Modeling and Designing an Intelligent Controller using Bond Graph for a Satellite Controlled by Magnetic Actuators

Modeling and Designing an Intelligent Controller using Bond Graph for a Satellite Controlled by Magnetic Actuators

Majid Habibi (K. N. Toosi University of Technology, Iran) and Alireza B. Novinzadeh (K. N. Toosi University of Technology, Iran)
Copyright: © 2012 |Pages: 19
DOI: 10.4018/ijimr.2012010105
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Satellite state control has always been an important topic in aerospace technology. Because it is required that when the satellite is stationary in orbit, it would be directed to a special object and this task should be performed in a situation where there isn’t access to the satellite. This task is performed using various technologies and one of these is the use of magnetic actuators. Magnetic actuators use mechanical torque that is resulted by interaction of electrical current of coils in the satellite and the earth’s magnetic field. The satellite is subjected to such disturbance torques, thus corrupting the direction of the satellite. This method has its advantages and disadvantages. Its drawback is that the magnetic torque is produced only perpendicular to the direction of the magnetic field and the axis of the coil. This paper models a satellite having magnetic actuators using bond graph, and finds out its state equations, and then constructs the control logic that is needed for its control. A model of three dimensional attitude maneuvers and magnetic systems using bond graph is described. The actuators are tuned using the method of particle swarm optimization (PSO). It is observed that using this method a small satellite reaches to the desired angle in a short time and becomes stationary.
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1. Introduction

Attitude control systems (ACS) (Figure 1) play a fundamental role in the operation of spacecraft as they constitute a mandatory feature both for the survival of a satellite and for the satisfactory achievement of mission goals. Several subsystems in a satellite may require a stable satellite for better performance or to function properly. For instance, radio communication will require less power if the antenna(s) can be pointed towards the Earth and the solar panels may increase power output if properly directed towards the Sun. While a number of possible approaches to the control of attitude dynamics have been developed through the years, a particularly effective and reliable one is constituted by the use of electromagnetic actuators, which turn out to be especially suitable in practice for low Earth orbit (LEO) satellites. Magnetic torquing is attractive for small, comparatively cheap satellite missions. Magnetic control systems are lightweight, require low power and are cost effective. There is broad literature covering the area of satellite magnetic control.

Figure 1.

Diagram of components of attitude control system


Such actuators operate on the basis of the interaction between a set of three orthogonal, current-driven magnetic coils and the magnetic field of the Earth (Wertz, 1978; Sidi, 1997), and therefore provide a very simple solution to the problem of generating torques on board a satellite. The 3-axis stabilization using magnetic torquing only for a gravity gradient stabilized satellite is a subject of a number of studies such as Usser and Ward (1989) and Wisniewski (1995). These approaches deal with linear analysis of the satellite motion, and 3-axis control is only obtained if a significant gravity gradient exists. We must mention that in this work we don’t consider gravity gradient.

In 1975, Schmidt described magnetic attitude control on three-axis stabilized, momentum-biased satellites. Here, a momentum wheel was mounted along the pitch axis to provide bias, or nominal angular momentum that is not zero. Schmidt showed that this system required minimum switching of the closed loop controller, and thus was reliable for long duration missions. This work was used towards the RCA Satcom geosynchronous satellite, which was three-axis stabilized using air core coils.

In particular, while periodic control has been already proven to be successful in various applications (see, e.g., Arcara, Bittanti, & Lovera, 2000), the feasibility of periodic techniques for the control of small satellites using magnetic actuators has become only recently a topic of active research (see, e.g., the recent works Pittelkau, 1993; De Marchi, Rocco, Morea, & Lovera, 1999; Wisniewski & Blanke, 1999; Wisniewski& Markley, 1999; Wang & Shtessel, 1999; Lovera, De Marchi, & Bittanti, 2002). It must also be mentioned that it’s important that the magnetic actuators be used in conjunction with momentum wheels for the purpose of momentum unloading of magnetic torquers, and also this method provides for more accurate control. Thus, the method is also used in this work.

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