Development of a Robust Altitude Control System for a Quadrocopter

In this report, we present the development of a robust altitude control system for a quadrocopter. The controller has been developed on the basis of a reasonable simple mathematical model. Therefore it must not be sensitive to deviations of the real system from the plant model, which is taken into consideration for controller design. Furthermore, the control system shall be adaptable for different types of input sensor data (e.g. pressure altitude, GPS, or SLAM position measurements). Since the quadrocopter should be able to operate outdoor, a good rejection of external disturbances such as wind gusts should be provided as well. Taking into account all the constraints mentioned above, the control system should still ensure good tracking performance. After the definition of a linear model for the vertical quadrocopter motion, the plant parameters were identified by an iterative comparison of simulation and experiment results. Based on this plant model an altitude control system has been developed according to the Linear Quadratic Gaussian (LQG) design with Loop Transfer Recovery (LTR) in order to fulfill the robustness requirements mentioned above. The LQG design includes a full state feedback controller as well as a Luenberger observer to provide estimates of the system states which cannot be measured.