The hypersonic vehicle model is characterized by strong coupling, nonlinearity, and acute changes of aerodynamic parameters, which are challenging for control system design. This study investigates a novel compound control scheme that combines the advantages of the Fractional-Order Proportional-Integral-Derivative (FOPID) controller and Linear Active Disturbance Rejection Control (LADRC) for reentry flight control of hypersonic vehicles with actuator faults. First, given that the controller has adjustable parameters, the frequency-domain analysis-method-based parameter tuning strategy is utilized for the FOPID controller and LADRC method (FOLADRC). Then, the influences of the actuator model on the anti-disturbance capability and parameter tuning of the FOLADRC-based closed-loop control system are analyzed. Finally, the simulation results indicate that the proposed FOLADRC approach has satisfactory performance in terms of rapidity, accuracy, and robustness under the normal operating condition and actuator fault condition.

The nonlinear extended state observer (ESO) is a novel observer for a class of nonlinear control system. However, the non-smooth structure of the nonlinear ESO makes it difficult to measure the stability. In this paper, the stability problem of the nonlinear ESO is considered. The describing function (DF) method is adopted to analyze the stability of high-order nonlinear ESOs. The main result of the paper shows the existence of the self-oscillation and a sufficient stability condition for high-order nonlinear ESOs. Based on the analysis results, we give a simple and fast parameter tuning method for the nonlinear ESO and the active disturbance rejection control (ADRC). Realistic application simulations show the effectiveness of the proposed parameter tuning method.

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This paper investigates the stability and performance of the linear active disturbance rejection control (LADRC)–based system with uncertainties and external disturbance via transfer functions and a frequency-domain view. The performance of LADRC is compared with the state-observer-based state feedback control (SOSFC) and state feedback control (SFC). First, the transfer functions and the error transfer functions for LADRC, SOSFC, and SFC are studied using the state-space method. It is proven that the LADRC-, SOSFC-, and SFC-based closed-loop systems have the same transfer function from the reference input to the output and achieve the same control effects for the nominal system. Then, it is proven for the first time that the LADRC has a better anti-interference ability than the SOSFC and SFC. Besides, the asymptotic stability condition of LADRC-based closed-loop system considering large parameter perturbations is given first. Moreover, the sensitivity analysis of the closed-loop system is carried out. The results show that the LADRC has stronger robustness under parameter perturbations. According to the results, we conclude that the LADRC is of great disturbance rejection ability and strong robustness.

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