• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
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• pp.46-48
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• 2005

This paper discusses a probabilistic method for power system security assessment. The security analysis relates to the ability of the electric power systems to survive sudden disturbances such as electric short circuits or unanticipated loss of system elements. It consists of both steady state and dynamic security analyses, which are not two separate issues but should be considered together. In steady state security analysis including voltage security analysis, the analysis checks that the system is operated within security limits by OPF (optimal power flow) after the transition to a new operating point. Until now, many utilities have difficulty in including dynamic aspects due to computational capabilities. On the other hand. dynamic security analysis is required to ensure that the transition may lead to an acceptable operating condition. Transient stability, which is the ability of power systems to maintain synchronism when subjected to a large disturbance. is a principal component in dynamic security analysis. Usually any loss of synchronism may cause additional outages and make the present steady state analysis of the post-contingency condition inadequate for unstable cases. This is the reason for the need of dynamic studies in power systems. Probabilistic criterion can be used to recognize the probabilistic nature of system components while considering system security. In this approach. we do not have to assign any predetermined margin of safety. A comprehensive conceptual framework for probabilistic static and dynamic assessment is presented in this paper. The simulation results of the Western System Coordinating Council (WSCC) system compare an analytical method with Monte-Carlo simulation (MCS).

• 조명전기설비학회논문지
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• 제24권5호
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• pp.44-54
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• 2010

SynRM 효율최적화 제어는 다른 교류전동기에 비해 SynRM의 효율이 낮기 때문에 에너지 절약과 환경보존의 관점에서 매우 중요하다. 본 논문에서는 다중 AFLC를 이용하여 철손을 고려한 SynRM의 새로운 효율 최적화 제어를 제안하였다. 최대효율에서 SynRM을 구동하기 위해 토크전류와 여자전류사이의 최적전류비를 분석하여 구한다. 본 논문에서는 동손과 철손을 최소로 하는 SynRM의 효율 최적화 제어를 제안하였다. 특정한 모터토크를 제공하는 d축과 q축 전류의 다양한 조합이 존재한다. 효율 최적화의 목적은 정상상태에서 최소 손실을 제공하는 d축과 q축 전류의 조합을 찾는 것이며, 제안된 제어기의 제어 성능은 다양한 동작조건의 분석을 통해 평가되었다. 분석된 결과는 제안된 알고리즘의 타당성을 입증한다.

• 전력전자학회논문지
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• 제20권5호
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• pp.410-420
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• 2015

This paper provides a comparison of power converter loss and thermal description for voltage source and current source type 5 MW-class medium-voltage topologies of wind turbines. Neutral-point clamped three-level converter is adopted for a voltage source type topology, whereas a two-level converter is employed for current source type topology, considering the popularity in the industry. To match the required voltage level of 4160 V with the same switching device of IGCT as in the voltage source converter, two active switches are connected in series for the case of current source converter. Transient thermal modeling of a four-layer Foster network for heat transfer is done to better estimate the transient junction and case temperature of power semiconductors during various operating conditions in wind turbines. The loss analysis is confirmed through PLECS simulations. Comparison result shows that the VSC-based wind turbine system has higher efficiency than the CSC under the rated operating conditions.

• 대한전기학회논문지
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• 제36권12호
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• pp.874-887
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• 1987

The efficiency of a synchronous motor can be substantially improved by controlling armature voltage, field excitation, and load angle on optimum values which yield minimum input power at any specified torque and speed. This improvement is particularly noticeable in the case of light loads. In addition, the control of armature input voltage improves the power factor at which the motor operates. Employed in the analysis is a new equivalent circuit model of the motor which incorporates the frequency dependent nature of the motor parameters and the effects of iron loss. The stability of synchronous motor operation is studied by applying the Nyquist stability criterion to the linearized equations which describe the behavior of the motor as the motor loads perturb about a steady-state operating point. This investigation reveals that, in some cases, the stable region of the motor is delineated from the results of a computer simulation. With a view to reducing harmonic loss and improving torque pulsation from harmonic components, a very poweful pulse amplitude modulation (PAM) method using an 16-bit microcomputer has been developed. This method has the advantages of simplicity of control algorithms and requires small memory space for storing thyristor trigger angles for a three-phase PAM inverter. The method can be used for smooth control of both modulation depth and frequency over a wide range.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.466-473
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• 2007

