Analytical modeling and preliminary fractional order velocity control of a small scale submersible

This paper presents the modeling and control of a small scale submersible equipped with one propeller. The modeling process takes into consideration physical elements such as fluid statics, viscous damping and propulsive thrust. A first order transfer function with time delay is developed to make the connection between the voltage applied to the motor actuating the propeller and the velocity of the submersible. The velocity control is realized with a Fractional Order Proportional Integral (FOPI) controller that ensures zero steady state error. The controller is designed based on frequency domain specifications such as gain crossover frequency, phase margin and robustness to gain variations. The obtained fractional controller is validated through simulation in terms of steady state error and disturbance rejection performance.