Design of failure-accommodating multiloop LQG-type controllers

This note investigates the stability of multiloop LQG-type controllers in the presence of actuator and sensor outages. For the linear quadratic state feedback (LQSF) regulator case, it is proved that the closed-loop stability can be maintained in the presence of certain actuator failure states by inserting appropriate constant gains in the control loops. The results are also applicable (via duality) to the design of state estimators which maintain stability in face of sensor failures, provided that the failure state is known or detected. This regulator-estimator combination yields an LQG-type controller which is tolerant to certain actuator and sensor failure states.