https://doi.org/10.5370/KIEE.2023.72.1.1

김인수(Insu Kim)

This study assumes a residential thermal and electric microgrid with distributed energy resources (DERs) composed of microturbines (MTs), photovoltaic systems (PVs), and wind turbines (WTs). The objective of this study is to find the optimal combination of MTs, PVs, and WTs for residential customers. For this purpose, this study defines the objective function to minimize not only the generation costs of electric, thermal energy, MTs, PVs, and WTs but also the voltage variations of the grid. Since HOMER can evaluate the lifecycle operating and maintenance costs of thermal and electric grids, this study evaluates the lifecycle cost functions of these DERs. If the cost function is fitted by second-order polynomials, quadratic programming (QP) can be used for an optimization problem because the cost function of QP is defined in the second order. Thus, using QP implemented in MATLAB, the optimal combination (e.g., the most effective capacity) of MTs, PVs, and WTs is determined. To validate the proposed method, an electric and thermal residential grid is modeled by the IEEE 13-bus test feeder. Using the backward and forward sweep power-flow method, the voltage variation of the test feeder enhanced by the DERs is evaluated. Next, cost functions and voltage variations are used as input to QP. A case study with the test feeder demonstrates the effectiveness of the proposed method.

https://doi.org/10.5370/KIEE.2023.72.1.9

김성일(Seongil Kim) ; 박영호(Young-Ho Park)

Industrial power systems include lots of non-linear loads which draw in non-sinusoidal currents. These non-sinusoidal currents are harmonic sources in the power systems, leading to power quality issues. A typical way to solve the power quality issues is to install single-tuned harmonic filter banks in parallel that provide low impedance paths for harmonic currents at their tuning orders, allowing for harmonic mitigation. Depending on harmonic orders, single-tuned harmonic filter banks have different switching characteristics: high amplitude and frequency back-to-back inrush currents of high-order harmonic filter banks; and high transient recovery voltage of low-order harmonic filter banks. This paper focuses on the latter to offer beneficial insights on power system design for safe and reliable harmonic filter bank switching. Theoretical analysis with electromagnetic transient studies describes how the high transient recovery voltage occurs in the low-order harmonic filter banks during the open operation of a circuit breaker. A field measurement on a second-order harmonic filter bank with 30 MVar and 33 kV proves that an excessive transient recovery voltage of approximately 92 kV can appear across the circuit breaker terminals. Lastly, this paper discusses the gap between this excessive voltage generated in a field and the test voltage specified in the IEC standard.

https://doi.org/10.5370/KIEE.2023.72.1.16

박준수(Jun-Su Park) ; 라마드한(Umar Fitra Ramadhan) ; 이재형(Jae-Hyeong Lee) ; 황성철(Sung-Chul Hwang) ; 윤민한(Min-Han Yoon)

Korean Power Systems are increasing their share of renewable energy as the worldwide ratio rises. The inertia of the power system is decreasing as the share of renewable energy sources rises. The system's low inertia may be contributing to issues with frequency stability, as indicated by a significant power imbalance. High Voltage Direct Current (HVDC) systems have been employed as a successful solution for flexible resources to address several issues brought on by the integration of renewable energy into the power system. The European Super Grid initiatives intend to include energy interconnections with HVDC systems used for energy transaction and frequency control, which would result in the construction of a power network connecting European countries to one another and to other regions. Similar to that, this paper has investigated how the use of frequency auxiliary control in the Korean Power System can help a China-Korea Voltage Source Converter (VSC) HVDC link increase the proportion of renewable energy sources and frequency stability. The impact of different frequency management systems, such as Emergency Power Control (EPC), Fast Frequency Response (FFR), and Limited Frequency Sensitive Mode (LFSM), on the frequency stability of the Korean power system was compared. Additionally, a study was carried out to optimize the frequency auxiliary controller's parameters based on ANN, and its effectiveness was tested by using it to control with different parameter settings.

https://doi.org/10.5370/KIEE.2023.72.1.24

이광호(Kwang-Ho Lee)

