Inner-loop reference governors: Placing reference governors inside the control loop by using passivity

We consider a reference governor placed inside a control loop. This inner-loop reference governor modifies the tracking error and not the reference command as in the case of the conventional, outer-loop reference governor. We derive conditions under which the reference governor is passive or exhibits a small lack of passivity. Utilizing these properties, we design an inner-loop reference governor algorithm for constraint enforcement and show that it exhibits similar properties to the outer-loop reference governor. We also derive limits on the rate of change of the reference input to guarantee recursive feasibility. An example is presented.