Hover Control Law Design Of A Stratospheric Airship

Due to its ability to hover at stratosphere carrying heavy payload for long endurance, stratospheric airship can be used as observational platform in near space, so it can be widely applied to both military and civil uses. While the design of the hover control law comes to be the precondition of all above, position control law and control strategy of stratospheric airship during hover is mainly discussed in the thesis, the main contents are as followed.First, based on the analysis of forces and torques, under some reasonable assumptions and simplifications, Newton's second law and momentum theorem are applied to establish a nonlinear six-degree-of-freedom model which serves as the foundation of the following chapters.Second, the nonlinear model is divided into longitudinal and lateral equations. Based on the longitudinal nonlinear model, the thrust is used to restrain the disturbance from the wind. In the hover control law, the altitude is adjusted first, and then the forward position is adjusted to the desired position. The altitude adjustment is implemented by using a double-loop PID control law, where the inner loop is used to realize the attitude stabilization, and the outer loop is used to adjust altitude to the desired position. Changes in the quality of stratospheric airship due to the changes of thermal environment and airship flexible deformation is considered as uncertainties in the model. The applicability of the PID controller to the uncertain model is validated.Third, output decoupling variable structure control method is designed to make stratospheric airship hover at the desired position. When the system slide into the sliding surface, the altitude and the forward position can be controlled respectively, and the states won't be disturbed by the uncertainty of the system.