Investigation On Trajectory Optimization And Guidance&control Scheme For A Type Of Gliding Guided Projectiles

Guided projectiles possess both the advantages of tactical missiles and conventional projectiles not only in term of low cost of single round,rapid respond,but also high attacking precision.As a result,guided projectiles are gradually becoming one of the key development trends to conventioanl munitions.In this dissertation,a type of low-spin guided projectile equipped with two pairs of canard surfaces is considered as the subject.Focusing on some theoretical and technical problems encountered during the research process,the reference trajectory optimization and the design of guidance and control system of this type of guided projectile are studied.Based on the aerodynamics and motion characteristics of low-spin guided projectiles,the six degree of freedom flight dynamic model is established.According to different applications,a simplified flight dynamic model which is used to investigate the reference trajectory,attitude control system model considering coupled effects of different channels,and guidance mathematical model are proposed respectively.Due to the large discrete errors and low accuracy of the conventional direct collocation method for solving trajectory optimization problems,an adaptive direct collocation method which involves a novel update scheme for discretization nodes is presented.In this method,the discretization nodes are automatically adjusted according to the discretization errors,which can increase the accuracy of direct collocation method while maintaining its high computation efficiency.Considering some typical uncertainties which may be encountered in a real operating environment,including the modeling error,errors in the parameters at the gliding start point,aerodynamic error and atmosphere error,a linear covariance based method is proposed to evaluate the sensitivity of the reference trajectory to these uncertainties.A method of trajectory optimization under uncertainties is proposed,which can provide a better reference for rational design of gliding guided projectile trajectory compared with other conventional trajectory optimization methods.According to the flight characteristics of the guided projectile,the entire trajectory is divided into four flight phases that connect to each other sequentially to ensure continuity,a multiphase trajectory optimization method is established to design the entire trajectory.This method can provide a better reference for the design of quadrant elevation,ignition time of the boost rocket,gliding start point and the flight attitude in the gliding phase.The reference trajectory tracking problem for unpowered gliding guided projectiles is studied.Combining the optimal control theory with Gauss pseudospectral method,an indirect Gauss pseudospectral trajectory tracking guidance law with analytical solution is proposed.This method does not need any integrations or iteration processes,and avoids solving Riccati differential equations,which can largely improve the computational efficiency.And this advantage is more obvious as the scale of solving problems increases.The computational accuracy of the proposed method is validated by comparing with GPOPS software.In addition,the algorithm can also easily handle the weight matrix of complex form,making the design of performance index function more flexible.In order to reduce the dependence of indirect Gauss pseudospectral trajectory guidance law on the projectile's mathematical model,another nonlinear reference trajectory tracking guidance law which is based on the philosophy of chasing virtual target is also proposed.The trajectory tracking dynamic model is established by introducing a virtual target moving along the reference trajectory.A desired line-of-sight angle is presented for the trajectory tracking problem.In order to follow the reference trajectory in finite time without singularity,the nonsingular fast terminal sliding mode control and the dynamic surface technique are employed to design the guidance law.The relationship between the error of line-of-sight angle and the path-following error is presented.It is demonstrated that the path-following error is ultimately bounded on the account of Lyapunov stability theorem.Numerical simulations analyze trajectory tracking performance of the above two guidance laws,meanwhile,their respective applicable characteristics are also summarized,which can provide some guidance for practical implementation.Considering the coupled effect between the pitch and yaw channels of low-spin guided projectiles,a novel attitude control scheme based on trajectory linearization control(TLC)is proposed.According to the time-scale separation principle,the projectile's highly coupled nonlinear system is separated into attitude loop and angular loop.Utilizing the combination of feedforward and feedback control frameworks,the tracking error of each loop converges exponentially along the reference trajectory,resulting a better control performance for the entire closed-loop system.In order to further improve the control quality of the attitude controller under perturbations,an improved scheme is proposed to maximize the robustness of TLC while maintaining its own inherent excellent characteristics.The peak phenomenon is effectively restrained by using Han tracking differentiator to calculate the derivatives of each reference signal.Considering the system modeling error,aerodynamic parameter perturbations and external disturbances,an extended state observer is designed to estimate and compensate the system uncertainties.Meanwhile,novel integral sliding surfaces are implemented to design the feedback control law of each loop.Simulation results show that the improved controller can maintain a good control performance in the presence of different interferences,which can meet the control requirements of high accuracy and strong robustness of glide-guided projectile.