Various concerns and efforts have been made to reduce greenhouse gas emissions to curb global warming. The cap-and-trade system is evaluated to provide an effective incentive to reduce emissions. As the emission trading is introduced in the power sector, the generation strategy with emission trading can be obtained by the combined market model with power generation and emission trading. The performance of ETS or carbon-neutral policies is dependent on the total amount of permits and the ratio of allocations. In this study, the maximization of Social Welfare(SW) is considered with the ratio of allocation as a variable. The relational expression for the emission price and Nash Equilibrium are derived for the condition for the optimal SW. In the numerical results, two types of generators are compared (high-cost low-emission vs. low-cost high-emission) from the viewpoint of the optimal allocation ratio and the emission price.

https://doi.org/10.5370/KIEE.2023.72.1.30

츄방제(Bangjie Qiu) ; 오윤식(Yun-Sik Oh)

In order to restore outage loads downstream of a faulty zone in distribution networks, service restoration should be taken by using normally open switches to transfer the loads to other feeders. This paper presents a service restoration scheme based on whale optimization algorithm (WOA) to rapidly search possible topology candidates satisfying operational constraints in distribution networks such as radial topology. Loop-based topology encoding scheme is utilized for ensuring that all topology candidates keep radial structure by opening only one line in each loop. WOA, one of the nature-inspired meta-heuristic algorithms, mimics hunting scheme of humpback whales to search such a broad solution space and find the best solution. Multiple case studies on IEEE 33-bus system are conducted under various conditions in order to verify its performance and it is proven that the proposed scheme is effective in finding the best service restoration plan.

https://doi.org/10.5370/KIEE.2023.72.1.37

황병창(Byeung-Chang Hwang) ; 민병기(Byeung-Gi Min) ; 김동준(Dong-Joon Kim) ; 윤종호(Chong-Ho Yoon)

In this paper, we propose a novel TSMB bus system with multiple bidirectional data transmission and time synchronization capability for IEDs(Intelligent Electronic Devices). Unlike the legacy unidirectional TMDS(Transition Minimized Differential Signaling) used for transfer digital video signals, the proposed bus system employs dual high-speed serial TMDS link for sending trigger signals from the FPGA of main processor module and receiving the sampled data from submodules such as either current or potential transformers. For simultaneous triggering multiple submdoules, we also employ the precision timing protocol processing capability in the main processor, which generates the wall clock pulse per second(PPS) synchronized to GPS. Adopting PLL for the PPS signal, we can provide the reference clock of 98.304MHz for supporting the data rate of 491.52 Mbps over each TMDS link. The data rate can support eight 24 bits ADCs for PTs or CTs in the single link, each of which requires 4800 samplings per second. An implemented TSMB bus system with FPGA consists of a single main processor with clock expander and eight submodules, in which each submodule is connected with the bidirectional TMDS link to the FPGA of main processor module. The jitter of 1 PPS between the two main processor modules was measured to be less than 102nsec at the maximum, and the jitter of the TSMB transmission data line was measured to be less than or equal to 660ps at the TP3 point of the receiving side, confirming that the TMDS specification was satisfied. Finally, the proposed time- synchronized multi-directional bus system can contribute to the improvement of the reliability and performance of the algorithm of the intelligent protection relay system through the optimal transmission of equivalent and simultaneous sampling data without the involvement of the processor.

https://doi.org/10.5370/KIEE.2023.72.1.46

이경민(Kyung-Min Lee) ; 박철원(Chul-Won Park)

Because renewable energy sources are environmentally friendly, they are recognized as important to address the climate crisis and achieve 2050 carbon neutrality. South Korea continues to expand the VRE power grid. Recently, an alternative using PMU based big data is being explored. In this paper, we apply and compare the DNN and SVM techniques that can identify the state of the VRE power grid using PMU big data that can be analyzed more precisely than SCADA/EMS. First, real-time PMU data is collected from the PMU operating in the VRE power grid. In order to be applied to the state identification algorithm, data structure-based data preprocessing is performed. After designing a technique that can determine the state of the VRE power grid using DNN and SVM, respectively, it is implemented using a Python tool. Finally, we compare the performance of the two proposed algorithms for state identification of eight states of the power grid.

