• 전기학회논문지P
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• 제51권4호
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• pp.175-185
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• 2002

In this paper, a new fully digital current control method of UPS inverter, which is based on an internal model control, is proposed. In the proposed control system, overshoots and oscillations due to the computation time-delay are compensated by explicit incorporation of the time-delay in the current control loop transfer function. The internal model controller is adopted to a second order deadbeat reference-to-output response which means that its response reaches the reference in two sampling time including computational time-delays. That is, the average current of filter capacitor is been exactly equal to the reference current with a time lag of two sampling intervals. Therefore, this method has an essentially overshoot free reference-to-output response with a minimum possible rise time. The effectiveness of the proposed control system has been verified by the simulation and experimental respectively. From the simulation and experimental results, the proposed system is achieved the robust characteristics to the calculation time delay and parameter variation as well as very fast dynamic performance, thus it can be effectively applied to the power supply for the critical load.

• 디지털산업정보학회논문지
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• 제12권4호
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• pp.71-79
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• 2016

This study proposes a performance model of a shared bus multi-processor system and analyzes the effect of input/output types on system performance and overload of shared resources. This system performance model reflects the memory reference time in relation to the effect of input/output types on shared resources and the input/output processing time in relation to the input/output processor, disk buffer, and device standby places. In addition, it demonstrates the contribution of input/output types to system performance for comprehensive analysis of system performance. As the concept of workload in the probability theory and the presented model are utilized, the result of operating and analyzing the model in various conditions of processor capability, cache miss ratio, page fault ratio, disk buffer hit ratio (input/output processor and controller), memory access time, and input/output block size. A simulation is conducted to verify the analysis result.

• 경영과학
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• 제27권3호
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• pp.87-98
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• 2010

In this paper, we drew upon IMP group's Interaction model to investigate the contributing impact of Inter-organizational system (IOS) on performance through enhancing inter-organizational relationship. While most extant literature studied the contribution of IOS from transaction efficiency perspective, the relational aspect of IOS contribution on the supply chain was addressed only by a few researches. As such, we intended to fill this gap of the IOS research stream. The conceptual model was developed, with reference to process theory, to analyze how the relational perspective could be applicable to IOS impact on performance. With the 129 sample data collected at the firm level,structural equation model using the LISREL was employed to validate the proposed research model. The empirical results supported the hypotheses such as the extent of IOS usage positively influences the interaction between the firms, which thereby enhances the extent of inter-firm partnership and performance. The results help better understanding the strategic use of IOS from relationship perspective.

• Journal of Power Electronics
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• 제16권6호
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• pp.2231-2242
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• 2016

A simplified model predictive control method is presented in this paper. This method is based on a future reference voltage vector for a three-phase four-leg voltage source inverter (VSI). Compared with the three-leg VSIs, the four-leg VSI increases the possible switching states from 8 to 16 owing to a fourth leg. Among the possible states, this should be considered in the model predictive control method for selecting an optimal state. The increased number of candidate switching states and the corresponding voltage vectors increase the calculation burden. The proposed technique can preselect 5 among the 16 possible voltage vectors produced by the three-phase four-leg voltage source inverters, based on the position of the future reference voltage vector. The discrete-time model of the future reference voltage vector is built to predict the future movement of the load currents, and its position is used to choose five preselected vectors at every sampling period. As a result, the proposed method can reduce calculation load by decreasing the candidate voltage vectors used in the cost function for the four-leg VSIs, while exhibiting the same performance as the conventional method. The effectiveness of the proposed method is demonstrated with simulation and experiment results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 A
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• pp.265-267
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• 2000

A method to compute the reactive powers of the added buses by the decoupled UPFC model for the optimal voltage profile is presented, by which the voltage magnitudes of PQ buses can get closer to the reference value(usually one p.u.). The performance index for assessing how much the voltage magnitude is closer to the reference value is defined as the squared sum of the present voltage minus the reference voltage multiplied by the weighting number associated with the relative importance of the buses. Numerical example in a 10-unit 39-bus power system with 2 UPFC's shows that the performance index can be very much reduced by operating multi UPFC's with the reactive powers for the optimal voltage profile proposed in this paper.

• 경영정보학연구
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• 제12권2호
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• pp.189-203
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• 2010

