Disturbance observer-based autonomous landing control of unmanned helicopters on moving shipboard

Abstract

In this paper, the autonomous landing control issue on moving shipboard is investigated for unmanned helicopters subject to disturbances. The issue is studied by stabilizing the error system of the helicopter and the shipboard. The landing process is divided into two phases, i.e., homing phase, where a hierarchical double-loop control scheme is developed such that the helicopter is forced to hover synchronously at a certain altitude over the shipboard, and landing phase, where a composite landing control scheme is proposed such that the helicopter lands vertically on the shipboard in synchronization with its attitudes. The velocity and acceleration information of the shipboard as well as lump disturbances are estimated through joint state and disturbance observers. The estimates are then incorporated into the baseline feedback controller, formulating composite active anti-disturbance landing control schemes. A continuous terminal sliding mode control method is proposed for the feedback controller design, which not only effectively mitigates the chattering of the control action, but also simplifies the design process of the controller. Numerical simulations demonstrate the effectiveness and superiorities of the proposed control schemes.

Improved high gain observer design for a class of disturbed nonlinear systems

“…For this end, one shall proceed as follows. First, one shall introduce a large class of systems which includes system (9) and where the expression of the output only depends on the system state and hence does not explicitly depend on the noise. A high gain observer that copes with the peaking phenomenon, referred to as NPHGO, will be designed for this class of systems and the main properties of the underlying observation error will be put forward.…”

“…A high gain observer that copes with the peaking phenomenon, referred to as NPHGO, will be designed for this class of systems and the main properties of the underlying observation error will be put forward. Then, one shall come back to system (9) to prove that it is included in the considered large class of systems and hence the proposed design of the NPHGO can be mimed leading thereby to a NPFHGO which copes not only with the peaking phenomenon problem but also with the observer sensitivity to noise.…”

“…with k = n and k 0 = i w ; w : [0, +∞[ → IR is a time varying unknown function the consideration of which shall be motivated later. All the other variables involved in system (10) keep the same meaning as in system (9). Notice that to avoid the redundance of variables, the same notation is used for the state variables and dimensions of systems (9) and system (10), i.e.…”

“…All the other variables involved in system (10) keep the same meaning as in system (9). Notice that to avoid the redundance of variables, the same notation is used for the state variables and dimensions of systems (9) and system (10), i.e. x and n. However, both systems are different since they assume different structures and the fact that the class of systems (10) includes systems (9) will be detailed later.…”

“…An intensive research activity has been devoted to the observer design for uniformly observable systems over the last four decades (see for instance [1][2][3][4][5][6][7][8][9][10] and references therein). A particular emphasis has been put on the Standard High Gain Observer (SHGO) design for fundamental as well as simplicity purposes [5].…”