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Issue 7, Volume 4, July 2007
ISSN: 1109-9445







Title of the Paper: Mixed H2/H∞ Self-Adaptive Fuzzy Algorithm to Control Satellite Attitude


Authors: Guo-Shing Huang, Zhi-Liang Zhang

Abstract: The main purpose of this paper is to propose a nonlinear H∞ and mixed d H2 /H∞ self-fuzzy algorithm to solve large-angle robust control problem. The attitude control is one of the studied problems in recent years. Under the space environment, there often exists an unpredictable interference which results some deviations of satelliteís attitude. Therefore, it needs to develop a controller still to keep the control ability to the system with respect to the uncertainty of the satellite system and unpredictable environment interference in order to achieve the required control goal and performance specification. In this paper, consider one ROCSAT-3 hardware structure, and use selffuzzy fuzzy algorithm to perform the attitude control with the time varying and uncertainty parameters. Then, we combine the nonlinear H∞ and mixed H2 /H∞ control law to reduce the impact of the satelliteís attitude system due to external disturbance. Through simulation results, it is shown that the proposed design method can make the ROCSAT-3 system efficiently achieve the desired stability and reject the external interference.

Keywords: Nonlinear H∞ control, Nonlinear mixed H2 /H∞ control, Self-fuzzy algorithm, Attitude control, Time varying parameter

Title of the Paper: Time Syntonization and Frequency Stabilizing Using GPS Carrier Phase with Extension Controller


Authors: Guo-Shing Huang

Abstract: This study discusses time syntonization and frequency stability calibration using GPS carrier phase measurements. Thus far most papers on this subject discussed using two GPS receiver measurements, and performing frequency stabilizing and vehicle positioning with the double differences. This paper proposes using a dual frequency GPS receiver and a novel extension controller neural network algorithm that can achieve the frequency stabilizing and coordinate positioning. The oscillation frequency of the rubidium atom clock is selected first as the satellite atom clock oscillation frequency as the criterion for adjusting the GPS receiver oscillator's frequency. The receiverís oscillation frequency is synchronized with the reference atomic clock oscillation frequency using the designed extension controller and extension neural network. To finish the frequency stabilizing and time syntonization, the time can be calibrated and the position precision on the vehicle improved. The position precision can be improved from about 3.5 meters to about 1.5 meters using the extension controller. The time error is improved from about 4.85◊10−7 seconds to about 2 .8 5 ◊ 1 0 − 8 seconds. Using the extension neural network to verify the position precision allows improvement from about 3.5 meters to about 1.3 meters. The time error is improved from about 4.85◊10−7 seconds to about 2 .8 ◊ 10 − 8 seconds. The system was verified experimentally as satisfying the exactness, feasibility and robustness of the initial concept.

Keywords: GPS, Carrier Phase, Extension Controller, Extension Neural Network

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