Design of Wave Filter for Dynamic Positioning Ships Based on Double Kalman Filter (DKF)

The dynamic positioning (DP) ship is affected by the wave forces at sea. The wave forces are composed of the second-order wave forces and the first-order wave forces. The second-order wave forces make the DP ship drift and can be compensated by the thrusters which are controlled by the controller. The first-order wave forces cause high-frequency oscillations in the DP ship and this part must be filtered out through wave filter. In this paper, the wave filter is designed on the base of double Kalman filter (DKF). The DKF is composed of the first-stage Kalman filter (KF) based on linear time-varying (LTV) systems and the second-stage linearized Kalman filter (LKF). The states estimated by the first-stage KF based on LTV systems are used as exogenous inputs for the second-stage LKF. The stability of DKF approach is proved to inherited from KF. The simulation results show the effectiveness of the wave filter based on DKF.