SINS nonlinear initial alignment methods for large misalignment angles based on EPEA

Euler platform error angles(EPEA) are adopted to describe the misalignment angles from the theoretical navigation coordinate system to the computational navigation coordinate system,and the strapdown inertial navigation system(SINS) nonlinear error model is derived for initial alignment at large initial misalignment angles.The simplified extended Kalman filter(EKF) and unscented Kalman filter(UKF) algorithms with damp solution are presented when both process noise and measurement noise are additive and the measurement equation is linear,and a comparison is made between the filtering processes for different misalignment angles.The Monte Carlo results from the stationary simulation show that both EKF and UKF algorithms can obtain satisfactory alignment accuracy under large and large azimuth misalignment angles.But UKF is superior in alignment time,alignment precision and application scope in most cases except for the case of small misalignment angles,and in such a situation they have the same alignment performance due to the fact that the linearization error of SINS becomes smaller.