• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.591-599
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• 2001

The paper identifies a severe form of core saturation instability in an DC/AC interaction system. It then seeks solutions to the problem by HVDC control means. This is achieved by a proper design of the Voltage Dependent Current Order Limiter (VDCOL), the Current Regulator and Timing Pulse generator. Supplementary control loops have also been introduced to result in a satisfactory performance as compared to that obtained one with the use of uncharacteristic harmonic filter on the AC side. Robustness of all the options has been demonstrated through recovery performance of the DC link in response to both I-phase and 3-phase 5 cycle faults on both rectifier and inverter commutating buses.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.556-558
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• 1994

This paper proposes a new converter that can reduce the harmonics like conventional 12-pulse dual thyrister converters with the input transformers. Both the bridges are controlled with the shifted firing angle and connected through current sharing reactors. Using the center tapped reactor, the DC link current is controlled with the different two values in order to make the input current waveform 12 pulses.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.392-396
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• 1994

A method which improves the efficiency of induction motor by controlling the input voltage by the three phase AC voltage controller is studied at the sides of theory and practice. At first, the principle of decreasing the input power and improving the efficiency by adjusting the amplitude of the input voltage according to the load rate is shown. Secondarily, the mathematical model of the three phase AC voltage controller-induction motor system is drived to translate the dynamic characteristics. The validity of the dynamic model is verified by simulation. The new driving method is also proposed, which regulates the rated speed's driving by the speed estimation from the firing angle and the magnitude reverse induced-voltage information. As a result, the digital control system is constructed. Expermintal results show desirable characteristics of proposed system.

• Proceedings of the KIEE Conference
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• 2007.11b
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• pp.142-144
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• 2007

최근 전력전자 기기의 사용 증가에 따른 고조파 발생으로 중성선 전류 증가, 보호기기 오동작, 노이즈 장애, 기기 과열 현상, 그리고 기기 수명단축 등 계통에 미치는 영향이 증가 하고 있다. 따라서 본 논문에서는 고조파로 인한 계통 영향을 실 계통을 이용해 분석하였다. 실 계통 모델링 후 3상 싸이리스터 컨버터 부하 투입 및 정호각에 따른 계통영향을 EMTP (Electro-Magnatic Transient Program)를 이용해 분석하였다.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.5 no.2
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• pp.84-95
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• 1991

Mostly, phase control method is used to control the single phase AC power. The phase control method has some advantages such as ease to control and simple configuration. But the retardation of firing angle causes a lagging current even if load is purely resistive. So phase control causes a lagging power factor and a low efficiency at the input side in comparing with the system without switching device. A new PWM control method which can improve these defects for single phase AC power control circuit is proposed in this paper. The performances of the single phase AC power control circuit using the proposed method was investigated theoretically. Both power factor and waveform of load current can be improved better than those of the conventional methods.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.5
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• pp.117-127
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• 1992

In this work, the possibility to diagnose valve lashes of an automotive diesel engine via cylinder head vibration/noise analysis is studied. First of all the measurement signals and conditions are selected after considering which signals and conditions are most suitable to diagonse valve lashes. Both accelerometer and microphone are used to measure cylinder head accelerations and acoustic pressure due to valve impact on cylinder head. The signals are measured in both cranking and engine firing conditions. Finally, it was found that acceleration signal obtained in engine operating condition is the most reliable signal to diagnose the valve lash condition. The valve closing angle and the peak acceleration due to valve close are chosen to analyze the valve lash condition. The measured cylinder head acceleration signals are statistically tested to derive information which are useful to judge the valve lash. In conclusion, it was found that the developed technique can be one of feasible methods to diagnose the valve conditions while the engine is in operation.

• Journal of the Korean Professional Engineers Association
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• v.23 no.6
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• pp.41-46
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• 1990

First of all, Under given condition such as bit gage of 36mm Drill bit with right class of jack-logs experimental test carried out from two face of Bench, firing of each hole brought 90 degree Angle face and them measured length of Burden and charged ammount of powder as following. (equation omitted) A=Activated Area A=ndi=m S=Peripheral length of Charged. room Ca=Rock Coeffiecency d : di=Hole diameter When constructed subway of Seoul in 1980 the blasting works increased complaint of ground vibration. in order to prevent the damage to structures. Some empirical equations were made as follows on condition with Jackleg Drill (Bit Gage ø 36mm) and within 30 meter distance between blasting site and structures. V=K(D / W)$\^$-n/ N=1.60-1.78 K=48-138 Project one of contineous works to above a determination of empirical equation on the cautious blasting vibration with Crawler Drill(ø 70-75mm) in long distance. V=41(equation omitted) V=124(equation omitted).

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1091-1093
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• 2001

The power semiconductor is widely used in the power plant or industrial field because of genealization and enlargement. It has been controlled and operated according to its own control method. Especially in case of Power plant, it plays a major role in AVR(Automatic Voltage Regulator) or electro chlorination control circuits. Generally, they used in Analog control system at above field. But each SCR current value is different because of load unbalance or switching characteristic variations, it may cause power plant unit trip or system disorder according to SCR element burn out or bad operating condition. Therefore, in this paper a development of 3 phase current balance control algorithm is described. it gets over the past analog control system limit, controls SCR gate firing angle for 3 phase current balance.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.793-798
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• 1993

In this study the attitude control of the KOREASAT is investigated. The KOREASAT is a geostationary satellite and its 3 attitude angles, namely, roll, pitch and yaw angles, are stabilized by using the 3-axis stabilization technique. In the pitch control loop, the pitch attitude angle received from the earth sensor is processed in the attitude processing electronics by using PI type control logic, and the control command is sent to the momentum wheel assembly to generate the control torque by varying the wheel rate. The roll/yaw attitude control is performed by activating a magnetic torquer or by firing appropriate thrusters. The magnetic torquer interacts with the earth magnetic field to produce the control torque, and the thrusters are used to control the larger roll attitude errors. In this study dynamic modelling of the satellite is performed. And the earth sensor, the momentum wheel, and the magnetic torquer are mathematically modelled. The 3-axis attitude control logic is implemented to make the closed-loop system and simulations are carried out to verify the implemented control laws.

• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.1-8
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• 1992

The effect of CaO impurity on the microstructural evolution during the sintering of ultrapure alumina(>99.999%) was studied under "clean" firing conditions. The sinterability of undoped alumina was low, but its microstructure was maintained uniform. In the case of CaO-doped alumina, the distribution of grain size and that of grain boundary dihedral angle became wider, and facetted pores observed frequently. When MgO was doped in addition to CaO, the sinterability increased drastically and the uniform microstructural characteristics resumed. This study suggests that the effect of CaO is to induce inhomogeneous microstructures presumably by anisotropic segregation to grain boundaries and pore surfaces, and that MgO suppresses the anisotropic segregation of Ca.