Autopilot Design by the Method of Simultaneous Stabilization and Parameter Optimization

Abstract

Abstract The paper presents a synthesis of a nonlinear ship steering control system through application of the simultaneous stabilization and parametric optimization methods. The ship steering control system is closed through the gyrocompass and autopilot. The loop consists of an autopilot, the steering gear subsystem, and a ship. For linearization of the nonlinear steering gear subsystem the procedure of quasi - linearization is used. The steering gear linearized model structure and initial parameters are determined by means of frequency characteristics of the steering gear subsystem, while the time response is utilized for the fine adjustment of parameters. The dynamics of the ship, treated as a linear part of the system, varies depending on conditions (trim, depth etc.) to which the ship is subjected, and can be described by a set of transfer functions. The linearized steering gear model together with a set of the ship linear models produce the nonlinear ship steering control system model with variable parameters. The obtained model consists of a set of transfer functions describing the complete system dynamics in open loop. After obtaining such a model of the system, an autopilot design is taking place by applying the simultaneous stabilization procedure. The obtained regulator stabilizes the system under given operating conditions, respectively, it stabilizes the set of transfer functions. The procedure of parametric optimization of the nonlinear system with variable parameters is used to improve the system dynamics, whereas through the simultaneous stabilization procedure only the system stability conditions are checked. The procedure is verified, and the obtained results confirm the advantage of the autopilot obtained in such a manner.