Research On Low Precision IMU-SINS/GPS Tight Combination Technology

Inertial navigation has the advantages of strong concealment,high short-term navigation accuracy,comprehensive navigation parameters,and fast data update rate,but its navigation parameter error will accumulate over time and cannot work alone for a long time.Global positioning navigation system GPS can provide high-precision navigation and positioning information for a long time,but in the occlusion area or high-speed dynamic process,the signal receiver is easy to lose lock and cannot be correctly positioned.Therefore,SINS and GPS can be combined to form a combined navigation system,which utilizes GPS long-term high-precision positioning information to suppress the error accumulation of SINS,and then utilizes the strong anti-interference ability of the inertial navigation system to enhance the anti-interference ability of GPS.This paper takes the SINS/GPS tight combination system based on pseudorange and pseudorange rate as the research content,and studies the low-precision IMU large-azimuth misalignment angle initial alignment,GPS satellite selection algorithm and observability analysis in tightly combined systems,suppressing inertial conduction error divergence when GPS is completely out of lock,propose corresponding improvements or solutions.Firstly,the paper introduces the navigation and positioning principle of SINS and GPS,deduces the SINS mechanics equation,and analyzes and deduces the navigation parameter error equation to facilitate the establishment of the mathematical model of the subsequent tight combination system.Secondly,the instantaneous position and velocity equation of GPS satellites are derived according to Kepler’s orbit law,and GPS visible stars are simulated by GPS satellite ephemeris data.Aiming at the shortcomings of GDOP and other satellite selection algorithms,a star selection algorithm based on SINS/GPS tight combination is proposed.The star selection algorithm first excludes some satellites based on the influence of satellite elevation and azimuth on system state observability.According to the height angle and the sum of the half angles of the base cone,the best satellite combination is determined,and the number of traversal combinations is small,and a large number of inverse matrix operations are not required.Finally,the feasibility of the improved star selection algorithm is verified by simulation.Then,the concept of observability and observability of the system is introduced.Aiming at the existing problems in the calculation process of the observability analysis method based on the system observability matrix SVD,an improved SVD observability analysis method is proposed.The method calculates the observability of each state quantity according to the singular value of the observability matrix of the PWCS system and the corresponding right singular value vector.The physical meaning is clear and the calculation is simpler.Finally,the observability calculated by the simulation method can describe the Kalman filter estimation effect of the system state more accurately,which indicates the correctness and feasibility of the method.Finally,for the low-precision IMU self-alignment,the azimuth misalignment angle is large,which causes the nonlinearity of the system.It is proposed to use the digital compass to assist the alignment of the SINS system.After that,the mathematical model of Kalman filter of tight combination system is constructed,and the rapid divergence of SINS error when GPS is completely unlocked is suppressed by digital compass and incomplete constraint method.Finally,the simulation comparison of various cases is carried out by Matlab,and the low precision of the design of this paper is verified.Feasibility and effectiveness of the SINS/GPS tight combination scheme.