Abstract
This paper proposes two kinds of dual-loop nonlinear robust control strategies that are implemented on an open-loop unstable two-degree-of-freedom (2-DOF) helicopter system with unmodeled dynamics and uncertainties. The inner feedback loop is considered as a nominal controller realized by an existing “intelligent” proportional differential controller (iPD) while the outer layer feedback control is regarded as a compensation loop. We study two different forms of outer loop in this paper. One is model-free sliding mode compensator (MFSMC) and another is model-free data-driven compensator (MFDDC). The combination of the shared inner loop and either of the outer loops forms two different kinds of model-free robust control strategies, i.e., iPD-MFSMC and iPD-MFDDC. Both robust control approaches are validated experimentally on the attitude tracking control of a 2-DOF laboratory helicopter, whose control objective is to have the helicopter attitudes, i.e., pitch and yaw motions, track specified trajectories. To demonstrate the utility of the two control approaches, we compare them with linear quadratic regulator (LQR), optimal feedback linearization control (OFLC) and iPD, respectively. The extensive comparison of the simulation and experimental results shows that the dual-loop robust control approaches are quite promising in controlling the systems with unknown dynamical models.
Highlights
Flight control of unmanned aerial vehicles (UAVs) is a popular topic in recent years
The combination between the intelligent’’ proportional differential controller (iPD) and modelfree sliding mode compensator (MFSMC) forms the first dualloop control structure we studied in this paper
The mixture of iPD and model-free data-driven compensator (MFDDC) fully exploits their respective advantages, broadens their application scope, and improves their control effects. This mixed control approach is the second dual-loop control structure we studied in this paper
Summary
Flight control of unmanned aerial vehicles (UAVs) is a popular topic in recent years. Qin et al.: Dual-Loop Robust Attitude Control for an Aerodynamic System With Unknown Dynamic Model a more accurate nonlinear system model for controller design is needed. In the work of [37], two model-free sliding mode control system structures are designed and validated by a set of real-time experimental results on a nonlinear laboratory twin-rotor aerodynamic system. With online measurement and offpolicy learning, Zhang et al [48] solved the continuoustime unknown nonzero-sum game with partially constrained inputs by a model-free ADP algorithm This method makes sense only if the right-hand side of system x = f (x)+g1(x)u1 +g2(x)u2 is Lipschitz continuous on a compact set ∈ n containing the origin and the system is stabilizable on. The pitch encoder and motor signals are transmitted via a slip ring, which eliminates the possibility of wires tangling and allows the yaw angle to rotate freely 360 degrees
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