민간 및 정부 전 분야에 걸쳐서 정보화사업에 대해 많은 투자가 이루어지고 있으며, 이에 대한 투자대비 성과를 측정하고자 많은 노력들이 수행되고 있다. 정보화사업에 대한 평가는 크게 수준평가와 성과평가로 구분되고 있으며, 수준평가는 정부차원으로 매년 측정하고 성과평가는 자체 평가로 수행되고 있다. 공공부문에 있어서는 범정부 성과참조모델(Performance Reference Model: PRM) ver. 2.0이 개발되어 공통 참조모델로써 정보화 성과평가의 기준을 제시하고 있다. 범정부 PRM은 가장 근간이 되는 평가분류체계와 표준 가시경로 및 성과관리 표준 양식으로 구성되어 있으며, 이를 통해 성과요소들을 분류하고 인과관계를 정의하고 있다. 효율적인 정보화사업을 관리하기 위해서는 성과에 대한 평가를 객관적으로 할 수 있는 정량적인 수치화가 필요하다. 범정부 PRM은 평가분류체계에서 측정범주는 제공하고 있지만, 측정범주별 적용기준에 대한 상대적 중요도는 제시하지 못하고 있다. 이에 본 연구에서는 공공부문 정보화사업의 성과평가의 공통기준으로 적용되고 있는 범정부 PRM의 측정범주에 대한 중요도 평가 및 우선순위를 도출하고자 한다. 연구모형은 Fuzzy QFD (Quality Function Deployment)를 이용하였으며, 측정범주의 중요도 도출시 범정부 PRM의 개발목적을 잘 반영할 수 있도록 설계하였다. 전문가의 의견을 수렴함에 있어 불확실성과 모호성을 최소화시키기 위하여 퍼지이론을 접목한 Fuzzy AHP(Analytic Hierarchy Process)와 FPP(Fuzzy Preference Programming) 방법을 적용하였다. 범정부 PRM의 개발목적에서는 성과관리 참조모델로써의 가장 기본적인 요구사항이라 할 수 있는 "정보화 성과관리를 위한 표준모형 제공"이 가장 중요한 요소로 도출되고 있다. 측정범주에 서는 고객영역에서 "서비스 품질"이 가장 높은 우선순위를 보이고 있다. 정보시스템의 서비스에 대한 품질 관리 및 향상방안에 보다 많은 투자와 노력이 필요함을 엿볼 수 있다. 범정부 PRM의 측정범주에 대한 중요도는 정부 및 공공기관에 공통의 평가기준을 제공할 수 있으며, 이를 통해 자체 평가결과를 상호 비교하여 보완/발전시킬 수 있는 기회를 제공한다. 향후 연구시 성과분류체계의 구조모형에 대한 정량적인 인과관계를 규명한다면, 범정부 PRM은 보다 객관적이고 효율적인 참조모델로 발전할 수 있을 것이다.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.222-231
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• 2016

This paper proposes a new method achieving computationally efficient attitude reference system for low cost strapdown sensors and microprocessor platform. The main idea in this method is to define and compare velocity differential vectors, geometrically computed from INS and GPS data with different update rate, for generating attitude error measurements which is further used for filter construction. A quaternion based Kalman filter configuration is applied for the attitude estimation with the adapted measurement model of differential vector comparison. Linearized model for Extended Kalman Filter and low pass filtered characteristics of measurement greatly extend the affordability of the proposed algorithm to the field of simple low cost embedded systems. For performance verification, experiment are done employing a practical low cost MEMS IMU and GPS receiver specification. Performance comparison with a high grade navigation system demonstrated good estimation result.

• 제어로봇시스템학회논문지
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• 제2권2호
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• pp.88-95
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• 1996

It is inevitable for local systems to have deviations which represent interactions and modeling errors originated from the decomposition process of a large scale system. This paper presents a decentralized control scheme for interconnected systems using local linear models and a neuro-coordinator. In the proposed method, the local system is composed of a linear model and unknown deviations caused by linearizing the subsystems around operating points or by estimating parameters of the subsystems. Because the local system has unmeasurable deviations we define a local reference model which consists of a local linear model and a neural network to estimate the deviations indirectly. The reference model is reformed into a linear model which has no deviations through a transformation of input variables and we obtain an optimum feedback control law which minimizes a local performance index. Finally, we derive a decentralized feedback control law which consists of local linear states and neural network outputs. In the decentralized control, the neuro-coordinator generates a corrective control signal to cancel the effect of deviations through backpropagation learning with the errors obtained from the differences of the local system outputs and reference model outputs. Also, the stability of local system is proved by the degree of learning of the neural network under an assumption on a neural network learning index. It is shown by computer simulations that the proposed control scheme can be applied successfully to the control of a biased two-link planar robot manipulator.

• Journal of Positioning, Navigation, and Timing
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• 제10권3호
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• pp.207-214
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• 2021

A new positioning technique for positioning of LTE base stations is proposed. The positioning information of the base station is absolutely necessary for model-based wireless positioning, and is required in some of the various merhodologies for estimating signals in an uncorrected area when construnting a database for fingerprinting-based positioning. Using the acquired location-based Reference Signal Received Power (RSRP) information to estimate the location of the base station, it is impossible with the existing trilateration methods. Therefore, in this paper, a method using reference particles is proposed. Particles are randomly generated in the application area, and signal propagation modeling is performed assuming that a base station is located in each particle. Based on this, the errors of measurements are calculated. The particle group with the minimum measurement errors is selected, the position of the base station is estimated through weighted summation, and the signal propagation model of the corresponding base station is built at the same time. The performance of the proposed technology is verified using data acquired in Seocho-dong, Seoul.

• 대한조선학회논문집
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• 제49권5호
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• pp.367-375
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• 2012

In this study, hull form of main vessel of Korean large purse seiner fishing industry is developed for the improvement of resistance performance as well as for the satisfaction to the Standard of Fishing Convention, ILO. Through the modification of reference hull form parameters and local characteristics, the hull form development is carried out. The optimum hull form parameters are searched by Sequential Quadratic Programing(SQP) method with the power estimation method of Holtrop & Mannen. To minimize the wave resistance, bulbous bow parameters are determined by the bulbous bow design method of Alvarino. The plasmatic curve is redesigned from that of the reference hull by using Lackenby method. The resistance performances of the reference and designed hull forms are estimated by using numerical simulation method. Also, the judgment of seakeeping ability and the estimation of intact stability for the designed hull form is carried out. As a result, the optimum hull form is proposed. To verify the improvement of resistance performance, model tests are carried out in towing tank. The results show that the resistance of the designed hull form is about 14% smaller than that of the reference hull from at design speed. A new hull form proposed in this study can contribute to the development of the main vessel hull form of Korean large purse seiner fishing system.