Dual Closed-loop Fuzzy PID Depth Control for Deep-sea Self-holding Intelligent Buoy

Considering the nonlinear and strong coupling characteristics of the motion model of a deep-sea self-holding intelligent buoy, we propose a fuzzy proportion-integral-derivative (PID) controller based on a dual closed-loop to control the buoy's depth. According to the buoyancy regulation system, we establish a nonlinear dynamic model based on the motion analysis of the buoy. We design a fuzzy controller for the outer deep feedback loop, and then we design a cascade fuzzy PID controller for deep-sea self-holding profile buoy according to the inner speed feedback loop and the fuzzy controller. The overshoot of the traditional PID depth controller is 5.6%, and it will eventually oscillate within a depth of ±30 meters. Compared with traditional PID depth controllers, within the same rise time, the overshoot of the fuzzy PID controller is 2.0%, and the depth error is within 1.0%. In the presence of external disturbances, the buoy can still be stabilized within the target depth by adjusting the dual closed-loop fuzzy PID depth controller. Simulation results demonstrate that the dual closed-loop fuzzy PID depth controller has better depth control ability and stability.