An adaptive notch filtering approach with frequency holder for attitude control of flexible launch vehicles

Purpose This study aims to investigate an adaptive notch filtering approach to suppress the effects of elastic vibration on the attitude control of flexible launch vehicles. Design/methodology/approach First, the dynamics model of the flexible launch vehicle and baseline PID controller are presented. Furthermore, the frequency identification algorithm based on a second-order notch filter is developed to identify the elastic vibration frequency. Finally, a frequency holder is developed to update the notch frequency of the adaptive notch filter. Findings The proposed adaptive notch filter with a frequency holder can identify the vibration frequency accurately, update the notch frequency appropriately and suppress the effects of the elastic vibration on the attitude control of flexible launch vehicles effectively. Originality/value A novel adaptive notch filter with a frequency holder is proposed to address the adaptive filtering problem of elastic vibrations under nonelastic interference and elastic frequency uncertainty. Compared with the conventional filter for attitude control of flexible launch vehicles, an adaptive filter with a proposed frequency holder is developed to solve the problem of the frequency real-time update during the vibration suppression and frequency keeping after the vibration suppression.