Optimal Fault Tolerant Error Governor for PID Controllers

The Error Governor (EG) paradigm considers the issue of dynamically changing the error which drives a feedback controller featured by bounded control action magnitude to prevent the actuators’ saturation and to avoid the slow wind-up effects due to integrator or slow dynamics. Fault Tolerant (FT) policies are control methods permitting to mitigate the effect of faults occurring on driven actuators by modifying the structure of the controller which provides the reference signal for such actuators. In this paper, a FT policy based on an optimal EG approach is proposed. The policy, termed Fault-Tolerant Error Governor (FT-EG), permits to introduce a FT action in a closed-loop system driven by PID controllers neglecting changes in the controller structure and, further, the wind-up issue given by nominal actuator saturation. The FT-EG is based on the solution of a constrained optimization problem and a computationally efficient version of the algorithm is presented. An analysis of control performance and the computational burden is provided, comparing in simulation studies the optimal FT-EG scheme performance with respect to control results provided by the baseline EG policy and saturated PID controller in the fault-free and the faulty scenario.