Nonlinear control of aerostat with input constraints based on nested saturation

The propellers of an aerostat are prone to both amplitude and rate saturations during the movement of the aerostat, thus affecting the stability and movement of the system. Generally, the conventional method of processing saturation can only handle the amplitude saturation of the system input, and the rate saturation problem is usually converted to an amplitude saturation problem, so it is a complex process. Therefore, it is worthwhile to study the control method that can simultaneously deal with amplitude and rate saturations. Some anti-windup compensator design methods can only be applied to linear systems, and some nonlinear anti-windup control methods for nonlinear systems require much online calculations to obtain the control law, which is not conducive to real-time control. Therefore, a novel control method was applied to the nonlinear research object. The nested saturation function could realize the bounded amplitude and differential of the input when used as a control law because of its specific form. Thus, it could be used to solve the amplitude and rate saturation problems in an aerostat system. This paper presented the design of an anti-windup controller for a nonlinear multi-propeller aerostat with amplitude and rate saturations of control input. First, the three-DOF model of the aerostat was established and transformed into two chain-like integral systems by taking forces other than propeller thrust as disturbances. Based on the theory of nested saturation control, the relationship between the amplitude and rate saturations of control inputs and the parameters of saturation function was obtained. Taking the aerostat as the research object, decoupled controller for longitudinal and lateral channels was designed to realize the bounded amplitude and rate of the system input. The global stability of the system was proved by the Lyapunov stability theorem, and the dynamic performance of the system was analyzed under different adjustable parameters. Considering the wind disturbance, the effectiveness and robustness of the controller was verified by simulations.