• 전기의세계
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• v.18 no.4
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• pp.22-30
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• 1969

The development of the frequency convertors using semiconductors devices makes it possible to control the speed of A.C. motors easily. It is now economically feasible to provide them with power at adjustble frequency using silicon-controlled rectifier (or thyristor) inverters. In such a case, in order to operate an induction motor efficiently over a wide speed range, it must be supplied from a variable frecuency source of which frequency is adjustable over the speep range of the motor. It is desired to observe the changes in characteristics as primary current, torque-speed of induction moter etc. at any optional frequncy. Although the charactheristies can be obtained by means of the conventional methods they require very complicated precedures of calcuations. The Current Diagram Method in this paper suggests a new approach to simpler calcuations of the characteristics, using the motor constants at reference frequency. The conclusions of this study are summarized as follows: (1) The equations of stator current at adjusted frequency were derived to construct graphical chart and the current circle required for the Current Diagrm Method. (2) The radius, center of the current circle and the vector locus, the basis for calculating the characteristics, at any desired frequency could be easily determined with the aid of both the derived graphical chart and current circle at reference frequency. (3) The method was shown to be applicable to the various types of 3-phase induction motors and also dealt with its application to the split-phase, condenser motors.

• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.86-91
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• 2010

In this paper, a double-layered frequency selective surface(FSS) superstrate was built and tested. The unit cell of the proposed FSS consists of a ring slot and a dipole-shaped structure and shows a complementary frequency response. Each unit cell is printed on two sides of a substrate. By using these double-layered structures, the first resonant frequency of the pass-band can be lowered. As a result, the size of the unit cell is minimized and the spacing between the other cells is reduced. The proposed FSS-dipole composite antenna is designed for the gain enhancement of wide-band code division multiple access(WCDMA) frequency bands(1.92~2.17 GHz) with a low quality factor(Q=0.17). To verify the gain enhancement performance of the FSS, an FSS-dipole composite antenna was created. Although the FSS layer enhances the gain of the primary radiation source of the dipole antenna, the FSS-dipole complex antenna cannot show a uniform gain over the entire desired frequency band. The experimental results show a gain enhancement of 3 dBi with an FSS superstrate in the WCDMA frequency band.

• Journal of Biosystems Engineering
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• v.36 no.6
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• pp.476-483
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• 2011

The aerial application using an unmanned helicopter has been already utilized and an attitude controller would be developed to enhance the operational convenience and safety of the operator. For a preliminary study of designing flight controller, a state space model for an RC helicopter would be identified. Frequency sweep flight tests were performed and time history data were acquired in the previous study. In this study, frequency response of the flight test data of a small unmanned helicopter was analyzed by using the CIFER software. The time history flight data consisted of three replications each for collective pitch, aileron, elevator and rudder sweep inputs. A total of 36 frequency responses were obtained for the four control stick inputs and nine outputs including linear velocities and accelerations and angular velocities in 3-axis. The results showed coherence values higher than 0.6 for every primary control inputs and corresponding on-axis outputs for the frequency range from 0.07 to 4 Hz. Also the analysis of conditioned frequency response showed its effectiveness in evaluating cross coupling effects. Based on the results, the dynamic characteristics of the model helicopter can further be analyzed in terms of transfer functions and the undamped natural frequency and damping ratio of each critical mode.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.6
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• pp.100-108
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• 2005

In this paper deals with the frequency control of the HVDC scheme linking Haenam to Cheju Island. The primary aim of the study is to develop and evaluate a new frequency control that can be employed without having to utilise the existing Synchronous Compensators(Gas Turbines). Transient condition studies are performed utilising the detailed control strategies for the HVDC link, implemented in PSCAD/EMTDC. Study cases are completed involving synchronous compensators trip and load ripping events and study plots presented. It is demonstrated that the existing frequency measurement can be replaced by one derived from the AC network alone, incorporated into a new frequency control algorithm and gives effective frequency control and dynamic performance.

• Journal of Power Electronics
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• v.10 no.6
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• pp.777-783
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• 2010

In order to drive gas discharge lamps, DC-AC converters with a LCC resonant tank, whose output voltage is adjusted by a variable frequency control are frequently used. However, when they are activated by varying the operating frequency, converters are frequently damaged by unstable operation, due to the rising and falling of the operating frequency near the resonant frequency. To solve this problem, a simple protection circuit for the power supply of a gas discharge lamp is proposed in this paper. This circuit senses the primary current of the main transformer. Using this protection circuit, the operating frequency of the lamp driving inverter system is kept close to and on the right side of the resonant frequency and the inverter is always operated in the ZVS condition. The resulting stable variable frequency operation allows various gas discharge lamps to be tested without the risk of damaging the main switches, because the protection circuit can protect the power MOSFETs of bridge converters from abnormal conditions. The validity and effectiveness of the proposed protection circuit are verified through the experimental results.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.4
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• pp.345-350
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• 2006

The study of the visual acuity and refraction status was performed to the students of primary school using eyeglasses in Kyung Nam region, Korea. Two hundred sixty three subjects with various styles of ametropia were analyzed the visual acuity and refraction examination by the subjective and objective tools. The results of study were as follows; 1) According to the increase of age of subjects, the visual acuity of binocular in naked eyes was decrease. However ametropia was increase. 2) The high frequency of ametropia types in the binocular was simple myopia, and the next order of high frequency was mixed astigmatism, myopic compound astigmatism, simple hyperopia, and hyperopic compound, respectively. 3) On the power of spherical refractive error of ametropia, the high frequency was -1.00 diopter, and the next order of high frequency was -2.00 diopter, +2.00 diopter, -3.00 diopter, and so on, respectively. 4) According to the increase of subjects ages, the changes of dioptric power of myopic spheric power was increase. however the frequency of the boy and girl was similar results, also the dioptric values of refractive status in binocular was similar results. As the results of this study, we conclude that the relationship of the visual acuity and refractive error status in primary students using eyeglasses was improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.120-130
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• 2009

