An application of the improved hybrid fuzzy PID control system

In this paper, the hybrid fuzzy PID control system of a pump-propelled autonomous underwater vehicle is presented. The small low-cost vehicle named ldquoU-FISHrdquo is the first one propelled and controlled by four pumps mounted on the stern. Due to the difficulty of building the model and the restriction of the computing power of the micro-controller, the hybrid fuzzy PID control algorithm, which is model-free and easy to realized, is a wise choice for this complex system. The open-loop experiments are firstly carried out to obtain the parameters of the vehicle, according to which we design the control law in details for the horizontal plane and the vertical plane separately. Finally, the close-loop experiments in which the U-FISH travels at different heading angles and depths show that the complex system responds quickly and reaches a satisfactory steady state in both of the planes simultaneously. Based upon the results, the feasibility of the control law is validated.