IFAC PapersOnLine 51-24 (2018) 812–817 ScienceDirect Available online at www.sciencedirect.com 2405-8963 © 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2018.09.668 © 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. 1. INTRODUCTION Many researchers have focused on the development of the methodologies for robust and reliable flight control systems. Nowadays, hypersonic reentry vehicle (HRVs) has attracted considerable attention in both military and civil fields (Parker et al. (2007); Xingling and Honglun (2014); Sziroczak and Smith (2016)). Due to its critical flight conditions, HRV has highly nonlinear characteristics, complex coupling effects combined with unknown multiple uncertainties and can be also affected by faults or failures to the actuators or sensors, which caused considerable challenges in designing control system for HRV (Zhang et al. (2015)). There are two typical approaches to deal with uncertain- ties and faults in the HRV controller design, which are adaptive control (Gibson et al. (2009); Zhang et al. (2015); Zhou et al. (2017)) and robust control (Fiorentini et al. (2008); Dorobantu et al. (2012)). Adaptive control scheme (Xu et al. (2016)) makes sure that controller can adapt to the varying uncertainties in the controlled HRV system. In contrast with an adaptive control, the robust control methods (Su et al. (2013)) are designed to work properly if the uncertain parameters or disturbances are within given bounds. Recently, various Uncertainty-Disturbance Estimation-based Control (UDEC) frameworks have been carried out to restrain or compensate disturbances and ⋆ This work was supported by National Natural Science Foun- dation of China under Grant 61703339. uncertainties in systems (Ginoya et al. (2014); Gao and Wang (2014); Kodhanda et al. (2017)). Thanks to efficien- t characteristics for disturbance observers Ginoya et al. (2014); Chang et al. (2017b,a), unmatched uncertainty compensation for HRV system based on the observation and backstepping procedure has been investigated (Davila (2013); Xingling and Honglun (2014); Guo et al. (2018)). Despite the high number of published works using this interesting characteristic, too few works take into accoun- t the effect of uncertainties/faults effect on the control efforts. In the recent work (Guo et al. (2017)), a novel coupling effect indicator is proposed to demonstrate the coupling effects on the system. This proposed control scheme achieved a better dynamic performance by explic- itly utilizing the system couplings in the controller design. This motivates the work of this paper, where a controller is designed based on faults/uncertainties indicators to reduce the control effort. In this context, an FTC scheme is presented for the hypersonic vehicle subjected to unmatched uncertainties and a class of actuator faults, by augmenting the control scheme from (Guo et al. (2017)). Firstly, the effect of the actuator faults and uncertainties on system stability and performance is analyzed to help with building their effect indicators. An improved disturbance observer is designed to estimate the unknown uncertainties/faults, that it does not need a priori information about the bounds on these uncertainties/faults. Then, a controller based on these indicators and estimated information is proposed, that can enforce and maintain the system tracking performance in Keywords: Fault tolerant control, adaptive disturbance observer, back-stepping, reduced control effort. Abstract: An active fault-tolerant control scheme is proposed in this paper for Hypersonic Reentry Vehicle (HRV) which subjected to actuator faults. Disturbance observer based com- pensation idea is incorporated with a fault/uncertainty effect-triggered control approach to deal with vehicle attitude tracking problem with unmatched uncertainties and actuator faults. First, an improved adaptive disturbance observer (ADO) is introduced to estimate the lumped uncertainties and actuator faults, which transforms the uncertain system to a matched structure. With the estimated lumped disturbance (uncertainties and actuator faults) from the observer, the control law is given based on the combination of back-stepping based techniques and sliding- mode algorithm. The proposed scheme can achieve robust tracking performance with reduced control effort by eliminating the detrimental uncertainty and actuator fault while keeping the beneficial uncertainty and actuator fault. Simulation results obtained on the reentry vehicle have demonstrated the effectiveness of the approach proposed. * Xidian University, Xi’an, China (e-mail: changjing.work@gmail.com;) ** Northwestern Polytechnical University, Xi’an, China (e-mail: Eason.work@qq.com;) *** University of Bordeaux, IMS Laboratory, Talence, France, (e-mail: jerome.cieslak@ims-bordeaux.fr) Jing Chang * Zongyi Guo ** J´ erˆ ome Cieslak *** A fault tolerant control scheme for the reentry vehicle with reduced control effort