[Paper Review] Development of a General Momentum Exchange Devices Fault Model for Spacecraft Fault-Tolerant Control System Design

Chengfei Yue, Qiang Shen+4 more|arXiv (Cornell University)|Jul 15, 2019

Magnetic Bearings and Levitation Dynamics40 references4 citations

TL;DR

This paper proposes a general fault model for momentum exchange devices (MEDs) such as reaction wheels and single gimbal control moment gyros (SGCMGs) by modeling them as cascade electric motor (EM)-variable speed drive (VSD) systems. The model categorizes faults into additive and multiplicative types, enabling simulation of various fault scenarios; simulation results show additive faults degrade control accuracy more severely than multiplicative faults, and the model supports both passive (additive equivalent) and active (multiplicative effectiveness estimation) fault-tolerant control strategies for SGCMG gimbal faults.

ABSTRACT

This paper investigates the mechanism of various faults of momentum exchange devices. These devices are modeled as a cascade electric motor EM - variable speed drive VSD system. Considering the mechanical part of the EM and the VSD system, the potential faults are reviewed and summarized. Thus with a clear understanding of these potential faults, a general fault model in a cascade multiplicative structure is established for momentum exchange devices. Based on this general model, various fault scenarios can be simulated, and the possible output can be appropriately visualized. In this paper, six types of working condition are identified and the corresponding fault models are constructed. Using this fault model, the control responses using reaction wheels and single gimbal control moment gyros under various fault conditions are demonstrated. The simulation results show the severities of the faults and demonstrate that the additive fault is more serious than the multiplicative fault from the viewpoint of control accuracy. Finally, existing fault-tolerant control strategies are brief summarized and potential approaches including both passive and active ones to accommodate gimbal fault of single gimbal control moment gyro is demonstrated.

Motivation & Objective

• To develop a unified fault modeling framework for momentum exchange devices (MEDs) including reaction wheels and CMGs, addressing the lack of comprehensive fault models in existing literature.
• To clarify why faults in MEDs can be categorized as additive or multiplicative, based on their physical origins in the EM-VSD system components.
• To extend the fault model from reaction wheels to more complex MEDs such as single gimbal control moment gyros (SGCMGs), enabling fault simulation and control response analysis.
• To demonstrate the impact of different fault types on spacecraft attitude control performance, particularly focusing on control accuracy degradation.
• To show how the proposed fault model can be integrated into both passive and active fault-tolerant control (FTC) strategies for SGCMG gimbal faults.

Proposed method

• Model MEDs as a cascade of electric motor (EM) and variable speed drive (VSD) systems, treating each control degree of freedom as an independent EM-VSD loop.
• Classify potential faults into multiplicative (e.g., stator, rotor, bearing, gear faults in EM) and additive (e.g., sensor and actuator faults in VSD) types based on their effect on system dynamics.
• Construct a general fault model in a cascade multiplicative structure to represent the combined effect of EM and VSD faults on torque generation.
• Simulate fault scenarios using six distinct working conditions to analyze control performance degradation under various fault types.
• Implement both passive and active FTC strategies: passive via additive equivalent bias estimation (local estimators), and active via multiplicative effectiveness matrix estimation and reconfigurable steering laws.
• Use the internal torque model τ = −h₀Aḋ − ω×H to decouple spacecraft dynamics from actuator dynamics, enabling fault-tolerant control design independent of actuator type.

Experimental results

Research questions

• RQ1 Why can faults in momentum exchange devices be modeled as additive or multiplicative, and what are the physical origins of each type?
• RQ2 How do different fault types (additive vs. multiplicative) affect the control accuracy of spacecraft attitude control systems using reaction wheels and SGCMGs?
• RQ3 Can a general fault model be developed that is applicable across different MED types, including reaction wheels and SGCMGs, based on their EM-VSD architecture?
• RQ4 What are the practical implications of additive versus multiplicative faults in terms of fault-tolerant control system design?
• RQ5 How can the proposed fault model be effectively integrated into both passive and active fault-tolerant control strategies for SGCMG gimbal faults?

Key findings

• Additive faults, such as sensor or actuator errors in the VSD system, have a more severe impact on control accuracy than multiplicative faults like rotor or bearing faults.
• The general fault model successfully captures the dynamics of various MEDs by modeling them as cascade EM-VSD systems, enabling consistent fault simulation across different actuator types.
• Simulations demonstrate that the fault model can effectively represent fault scenarios in both reaction wheels and SGCMGs, showing distinct control performance degradation patterns.
• The proposed fault model supports both passive and active fault-tolerant control strategies: passive via additive bias estimation and active via multiplicative effectiveness matrix estimation.
• The effectiveness of the fault model is validated through simulation of spacecraft attitude control under multiple fault conditions, confirming its utility in FTC system design.
• The study provides a foundation for future work on local estimator design and effectiveness matrix estimation for SGCMG gimbal fault accommodation.