Binglong Cong

Disturbance observer based time-varying sliding mode control for uncertain mechanical system

It is now well known that the time-varying sliding mode control (TVSMC) is characterized by its global robustness against matched model uncertainties and disturbances. The accurate tracking problem of the mechanical system in the presence of the parametric uncertainty and external disturbance is addressed in the TVSMC framework. Firstly, an exponential TVSMC algorithm is designed and the main features are analyzed. Especially, the control parameter is obtained by solving an optimal problem. Subsequently, the global chattering problem in TVSMC is considered. To reduce the static error resulting from the continuous TVSMC algorithm, a disturbance observer based time-varying sliding mode control (DOTVSMC) algorithm is presented. The detailed design principle and the stability of the closed-loop system under the composite controller are provided. Simulation results verify the effectiveness of the proposed algorithm.

Disturbance observer-based adaptive integral sliding mode control for rigid spacecraft attitude maneuvers:

This article considers the attitude tracking problem of a rigid spacecraft involving inertia matrix uncertainty and external disturbance. The adaptive sliding mode control is utilized for the attitude controller design. The major concern is reducing the switching gain generated by current adaptive sliding mode control, thereby alleviating the chattering problem. By eliminating the influence of initial tracking error from the switching gain adaptation, an adaptive integral sliding mode control scheme is first presented. As compared with current adaptive sliding mode control, a much smaller switching gain is produced. Then, a disturbance observer-based adaptive integral sliding mode control design is proposed to further enhance the result. To this end, the joint effect caused by external disturbance and inertia matrix uncertainty, referred as lumped uncertainty, is divided into a slow varying part and a rapid varying part. By compensating the slow varying component via a disturbance observer, the switching gain is only required to be larger than the upper bound on the rapid varying component. The effectiveness of the proposed strategies, especially the switching gain reduction ability, is verified by both theoretical analysis and simulation results.

A Precise and Robust Control Strategy for Rigid Spacecraft Eigenaxis Rotation

Eigenaxis rotation is generally regarded as a near-minimum time strategy for rapid attitude maneuver due to its constitution of the shortest angular path between two orientations. In this paper, the robust control problem of rigid spacecraft eigenaxis rotation is investigated via time-varying sliding mode control (TVSMC) technique. Both external disturbance and parameter variation are taken into account. Major features of this robust eigenaxis rotation strategy are first demonstrated by a TVSMC algorithm. Global sliding phase is proved as well as the closed-loop system stability. Additionally, the necessary condition for eigenaxis rotation is provided. Subsequently, to suppress the global chattering and improve the control accuracy, a disturbance observer-based time-varying sliding mode control (DOTVSMC) algorithm is presented, where the boundary layer approach is used to soften the chattering and a disturbance observer is designed to attenuate undesired effect. The spacecraft attitude is represented by modified Rodrigues parameter (MRP) for the non-redundancy. Finally, a numerical simulation is employed to illustrate the effectiveness of the proposed strategy, where the pulse-width pulse-frequency (PWPF) technique is utilized to modulate the on-off thrusters.

Improved Adaptive Sliding Mode Control for Rigid Spacecraft Attitude Tracking

AbstractThis paper considers the attitude tracking problem of a rigid spacecraft involving inertia matrix uncertainty and external disturbance. First, an adaptive integral sliding mode control (ISMC) is proposed for when the upper bound on the lumped uncertainty is unknown in advance. It is shown that such a combination can produce a much smaller switching gain than the current adaptive sliding mode control (ASMC); hence, the overadaptation problem in existing ASMC design is effectively solved. Additionally, the system performance is improved by virtue of the global sliding mode feature of ISMC. A similar, but more flexible, ASMC design is introduced to further enhance the results; this design is developed on the basis of the reference trajectory scheme. The validity of the proposed strategies is verified by both theoretical analysis and simulation results.

