https://doi.org/10.5370/KIEE.2023.72.3.341

장지연(Min-Seong Kang) ; 김인수(Ki-Hyun Kim)

For carbon neutrality, many countries are increasing the rate of renewable energy-based distributed generators (DGs). The DG has advantages such as voltage drop compensation and power loss reduction. However, reverse current flows and overvoltage phenomenons occur due to the penetration of DGs. DGs have different output characteristics from synchronous generators, so when DGs penetrate the grid, DGs inevitably affect the power flow and power quality of the grid. Therefore, it is necessary to check transient stability when DGs penetrate the power system. In this study, the IEEE 9-bus system, a looped system, was set as a testbed. In addition, inverter-based photovoltaic (PV) systems were used as an example of DGs. And the critical frequency limitation time was determined according to the penetration level of DGs. This study also checked the effect of reducing frequency variations through specific methodology of the PV system. Events such as fault occurrence, switch opening, fault clearing, and switch closing were set. And all the simulations for the transient analysis were conducted through DIgSILENT Power Factory.

https://doi.org/10.5370/KIEE.2023.72.3.349

김동휘(Dong-Hwi Kim) ; 장정수(Jung-Soo Jang) ; 허진(Jin Hur) ; 정승민(Seungmin Jung) ; 윤민한(Minhan Yoon)

The increasing use of inverter-based resources, while reducing synchronous generators, decreases the system's inertia, leading to an increased risk of power outages. The shift from a centralized power generation structure to a decentralized structure can be effective for stable operation of inverter-based power generation sources and to mitigate the risks of power outages. The grid forming inverter can perform the same role as a synchronous generator and can contribute to energizing primary restorative transmission systems. Grid-forming inverters must meet several requirements to replace synchronous generators in power systems. One of the most important requirements is the ability to operate as AC voltage sources. This means that the grid-forming inverter must be able to provide a stable AC voltage to the grid, just like a synchronous generator. To address this, a black start study using inverter resources was conducted, and a pumping generator-IBR cooperative black start was simulated through cooperation with an existing black start resource. The paper proposed the grid-synchronization method of grid-forming inverter and emphasizes the need for independent and quick recovery of inverter resources, which must operate as AC voltage sources to replace synchronous generators and contribute the primary power system restoration. The effectiveness of the proposed method to increase the input capacity and speed by stably inputting through synchronization has been studied and were verified through PSCAD/EMTDC simulation.

https://doi.org/10.5370/KIEE.2023.72.3.356

설영훈(Young-Hoon Seol) ; 이대한(Dae-Han Lee) ; 윤아윤(Ah-Yun Yoon)

In this paper, we propose the optimal operation algorithm for electric vehicle (EV) charging system connected with PV and ESS. The conventional method of the EV charging system in which PV and ESS are connected uses ESS only when PV generation is larger than the EV charging amount. In conventional method, the utilization of ESS is low, and the profit of the EV charging service provider is low. Therefore, this paper proposes the optimal operation method for EV charging system that uses ESS to charge during off-peak-load and discharge during peak-load. In the case study, each profits of EV charging service provider applying various EV charging pattern to the conventional method and the proposed method were compared and analyzed.

https://doi.org/10.5370/KIEE.2023.72.3.363

곽순혁(Sun-Hyeok Kwak) ; 고웅(Woong Ko)

Aggregators of distributed energy resources and consumers in the distributed energy system can transact electricity with various ways. The aggregators and the consumers can contract the appropriate power generation or power demand due to advances in the power communication. Although the aggregators and the consumers would not contract others in the conventional power system, the necessity of transaction between them will increase in the decentralized power system. The adequate operation strategies for aggregators and consumers are required to enhance their contracts and increase their benefit. In this study, we propose an operation strategy for distributed energy resources aggregators and consumers in order to maximize the social welfare. The proposed model considers the transaction between the aggregator and the consumer. The results demonstrate that the maximum social welfare can be achieved by considering the transaction between the aggregator and the consumer.

https://doi.org/10.5370/KIEE.2023.72.3.374

노상수(Sang-Su Noh) ; 한재웅(Jae-Woong Han) ; 조민승(Min-Seung Cho) ; 송화창(Hwa-Chang Song)

