• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1020-1023
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• 1998

This paper presents a new approach to large-scale optimal generator maintenance scheduling. To do this, we developed a kind of discrete sensitivity index of each generator by using difference of objective fuction when it is on and off status. Based on the sensitivity value, we applied the conventional priority approach as an optimization method in the order of each generator's sensitivity measure. By applying the developed method, we can efficiently search the state space and dramatically reduce the computation time in a large scale power system.

• KIEE International Transactions on Power Engineering
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• v.4A no.4
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• pp.207-213
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• 2004

In this paper, the on-line volt/var control algorithms of the Load Tap Changer (LTC) transformer and Shunt Capacitor (SC) are proposed for distribution volt/var compensation. In the existing volt/var control of the distribution substation, the feeder voltage and reactive power demand of the distribution are mainly controlled by the LTC transformer tap position and on/off operation of the Sc. It is very difficult to maintain volt/var at the distribution networks within the satisfactory levels due to the discrete operation characteristics of the LTC and SC. In addition, there is the limitation of the LTC and SC operation times, which affects their functional lifetimes. The proposed volt/var control algorithm determines an optimal tap position of the LTC and on/off status of the SC at a distribution substation with multiple connected feeders. The mathematical equations of the proposed method are introduced. A simple case study is performed to verify the effectiveness of the proposed method.

• Journal of Power Electronics
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• v.19 no.1
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• pp.168-178
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• 2019

Discrete space vector modulation (DSVM) is an effective method to improve the steady-state performance of the finite control set predictive control for permanent magnet synchronous motor drive systems. However, it requires complex computations due to the presence of numerous virtual voltage vectors. This paper proposes an improved finite control set model-free predictive control using DSVM to reduce the computational burden. First, model-free deadbeat current control is used to generate the reference voltage vector. Then, based on the principle that the voltage vector closest to the reference voltage vector minimizes the cost function, the optimal voltage vector is obtained in an effective way which avoids evaluation of the cost function. Additionally, in order to implement double-objective control, a two-level decisional cost function is designed to sequentially reduce the stator currents tracking error and the inverter switching frequency. The effectiveness of the proposed control is validated based on experimental tests.

• Journal of the Korea Society for Simulation
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• v.24 no.3
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• pp.97-105
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• 2015

This paper is to analyze the efficiency of power consumption in logistic systems that are based on self-driving roller conveyors by the simulation technology. The improvement of the efficiency brings advantages for reducing greenhouse gas emission and logistics costs. A self-driving roller conveyor is operated only when products are loaded on itself. Thus, the self-driving roller conveyor systems consume less electric power than continuous-driving roller conveyor systems. In this paper, we design a DEVS (Discrete-Event based System) based simulation model and construct self-driving roller and continuous-driving roller conveyor models. For the verification and validation of the designed simulation system and conveyor models, we model a corresponding logistic model for the experimental environment and compare between the model and a real system. The main objective of this paper is to describe the power consumption advantage of self-driving roller conveyor based logistic systems using a simulation method.

• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.71-77
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• 2009

OFDM(Orthogonal Frequency Division Multiplexing) signals sutler serious nonlinear distortion in the nonlinear HPA(High Power Amplifier) because of high PAPR(Peak Average Power Ratio). Nonlinear distortion can be improved by a pre-distorter, but this pre-distorter is insufficient when the PAPR is very high in an OPFDM system. In this paper, a DFT(Discrete Fourier Transform) transform technique is introduced for PAPR reduction. It is especially important to consider the memory effect of HPA for more precise predistortion. Therefore, in this paper, we consider two models, the TWTA(Traveling-Wave Tube Amplifier) model of Saleh without a memory effect and the HPA memory polynomial model that has a memory effect. We design a pre-distorter and an adaptive pre-distorter that uses the NLMS(Normalized Least Mean Square) algorithm for the compensation of this nonlinear distortion. Without the consideration of a memory effect, the system performance would be degraded, even if the pre-distorter is used for the compensation of the nonlinear distortion. From the simulation results, we can confirm that the proposed system shows an improvement in performance.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.3
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• pp.175-181
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• 2004

The protection against transient instability and consequent out-of-step condition is a major concern for the utility industry. Unstable system may cause serious damage to system elements such as generators and transmission lines. Therefore, out-of-step detection is essential to operate a system safely. The detection of out-of-step is generally based upon the rate of movement of the apparent impedance. However such relay monitors only the apparent impedance which may not be sufficient to correctly detect all forms of out-of-step and cannot cope with out-of-step for a more complex type of instability such as very fast power swing. This paper presents the out-of-step detection algorithm using voltage frequency deviation. The digital filters based on discrete Fourier transforms (DFT) to calculate the frequency of a sinusoid voltage are used, and the generator angle is estimated using the deviation of the calculated frequency component of the voltage. The proposed out-of-step algorithm is based on the assessment of a transient stability using equal area criterion. The proposed out-of-step algorithm is verified and tested by using EMTP MODELS.

