• 전자공학회논문지B
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• 제33B권3호
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• pp.193-201
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• 1996

The space power system for communication satellite which employs the direct energy transfer (DET) method consists of solar array, battry, shunt regulator, charger/discharger and power control unit (PCU). In this paper, the development of the DET power system charger/discharger unit and a microprocessor based PCU is developed for simplicity and flexiblity in the modificatin of control algorithm. A 28V bus voltage, 400W power rting power simulator is built and tested to verify the operation of the simulator at each mode and the stability of mode transition is analyzed.

• 대한전자공학회논문지
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• 제16권2호
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• pp.15-18
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• 1979

집적황학 도파관을 만들기 위해 LiNbO3 substrate 태로 전위원소인 Ti를 확산시켰다. L O out-diffusion 모드를 제거시킴으로써 단일 모드 도파관이 제작 될 구 있었다. 특성 측정에는 He- Ne 레이저(λ= 0.6328μm)와 프리즘 결합 방법이 사용되었다.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 2000년도 춘계학술대회 학술발표 논문집
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• pp.249-255
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• 2000

HRIV(Hybrid Rule-Interval Variation) method is presented to stabilize a class of nonlinear systems, where SMC(Sliding Mode Control) and ADC (ADaptive Control) schemes are incorporated to overcome the unstable characteristics of a conventional FLC(Fuzzy Logic Control). HRIV method consists of two modes: I-mode (Integral Sliding Mode PLC) and R-mode(RIV method). In I-mode, SMC is used to compensate for MAE(Minimum Approximation Error) caused by the heuristic characteristics of FLC. In R-mode, RIV method reduces interval lengths of rules as states converge to an equilibrium point, which makes the defined Lyapunov function candidate negative semi-definite without considering MAE, and the new uncertain parameters generated in R-mode are compensated by SMC. In RIV method, the overcontraction problem that the states are out of a rule-table can happen by the excessive reduction of rule intervals, which is solved with a dynamic modification of rule-intervals and a transition to I-mode. Especially, HRIV method has advantages to use the analytic upper bound of MAE and to reduce Its effect in the control input, compared with the previous researches. Finally, the proposed method is applied to stabilize a simple nonlinear system and a modified inverted pendulum system in simulation experiments.

• Advances in aircraft and spacecraft science
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• 제5권4호
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• pp.431-444
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• 2018

Numerical simulations have been conducted to study the unstart/restart characteristics of an over-under turbine-based combined-cycle propulsion system (TBCC) inlet during the inlet transition phase. A dual-solution area exists according to the Kantrowitz theory, in which the inlet states may be different even with the same input parameters. The entire transition process was divided into five stages and the unstart/restart hysteresis loop for each stage was also obtained. These loops construct a hysteresis surface which separates the operating space of the engine into three parts: in which a) inlet can maintain a started state; b) inlet keeps an unstarted state; c) inlet state depends on its initial state. During the transition, the operation of the engine follows a certain order with different backpressures and splitter angles, namely control route, which may result in disparate inlet states. Nine control routes with different backpressures and transition stages were designed to illuminate the route-dependent behavior of the inlet. The control routes operating towards the unstart boundary can make the inlet transit from a started state into an unstarted one. But operating backward the same route cannot make the inlet restart, additional effort should be made.

• Journal of Welding and Joining
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• 제14권5호
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• pp.145-150
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• 1996

The variation of spatter generation in gas metal arc welding with welding conditions and wire compositions was investigated and interpreted in terms of arc stability. The transition range from a short circuit mode to a spray mode in the mixed gas welding showed an unstable arc and generated the largest amount of spatters. Titanium reduced spatters only in the globular mode of $CO_2$welding and silicon and manganese showed the same effect The effect of silicon and manganese, however, was no longer seen when titanium was added simultaneously to the wire. It is believed that deoxidizers easily form oxides on the anode and make the arc stable even in DCRP welding. The wires with deoxidizers also showed low short circuit frequency, resulting in the increase of large size spatters.

• ETRI Journal
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• 제39권3호
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• pp.310-318
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• 2017

Unified speech and audio coding (USAC) is one of the latest coding technologies. It is based on a switchable coding structure, and has demonstrated the highest levels of performance for both speech and music contents. In this paper, we propose an extended version of USAC with a single-mode of operation-which does not require a switching system-by extending the linear prediction-coding mode. The main concept of this extension is the adoption of the advantages of frequency-domain coding schemes, such as windowing and transition control. Subjective test results indicate that the proposed scheme covers speech, music, and mixed streams with adequate levels of performance. The obtained quality levels are comparable with those of USAC.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.104-109
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• 2000

The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoutic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding. Acoustic radiation is more intense, with multiple frequencies present.

• Journal of Power Electronics
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• 제11권6호
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• pp.846-855
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• 2011

This paper proposes a control mode switching scheme between vector control and constant V/f control for induction machine (IM) drives for maximum torque utilization in a higher speed region. For the constant V/f scheme, a smooth transition method from the linear range of PWM up to the six-step mode is applied, by which the machine flux and torque can be kept constant in a high-speed range. Also, a careful consideration of the initial phase angle of the voltage in the transient state of the control mode change between the vector control and V/f schemes is described. The validity of the proposed strategy is verified by the experiment result for a 3-kW induction motor drives.

• 한국통신학회논문지
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• 제28권8A호
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• pp.644-649
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• 2003

새로운 구조의 622Mbps급 버스트 모드 클럭/데이터 복원 회로를 구현하였다. 회로는 2개의 muxed oscillator (MO)와 위상 동기 회로 등으로 구성되어 있으며, passive optical network(PON) 시스템에 사용될 수 있도록 instantaneous locking 특성을 갖는다. 또한. 지터가 내재된 데이터가 인가되어도 데이터에 따라 클럭이 연동되어 항상 최적의 샘플링 포인트를 갖는다. 이 회로는 0.35$\mu\textrm{m}$ CMOS 공정을 이용하여 제작되었다. 측정 결과 제안된 클럭/데이터 복원 회로는 400Mbps 680MbPs 까지의 버스트 모드 입력 데이터를 에러없이 복원하였다.

• 전력전자학회논문지
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• 제21권3호
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• pp.200-206
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• 2016

In the microgrid, inverters for energy storage system are generally constructed in a parallel structure because of capacity expandability, convenience of system maintenance, and reliability improvement. Parallel inverters are required to provide stable voltage to the critical load in PCC and to accurately share the current between each inverter. Furthermore, when islanding occurs, the inverters should change its operating mode from grid-connected mode to stand-alone mode. However, during clearing time and control mode change, the conventional control method has a negative impact on the critical load, that is, severe fluctuating voltage. In this study, a parallel operation control method is proposed. This method provides seamless mode transfer for the entire transition period, including clearing time and control mode change, and has accurate current sharing between each inverter. The proposed control method is validated through simulation and experiment.