KEPCO is pursing 970MW ESS(Energy Storage System, 전기저장장치) for system stabilization in order to maintain stable frequency due to expansion of renewable energy and to alleviate power generation constraints on the East Coast. The ESS battery charging and discharging usage pattern depends on the frequency variation trend and the frequency of generator dropout, and the battery life is calculated according to the usage pattern and the appropriate installation quantity is calculated based on this. In this paper, the battery life calculation standard suitable for ESS stabilizing power system is established considering the frequency in the steady state and the generator dropout in the transient state. It is expected that large-scale ESS will be constructed efficiently and operated stably by calculating and applying appropriate ESS battery installation quantity which has best value for actual operation.

https://doi.org/10.5370/KIEE.2023.72.3.381

김종겸(Jong-Gyeum Kim) ; 박영진(Young-Jeen Park)

Induction generators are widely used in mini- or micro-scale hydroelectric power plants. In the case of hydroelectric power generation in which changes in flow rate and head are large, the operation of the induction generator is often lower than the rated output. An induction generator is an inductive load and has a lagging power factor, and when operated at rated output, the power factor is around 0.8. The utility recommends that the customer compensate for the low power factor. The power factor compensation is planned so that the power factor of the induction generator will be about 0.95 under the condition of operating at the rated capacity. When the output of the induction generator decreases, the reactive power required for magnetization has a low change, but the active power decreases and the power factor is further lowered. At this time, a self-excitation phenomenon in which the reactive power for power factor compensation becomes higher than the reactive power required for magnetization may occur. When the self-excitation phenomenon occurs, electrical stress is provided to the induction generator, so in order to reduce the occurrence probability, the extent to which the generator's output can be operated was analyzed. As a result of the analysis, it was confirmed that the possibility of self-excitation can be reduced if the output of the induction generator is operated not to be less than 60% of the rated value.

https://doi.org/10.5370/KIEE.2023.72.3.387

박현룡(Hyun-Yong Park) ; 임희성(Hee-Sung Lim) ; 이교범(Kyo-Beum Lee)

This paper proposes an estimation method for Lithium-Ion Batteries SOH by learning the batteries’ internal parameters using the Convolution Neural Network and the Gated Recurrent Unit. Various equivalent circuit models exist to represent the batteries’ internal parameters. Among these equivalent circuit models, the most representative model is the Randles model, and the data measured based on the Randles model is used as learning input data. The internal parameters of batteries change non-linearly depending on the operation condition and use time. So, nonlinear features are extracted using the CNN input as the batteries' parameters. The extracted features are used as an input of the GRU to learn the characteristics of change over time, and SOH is predicted through this. The learning dataset utilizes 17IND10 LibForSecUse of EMPIR, which validates the performance of the proposed model.

https://doi.org/10.5370/KIEE.2023.72.3.395

신은결(Eun-Kyeol Shin) ; 이교범(Kyo-Beum Lee)

This paper proposes the direct torque control (DTC) of interior permanent magnet synchronous motors (IPMSMs) for fast dynamic response with constant switching frequency. The conventional DTC is constructed based on the hysteresis flux and torque controllers with the flux and torque errors as input. The switching frequency of DTC is not constant. In the DTC with constant switching frequency, a torque regulator with a constant switching frequency is applied to overcome this problem, instead of the hysteresis torque controller for the conventional DTC. The DTC with constant switching frequency uses a torque regulator with a proportional-integral (PI) torque controller and a triangular carrier to realize a constant switching frequency. Compared to the conventional DTC, the DTC with constant switching frequency has the poor dynamic response because both voltage vectors increasing and decreasing torque are selected in the transient state. In this paper, the bandwidth of PI torque controller is varied to improve the dynamic response of the DTC with constant switching frequency. The effectiveness of the proposed method is verified through simulation results.

https://doi.org/10.5370/KIEE.2023.72.3.402

박지환(Ji-Hwan Park) ; 강경수(Kyeong-Soo Kang) ; 박준형(Junhyeong Park) ; 이수연(Soo-Yeon Lee)

Gate bias stress can change the threshold voltage of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT). Especially, short-term degradation of threshold voltage should be compensated since it causes motion artifacts in the display. Therefore, a new short-term degradation model was proposed based on the stretched-exponential model. Moreover, the accuracy of the proposed model was confirmed by calculating the coefficient of determination between the measured data and the fitted data.

https://doi.org/10.5370/KIEE.2023.72.3.406

김민기(Minki KIM) ; 박정호(James Jungho Pak)

