Extended Disturbance Observer With Measurement Noise Reduction for Spacecraft Attitude Stabilization

The attitude stabilization of flexible spacecraft is significantly affected by environmental disturbances, elastic vibration of flexible appendages, and model uncertainties. These disturbances and uncertainties can be accurately estimated by the extended disturbance observer (EDO). However, the EDO is sensitive to measurement noise when high-order and large bandwidth are chosen. Thus, the output of the EDO will contain too much high-frequency noise which can degrade the attitude stability of the spacecraft and cause heavier chattering of the actuators. In order to suppress the effect of measurement noise, a noise reduction EDO (NREDO) is proposed in this paper. First, a dynamical model of disturbance is reconstructed by augmenting the integral of the virtual measurement of the lumped disturbance as a new state. Second, the NREDO is designed by utilizing the estimation error of the augmented state to update the observer estimates. Thereafter, the disturbance estimation accuracy is analyzed for the EDO and NREDO in the frequency domain in the presence of measurement noises. Finally, the simulations are conducted to verify the effectiveness of the proposed controller. The theoretical analysis and simulation results demonstrated that the NREDO can not only effectively suppress the effect of measurement noise, but also inherit the advantages of the EDO in avoiding redundant estimation of the system states and dealing with the nonlinear item of the spacecraft model. Improved attitude control performance can be achieved under the proposed NREDO-based controller.