Attitude dynamic tracking control of an agile satellite using a fixed-structured H∞ synthesis method

Abstract

It is a challenging control problem for an agile satellite to observe a rapidly moving target with high dynamic tracking precision. This paper presents a robust and high-accuracy attitude control law for an agile satellite with flexible solar arrays. Model uncertainties caused by vibration of flexible appendages are described as an uncertainty weighting function in the framework of robust H∞ control. However, using the traditional H∞ synthesis method, the resulting dynamic output-feedback controller is not suitable for practical implementation due to its complicated structure and high order. To deal with this issue, an H∞ controller with a fixed proportional-integral-derivative (PID) structure is proposed, and the PID control gains are determined by solving a set of linear matrix inequalities with minimizing the H∞ norm of the feedback control system. Moreover, a feedforward compensator is included to further improve the dynamic performance of the system, achieving a faster response with a smaller dynamic tracking error. Simulations are carried out to demonstrate that the proposed control system can achieve high-precision and rapid maneuver tracking performance for abruptly changing attitude command signals in presence of modeling uncertainties.