Research on improved PID Dynamic Positioning System Based on Nonlinear Observer

In view of the difficulty in measuring the kinematic velocity and high frequency (HF) environmental disturbance of ship dynamic positioning system (DPS), a method of proportional-derivative (PD) control compensated by nonlinear passive observer has been proposed. Through the environmental force estimated by observer acting on bias compensation control, not only can the dynamic response speed of closed-loop system be improved, but also the negative effects on system-controlling precision and thrusters-acting frequency, most of which are caused by HF disturbance, are avoided. Using the Lyapunov stability theory and global stability method of nonlinear cascade system prove the closed-loop stability of designed system. Comparing the results with existing PID type control system, the proposed control algorithm could improve the dynamic response performance of ship and effectively filter HF disturbance on control stability accuracy.