https://doi.org/10.5370/KIEE.2023.72.1.52

이충희(Chung-Hui Lee) ; 신희성(Hui-Seong Shin) ; 김기찬(Ki-Chan Kim)

In this paper, a notch is applied to the rotor to reduce the torque ripple of the double V-type IPMSM. In order to apply the notch, it is applied in consideration of the saturation and rigidity limits of the rib part, and torque ripple is optimized by varying the size of the notch according to the barrier layer.

https://doi.org/10.5370/KIEE.2023.72.1.57

김남호(Nam-Ho Kim) ; 김찬호(Chan-Ho Kim) ; 지태혁(Tae-Hyuk Ji) ; 윤한준(Han-Joon Yoon) ; 오호진(Ho-Jin Oh) ; 정상용(Sang-Yong Jung)

In this article, the analysis of electromagnetic performances and loss according to the operating ranges are conducted through the comparative study with surfaced mounted permanent magnet synchronous machine(SPMSM) and vernier PM machine(VPMM), which is classified into flux modulation pole and no flux modulation pole types. We investigated SPMSM and VPMM show different flux weakening capability at high speed, VPMM can maintain high torque due to the flux modulation effect but SPMSM was not. We revealed that high torque and power factor are related with the gear ratio closely for VPMM and SPMSM. Furthermore, VPMM with high gear ratio model is subjected to the influence of eddy current which causes degradation of the output torque and the loss of rotor core tends to be increased depending on levels of flux modulation.

https://doi.org/10.5370/KIEE.2023.72.1.65

조재훈(Jae-Hoon Cho) ; 윤한준(Han-Joon Yoon) ; 전성배(Sung-Bae Jun) ; 정상용(Sang-Yong Jung)

This paper analyzes the electromagnetic characteristics of wound field synchronous motor (WFSM) for home appliances according to pole slot combination. The analyzed factors are output torque, total harmonic distortion (THD) of back-EMF, cogging torque, efficiency and power factor (PF) which should be considered when designing motors. The pole slot combinations are selected with same number of slots per pole per phase (NSPP) of prototype interior permanent magnet synchronous motor (IPMSM). Because the electromagnetic performances show specific tendencies depending on the number of poles and each performance tends to be different, this study can be a reference in determining pole slot combinations of WFSM.

https://doi.org/10.5370/KIEE.2023.72.1.71

송민근(Min-Geun Song) ; 이우철(Woo-Cheol Lee)

The PV (photovoltaic) system can be used with RL loads on the grid side. However, when RL Load is connected, the phase of the grid current and voltage will not match due to the reactive current component. The reactive current generated at this time can be compensated by the inverter. In the case of such a single-phase PV system, a total of two current sensors are used to detect the inverter output current and the RL load current. This paper proposes a compensation technique using one current sensor without using two current sensors in a single-phase photovoltaic power generation system connected with an RL load.

https://doi.org/10.5370/KIEE.2023.72.1.79

최주승(Juseung Choi) ; 백승묵(Seung-Mook Baek)

As the proportion of renewable energy sources that are intermittent and variability increases, system uncertainty is increasing, and a probabilistic analysis that can reflect these characteristics is required. In this paper, we propose a method for generating a probablistic wind power generation model using kernel density estimation. The boundary bias problem caused by using kernel density estimation for wind power generation data is eliminated through the boundary correction method, and a bandwidth suitable for the data can be selected through the bandwidth selector. Scenarios were created from probabilistic models made in various ways, and the accuracy of the models was validated by comparing them with real data. As a result, the accuracy was improved when the scenario was created by generating the model directly from the wind power generation data by estimating the kernel density estimation.

https://doi.org/10.5370/KIEE.2023.72.1.87

차우신(Wu-Shin Cha) ; 이준식(Junsik Lee) ; (Malkeshkumar Patel) ; 이기범(Kibum Lee) ; 김준동(Joondong Kim)