The comparison for the performance of heating systems, district heating and separate heating and power, is carried out in terms of energy consumption and environment on the basis of real operating data. The efficiency of boiler and the heat loss within the housing are assumed with reasonable manner due to the lack of reliable data regarding those quantities. The assessment for the established criteria of previous studies is performed and the new criteria for the analysis is proposed. It is shown that the district heating system is superior to the separate heating and power system from the point of view of reduction of energy use and environment improvement. The sensitivity study for those quantities with uncertainty such as the boiler efficiency and heat loss within the housing is carried out also and the reasons for the analysis results are discussed in detail.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.485-486
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• 2016

This paper proposes a new hybrid five-level voltage-source inverter topology, based on the conventional five-level active neutral-point-clamped topology (5L-ANPC), where the lower number of switching devices is required, resulting in saving the cost. The operating principle and control method of the proposed topology is described. The comparison of THD, power losses, loss distribution, and cost of components are evaluated among the proposed topology, the 5L-ANPC and 5L-DCI (diode-clamped inverters) topology.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.236-241
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• 2001

This paper presents a novel prototype of active voltage-clamping capacitor-assisted edge resonant soft switching PWM inverter operating at a constant frequency variable power (VPCF) regulation scheme, which is suitable for consumer high-power induction-heating cooking appliances. New generation IGBT with a trench gate is particularly improved in order to reduce conduction loss due to its lowered saturation voltage characteristics. The soft switching load resonant and quasi-resonant inverter designed distinctively using the latest IGBTs is evaluated from an experimental point of view.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.890-891
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• 2011

This paper presents efficiency improvement of a universal motor used in a vacuum cleaner. The transient computation is carried out by employing finite element analysis with nonlinear material curves. Working point of magnetic field is investigated and operating frequencies are analyzed using harmonics analysis. New non-oriented electrical steel is developed for the motor regarding permeability and iron loss at the frequencies. Accordingly, new electrical steel is applied to the motor, which leads to improve efficiency of the motor.

• 대한기계학회논문집B
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• 제40권8호
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• pp.519-525
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• 2016

펌프 성능 관점에서 바라보면 회전날개의 충격손실을 최소화하는 것은 매우 중요하다. 본 연구는 회전날개의 충격손실에 직접적으로 영향을 미치는 흡입 케이싱 내에 설치되는 안내깃의 형상 및 설치 각 변화가 축류 펌프의 성능에 미치는 효과를 수치 해석 방법을 통해 살펴보았다. 그리고 주어진 운전조건에서 흡입 케이싱 내에 설치되는 안내깃의 최적형상 및 설치 각을 최적화 기법을 사용하여 최적화하였다.

• 보건행정학회지
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• 제6권1호
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• pp.85-109
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• 1996

Telemedicine can increase accessibility to advance medical technology at the university hospital for community residents living in a remote area. This paper focused on the economic evaluation of telemedicine to identify important factors influencing costs and benefits and to understand how these factors can be changed to improve economic performance of the telemedicine. When the telemedicine project currently operating in Korea was evaluated based on the traditional cost-benefit analysis, the results showed a heavy net loss wiht a B/C ration of 0.56. As several values were added to the analysis based on the Information Economics approach, B/C ratios steadly increased. When the saving of medical expenses from the early detection of diseases was taken into a consideration, the ration exceeded the break-even point. >From the sensitivity analysis, a number of patients and the cost for equipment and communication were found to be the key factors for influencing economic performance of telemedicine.