• Journal of Electrical Engineering and Technology
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• v.13 no.6
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• pp.2254-2261
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• 2018

This paper analyzes stability of current control in respect of four cases of battery energy storage system (BESS) in a stand-alone microgrid. The stand-alone microgrid is composed of BESS, diesel generator and controllable loads, where all of them have a rated power of 50kW. The four cases are considered as following: 1) BESS with a stiff grid 2) BESS with the diesel generator 3) BESS with passive damping + diesel generator 4) BESS with active damping + diesel generator, and their stabilities are analyzed in the frequency domain and discrete time domain. The comparative analysis for four cases are verified through simulation and experiments through demonstration site of the stand-alone microgrid, where the DC link is connected to a 115kW battery bank composed of 48 lead-acid batteries (400AH/12V). Experimental results show a good agreement with the analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.647-650
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• 2000

For the failure diagnosis of industrial system like various manufacturing systems, power plants and etc, many failure diagnosis approaches are considered. Here we are focus on the DES approach for failure diagnosis. We treats of failure recovery problem that is euly not mentioned in DES approach. The procedure to design a recoverable diagnoser is presented. And the recoverability, necessary and sufficient condition fur recoverability are defined. Then we make the high-level diagnoser to reduce the state size of recoverable diagnsoer. Finally, a pump-valve system example is presented.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10b
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• pp.1659-1663
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• 1991

A new control design methodology is presented here which is based on a nonlinear time-series reference model. It is indicated by highly nonlinear simulations that such designs successfully stabilize troublesome aircraft maneuvers undergoing large changes in angle of attack as well as large electric power transients due to line faults. In both applications, the nonlinear controller was significantly better than the corresponding linear adaptive controller. For the electric power network, a flexible a.c. transmission system (FACTS) with series capacitor power feedback control is studied. A bilinear auto-regressive moving average (BARMA) reference model is identified from system data and the feedback control manipulated according to a desired reference state. The control is optimized according to a predictive one-step quadratic performance index (J). A similar algorithm is derived for control of rapid changes in aircraft angle of attack over a normally unstable flight regime. In the latter case, however, a generalization of a bilinear time-series model reference includes quadratic and cubic terms in angle of attack. These applications are typical of the numerous plants for which nonlinear adaptive control has the potential to provide significant performance improvements. For aircraft control, significant maneuverability gains can provide safer transportation under large windshear disturbances as well as tactical advantages. For FACTS, there is the potential for significant increase in admissible electric power transmission over available transmission lines along with energy conservation. Electric power systems are inherently nonlinear for significant transient variations from synchronism such as may result for large fault disturbances. In such cases, traditional linear controllers may not stabilize the swing (in rotor angle) without inefficient energy wasting strategies to shed loads, etc. Fortunately, the advent of power electronics (e.g., high-speed thyristors) admits the possibility of adaptive control by means of FACTS. Line admittance manipulation seems to be an effective means to achieve stabilization and high efficiency for such FACTS. This results in parametric (or multiplicative) control of a highly nonlinear plant.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.6
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• pp.37-46
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• 2015

The wireless electrocardiographic monitoring system(WDMS) is designed to be long term monitoring for the early detection of cardiac disorders. The current version of the WDMS can identify two types of cardiac rhythms in real-time, such as atrial fibrillation(AF) and normal sinus rhythm(NSR), which are very important to track cardiac-rhythm disorders. In this study, we proposed the analysis method to discriminate the characteristics statistically evaluated in both time and frequency domains between AF and NSR using various parameters in the heart rate variability(HRV). And we applied various ECG detection methods (e.g., difference operation method) and compared the results with those of the discrete wavelet transform(DWT) method. From the statistically results, we found that the parameters such as STD RR, STD HR, RMSSD, NN50, pNN50, RR Trian, and TNN(p<0.05) are significantly different between the AF and NSR patients in time domain. On the other hand, the frequency domain analysis results showed a significant difference in VLF power($ms^2$), LF power($ms^2$), HF power($ms^2$), VLF(%), LF(%), and HF(%). In particular, the parameters such as STD RR, RMSSD, NN50, pNN50, VLF power, LF power and HF power were considered as the most useful parameters in both AF and NSR patient groups. Our proposed method can be efficiently applied to early detection of abnormal conditions and prevent the such abnormals from becoming serious.