Fault Estimation and Fault-Tolerant Control for Control Moment Gyro Actuated High Agility Spacecraft

摘要

Control moment gyroscopes (CMGs) are widely used in the attitude determination and control of high agility spacecraft owing to their torque amplification property. However, situations of unexpected fault or failure of the CMG can cause severe performance degradation or even mission failure. To improve the robustness of spacecraft attitude control, this paper investigates the modelling, fault estimation and fault-tolerant control problem as applied to CMG actuated spacecraft. Firstly, the CMG is modelled as a cascade combination of an electrical motor and variable speed drive (EM-VSD) system. Each control freedom here corresponds to an EM-VSD loop. For a single gimbal CMG (SGCMG), it contains a gimbal control loop and wheel speed control loop. In the gimbal control loop, the EM-VSD system is used to generate the gimbal angular velocity, which produces the gyroscopic output control torque. In the wheel speed control loop, the EM-VSD system governs the constant wheel speed, resulting in a constant angular momentum. Potential faults lie in the mechanical part of the EM, sensors, actuators, VSD and electrical part of these components. Hence, the fault can be modelled as an effectiveness loss fault and an additive bias fault, which correspond to an appropriate combination of multiplicative fault and additive fault mathematically. Secondly, a lumped bias is introduced to model the total effect of the multiplicative fault and additive fault. Then a second order sliding mode observer is constructed to estimate the lumped bias. Finally, a fault tolerant control strategy that appropriately combines the estimates of the lumped bias is developed to accommodate the CMG faults. To verify the effectiveness of the proposed estimation method and fault-tolerant strategy, numerical simulations on a rigid spacecraft manoeuvre are conducted. Simulation results show that spacecraft reorientation can be achieved under the various fault scenarios with a high level of responsiveness.