自适应非奇异快速终端滑模固定时间收敛制导律

针对机动目标的末制导拦截问题，设计了一种带攻击角度约束的非奇异快速终端滑模固定时间收敛制导律。与有限时间收敛终端滑模制导律相比，所提制导律能够确保弹目视线（LOS）角和弹目视线角速率在固定时间内是收敛的，并且收敛时间是独立于制导系统初始条件的，可以根据制导律参数预先给定。构造了一种新型的非奇异快速终端滑模面，有效解决了奇异性问题，同时通过合理地改变滑模面与弹目视线角跟踪误差的趋近律指数，使得制导系统比现有的固定时间收敛控制具有更快的收敛速率。此外，设计了一种自适应律，针对目标机动引起的未知扰动进行估计，使得制导律的设计无需预先知道任何关于目标机动的信息。通过仿真实验验证了所提制导律能够使导弹成功拦截机动目标，并且与现有制导律相比，具有更快的系统收敛速率、更高的拦截精度及更短的拦截时间。 

Adaptive nonsingular fast terminal sliding mode guidance law with fixed-time convergence

To deal with the terminal guidance problem of missiles for intercepting maneuvering targets, a nonsingular fixed-time convergent fast terminal sliding mode guidance law is developed with impact angle constraints. Compared with finite-time convergent terminal sliding mode guidance laws, the proposed guidance law ensures that the line of sight (LOS) angle and the LOS angular rate are fixed-time convergent. The convergence time is independent of the initial states of the guidance system and can be set in advance by the guidance law's parameters. Compared with conventional fixed-time convergent control, a novel nonsingular terminal sliding mode is designed to solve the singularity problem and the faster convergence rate is guaranteed by regulating the index of the approaching laws of the sliding surface and the LOS angle error. Besides, an adaptive law for unknown upper bound estimation of the target acceleration is presented and a priori information on the target acceleration is not required to be known. Finally, simulation results show that the missile can intercept the maneuvering targets effectively with the proposed guidance law. Besides, comparison with the existing guidance laws indicates that the faster convergence rate of the guidance system, the shorter intercept time and the higher intercept accuracy are achieved by the proposed guidance law.