• 제어로봇시스템학회:학술대회논문집
• /
• 2003.10a
• /
• pp.1231-1234
• /
• 2003

A sensor working in outdoor may generate some faulty signal owing to dust and high temperature. This paper describes an intelligent sensor system and controller which has a reconstruction mechanism for faulty signal. The faulty signals are dievided into two types as linear distortion and non linear distortion, respectively. The linear distorted signal is due to dust, and non linear distorted signal is due to physical breakdown of sensor or high temperature. These distorted signal have been reconstructed by the proposed method based on polynomial regression method and principal component analysis approach.. The proposed method has been applied to sun tracking system working in outdoor. For a robust and precision control of sun tracker, a fuzzy controller was also proposed. The fuzzy controller controls the tracker by using the collected sensor signal. The tolerance of the position control is within 1.5 degree. To show the validity of the developed system, some experiments in the field were illustrated.

• Bulletin of the Korean Space Science Society
• /
• 2008.10a
• /
• pp.28.2-28.2
• /
• 2008

Recently, star sensors have been successfully used as main attitude sensors for attitude control in many satellites. This research presents the star visibility analysis for star trackers and the goal of this analysis is to make sure that the star tracker implementation is suitable to the mission profile and scenario and satisfies the requirement of attitude orbit control system. As a main optical attitude sensor imaging stars, accomodations of a star tracker should be optimized in order to improve the probability of the usage by avoiding the blinding (the unavailability) by the Sun and the Earth. For the analysis, a statistical approach and a time simulation approach are used. The statistical approach is based on the generation of numerous cases, to derive relevant statistics about Earth and Sun proximity probabilites for different lines of sight. The time simulation approach is performed for one orbit to check the statistical result and to refine the statistical result and accomodations of star trackers. In order to perform simulations first of all, an orbit and specific mission profiles of a satellite are set, next the earth proximity probability and the sun proximity probability are calculated by considering the attitude maneuvers and the geometry of the orbit, and then finally the unavailability positions are estimated. As a result, the optimized accomodations of two star trackers are suggested for the low earth orbit satellite.

• Korean Journal of Remote Sensing
• /
• v.31 no.4
• /
• pp.353-360
• /
• 2015

Earth's gravity field recovery was improved after the pre-processing upgrade of the Gravity Recovery And Climate Experiments (GRACE) satellite's star trackers. The star tracker measurements were filtered with a tighter low-pass filtering of 0.025Hz cutoff frequency, instead of a nominal filtering of 0.1Hz cutoff frequency. In addition, a jump removal algorithm was applied to remove discontinuities, due to direct Sun and/or Moon interventions, in the star tracker measurements. During the K-Band Ranging (KBR) calibration maneuvers, large attitude variations could be detected concurrently by both of the star trackers and the accelerometer. The misalignment angles of star trackers between the true frame and the normal frame could be determined by comparing measurements from these sensors. In this paper, new Earth' gravity field maps were obtained using above improvement. Based on comparisons to nominal Earth's gravity field maps, the new Earth's gravity field maps were found better than the nominal ones. Among the applied methods, the misalignment calibration of the star trackers had a major impact on the improvement of the new Earth's gravity field maps.

• Aerospace Engineering and Technology
• /
• v.5 no.2
• /
• pp.90-101
• /
• 2006

In this paper, the calibration parameters of the gyros and star hackers are estimated by using an on-orbit AOCS sensor calibration algorithm. The calibration algorithm was implemented by Kalman filter. In order to estimate gyro calibration parameters, the calibration algorithm requires calibration maneuver and it was analyzed whether the star trackers are protected by Sun, Moon and Earth or not. Also the star tracker calibration algorithm used the camera image information. This kinds of camera image information simulated ground control point and orbit information. The estimated accuracy of star tracker calibration parameters depends on camera image information.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.2
• /
• pp.96-100
• /
• 2006

