Nonlinear Model Predictive Control of Urban Air Mobility Aircraft for Vibration Suppression and Trajectory Tracking

Abstract This paper presents the development and simulation of the Nonlinear Model Predictive Controller (NMPC) of a tiltrotor urban air mobility (UAM) aircraft. The free flight of the aircraft is governed by a set of nonlinear rigid-body dynamic equations with multiple tiltrotors and their gyroscopic and inertial effects. As a comparison, a feedback Linear-Quadratic Regulator (LQR) is also designed. The control variables include two rotors‘ spin rates, in addition to the traditional elevator, aileron, and rudder deflections. Both controllers are compared in two cases: level flight for vibration suppression and lateral trajectory path tracking. Even though similar results can be obtained in the vibration suppression with the NMPC and LQR, better performance of the NMPC can be observed in the path-tracking case. Unlike the vibration control case, the nonlinear nature of the aircraft flight dynamics should be accounted for by the controller design to properly track the ever-changing path reference, which is not the case for the LQR. In short, while the NMPC has a higher computational cost, it also demonstrates a much better control performance than the LQR.