H∞ controller design for the longitudinal model of submarines with input constraints

This paper considers the control problems of submarine movement of depth-keeping and pitch angle-keeping in vertical plane under actuator output constraints. By using the longitudinal linearization model, a robust H_∞ controller is designed based on reduced-order observer. The controller can restrict the magnitude of inputs, and guarantee the submarine in vertical-plane movement with high stability precision. In addition, an algorithm of max stability robustness bound for every uncertainty parameter is provided, which can guarantee the closed loop system has H_∞-performance. Finally, the method is applied to control the vertical-plane movement of submarine with linear and nonlinear models, and the results of simulation show that the controller has good robustness.