In this paper, we propose a receiver structure for frequency synchronization in OFDMA (Orthogonal Frequency Division Multiple Access) system which is considered as 3GPP LTE(Long Term Evolution) downlink. In general, OFDMA frequency synchronization consists of two parts: coarse synchronization and fine synchronization. We consider P-SCH (Primary-Synchronization Channel) and CP (Cyclic Prefix) of OFDMA symbol for coarse synchronization and fine synchronization, respectively. The P-SCH signal has two remarkable disadvantages that it does not have sufficiently many sub-carriers and its differential correlation characteristic is not good due to ZC (Zadoff Chu) sequence-specific property. Hence, conventional frequency synchronization algorithms cannot obtain satisfactory performance gain. In this paper, we propose a modified differential correlation algorithm to improve performance of the coarse frequency synchronization. Also, we introduce an effective PLL (Phase Locked Loop) structure to guarantee stable performance of the fine frequency synchronization. Simulation results verify that the proposed algorithm has superior performance to the conventional algorithms and the 2nd-order PLL is effective to track the fine frequency offset even in high mobility.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4_1
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• pp.9-21
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• 1992

The effectiveness of the isolation system installed at the base of the primary structure and at the support of the substructure mounted on the primary structure is evaluated for reducing of structural responses under different earthquakes in this paper. The structural responses are analyzed to identify its behavior due to the input motion characteristics such as various peak acceleration and frequency content. Three analytical models are used to evaluate the effectiveness of the isolation system in this study as follows: fixed-base primary structure with support-fixed substructure, base-isolated primary structure with support-fixed substructure, and fixed-base primary structure with support-isolated substruciure. A computer code (KBISAP) is used for numerical integration of equation of motion considering the interaction between the primary structure and the secondary structure. The matrix condensation technique and constant average acceleration method are utilized in this program. And also, the effective stiffness of the base-isolator on reducing the structural response are evaluated for various earthquakes through the relationship of the acceleration - displacement.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.677-687
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• 2018

This paper presents a novel power decoupling control scheme with the bidirectional buck-boost converter for primary-side regulation photovoltaic (PV) micro-inverter. With the proposed power decoupling control scheme, small-capacitance film capacitors are used to overcome the life-span and reliability limitations of the large-capacitance electrolytic capacitors. Then, an improved flyback PV inverter is employed in continuous conduction mode with primary-side regulation for the PV power conditioning. The proposed power-decoupling controller shares the reference for primary side current regulation of the flyback PV inverter. The decoupling controller shapes the input current of the bidirectional buck-boost converter. The shared reference eliminates the phase-delay between the input current to the bidirectional buck-boost converter and the double frequency current at the PV primary current. The elimination of the phase-delay in dynamic response enhances the ripple rejection capability of the power decoupling buck-boost converter even with small film capacitor. With proposed power decoupling control scheme, the additional advantage of the primary-side regulation of flyback PV inverter is that there is no need to have an extra current sensor for obtaining the ripplecurrent reference of the decoupling current-controller of the power-decoupling buck-boost converter. Therefore, the proposed power decoupling control scheme is cost-effective as well as the size benefit. A new transient analysis is carried out which includes the source voltage dynamics instead of considering the source voltage as a pure voltage source. For verification of the proposed control scheme, simulation and experimental results are presented.

• Clinical and Experimental Reproductive Medicine
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• v.26 no.3
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• pp.467-474
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• 1999

Objectives: Cytogenetic investigations were carried out on 770 women with primary (n=560) and secondary amenorrhea (n=210) to determine the frequency of chromosomal or genetic causes of amenorrhea. Materials and Methods: In 770 women with primary amenorrhea (n=560) and secondary amenorrhea (n=210), chromosomal analysis were performed. Results: 1) The most prevalent age group is 16-20 years of age group with primary amenorrhea and 26-30 years of age group with secondary amenorrhea. 2) Out of 560 cases of primary amenorrhea, 343 cases (61.3%) had the normal chromosome constitution and 217 cases (38.7%) had the abnormal chromosome constitution including 46,XY. 3) In 217 cases of abnormal chromosome of primary amenorrhea, 57 cases (26.3%) had 45,X and 34 cases (15.8%) had the 46,XY, 24 cases (11.0%) had 45,X/46,X,i (Xq), 23 cases (10.6%) had 45,X/46,X,+mar and 14 cases (6.6%) had 45,X/46,XY. 4) Out of 210 cases of secondary amenorrhea, 181 cases (86.2%) had the normal chromosome constitution and 29 cases (13.8%) had the abnormal chromosome. 5) In 29 cases of abnormal chromosome of secondary amenorrhea, 7 cases (24.1%) had 45,X/46, X,i (Xq), 4 cases (13.8%) had 45,X/46,XX. Conclusion: High percentage of chromosomal abnormalities was diagnosed in primary amenorrhea and most of them were sex chromosome anomalies. In secondary amenorrhea, the prevalence was lower than primary amenorrhea, so a preselection of patients with secondary amenorrhea for cytogenetic investigations seems to be necessary.