• 전기의세계
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• v.26 no.2
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• pp.99-103
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• 1977

The object of this work is to study an optimal design problem of the proportional load-frequency controller for the single-control area power system. The selfservice power station is still a popular means as a power supplying source on ships or in a certain manufacturing area. The power system of this kind can be formulated as a single control-area system and it attracts a certain academic interest in controlling the system frequency under disturbances. In this paper, the single control-area system is mathematically formulated as a linear, time-invariant system in state-space under certain assumptions. The optimal proportional control law and the realization of the controller in closed loop-version is studied so that the final system designed can attain the system frequency to the nominal stationing value after the small load-disturbance. As in general cases of optimal design problems, the performance index is assumed to be quadratic in states and the control effort, and the infinite time control process is assumed in this work. The final control system realized depicts certain improvements in case study; in stability, transient responses and in steady-state frequency deviation, even though the steady state error did not attain the zero value.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2064-2069
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• 2008

The Resonance Control Cooling System (RCCS) prototype installed in KAERI site has been designed to control the resonant frequency of the normal conducting drift tube linac (DTL) for the Proton Engineering Frontier Project (PEFP). The RCCS water pumping skid is composed of two channels as a by-passing the cooling water and a plate heat exchanger. The required temperature can be achieved by mixing both channels in order to control its the resonant frequency at 350 MHz. The temperature controlled water pumping skid operates in combination with the Low Level Radio Frequency (LLRF) system. We have discussed the design, modeling with each components, control scheme, fabrication and test results of the water pumping skid for resonant frequency control of the DTL cavity. In conclusion, the fabricated RCCS prototype through the optimization of modeling has corresponded with the design requirement and concept.

• Journal of Electrical Engineering and Technology
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• v.11 no.4
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• pp.921-930
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• 2016

This paper proposes a design and control method for a high-voltage direction current modular multilevel converter (HVDC-MMC) considering the capacitor voltage ripple of the submodule (SM). The capacitor voltage ripple consists of the line frequency and double-line-frequency components. The double line- frequency component does not fluctuate according to the active power, whereas the line-frequency component is highly influenced by the grid-side voltage and current. If the grid voltage drops, a conventional converter increases the current to maintain the active power. A grid voltage drops, current increment, or both occur with a capacitor voltage ripple higher than the limit value. In order to reliably control an MMC within a limit value, the SM capacitor should be designed on the basis of the capacitor voltage ripple. In this paper, the capacitor voltage ripple according to the grid voltage and current are analyzed, and the proposed control method includes a current limitation method considering the capacitor voltage ripple. The proposed design and control method are verified through simulation using PSCAD/EMTDC.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.857-861
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• 2004

An active method that improves low frequency characteristics of a reverberation chamber has been proposed. Spatial uniformity of sound pressure at low frequency has been increased by applying active noise control system. The system acts as frequency selective damping materials, which decreases resonance at low frequency and leave high frequency sound field as it is. Linearity of the chamber, which is essential for sound power measurement in the chamber, is guaranteed since fixed control logic has been adopted. Simple application and tests have been done in a small sized rectangular reverberation chamber which has 400Hz cutoff, Loud speakers were used to simulate a noise source and to construct an active noise control system. The spatial distribution of a sound field at 250Hz, 315Hz and 400Hz bands has been measured before and after control. The standard deviation of sound field has been decreased from 3.4dB to 2.5dB. The results show the possibility of active control system as a sound diffuser.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1836-1840
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• 2003

This paper, we propose a new phase-locked loop (PLL) system with the controllable output phase, independent from the output frequency, and lock-up time. This PLL system has a dual control loop is described, the inner loop greatly improved VCO characteristic such as faster speed response as well as higher operation bandwidth, to minimize the effect of the VCO noise and the power supply variation and also get better linearity of VCO output. The main loop is the heart of this PLL which greatly improved the output frequency instability due to the external high frequency noise coupling to the input reference frequency also the main loop can control the output phase, independent from the output frequency, and reduce the lock-up time of the step frequency response. The experimental results confirm the validity of the proposed strategy.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.6
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• pp.557-567
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• 1990

