Controller Design for Heave and Surge Motions for AUVs

In this paper, we constructed a simulation block for an underwater vehicle using the MATLAB Simulink tools. The equation of motion and parameters are referred from the MIT Autolycus. First, the step responses are checked to see the correctness of the model. Then the linear models for heave and surge motions are obtained using the system Identification tool in MATLAB Simulink using the step responses from the nonlinear model. A 2-degree-of-freedom PID controller is designed, and the performance and stability margins of the control loops are analyzed. It is found that both controllers have big gain margins and 69-degree phase margins. The bandwidths of the surge control loop and heave control loop are both 2 rad/sec. Both step responses show that the steady-state errors and maximum overshoot are small. We checked the linearly obtained controller on the nonlinear plant model and the results are good enough.