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As an extremely dangerous phenomenon in autonomous aerial refueling (AAR), the flexible refueling hose vibration caused by the receiver aircraft’s excessive closure speed should be suppressed once it appears. This paper proposed a permanent magnet synchronous motor (PMSM) based refueling hose servo take-up system for the vibration suppression of the flexible refueling hose. A rapid back-stepping based anti-disturbance nonsingular fast terminal sliding mode (NFTSM) control scheme with a specially established finite-time convergence NFTSM observer is proposed for the PMSM based hose servo take-up system under uncertainties and disturbances. The unmeasured load torque and other disturbances in the PMSM system are reconstituted by the NFTSM observer and to be compensated during the controller design. Then, with the back-stepping technique, a rapid anti-disturbance NFTSM controller is proposed for the PMSM angular tracking to improve the tracking error convergence speed and tracking precision. The proposed vibration suppression scheme is then applied to PMSM based hose servo take-up system for the refueling hose vibration suppression in AAR. Simulation results show the proposed scheme can suppress the hose vibration rapidly and accurately even the system is exposed to strong uncertainties and probe position disturbances, it is more competitive in tracking accuracy, tracking error convergence speed and robustness. [ABSTRACT FROM AUTHOR]

Autonomous aerial refueling (AAR) exact docking control has always been an intractable problem due to the strong nonlinearity, the tight coupling of the 6 DOF aircraft model and the complex disturbances of the multiple environment flows. In this paper, the strongly coupled nonlinear 6 DOF model of the receiver aircraft which considers the multiple flow disturbances is established in the affine nonlinear form to facilitate the nonlinear controller design. The items reflecting the influence of the unknown flow disturbances in the receiver dynamics are taken as the components of the “lumped disturbances” together with the items which have no linear correlation with the virtual control variables. These unmeasurable lumped disturbances are estimated and compensated by a specially designed high order sliding mode observer (HOSMO) with excellent estimation property. With the compensation of the estimated lumped disturbances, a back-stepping high order sliding mode based exact docking flight controller is proposed for AAR in the presence of multiple flow disturbances. Extensive simulation results demonstrate the feasibility and superiority of the proposed docking controller. [ABSTRACT FROM AUTHOR]

• The flexibly towed drogue vehicle's 6 DOF nonlinear affine dynamics is formulated. • DSC-HOSMO based trajectory controller is proposed for the aerial recovery drogue. • The effects of the cable tensions and airflows are reconstituted by HOSMOs. • The method can avoid explosion of complexity and enhance anti-disturbance ability. This paper focuses on the anti-disturbance trajectory stabilization problem of the flexible cable towed aerial recovery drogue under multiple unknown airflow disturbances. Firstly, the 6 degrees of freedom (DOF) dynamics of the towed drogue are established in affine nonlinear form for nonlinear control design. Then, several finite-time convergent high order sliding mode observers (HOSMO) are designed to accurately estimate these lumped disturbances which include the effects of the unmeasurable tensions and airflow disturbance in each subsystem of the drogue's dynamics. With the feed-forward compensations of these estimated disturbances, a HOSMO based anti-disturbance back-stepping controller is proposed to stabilize aerial recovery drogue subjecting to the unmeasurable cable tensions and airflow disturbances. The dynamic surface control (DSC) technique is used to avoid the "explosion of complexity" problem in the standard back-stepping. Also, the closed-loop stability is analyzed to show all the signals are ultimately bounded. Therewith, the proposed method's performance and effectiveness for the aerial recovery drogue are compared with the case without any active stabilizer. [ABSTRACT FROM AUTHOR]