• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.23-28
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• 2022

The eLoran system is a high-power terrestrial navigation system that is recognized as the most appropriate alternative to complement the GNSS's vulnerability to radio frequency interference. Accordingly, Korea has conducted eLoran technology development projects since 2016. The eLoran system developed in Korea provides 20 m positioning accuracy to maritime user in Incheon and Pyeongtaek harbor. To accurately calculate the position with the eLoran signal, it is necessary to apply a compensation method that mitigates the propagation delay. In this paper, we develop the compensation method to mitigate the eLoran signal propagation delay and evaluate the positioning performance in Incheon harbor. The propagation delay due to the terrain characteristics is pre-surveyed and stored in the user receiver. Real-time fluctuations in propagation delay compared to the pre-stored data are mitigated by the temporal correction generated at a nearby differential Loran station. Finally, two performance evaluation tests were performed to verify the positioning accuracy of the Korean eLoran system. The first test took place in December 2020 and the second in April 2021. As a result, the Korean eLoran service has been confirmed to provide 20 m location accuracy without GPS.

• Proceedings of the KIEE Conference
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• 1990.07a
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• pp.421-424
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• 1990

In this parer, the parameter for control variable is consist of value that take measured the input line current and input total power-factor, and the compensation susceptance is calculated by its parameters. The compensator can reduce the reactive power generation by the system to zero, thus the input total power-factor is kept on sustaining the unit power- factor.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.2
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• pp.217-224
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• 2009

This paper presents a new AC/DC converter scheme for HVDC system to achieve a high power factor operation. The new AC/DC converter consists of two 12-pulse bridge converters in series: the primary and auxiliary converters. Ignition angles of the main and auxiliary converters are controlled independently to maintain the nominal DC voltage and control auxiliary voltage. The resulted DC voltage obtained by superimposing the above two phase modulated voltages can be controlled very rapidly over a wide range, and a high power factor operation is achieved. Performance improvements in power factor and harmonic distortion are validated by theoretic derivations and experiments with prototype HVDC system. With the proposed converters, investment for reactive power compensation and filter in HVDC system can be saved significantly.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.3
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• pp.195-201
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• 2013

In this paper, we present optimization technique for the response time of DVR (Dynamic Voltage Restorer) and the possible compensation range of voltage dip by the DVR system. To protect 3-phase phase-controlled rectifier from voltage dip, DVR system needs to have optimum response time as an important design factor. Although the fast response time of DVR ensures wider range of voltage dip, DVR controller has so high cost and poor stability. This paper proposes DVR system with optimum response time required for certain intensity of voltage dips and good stability to support possible compensation range of voltage dip. Proposed technique showed optimum response time and good stability for overall system. We believe that proposed technique is reliable and useful in DVR design.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.2
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• pp.191-198
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• 2013

Geo-pointing is a function that maintains LOS(Line of Sight) to a stationary ground target by controlling azimuth and elevation angles of a EOS(Electro-Optical System) which are calculated from aircraft navigation data and target coordinates. In design and implementation of the geo-pointing, a transmission time delay between GPS/INS and EOS is a major degradation factor of the geo-pointing performance when the aircraft is rapidly maneuvered especially. In this paper, a kalman filter is designed to compensate the transmission time delay of aircraft navigation data. Simulation and test results show that the geo-pointing performance is enhanced by the proposed compensation technique.

• The Korean Journal of Health Service Management
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• v.9 no.3
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• pp.13-30
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• 2015

Objectives : The aim of this study was to investigate changes in job satisfaction of hospital workers according to different occupations at a university hospital in Seoul. Methods : A survey questionnaire was sent out to people working in a University Hospital in Seoul. Four hundred questionnaires were included in the final analysis. Results : The results of this study are as follows. Sense of accomplishment was a significant job satisfaction factor resulting in a high level of satisfaction. Work environment, compensation and job stability also affected job satisfaction; however, satisfaction levels appeared to be relatively low. Conclusions : When looking at the most important factors among the influencing factors that the members of the organization thought were most important for job satisfaction, the results showed that achievement, work environment, job stability and compensation were important factors.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.488-493
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• 2005

In gun stabilization systems, the torque comes from the unbalance mass of gun and the base acceleration is an important source of disturbance which degrades stabilization performance. Fatigue of gear train is another important factor affecting structural safety problems. In this paper, a feedback control gain is designed by optimal control weighting to difference between motor and gun velocity, and a feedforward controller using FXLMS algorithm is adopted to investigate those problems. Experimental results show that the feedforward compensator based on FXLMS can reduce the disturbance effects. The directional convergence property according to initial conditions of the FXLMS is also shown through experiments.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.447-450
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• 1991

A novel effective calculation method of the compensation current commands of active power filter using voltage source PWM converter is proposed on the basis of the instantaneous reactive power theory. The load currents and the phase of the source voltages are used for the simplification of the calculations and the reduction of the its time. And the calculation of the currents is performed by DSP 32014 within 50 uSEC. For reducing the DC voltage and saving the costs, a passive power filters are used. The simulation results of the effects of the active power filter with a passive filter are presented.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.369-372
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• 1994

In this paper, a voltage type dual PWM converter which achives the bidirectional power flow between a AC supply and a DC bus voltage is described. In PWM modulator, there exist a time difference between the sampling time and carrier wave, it achieves stable modulation even the disturbance in the synchronous AC source voltage. And this paper proposes the compensation method and the control method related a disturbance of synchronous signal using the low pass filter and phase shifter for the stable modulation. As a result the voltage type dual PWM converter makes the imput current wave as sinusoid, and performs the high power factor driving.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.992-994
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• 1992

Diode rectifier has many low order harmonics in line currents. So, power factor of input side is relatively low. Recently, PWM conveters have been actively studied in order to reduce the harmonics. This paper describes a voltage source PWM rectifier with feed-forward compensation of instantaneous load power. By adding feed-forward compensation to dc link voltage control loop, the fluctuation of dc link voltage at a sudden load change can be considerably suppressed. Simulation based on analytical approach Was performed and the results of it showed a good agreement with theory.