Optically transparent and electrically conductive films were investigated for the flexible and transparent heaters. Metal (Ag), silver nanowires (AgNWs) and metal oxide (ITO or ZnO) were employed to form the various types of transparent heaters. A single-layered ITO, metal hybrid AgNWs (ZnO/AgNWs) and ZnO/Ag/ZnO composite were manufactured on PET substrates. Each case was tailored by large-scale device (150 mm x 100 mm). For each structure, visible light transmittance, electrical conductivity, and heating performances were investigated to show the enhanced performances from the ZnO/Ag/ZnO composite, which showed the excellent transmittable (77% at wavelength of 550 nm) and outperforming heating performances to reach 146° C with fast heating speed. The improved performances are mainly attributed to the structure of ZnO/Ag/ZnO, where the thin Ag governs the electrical property with good optical feature. This study suggests that the ZnO/Ag/ZnO transparent heater has the excellent optical and electrical properties with good flexibility and affordable scalability to enlighten the large-scale and flexible heating applications.

https://doi.org/10.5370/KIEE.2023.72.1.93

조정현(Junghyun Cho) ; 서예준(Yejune Seo) ; 고재원(Jaewon Koh) ; 장지연(Jiyeon Jang) ; 이예진(Yejin Lee) ; 박중기(Joong-ki Park) ; 이호섭(Ho-Sub Lee) ; 강승택(Sungtek Kahng)

This paper presents a compact branch-line coupler working for receiving GPS signals at two adjacent frequencies as one geometry. The GPS receiver must have the feed circuit handling a circularly polarized electric field entering the radiating element leading up to division into quadrature branches, which has been used in the conventional works. But, it takes one frequency and a new approach is needed to take two frequencies. A lattice comprising segments loaded with series and parallel capacitors and circumferential inductors is built to make the branch-line coupler handle two frequencies. L1 and L2 bands for GPS are chosen and the circuit modelling is conducted to design the component. The method is verified by running a microwave circuit simulator and measurement of the s-parameters of the fabricated prototype. The power division and reflection coefficient at 1.5 GHz as L1- and 1.2 GHz as L2-band show the result is in good agreement with the required performance.

https://doi.org/10.5370/KIEE.2023.72.1.102

김진훈(Jin-Hoon Kim)

In this paper, we consider the stability of time-delayed linear systems. First, based on the segmentation of interval and the S-procedure, we derive a new sufficient condition guaranteeing that a quadratic function is negative for a closed interval. Of course, necessary and sufficient conditions exist, but these are computationally burdensome due to too many additional variables, so sufficient conditions with few variables are required. Next, we choose an LKF and find the upper bound of its time derivative along the trajectories of systems. To transform it into the form of LMI, we apply the Bessel-Legendre inequality, the reciprocally convex inequality, and derived quadratic negative condition. Finally, two well-known numerical examples are provided to show that the proposed results are valid and less conservative

https://doi.org/10.5370/KIEE.2023.72.1.108

강성재(Sungjae Kang) ; 김세준(Sejun Kim) ; 서기성(Kisung Seo)

Occluded person re-identification is a very difficult because the specific person is occluded by obstacles or other persons or by oneself. Major works adopt transformer-based approach show excellent performances, but they used a basic transformer only. In this paper, we suggest the various techniques to improve the transformer-based Re-ID method for the occluded person as follows. First, after extracting the heatmap and then deleting random body parts on the heat map, accurate keypoint information is obtained in data augmentation. Second, Cross-attention between the keypoint heatmap and the output of the transformer's middle layer is provided to focus more on the non-occluded person area. Third K-menas clustering is utilized to enhance the representation of local features, and the structure of the network is proposed to improve the diversity of the features. We evaluate mAP and Rank-1 performance on the Occluded-Duke and Market-1501 dataset and compare the proposed model with existing state-of-the-art techniques. Experimental results show that our method outperforms state-of-the-art methods.

https://doi.org/10.5370/KIEE.2023.72.1.114

신창용(Changyong Shin)