This paper describes the static and dynamic characteristic analysis of the Series Resonant DC to DC Converter with frequency control. The natural commutation of all switch element is realized when the switching frequency is below the resonant frequency of the tank circuit, and the analysis is limited to only this region. For the analysis method, state plane technique is adopted, and each operation mode is defined from normalized switching frequency Fsn. Under this condition, circuit performance is analyzed ideally. The physical characteristics of the series resonant converter is easily grasped by this analysis method with frequency control and this analytical results are directly applicable to the actual converter design. The validity of the analysis is verified by comparing with experimental results and the stability of the converter is confirmed against small variations around the operating point by conventional frequency domain analysis.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.354-355
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• 2018

Flywheel energy storage system (FESS) operates motor or generator by utilizing the stored kinetic energy in the rotating mass. Thus, the FESS can support the frequency control of the power system. However, the FESS is disabled when the rotor speed reaches to its minium value. Thus, the second frequency dip occurs in the power system. This paper proposes the frequency control scheme of FESS based on a variable gain depending on the rotor speed and frequency deviation. The proposed scheme prevents the second frequency dip because the variable gain decreases depending on the stored in the FESS. The performance of the proposed scheme is investigated for the IEEE 14-bus system.

• Physical Therapy Korea
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• v.6 no.2
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• pp.16-31
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• 1999

The purpose of this study was to assess the fatigue in lumbar and abdominal muscles in patients with chronic low back pain compared with normal subjects using spectral analysis with mean power frequency and median power frequency. The experimental group consisted of twenty subjects who had experienced chronic low back pain for over one year after the onset day. A control group consisted of twenty normal subjects with no history of low back pain. All subjects stood in an apparatus to perform sustained contraction in the lumbar and abdominal muscles for 30 seconds with 60% maximal voluntary isometric contraction (MVIC). The resulting electromyographic (EMG) recorded time serial data were transformed into frequency serial data by Fast Fourier Transformation (FFT). The results were as follows: 1) lumbar muscles measured, the frequency change ratio of both median power frequency and mean power frequency was significantly greater for experimental group compared with control group group (p<0.05). In measured two abdominal muscles (inferior rectus abdominis, obliquus externus abdominis) except superior rectus abdominis, the frequency change ratio of both median power frequency and mean power frequency was significantly greater for experimental group compared with control group (p<0.05). 2) In all three (longissimus thoracis, iliocostalis lumborum, multifidus) lumbar muscles measured, the initial frequency value of both median power frequency and mean power frequency was significantly lower for the experimental group compared with the control group (p<0.05). In the two (inferior rectus abdominis, obliquus externus abdominis) abdominal muscles measured (superior rectus abdominis not included), the initial frequency value of both median power frequency and mean power frequency was significantly lower for the experimental group compared with the control group (p<0.05). These results suggest that in patients with chronic low back pain there is a trend for more fatigue to occur in both lumbar and abdominal muscles than in the normal control group. This would seem to suggest that in treatment programs for patients with chronic low back pain, improvement of endurance in all trunk muscles should be considered.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1052-1055
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• 1996

Piezoelectric actuator is widely used in precision positioning applications due to its excellent positioning resolution. However, serious hysteresis nonlinearity of the actuator deteriorates its precise positioning capability. Evenworse, its hysteresis nonlinearity changes as the actuator input frequency varies. In this study, a simple feedforward scheme is proposed and tested through experiments for precision position control when the variance of the system input frequency is significant.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1410-1414
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• 1990

A method of speed sensorless vector control of induction motor is proposed in this paper. This method uses the slip frequency estimated by only the primary voltage and current. As this slip frequency accords with the command value of it, the commanded primary frequency is controlled. The validity of the method is confirmed by the simulation and experimental results.