| This article discusses the importance of navigation systems for underwater vehicles,which allow them to accurately determine their position and attitude.Errors in navigation information can lead to decreased control accuracy and even mission failure.The primary navigation system for underwater vehicles is usually a strapdown inertial navigation system,supplemented by acoustic and geophysical field navigation systems.Limited by current underwater navigation systems,which cannot meet the requirements of long-duration and long-distance missions due to the limited range of acoustic systems and the availability of geophysical field databases.In particular,when auxiliary navigation devices fail,the role of the inertial navigation system becomes particularly critical.Therefore,research is needed to address key challenges such as initial alignment in the moored state,heave measurement and global navigation without GNSS,in order to provide a foundation and direction for the development of new underwater vehicles for scenarios such as navigating in complex and dynamic underwater environments,or when GNSS is unavailable.The main research work carried out in this article includes the following four points:1)Aimed at the problem of long and difficult initial alignment caused by wave disturbances in the moored state of underwater vehicles,the proposed solution is a precise alignment controller based on H∞ control theory for both roll/pitch and heading alignments.Through simulation,initial alignment time of 6 minutes was achieved with precision of approximately 17.21″ for roll alignment,18.78″ for pitch alignment,and 2.628′ for heading alignment.The repeating precision was approximately 2.23″ for roll alignment,1.90″ for pitch alignment,and 0.28′ for heading alignment.Sea trials indicated that alignment time was around 400 seconds without significant misalignment angles,but could reach up to 13 minutes with large misalignment angles,where this proposed method exhibited good convergence abilities.2)The inertial navigation system’s height channel divergence in the absence of external assistance,which prevents accurate heave measurement.The proposed solution is an adaptive high-pass filter based on the fluctuation characteristics of attitude angles,which extracts heave information by extracting wave frequencies from three attitude angle information and weighting them to obtain the cutoff frequency of the filter.Adaptive filtering is then achieved by sliding a window to extract the frequency.Validation through sea trials show that this method is effective,with a root-mean-square of 3.6mm for vertical displacement within±3cm of the vehicle’s fluctuation range in 1 hour.3)The proposed solution to the problem of limited global navigation for underwater vehicles based on the geographical coordinate system(restricted to 75°N to 75°S),is a global navigation method based on the ECEF coordinate system for underwater applications,which has been shown to be feasible through simulations and validated by sea trials in the near-polar regions,with velocity error better than that achieved using the geographical coordinate system.4)An INS/DVL global integrated navigation method based on ECEF coordinate system is proposed.The state equation and observation equation of INS/DVL integrated navigation based on ECEF coordinate system are established.The parameters of integrated navigation are estimated by iterative EKF filter.The effectiveness of the method is verified by the sea trials,with a total distance traveled of 14 km.The measured errors were 0.15m/s in eastern velocity,0.1m/s in northern velocity,and approximately 0.7% D in navigation accuracy. |
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