While lithium-ion battery (LIB) is limited in its large-scale energy storage usage due to the scarcity of lithium resource, sodium-ion battery (SIB) is a promising alternative to LIB in the field of large-scale energy storage since sodium is abundant resource. When the chemical reaction of SIB is converted into electrical energy, sodium ions are inserted more slowly because the radius of the sodium ion is larger than lithium ion, which causes a decrease in capacitance, deforms the structure in the electrode, and deteriorates the electrochemical performance. To solve this problem, the development of SIB anode material with high capacity and structural stability is investigated. Transition metal oxide (TMO) and transition metal dichalcogenide (TMD) are considered to be promising anode materials for SIB since they have high capacity and high energy density. The review of the edvelopment trend of TMO-based anode material for SID performance improvement will lead us to realize better SIB.

https://doi.org/10.5370/KIEE.2023.72.3.413

장민영(Min-young Jang) ; 이정일(Jung-il Lee) ; 정남준(Nam-joon Jung) ; 고영준(Yeong-jun Koh)

The electricity consumption data is collected using the communication network from the smart meter. Missing values occur depending on the status of the meter and the communication network environment. In previous studies, missing value interpolation was suggested as a method of using electricity users' past electricity usage patterns, but autocorrelation in artificial intelligence techniques can reduce generalization performance. In this study, the method of generating deep learning models by business improved the stability and efficiency of the model compared to the method of interpolation by electricity user. An interpolation model creation method was presented by comparing four LSTM models with higher accuracy than GRU.

https://doi.org/10.5370/KIEE.2023.72.3.419

신지강(Jikang Shin) ; 이성호(Sungho Lee) ; 서호진(Hojin Seo) ; 임정선(Jeong-Seon Im) ; 조희(Hee Cho) ; 황명하(Myeong-Ha Hwang)

Robotic process automation (RPA) is a software workflow technology that automates simple and repetitive software-driven tasks that are traditionally carried out by humans. It is used in many companies and has resulted in the publication of numerous use cases. Notably, several failure-related risk factors have been identified, and the operation and maintenance of commercial RPA solutions is very expensive; hence, many firms have trouble reaping the benefits. Moreover, the utilization measures designed to maximize RPA benefits are terribly insufficient. For these reasons, this study proposes an open-source RPA framework for enterprise (EnterRPA) that leverages an integrated web system to improve ease-of-use and user-friendliness over existing RPAs. By applying EnterRPA to six tasks mainly performed manually by employees, we achieved a dramatic reduction from the status quo in work processing time and realized distinct improvements in operational efficiency, quality of service, implementation and integration efficacy, and risk management and compliance. We continue to support users as they create and deploy new workflows through EnterRPA and plan to expand its service areas.

https://doi.org/10.5370/KIEE.2023.72.3.428

김태경(Tae-kyeong Kim) ; 조현종(Hyun-chong Cho)

The need for renewable energy is increasing due to problems such as environmental pollution and resource depletion. Solar energy is the largest type of renewable energy and is increasing. However, when a micro-crack is formed in a solar cell, it greatly affects the photovoltaic power generation system. This degrades the performance of the solar power system and can be easily damaged. In this paper, solar cell defects were detected through Electroluminescent (EL) images. The Vision Transformer-Huge model was used to extract solar cell defect features. In addition, the CIFAR-10 augmentation policy and Imagenet augmentation policy included in Auto-augment were used to increase the performance of the model for the small dataset. When using the augmentation policy, the characteristics of the solar cell defect may disappear from the data, so filtering was performed with the model learned from the original data. For filtering, only images with a prediction probability of 70% or more of augmented images through the Soft-max function were used. When comparing the performance of the proposed methods and the method learned with the original data, it showed excellent performance. As a result, the proposed model showed a performance improvement of about 5% based on accuracy, and a recall value of about 93% was obtained.

https://doi.org/10.5370/KIEE.2023.72.3.434

권순용(SoonYong Gwon) ; 서기성(Kisung Seo)

Restoring low-resolution gray images to high-resolution color images is a challenging task known as the ill-posed problem with no fixed answer. In addition to the traditional image processing techniques, deep learning methods have recently been attempted, but it is still very difficult to restore images naturally. Various and effective approaches have been developed for each colorization and enhancing resolution of images, but simply combining the two techniques results in accumulation of errors. To solve the above problem, we propose a network that separates the loss function between colorization and super-resolution with adding a super-resolution model in parallel to maintain the performance of super-resolution. The performance of the proposed method on the DIV2K, ImageNet-1k validation dataset was compared to others via PSNR, SSIM, and FID metrics. Experimental results show that our method outperforms existing methods.

https://doi.org/10.5370/KIEE.2023.72.3.440

김태훈(Tae-Hoon Kim) ; 박종진(Jong-Jin Park)

