To achieve the quick observation and accurate compensation of bounded uncertain disturbances in control systems, a predefined-time convergence extended state observer is proposed, and this is tested using a typical guidance problem. Firstly, the theory of predefined-time convergence is introduced. For the disturbance issue in nth-order uncertain systems, a predefined-time convergence extended state observer is proposed based on a switching strategy, and its predefined-time convergence characteristic is proven using Lyapunov theory. Secondly, by combining disturbance observation and compensation control, a less-aggressive Hit-to-Kill guidance law based on the predefined-time convergence extended state observer is designed in three-dimensional space, and the stability of this guidance law is proven using Lyapunov theory. Finally, numerical simulation results show that the convergence time of the tracking error for the proposed observer can be precisely controlled, and the improved adaptability of both the observer and the guidance law under target maneuvers is demonstrated.
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