Research On Parallel Implementation Of Strapdown Inertial Navigation Systems Under High Dynamic Conditions

Considering the high-speed and high-maneuvering features of hypersonic cruise missiles, this thesis systematically investigates the parallel implementation of SINS under high dynamic conditions, which involves the initial alignment algorithm, parallel Kalman filter design, strapdown algorithm, parallel strapdown algorithm design and FPGA implementation. The main contents of this thesis are summarized as follows:1. Similar to the matching mechanism of SINS/GPS integrated navigation systems, three parallel system architectures of navigation computer are proposed based on the analysis of SINS functional requirements and performance requirements, namely, loosely-parallel architecture, deep-parallel architecture and totally-parallel architecture. In the totally-parallel architecture, all calculations of SINS are performed on the parallel mode; it needs to design new initial alignment and strapdown algorithms of SINS, namely, parallel strapdown algorithm and parallel initial alignment algorithm.2. Considering that the vehicle is inevitably subject to the impact of rocking disturbances by wind gust or engine idling, etc. on the initial alignment, a strapdown compass alignment method based on dynamic gain adjustment (DGA-Compass) and a new Kalman alignment method (New-Kalman) are proposed and comparatively analyzed for the effectiveness of their alignment algorithms under different disturbance conditions. In the DGA-Compass alignment algorithm, the gain parameter is dynamically adjusted based on the expected alignment time and attitude change of vehicle to make the attitude angle output of system track the low-frequency and large-amplitude rocking disturbance, so the convergence speed of compass alignment can be accelerated, that is, the alignment time is reduced; in the New-Kalman alignment algorithm, level accelerometer measurements are introduced into the observations of the Kalman filter to improve the performance of alignment algorithm.3. Considering the limitation of Kalman filter real-time tracking the attitude change of vehicle, a parallel systolic array structure implementation of Kalman filter algorithm is proposed based on the Faddeeva algorithm. For any given two or more matrices, matrix operations (matrix inversion, matrix multiplication and matrix addition) or combined operations can be computed by their corresponding Faddeeva algorithm. From the regularity, modularity and other features of systolic array structure, it is shown that systolic array structure is a good structure to achieve the Faddeeva algorithm. Kalman filter can be expressed in the form of some matrix operations, and then can be mapped to the parallel array structure based on Faddeeva algorithm.4. Considering the high-speed and high-maneuvering features of hypersonic cruise missiles, a new strapdown algorithm suitable for the high dynamic conditions is proposed, in which the single-speed structure is used based on the performance of current navigation computer (high speed and high throughput). And new generalized optimization coning and sculling compensation algorithms are proposed to solve the coning movement in the attitude updating algorithm and the sculling movement in the velocity updating algorithm. Different from existing algorithms, the updating rates of the coning and sculling compensations are unrelated with the number of the gyro incremental angle samples and the number of the accelerometer incremental velocity samples. When the output sampling rate of inertial sensors remains constant, this algorithm allows increasing the updating rate of the coning and sculling compensation, yet with higher-order algorithm to improve the accuracy of system.5. Taking into account that the attitude updating algorithm is the core of strapdown algorithm, and the major factor influencing system accuracy, especially for the high-speed and high-maneuvering hypersonic cruise vehicles, the relationship between the attitude errors and the coning compensation updating rate as well as the order of the coning compensation is deduced for quantitative analysis of the new coning compensation algorithm under typical coning movement conditions. Through analysis, it is shown that relative to the update rate, the relationship between the order of coning compensation and attitude error is more complex. When a vehicle moves with "normal" dynamics (characterized by a small or moderate coning movement frequency), both the increase of the updating rate of the coning compensation and the increase of the number of gyro incremental angle samples benefit the reduction of the attitude error. When a vehicle is in a high dynamic motion described by a larger frequency, however, in consideration of the technical limitations on the updating rate of the coning compensation (e.g., due to the limited computation speed of the navigation computer), the choice of the sampling number of gyro incremental angles must be made carefully.6. Since reducing the update cycle (namely, increasing the update rate) can improve the accuracy of SINS, especially for the high-speed and high- maneuvering hypersonic cruise vehicles, a parallel strapdown algorithm structure is proposed. According to the design techniques of parallel algorithm (i.e., divide-and-conquer strategy and pipelining), the strapdown algorithm is parallel designed, and the parallel design is quantificationally analyzed. By the comparative analysis of the performance, it is shown that this parallel strapdown algorithm on the FPGA platform can greatly decrease the execution time of algorithm to meet the real-time and high precision requirements of system on the high dynamic environment, comparative with the existing implemented on the DSP platform.7. From the perspective of system, the FPGA implementation of parallel strapdown algorithm and parallel Kalman filter initial alignment algorithm is analyzed in detail, respectively. Among them, the Xilinx embedded IP hardware MicroBlaze is used for controlling and scheduling the execution of each module in the parallel algorithms. Through car test, it is shown that the FPGA hardware implementation of SINS is feasible. This provides a solid basis for increasing the accuracy and real-time of SINS under the high dynamic conditons, and has a very good practical and theoretical value.