H/sup ∞/-optimal tracking control techniques for nonlinear underactuated systems

Presents techniques for controlling the motion of an underactuated vehicle when disturbances are present and only imperfect state measurements are available for feedback. A state feedback controller is developed and then it is converted to an imperfect state measurement feedback controller. The state feedback tracking control law uses an H/sup /spl infin//-optimal design and produces a locally exponentially stable closed-loop system. The imperfect state measurement feedback controller combines the state feedback control law with an H/sup /spl infin//-filter to estimate the states and achieves a modified form of disturbance attenuation. The state estimator exploits a unique structure in the nonlinear equations of motion to develop a direct solution. MATLAB simulations illustrate both control algorithms for an underactuated ship model.