Search

We propose a reliability-based anti-disturbance control (RADC) method for systems with parametric stochastic uncertainty based on the linear matrix inequality (LMI) and the limit state function. Differing from the existing anti-disturbance control, the parametric stochastic uncertainty is considered in both the concerned system and the exogenous disturbance system. With this consideration, the condition for system stability and performance robustness is described by a stochastic LMI which holds with a certain probability (reliability). Through the limit state function method, the stochastic LMI is subtly transformed into two probabilistic LMIs for two different cases. The proposed probabilistic LMIs contain two probabilistic parameters of reliability indexes that quantify the effect of parametric stochastic uncertainty. At different prescribed reliability indexes, controllers with different reliability can be flexibly and reliably designed. Two illustrative examples with Monte-Carlo verification are presented to demonstrate the feasibility and effectiveness of the proposed RADC method. • A reliability model for uncertain systems is established by stochastic LMI. • A novel concept/method of probabilistic LMI for RADC is proposed. • The proposed RADC greatly extends the application of traditional LMI. [ABSTRACT FROM AUTHOR]

The performance of the gimbal servo system in control moment gyro (CMG), which includes precision, lifespan etc., is one of the crucial factors of spacecraft attitude control. The various practical disturbances, however, will not only deteriorate the velocity‐tracking accuracy but will also cause the abnormal gimbal velocity problem (especially peak phenomenon). To this end, this paper proposes a refined anti‐disturbance control method to deal with velocity output constraints and multiple disturbances. Starting with fully understanding the prior information of multiple disturbances, a refined disturbance observer with a low conservativeness is designed to accurately estimate disturbances. The disturbance‐estimation error is analyzed in detail to ensure convergence to a bounded region. Subsequently, a novel barrier Lyapunov function‐based backstepping controller is proposed that considers the residuals of disturbance estimation to simultaneously achieve multiple disturbances attenuation and compensation, and handle velocity output constraints. Notably, the gimbal's maximum velocity is precisely limited to a pre‐specified low range, which benefits the CMG's lifespan and performance. Finally, both simulation and experimental results show that the proposed method performs better in disturbance estimation, velocity tracking, and robustness. [ABSTRACT FROM AUTHOR]

Robustness of positive systems with respect to disturbances is a challenging issue of both theoretical and practical importance. In this study, the stabilisation control problem of positive systems with disturbances is investigated. More generalised disturbances are considered here, including positive modelled disturbances and general disturbances. A disturbance observer is designed to estimate the disturbances and a sufficient and necessary condition for stabilisation is derived. For positive disturbances, a sufficient condition with the use of the convergence law for the existence of controller is proposed, and this problem can be formulated as a linear programming problem. Furthermore, the corresponding theory is expanded to generally modelled disturbances, which enriches the theories about anti‐disturbance control of positive systems. Meanwhile, the analysis is given in detail to promote the theoretical completeness, including conservations of hypothesis and positivity constraints of disturbance estimation values. Simulation results show that the proposed scheme can guarantee the positivity of systems and improve the system performances for generalised disturbances. [ABSTRACT FROM AUTHOR]

The attitude control problem is much more complicated due to the existence of faults and multiple disturbances simultaneously in satellites. In this paper, an adaptive fault tolerant attitude control method is presented for satellites with both time-varying actuator faults and multiple disturbances. Differing from previous results, the first part of the multiple disturbance is the uncertain modelled disturbance and the second part represents an uncertain variable bounded by a given function. A composite observer is designed to estimate the uncertain modelled disturbance and the time-varying fault simultaneously. Then, a new fault tolerant control strategy consisting of disturbance observer based control, fault accommodation and an adaptive controller is constructed to reconfigure the concerned systems and so as to achieve the anti-disturbance performance. In the proposed method, the modelled disturbance can be rejected by its estimation and the uncertain bounded disturbance can be compensated by the adaptive compensation term. The simulation results are given to show the efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

As a class of autonomous deep-space exploration robots, Mars lander is simultaneously affected by wind disturbance and actuator fault, which hinders precise landing on Mars. In this article, we propose a composite guidance approach by combining disturbance observer and iterative learning observer together. The Mars wind disturbance is dealt by the disturbance observer providing wind estimation which is rejected through feed-forward channel. Meanwhile, the iterative learning observer is used to estimate the deficiency of actuators. The proposed guidance scheme ensures not only the precision but also the reliability of the Mars guidance system. The stability of the closed-loop system is analyzed. Simulations made in different situations demonstrate the performance of the proposed approach. [ABSTRACT FROM AUTHOR]