(Yong-Jin Shin) ; 이우철(Woo-Cheol Lee)

This paper presents an enhanced Phase-Locked Loop (PLL) method using the Goertzel algorithm to improve the performance of Power Factor Correction (PFC) and LLC resonant converters. By eliminating the current sensor at the DC-link capacitor and allowing the LLC converter to operate within the PFC converter's frequency range, the new method ensures efficient Zero Current Switching (ZCS). Experimental and simulation results demonstrate that our approach significantly improves the power factor compared to conventional methods. This solution simplifies the circuit design, reduces overall costs, and increases system reliability.

https://doi.org/10.5370/KIEE.2024.73.7.1198

서채린(Chae-Lin Seo) ; 진창수(Chang-Soo Jin) ; 연순화(Sun-Hwa Yeon) ; 신경희(Kyung-Hee Shin) ; 신동욱(Dong-Wook Shin)

In this study, Fe-2,3diaminophenazine was synthesized by reacting Fe(III) ions with 2,3-diaminophenazine in a 1:3 ratio. The electrochemical properties were evaluated using cyclic voltammetry, indicating reversible reactions based on the Ip.c/Ip,a value. Flow cell charge-discharge tests were conducted on the synthesized compound. It maintained a high current efficiency of 99.6% over 50 cycles, exhibiting 77.8% of theoretical capacity in the first cycle and retaining 64% of the initial capacity after 50 cycles. These suggest that the synthesized Fe-2,3diaminophenazine is well-suited as a cathode material for aqueous redox flow batteries, highlighting its promising potential for practical applications in energy storage systems.

https://doi.org/10.5370/KIEE.2024.73.7.1204

김준선(Jun-Seon Kim) ; 이현수(Hyun-Soo Lee) ; 이재호(Jae-Ho Lee) ; 서동욱(Dong-Wook Seo)

This paper presents an impedance boundary conditioned physical optics (IBC PO) formula suitable for calculating θ- and ?-polarized scattered field from a scatterer with an impedance surface. In addition, while in previous studies, a formula using some of the diffraction coefficients was conceptually used to determine the PO edge contribution required to obtain the fringe field, in this paper, the scattering coefficient of the PO edge contribution was obtained by deriving a formula from the definition of the PO edge contribution. The IBC PO was applied to a coated rectangular metal plate and verified by comparing it with the results of the method of moments and VIRAF tool. The proposed PO edge contribution formula was verified by applying it to a two-dimensional impedance wedge. To verify the total scattered wave, which is the sum of the IBC PO and the fringe field, the proposed formula and VIRAF tool were applied to a cylindrical scatterer composed of a combination of curved wedges.

https://doi.org/10.5370/KIEE.2024.73.7.1213

김진훈(Jin-Hoon Kim)

Many results on the stability of time-delayed linear systems with time-varying time delays have been obtained using a single Lyapunov-Krasovskii functional(LKF). This paper presents a stability result using multiple LKFs dependent on the time delay interval. Multiple LKFs are different LKFs selected in each region partitioned by the size of the time delay. First, we present a result that guarantees stability in the case of a general -multiple LKFs. Next, based on this, we present a result in the form of linear matrix inequality(LMI) that guarantees stability in the case of   . Finally, the usefulness of the presented result is shown through two well-known benchmark examples.

https://doi.org/10.5370/KIEE.2024.73.7.1220

한광희(Kwang-Hee Han) ; 한지은(Jieun Han) ; 황익호(Ick-Ho Whang) ; 나원상(Won-Sang Ra)

This paper proposes a new autopilot topology with its optimal design methodology for canard-controlled unmanned aerial vehicles(UAVs). While the traditional three-loop autopilot has been considered as a rule of thumb to control a tail-controlled UAV, it is questionable whether this topology also becomes one of the best choices for UAVs with other wing configurations. To identify a probable improvement of the existing approach, the topological property of the conventional three-loop autopilot is investigated. As a result, it is shown that the three-loop autopilot consists of a full-state feedback controller with an angle-of-attack estimator as well as an integral compensator in its feedforward path. Based on this observation, a modified three-loop autopilot is suggested by replacing the integral compensator with the proportional-integral one to improve the acceleration tracking performance. The control gains of our autopilot are designed by solving the optimal output feedback control problem. To cope with the lack of stability margin due to un-modeled actuator dynamics, the weighting matrix associated with the cost function of the problem is systematically chosen to guarantee the desired phase margin and the gain cross-over frequency. Simulation results confirm that the proposed method shows better performance for canard-controlled UAVs than the existing topology.

https://doi.org/10.5370/KIEE.2024.73.7.1232

김태원(Tae-Won Kim) ; 조상묵(Sang-Muk Cho) ; 김동현(Dong-Hyeon Kim) ; 김현돈(Hyun-Don Kim) ; 김도윤(Do-Yoon Kim)

