A low-complexity state feedback fault-tolerant control scheme guaranteeing prescribed tracking performance is proposed for a family of uncertain nonlinear systems with unknown control directions. ...Contrary to the current state-of-the-art, novel error transformation functions and new update laws related to performance functions are introduced to the control design such that no compensators or approximation structures are needed, in spite of actuation faults, component faults, and unknown nonlinearities. The proposed method is verified via a simulation on an inverted pendulum.
This article is concerned with the output-feedback tracking control problem for a class of nonlinear systems. The challenge lies in how to drive the tracking error to a prescribed region in a given ...time globally, under both unknown nonlinear functions and unknown virtual control coefficients. To deal with the unknown control direction, an orientation function is exploited in lieu of the Nussbaum gain technique, the supervisory switching strategy, and the parameter estimation approach. To attain global tracking performance, a tuning function is employed to adjust the tracking error, and a barrier function is used to combat this error. The resulting controller guarantees the prescribed tracking performance and the boundedness of the signals in the closed loop for any initial condition.
This paper focuses on the problem of output tracking with prescribed transient and steady-state performance for strict-feedback systems with unknown nonlinear functions and unmatched disturbances. In ...lieu of Nussbaum gain techniques, parameter estimation algorithms and switching control strategies, a continuous static low-complexity control solution is provided by means of a novel combination of smooth orientation functions and error transformation functions. The proposed method possesses inherent robustness against model uncertainties, disturbances, and virtual control signal derivatives, thus eliminating the needs to introduce extra robust control schemes and compute analytic derivatives. Comparative simulation results further illustrate the above theoretical findings.
This paper studies the fault-tolerant tracking control problem for a class of strict-feedback nonlinear systems subjected to actuator faults and external disturbances. The prior knowledge for ...actuator fault, nonlinearity, and external disturbance is totally unknown, besides the control directions. Based on a backstepping approach, an adaptive fault-tolerant control scheme is developed, without utilizing neural networks. In the control design, a group of new feedback mechanisms are proposed to compensate for the unknown system dynamics and actuator faults. Furthermore, to relax a requirement of the initial system states, a modification technique is designed to adjust the reference signal and virtual control laws for a short time. It is shown that the global closed-loop stability is guaranteed and the tracking performance is achieved. The above result is illustrated via simulations on a one-link manipulator and a ship autopilot.
This article is concerned with the high-performance control problem for the nonlinear systems in the sense of not only fast accurate reference tracking but also active damping of error oscillations ...caused by disturbances and unmodeled dynamics. A novel proportional-integral (PI) funnel control approach with rigorous theoretical insurance is put forward to handle this problem. In contrast with the existing solutions that work for weekly nonlinear systems or rely on available knowledge of the system nonlinearities, it is applicable to the lower-triangular systems with unknown multiplicative and additive nonlinearities, unmatched disturbances, and time-varying parameters. Moreover, it preserves the unique simplicity of PI control and funnel control, without the needs for function approximation, parameter identification, disturbance estimation, derivative calculation, or command filtering. The above theoretical findings are illustrated by a comparative simulation on a jet engine compressor.
This article investigates the trajectory tracking control problem for a family of underactuated autonomous surface vessels under the condition of model uncertainties, actuator faults, and ...environmental disturbances. The emphasis or difficulty is how to ensure the trajectory tracking with specified accuracy in the fixed-time settings. A new-type fault-tolerant tracking control strategy is developed based on the marriage of a novel bounding function and a method of handling constraints. Compared with the existing results it can be noted that: first, the position error enters into a preassigned residual set in a priori designate time and remains there; second, no adaptive mechanisms, disturbance observers, or command filters are involved, leading to a simplicity control attribute. Results from a comparative simulation on the CyberShip II further illustrate the above theoretical findings.
This paper investigates the tracking control problem for a family of strict-feedback systems in the presence of unknown nonlinearities and immeasurable system states. A low-complexity adaptive fuzzy ...output feedback control scheme is proposed, based on a backstepping method. In the control design, a fuzzy adaptive state observer is first employed to estimate the unmeasured states. Then, a novel error transformation approach together with a new modification mechanism is introduced to guarantee the finite-time convergence of the output error to a predefined region and ensure the closed-loop stability. Compared with the existing methods, the main advantages of our approach are that: 1) without using extra command filters or auxiliary dynamic surface control techniques, the problem of explosion of complexity can still be addressed and 2) the design procedures are independent of the initial conditions. Finally, two practical examples are performed to further illustrate the above theoretic findings.
This paper explores the output-constrained tracking control problem for unknown Euler–Lagrange systems subject to actuator faults, in the case where the reference trajectory is unknown in advance. ...The presence of actuator faults may lead to the loss of strong controllability of the system assumed in the existing literature on robust control of multi-input multi-output nonlinear systems. The lack of a priori knowledge on the reference trajectory renders the current constraint-handling techniques to achieve prescribed tracking accuracy infeasible. To conquer the above obstacles, a novel fault compensation scheme is designed in this paper, and a new-type error boundary is introduced to the control design. It is proved that the proposed approach guarantees output tracking with prescribed accuracy and constraint satisfactions simultaneously, even if actuator faults occur. A comparative simulation on a robot manipulator is conducted to further illustrate the established theoretical findings.
This article is concerned with the trajectory tracking control problem for the wheeled mobile robots (WMRs) subject to actuator faults. The challenge lies in the partial loss of effectiveness of the ...actuated wheels which results in the loss of strong controllability of the WMR, rendering the classical fault-tolerant control methods infeasible. To overcome this obstacle, a novel mixed-gain adaption technique is put forward and is skillfully combined with the robust prescribed performance control method. The resulting control achieves trajectory tracking of the WMR with the predefined settling time and accuracy, against the actuator faults, the model uncertainties, and the disturbances. Moreover, it exhibits significant simplicity, without parameter identification, function approximation, disturbance estimation, or fault estimation. The theoretical findings are illustrated by a comparative simulation.
This article is concerned with the global prescribed performance control (PPC) problem for the fully interconnected nonlinear systems with nonparametric uncertainties and mismatched disturbances. The ...allowable state interconnections need only to be continuous, without matching conditions or growth conditions which are widely used in the related works. Moreover, different from the existing global PPC designs, we aim at achieving independent performance specifications for all the errors, whose setting time and accuracy are permitted to be arbitrarily predefined. To this end, a novel decentralized robust global PPC approach is put forward in this article. Herein, heterogeneous tuning functions are skillfully introduced to the PPC design to adjust the errors independently. In addition, a constraint analysis framework based on dialectic by contradiction is established to reveal the inherent robustness of the proposed control against the state interconnections. Two comparative experiments on a coupled tanks apparatus are conducted to demonstrate the theoretical findings.
