Adaptive Attitude Control Law Research Articles

Continuous appointed‐time prescribed performance attitude tracking control for rigid spacecraft with actuator faults on SO(3)

AbstractIn this article, the attitude tracking problem for rigid spacecraft subject to external disturbance, inertia uncertainties, and actuator faults is investigated. A novel continuous control strategy is proposed to guarantee that the attitude tracking errors converge with desired performance before an appointed time. In addition, the proposed control law can enable the closed‐loop system to be unwinding‐free. For the purpose, a modified appointed‐time performance function (APF) is used to construct a disturbance observer‐based adaptive attitude control law based on the special orthogonal group (SO(3)). With the aid of the modified APFs, desired performance metrics, including transient and steady‐state performance, on the attitude tracking error can be specified in advance without the requirement for initial values of the tracking system to avoid singularity. By resorting to error transformation and backstepping technique, the control design process is simplified and a few control gains are involved in the proposed control law. Rigorous stability analysis based on the Lyapunov theory is provided to prove the appointed‐time stability of the attitude tracking error as well as the boundedness of all signals in the closed‐loop system despite external disturbance, inertia uncertainties, and actuator faults. Finally, numerical simulations are conducted to support the analysis.

Nussbaum Gain-Based Cone Angle Constrained Fault-Tolerant Attitude Control with Time-Varying Inertia

This paper proposes a robust adaptive attitude control law for handling a class of actuator faults in the presence of various challenges, such as time-varying inertia, attitude constraints, and input saturation. The proposed approach uses cone angles to represent orientation errors, which are constrained within a performance function to ensure desired transient and steady-state behaviour during reference tracking. Input saturation is approximated using a smooth hyperbolic tangent function. The Nussbaum gain technique is used to handle the unknown control coefficients, which guarantees uniformly ultimately bounded stability in the presence of uncertainties and disturbances. The paper also proposes a norm-based disturbance approximation to estimate the total uncertainty during the Lyapunov analysis. Numerical simulations demonstrate the effectiveness of the proposed control law.

Data driven adaptive robust attitude control for a small size unmanned helicopter

In this paper, the data driven based control design problem for a small size unmanned helicopter is investigated. The helicopter is subjected to the effects associated with modeling uncertainties and unknown external disturbances. A new model free robust adaptive attitude control law is proposed with the combination of the model-free-adaptive-control (MFAC) design, the immersion and invariance (I&I) approach, and the super-twisting technique. Different from the most existing linear or nonlinear model-dependent control designs for unmanned helicopters, the proposed control strategy requires very less model knowledge. The controller depends mainly on the input and output data of the helicopter, and no boundedness knowledge of the unknown disturbances is required. Stability of the closed-loop system has been proved. Real-time flight experiments have been performed on the self-developed helicopter testbed only with the available feedback data of the helicopter. The experimental results have validated the good robustness of the proposed control methodology.

Adaptive parameter identification based nadir-pointing control of spacecraft with misaligned rotational component

The kinematics and dynamics of a nadir-pointing spacecraft with rotational component are derived in the presence of both the parallel and angular misalignments. Based on the derived model, the nadir-pointing control problem is formulated and an adaptive attitude control law with parameter identification is developed. In the proposed control law, periodic angular reference signal is exerted firstly to tune the adaptive parameters, and the misalignments of the rotational component are identified simultaneously. Using the identified parameters, high precision nadir-pointing control is achieved. The stability and effectiveness of the proposed method are verified through Lyapunov method and Monte Carlo analysis.

In-flight results of adaptive attitude control law for a microsatellite

Because satellites usually do not experience large changes of mass, center of gravity or inertia in orbit, linear time invariant (LTI) controllers have been widely used to control their attitude. But, as the pointing requirements become more stringent and the satellite’s structure more complex with large steerable and/or deployable appendices and flexible modes occurring in the control bandwidth, one unique LTI controller is no longer sufficient. One solution consists in designing several LTI controllers, one for each set point, but the switching between them is difficult to tune and validate. Another interesting solution is to use adaptive controllers, which could present at least two advantages: first, as the controller automatically and continuously adapts to the set point without changing the structure, no switching logic is needed in the software; second, performance and stability of the closed-loop system can be assessed directly on the whole flight domain. To evaluate the real benefits of adaptive control for satellites, in terms of design, validation and performances, CNES selected it as end-of-life experiment on PICARD microsatellite. This paper describes the design, validation and in-flight results of the new adaptive attitude control law, compared to nominal control law.

Adaptive Spacecraft Attitude Control with Actuator Saturation

P RACTICAL spacecraft attitude control systems must operate in the presence of disturbances, modeling errors, and actuator limitations. These issues have been the subject of much research interest. Adaptive control, where the unknown system parameters are estimated adaptively, is one of the proposed approaches for dealing with modeling uncertainty (see, for example, [1–4]). Both [1,2] deal with the attitude tracking problem, but they do not treat disturbances or actuator saturation. Reference [3] also deals with the tracking problem; it includes actuator saturation but not disturbances. Reference [4] includes bounded disturbances, but it does not treat actuator saturation, and it only deals with the attitude regulator problem. Recently, new control laws have been obtained that treat both disturbances and actuator limitations simultaneously [5–8]. References [5,6] deal with the attitude regulation problem only. References [7,8] treat the attitude tracking problem, and both present globally convergent control laws, given bounds on the spacecraft inertia matrix and the disturbances. The advantage of these approaches is that the form of the disturbance need not be known, only the bound. On the other hand, these approaches have no ability to learn the system model, which could be a useful feature if the attitude motion is to be optimized. This Note shows that, when an adaptive attitude control law based on the form given in [2] is appropriately designed, any linearly parameterizable disturbances can be accommodated; the closed-loop system is stable, with asymptotic tracking in the presence of actuator saturation. The unknown system parameters are learned adaptively.

Adaptive Control of Nonlinear Attitude Motions Realizing Linear Closed Loop Dynamics

An adaptive attitude control law is presented that realizes linear closed-loop dynamics in the attitude error vector. The modified Rodrigues parameters (MRPs) are used as the kinematic variables since they are nonsingular for all possible rotations. The desired linear closed-loop dynamics can be of either PD or PID form. Only a crude estimate of the moment of inertia matrix is assumed to be known. An open-loop nonlinear control law is presented which yields linear closed-loop dynamics in terms of the MRPs. An adaptive control law is developed which asymptotically enforces these desired linear closed-loop dynamics in the presence of large inertia and external disturbance model errors. Since the unforced closed-loop dynamics are nominally linear, standard linear control methodologies can be employed to satisfy design requirements. The adaptive control law is shown to track the desired linear performance asymptotically without requiring a priori knowledge of either the inertia matrix or external disturbance.