On Active Disturbance Compression Control by Twice-Extended State Observer for Laser Pointing System

In the laser pointing system (LPS), moving platforms cause nonnegligible external vibrations that harm the pointing accuracy. The bounds of the lumped disturbance and its derivative, however, place a cap on the convergence of the extended state observer's (ESO) estimating error. In this article, the composite disturbance suppression concept and active disturbance compression control (ADCC) system are first put forth, with the subsystem being suggested to correct the primary system's residual disturbance suppression error. Second, a case of the second-order ADCC system, the twice-extended state observer (TESO), is presented to actively compress and reduce the bounds of the lumped disturbance and its derivative. TESO yields much better estimation performance on both states and disturbance than typical ESO, while it just requires the same modeling information and bandwidth. Third, the twice-extended active disturbance rejection control approach, employing the TESO as the kernel, is proposed to enhance tracking and disturbance rejection performance. Finally, tuning laws and convergence analyses are offered, and experiments on the LPS demonstrate the method's superiority.