System Identification and Control Design for a Stratospheric Flight Mission of a Solar Electric Aircraft

Abstract

A system identification approach is presented for Elektra Two Solar OPS, a high altitude long endurance (HALE) aircraft for stratospheric flight missions. A linear longitudinal model of the aircraft has been developed using a Two Step Method based system identification approach, which provides the biases in the states in the first step along with the force and moment parameters of a system in the second step unlike other common system identification approaches. In order to prove the credibility of the identified aircraft longitudinal model, the identified model has been validated using various methods including some statistical measures, a validation set from the flight test recorded data and a forward simulation to compute the states from the identified model. An optimization based controller tuning method has been presented based on a control design which was manually tuned in flight, using Ziegler-Nichols method which is not a reliable method for such stratospheric flight missions. The applicability of the designed controller has been verified using various methods. A frequency and time domain analysis has been performed to analyse the stability margins and compare other characteristics. A robustness analysis has been performed using Monte-Carlo simulations for a gust disturbance and the model parameter variations in order to validate the robust behaviour of the designed controller. Extensive simulation studies demonstrate that the proposed approach is capable of achieving a an acceptable model of the aircraft which is suitable to be used for the ultimate goal of autonomous stratospheric flight.