• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.102-105
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• 2000

A simple digital control system has been developed for the frequency stabilization of an internal mirror He-Ne laser. The system is based on one chip microprocessor with embedded Basic interpreter. To stabilize the laser output frequency, the signal such as power difference or beat frequency between two modes is supplied and processed by a microprocessor, and control signal is fed to the heating coil would round the laser tube for adjusting the spacing of the laser cavity mirror. Newly developed frequency stabilization system is totally digitized. The system and the frequency stability performance are briefly described.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.260-263
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• 2003

Lasers are used as the source of the interferometers in the industrial field. These lasers need 2 requirements. The first is the narrow linewidth of laser for the long coherence length. The second is the stabilized frequency of laser for the precision measurement. Now HeNe lasers are mostly used and the frequency stability is about 10$^{-9}$ . In this paper, we construct the HeNe laser systems of frequency stabilization using typical 2 method, the beat frequency stabilization method and the intensity difference method. So, we get the frequency stabilities of 2.01$\times$10$^{-9}$ (0.1s), 3.4$\times$10$^{-9}$ (0.1s).

• 전자공학회논문지S
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• 제35S권7호
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• pp.6-13
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• 1998

To constoruct a multi-channel system like Optical Frequency Division Multiplexing (OFDM) with the vast amount of transmission capability, a frequency stabilization is essential technique for getting narrower channel spacing and for minimizing fluctuation of oscillation frquency of each channel. This paper proposes a novel multi-channel optical frequency stabilization scheme that uses wavelength crossover properties of a Arrayed Waveguide Grating(AWG). The proposed scheme includes an effective control algorithm that carries out frequency stabilization of all channels through a simple control circuit, simulaneously. And also, a design method of AWG is included which has higher resolutio in consideration of system loss.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.188-191
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• 2005

A common feature in various methods of optical interferometry for absolute distance measurements is the use of multiple monochromatic light components either in sequence or in parallel at the same time. Two or multiple wavelength synthesis has been studied though its performance is vulnerable to the frequency instability of the light source. Recently continuous frequency modulation is considered a promising method with availability of wide band tunable diode lasers, which also have frequency instability errors. We can lock frequencies of these third-party light sources to the modes of the femtosecond laser which is stabilized to the precision of the standard radio frequency. To this end, we have stabilized all the modes of the femtosecond laser to the atomic frequency standard by using powerful tools of frequency-domain laser stabilization.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.259-262
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• 2002

Application of combustion stabilization devices such as baffle and acoustic cavity to liquid propellant rocket engine is investigated to suppress high-frequency combustion instability, i.e., acoustic instability. First, these damping devices are designed based on linear damping theory. As a principal design parameter, damping factor is considered and calculated numerically in the chambers with various specifications of these devices. Next, the unbaffled chambers with/without acoustic cavities are tested experimentally for several operating conditions. The unbaffled chamber shows the specific stability characteristics depending on the operating condition and has small dynamic stability margin. The most hazardous frequency is clearly identified through Fast Fourier Transform. As a result, the acoustic cavity with the present design has little stabilization effect in this specific chamber. Finally, stability rating tests are conducted with the baffled chamber, where evident combustion stabilization is observed, which indicates sufficient damping effect. Thrust loss caused by baffle installation is about $2{\%}$.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1988년도 한국자동제어학술회의논문집(국내학술편); 한국전력공사연수원, 서울; 21-22 Oct. 1988
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• pp.148-153
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• 1988

In this study, the stabilization of moving sight using a gyro is investigated. At first, Linear Compensator was design by linearizing gyro, torque motor and several parameters from a given required frequency response curve. By using this, System Control Performance was analyzed by back EMF, torque saturation and Coulomb friction effects. Also stabilization Performance by disturbances and Paramter variations were simulated.

• Journal of Power Electronics
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• 제18권3호
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• pp.853-862
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• 2018

Frequency coupling in the phase domain is a recently reported phenomenon for phase locked loop (PLL) based three-phase grid-inverter systems. This paper investigates the mechanism and stabilization method for the frequency coupling to the stability of grid-inverter systems. Self and accompanying admittance models are employed to represent the frequency coupling characteristics of the inverter, and a small signal equivalent circuit of a grid-inverter system is set up to reveal the mechanism of the frequency coupling to the system stability. The analysis reveals that the equivalent inverter admittance is changed due to the frequency coupling of the inverter, and the system stability is affected. In the end, retuning the bandwidth of the phase locked loop is presented to stabilize the three-phase grid-inverter system. Experimental results are given to verify the analysis and the stabilization scheme.

• Journal of Power Electronics
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• 제18권2호
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• pp.547-557
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• 2018

This work proposes a control method of frequency stabilization for grid integration of large-scale wind farms via the voltage source converter-based high-voltage direct current (VSC-HVDC) technology. First, the topology of grid integration of a large-scale wind farm via the VSC-HVDC link is provided, and simple control strategies for wind turbines, wind farm side VSC (WFVSC), and grid side VSC are presented. Second, a mathematical model between the phase angle of WFVSC and the frequency of the wind farm is established. The control principle of the large-scale wind power integrated system is analyzed in theory in accordance with the mathematical model. Third, frequency and AC voltage controllers of WFVSC are designed based on the mathematical model of the relationships between the phase angle of WFVSC and the frequency of the wind farm, and between the modulation index of WFVSC and the voltage of the wind farm. Corresponding controller structures are established by deriving a transfer function, and an optimization method for selecting the parameters of the frequency controller is presented. Finally, a case study is performed under different operating conditions by using the DIgSILENT/PowerFactory software. Results show that the proposed control method has good performance in the frequency stabilization of the large-scale wind power integrated system via the VSC-HVDC technology.

• ETRI Journal
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• 제28권5호
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• pp.615-620
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• 2006

In this paper, we discuss the quantification of Mach-Zehnder interferometer (MZI) thermal stabilization which is needed in optical phase shaped binary transmission (PSBT) links. Considering the thermo-optic and thermal expansion effects, we revisit the analytical expression for the thermal drift (GHz/$^{\circ}C$) of the MZI center frequency (denoted here by the 'MZI spectral drift'). An MZI is then used in an experimental transmission system using the optical PSBT format. We study the effect of spectral MZI drift by using a thermally stabilized interferometer and applying a frequency shift to the optical carrier. By using the thermal drift coefficient of the MZI, we find that to ensure low bit error rate fluctuations due to the MZI drift, the thermal stabilization of the device must have an accuracy of $0.5^{\circ}C$.

• 한국소음진동공학회논문집
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• 제21권2호
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• pp.178-185
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• 2011

Optical image stabilization is a device to compensate the camera movement in the exposure time. The compensation is implemented by movable lens or image sensor that adjusts the optical path to the camera movement. Generally, the camera is moved by a handshake, thus the handshake is considered as an external disturbance. However, there are many other vibrations such as car and train vibration. In this paper, the optical image stabilization system in high frequency region is presented. Notch filter and lead compensator are designed and applied to improve the stability without changing the actuator. To verify the performance of the optical image stabilization system in high frequency region, the experiment equipment with moving object is established. It is confirmed that the opticalimage stabilization system does not diverge at the resonance frequency.