The Simulation For Upwind Control Strategy Of Airship Autonomous Control System

Airship is a steerable aircraft which is lighter than the air. Due to its advantages; it has been put into military and civilian applications. Communication platform carried by airship for wireless base stations and sentinel surveillance of specific regions are two of its applications. These kinds of tasks require airship suspended in the air for a long time period in a boundary. To successfully complete the goal of fixed-point suspension, it is necessary to consider the effect of wind on the airship; when the wind blows from the lateral side of the airship and thus make it float away from its original position to a certain extent, the task can not be normally finished. Therefore, studying the upwind control strategy for airship is needed.The paper puts unmanned airship as the research object, makes researches into airship’s upwind control strategy, jobs done are in the following aspects:(1) Establishment of airship’s mathematical model: firstly, non-linear differential equations about airship’s six degrees of freedom are constructed by referring to related literature. Nonlinear models are difficult to be modified by some of the more mature theory, so it is necessary to do model linearization. When the airship’s velocity, yaw angle, pitch angle and roll angle deviate from initial value of the above variable in a smaller boundary, its mathematical model can be modified by linearization through the method of small disturbance. However, in the process of airship’s yaw angel adjustment to the upwind direction, the changing of aerodynamic parameters is relatively large, thus it is not suitable that the whole adjustment process is transformed into only one linear equation. Therefore, the process is divided into several small processes; linearization is adopted in each small process.(2) Construction of wind field model: Computer simulation for airship upwind control does not truly reflect the actual situation, when the velocity of wind remains the same value. This article considers changes in wind speed over time as a random process to create a turbulent wind field. A specific ARMA model is adopted. First, according to statistics of the long-term observation of wind, wind speed frequency spectrum is deduced; and then the model parameters are inferred by using the spectrum; Finally, the article use this model to generate a turbulent wind field model for a specified mean wind speed.(3) Design of algorithm for upwind control in a fixed boundary: yaw angle control is an important part of the whole control algorithm. Yaw angle control in accordance with the adequacy of the rudder effect is separated into two types of circumstances to deal with. Firstly, let’s consider the situation that rudder effect is adequate. In this case, aerodynamic parameters in the process of airship upwind gradually adjustment changes a lot. Even the same input of rudder angle will cause a great difference in the output of yaw angle. Thus, adaptive control method is induced to reduce the impact of changing parameters on the angle output. In another case of low rudder effect, yaw angle adjustment is done by the difference of engine thrust. When the yaw angle adjustment process is done, the airship position maybe deviates from the initial position which exceeded the allowed range of error distance; next, control algorithm of flying back to the original location is adopted. The paper uses a method which I called "spiral" airship trajectory adjustment strategy to achieve adjustment goal. In this method, a specific complex issue is converted to a series of the same sub-issues, and finally control algorithm is verified through a matlab simulation, the results indicate the feasibility of the algorithm.