Decentralized, Cooperative Control of Multivehicle Systems: Design and Stability Analysis

摘要

This dissertation addresses the design and stability analysis of decentralized, cooperativecontrol laws for multivehicle systems. Advances in communication, navigation,and surveillance systems have enabled greater autonomy in multivehicle systems, andthere is a shift toward decentralized, cooperative systems for computational efficiencyand robustness. In a decentralized control scheme, control inputs are determinedonboard each vehicle; therefore, decentralized controllers are more efficient for largenumbers of vehicles, and the system is more robust to communication failures andreconfiguration.The design of decentralized, cooperative control laws is explored for a nonlinearvehicle model that can be represented in a double-integrator form. Cooperative controllersare functions of spacing errors with respect to other vehicles in the system,where the communication structure defines the information that is available to eachvehicle. Control inputs are selected to achieve internal stability, or zero steady-statespacing errors, between vehicles in the system.Closed-loop equations of motion for the cooperative system can be written in astructural form, where damping and stiffness matrices contain control gains acting onthe velocity and positions of the vehicles, respectively. The form of the stiffness matrixis determined by the communication structure, where different communication structures yield different control forms. Communication structures are compared usingtwo structural analysis tools: modal cost and frequency-response functions, whichevaluate the response of the multivehicle systems to disturbances. The frequency-responseinformation is shown to reveal the string stability of different cooperativecontrol forms.The effects of time delays in the feedback states of the cooperative control lawson system stability are also investigated. Closed-loop equations of motion are modeledas delay differential equations, and two stability notions are presented: delay-independentand delay-dependent stability.Lastly, two additional cooperative control forms are investigated. The first controlform spaces vehicles along an arbitrary path, where distances between vehiclesare constant for a given spacing parameter. This control form shows advantages overspacing vehicles using control laws designed in an inertial frame. The second controlform employs a time-based spacing scheme, which spaces vehicles at constant-timeintervals at a desired endpoint. The stability of these control forms is presented.