State estimation of VTOL octorotor for altitude control by using hybrid extended Kalman filter

In this paper, state variables of eight-rotor Vertical Take-off and Landing (VTOL) aircraft are estimated and used in the feedback loop for altitude control. Due to output measurement noise, the measured signal cannot be directly used in estimation and control. To study the effect of filtering on system's performance, we consider three modes of filtering, namely, (1) no filter, (2) firstorder low-pass filter, and (3) hybrid extended Kalman filter. System control in the no filter mode is not favorable. There is significant tracking error, and control signal consists of frequent fluctuations with large amplitude. In the second mode, when using first-order low-pass filter, tracking condition of altitude reference signal is better, but the control signal still has frequent fluctuations with large amplitude and could not be implemented. In the third mode, when hybrid extended Kalman filter is used, tracking of reference signal is performed well and the control signal is in good condition with mitigated fluctuations and bounded amplitude.