Passive fault tolerant servo control against one device failure out of sensors and actuators

This paper concerns with a design of passive fault tolerant servo systems against one device failure out of sensors and actuators. In case that a device breaks down, integrators generate ramp signals in the closed-loop system. This paper proposes to use limiting (saturation) devices to block such undesirable ramp signals. As activated limiting devices are modeled as zero transfer functions, the design problem can be formulated as a simultaneous stabilization problem. Unfortunately, even if the controller is appropriately designed for the simultaneous stabilization problem, unintended saturations might occur and make the closed-loop system unstable. This paper shows that the row diagonal dominance properties of both the controller integral gain and the product of the controller integral gain and plant DC gain are important to avoid such unintended saturations. These row diagonal dominance properties can be formulated as additional linear constraints to the simultaneous stabilization problem.