• Journal of Power Electronics
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• 제8권4호
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• pp.301-308
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• 2008

This paper proposes a method of improving the stability in sensor-less control of permanent magnet synchronous motors. The control method for low-speed region is divided into two: One is a high frequency method, which involves a problem of reverse rotation once misdetection of the permanent magnet polarity should occur, and another one is a current drive method, which has a problem that phase and speed oscillations are caused by quick speed changes. Hence, authors propose adoption of the current drive method for the basic control system with added compensation of stabilization by means of the high frequency method. This combination secures stable control with no risk of reversal and less vibration. In addition, authors have also considered a frequency separation filter of a shorter delay time so that current control performance will not lower even when high frequencies are introduced. This filter has achieved simplified compensation using repetitive characteristic through the utilization of the periodicity of high frequency current. Simulation and experiment have been conducted to verify that the stable performance of this system is improved.

• 한국시스템다이내믹스연구
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• 제7권2호
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• pp.57-80
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• 2006

Nuclear technology made a great contribution to the national economy and society by localization of nuclear power plant design, and by stabilization of electricity price, etc. It is very important to conduct the retrospective analysis for the nuclear technology contribution to the national economy and society, but it is more important to conduct prospective analysis for the nuclear technology contribution. The term "technology value" is often used in the prospective analysis to value the result of technology development. There are various definitions of technology value, but generally it means the increment of future revenue or the reduction of future cost by technology development. These technology valuation methods are widely used in various fields (information technology or energy technology, etc). The main objective of this research is to develop valuation methodology that represents unique characteristics of nuclear power technology. The valuation methodology that incorporates market share changes of generation technologies was developed. The technology valuation model which consists of five modules (electricity demand forecast module, technology development module, market share module, electricity generation module, total cost module) to incorporate market share changes of generation technologies was developed. The nuclear power technology value assessed by this technology valuation model was 3 times more than the value assessed by the conventional method. So it was confirmed that it is very important to incorporates market share changes of generation technologies. The valuation results of nuclear power technology in this study can be used as policy data for ensuring the benefits of nuclear power R&D (Research and Development) investment.

• 동력기계공학회지
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• 제3권4호
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• pp.79-85
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• 1999

The magnetic levitation system is utilized in the magnetic bearing of high-speed rotor system because of little friction, no lubrication, no noise and so on. The magnetic levitation system needs the feedback controller for the stabilization of system, and gap sensors are generally used to measure the gap. The use of sensor easily goes into troublesome caused by sensor failure discord between the measurement point and the control point etc. This paper gives a controller design method of magnetic levitation system which satisfies the given $H_{\infty}$ control performance and the robust stability of the presence of physical parameter perturbations. To the end, we investigated the validity of the designed controller through results of simulation.

• International Journal of Control, Automation, and Systems
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• 제6권4호
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• pp.506-514
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• 2008

This paper presents an intelligent model; named as free model, approach for a closed-loop system identification using input and output data and its application to design a power system stabilizer (PSS). The free model concept is introduced as an alternative intelligent system technique to design a controller for such dynamic system, which is complex, difficult to know, or unknown, with input and output data only, and it does not require the detail knowledge of mathematical model for the system. In the free model, the data used has incremental forms using backward difference operators. The parameters of the free model can be obtained by simultaneous perturbation stochastic approximation (SPSA) method. A linear transformation is introduced to convert the free model into a linear model so that a conventional linear controller design method can be applied. In this paper, the feasibility of the proposed method is demonstrated in a one-machine infinite bus power system. The linear quadratic regulator (LQR) method is applied to the free model to design a PSS for the system, and compared with the conventional PSS. The proposed SPSA-based LQR controller is robust in different loading conditions and system failures such as the outage of a major transmission line or a three phase to ground fault which causes the change of the system structure.