In this paper, we proposed a new UNet model to segment teeth from dental CBCT data for orthodontic treatment. The proposed model uses both the inter-connection and intra-connection proposed by UNet3+ and the nested convolution block proposed by UNet++ in order to utilize the skip connection structure designed to improve performance in the existing UNet series of models. Also, in order to reduce the number of parameters to be learned, the convolution operation is used once or twice in the convolution block. For performance improvement, deep supervision was used for learning on a total of 8 nodes. The proposed layered UNet model shows better segmentation results than the existing UNet3+ and has excellent accuracy even though a small number of image data is used for learning. As a result of the simulation, the proposed layered UNet model using two convolution operations was the best with loss function values of 0.92, 0.85, and 0.79 for training, validation, and test data.

https://doi.org/10.5370/KIEE.2023.72.3.447

김재호(Jae-Ho Kim) ; 황선남(Sunnam Hwang) ; 김경호(Kyung-Ho Kim)

This design is about low-energy optical therapy using the photo-chemical effect of light rays on the living body using RED LED and IR LED, and it is about the emisson wavelength and power density of LED. The amount of power in light transmitted to the body by 660nm red light and 830nm near-infrared light passing through the skin was simulated according to the skin depth and the absorption coefficient of fat. In addition, the power density for the interference effect between adjacent LED was calculated for the arrangement of LED. As for the power density according to the skin depth, it was confirmed that the power density at the abdominal depth of 3.5cm would supply about 0.44mW/cm2 of energy by adding the red light power density of 1.76mW/cm2 and the power density by the IR LED.

https://doi.org/10.5370/KIEE.2023.72.3.453

강민성(Min-Seong Kang) ; 김기현(Ki-Hyun Kim) ; 구경완(Kyung-Wan Koo) ; 박상호(Sang-Ho Park)

The RE100 campaign in response to the climate crisis began mainly with global companies and global efforts to reducing carbon. Carbon neutral of agricultural and livestock will be the inevitable change also, and various studies for carbon neutral were conducted by applying RE100 with using energy from utilizing livestock manure which was continuously problematic. Based on this study and demonstration, livestock manure and waste became electricity and can get accreditation for agricultural RE100 beyond simple electrification. Also, see the possibility through registration of carbon reduction methodology and so on, that will show the way of the carbon neutral for agriculture. Based on the result of this study, waste and livestock manure became electrification, also additional value such as reduction of greenhouse gases and RE100 certification by operate resource circulation facilities which demonstrate research case that create economic efforts. Accordingly, we will reach RE100 of agricultural by cooperate with the Ministry of Agriculture, Food and Rural Affairs, Ministry of Environment and Korea Energy Agency.

https://doi.org/10.5370/KIEE.2023.72.3.459

박광묵(Kwang-Muk Park) ; 최동환(Dong-Hwan Choi) ; 방준호(Jun-Ho Bang) ; 유인호(In-Ho Ryu) ; 김태형(Tae-Hyung Kim) ; 소병문(Byung-Moon) ; 송제호(SoJe-Ho Song) ; 박형균(Hyeong-Gyoon Park)

In this study, ignition experiments were conducted with XLPE insulators in cables according to the electrodes’ forms (a flat electrode and a round electrode) while generating a 100 W?class direct current (DC) arc. The experiments generated series arcs by applying the newly revised standard UL 1699B. Arcing current and arcing voltage were measured through experiment. The ignition time was compared according to electrode forms using measured data, and the reliability analysis on the arc duration was conducted using a statistical analysis program. Afterward, analysis results were depicted with cumulative density function and probability distribution diagrams to check the distribution patterns, and the time to reach ignition was exhibited using statistical values according to percentiles. The integrated probability distribution diagram can be said to be the result of reflecting a variety of wire forms where the DC arc generation wires were placed in photovoltaic equipment.

https://doi.org/10.5370/KIEE.2023.72.3.467

채동주(Dong-Ju Chae) ; 강해권(Hae-Gweon Kang) ; 임승택(Seung-Taek Lim) ; 오찬혁(Chan-Hyeok Oh) ; 이기연(Ki-Yeon Lee)

Microgrid is being reviewed in many power systems as a supplement that can compensate for the shortcomings of central power supply, such as a remote and an out-of-the-way power supply. Simulated verification is needed to establish an electrical protection cooperation system, such as protection of human/livestock and power facilities and prevention of ripple to nearby areas. In this paper, verification of the optimal protection cooperation system valid under all assumed on/off grid conditions was conducted by reviewing the possibility of the location of ground fault, installation location of protection device, and relay element.