Control
Sevil M. Sadigh; Narges Talebi Motlagh; Hossein Behesgti; Sahand Moharrami; Moharram Shameli
Abstract
In this paper, an adaptive fault-tolerant control based on modified nonsingular fast terminal sliding mode control is developed for attitude tracking of a satellite with three magnetorquers and one reaction wheel. The proposed approach is designed to be robust in the presence of actuator faults, external ...
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In this paper, an adaptive fault-tolerant control based on modified nonsingular fast terminal sliding mode control is developed for attitude tracking of a satellite with three magnetorquers and one reaction wheel. The proposed approach is designed to be robust in the presence of actuator faults, external disturbances, and inertia uncertainties and preserve the acceptable performance of system. The adaptive law is designed to estimate the upper bound of uncertain expressions, increase the tracking accuracy, and improve the performance of system. This parameter with a coefficient of sliding surface variable are used in the reaching phase of control law to achieve the chattering-free phenomenon. Stability and finite-time convergence of attitude variables is proved by the extended Lyapunov condition. To increase the tracking accuracy and compensate the required torque, a reaction wheel is used as a redundancy. Also, for increasing the control accuracy, the dynamics of this actuator is considered as well as the constraints of magnetorquers and reaction wheel. The simulations are performed and compared with the similar control method under the mentioned conditions to evaluate the performance of the proposed method. The results show the finite-time convergence, increasing the tracking accuracy, smoothing of satellite attitude changes, and generating the chattering-free control signals.
adel Pourtaghi Marzrood; Arezoo Esmaeili; adel Pourtaghi marzrood; Moharram Shameli
Abstract
Backflow is a phenomenon that occurs due to the increase of upstream pressure compared to downstream pressure. In converging-diverging nozzles, by increasing the outlet pressure compared to the design pressure, the phenomenon of backflow is observed in the divergent part, which causes a decrease in the ...
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Backflow is a phenomenon that occurs due to the increase of upstream pressure compared to downstream pressure. In converging-diverging nozzles, by increasing the outlet pressure compared to the design pressure, the phenomenon of backflow is observed in the divergent part, which causes a decrease in the output velocity and thrust. In this paper, a converging- diverging nozzle with suitable expansion ratio for vacuum condition is selected and the propellant flow, which is considered as butane in this research, is simulated by finite volume method for output pressure equal to vacuum pressure and atmospheric pressure conditions. It has seen that in the atmospheric pressure, backflow occurs in the nozzle in order to determine the appropriate expansion ratio for the nozzle operating in atmospheric pressure, the flow inside the nozzle is simulated for the different expansion ratios and the average outlet axial velocity at the output of theses nozzles is obtained. According to the results, the most suitable expansion ratio of the surface has the highest average axial velocity. Also, to verify the obtained results from finite element simulation, four nozzles with different surface expansion ratios were manufactured and the thrust force obtained from experimental test on the measuring stand with equivalent results obtained from the simulations were compared