To improve spectral efficiency in multi-cell systems, we propose a multiple-input multiple-output (MIMO) non-orthogonal multiple access technique that simultaneously transmits multiple data streams to a cluster consisting of one cell-center user and one cell-edge user. Based on the MIMO channel state of the cell-center user, the proposed technique for single-cell systems finds the receive beamforming matrix for the user and performs power allocation to its data streams. Considering the MIMO channel state of the cell-edge user and interference from the cell-center user, the technique designs the receive beamforming matrix for the cell-edge user and allocates the power for the user to its data streams. By extending this technique to multi-cell systems, the proposed technique finds the receive beamforming matrix for the cell-center user and performs power allocation to its data streams according to its MIMO channel state and interference from neighboring cells. The receive beamforming matrix design and power allocation for the cell-edge user is performed based on its MIMO channel state, interference from the cell-center user, and interference from neighboring cells. Simulation results demonstrate that the proposed technique achieves better performance than the existing techniques in terms of data rates and outage probabilities for the users

https://doi.org/10.5370/KIEE.2023.72.1.124

강해권(Hae-Gweon Kang) ; 한가람(Ga-Ram Han) ; 최동환(Dong-Hwan Choi) ; 김재진(Jae-Jin Kim) ; 유인호(In-Ho Ryu)

Domestic low-voltage electrical equipments have an environment prone to ground potential interference, due to the characteristics of grounding system. This ground potential interference affects electrical equipments and communication facilities, and amplify the error of ground resistance measurement. It is desirable to find and eliminate the root cause of ground potential interference, however it is difficult to remove that in an environment such as in a dense urban area or an area adjacent to the transmission line. In this paper, the pattern of the potential interference voltage and the effect on the conventional ground resistance measurement are analyzed based on the actual field measurement cases of the ground potential interference, and propose a ground resistance measurement method that reflects the characteristics of ground potential interference.

https://doi.org/10.5370/KIEE.2023.72.1.131

조기룡(Gi-Ryong Jo) ; 황민(Min Hwang) ; 김영석(Young-Seok Kim)

The electrical safety management act stipulates the implementation of a safety class system for inspection that overcomes the pass-fail system to raise the class of safety management for electrical facilities. Because the conventional safety class system only applies to scheduled outage inspection of electrical facilities, difficulties arise in implementing uninterruptible inspection of electrical facilities. This paper proposes the method for applying a safety class system that utilizes the results of the uninterruptible inspection. To achieve this, the proposed method recalculates the weight factor based on the conventional inspection items and constructs safety class assessment items for the application of uninterruptible inspection results. The performance of the proposed method was investigated using periodic inspection data in real site. The results of the case study indicate that the proposed method can derive the safety class by performing an uninterruptible inspection compared to a safety class based interruptible inspection.

https://doi.org/10.5370/KIEE.2023.72.1.138

박상용(Sang-Yong Park) ; 김지혜(Ji-Hye Kim) ; 김건웅(Geon-Woong Kim) ; 정지솔(Ji-Sol Jeong) ; 최효상(Hyo-Sang Choi)

This paper compared and analyzed the arc-induction efficiency of a superconducting arc-induction type DC circuit breaker. The superconducting arc-induction type DC circuit breaker comprises superconducting magnets, a mechanical cutoff contact, and an induction needle. In addition, by inducing the arc generated from the mechanical contact using the induction needle connected in series with the ground wire, the high efficiency of the arc extinguishing operation is performed. However, to perform a reliable arc-induction operation, verification of the use of an appropriate induction needle is required. Therefore, we compared and analyzed the arc-induction characteristics depending on the arc length between the mechanical contacts and the presence or absence of superconducting magnets. As a result, it was confirmed that the blocking operation time was shortened by about 21 times depending on the presence or absence of the superconducting magnet, and the result that the arc length affected the arc-induction rate was confirmed

https://doi.org/10.5370/KIEE.2023.72.1.145

정현영(Hyun-Young Jung) ; 박진영(Jin-Young Park) ; 안길영(Kil-Young Ahn) ; 홍종필(Jong-Phil Hong)

In this paper, we propose an algorithm with high-reliability for A-Type leakage current detection by applying a Fourier transform. In this study, Fourier transforms were used to improve the reliability of distinguishing between A-type leakage currents and normal currents due to ZCT saturation. The components of each current waveform were analyzed and verified in the frequency domain, and an algorithm using the content of the third harmonic compared to the fundamental was applied. By applying the proposed algorithm, high-reliability were secured compared to the operation of the existing analog A-Type earth leakage circuit breaker.