Robust Control of Vectored Thrust Aerial Vehicles Via Variable Structure Control Methods

Robust Control of Vectored Thrust Aerial Vehicles via Variable Structure Control Methods Hiranya S. Jayakody A Thesis presented for the degree of Doctor of Philosophy School of Mechanical and Manufacturing Engineering University of New South Wales Australia August 17, 2016 ii PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: JAYAKODY First name: HIRANYA Other name/s: SAMANGA Abbreviation for degree as given in the Universtty calendar: PhD- MTRN 1662 School: School of Mechanical and Manufacturing Engineering Faculty: Engineering Title: Robust Control of Vectored Thrust Aerial Vehicles via Variable Structure Control Methods Abstract 350 words maximum: (PLEASE TYPE) The popularity of Unmanned Aerial Vehicles (UAVs) has grown rapidly in many civil and military f'PPiications in the last few decades. Recent UAV applications include crop monitoring, terrain mapping and aerial photography, where one or several image sensors attached to the UAV provide important terrain information. A thrust vectoring aerial vehicle, a vehicle with the .ability to change the direction of thrust generated while keeping the UAV body at a zero roll and pitch orientation, can serve well in such applications by allowing the sensors to capture stable image data without additional gimbals, reducing the payload and cost while increasing the flight endurance. Furthermore, thrust vectoring UAVs can perform fast forward flight as well as hover operations with non-zero pitch: features which can serve well in military applications. The first part of this research focuses on developing a comprehensive dynamic model and a low level attitude and position control structure for a tri-rotor UAV with thrust vectoring capabiltty, namely the Vectored Thrust Aerial Vehicle. Nonlinear dynamics of UAVs require robust control methods to realize stable flight. Special attention needs to be given to wind gust disturbances, and parametric uncertainties. Sliding Mode Control , a type of Variable Structure Controller, has served well over the years in controlling UAVs and other dynamic systems. However, conventional Sliding Mode Control results in a high frequency switching behavior of the ccintrol signal. Furthermore, Sliding Mode Control does not focus on fast set-point regulation or tracking, which can be advantageous for UAVs and many other robotic systems. Taking these research gaps into account, this work presents an Adaptive Variable Structure Control method, which can acquire fast set-point regulation while maintaining robustness against external disturbances and uncertainties. The adaptive algorithm developed in this work is fundamentally different from current Adaptive Sliding Mode Control and other Variable Structure methods. Simulation and experimental results are provided to demonstrate the superiority of the proposed approach compared to Sliding Mode Control. The novel adaptive algorithm is applicable to many nonlinear dynamic systems including UAVs, robot arm manipulators and space robots. The same adaptive concept is then utilized to develop an Adaptive Second Order Sliding Mode Controller. Compared to existing Second Order Sliding Mode Control methods, the proposed methodology is able to produce reduced sliding manifold reach times and consume less amount of control resources: features which are particularly advantageous for systems wtth limited control resources. Simulations are conducted to evaluate the performance of the proposed Adaptive Second Order Sliding Mode Control algorithm. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. 1 retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (!hi~ is applicable to doctoral theses only). The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS Originality Statement ‘I hereby declare that this submission is my own work and to the best of my knowl- edge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed ................................... Date ................................... iii Copyright Statement ‘I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.’ Signed ................................... Date ................................... iv Authenticity Statement ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed ................................... Date ................................... v Abstract The popularity of Unmanned Aerial Vehicles (UAVs) has grown rapidly in the past several decades in many civil and military applications. Recent roles of UAVs include applications such as crop monitoring in broad acre farming, terrain mapping, aerial photography and videography, and monitoring of large structures, where one or several image sensors attached to the UAV platform collect and process thermal, visual and laser data to provide valuable information on the objects and land below. A thrust vectoring aerial vehicle, a vehicle with the ability to change the direction of thrust generated while keeping the UAV body at a zero roll and pitch orientation, can serve well in such applications where the zero-roll-pitch vehicle body allows the sensors to capture stable image data without the aid of a gimbal, reducing the payload and cost while increasing the flight endurance. Furthermore, thrust vectoring UAVs can perform fast forward flight as well as hover operations with non-zero pitch: features which can serve well in military applications. The first part of this research focuses on developing a comprehensive dynamic model and a low level attitude and position control structure for a tri-rotor UAV with thrust vectoring capability, namely the Vectored Thrust Aerial Vehicle. Nonlinear unstable dynamics of UAVs require robust control methods to realize stable flight. Special attention needs to be given to the disturbances caused by sudden wind gusts during UAV flight, and to the uncertainties caused by system parameters. Sliding Mode Control , a type of nonlinear Variable Structure Control approach, has served well over the years in controlling UAVs and other complex dynamic systems while handling disturbances and uncertainties in a robust manner. However, conventional Sliding Mode Control results in a high frequency switching behavior of the control signal, referred to as chattering. Furthermore, Sliding Mode vi vii Control inherently does not focus on fast set-point regulation or tracking, which is a desirable characteristic for UAVs and robotic systems in general. Taking these research gaps into account, this work presents an Adaptive Variable Structure Control method for nonlinear dynamic systems, which has the ability to acquire fast set-point regulation control while maintaining robustness against external disturbances and parametric uncertainties. It is important to note that the adaptive algorithm developed in this work is fundamentally different from current Adaptive Sliding Mode Control and other Variable Structure Control methods. The proposed methodology

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