Research On Rapid Alignment Algorithm Of SINS In Polar Regions

The poor natural environment in the polar region is a main difficulty in polar navigation.Problems such as convergence of geomagnetic force lines,magnetic field anomalies and multipath effects lead to the failure of common navigation methods such as radio navigation,geomagnetic navigation and satellite navigation in polar environment,Strap-down inertial navigation system(SINS)which can autonomous navigation all day,all time and has strong concealment,is almost the only choice for polar navigation.Initial alignment,as the premise of SINS navigation,is one of the most important technologies of SINS.The accuracy of initial alignment affects the SINS navigation accuracy directly.How to accomplish SINS initial alignment with both high precision and short convergence time in the polar regions is still one of the most popular issues concerned by many scholars.Therefore,this work is of great significance.In this paper,the problem of SINS rapid initial alignment in the polar regions is studied.Using the real-time output of gyroscope and accelerometer,the precise alignment of initial alignment is completed.The research work of this paper is mainly divided into the following parts:Firstly,the reason for the invalid of traditional SINS initial alignment method based on North pointing mechanical arrangement fails in the polar region is analyzed,and a new mechanical arrangement of the pseudo-earth frame based on CGCS2000 ellipsoid earth model is proposed.At present,the commonly used mechanical arrangement in the polar regions are the grid frame mechanical arrangement and the transverse earth frame mechanical arrangement.However,the former is very complex in calculation and it may diverge in azimuth settlement,while the latter has principle error.Based on the problems above,this paper proposes an improved mechanical arrangement of pseudo earth frame based on ellipsoid earth model.The pseudo earth frame is established by the initial position of the carrier and the ellipsoid earth model parameters of the latest CGCS2000 national geodetic coordinate system in China are used to reduce the principle error caused by the spherical earth model,and to solve the engineering implementation difficulties caused by switching of the mechanical arrangements between high and low latitudes.The feasibility of this new mechanical arrangement is verified by simulations of both middle and high latitudes.Secondly,a rapid initial alignment algorithm based on the expansion of observation vectors is proposed on the basis of the establishment of the suitable mechanical arrangement for the polar region.Without changing the system state equation,the projection of the earth rotation in the calculated pseudo geographical coordinate system is introduced as the expanded observation vector,so as to shorten the initial alignment time without affecting the alignment accuracy.Finally,semi-physical simulation shows that in polar regions,even in the case of latitude of 88.5° and initial misalignment angle of 3°,the azimuth misalignment error can be reduced within 0.2° in 60 s.It has significant engineering application value.Finally,aiming at the problem of inaccuracy and long convergence time of traditional Kalman filter model under the condition of large misalignment angles,a rapid two-position alignment method based on strong tracking filter is proposed.During the initial alignment of SINS,the coarse alignment is generally carried out first,so that the misalignment angle is reduced to the linear error model under the assumption of small misalignment angle,and then the fine alignment is carried out.In this method,the feedback correction filter structure and the strong tracking filter are used.The steps of coarse alignment are omitted under the condition of large misalignment angle,so the total time of initial alignment is shortened,and the accuracy is not much different from that under the condition of small misalignment angle.On this basis,the two-position alignment method is used to determine the rotation angle of the optimal two-position alignment and design the optimal two position alignment process in order to further improve the initial alignment accuracy.The simulation results show that the method is suitable for the initial alignment of large polar misalignment.