• Journal of Power Electronics
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• v.11 no.3
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• pp.256-263
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• 2011

This paper utilizes free oscillation and energy injection principles to generate and control the high frequency current in the primary track of a contactless power transfer system. Here the primary power inverter maintains natural resonance while ensuring near constant current magnitude in the primary track as required for multiple independent loads. Such energy injection controllers exhibit low switching frequency and achieve ZCS (Zero Current Switching) by detecting the high frequency current, thus the switching stress, power losses and EMI of the inverter are low. An example full bridge topology is investigated for a contactless power transfer system with multiple pickups. Theoretical analysis, simulation and experimental results show that the proposed system has a fast and smooth start-up transient response. The output track current is fully controllable with a sufficiently good waveform for contactless power transfer applications.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.7
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• pp.883-888
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• 2014

The paper describes the parameter tuning of power system stabilizer (PSS) for a power plant based on hybrid system modeling. The existing tuning method based on bode plot and root locus is well applied to keep power system stable. However, due to linearization of power system and an assumption that the parameter ratio of the lead-lag compensator in PSS is fixed, the results cannot guarantee the optimal performances to damp out low-frequency oscillation. Therefore, in this paper, hybrid system modeling, which has a DAIS (differential-algebraic-impusive-switched) structure, is applied to conduct nonlinear modeling for power system and find optimal parameter set of the PSS. The performances of the proposed method are carried out by time domain simulation with a single machine connected to infinite bus (SMIB) system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.480-480
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• 2007

A large diameter plasma filled backward wave oscillator is investigated experimentally. The parameters of slow wave structure are chosen so that the oscillation frequency is high beam energy. Plasma is produced by the beam and it has favorable effects on beam propagation and Cerenkov oscillation.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.403-404
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• 2010

태양전지는 일사량 및 온도에 의해 출력 특성이 변화하여 최대전력을 얻을 수 있는 위치도 변화한다. 따라서 태양전지의 동작점을 최대 전력점에서 동작하게 하는 최대전력점 추적(MPPT, Maximum Power Point Tracking) 이 필요하다. 본 논문에서는 P&O 방식처럼 자려진동을 하지 않고 최대 동작점에서 머물면서 동작하는 NOC(Non-Oscillation Control) 방법을 제안한다. 이 방식은 빠르게 최대 동작점을 찾을 수 있고 특히 급격한 일사량 변동에 대해 유리한 장점을 갖는다. 최종적으로 제안된 제어기법의 타당성을 검증하기 위하여 3KW급으로 수행된 MPPT 모의 실험을 제시한다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.2
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• pp.162-168
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• 2008

In this paper, the RCF(Resistive Companion Form) analysis method is applied to analyze small signal stability of power systems including thyristor controlled FACTS(Flexible AC Transmission System) equipments such as TCSC(Thyristor Controlled Series Capacitor). The eigenvalue sensitivity analysis algorithm in discrete systems based on the RCF analysis method is presented and applied to the power system including TCSC. As a result of simulation, the RCF analysis method is very useful to precisely calculate the variations of eigenvalues or newly generated unstable oscillation modes after periodic switching operations of TCSC. Also the eigenvalue sensitivity analysis method based on the RCF analysis method enabled to precisely calculate eigenvalue sensitivity coefficients of controller parameters about the dominant oscillation mode after periodic switching operations in discrete systems. These simulation results are different from those of the conventional continuous system analysis method such as the state space equation and showed that the RCF analysis method is very useful to analyze the discrete power systems including periodically operated switching equipments such as TCSC.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.3
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• pp.140-151
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• 2004

This paper presents the HVDC system modelling for analysis of subsynchronous oscillation and the design of the subsynchronous oscillation damping controller in HVDC system with the aid of novel eigenvalue analysis program. The HVDC system models include both the steady-state model for power flow calculation and the dynamic model for constructing the state matrix. The design procedures of the subsynchronous oscillation damping controller (SODC), which is integrated with PI controller at rectifier, consist of three steps:1) to identify the dominant torsional oscillation mode in the AC/DC system;2) to determine the parameters of the SODC for compensating the phase lagging due to the rectifier controller;3) to validate the control parameters and to determine the appropriate gain using a time-domain simulation program. The proposed design method has been tested against two AC/DC systems for validation.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.286-288
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• 2005

Conventional phase shift full bridge (PSFB) converter has serious voltage oscillation problem across the secondary rectifier diodes, which would require the dissipate snubber circuit, thus degrades the overall efficiency. To overcome this problem, a new voltage oscillation reduction technique (VORT) which effectively reduce the voltage oscillation of the secondary rectifier diodes for phase shift 1011 bridge converter is proposed. Therefore, no dissipate snubber for rectifier diodes is needed. In addition, since it has wide zero voltage switching (ZVS) range, high efficiency can be achieved. Operational principle, analysis of voltage oscillation, and design consideration are presented compare with that of the conventional PSFB converter. To confirm the validity of the proposed VORT, experimental results from a 420W, 385Vdc/210Vdc prototype are presented.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.918-924
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• 2020

Film boiling is of great importance in nuclear safety as it directly influences the integrity of nuclear fuel in case of accidents involving loss of coolant. Recently, nuclear power plant safety under earthquake conditions has received much attention. However, to the best of our knowledge, there are no existing studies reporting film boiling in an oscillating system. Most previous studies for film boiling were performed on stationary systems. In this study, numerical simulations were performed for saturated film boiling of water on a horizontal surface under low frequencies to investigate the effect of system oscillation on film boiling heat transfer. A coupled level-set and volume-of-fluid method was used to track the interface between the vapor and liquid phases. With a fixed oscillation amplitude, overall, heat transfer decreases with oscillation frequency. However, there is a frequency region in which heat transfer remains nearly constant. This lock-on phenomenon occurs when the oscillation frequency is near the natural bubble release frequency. With a fixed oscillation frequency, heat transfer decreases with oscillation amplitude. With a fixed maximum amplitude of the additional gravity, heat transfer is affected little by the combination of oscillation amplitude and frequency.

• Progress in Superconductivity
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• v.3 no.2
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• pp.224-228
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• 2002

We investigated the quench properties of superconducting fault current limiters (SFCLs) connected in parallel. It was carried out as an effort to scale up the current capacity of SFCL toys texts. SFCLs were based on $YBa_2$$Cu_3$$O_{7}$ films coated in-situ with a gold layer and fabricated by patterning the films into 2 mm wide and 42 cm long meander lines by photolithography. Two SFCLS were connected in parallel and tested with simulated AC fault currents. Initially the current was divided unequally into branches of parallel connection due to unequal resistance of the branches. However, once quench started in the SFCLs, the current oscillated between the branches and then was distributed nearly equally between the branches. In other words, the elements quenched simultaneously. The oscillation amplitude decreased as the source voltage was increased: the oscillation was the most prominent near the quench current. The observed oscillation and the consequent simultaneous quench was understood in terms of quench start and development in the SFCLs.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.228-229
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• 2006

The RCF analysis method is used to analyze small signal stability of power systems including GTO controlled FACTS equipment such as STATCOM. To apply the RCF analysis method in power system small signal stability problems, the state transition equations of power system equipments and power systems with STATCOM are presented. In eigenvalue analysis of power systems by the RCF analysis method, the STATCOM is modelled into the equivalents voltage source model and the PWM switching circuit model. As a result of simulation, the RCF analysis method is very powerful to calculate the oscillation modes exactly after the switching operations, and useful to analyze the small signal stability of power systems with periodically operated switching device such as the STATCOM.