H ∞ control design to include nonlinearities. First report: saturation of the rudder.

In designing a control system for large vessels, there are two kinds of nonlinearities which must be considered. One is the nonlinearity in equations of motion and the other is the saturation in control devices such as engine output or rudders. These nonlinearities can strongly affect the performance of the control system. A new method to deal with the nonlinearity of saturation has been proposed in this paper. The saturation is considered as a variation of gain in the system. A control system with gain variation can be designed by H_∞ control theory. As an example, a course-keeping control system for a course-unstable ship has been presented. The results show that the method proposed is effective. [ABSTRACT FROM AUTHOR]