Transfer alignment error compensator design using H∞ filter

This paper deals with the transfer alignment problem of the strapdown inertial navigation system subjected to roll and pitch motions of the ship. Specifically, to reduce alignment errors induced by measurement time-delay and ship body flexure, an error compensation method is deviced based on state augmentation and robust state estimation. A linearized error model for the velocity and attitude matching transfer alignment system is first derived by linearizing the nonlinear measurement equation with respect to its time delay and dominant Y-axis flexure, and augmenting the delay state and the flexure state into the conventional linear state equations. Then an H_∞ filter is introduced to account for modeling uncertainties of the time-delay and the ship body flexure. The simulation results show that the present method is effective enough resulting in considerably less azimuth alignment errors.