Pilot Induced Oscillation Mitigation for Unmanned Aircraft Systems: An Adaptive Control Allocation Approach

This paper proposes an adaptive control allocation method that can make unmanned aircraft systems recover from pilot induced oscillations. Pilot induced oscillations are undesired oscillations due to an unintentional and detrimental coupling between the aircraft and the pilot. These oscillations may be instigated due to disturbances, aggressive maneuvers and actuator saturation. Different from manned aircraft, pilot induced oscillations in unmanned aircraft systems are harder to handle due to communication time delays between the operator and the aircraft. The task of a conventional control allocator is to distribute the control effort among redundant actuators to realize a desired virtual control input. When actuators rate saturate, the difference between the desired and the achieved virtual control input introduces an effective time delay to the system dynamics which causes oscillations. In the proposed approach, instead of minimizing the error between the desired and achieved virtual control inputs, the derivative of this error is minimized which eliminates the introduced time delay effect and damps undesired oscillations. Differently from earlier works conducted by the authors, in this work, the proposed pilot induced oscillation mitigation methodology is developed for systems with parametric uncertainty. In the simulations, it is demonstrated that the proposed approach successfully damps pilot induced oscillations that are instigated by a high gain pilot command.