Control Of Advanced Flight Vehicles With Nonminimum Phase Properties

With the development of aerospace technology,the research on advanced flight vehicles becomes a boom in recent years.Among others,hypersonic vehicles(HSV),reusable launch vehicles(RLV),and vertical take-off and landing vehicles(VTOL)have attracted a lot of attention from countries all over the world due to their significant military and civil values.It is shown that all the three kinds of advanced flight vehicles given above may exhibit nonminimum phase properties.The unstable zero dynamics in the model disable the application of traditional control methods,which is the most challenging problem in designing flight control systems.This thesis focuses on the above research topic with the goal to enhance flight safety.By developing new theory and new methods for the control of nonminimum phase systems,we finally achieve stable and high-accuracy control for advanced flight vehicles with nonminimum phase properties.The main contributions of this thesis are as follows.(1)Extended-loop backstepping is proposed for stable controller design of hypersonic vehicles.Based on the analysis of model structure,we point out the principle to obtain a stable controller via backstepping,that is,by using extended-loop backstepping.By extending the control loop to cover the internal dynamics,it allows to achieve output tracking as well as internal stability.Based on the extended control loop,an adaptive backstepping controller is designed.The proposed method shows good tracking performance and is robust.It provides a new way for the stable control of slightly nonminimum phase systems.(2)Output-redefinition-based dynamic inversion control is proposed for hypersonic vehicles.Firstly,output redefinition is performed to obtain stable zero dynamics.Three choices are given to construct a minimum phase new output,including using an internal state as a new output,using a statically synthetic output,and using a synthetic output with an integral item.Then,a stable controller is obtained by using dynamic inversion to the new output.The proposed method provides a systemtatic way for the control of general nonminimum phase systems,which allows us to make a tradeoff between robustness and control performance.(3)Optimal bounded inversion is proposed to achieve precision output tracking for an underactuated RLV.Firstly,output redefinition is performed to obtain stable zero dynamics.Then,optimal bounded inversion is proposed to obtain the ideal internal dynamics(IID)which are required for exact tracking.Finally,a tracking controller is designed based on the new output by using backstepping,and an anti-windup strategy is proposed to prevent input saturation through feedback error clipping.The overall controller successfully achieves precision output tracking for an RLV in the circumstance of underactuation.(4)Exact output tracking is achieved for a VTOL with uncertain parameters by using experience replay.Firstly,the experience replay technique is applied to identify the uncertain parameters in the model.Then,the IID is obtained by using optimal bounded inversion based on the identified parameters and is incorporated into the tracking controller to achieve exact tracking.The proposed method provides an efficient way to solve the exact tracking control problem for uncertain nonminimum phase systems.(5)Universal tracking controller(UTC)is proposed for both minimum phase and nonminimum phase systems.UTC is an extension of PID control for state-space model.UTC reveals the relationship between PID control and many other control techniques and gives us a new prespective to view PID control.Besides,UTC also reflects the performance limitations of nonminimum phase systems.