Switching Gain Reduction in Adaptive Sliding Mode Control for Rigid Spacecraft Attitude Maneuvers

This paper investigates the overadaptation problem in current adaptive sliding mode control (ASMC) for rigid spacecraft attitude maneuvers. The inertia matrix uncertainty and external disturbance are taken into account, and an adaptive scheme is employed for the switching gain calculation. A detailed analysis of existing ASMC design reveals the fact that the switching gain would be overestimated if the ASMC algorithm is developed in the framework of conventional sliding mode control (SMC), owing to the unrelated adaptation caused by initial tracking error. The global sliding mode concept of integral sliding mode control (ISMC) is exploited to solve such a problem. The advantages of the proposed strategy are twofold. First, a much smaller switching gain is generated as compared to conventional ASMC. Second, the resulting small switching gain would not slow down the system response. The advantages of the proposed strategy are verified by both theoretical analysis and simulation results.

Time-varying sliding mode control for spacecraft attitude maneuver with angular velocity constraint

In this paper, the attitude control problem for uncertain spacecraft under angular velocity constraint is addressed. Both parametric uncertainty and external disturbance are considered in the spacecrafts dynamics. The spacecrafts attitude is represented by modified Rodrigues parameter (MRP) for its non-redundancy. A time-varying sliding mode control (TVSMC) algorithm is derived for attitude control system. The proposed control algorithm eliminates the reaching phase of the conventional time-invariant sliding mode control (SMC) and guarantees the sliding mode occurrence all the time. Moreover, the control parameter is adjusted to avoid the angular velocity constraint during the maneuver. Finally, a numerical simulation is employed to verify the proposed control algorithm.

Backstepping based adaptive sliding mode control for spacecraft attitude maneuvers

This paper aims to address the robust control problem of rigid spacecraft attitude maneuvers in the presence of inertia matrix uncertainty and external disturbance. A back-stepping based adaptive sliding mode control (B-ASMC) design is proposed as a solution, where the upper bounds of the parametric uncertainty and disturbance are not required in advance. Compared to current adaptive sliding mode control (ASMC) design, the B-ASMC design has two advantages. Theoretically, the asymptotical stability of the attitude states rather than the sliding function is guaranteed. Practically, the over-adaptation problem in current ASMC design is alleviated and the system performance is improved. Detailed design principle and rigorous closed-loop system stability analysis are provided. A large angle attitude maneuver is employed in the numerical simulation to verify the effectiveness of the proposed algorithm.

A Novel Robust Control Strategy for Spacecraft Eigenaxis Rotations

Abstract This paper addresses the control problem of spacecraft eigenaxis rotations in the presence of parametric uncertainty and external disturbance. We develop a novel robust control strategy for eigenaxis rotation via the time-varying sliding mode control (TVSMC) technique. The general design principle is provided and the characteristic of the eigenaxis rotation is proved mathematically. Modified Rodrigues parameters (MRPs) are utilized as the attitude parameters for the non-redundancy. In particular, a TVSMC eigenaxis algorithm with an exponential time-varying sliding surface is designed to illustrate the main features of the proposed strategy. The effectiveness of the proposed strategy is demonstrated by simulation results.

Robust Attitude Control with Improved Transient Performance

Abstract This paper aims to present a robust attitude control strategy with guaranteed transient performance. Firstly, a Lyapunov-based control law is designed to achieve high-performance attitude control in the absence of disturbance and parameter variation. The proposed control law uses small feedback gains to suppress the control torque at large attitude error, and increases those gains with the convergence of attitude error to accelerate the system response. The overshooting phenomenon is also avoided by imposing a restriction on the parameter selection. Then, the integral sliding mode control technique is employed to improve the robustness, where the Lyapunov-based control law is used as the equivalent control part. Theoretical analysis and simulation results verify the effectiveness of the proposed strategy.

Robust control of spacecraft eigenaxis maneuver via integral sliding mode

The control problem of spacecraft eigenaxis maneuver in the presence of parametric uncertainty and external disturbance is addressed in this paper. Modified Rodrigues parameters (MRPs) are utilized as the attitude parameters for the non-redundancy. An eigenaxis maneuver control law with feedback and feed-forward terms is presented for the nominal system. The transient response of close loop system can be adjusted according to an approximate second order system. To improve the robustness, integral sliding mode (ISM) technique is adopted to reject undesirable effects and track nominal trajectory. The resulting controller can perform the eigenaxis maneuver in the presence of parametric uncertainty and external disturbance while possess good system performance. The effectiveness of the proposed method is demonstrated by simulation results.