Stabilization of Low Earth Orbit Satellite Attitude Control System Using Robust Proportional-Integral-Derivative-Tuned Compensator

The impact of effective satellite attitude control system (SACS) is that it can ensure both quality and reliability of data acquisition by a low earth orbit (LEO) satellite. This work presents design of adaptive controller for satellite y-axis attitude control system (ACS). With several techniques proposed in literature, there is still need to improve the tracking error and robustness of the control system in the presence of disturbance. In order to achieve this, the transfer function models of amplifier, actuator, and satellite structure for determining the transfer function a LEO satellite yaw-axis attitude were obtained. This work presents a yaw-axis ACS for LEO satellite using Proportional Integral and Derivative Tuned Compensator (PID-TC). The compensator was designed using the control system toolbox of MATLAB based on PID Tuning design method using robust response time tuning technique with interactive (adjustable performance and robustness) design mode at a bandwidth of 44.5 rad/s. The compensator was added to position control loop of yaw-axis. Simulations were carried out in MATLAB environment for four separate cases by applying unit forced input to examine the various step responses. Initial simulation without the inclusion of the compensator (PID-TC) in the control loop resulting in rise time of 2.16 s, settling time of 22.14 s and 38.63% overshoot. Thus, in terms of the performance criteria defined for the system, all conditions were not met specifically the settling time and the overshoot. Hence, a PID-TC controller was designed and introduced into the system, which resulted in transient and steady-state performances of the system being characterized by rise time of 3.82, settling time of 7.30 s, overshoot of 3.88%, and steady-state error (0). Generally, simulation results revealed that the proposed PID-TC controller meets all the performance criteria for a typical controller for LEO satellite yaw-axis attitude control system as defined in previous studies. The robustness of the designed PID-TC was examined by introducing a unit disturbance load torque and the step response simulation plot indicated that the achieved reduced rise time (1.82 s) and settling time (6.90 s) but with slight deterioration in smoothness and stability (as the overshoot was increased to 4.14%). When compared to the classical PID and Linear Quadratic Regulator (LQR), the PID-TC system provided the best dynamic response performance with in terms of convergence to steady-state (measured considering settling time), smoothness in response and stability both in the absence and presence of load torque disturbance. The significance of this work is that a robust PID-TC controller has been used to provide improved yaw angle (or attitude) tracking for LEO satellite in the absence and in the presence of load torque disturbance.