• 동력기계공학회지
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• 제1권1호
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• pp.144-153
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• 1997

The magnetic levitation system is utilized in the magnetic bearing of high-speed rotor because of little friction, no lubrication, no noise and so on. The magnetic levitation system need the feedback controller for the stabilization of system, and gap sensors are generally used to measure the gap. The use of gap sensors brings out the increase of the number of troublesome, and the decrease of the control performance because of the dislocation between the measurement point and the control point. This paper presents the design of the gap estimation circuit for the sensorless method proposed by authors in the magnetic levitation system. We made the gap estimation circuit which was composed of both the superposition circuit and the measuring circuit. And we investigated the validity of the usefulness of the proposed sensorless method in the magnetic levitation system through results of actual experiment.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1689-1695
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• 2019

This study suggests a simple economic model to analyze electricity grid that consists of different power sources. The substitutability of renewable energy for nuclear power in Korean electricity transmission network is investigated by suggested model. The monthly data from January 2006 to December 2013 reported by Electricity Power Statistics Information System (EPSIS) of Korea Power EXchange (KPX) are used. To estimate the elasticities of substitution among four power sources (i.e. coal, natural gas, nuclear power, and renewable energy), this paper uses the trans-log cost function model on which local concavity restrictions are imposed. The estimated Hicks-Allen and Morishima elasticity of substitution shows that renewable electricity and nuclear power are complementary. The results also evidenced that renewable electricity and fossil fueled thermal power generation are substitutes.

• 한국안전학회지
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• 제25권5호
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• pp.15-21
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• 2010

Regenerative Energy Storage System(ESS) is a system that saves regenerative energy which generated instantly in the regenerative braking of Electric Multiple Unit(EMU) and disappear, and reuse the stored energy when EMU is in powering. Such system related to a research field of renewable energy which emerged concerning climate change and high oil prices. In the case of existing domestic rolling stock, about 25% to 30% of generated regenerative energy is restored to power source and is regarded as direct factor of raising catenary voltage. Such rapid change of catenary voltage is a cause of the failure of EMU's electronic equipment and lowering its reliability and is also a cause of train's fault occurred by tripping circuit breaker. In this paper, we intend to investigate the effect on blending characteristics of electric-braking and pneumatic-braking whether the regenerative energy storage system is used or not in urban transit DC 1,500V feeding system, while trains run. And we also intend to investigate its effect on stabilization of the blending, fluctuation of catenary voltage and various electric equipments.

• Journal of Advanced Marine Engineering and Technology
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• 제33권7호
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• pp.1012-1016
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• 2009

This paper describes the control and monitoring system for OWEC (Overtopping Wave Energy Converter) which shows the characteristic of power stabilization in overtopping wave energy converter system. Overtopping waves generates different water pressure and the turbine is rotated by this pressure. As a result, overtopping wave energy converter is able to convert wave energy into electricity. Small size of overtopping wave energy converter is developed to simulate the control monitoring system which is able to control power generation and also monitor the system condition. The result shows the reduction of fluctuation from the overtopping wave energy system by the developed control monitoring system. In addition, the DB(Data Base) of test results are contributed to the research and development for OWEC.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.683-686
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• 1998

In this paper, the power factor correction (PFC) system for inverter air-conditioner that has not only good harmonic characteristics but also cost down-merit compared with the conventional inverter type is proposed. The detail design procedures to get cost-down merits are introduced. And it is shown that the PFC system performances also can be improved by the virtue of the stabilization of output voltage. The proto type system is implemented and tested to virify the additional good performances of the proposed system, and its simulation and experimental results are presented.

• 전기학회논문지
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• 제64권3호
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• pp.370-374
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• 2015

Various protective equiptments are used for the power system control and protection. Numerous facilities are monitored at the same time in real time and introduction of optimization method and analysis of the method are required for generation control and facility management considering the demand fluctuations. However, the existing system analysis programs are difficult to link with the other sw and there are some problems with user convenience. To solve these problems the present conditions of the system are figured out in real time and the equipment insert method was estimated by optimization method, and the system that showed the system analysis program is developed. PSS/E has been used as system anlysis program for stabilizing system development which applied the optimization. method and Python language is applied in order to link the input and output values with the DB automatically. Lastly, DLL of matlab has been made included in C++ for solving the objective function using opmization method.By linking this to DB, power flow was calculated in PSS/E and the result was represented by Intouch screen.