Robust Control For Uncertain Systems And Its Applications To Ship Motion Control

Robust Control for Uncertain Systems and Its Applications to Ship Motion ControlAbstractThe robust control for uncertain systems and its applications to ship motion control are systemically investigated in this thesis. In view of a large number of researches in the area of ship motion control, it can be concluded that are three problems unsolved up till present time. The first is that uncertainty is always existed in the mathematical model used for designing controller, which has not been given a full attention yet, second problem is that non-linearity is not included in the model when designing the controller, the last is that the actuator dynamics was not considered when designing the controller. It is found that the robust control theory for uncertain systems can be used to solve the above mentioned problems. So the robust control theory is studied in detail in this thesis first, including robust control strategy in the presence of matched uncertainty and unmatched uncertainty, robust control strategy for non-linear system with uncertainty. Then the above theoretical control strategies have been applied to steering autopilot design and fin control design for ship roll stabilization.In the respect of the robust control for linear system with matched uncertainty, a review of some available control algorithms is made in this thesis, which laid a foundation for practical applications to ship motion controller design. And the scheme for constructing sliding mode hyperplane with the solution of the algebraic Riccati equation of nominal system is proposed. Based on the above scheme, two classes of variable structure robust control algorithms with continuous performance and globally practical stability are presented for a class of uncertain MIMO systems. No orthogonal transformation is needed in these algorithms, so the design procedure can be simplified. In accordance with the fact that the present available robust control strategy lead to a discontinuous action on the hyperplane of state space, two continuous-type robust controllers were established in this thesis to overcome the shortcoming.In the respect of robust control in the presence of unmatched uncertainty, four types of uncertainty bound are put forward, and robust control design based on algebraic Riccati equation approach and H^-norm approach are studied with respect to each type of uncertainty bound. The major contributions of this thesis are the development of three classes of variable structure robust controllers for mismatched uncertain systems, which laid a foundation of investigating effects of the actuator in ship motion control system.In the respect of the robust control for uncertain non-linear systems, when assuming that system's robust relative degree is equal to the system's degree, on the basis of robust feedback linearization technique, three classes of state feedback robust control schemes are presented by using of pole-placement method,and three classes of variable structure robust control schemes are also proposed in this thesis. For some non-linear systems with uncertainty bound may be a structure unknown non-linear function, "ia hfew scheme" for approximating uncertainty bound by using fu.fezy-'io'gic System is given, and av robust adaptive fuzzy control algorithm is proposed that can guarantee the closed-loop system to converge exponentially towards a residual ball abound the equilibrium was proposed. The main features of the algorithm can be viewed from two aspects: firstly the prerequisite for understand of the controlled system is relaxed, and secondly no matter how many rules in the fuzzy system are used, only one parameter needs to be adapted on-line, so the computation load of the algorithm can be reduced. In order to make study of effects of the actuator in uncertain nonlinear systems, a variable structure robust adaptive control strategy is established in accordance with the extended matched uncertain non-linear systems.To inspect the performance of ship motion control systems, a high precision ship mot...