We develop the Dual Head Star Tracker (DHST) to obtain the attitude information of science and Technology Satellite2 (STSAT-2). Because most of star sensor has only one head camera, star recognition is impossible when camera point to sun or earth. We therefore considered the DHST which can obtain star images from two spots simultaneously. That is, even though we fail a star recognition from an image obtained by one camera, it is possible to recognize stars from an image obtained by the other camera. In this paper, we introduce engineer model (EM) of the DHST and propose a star recognition and a star track algorithm.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.11
• /
• pp.180-187
• /
• 2013

The dinger in solar generation is the amount of sunlight which the solar cells absorb. Various types of solar trackers, which rotate themselves in order to make the solar cells face the sun as much as possible, have been developed, and especially the method of tracking with two axes has greatly contributed in increasing the generation amount at work sites. Among theses 2-axis solar trackers, the inclination-dependent 2-axis solar tracker are widely utilized for its advantages of requiring less initial investment and easy maintenance due to a solid structure. However, the drawback is that the generation efficiency is relatively low because of the structural restriction that limits the rotation angle, thus making it less efficient when tracking the sun. This paper proposes a method to increase the generation efficiency of the inclination-dependent 2-axis solar tracker. It also contains the derived equations needed for precise controlling along with a method to keep tracking with the other axis even when one has reached its angle limit. To confirm that the proposed method increases the amount of incidence onto the solar cells, formulas needed for operation on the proposed method and tracking the exact position of the sun are derived, and applying this to the quarterly data of Korea Astronomy and Space Science Institute it shows maximum over 11.1% more incidence compared to existing methods.

• Proceedings of the KIEE Conference
• /
• 2009.04a
• /
• pp.40-42
• /
• 2009

The economic growth and highly industrialized society have increased the demand for electricity power. As a result, concerns were focused on the energy resource scarcity and global warming. That is why the photovoltaic generation system to address these concerns has been in the spotlight recently. In this thesis, a utility interactive photovoltaic generation system was operated experimentally for the purpose of promoting the spread of the photovoltaic generation system in the future. Also, the effect of the type of array structure has on the performance of the photovoltaic generation system was evaluated quantitatively and by analyzing the comprehensive operating characteristics, the following results were obtained. In the demo system operated for a year, the average irradiation was measured to be 455,076 $[W/m^2]$ and the maximum irradiation to be 626,622 $[W/m^2]$ in May, up 171,546 $[W/m^2]$ or 38[%] compared with the average irradiation. The minimum irradiation was observed to be 294,022$[W/m^2]$ in December, down 161,054 $[W/m^2]$ or 35[%] compared with the average irradiation. The generation power in situation where there is plenty of irradiation was more than the average one, and the generation power in the fixed system amounted to 32[%], the single-axis tracker to 37[%], and the dual-axis tracker to 39[%]. The generation power in situation where there is little irradiation was less than the average one, and the generation power in the dual-axis tracker amounted to 41[%], the single-axis tracker to 40[%], and the fixed system to 36[%].

• Journal of the Korea Institute of Military Science and Technology
• /
• v.10 no.4
• /
• pp.145-151
• /
• 2007

This paper considers new filter gains for the ${\alpha}\;-\;{\beta}$ tracker which is optimized particularly to minimize the tracking gate size. Optimizing the performance index which is composed of tracking errors due to target maneuver and measurement noise is not different from the existing method to obtain the ${\alpha}\;-\;{\beta}$ gains. However, holding the probability 0.997 that a target exists in the tracking gate and minimizing the gate size produce the new result not similar to the existing ${\alpha}\;-\;{\beta}$ gains.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.8 no.3
• /
• pp.260-265
• /
• 2003

The energy of PV system is different as the elevation and aximuth of the sun. This paper deals with the economical position tracking system development for the stand alone PV system. We have made more economical solar position tracking system which is used a tracking program than other similar systems. It is applied to the solar lighting lamp. We have made a comparative study of the energy amount between the fixed type and the tracking type during some period. The improved efficiency of the system is about 86 %.

• Proceedings of the KIPE Conference
• /
• 2002.07a
• /
• pp.559-562
• /
• 2002

In the photovoltaic power system, it is required that we obtain as much as generated power as possible. This paper describes improved stand-alone photovoltaic system efficiency(SPVS) using the sun position tracker for the solar lighting lamp through the comparison test of the power efficiency between the tacking type and the non-tacking type one.