Unmanned Helicopter Non-fragile Robust Flight Control Research Based On H_∞ Loop Shaping

Unmanned Helicopter (UMH) is more and more important in military and civilian use nowadays. UMH is a typical multi-input multi-output (MIMO) system including many characteristics, such as non-stability, strong coupling, uncertainty, great model differences in full envelope and fragility in flight controller so that it is hard for us to control UMH. The thesis discusses the problems on how to design the flight controller of UMH.Firstly, a brief review is provided on UMH flight control, non-fragile control and H_∞loop shaping. And the related key issues of the UMH flight control are analyzed.Secondly, the problem of non-fragile robust stability and decoupling control is addressed for the system with coprime factor uncertainties both in plant and controller. The necessary condition for the problem is derived, and an optimization design approach for robust controller is provided. Furthermore, aiming at normalized coprime factor uncertainties of the plant and controller, an optimal non-fragile robust controller design method based on H_∞loop shaping is provided.Thirdly, after analyzing the demands of loop shaping, the thesis proposes an improved selection method of weight functions of H_∞loop shaping. Generally, the weight functions are chosen by trial and error, so that the synthetical performance index of the controller is hard to meet the frequency and time domain performance requirements. The improved method is based on engineering design and applied chaos optimization with non-fragile constraint. Compared with normal weight selection method, it can reduce the iteration times of weight function selection, and ensure the synthetical performance of the resulting controller. Simulation results demonstrate that it is effective of using the improved selection method to design controller which can meet the design demands.Fourthly, for meeting handling qualities requirements of ADS-33E, a robust ACAH controller and a non-fragile robust ACAH controller of a UMH are designed based on H_∞loop shaping, and then the performance comparisons between the two controllers are given. The digital simulation results show that the non-fragile robust controller has good robustness, non-fragile robust stability and decoupling performance which is better than the robust one. And then a hard-in-loop simulation is carried out to the non-fragile robust ACAH controller and the results demonstrate its validity.Fifthly, the thesis develops a full envelope robust control strategy of UMH. A double loop controller structure is proposed at first. And based on that structure, a new approach of how to divide UMH flight regions and select the nominal plant in corresponding region is presented which is proved to be effective in maintaining the robustness and performance of the UMH.In the end, a non-fragile robust ACAH controller in full envelope of a UMH is designed based on H_∞loop shaping. Furthermore, the controller structures of speed and position are obtained. Then the digital and hard-in-loop simulations of the full envelope controller of a UMH are carried out, and the simulation and experiment results show that the control system has good tracking and decoupling performance, strong anti-disturb ability and satisfy non-fragile performance.