Smith predictor based delay compensation for a hardware-in-the-loop docking simulator

Abstract

The hardware-in-the-loop (HIL) simulator is an important equipment to test the performance of the docking mechanisms (DMs) in the docking process of two spacecrafts on the ground. However, the design and control of the HIL simulator is very challenging due to the simulation divergence caused by the time delay. The phase lead is a common approach to compensate the time delay. In this study, it is found that the simulation is still divergent using the traditional phase lead compensation approach when the contact frequency increases to a threshold value depending on the HIL simulator. In practice, because the experimental contact frequency is time-varying and unknown, traditional phase lead compensation approach could make the system instable and divergent. The Smith predictor based delay compensation is proposed in this study. It integrates the Smith predictor and the phase lead compensation. The contact model of the DMs is not required. The simulation system is stable and convergent when the contact frequency increases and satisfies the stability condition. The HIL simulation with a little convergence is better than the divergent simulation because the previous one can be considered to have some simulation error while the latter one could destroy the hardware. The phase and stability analyses are given to prove the simulation convergence and the closed-loop stability. Simulations and experiments are used to verify the effectiveness of the proposed compensation approach.