To train a classifier using a Deep Neural Network (DNN), a substantial amount of data sets is required. However, in cases where data acquisition is challenging or the environment undergoes changes, obtaining sufficient data for training can be problematic. Data augmentation and synthesis can be used to increase the quantity of data for training. The data generated through augmentation or synthesis should closely resemble real data and accurately reflect the environments and characteristics that users aim to model. Without this resemblance, using the generated data may not yield the desired results in the actual environment. In this paper, we propose an empirical method for selecting synthetic training data that enhances the performance of a belt conveyor fault classifier model in environments where data acquisition is challenging, without compromising the existing performance of the model

https://doi.org/10.5370/KIEE.2024.73.7.1239

박천수(Cheon-Soo Park) ; 이일무(Ii-Moo Lee) ; 이주철(Ju-Cheol Lee) ; 홍준표(Jun-Pyo Hong) ; 남아영(Ah-Young Nam) ; 김홍기(Hong-Gi Kim)

One of the causes of the recent EESS fire in Korea was found to be a lack of management of the operating environment. In particular, the new and renewable energy-connected EESS installed in mountainous and coastal areas is operated in an environment where condensation is likely to occur due to the large difference in weather and exposure to a large amount of dust. Insulation is destroyed between the cell and the module enclosure, which can lead to a fire due to repeated condensation and drying in the battery module. To prevent this, attention is required to external environmental factors such as temperature and humidity in the installation space for the stable operation of EESS. Therefore, this paper proposes environmental requirements for the stable operation and management of EESS by identifying major items of environmental factors that may cause damage in the operation and management of EESS and seeking ways to minimize them.

https://doi.org/10.5370/KIEE.2024.73.7.1246

문병민(Byung-Min Moon) ; 오효석(Hyo-Seok Oh) ; 전승표(Seung-Pyo Jeon) ; 최용은(Yong-Eun Choi) ; 장진영(Chin-Young Chang) ; 김재문(Jae-Moon Kim)

In this study, we conducted a study aimed at replacing the DC motor, which drives the electric doors of EMU, with a BLDC (Brushless DC) motor. The existing DC motor has contact parts such as brushes and a commutator, which require regular maintenance due to wear caused by rotational contact. This results in decreased motor efficiency, impedes normal door opening and closing operations, and affects the operational lifespan of the drive unit. To overcome these issues and enhance the door system's performance, we propose the adoption of BLDC motors. BLDC motors operate without brushes and a commutator, reducing friction-related heat issues and lowering the probability of malfunctions. They enable stable door operations even with lower power consumption and allow precise control of position and speed using hall sensors. We developed a prototype BLDC motor door hardware based on the existing electric door profile. The motor speed and panel position were controlled through the Hall sensor of the BLDC motor. Additionally, various conditions were experimented based on the existing door speed profile to verify the reliability of the BLDC motor door position control.

https://doi.org/10.5370/KIEE.2024.73.7.1252

김종겸(Jong-Gyeum Kim)

The induction machine can be operated as an induction motor or induction generator by adjusting the rotor speed before and after the synchronous speed. Induction machines are widely used in industrial sites because they are more advantageous than other rotating machines in terms of convenience of maintenance, robust and economical price. The biggest disadvantage of this induction machine is that the voltage drop is high due to the flow of large current when starting or connecting to the grid. Since the induction generator starts and then connects to the grid near synchronous speed, there is no need to set the value of the locked rotor current high to generate a large torque when starting like an induction motor. When an induction generator generates power and sends it to the grid, it must pass through a motor operating area lower than synchronous speed. This is because the reactive power required for magnetization must be supplied from the grid. At this time, a large voltage drop may occur, mainly in the distribution system. In this study, we analyzed how the voltage drop, change in power, and power factor vary depending on the size of the current depending on the magnification of rotor locked current when developing a three-phase double squirrel cage induction generator and connecting it to the grid.

https://doi.org/10.5370/KIEE.2024.73.7.1258

이정훈(Jung-Hoon Lee)

Smart factory control, required in small-scale factory, is an accurate and clear function that controls factory devices by transmitting sensor data to a server and monitoring it on smart devices. Accordingly, in this paper, a microcontroller capable of information transmission and device control was selected, and a sensor interface, communication using a Wi-Fi shield, and data communication format with the server were designed. And it was proven that the proposed interface method is useful by actually implementing the relevant part, connecting it with a microcontroller(Arduino), server, and smart device, and checking its function.

https://doi.org/10.5370/KIEE.2024.73.7.1264

김준혁(Jun-Hyeok Kim)

This study addresses the impact of water content on the lifespan of distribution transformers. While previous studies have primarily focused on large-scale transformers in transmission and substation facilities, this research specifically examines distribution transformers. It highlights the limitations of current methods for measuring water content, especially in practical scenarios such as pole-mounted transformers where oil extraction requires operational downtime. By analyzing data from 150 distribution transformers in the field, this study establishes correlations between load data, transformer age, and water content. Additionally, it proposes a polynomial-based optimal estimation formula to statistically analyze water content based on years of use, providing valuable insights for efficient asset management strategies.