• 대한전기학회논문지
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• 제41권1호
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• pp.32-41
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• 1992

This paper presents a comprehensive study on the stability of several control schemes for the induction motor driven by current source inverters. A stator voltage controlled current source inverter drive system without a speed sensor is investigated in order to find appropriate control schemes, which are primarily based on direct or, alternatively, indirect frequency control scheme. It can be seen, especially that an introduction of the indirect frequency control method improves the inherent instability of the current source inverter drive system for the induction motor. The overall control systems with either voltage control loop or current and voltage control loops in addition to each frequency control scheme, are analyzed by utilizing the root locus method and simulated by computer to show the validity of this analysis.

• 전기의세계
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• 제17권3호
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• pp.29-38
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• 1968

The development of the frequency converter using semiconductor enables to easily control the speed of A.C. motors. It is now technically possible and economically feasible to provide them with power at variable frequency, using silicon-controlled-rectifier (or thyristor) inverters. In such a case, if an induction motor is to be operated efficiently over a wide speed range, it must be supplied from a variable-frequency source whose frequency is adjustable over a range similar to that required for the motor speed. It is desired to observe how several characteristics are changed such as primary current, torque-speed, etc. Although the characteristics could be obtained by means of the conventional method, it requires very complicated calculation. It is assumed that the charateristics above are easily investigated by means of current diagram method from variable circuit constants relating to the motor which is designed in rated frequency. In this paper, the results of the study on the current-diagram method and its application are described as follows; (1) In order to discuss the construction of current diagram, the equation of the stator current with adjustable frequency was derived for applying the Current Diagram Method. (2) The radius, the center of the current circle and current vector locus at any desired frequency could be easily determined with the aid of both above mentioned equation and the standard current diagram at reference frequency. (3) This method could be applicable to the various types of Induction Motors, and this paper has dealt with its application to the capacitor, split-phase and 2-phase types of motors.

• 전기의세계
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• 제18권4호
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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.

• 전기의세계
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• 제18권5호
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• pp.20-25
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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 adjustable 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 frequency source of which frequency is adjustable over the speed range of the motor. It is desired to observe the changes in characteristics as primary current, torque-speed of induction motor etc. at any optional frequency. Although the characteristics can be obtained by means of the conventional methods, they require very complicated precedures of calculations. The Current Diagram Method in this paper suggests a new approach to simpler calculations 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 Diagram 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.

• 전력전자학회논문지
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• 제21권2호
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• pp.168-174
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• 2016

In this paper, current control using PI controller in the synchronous reference frame is analyzed through the relationship among bandwidth, resonance frequency, and sampling frequency in the grid-connected inverter with LCL filter. Stability is investigated by using bode plot in frequency domain and root locus in discrete domain. The feedback variable is the grid current, which is regulated by the PI controller in the synchronous reference frame. System delay is modeled as 1.5Ts, which contains computational and PWM modulator delay. Two resonance frequencies are given at 815 Hz and 3.16 kHz from LCL filter parameters. Sufficient phase and gain margins can be obtained to guarantee stable current control, in case that resonance frequency is above one-sixth of the sampling frequency. Unstable current control is performed when resonance frequency is below one-sixth of the sampling frequency. Analysis results of stability from frequency response and discrete response is the same regardless of resonance frequency. Finally, stability of current control based on theoretical analysis is clearly verified through simulation and experiment in grid-connected inverters with LCL filter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.583-586
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• 1991

This paper presents a comprehensive study on the stability of several control schemes for the induction motor driven by current source inverters. A stator voltage-controlled current source inverter drive system without a speed sensor is investigated in order to find appropriate control schemes, which are primarily based on direct or, alternatively, indirect frequency control scheme. The overall control systems with either voltage control loop or current and voltage control loops provided in addition to each frequency control scheme are analyzed by utilizing the root locus method and simulated by computer to illustrate the validity of this analysis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.330-335
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• 1996

The well-conditioned observer design method is extended for two-output systems where observer gains are not determined uniquely with respect to the desired observer poles. Similar to the previous results, this design method makes off-diagonal elements of the observer upper-left submatrix skew-symmetric and simulataneously, places the eigenvalues of the observer matrix widely separated by selecting upper two rows of the observer gain. The proposed design method is evaluated in a spindle-drive example where the load speed is estimated based on motor speed and the armature current.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2006년도 추계학술대회 발표논문집
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• pp.99-108
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• 2006

Three experiments were conducted to determine the exact locus of the frequency effect in speech production. In Experiment 1. a picture naming task was used to replicate whether the word frequency effect is due to the processes involved in lexical access or not. The robust word frequency effect of 31ms was obtained. The question to be addressed in Experiment 2 is whether the word frequency effect is originated from the level where a lemma is selected. To the end, using a picture-word interference task, the significance of interactions between the effects of target frequency, distractor frequency and semantic relatedness were tested. Interaction between the distractor frequency and semantic relatedness variables was significant. And interaction between the target and distractor frequency variables showed a significant tendency. In addition, the results of Experiment 2 suggest that the mechanism underlying the word frequency effect is encoded as different resting activation level of lemmas. Experiment 3 explored whether the word frequency effect is attributed to the lexeme level where phonological information of words is represented or not. A methodological logic applied to Experiment 3 was the same as to Experiment 2. Any interaction was not significant. In conclusion, the present study obtained the evidence supporting two assumptions: (a) the locus of the word frequency effect exists in the processes involved in lemma selection, (b) the mechanism for the word frequency effect is encoded as different resting activation level of lemmas. In order to explain the word frequency effect obtained in this study, the core assumptions of current production models need to be modified.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.98-99
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• 2017

A discrete time domain modeling for the current-mode-controlled buck LED driver is presented in this paper. Based on the modeling result, a root locus analysis for the buck LED driver with slope compensation is done to derive the stability boundaries of feedback gains.

• 여성건강간호학회지
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• 제16권2호
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• pp.157-165
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• 2010

Purpose: The purpose of this study was to identify differences in Health Locus of Control (HLOC), depression, wellbeing, and Health Promoting Lifestyle Profile II (HPLP) between middle aged Korean and Korean-American women. Methods: Data from 80 Korean-American women living in Los Angeles, USA and 82 Korean women living in W-city, Korea, were collected using a self administered questionnaire including items on HLOC, HPLP, a Wellbeing Index and Major Depression Inventory. Results: There were statistically significant differences between the middle aged Koreans and Korean-Americans on mean age, education, religion, and current health insurance. Significant differences were found on HLOC (F= 2.504, p=.033) and Wellbeing (F=2.451, p=.036). The results also showed significant differences on HPLP (total HPLP, F=4.655, p=.001; physical activity, F=2.967, p=.014; nutrition, F=4.250, p=.001; spiritual growth, F=4.398, p=.001; interpersonal relations, F=2.648, p=.025; and stress management, F=5.201, p<.001) using ANCOVA. However, there were no significant differences on depression, or health responsibility in HPLP between the groups. Conclusion: Understanding middle aged women's health adjustments based on their culture will enhance the ability of health professionals to provide culturally congruent care and enable middle aged women to develop healthy lifestyles.