A definition of the degree of disturbance rejection

The problem of rejecting disturbances that are known a priori to reside in a particular function class is treated. Two scalar measures, the degree of disturbance rejection (DODR) and the degree of disturbability (DOD) are defined and shown to be useful in rating a candidate controller's ability to counter the expected disturbances. The measures can thus be used as criteria for controller design and actuator placement. It is shown that the DODR can guarantee that constraints on the control action will not be violated. The DOD assumes a closed-loop controller realization, and this gives a simplified formulation in terms of one state space region instead of two. With the DOD, a variety of performance indices can be considered, together with a spectrum of possible controller implementations.